6.5.18 · D1Co-packaged optics trends
Intuition Is poore topic ka EK core ideaEk switch chip ko apne bits fiber par light ke pulses ke roop mein bhejna hota hai, lekin bits chip ke andar electricity ke roop mein paida hoti hain — aur electricity ko lambe copper wire se push karna energy waste karta hai aur signal ko blur kar deta hai. Co-packaged optics bas "electricity → light" converter ko chip ke bilkul paas la deta hai, taaki electrical wire haath ki span se nail ki size tak chhoti ho jaaye, power bachaye aur signal saaf ho jaaye.
Parent note Co-packaged Optics Trends ko sach mein samajhne ke liye, pehle tujhe har symbol aur word apna banana hoga jis par woh note tikaa hai. Hum har ek cheez ko zero se banayenge, ek aisi order mein jahan seedhi ki har paaydaan neeche waali par tikti hai.
Ek bit ek akela haan/naa ka jawab hai — ek 1 0
Definition Electrical wire (channel)Ek wire (jise channel ya trace bhi kehte hain) ek patla metal path hai — usually copper — jo ek bit ko voltage ke ek chhote bump ke roop mein carry karta hai. Socho ek garden hose: tum ek end mein pulse daalo, woh doosre end se nikalti hai, lekin thodi kamzor ho jaati hai.
Neeche wali picture woh poora physical stage hai jis par hum khade hain: ek chip, ek wire, aur door ek cheez jo electrical pulse ko light ki flash mein badal deti hai.
Red pulse dekho: chip par tall aur sharp start hoti hai, aur jab tak woh door end (optics) tak pahunchi hai tab tak short aur smeared ho gayi hai. Woh smearing hi woh dushman hai jis se poora topic ladhta hai. Is signalling par related depth SerDes and Wireline Links mein milegi.
B Bandwidth B har second chip se kitne bits nikalte hain — bits per second (bit/s) mein measure hoti hai. Bada switch = chauda dariya = bada B
per second kyun count karte hain
Wire ka kaam bits ko rokna nahi, balki move karna hai. Isliye useful measure ek rate hai: ek second mein ek line cross karne waale bits — bilkul waise jaise motorway par cars per minute count karna, country mein total cars nahi.
Unit hazaar ki powers mein badhti hai. Tumhe is ladder mein fluent hona chahiye, kyunki parent note seedha trillions par jump karta hai.
Question — 51.2 51.2 × 1 0 12 = 5.12 × 1 0 13
Switch chip capacity doubling karti rehti hai (12.8 → 25.6 → 51.2 → 102.4 Tb/s); reasons Switch ASIC Bandwidth Scaling mein hain.
Definition Energy per bitE b Energy per bit E b ek single bit ko wire se push karne mein kitni energy lagti hai — picojoules per bit (pJ/bit) mein measure hoti hai.
Pehle hume do sub-ideas chahiye: joule kya hota hai, aur pico ka matlab kya hai.
Definition Joule (J) aur picojoule (pJ)Joule energy ki standard unit hai — roughly ek chhota seb ek metre uthane ki energy. Picojoule uska ek trillionth hai: 1 pJ = 1 0 − 12 J 1 0 13
Intuition "Per bit" honest unit kyun haiAgar tum sirf total watts quote karte, to tum ek chhote switch aur bade switch ko compare nahi kar sakte — bada wala zyada bits move karta hai isliye zyaada jalega. Energy ko bits ki sankhya se divide karna ek fair, per-unit price tag deta hai. Kam E b
P Power P energy spent per second hai. Iski unit watt hai: 1 W = 1 J/s
Ab hum parent note ka central formula un pieces se assemble kar sakte hain jo hum ne abhi banaye.
Worked example Formula ko dono taraf se padhoE b = 5 pJ/bit B = 51.2 Tb/s P = ( 5 × 1 0 − 12 J/bit ) ( 51.2 × 1 0 12 bit/s ) = 256 W . E b 1 pJ/bit same B P = 51.2 W Same bits, power ek-paanchwa — kyunki sirf price tag E b
Common mistake Energy per bit ko power se confuse karnaE b bit ) aur P W = J/s) alag cheezein hain. E b fixed price hai; P B E b P
Parent note claim karta hai ki E b badhta hai. Yahan us reasoning ki chain hai.
f Frequency f ek second mein signal kitni baar upar-neeche wiggle karta hai — hertz (Hz) mein measure hoti hai. Tez bits = zyada f
L Length L electrical wire kitni door tak jaata hai — kuch millimetres (CPO) se ~30 centimetres (faceplate) tak.
