Introduction to Nanophotonics and Plasmonics

foreign [Music] from the Department of electronics and electrical engineering ID guwahati welcome to lecture one of my course on Nano photonics plasmonics and metamaterials this course will provide a detailed introduction to these three pillars of the future photonic Technologies by covering their fundamentals and recent advancements with the growing dominance of 5G Technologies internet of things and emerging applications of artificial intelligence and machine learning in every aspect of human life this course on Nano photonics has become more relevant and important than ever before it is the solution to meet the demands of extremely high computational speed requirement and the ultra fast data transfer rate of the future besides keeping the power consumption minimals Nano photonics allows one to achieve terahertz speech at nanometer scale bringing together the best of the electronics and photonics world this course will first cover the fundamentals of Nano photonics principles of photonic crystals plasmonics or metal Optics excitation of surface plus bounds and their applications later on the course will also focus on metamaterials and meta surfaces covering their fundamentals and various applications such as tunable devices absorbers super lens hyperlens transformation Optics clocking Etc the course will also introduce new alternative materials for Nano photonics to mids meet today's demand and summarize different techniques for fabrication and characterization of nanoscale devices the course is designed for undergraduate and postgraduate students with basic knowledge of physics and electromagnetics the course will actually bring the emerging fields of nanophotonics plus phonics and metamaterials to your doorstep via the swam platform for the first time and we hope that UG and PG students with background in electronics instrumentation physics chemistry Material Science and Engineering chemical engineering and any researcher and Industry people working in the broad areas of photonics will get benefited from this course this course will surely motivate you to explore and study further in this exciting field of research which has got truly endless opportunities here is the detailed course plan we will cover eight modules over the span of 36 lectures as you can see module 1 is Introduction and it will be covered in the first week with three lectures covering the introduction of Nan photonics and plasmonics introduction to mathematerials and meta surfaces and their overview and current status the second module will be on fundamentals of nanophotonics which will be covered over week two and three in week 2 we'll discuss about the electromagnetic theory of light electromagnetic properties of material and electromagnetic waves in dielectric media so that will take care of the light matter interaction in week 3 we'll first study the polarization properties of light reflection and refraction in details when light hits at a interface using the frenel's equation and will understand the absorption dispersion and scattering properties of light module 3 will cover the electromagnetic waves in periodic structures that will be covered in week four and five so let 10 to 12 will cover the Matrix theory of dielectric layered media 1D photonic crystals dispersion relation and photonic band Gap structures in week 5 we'll cover the real and reciprocal ledisis 2D and 3D photonic crystals and discuss emerging applications of photonic crystals foreign model 4 will cover metal Optics that is it will introduce plasmonics in details with its fundamentals so in week 6 we'll cover Optical properties of metal then surface plus Bond fluorideons spp their fundamentals and application of spps in week 7 we'll cover the localized surface plus Bond resonance plasmonic nanoparticles based antennas and web guides and different applications of localized surface plus Bond resonance next we'll move on to module 4 that will be covered in week 8 and 9 and this module 5 will cover matter materials their fundamentals and applications week 8 will cover the fundamentals of Banda materials effective medium theories and introduce single and double negative metamaterials week 9 we'll discuss perfect absorbers and super lens hyperbolic metamaterials and hyperlens tunable photonic metamaterial based devices moving on to module 6 we'll cover meta surfaces in week 10 and the lectures will cover matter surfaces and frequency selective surfaces guided mode resonances applications of meta surface and guided mode resonance based devices module 7 will be on transformation Optics that will be covered in week 11. that will discuss transformation Optics and invisibility clocks carpet cloaking and transformation Optics metamaterials and introduction to different alternative metamaterials or rather different alternative materials for this kind of applications module 8 will discuss realization of nanophotonic devices and that is the final module that will be covered in week 12 over lectures from 34 to 36 that will discuss the Nano fabrication different physical methods and chemical methods involved and we'll also discuss lithography and pattern transfer to obtain those nanoscale devices that we'll be discussing in this course moreover we'll also discuss about the Nano photonic characterization methods now before we begin the course let us first have a look at the entire electromagnetic spectrum as you can see on the screen so electromagnetic radiation ranges from Radio to gamma rays so in this figure it shows the wavelength in meter so radio waves typically have hundreds of meters as their wavelength and it goes down to even 10 to the power minus 12 meter for gamma rays so this is how you know the wavelength is getting reduced when it moves from Radio to gamma rays and this particular demonstration shows you that what is the comparable size of the wavelength so you can see radio waves are more or less of the size of the buildings microwave you all must be familiar with microwave radiation are typically having you know 10 to the minus 2 so that's like centimeter scale and the size is typically of the honeybee and as you go you know towards visible ultraviolet X-ray and gamma ray your wavelength is getting reduced and the size comparable sizes are also getting reduced the corresponding frequency can also be seen here so if you consider one particular case something like microwave which is very commonly used device these days so you can see microwave the frequency range is in you know close to 10 to the power 9 Hertz that is gigahertz range so that way you can actually look into the scale and find out what is the corresponding frequency from each of this waves that are included in the electromagnetic spectrum so keep this particular image in your mind because that will give you a clarity about what frequency range what wavelength range we are talking about now the top part of the figure also tells that you know which rays are able to penetrate Earth atmosphere why means it is able to penetrate no means it is not able to penetrate when it is not able to penetrate our atmosphere means it is getting absorbed in the atmosphere okay and the bottom most one shows the temperature of the black bodies that are able to radiate so what temperature of the black body will be able to radiate it will give up a radiation in this particular frequency range so that you can see here like if you have an object which is like one Kelvin so you can get a microwave kind of radiation when you move to say 100 Kelvin or in the range of say 10 000 Kelvin the the object can emit visible radiation now why we are focusing on visible to some extent because there is the only small fraction in this entire electromagnetic spectrum that is visible to human eyes and it typically starts from Violet to Red so 400 nanometer or 380 nanometer to be precise to 700 or 780 nanometer in some literature so that is the range 380 to 780 nanometer is visible to human light and when we talk about this wavelength and frequency I believe all you all of you remember this cheat sheet of converting frequency to wavelength so if you are able to express the speed of light in vacuum C that is 3 into 10 to Power 8 meter per second as 30 gigahertz centimeter that allows you a quick conversion so if you have 30 gigahertz frequency the wavelength is one centimeter and so on if you have one gigahertz frequency the wavelength will be 30 centimeter so that way you can quickly convert between frequency and wavelength now to understand Nano photonics which is the topic of this course let us first begin with a very broad topic that all of us have studied in our school days and that's Optics so what is Optics it's a branch of physics studying the behavior and properties of light now one is a light I do not only mean visible light I also mean ultraviolet visible and infrared light so that is the range of X typically covers okay and it includes the interaction of light with matter and construction of instruments that can actually that uses this kind of light for manipulation or detection some examples like optical fiber camera wireless mouse which I am using right now lasers binoculars Periscope microscope telescope then Blu-ray devices DVDs Etc these are all based on Optics now you can classify Optics broadly into three subfields the first one is geometrical Optics and as you know it's a very crude approximation so in this approximation light is considered as Rays or particles that explains how light travels in a straight line so straight from our school book you can see using a lens you are able to image a particular object and this can be very well explained using the ray approximation that is the geometrical Optics now there are certain phenomena where you know this kind of approximation of geometrical appetics is not enough so we need to actually go to another subfield which is called physical Optics where light is considered as a wave to explain certain phenomena something like bending of light a diffraction scattering from an object and the phenomena of interference that you might have seen or studied done experiment as well in your school days now that you are able to actually explain this interference fringes by considering light is a wave the third one is the most exact approximation where light is considered as both particles photons and waves so that is also known as particle wave Duality so the phenomena of laser is explained well explained in this particular now let us have a quick look into various soft fields of this UV visible and IR spectrum so if you closely look into this particular figure shown here as the list shown here ultraviolet has got many sub bands extreme UV vacuum UV deep UV mid up and near UV and then these are the energy EV means these are the energy associated this is the wavelength range and this is the frequency range similarly for Visible you can start with Violet to red and you can see the Violet is from 380 to 435 red wavelength are from 625 to 780. when I say infrared there are