6.5.15 · D5 · HinglishAdvanced & Emerging Architectures
Question bank — Photonic and optical interconnects
6.5.15 · D5· Hardware › Advanced & Emerging Architectures › Photonic and optical interconnects
True or false — justify karo
True or false: Silicon waveguide mein ek photon, achhe copper trace mein electrical signal se zyada fast travel karta hai.
False — silicon mein light pe chalti hai, jo aksar copper trace ki signal velocity se per metre slower hoti hai, kyunki copper trace ki velocity already ka bada fraction hoti hai. Dekho Refractive index and speed of light in media.
True or false: Photonics ki sabse badi jeet raw latency cut karna hai.
False — asli jeet bandwidth density aur energy per bit hai; latency sirf indirectly improve hoti hai repeaters aur retimers hatane se.
True or false: Copper wire ki length double karne se uski RC delay double ho jaati hai.
False — yeh quadruple ho jaati hai, kyunki jo ke saath scale karta hai; aur dono ke saath badhte hain, isliye unka product ke saath badhta hai. Dekho Copper interconnects and RC delay.
True or false: Photonic waveguide ka transit time bhi ki tarah badhta hai.
False — transit time hai, jo mein linear hai, kyunki light bas propagate karti hai; kuch charge aur discharge nahi ho raha.
True or false: WDM capacity ko free mein badhata hai kyunki extra colours ek doosre ki bandwidth nahi churaate.
True linear sense mein — kyunki independent colours add hote hain — lekin power ya thermal budget mein free nahi; har channel ko apna khud ka source/ring chahiye. Dekho Wavelength Division Multiplexing (WDM).
True or false: Ek photodetector directly voltage output karta hai, modulator ko mirror karta hua.
False — ek photodiode ek chhota current output karta hai; ek usable voltage banane ke liye TIA chahiye, aur isme real energy lagti hai.
True or false: Silicon laser banane ke liye achha material hai.
False — silicon ka indirect bandgap hai aur yeh light poorly emit karta hai; lasers III–V materials (InP, GaAs) use karte hain jo bonded ya co-packaged hote hain. Dekho Silicon Photonics.
True or false: Ek Mach–Zehnder modulator mein, ka phase shift maximum brightness deta hai.
False — zero power deta hai (destructive interference, bit 0); full power deta hai. Yaad karo . Dekho Mach-Zehnder Modulator.
True or false: Photonic link ki energy per bit roughly distance ke saath badhti hai, jaise copper mein.
False — ek baar light launch ho jaaye toh yeh roughly distance-independent hoti hai, jabki copper ki energy per bit distance ke saath badhti hai. Dekho Energy per bit as an efficiency metric.
Error dhundo
"Kyunki hai, hum badhake bandwidth unlimited bana sakte hain." — error dhundo.
bounded hai: channels ko crosstalk avoid karne ke liye apart rakhna padta hai, aur usable optical band (jaise C-band) finite hai; har channel power bhi draw karta hai aur thermal tuning bhi chahiye.
"Photons waveguide ko bilkul heat nahi karte, isliye photonic links zero energy dissipate karte hain." — error dhundo.
Transport medium muskil se heat karta hai, lekin laser, modulator drivers, aur TIA sab real power burn karte hain — electrical ends energy budget dominate karte hain.
"Ek micro-ring resonator saari wavelengths ko equally block karta hai, ek generic shutter ki tarah kaam karta hai." — error dhundo.
Ek ring sirf ek resonant wavelength pe light trap karta hai; yahi selectivity exactly hai jo ise WDM ke saath pair karti hai (ek ring per colour), ek broadband shutter ke unlike.
"Kyunki power field amplitude hai, MZM output hai." — error dhundo.
Power field ka square hota hai, ; do phasors ke sum ko square karna hi woh hai jo interference term produce karta hai.
"Skin effect high frequency pe copper resistance ko girata hai, speed mein help karta hai." — error dhundo.
Iska ulta — current surface ki taraf crowd hoti hai, isliye effective resistance roughly ke saath badhti hai, high data rates pe loss worse hota hai.
"E-O-E ka matlab signal end to end optical rehta hai." — error dhundo.
E-O-E Electrical→Optical→Electrical hai: data electrons se start aur end hota hai; light sirf beech mein ise carry karti hai.
Why questions
WDM capacity linearly kyun add karta hai instead of ek electrical bus ki tarah time mein share karne ke?
Different colours alag wavelengths occupy karte hain aur interfere nahi karte, isliye yeh simultaneously transmit karte hain; shared electrical bus ko ek medium ko time-slice karna padta hai, capacity add karne ki jagah divide karta hai.
carrier ek plus kyun hai jab hum sirf kuch GHz pe modulate karte hain?
Kuch-GHz ka data wiggle optical carrier ka tiny fraction hai, enormous frequency headroom chhod ke — carrier kahin bhi saturate ke close nahi hai.
Interference Mach–Zehnder ko "logic" karne deta hai kyun?
Light ko split karna aur electrically-set phase shift ke baad recombine karna do arms ko add (bright = 1) ya cancel (dark = 0) karta hai, isliye ek voltage jo control karta hai literally bit switch karta hai. Dekho Mach-Zehnder Modulator.
Co-packaged optics "pin wall" se escape karne mein kyun help karta hai?
Laser aur modulator ko CPU/GPU package ke bilkul paas rakhne se bandwidth fibre/waveguides pe leave kar sakti hai instead of limited electrical package pins ke. Dekho Co-packaged optics.
On-chip photonic NoC abhi bhi "emerging" kyun hai instead of mainstream ke?
CMOS mein lasers integrate karna aur ring resonators ko thermal tuning ke zariye apni target wavelength pe rakhna hard, power-hungry problems hain jo abhi tak saste mein solve nahi hue.
Edge cases
pe MZM output kya hai?
— halfway "quadrature" point, bias ke liye useful lekin ek clean 0 ya 1 ke liye ambiguous.
Agar chip heat ho jaaye aur micro-ring ki resonance drift kar jaaye toh kya hoga?
Uski resonant wavelength intended channel se shift ho jaati hai, isliye yeh sahi colour select karna band kar deta hai — yahi reason hai ki resonance hold karne ke liye active thermal tuning required hai.
Bahut chhote copper wire ki limit mein, kya photonics abhi bhi jeetta hai?
Zaruri nahi — chhote lengths pe delay tiny hoti hai aur laser + modulator + TIA ka fixed cost dominate karta hai, isliye copper short links ke liye sasta aur lower-energy ho sakta hai.
Jab zero light aata hai (ek "0" bit), photodetector current kya hota hai?
Ideally , lekin real diodes ek chhota dark current leak karte hain, isliye receiver ko clean 0 read karne ke liye us floor se upar threshold karna padta hai.
pe, MZM output se kaise compare karta hai?
Identical — , full brightness; response mein periodic hai, isliye drive voltage ko sirf ek swing tak pahunchna padta hai toggle karne ke liye.
Recall Ek-line summary jo saath le jaao
Photons bandwidth density aur energy pe jeette hain, raw metres-per-second pe nahi; "unlimited" ya "faster" ka har claim ek boundary chhupata hai — crosstalk, finite band, indirect bandgap, ya electrical ends jo abhi bhi power burn karte hain.