Pratica di Shadowing: Introduction to Optoelectronics and Photonics - Impara a parlare inglese con i video

So in this video, I'm going to give an overview of optoelectronics and photonics.

And this is going to be the subject of many future videos on this discipline.

But what are the questions that we're trying to ask when we talk about optoelectronics and photonics?

Well, the core questions are first, how does light interact with matter?

and so from our everyday experience we sort of know that

if you send a beam of light at some material we know

that some of it is going to get absorbed so some of it's going to get absorbed

some might get reflected back to our eyes

so we can actually see it and depending on the material some might get transmitted through it.

So materials can be transparent, for example.

And so we're interested in what's happening exactly inside this black box.

So what is the process of absorption, reflection, and transmission look like?

And absorption is going to be our primary focus because this is sort of the core of how optoelectronic devices operate.

And once we understand this, we're going to answer the question that engineers are generally more interested in, which is, how can we create devices?

How can we create devices, devices is spelled with an E, that manipulate light?

so these are the likes of lasers LEDs absorption modulators all sorts of other other cool fun devices

and once we understand how light interacts with matter then we'll be able to start to understand

and answer the question of how we would go about designing a laser

or an LED

or how we go about analyzing them like what their limitations are what their spectrum looks like what their emission

or absorption spectrum looks like

and how we expect them to behave in a circuit now personally I think optoelectronics is probably the coolest

of all the disciplines I've been a part of and that's just

because it's so complicated like it's it requires so many different

so many different domains of knowledge you need to understand quantum

mechanics you need to understand electromagnetics you need to understand to

a certain degree circuits device physics devices physics doesn't start with

an s device physics to a certain extent you need to understand optics

and more general electronics and you need to understand most challenging is how all of these sort of behave together,

how one flows into another, and how they interact with each other.

And so I think optoelectronics is super cool to study for this reason.

And it sort of brings together many different domains of knowledge into a coherent model, which is really, really cool.

And so where do we start?

How do we go about figuring out how we're going to create devices?

Well, we're going to start with the two energy level system.

So these are just two different energy levels.

These aren't bands.

This isn't a band diagram like you might expect.

And each of these energy levels has some wave function associated with it.

So it's got some state, some electronic state that's associated with it.

And maybe we've got an electron up here residing in this state.

Maybe we've got an electron down here residing in this state

and we want to know what happens

or maybe we've got an electron in both

or neither we want to know what happens when I send in light

so when I send in light of a certain frequency

or equivalently a certain energy

so what happens to this system what happens to these electrons

where do they go what happens to the the energies of the system

if anything and once we understand just how two individual energy levels interact.

Just two.

So one, two.

From there, we'll be able to figure out how entire materials interact.

So from there, we go to analyzing the band structure or what's called the band structure of materials.

And you might see diagrams that look something like this.

So this is what band diagrams often look like in photonics.

And we'll go through, Don't worry if this scares you.

This is an energy momentum diagram And we'll go over what exactly everything means here, but briefly, energy is on the y -axis,

momentum is on the x -axis, and this lets us figure out how electrons and holes,

and in particular photons, are emitted and absorbed by this material.

So a photon, for example, we've got an electron up here and a hole down here.

We're allowed to emit a photon as these two recombine with each other.

So this is the conduction band and these are the various valence bands.

And so once we figure that out, once we figure out where photons are allowed to go between,

and we're also we'll also analyze things like quasi Fermi levels

so EFC and EFV and how these affect how these affect our absorption

or how the how these affect our band diagrams

and how we go about representing them once once we understand

this we can move to actually analyzing the absorption spectrum

or the absorption and gain spectrum of semiconductor devices

and specifically of bulk devices or if I've in other words

if I've just got a slab for example of germanium

or gallium arsenide or something what happens

when I send in light to this material how much of it is going to get absorbed within the material

and we'll actually be able to derive and plot what this absorption specter will look like, or what this absorption and gain specter will look like.

And we'll figure out how exactly that depends on things like the carrier concentration inside the material.

So this is alpha, and this is h bar omega, for example, on this axis.

And so alpha is the absorption coefficient.

And it will turn out that we can actually get negative absorption some of the time.

And this is called gain.

So this region where we have negative absorption is called gain.

So this is alpha equals zero on the y -axis.

And we'll understand how we go about getting gain out of a material or negative absorption.

And this is the basis for pretty much all lasers.

You need a material that gives you gain, and you'll see why in future videos.

