Pratique du Shadowing: Introduction to Optoelectronics and Photonics - Apprendre l'anglais à l'oral avec la vidéo

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.

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

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what happens when you inject electrons or holes

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and where the energy levels are of this system

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and from there the last thing you need to understand before

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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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Vocabulaire et conseils d’expression pour cette leçon

Cette vidéo contient 166 phrases et 2075 mots à répéter en shadowing. La partie parlée dure 14:40. Le locuteur parle à un rythme régulier d’environ 141 mots par minute, confortable pour le shadowing. 83 % des mots font partie des 3 000 mots les plus courants en anglais ; le reste mérite d’être vu avant de commencer.

Vocabulaire clé de cette vidéo

15 mots de la vidéo à retenir, avec leur prononciation et leur sens :

Mot	Prononciation	Sens
absorption nom	/æbˈsɔɹp.ʃn̩/	absorption
analyze verbe	/ˈæn.əˌlaɪz/	analyser
laser nom	/ˈleɪzɚ/	laser
quantum nom	/ˈkwɑntəm/	quantité
mirror nom	/ˈmiɹɚ/	glace, miroir
spectrum nom	/ˈspɛktɹəm/	spectre
diagram nom	/ˈdaɪ.ə.ɡɹæm/	diagramme, schéma
absorb verbe	/æbˈsɔɹb/	absorber
optical adjectif	/ˈɑptɪkəl/	optique
interact verbe	/ɪn.təˈɹækt/	interagir
behave verbe	/bɪˈheɪv/	se comporter
axis nom	/ˈæksɪs/	axe
electron nom	/ɪˈlɛk.tɹɑn/	électron
physics nom	/ˈfɪz.ɪks/	physique
alpha nom	/ˈæl.fə/	alpha

Les verbes à particule que vous entendrez

Mot	Sens
figure out verbe	cerner
turn out verbe	se finir, se terminer
go through verbe	traverser
look forward to verbe	avoir hâte de, attendre avec impatience

La grammaire de cette vidéo

Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :

Structure	Dans la vidéo
Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait	is spelled · are emitted · are allowed
Present perfect have/has + participe passé — une action passée qui compte encore maintenant	I've been · you've ever taken

Prononciation à surveiller

Le locuteur utilise 53 contractions et formes réduites, comme we'll, we're, we've. Prononcez-les sous leur forme courte, telles que vous les entendez.

Les sons « sh » et « zh »: absorption /æbˈsɔɹp.ʃn̩/, associate /əˈsoʊʃi.ət/, limitation /lɪmɪˈteɪʃən/, efficient /ɪˈfɪʃənt/, transmission /tɹænsˈmɪʃən/
Mots longs — placez bien l’accent: associate /əˈsoʊʃi.ət/, momentum /ˌmə(ʊ)ˈmɛntəm/, limitation /lɪmɪˈteɪʃən/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/, concentration /ˌkɑn.sənˈtɹeɪ.ʃən/

Comment s’entraîner avec cette vidéo

Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
Répétez phrase par phrase à vitesse normale, en reprenant chacune jusqu’à ce que votre rythme corresponde à celui du locuteur.
Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme absorption, analyze, laser.

Qu'est-ce que la technique du Shadowing ?

Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.

Technique du shadowing : lire le guide complet étape par étape →

Pratique du Shadowing: Introduction to Optoelectronics and Photonics - Apprendre l'anglais à l'oral avec la vidéo

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