three sub-ranges neon infrared mid infrared and far infrared so they're also in near infrared you can have IR a IRB okay and you can see these are the wavelength range so I'll not go into the details of reading out each of these details you can refer to this particular figure here or the chart here and you can understand different sub ranges in this UV visible IR spectrum now let us introduce a new term called photonics where photonics is basically a subcategory of Optics that focuses on the Science and Technology of photons so photonics is often used interchangeably with Optics but they do have distinct meanings they're not same exactly Optics whenever we discuss Optics it's basically a broad branch of physics that studies the general behavior and properties of light as visualize vision and perception whereas photonics involves in generation detection and manipulation of light in the form of photons so photonics is concerned with absorption and emission of light mainly besides its transmission modulation signal processing switching and amplification so the picture here depicts absorption of a photon where the photon energy delivered to the electron moves it to a higher energy level or outer orbit so this phenomena is called absorption the opposite also takes place that when you know the electron jumps from a higher energy level to a lower energy level okay a photon is emitted which has got energy equivalent to the difference between the two energy levels so this phenomena is called emission now photonics have got a lot of applications so the typical application areas of photonics are in the field of broadband internet and you know information technology so thanks to photonics I am able to reach to your doorstep today with this lecture because photonics are the optical fibers are the backbone of the entire internet they are not only providing fast internet connection okay photonics also enabling free space Optical Communications Optical computation for quantum photonics and all these things so there are going to be lot of applications of photonics in the future Healthcare and biophotonics so orphotronics and Optics are used in various non-invasive Medical Diagnostic if you remember from the covet time sp02 measurement that was an application of photonics than laser-based surgery that is happening day in and out targeted cancer therapy Ophthalmology everything can be done using you know photonics lighting and energy saving that is another big sector where photonics have tremendously contributed almost entire lighting industry is and the display industry is Shifting towards photonics because they are more energy efficient so you see LED lighting almost everywhere these days moreover solar power with the photovoltaic cell they are also becoming one of the most popular now renewable energy sources because of their competitive pricing as against other renewable energy sources coming to Safety and Security aspects photonics are also very much useful in providing Safety and Security by means of optical Metrology means very fast runtime measurement of a distance and time using lasers so that will be very important in autonomous vehicles moreover you can also think of security Arrangements something like fiber brake rating sensor based you know border fencing then high speed cameras infrared motion detectors there are also different space Technologies something like satellite surveillance system navigation Imaging night vision anti-missile systems high power directed weapon systems which are like you know laser guns and all these things are becoming more and more popular in the Modern Warfare then the other application will be in the you know high quality Manufacturing so you can actually do high quality manufacturing and precise manufacturing using laser so material processing something like cutting welding shouldering marking all this thing surface modification all these things can be done using laser so as you can see photonics more or less has gone application in almost every aspect of human life and that is why it's a very very important subject to know right now we have understood two things Optics and photonics now if you compare Optics and photonics what is the main difference the main difference comes from the relative size d of the constitutive Elements which are interacting with the electromagnetic waves of wavelength say Lambda so in Optics we are actually dealing with constant elements something like lenses mirrors prisms beam splitter all these things which are having Dimensions much much larger than the wavelength of light whereas in photonics we actually bring the dimensions comparable that means you know the size of the material of the matter that is interacting with light also has got a comparable dimension so here you see in particular example of total internal reflection that is taking place in a class rod now this particular phenomena is the basics of you know light propagation through Optical fibers when I consider Optical fibers that's a typical photonics application why so what is the dimension of the optical fiber if you look into a single mode fiber it has got a diameter of seven to ten micrometer and what is the wavelength of light as we understand it is like 400 nanometers so it's like 0.4 micrometer 2.8 almost 0.8 micrometer so they are almost comparable so that is where photonics becomes you know relevant so when I say photonics this is the main factor that the size of the constituent materials or elements will be comparable to the wavelength of light and that allows you generation processing guiding and sensing of light so what are the typical applications lasers amplifiers photodiodes light sensors Optical fibers so all these are basically the optical tools that fall under the bucket of photonics so naturally there will be a curiosity to know that what happens when the size of the constitutive elements become much smaller than you know the wavelength of light so that is where Nano photonics comes into picture so nanopotronics is basically the field where the elements which are interacting with light has got Dimensions sub wavelength okay that is much smaller than the length of light so nanofotronics typically covers light matter interaction at nanoscale okay so Nano photonics allow you to design devices which can slow down enhance produce or manipulate light by understanding how light behaves as it propagates or travel through you know sub wavelength dimensions and in short nanopotonics will actually um tell you about the photon interactions with nanostructures such as Nano metallic particles or metallic nanoparticles you can say nanocrystals semiconductor Nano dots photonic crystals and biometric biomaterials such as tissues DNS Etc so this is where the Nano photonics comes into the picture in short nanophotronics is the study of the behavior of light on the nanometer scale or you can say it is the interaction interaction of a nanometer skill object with light so again it covers the interaction light matter interaction at nanoscale why it is important you know because it allows you to manipulate light at nanoscale and that that capability that spatial power comes to you when you actually make light to interact with some elements which are having much smaller than the wavelength of light why should we study nanopotronics we understood what is nanopotonic starting from what is Optics what is photonics and then we understood what is nanophotonics now we need to know why we should study nanophotonics now in this era of information and Technology you can see that the world economy is more or less getting digitized using internet like e-entertainment then e-commerce everything is booming so you need you know a backbone infrastructure that can support that thing and the development that is happening if you take computers smartphones tablets smart watches these items have become Inseparable part of our life you cannot actually imagine a day without this and everybody is now having multiple devices so that actually puts a lot of you know load on the internet and with this growing demand of data sharing internet also you know becomes a huge Storehouse of data so whenever you are Googling something or you are making a search you want the data to come to you very fast but where from you have to store it somewhere right so you also need you know lot of storage a lot of computation power to search in this huge storage what you have looked for so all these things are putting a huge load in terms of energy requirement speed requirement Computing speed and you know the power requirement so everything is becoming more and more complex and you can see the rise of global internet users so with world population being 8 billion right now we have more than 5 billion you know internet users that's like more than 60 percent of the world population and do you think it's going to be less no it's going to be even more and more in the future even kids are now getting into using all this you know tablets and smartphones so the global data traffic is going to reach 475 exabyte per month and that's the traffic estimated by the end of 2023 and do you think that's all no that's not at all that is just the tip of the iceberg if you see the tsunami of data traffic is actually approaching look at this particular graph so here you can see 2023 here we are so M2M is like machine to machine when say a machine is talking to another machine like a chatbot or something like that and without M2M that is like human to human and all these things so there are two categories the data has been split so you can see the total traffic per month is 475 exabyte by 2023 and that will go up to this level in 2013. so that's a huge jump and if you are wondering what is xavite so let's start with GB I think all of us are well aware of GB now so 1GB is 1024 MB then you take 1024 GB you get a terabyte you take 1024 terabytes you get a petabyte 1024 petabytes will give you one exabyte so this is the scale of data we are talking about now with such a huge thing coming to our to to our side we need to be prepared and one of the key challenges for 21st century has been to supply efficient accessibility over internet to billions of people so you want more and more people to be connected and that is the desire so that will require huge bandwidth and error free connections and do if you think only of internet as a cloud that's not correct Internet also means millions of data centers are actually linked to each other they are talking to each other through the translucentic cables the optical fiber cables which are laid through the you know ocean flow to connect different continents and this is carrying so much of data you can't imagine so all this are happening at a cost so when you actually say you know you are doing a Google Search and you are getting your search results a that that particular Google search actually emits almost 500 kilogram of CO2 every second now you can understand how much power is being utilized how much energy is being consumed and that is how it