Paper Review IEEE Journal of Quantum Electronics, Feb 1985 Special - PowerPoint PPT Presentation

Paper Review IEEE Journal of Quantum Electronics, Feb 1985 Special Topics in Optical Engineering II (15/1) Minkyu Kim

Contents  Semiconductor laser review  High speed semiconductor laser  Parasitic elements limitations  Intermodulation products  Intensity noise  Large signal effects  Conclusion Special Topics in Optical Engineering II (15/1) Minkyu Kim

Interaction between light and matters <Photon interacting with an hydrogen atom> ℎ𝜉  Three interaction + - processes are possible Absorption Spontaneous Emission Stimulated Emission 𝑆 12 = 𝐶 12 ∙ 𝑂 1 ∙ 𝜍 𝑆 𝑡𝑞 = 𝐶 𝑡𝑞 ∙ 𝑂 2 𝑆 21 = 𝐶 21 ∙ 𝑂 2 ∙ 𝜍 𝜍 : photon density, 𝑂 1,2 : electron density at 𝐹 1,2 𝐶 12,21,𝑡𝑞 : constants Special Topics in Optical Engineering II (15/1) Minkyu Kim

Interaction between light and matters 𝑆 12 = 𝑆 𝑡𝑞 + 𝑆 21 : Equilibrium condition = 8𝜌ℎ𝜉 3 = 1, 𝐶 𝑡𝑞 𝐶 21 𝑂 2 𝐹 2 −𝐹 1 𝑂 1 = exp − : Statistical mechanics 𝑑 3 𝑙𝑈 𝐶 12 𝐶 12 8𝜌ℎ𝜉 3 𝜍 ℎ𝜉 = 𝑙𝑈 −1} : Black-body radiation 𝑑 3 {exp ℎ𝜉 Absorption Spontaneous Emission Stimulated Emission 𝑆 12 = 𝐶 12 ∙ 𝑂 1 ∙ 𝜍 𝑆 𝑡𝑞 = 𝐶 𝑡𝑞 ∙ 𝑂 2 𝑆 21 = 𝐶 21 ∙ 𝑂 2 ∙ 𝜍 𝜍 : photon density, 𝑂 1,2 : electron density at 𝐹 1,2 𝐶 12,21,𝑡𝑞 : constants Special Topics in Optical Engineering II (15/1) Minkyu Kim

Optical amplifier Amplifier Stimulated emission should be dominant 𝑄 𝑗𝑜 𝑄 𝑝𝑣𝑢 = 𝐻 ∙ 𝑄 𝑗𝑜 Pumping  𝑂 2 > 𝑂 1 (Population Inversion) Special Topics in Optical Engineering II (15/1) Minkyu Kim

LASER LASER : Light Amplification by Stimulated Emission of Radiation LASER = Optical amplifier + Mirrors • Use initial photon produced by spontaneous emission • Recycle photons produced by stimulated emission • Use mirrors for recycling photons • Condition for sustaining photons in laser ⑴ 𝑓 𝑕𝑀 = 1 𝑆 (Gain > mirror loss) ⑵ 𝑓 −𝑘2𝑜𝑙 0 𝑀 = 1 (No loss after one round trip) Special Topics in Optical Engineering II (15/1) Minkyu Kim

Conditions for lasing Lasing conditions : ⑴ 𝑓 𝑕𝑀 = 1 1 1 𝑆  𝑕 𝑢ℎ = L ln 𝑆 ⑵ 𝑓 −𝑘2𝑜𝑙 0 𝑀 = 1  𝜇 𝑜 = 2𝑀 𝑛 (𝑛 = 1,2,3, … ) Special Topics in Optical Engineering II (15/1) Minkyu Kim

Semiconductor laser Absorption Spontaneous Emission Stimulated Emission 𝑆 𝑡𝑞 ℎ𝜉 = 𝐶 𝑡𝑞 ∙ 𝑂 2 (𝐹 2 ) ∙ 𝑄 1 (𝐹 1 ) 𝑆 12 ℎ𝜉 = 𝐶 12 ∙ 𝑂 1 (𝐹 1 ) ∙ 𝑄 2 (𝐹 2 ) ∙ 𝜍(ℎ𝜉) 𝑆 21 ℎ𝜉 = 𝐶 21 ∙ 𝑂 2 (𝐹 2 ) ∙ 𝑄 1 (𝐹 1 ) ∙ 𝜍(ℎ𝜉) 𝑂 2 ∙𝑄 1 𝑂 1 ∙𝑄 2 > 1  Electron & hole should be injected For population inversion, (Forward bias in PN junction) Special Topics in Optical Engineering II (15/1) Minkyu Kim