But it turns out that instead of just having this hunk of material here,

so instead of just having this hunk of germanium or gallium arsenide or whatever light emitting or absorbing material,

it's actually way, way more efficient to have what are called quantum wells inside your system.

And so we'll analyze what exactly the absorption spectra looks like in that case, and it will turn out to look something like this.

Instead of this smoothly varying thing, we've actually got a staircase going on, and so this is for quantum wells.

We'll also briefly analyze things like quantum wires and quantum dots and what their absorption spectra look like.

And just as with the bulk case, we can also have gain in our quantum well.

So for certain, under certain conditions, we can have negative absorption.

And then it just tracks out whatever our gain looked like previously.

But we'll analyze when we can get this.

So when we can get this bizarre negative absorption, also known as gain, and what conditions need to be met for us to do that.

We'll also go over how you actually make these quantum wells, and what they look like, not just their conduction band, but also their valence band,

and what the consequences are of us having two of these.

And so this, for example, might be indium gallium arsenide.

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This might be gallium arsenide.

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And this is what's called a heterostructure.

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A heterostructure.

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And these are the basis for how all quantum wells are made.

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And this is how most modern lasers and LEDs are fabricated.

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So heterostructures are really the core of all of modern active optical devices.

106

And so we'll understand how to analyze them, what their band diagrams look like,

107

what happens when you inject electrons or holes

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and where the energy levels are of this system

109

and from there the last thing you need to understand before

110

you understand lasers is mirrors in particular mirrors in the configuration of resonators

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so we'll go over how resonators behave so if we've got some incident I didn't.

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electric field or some light, what happens as it bounces back and forth inside a mirror or inside a set of two mirrors?

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And so we'll analyze all of these bounces.

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And if we've got some material inside these two mirrors, which maybe it absorbs light,

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or maybe it has a certain negative absorption or a certain gain, what happens? So what happens here? And also,

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why do we even want to use resonators like why why

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can't we just stick chunks of optical optically active material

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that has a certain gain or a certain absorption and send light

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or send an electric field uh into that like what what's what's wrong with

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that why do we need these uh why do we need these resonators

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and to analyze these resonators we'll be going over the scattering matrix

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which is sort of the central way of analyzing them it's it's quite intuitive

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if you've ever taken like an RF course before or circuits class

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or electromagnetics and this is connected to the transfer matrix of the system

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and these are actually used in practice

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so I actually use these use transfer matrix simulators to calculate

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what my how my optical devices will behave in my research

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and it's spectacularly accurate like it's just fabulous and after we understand mirrors

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and resonators we'll finally be able to understand devices so things like LEDs

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things like lasers also for example modulators so this is a central focus of my research right now.

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And so I'm probably going to make a few videos on it.

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But also things like photodetectors.

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So photodetectors, these might be photodiodes, these might be photoconductors.

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And we'll analyze briefly noise in all of these systems.

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So lasers, LEDs, and photodetectors, and how this impacts device performance.

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We'll also not just analyze these in what's called steady state,

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or how these devices behave when you just sort of apply a constant voltage or a constant current,

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but also what happens when you vary the current, or what are the dynamics of the system?

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How fast can I get my LEDs or my lasers or my photodetectors to operate?

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What are the limitations there?

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And last but not least, we need to get light in and out of these systems.

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And so we're going to go over waveguides.

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so we're going to go over how we actually transport light

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from point a to point b on something like a photonic integrated circuit

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or just across some distance and waveguides are the central way of doing this

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so these are optical fibers are one kind of waveguide

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but we've also got slab waveguides as well as rectangular waveguides and other sorts of waveguides

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And waveguides are critical to sort of any time you want

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to move light from point A to point B without a massive amount of loss between the two points.

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You really need a waveguide.

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Now, you could also use lenses, or you could also use an optical system.

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But this is the subject of optics.

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And so this I go, I actually do have some videos right now in optics.

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And so you can give those a look if you like.

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and we might have time for some other special topics here

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and there so I might get into coupled mode theory

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which is something I've been meaning to learn for a very long time

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and maybe some other advanced topics as well depending on what the what the comments section pops up with

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but I'm really looking forward to you

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and taking this journey with me to learn optoelectronics

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and photonics it's it's a really cool discipline

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and I think you'll have a lot of fun and

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so with that I just want to say thanks for watching the video

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and if you have any questions or comments

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or video requests Just put them down in the in the comment section below

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and don't forget to like and subscribe for more optoelectronics and photonics videos

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Vocabolario e note di pronuncia per questa lezione

Questo video contiene 166 frasi e 2075 parole da ripetere con lo shadowing. Il parlato dura 14:40. Chi parla mantiene un ritmo costante di circa 141 parole al minuto, comodo per lo shadowing. Il 83% delle parole rientra nelle 3.000 più comuni dell’inglese; conviene studiare le altre prima di iniziare.