will also affect the you know uh global warming issue so what do you want you actually want power efficient systems and this is the problem that is data centers are likely to face challenges in limiting their you know energy consumption which is likely to go up at a rate of 10 percent per year so this is the forecast of how the energy consumption in data center will increase from 2014 to 2030 and you can see more or less it is kind of increasing steadily at a rate of 10 percent every year so with the growing demand of Internet penetration over the World there is also demand for high speed connectivity scaling up store and process of data traffic and this is a forecast not forecast this is a result a report showing that you know by January 2023 we already have 50 almost 60 percent urbanization okay people connecting to you know in the cities and then you have 68 population using mobile phones almost 64 people using internet and there are more or less about 60 people also are active social media users so these are all actually Trends showing you that how much load is going to come on the internet so scaling up the data centers to handle this much amount of incoming data traffic is one solution but that will also take the overall carbon footprint very very high because almost linearly the carbon footprint is also increase so the need of the hour is to develop miniaturized and energy efficient systems for modern communication Technologies we'll first look into that is modern Electronics capable of handling this so modern Electronics have done fantastically well so far it has got you know achieved a lot in terms of device integration miniaturization power efficiency and information processing speed no complaints they have done tremendously well information and communication technology devices in the society they contribute so approximately 30 percent of the electricity usage worldwide so they are now becoming a major factor who is consuming energy and power so these are all different now devices which are connected to Internet and they are also consuming power because they are continuously you know Computing processing information so the growing consumption of energy by this ICT devices will also proportionally increase the CO2 emission so all these things is not going to make our life simple with too much of data computation carbon dioxide emission is also increasing global warming so that is going to get back to us very badly so how do you handle this so one solution to control the universal growth of this energy consumption is to reduce the transistors size on the semiconductor chip why so because smaller transistors will require less power for their functioning and this will reduce the overall enough power consumption of the chip and loop less power means the chip will also get less less heated up and that will also allow us to increase the clock speed further so it is actually helping us to a great extent now since the announcement of integrated Electronics the semiconductor industry had adopted an approximation predicted by Dr Moore or Gordon Moore in 1965 Dr Moore predicted that in order to scale up the device scale the device size and enhance the microprocessors performance the transistor density in a particular chip or a single IC needs to be doubled every 1.5 years to two years means within 18 to 24 months the number of transistors in a chip will roughly double and over the last 50 years this assumption has been the roadmap for all the electronics Industry and although Moore's Law is not a natural law but the growing rate of data hungry Communication System more or less you know this law has been widely adopted by almost every semiconductor industry but however with billions of transistors in the chip so this is how till now things are going fine so it's doubling you know clock speed and the power density as you can see here all these are going the way more has predicted okay with with a requirement increasing day by day there is a point where you know more slow will no longer be able to sustain itself okay so that is where you know you have to think of some alternative so as the data traffic increases every year we need faster data rate with miniaturized IC so this is this is our requirement but then what is Stopping Us in getting higher and higher speed that will be you know the RC delay with the device sizes becoming smaller and smaller that actually increases your data processing okay in a small volume but the RC delay or resistive capacitive delay in the electronic circuit they become a major bottleneck now why do you see this RC delay any transistor you can model as a equivalent RC network every node in the electronic circuit can be thought of a capacitive nature so to charge your discharge that node there is a finite time charging and discharging time and that that restricts the speed Beyond which you cannot go also when you think of you know IC wirings or interconnect they there also you can model the interconnect using equivalent RC delay model and wherever this RC delays are coming there is a restriction on the overall speed so you cannot actually get better and why miniaturization actually impacting that because when you miniaturize your electric interconnects they are Getting Thinner and with that the resistivity per length is actually increasing so miniaturization allows you to pack more devices but then the speed is getting reduced because of this RC delay is getting into the picture so we want to increase the usage in the smart devices and meet the demand of data that is that it will be placing huge liability on the radio network so we understood that scaling down on transistors can reduce the energy consumption but that will also bring in few issues something like the energy dissipation from thinner interconnects will increase because you know the resistivity per unit length will increase in for a shorter interconnect then people like semiconductor people industry actually moved on to explore what is called multi-core processor design so instead of having only one core you can actually split your course and parallelize the processing so that can actually bring down the overall power consumption but is this going to help us in the long run with the amount of data traffic that you have seen coming our way we have seen a tsunami of data traffic coming to our way so we have to somehow move on to Optical technology where there is no RC delay that is restricting the amount of data rate that we can achieve so we have to go to photonic Technologies to handle this you know enormous amount of data traffic and that will also when you do everything in the optical field that will also reduce the power and energy consumption at the data centers so integrated macro photonics have done well it can actually so this is a particular or typical diagram of a canonical um photonic system where you have a RF system or antenna that is bringing in the RF input you have a Laser Source that is giving you the light you have an optical modulator you do the signal processing in the optical domain you detect it that means it you are finally converting it back to current and then you give the RF output to the receiver so that way you can incorporate photonics with microwave and can do you know speed up the system so integrated macro photonics can reduce the device footprint that is possible to some extent by confined confining light in the ultra small volume and that will enhance the light matter interaction so they will definitely offer a less complex signal processing architecture here you will be doing the optical signal processing and you can also achieve a higher data transfer rate with improved SNR and you can get a lower power dissipation so looks like you know integrated micro photonics can solve all our major problems something like handling of the high speed data traffic lowering of the energy consumption per unit data and also meeting the bandwidth requirements and it is also possible to do some integration with the existing intra chip and internship electrical data communication systems such as this one so this is a typical diagram which shows integration between electronics and photonic circuits on the same chip for better signal processing so what is the problem then what is stopping microwave photonics or it is able to provide us all the solutions that we're looking for one problem that you can think of in micro photonics is that when you are in the field of photonics you cannot scale down your devices to nanoscale is that clear so when you are in photonics you have a limit called diffraction limit of light diffraction limit of light tells you that light cannot be squished in a volume which is lesser than Lambda by 2. so you cannot actually go sub wavelength with photons or you can say light cannot be squished into sub wavelength volumes so this is where the technology situation right now is electronics Industry has done very well in terms of miniaturization so you can get you know your critical device Dimension down to you know 10 nanometer or even below but the maximum speed that you can get from Electronics devices is restricted up to gigahertz you cannot go beyond that because of the RC delays now if you look into photonics they have done very well in overcoming the RC delay issues but there is a particular size restriction for the photonic circuits and this limit is set by the diffraction limit of light so you want to have something here which can actually go and work in terahertz speed but allow you also to give you know device Dimensions which are in nanometer scale and this is where plasmonics will come into picture so plasmonics is a field that brings in the best of both electronics and photonics world so plasmonics will naturally interfere with the you know similar size electronic devices so it is very easy to match with the electronics part as well as they can also naturally interfere with the photonics one because they have similar operating speed so the situation is like this Electronics can provide miniaturized devices with critical Dimensions less than 10 nanometer but the maximum speed you can achieve is restricted to gigahertz due to the RC delay issues with the electronics and if you look at photonics photonics can help to reach terahertz operating speed but the miniaturization is not possible below one micrometer that is typically the you know critical device dimension for photonics and this limit is set by the diffraction limit so what is the way out so that is where plasmonics coming to the picture so plasmonics will enable and improved Synergy between electronics and photonics because plasmonics naturally interfere with similar size electronic devices and plasmonics can naturally interfere with also similarly operating speed photonic Network so plasmonics is in a position to offer terahertz Speed in nanometer scale bringing together the best of the both electronics and photonics worlds and as you can see that this field will require inputs from Optical engineering electrical engineering and nanotechnology