A Attenuation A wire ke saath signal kitna kamzor hota hai . Yeh decibels (dB) mein measure hota hai — ek compressed scale jahan har extra 3 dB aadha signal bachta hai. Zyada dB lost = door end par ek dhundla, zyada garbled pulse.
Do curves dekho: lamba wire (magenta) frequency badhne par tezi se girta hai; chhota wire (orange) muskil se thoda dip karta hai. Same copper, sirf L
Intuition Decibel, feel karo"dB" se daro mat. Bas yaad rakho: 0 − 3 − 6 − 20 − 30
Wire ka poora point optics tak pahunchna hai, isliye woh parts jaano jo electricity ko light mein aur wapas badate hain.
Ek modulator electrical bit leta hai aur use light ke beam par stamp kar deta hai — 1 0
Definition Photodetector + TIAEk photodetector ulta kaam karta hai: light use hit karti hai aur woh ek tiny electrical current produce karta hai. Ek TIA (trans-impedance amplifier) phir us faint current ko ek clean voltage mein boost karta hai jo chip padh sake.
SerDes (Serializer/Deserializer) woh chip block hai jo bahut saare slow parallel bits ko ek fast serial stream mein pack karta hai wire drive karne ke liye, aur doosre end par unpack karta hai. Yahi woh piece hai jiska E b SerDes and Wireline Links .
Yeh converters usually Silicon Photonics mein banaye jaate hain aur ASIC ke paas 2.5D and 3D Packaging use karke rakhe jaate hain. Kyunki optics heat se nafrat karte hain, Thermal Management in Packages central headache hai — ek garam ASIC paas mein lasers ko drift karwa deta hai.
Definition Pluggable moduleEk pluggable (jaise QSFP-DD, OSFP) ek removable optics cartridge hai jo switch ke front panel mein click hoti hai . Swap karna aasaan hai, lekin us tak electrical wire lambi hoti hai (~15–30 cm). Dekho Pluggable Optical Modules (QSFP-DD, OSFP) .
Definition Linear Pluggable Optics (LPO)LPO pluggable ki swappable body rakhti hai lekin power-hungry DSP nikalti hai , is baat par rely karti hai ki short-reach signal apne aap kaafi clean hai. Ek beech ka raasta — zyaatar power win, kam risk. Dekho Linear Pluggable Optics (LPO) .
Poora safar — pluggable → on-board → co-packaged → monolithic — woh integration spectrum hai jo parent note tabulate karta hai. Yeh sab ek bade data-center network ke andar rehta hai.
bandwidth B: bits per second
energy per bit Eb: pJ per bit
power P = Eb times B: watts
attenuation A grows with L and f
frequency f: wiggles per second
WHY: short reach cuts power
modulator plus detector plus SerDes
Ise bottom-up padho: bits aur wires bandwidth aur energy-per-bit banate hain, jo power mein multiply hote hain; wire length aur frequency attenuation set karte hain, jo energy-per-bit badhata hai; saath mein woh case banate hain ki short reach = low power , jo exactly CPO deliver karta hai.
Khud test karo — tum parent note ke liye ready ho sirf tab jab har reveal obvious lage.
Bit kya hota hai ek binary haan/naa value, ek single 1 0
Bandwidth B chip se har second kitne bits nikalte hain (bit/s); 1 Tb/s = 1 0 12
Energy per bit E b ek bit move karne ki energy cost, pJ/bit mein, jahan 1 pJ = 1 0 − 12
Interface-power formula aur uske units kyun kaam karte hain P = E b × B
Ek watt kya hota hai ek joule per second, 1 W = 1 J/s
Attenuation A decibels (dB) mein; − 3
Loss length par kyun depend karta hai A ≈ α ( f ) L L
Skin effect vs dielectric loss skin
∝ f (current surface par crowd karta hai); dielectric
∝ f (insulator energy absorb karta hai).
Modulator kya karta hai electrical bit ko light beam par stamp karta hai (on = 1, dim = 0).
Photodetector + TIA kya karta hai received light ko tiny current mein convert karta hai, phir use readable voltage mein amplify karta hai.
SerDes kya karta hai parallel bits ko ek fast stream mein serialize karta hai (aur wapas); iski E b
Pluggable module kya hota hai ek removable front-panel optics cartridge (QSFP-DD, OSFP) jiska electrical reach lamba hota hai.
LPO, CPO se kaise alag hai swappable pluggable form factor rakhta hai lekin DSP remove kar deta hai, optics ko package par move nahi karta.