Vocaboli chiave di questo video

15 parole del video che vale la pena imparare, con pronuncia e significato:

Parola	Pronuncia	Significato
analyze verbo	/ˈæn.əˌlaɪz/	analizzare
laser sostantivo	/ˈleɪzɚ/	laser
mirror sostantivo	/ˈmiɹɚ/	specchio
spectrum sostantivo	/ˈspɛktɹəm/	spettro
diagram sostantivo	/ˈdaɪ.ə.ɡɹæm/	diagramma
absorb verbo	/æbˈsɔɹb/	assorbire, incorporare
interact verbo	/ɪn.təˈɹækt/	interagire
behave verbo	/bɪˈheɪv/	comportarsi, agire
axis sostantivo	/ˈæksɪs/	asse
electron sostantivo	/ɪˈlɛk.tɹɑn/	elettrone
physics sostantivo	/ˈfɪz.ɪks/	fisica
alpha sostantivo	/ˈæl.fə/	alfa
discipline sostantivo	/ˈdɪsəplɪn/	disciplina
briefly avverbio	/ˈbɹiːfli/	concisamente, brevemente
depend verbo	/dɪˈpɛnd/	dipendere

I phrasal verb che sentirai

Parola	Significato
figure out verbo	scoprire, rendersi conto
turn out verbo	risultare
go through verbo	attraversare
look forward to verbo	non vedere l'ora

La grammatica di questo video

Le strutture che chi parla usa di più, con le parole esatte del video:

Struttura	Nel video
Forma passiva be + participio passato — conta ciò che accade, non chi lo fa	is spelled · are emitted · are allowed
Present perfect have/has + participio passato — un’azione passata che conta ancora adesso	I've been · you've ever taken

Pronuncia a cui fare attenzione

Chi parla usa 53 contrazioni e forme ridotte, come we'll, we're, we've. Pronunciale nella forma breve, così come le senti.

I suoni “sh” e “zh”: absorption /æbˈsɔɹp.ʃn̩/, associate /əˈsoʊʃi.ət/, limitation /lɪmɪˈteɪʃən/, efficient /ɪˈfɪʃənt/, transmission /tɹænsˈmɪʃən/
Parole lunghe — attenzione all’accento: associate /əˈsoʊʃi.ət/, momentum /ˌmə(ʊ)ˈmɛntəm/, limitation /lɪmɪˈteɪʃən/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/, concentration /ˌkɑn.sənˈtɹeɪ.ʃən/

Come esercitarsi con questo video

Ascolta tutto il video una volta senza parlare e annota le parole che non conosci.
Fai shadowing frase per frase a velocità normale, ripetendo ognuna finché il tuo ritmo coincide con quello di chi parla.
Registrati e confronta con l’originale, facendo attenzione a parole come analyze, laser, mirror.

Cos'è la tecnica dello Shadowing?

Shadowing è una tecnica di apprendimento delle lingue supportata da studi scientifici, originariamente sviluppata per la formazione dei traduttori professionisti e resa popolare dal poliglotta Dr. Alexander Arguelles. Il metodo è semplice ma potente: ascolti un audio in inglese di madrelingua e lo ripeti immediatamente ad alta voce — come un'ombra che segue il parlante con un ritardo di solo 1–2 secondi. A differenza dell'ascolto passivo o degli esercizi di grammatica, lo shadowing costringe il tuo cervello e i muscoli della bocca a elaborare e riprodurre simultaneamente i modelli di discorso reale. La ricerca dimostra che migliora significativamente la precisione della pronuncia, l'intonazione, il ritmo, il discorso connesso, la comprensione dell'ascolto e la fluidità del parlato — rendendolo uno dei metodi più efficaci per la preparazione alla prova di speaking dell'IELTS e per la comunicazione reale in inglese.

Tecnica dello shadowing: leggi la guida completa passo dopo passo →

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Vocabolario e note di pronuncia per questa lezione

Vocaboli chiave di questo video

I phrasal verb che sentirai

La grammatica di questo video

Pronuncia a cui fare attenzione

Come esercitarsi con questo video

Cos'è la tecnica dello Shadowing?