so this week it becomes a truly interdisciplinary field of study and that is how nanophotonics and a sub part of it is metallic nanoplasmonics or simply plasmonics that can help deliver the best of the Two Worlds and this can actually help us meet the upcoming data traffic requirements so we understood how nanopotonics and then what is plasmonics so if you say plasmonics you can also call it metallic nanoplasmonics they are more or less interchangeably used this is a relatively young branch of research and as you understand this is a part of nanopotonics plasmonics can confine electromagnetic field below the diffraction limit so this is where the good thing is and it provides solution for future on chip nanoscale devices it allows to scale down the integrated photonic devices to nanoscale so the miniaturization is possible here plasmonics concerns about the investigation of electron oscillations in metallic noun structures which are known in surface response and what are the surface plus bonds they have will come to that soon the surface plus bonds have very interesting Optical properties so signals coming from an optical fiber can be squeezed into software length volume using plasmonics by taking help of surface response as you can see in this figure surface plus bonds can propagate as a coherent electromagnetic oscillation on the so spp means surface plus one polyatons which are the propagating surface response so they can propagate along metal dielectric interface so in this case you can think of gold as a metal so gold Air interface it can propagate and you can also see here that the dimension is deep sub wavelength the separation s is less than 1 by 10 times Lambda naught so you are basically talking about separation which are Lambda naught by ten so this tiny or deep sub wavelet scale separation is also supported used by surface response you can also make you know surface plus bonds to propagate a long distance here an experimental result shows that if you take a silver nanowire and you launch light in one end of it say here this bright spot shows light excitation in one end of the silver nanowire okay and then the light of the photons are converted into surface plus bonds so what are surface plus bonds these are basically surface electrons okay so from photons you are actually transferring back your energy to some kind of electrons and those surface electrons propagate along the surface of this nanowire that is at the interface of say if it is a silver nanowire and air is the surrounding media so the electron wave will propagate along silver Air interface and at the end it can again come back as light okay so this kind of propagation and squeezing of energy in deep sub wavelength scale is possible in Plus One X so I have taken the name of plasma several times while talking about plasmonics let's try to understand what is plasmon plasma is basically a density wave in an electron gas so if you try to imagine what is a density wave you can think of sound wave okay and that is basically a density wave in a gas consisting of molecules what do plasmas exist they exist mainly in metals where there are abundance of electrons and the electrons are weakly bound to the atoms and they can freely roam around so the electrons in a metal can actually uble like a piece of jelly that is like it can actually move like this so pulled back by the attraction of the positive metal ions so when the when the electrons move up they leave the positive metal ions so that attraction actually pull them back so that is how the ubling of the electron cloud takes place and when this all the electrons you know they oscillate in the same frequency we call that a plasma frequency Omega p and that is the case where the electron gas has resonance and when you say resonance it is like you know it is basically the billions of electrons they oscillate in sink and we can also Define plus bonds as a collective wave where these billions of electrons oscillating in zinc so we have discuss two types of s surface plus Bonds are there one could be propagating surface plus bonds or Surface plus one polaroidance that can be excited with different coupling mechanism that will study in details later on but you can actually make you know surface plus bonds to propagate along a metal dielectric interface as shown here so there is H Nu there is light being used to excite so the exciting mechanism is not shown I'll discuss that the DirectX addition is not possible but by taking help of some kind of grating or prism couplers you can actually excite surface plus bonds so this is the material and dielectric interface and as you can see metal has got a large negative permittivity at this Optical frequency so the field penetrates very less towards the metal and mostly it is in the dielectric and this is how it will propagate while propagating the field is also leaking out as you can see and as the field will die down while propagation and that will be the distance over which the plus bonds can propagate there is another type of plus one also possible that is called localized surface plus one and as the name suggests that this response are basically localized on nanostructure something like metallic nanoparticles and this plus bonds can be directly excited using just by Shining Light on it you do not require a special mechanism to excite those plus bonds and if you look into plasmonics the funny thing is you know the plasmonics though it is a you know savior of mankind in the future but the history or the Genesis of plasmonics dates back to Roman so Romans were the nanotechnology Pioneer how this came into picture so you look into the figure here it shows the image of the same leica's cup it's a cup okay so that is kept in British museum so when you put light from the front to see what is the color of the cup you see it's green but if you put the light source at the back the cup appears red that is something amazing usually if you take a you know yellow kind of thing yellow glass or whatever it just think of it that when you look it from front or back more or less it will look same but here in this case there is a difference in the colors one you are looking from the front and the back and when scientists actually look into the details of this class they have figured out that there are tiny nanoparticles involved in this particular like a girl's cup so that is where the nanotechnology actually came in and because of this nanoparticles only in the scattering mode this glass is looking green and because of the absorption of the nanoparticles I'll go into more details of it later on this glass is looking the cup is looking red so surface plus Bond when they resonate with the frequency of the incoming light you can actually get surface plus one resonance and this resonance will significantly enhance the light scattering and absorption capability of this tiny nanoparticles as you can see here if you take gold nanoparticles over size you know 20 to 150 nanometer the resonance wavelength can change from 520 to 660 nanometer for silver if you consider the same size you can actually tune the resonance of surface plus bonds over a different range it's again similarly wide range but different range 382 600 nanometer so one need to keep in mind that this resonance is not only dependent on the material of the null particles their size it is also dependent on their shape and also the surrounding media that is around this particular nanoparticles so there is a graph of localized surface plus one resonance tunability as you can see here this is for silver nanosphere this is the range over which you can you know you can choose silver nanosphere and change the size of it to go from UV to visible range okay you can look for gold nanospheres that can give you more more or less within visible range only but if you choose Nano shells or Nano X that these are like ellipsoid kind of structure you actually get a very wide tunability starting from visible to Mid infrared similarly you can choose for Nano rods which are like cylinders Nano cylinders triangles Cube nanorize all different shapes are possible so you are able to change the surface plus one resonance over a wide white frequency range okay but as you can see everything within UV visible and infrared and why it is important so the ability to focus light and manipulate light at the nanometer scale has got a lot of potential and this is what has been claimed by the pioneer of plasmonics Professor Harry Atwater at Celtic us so he he actually foreseen that this field is going to be very very exciting and it is compelling because you can see lot of applications of this particular field in nanoscale devices you can as you have seen you can you know propagate surface plus bonds over nanoscale distances you can confine energy with deep sub wavelength spacing so all those will allow you to get nanoskill devices you can make directional Nano antennas for your circuits using this kind of metallic nanoparticles or dielectric nanoparticles you can think of plasmonic solar cells where nanoparticles with enhanced absorption at their resonance will allow you to absorb more light to be converted into electricity so they can be you know added to solar cell to increase their efficiencies you can think of photothermal cancer therapy using nanoparticles where nanoparticles can be plasmonic nanoparticles can be injected into bloodstream with some you know targeted delivery so that this nanoparticles go and sit on there uh cancer tumor and you can shine light from the outside neon infrared light is able to penetrate the skin and it can go inside nanoparticles having resonance at that particular wavelength will be able to absorb light very strongly and that with absorption the nanoparticles will heat it up and that increase in temperature will kill the cancer cells so you can see these nanoparticles can be your savior they can be also used for biological and chemical sensing where you know the change in the refractive index of the surrounding media of the nanoparticles can be sensed as you know shift in the plasma resonance Peak wavelength so you can actually sense very very tiny amount of molecules present using this kind of sensors this also can help you achieve very high density optical storage something like this one um up to 5D optical storage so here the you know images are imprinted in different layers at different wavelengths and polarization so these are only some specific applications you can think of a lot more applications using plasmonics so this is the future going ahead so that is all for today's lecture and we'll try to cover the introduction to matter surfaces and metamaterials in the next lecture so thank you in case you have any query you can send it send it to me at this email address dev.shikhtar at the rate iitg.ac.in but do not forget to mention mooc in the subject of your email thank you thank you [Music]

foreign [Music] from the Department of electronics and electrical engineering ID guwahati welcome to lecture one of my course on Nano photonics plasmonics and metamaterials this course will provide a detailed introduction to these three pillars of the future photonic Technologies by covering their fundamentals and recent advancements with the growing dominance of 5G Technologies internet of things and emerging applications of artificial intelligence and machine learning in every aspect of human life this course on Nano photonics has become more relevant and important than ever before it is the solution to meet the demands of extremely high computational speed requirement and the ultra fast data transfer rate of the future besides keeping the power consumption minimals Nano photonics allows one to achieve terahertz speech at nanometer scale bringing together the best of the electronics and photonics world this course will first cover the fundamentals of Nano photonics principles of photonic crystals plasmonics or metal Optics excitation of surface plus bounds and their applications later on the course will also focus on metamaterials and meta surfaces covering their fundamentals and various applications such as tunable devices absorbers super lens hyperlens transformation Optics clocking Etc the course will also introduce new alternative materials for Nano photonics to mids meet today&#39;s demand and summarize different techniques for fabrication and characterization of nanoscale devices the course is designed for undergraduate and postgraduate students with basic knowledge of physics and electromagnetics the course will actually bring the emerging fields of nanophotonics plus phonics and metamaterials to your doorstep via the swam platform for the first time and we hope that UG and PG students with background in electronics instrumentation physics chemistry Material Science and Engineering chemical engineering and any researcher and Industry people working in the broad areas of photonics will get benefited from this course this course will surely motivate you to explore and study further in this exciting field of research which has got truly endless opportunities here is the detailed course plan we will cover eight modules over the span of 36 lectures as you can see module 1 is Introduction and it will be covered in the first week with three lectures covering the introduction of Nan photonics and plasmonics introduction to mathematerials and meta surfaces and their overview and current status the second module will be on fundamentals of nanophotonics which will be covered over week two and three in week 2 we&#39;ll discuss about the electromagnetic theory of light electromagnetic properties of material and electromagnetic waves in dielectric media so that will take care of the light matter interaction in week 3 we&#39;ll first study the polarization properties of light reflection and refraction in details when light hits at a interface using the frenel&#39;s equation and will understand the absorption dispersion and scattering properties of light module 3 will cover the electromagnetic waves in periodic structures that will be covered in week four and five so let 10 to 12 will cover the Matrix theory of dielectric layered media 1D photonic crystals dispersion relation and photonic band Gap structures in week 5 we&#39;ll cover the real and reciprocal ledisis 2D and 3D photonic crystals and discuss emerging applications of photonic crystals foreign model 4 will cover metal Optics that is it will introduce plasmonics in details with its fundamentals so in week 6 we&#39;ll cover Optical properties of metal then surface plus Bond fluorideons spp their fundamentals and application of spps in week 7 we&#39;ll cover the localized surface plus Bond resonance plasmonic nanoparticles based antennas and web guides and different applications of localized surface plus Bond resonance next we&#39;ll move on to module 4 that will be covered in week 8 and 9 and this module 5 will cover matter materials their fundamentals and applications week 8 will cover the fundamentals of Banda materials effective medium theories and introduce single and double negative metamaterials week 9 we&#39;ll discuss perfect absorbers and super lens hyperbolic metamaterials and hyperlens tunable photonic metamaterial based devices moving on to module 6 we&#39;ll cover meta surfaces in week 10 and the lectures will cover matter surfaces and frequency selective surfaces guided mode resonances applications of meta surface and guided mode resonance based devices module 7 will be on transformation Optics that will be covered in week 11. that will discuss transformation Optics and invisibility clocks carpet cloaking and transformation Optics metamaterials and introduction to different alternative metamaterials or rather different alternative materials for this kind of applications module 8 will discuss realization of nanophotonic devices and that is the final module that will be covered in week 12 over lectures from 34 to 36 that will discuss the Nano fabrication different physical methods and chemical methods involved and we&#39;ll also discuss lithography and pattern transfer to obtain those nanoscale devices that we&#39;ll be discussing in this course moreover we&#39;ll also discuss about the Nano photonic characterization methods now before we begin the course let us first have a look at the entire electromagnetic spectrum as you can see on the screen so electromagnetic radiation ranges from Radio to gamma rays so in this figure it shows the wavelength in meter so radio waves typically have hundreds of meters as their wavelength and it goes down to even 10 to the power minus 12 meter for gamma rays so this is how you know the wavelength is getting reduced when it moves from Radio to gamma rays and this particular demonstration shows you that what is the comparable size of the wavelength so you can see radio waves are more or less of the size of the buildings microwave you all must be familiar with microwave radiation are typically having you know 10 to the minus 2 so that&#39;s like centimeter scale and the size is typically of the honeybee and as you go you know towards visible ultraviolet X-ray and gamma ray your wavelength is getting reduced and the size comparable sizes are also getting reduced the corresponding frequency can also be seen here so if you consider one particular case something like microwave which is very commonly used device these days so you can see microwave the frequency range is in you know close to 10 to the power 9 Hertz that is gigahertz range so that way you can actually look into the scale and find out what is the corresponding frequency from each of this waves that are included in the electromagnetic spectrum so keep this particular image in your mind because that will give you a clarity about what frequency range what wavelength range we are talking about now the top part of the figure also tells that you know which rays are able to penetrate Earth atmosphere why means it is able to penetrate no means it is not able to penetrate when it is not able to penetrate our atmosphere means it is getting absorbed in the atmosphere okay and the bottom most one shows the temperature of the black bodies that are able to radiate so what temperature of the black body will be able to radiate it will give up a radiation in this particular frequency range so that you can see here like if you have an object which is like one Kelvin so you can get a microwave kind of radiation when you move to say 100 Kelvin or in the range of say 10 000 Kelvin the the object can emit visible radiation now why we are focusing on visible to some extent because there is the only small fraction in this entire electromagnetic spectrum that is visible to human eyes and it typically starts from Violet to Red so 400 nanometer or 380 nanometer to be precise to 700 or 780 nanometer in some literature so that is the range 380 to 780 nanometer is visible to human light and when we talk about this wavelength and frequency I believe all you all of you remember this cheat sheet of converting frequency to wavelength so if you are able to express the speed of light in vacuum C that is 3 into 10 to Power 8 meter per second as 30 gigahertz centimeter that allows you a quick conversion so if you have 30 gigahertz frequency the wavelength is one centimeter and so on if you have one gigahertz frequency the wavelength will be 30 centimeter so that way you can quickly convert between frequency and wavelength now to understand Nano photonics which is the topic of this course let us first begin with a very broad topic that all of us have studied in our school days and that&#39;s Optics so what is Optics it&#39;s a branch of physics studying the behavior and properties of light now one is a light I do not only mean visible light I also mean ultraviolet visible and infrared light so that is the range of X typically covers okay and it includes the interaction of light with matter and construction of instruments that can actually that uses this kind of light for manipulation or detection some examples like optical fiber camera wireless mouse which I am using right now lasers binoculars Periscope microscope telescope then Blu-ray devices DVDs Etc these are all based on Optics now you can classify Optics broadly into three subfields the first one is geometrical Optics and as you know it&#39;s a very crude approximation so in this approximation light is considered as Rays or particles that explains how light travels in a straight line so straight from our school book you can see using a lens you are able to image a particular object and this can be very well explained using the ray approximation that is the geometrical Optics now there are certain phenomena where you know this kind of approximation of geometrical appetics is not enough so we need to actually go to another subfield which is called physical Optics where light is considered as a wave to explain certain phenomena something like bending of light a diffraction scattering from an object and the phenomena of interference that you might have seen or studied done experiment as well in your school days now that you are able to actually explain this interference fringes by considering light is a wave the third one is the most exact approximation where light is considered as both particles photons and waves so that is also known as particle wave Duality so the phenomena of laser is explained well explained in this particular now let us have a quick look into various soft fields of this UV visible and IR spectrum so if you closely look into this particular figure shown here as the list shown here ultraviolet has got many sub bands extreme UV vacuum UV deep UV mid up and near UV and then these are the energy EV means these are the energy associated this is the wavelength range and this is the frequency range similarly for Visible you can start with Violet to red and you can see the Violet is from 380 to 435 red wavelength are from 625 to 780. when I say infrared there are three sub-ranges neon infrared mid infrared and far infrared so they&#39;re also in near infrared you can have IR a IRB okay and you can see these are the wavelength range so I&#39;ll not go into the details of reading out each of these details you can refer to this particular figure here or the chart here and you can understand different sub ranges in this UV visible IR spectrum now let us introduce a new term called photonics where photonics is basically a subcategory of Optics that focuses on the Science and Technology of photons so photonics is often used interchangeably with Optics but they do have distinct meanings they&#39;re not same exactly Optics whenever we discuss Optics it&#39;s basically a broad branch of physics that studies the general behavior and properties of light as visualize vision and perception whereas photonics involves in generation detection and manipulation of light in the form of photons so photonics is concerned with absorption and emission of light mainly besides its transmission modulation signal processing switching and amplification so the picture here depicts absorption of a photon where the photon energy delivered to the electron moves it to a higher energy level or outer orbit so this phenomena is called absorption the opposite also takes place that when you know the electron jumps from a higher energy level to a lower energy level okay a photon is emitted which has got energy equivalent to the difference between the two energy levels so this phenomena is called emission now photonics have got a lot of applications so the typical application areas of photonics are in the field of broadband internet and you know information technology so thanks to photonics I am able to reach to your doorstep today with this lecture because photonics are the optical fibers are the backbone of the entire internet they are not only providing fast internet connection okay photonics also enabling free space Optical Communications Optical computation for quantum photonics and all these things so there are going to be lot of applications of photonics in the future Healthcare and biophotonics so orphotronics and Optics are used in various non-invasive Medical Diagnostic if you remember from the covet time sp02 measurement that was an application of photonics than laser-based surgery that is happening day in and out targeted cancer therapy Ophthalmology everything can be done using you know photonics lighting and energy saving that is another big sector where photonics have tremendously contributed almost entire lighting industry is and the display industry is Shifting towards photonics because they are more energy efficient so you see LED lighting almost everywhere these days moreover solar power with the photovoltaic cell they are also becoming one of the most popular now renewable energy sources because of their competitive pricing as against other renewable energy sources coming to Safety and Security aspects photonics are also very much useful in providing Safety and Security by means of optical Metrology means very fast runtime measurement of a distance and time using lasers so that will be very important in autonomous vehicles moreover you can also think of security Arrangements something like fiber brake rating sensor based you know border fencing then high speed cameras infrared motion detectors there are also different space Technologies something like satellite surveillance system navigation Imaging night vision anti-missile systems high power directed weapon systems which are like you know laser guns and all these things are becoming more and more popular in the Modern Warfare then the other application will be in the you know high quality Manufacturing so you can actually do high quality manufacturing and precise manufacturing using laser so material processing something like cutting welding shouldering marking all this thing surface modification all these things can be done using laser so as you can see photonics more or less has gone application in almost every aspect of human life and that is why it&#39;s a very very important subject to know right now we have understood two things Optics and photonics now if you compare Optics and photonics what is the main difference the main difference comes from the relative size d of the constitutive Elements which are interacting with the electromagnetic waves of wavelength say Lambda so in Optics we are actually dealing with constant elements something like lenses mirrors prisms beam splitter all these things which are having Dimensions much much larger than the wavelength of light whereas in photonics we actually bring the dimensions comparable that means you know the size of the material of the matter that is interacting with light also has got a comparable dimension so here you see in particular example of total internal reflection that is taking place in a class rod now this particular phenomena is the basics of you know light propagation through Optical fibers when I consider Optical fibers that&#39;s a typical photonics application why so what is the dimension of the optical fiber if you look into a single mode fiber it has got a diameter of seven to ten micrometer and what is the wavelength of light as we understand it is like 400 nanometers so it&#39;s like 0.4 micrometer 2.8 almost 0.8 micrometer so they are almost comparable so that is where photonics becomes you know relevant so when I say photonics this is the main factor that the size of the constituent materials or elements will be comparable to the wavelength of light and that allows you generation processing guiding and sensing of light so what are the typical applications lasers amplifiers photodiodes light sensors Optical fibers so all these are basically the optical tools that fall under the bucket of photonics so naturally there will be a curiosity to know that what happens when the size of the constitutive elements become much smaller than you know the wavelength of light so that is where Nano photonics comes into picture so nanopotronics is basically the field where the elements which are interacting with light has got Dimensions sub wavelength okay that is much smaller than the length of light so nanofotronics typically covers light matter interaction at nanoscale okay so Nano photonics allow you to design devices which can slow down enhance produce or manipulate light by understanding how light behaves as it propagates or travel through you know sub wavelength dimensions and in short nanopotonics will actually um tell you about the photon interactions with nanostructures such as Nano metallic particles or metallic nanoparticles you can say nanocrystals semiconductor Nano dots photonic crystals and biometric biomaterials such as tissues DNS Etc so this is where the Nano photonics comes into the picture in short nanophotronics is the study of the behavior of light on the nanometer scale or you can say it is the interaction interaction of a nanometer skill object with light so again it covers the interaction light matter interaction at nanoscale why it is important you know because it allows you to manipulate light at nanoscale and that that capability that spatial power comes to you when you actually make light to interact with some elements which are having much smaller than the wavelength of light why should we study nanopotronics we understood what is nanopotonic starting from what is Optics what is photonics and then we understood what is nanophotonics now we need to know why we should study nanophotonics now in this era of information and Technology you can see that the world economy is more or less getting digitized using internet like e-entertainment then e-commerce everything is booming so you need you know a backbone infrastructure that can support that thing and the development that is happening if you take computers smartphones tablets smart watches these items have become Inseparable part of our life you cannot actually imagine a day without this and everybody is now having multiple devices so that actually puts a lot of you know load on the internet and with this growing demand of data sharing internet also you know becomes a huge Storehouse of data so whenever you are Googling something or you are making a search you want the data to come to you very fast but where from you have to store it somewhere right so you also need you know lot of storage a lot of computation power to search in this huge storage what you have looked for so all these things are putting a huge load in terms of energy requirement speed requirement Computing speed and you know the power requirement so everything is becoming more and more complex and you can see the rise of global internet users so with world population being 8 billion right now we have more than 5 billion you know internet users that&#39;s like more than 60 percent of the world population and do you think it&#39;s going to be less no it&#39;s going to be even more and more in the future even kids are now getting into using all this you know tablets and smartphones so the global data traffic is going to reach 475 exabyte per month and that&#39;s the traffic estimated by the end of 2023 and do you think that&#39;s all no that&#39;s not at all that is just the tip of the iceberg if you see the tsunami of data traffic is actually approaching look at this particular graph so here you can see 2023 here we are so M2M is like machine to machine when say a machine is talking to another machine like a chatbot or something like that and without M2M that is like human to human and all these things so there are two categories the data has been split so you can see the total traffic per month is 475 exabyte by 2023 and that will go up to this level in 2013. so that&#39;s a huge jump and if you are wondering what is xavite so let&#39;s start with GB I think all of us are well aware of GB now so 1GB is 1024 MB then you take 1024 GB you get a terabyte you take 1024 terabytes you get a petabyte 1024 petabytes will give you one exabyte so this is the scale of data we are talking about now with such a huge thing coming to our to to our side we need to be prepared and one of the key challenges for 21st century has been to supply efficient accessibility over internet to billions of people so you want more and more people to be connected and that is the desire so that will require huge bandwidth and error free connections and do if you think only of internet as a cloud that&#39;s not correct Internet also means millions of data centers are actually linked to each other they are talking to each other through the translucentic cables the optical fiber cables which are laid through the you know ocean flow to connect different continents and this is carrying so much of data you can&#39;t imagine so all this are happening at a cost so when you actually say you know you are doing a Google Search and you are getting your search results a that that particular Google search actually emits almost 500 kilogram of CO2 every second now you can understand how much power is being utilized how much energy is being consumed and that is how it will also affect the you know uh global warming issue so what do you want you actually want power efficient systems and this is the problem that is data centers are likely to face challenges in limiting their you know energy consumption which is likely to go up at a rate of 10 percent per year so this is the forecast of how the energy consumption in data center will increase from 2014 to 2030 and you can see more or less it is kind of increasing steadily at a rate of 10 percent every year so with the growing demand of Internet penetration over the World there is also demand for high speed connectivity scaling up store and process of data traffic and this is a forecast not forecast this is a result a report showing that you know by January 2023 we already have 50 almost 60 percent urbanization okay people connecting to you know in the cities and then you have 68 population using mobile phones almost 64 people using internet and there are more or less about 60 people also are active social media users so these are all actually Trends showing you that how much load is going to come on the internet so scaling up the data centers to handle this much amount of incoming data traffic is one solution but that will also take the overall carbon footprint very very high because almost linearly the carbon footprint is also increase so the need of the hour is to develop miniaturized and energy efficient systems for modern communication Technologies we&#39;ll first look into that is modern Electronics capable of handling this so modern Electronics have done fantastically well so far it has got you know achieved a lot in terms of device integration miniaturization power efficiency and information processing speed no complaints they have done tremendously well information and communication technology devices in the society they contribute so approximately 30 percent of the electricity usage worldwide so they are now becoming a major factor who is consuming energy and power so these are all different now devices which are connected to Internet and they are also consuming power because they are continuously you know Computing processing information so the growing consumption of energy by this ICT devices will also proportionally increase the CO2 emission so all these things is not going to make our life simple with too much of data computation carbon dioxide emission is also increasing global warming so that is going to get back to us very badly so how do you handle this so one solution to control the universal growth of this energy consumption is to reduce the transistors size on the semiconductor chip why so because smaller transistors will require less power for their functioning and this will reduce the overall enough power consumption of the chip and loop less power means the chip will also get less less heated up and that will also allow us to increase the clock speed further so it is actually helping us to a great extent now since the announcement of integrated Electronics the semiconductor industry had adopted an approximation predicted by Dr Moore or Gordon Moore in 1965 Dr Moore predicted that in order to scale up the device scale the device size and enhance the microprocessors performance the transistor density in a particular chip or a single IC needs to be doubled every 1.5 years to two years means within 18 to 24 months the number of transistors in a chip will roughly double and over the last 50 years this assumption has been the roadmap for all the electronics Industry and although Moore&#39;s Law is not a natural law but the growing rate of data hungry Communication System more or less you know this law has been widely adopted by almost every semiconductor industry but however with billions of transistors in the chip so this is how till now things are going fine so it&#39;s doubling you know clock speed and the power density as you can see here all these are going the way more has predicted okay with with a requirement increasing day by day there is a point where you know more slow will no longer be able to sustain itself okay so that is where you know you have to think of some alternative so as the data traffic increases every year we need faster data rate with miniaturized IC so this is this is our requirement but then what is Stopping Us in getting higher and higher speed that will be you know the RC delay with the device sizes becoming smaller and smaller that actually increases your data processing okay in a small volume but the RC delay or resistive capacitive delay in the electronic circuit they become a major bottleneck now why do you see this RC delay any transistor you can model as a equivalent RC network every node in the electronic circuit can be thought of a capacitive nature so to charge your discharge that node there is a finite time charging and discharging time and that that restricts the speed Beyond which you cannot go also when you think of you know IC wirings or interconnect they there also you can model the interconnect using equivalent RC delay model and wherever this RC delays are coming there is a restriction on the overall speed so you cannot actually get better and why miniaturization actually impacting that because when you miniaturize your electric interconnects they are Getting Thinner and with that the resistivity per length is actually increasing so miniaturization allows you to pack more devices but then the speed is getting reduced because of this RC delay is getting into the picture so we want to increase the usage in the smart devices and meet the demand of data that is that it will be placing huge liability on the radio network so we understood that scaling down on transistors can reduce the energy consumption but that will also bring in few issues something like the energy dissipation from thinner interconnects will increase because you know the resistivity per unit length will increase in for a shorter interconnect then people like semiconductor people industry actually moved on to explore what is called multi-core processor design so instead of having only one core you can actually split your course and parallelize the processing so that can actually bring down the overall power consumption but is this going to help us in the long run with the amount of data traffic that you have seen coming our way we have seen a tsunami of data traffic coming to our way so we have to somehow move on to Optical technology where there is no RC delay that is restricting the amount of data rate that we can achieve so we have to go to photonic Technologies to handle this you know enormous amount of data traffic and that will also when you do everything in the optical field that will also reduce the power and energy consumption at the data centers so integrated macro photonics have done well it can actually so this is a particular or typical diagram of a canonical um photonic system where you have a RF system or antenna that is bringing in the RF input you have a Laser Source that is giving you the light you have an optical modulator you do the signal processing in the optical domain you detect it that means it you are finally converting it back to current and then you give the RF output to the receiver so that way you can incorporate photonics with microwave and can do you know speed up the system so integrated macro photonics can reduce the device footprint that is possible to some extent by confined confining light in the ultra small volume and that will enhance the light matter interaction so they will definitely offer a less complex signal processing architecture here you will be doing the optical signal processing and you can also achieve a higher data transfer rate with improved SNR and you can get a lower power dissipation so looks like you know integrated micro photonics can solve all our major problems something like handling of the high speed data traffic lowering of the energy consumption per unit data and also meeting the bandwidth requirements and it is also possible to do some integration with the existing intra chip and internship electrical data communication systems such as this one so this is a typical diagram which shows integration between electronics and photonic circuits on the same chip for better signal processing so what is the problem then what is stopping microwave photonics or it is able to provide us all the solutions that we&#39;re looking for one problem that you can think of in micro photonics is that when you are in the field of photonics you cannot scale down your devices to nanoscale is that clear so when you are in photonics you have a limit called diffraction limit of light diffraction limit of light tells you that light cannot be squished in a volume which is lesser than Lambda by 2. so you cannot actually go sub wavelength with photons or you can say light cannot be squished into sub wavelength volumes so this is where the technology situation right now is electronics Industry has done very well in terms of miniaturization so you can get you know your critical device Dimension down to you know 10 nanometer or even below but the maximum speed that you can get from Electronics devices is restricted up to gigahertz you cannot go beyond that because of the RC delays now if you look into photonics they have done very well in overcoming the RC delay issues but there is a particular size restriction for the photonic circuits and this limit is set by the diffraction limit of light so you want to have something here which can actually go and work in terahertz speed but allow you also to give you know device Dimensions which are in nanometer scale and this is where plasmonics will come into picture so plasmonics is a field that brings in the best of both electronics and photonics world so plasmonics will naturally interfere with the you know similar size electronic devices so it is very easy to match with the electronics part as well as they can also naturally interfere with the photonics one because they have similar operating speed so the situation is like this Electronics can provide miniaturized devices with critical Dimensions less than 10 nanometer but the maximum speed you can achieve is restricted to gigahertz due to the RC delay issues with the electronics and if you look at photonics photonics can help to reach terahertz operating speed but the miniaturization is not possible below one micrometer that is typically the you know critical device dimension for photonics and this limit is set by the diffraction limit so what is the way out so that is where plasmonics coming to the picture so plasmonics will enable and improved Synergy between electronics and photonics because plasmonics naturally interfere with similar size electronic devices and plasmonics can naturally interfere with also similarly operating speed photonic Network so plasmonics is in a position to offer terahertz Speed in nanometer scale bringing together the best of the both electronics and photonics worlds and as you can see that this field will require inputs from Optical engineering electrical engineering and nanotechnology so this week it becomes a truly interdisciplinary field of study and that is how nanophotonics and a sub part of it is metallic nanoplasmonics or simply plasmonics that can help deliver the best of the Two Worlds and this can actually help us meet the upcoming data traffic requirements so we understood how nanopotonics and then what is plasmonics so if you say plasmonics you can also call it metallic nanoplasmonics they are more or less interchangeably used this is a relatively young branch of research and as you understand this is a part of nanopotonics plasmonics can confine electromagnetic field below the diffraction limit so this is where the good thing is and it provides solution for future on chip nanoscale devices it allows to scale down the integrated photonic devices to nanoscale so the miniaturization is possible here plasmonics concerns about the investigation of electron oscillations in metallic noun structures which are known in surface response and what are the surface plus bonds they have will come to that soon the surface plus bonds have very interesting Optical properties so signals coming from an optical fiber can be squeezed into software length volume using plasmonics by taking help of surface response as you can see in this figure surface plus bonds can propagate as a coherent electromagnetic oscillation on the so spp means surface plus one polyatons which are the propagating surface response so they can propagate along metal dielectric interface so in this case you can think of gold as a metal so gold Air interface it can propagate and you can also see here that the dimension is deep sub wavelength the separation s is less than 1 by 10 times Lambda naught so you are basically talking about separation which are Lambda naught by ten so this tiny or deep sub wavelet scale separation is also supported used by surface response you can also make you know surface plus bonds to propagate a long distance here an experimental result shows that if you take a silver nanowire and you launch light in one end of it say here this bright spot shows light excitation in one end of the silver nanowire okay and then the light of the photons are converted into surface plus bonds so what are surface plus bonds these are basically surface electrons okay so from photons you are actually transferring back your energy to some kind of electrons and those surface electrons propagate along the surface of this nanowire that is at the interface of say if it is a silver nanowire and air is the surrounding media so the electron wave will propagate along silver Air interface and at the end it can again come back as light okay so this kind of propagation and squeezing of energy in deep sub wavelength scale is possible in Plus One X so I have taken the name of plasma several times while talking about plasmonics let&#39;s try to understand what is plasmon plasma is basically a density wave in an electron gas so if you try to imagine what is a density wave you can think of sound wave okay and that is basically a density wave in a gas consisting of molecules what do plasmas exist they exist mainly in metals where there are abundance of electrons and the electrons are weakly bound to the atoms and they can freely roam around so the electrons in a metal can actually uble like a piece of jelly that is like it can actually move like this so pulled back by the attraction of the positive metal ions so when the when the electrons move up they leave the positive metal ions so that attraction actually pull them back so that is how the ubling of the electron cloud takes place and when this all the electrons you know they oscillate in the same frequency we call that a plasma frequency Omega p and that is the case where the electron gas has resonance and when you say resonance it is like you know it is basically the billions of electrons they oscillate in sink and we can also Define plus bonds as a collective wave where these billions of electrons oscillating in zinc so we have discuss two types of s surface plus Bonds are there one could be propagating surface plus bonds or Surface plus one polaroidance that can be excited with different coupling mechanism that will study in details later on but you can actually make you know surface plus bonds to propagate along a metal dielectric interface as shown here so there is H Nu there is light being used to excite so the exciting mechanism is not shown I&#39;ll discuss that the DirectX addition is not possible but by taking help of some kind of grating or prism couplers you can actually excite surface plus bonds so this is the material and dielectric interface and as you can see metal has got a large negative permittivity at this Optical frequency so the field penetrates very less towards the metal and mostly it is in the dielectric and this is how it will propagate while propagating the field is also leaking out as you can see and as the field will die down while propagation and that will be the distance over which the plus bonds can propagate there is another type of plus one also possible that is called localized surface plus one and as the name suggests that this response are basically localized on nanostructure something like metallic nanoparticles and this plus bonds can be directly excited using just by Shining Light on it you do not require a special mechanism to excite those plus bonds and if you look into plasmonics the funny thing is you know the plasmonics though it is a you know savior of mankind in the future but the history or the Genesis of plasmonics dates back to Roman so Romans were the nanotechnology Pioneer how this came into picture so you look into the figure here it shows the image of the same leica&#39;s cup it&#39;s a cup okay so that is kept in British museum so when you put light from the front to see what is the color of the cup you see it&#39;s green but if you put the light source at the back the cup appears red that is something amazing usually if you take a you know yellow kind of thing yellow glass or whatever it just think of it that when you look it from front or back more or less it will look same but here in this case there is a difference in the colors one you are looking from the front and the back and when scientists actually look into the details of this class they have figured out that there are tiny nanoparticles involved in this particular like a girl&#39;s cup so that is where the nanotechnology actually came in and because of this nanoparticles only in the scattering mode this glass is looking green and because of the absorption of the nanoparticles I&#39;ll go into more details of it later on this glass is looking the cup is looking red so surface plus Bond when they resonate with the frequency of the incoming light you can actually get surface plus one resonance and this resonance will significantly enhance the light scattering and absorption capability of this tiny nanoparticles as you can see here if you take gold nanoparticles over size you know 20 to 150 nanometer the resonance wavelength can change from 520 to 660 nanometer for silver if you consider the same size you can actually tune the resonance of surface plus bonds over a different range it&#39;s again similarly wide range but different range 382 600 nanometer so one need to keep in mind that this resonance is not only dependent on the material of the null particles their size it is also dependent on their shape and also the surrounding media that is around this particular nanoparticles so there is a graph of localized surface plus one resonance tunability as you can see here this is for silver nanosphere this is the range over which you can you know you can choose silver nanosphere and change the size of it to go from UV to visible range okay you can look for gold nanospheres that can give you more more or less within visible range only but if you choose Nano shells or Nano X that these are like ellipsoid kind of structure you actually get a very wide tunability starting from visible to Mid infrared similarly you can choose for Nano rods which are like cylinders Nano cylinders triangles Cube nanorize all different shapes are possible so you are able to change the surface plus one resonance over a wide white frequency range okay but as you can see everything within UV visible and infrared and why it is important so the ability to focus light and manipulate light at the nanometer scale has got a lot of potential and this is what has been claimed by the pioneer of plasmonics Professor Harry Atwater at Celtic us so he he actually foreseen that this field is going to be very very exciting and it is compelling because you can see lot of applications of this particular field in nanoscale devices you can as you have seen you can you know propagate surface plus bonds over nanoscale distances you can confine energy with deep sub wavelength spacing so all those will allow you to get nanoskill devices you can make directional Nano antennas for your circuits using this kind of metallic nanoparticles or dielectric nanoparticles you can think of plasmonic solar cells where nanoparticles with enhanced absorption at their resonance will allow you to absorb more light to be converted into electricity so they can be you know added to solar cell to increase their efficiencies you can think of photothermal cancer therapy using nanoparticles where nanoparticles can be plasmonic nanoparticles can be injected into bloodstream with some you know targeted delivery so that this nanoparticles go and sit on there uh cancer tumor and you can shine light from the outside neon infrared light is able to penetrate the skin and it can go inside nanoparticles having resonance at that particular wavelength will be able to absorb light very strongly and that with absorption the nanoparticles will heat it up and that increase in temperature will kill the cancer cells so you can see these nanoparticles can be your savior they can be also used for biological and chemical sensing where you know the change in the refractive index of the surrounding media of the nanoparticles can be sensed as you know shift in the plasma resonance Peak wavelength so you can actually sense very very tiny amount of molecules present using this kind of sensors this also can help you achieve very high density optical storage something like this one um up to 5D optical storage so here the you know images are imprinted in different layers at different wavelengths and polarization so these are only some specific applications you can think of a lot more applications using plasmonics so this is the future going ahead so that is all for today&#39;s lecture and we&#39;ll try to cover the introduction to matter surfaces and metamaterials in the next lecture so thank you in case you have any query you can send it send it to me at this email address dev.shikhtar at the rate iitg.ac.in but do not forget to mention mooc in the subject of your email thank you thank you [Music]

Transcript for:Introduction to Nanophotonics and Plasmonics

Transcript for:
Introduction to Nanophotonics and Plasmonics