Semiconductor laser structure Special Topics in Optical Engineering II (15/1) Minkyu Kim

High speed semiconductor laser 𝑂 : carrier density Rate equations 𝑂 𝑝𝑛 : carrier density for transparency 𝑄 : photon density 𝑒𝑂 𝐾 𝑂 𝐾 : pump current density 𝑒𝑢 = 𝑓𝑒 − 𝜐 𝑡 − 𝐵 𝑂 − 𝑂 𝑝𝑛 𝑄 ⑴ 𝑒 : thickness of active layer 𝜐 𝑡 : spontaneous recombination lifetime of carriers 𝑒𝑄 𝑄 𝑂 𝑒𝑢 = 𝐵 𝑂 − 𝑂 𝑝𝑛 𝑄 − 𝜐 𝑞 + 𝛾 ⑵ 𝜐 𝑞 : photon lifetime 𝜐 𝑡 𝐵 : optical gain coefficient 𝛾 : fraction of spontaneous emission entering to lasing mode Small signal & linearization 𝑈 𝑠𝑓𝑚𝑏𝑦𝑏𝑢𝑗𝑝𝑜 𝑝𝑡𝑑𝑗𝑚𝑚𝑏𝑢𝑗𝑝𝑜 𝑔𝑠𝑓𝑟𝑣𝑓𝑜𝑑𝑧 = 1 𝐵𝑞 0 𝑔 2𝜌 𝜐 𝑞 𝐁 ↑, 𝐪 𝟏 ↑, 𝛖 𝐪 ↓  high speed semiconductor laser Special Topics in Optical Engineering II (15/1) Minkyu Kim

Parasitic elements limitation Semiconductor laser 𝐽 𝐽 Bonding wire oxide insulator p doped confining layer active layer Contact n doped confining layer resistance Parasitic Intrinsic capacitance diode Substrate Circuit modeling 𝜃 = 𝑑𝑣𝑠𝑠𝑓𝑜𝑢 𝑔𝑚𝑝𝑥𝑗𝑜𝑕 𝑗𝑜𝑢𝑝 𝑢ℎ𝑓 𝑗𝑜𝑢𝑠𝑗𝑜𝑡𝑗𝑑 𝑒𝑗𝑝𝑒𝑓 𝑤𝑝𝑚𝑢𝑏𝑕𝑓 𝑝𝑔 𝑢ℎ𝑓 𝑡𝑗𝑕𝑜𝑏𝑚 𝑡𝑝𝑣𝑠𝑑𝑓 50 + 𝑆 𝑀𝑆𝐷(50 + 𝑆) 𝜕 0 = 𝑀𝑆𝐷 , 𝑅 = 1 𝑀 + 50𝑆𝐷 = 𝑡 2 𝑡 2 + 𝜕 0 𝑅 + 1 𝜕 0  Second-order low pass filter type Special Topics in Optical Engineering II (15/1) Minkyu Kim

Parasitic elements limitation Special Topics in Optical Engineering II (15/1) Minkyu Kim

Parasitic elements limitation Circuit modeling 1+𝑓 −2𝑙𝑋 𝑎 = 𝑎 0 1−𝑓 −2𝑙𝑋 , W : width of top contact 𝑆 𝑒𝑗𝑡𝑢 𝑎 0 = , 𝑙 = 𝑘𝜕𝑆 𝑒𝑗𝑡𝑢 𝐷 𝑒𝑗𝑡𝑢 𝑘𝜕𝐷 𝑒𝑗𝑡𝑢 Higher frequency  higher propagation constant(k)  electric field cannot penetrate far beyond laser junction Special Topics in Optical Engineering II (15/1) Minkyu Kim

Intermodulation products Third order intermodulation Third order intermodulation can be a problem in multichannel frequency division transmission Special Topics in Optical Engineering II (15/1) Minkyu Kim

Intensity noise 𝑆𝑓𝑚𝑏𝑢𝑗𝑤𝑓 𝐽𝑜𝑢𝑓𝑜𝑡𝑗𝑢𝑧 𝑂𝑝𝑗𝑡𝑓 𝑆𝐽𝑂 = < Δ𝑄 > 2 < 𝑄 0 > 2 𝑄 0 : average light output power < Δ𝑄 > 2 : mean square intensity fluctuation spectral density of the light output 𝜕 3 1 With rate equations, 𝑆𝐽𝑂 ~ 2 𝑞 0 𝜕2 + 𝜕2 2 −1 4 𝜐𝑆 2 𝜕𝑆 𝜕𝑆 Special Topics in Optical Engineering II (15/1) Minkyu Kim

Large signal effects Non-linearity problem for large signal Optical modulation depth for high speed below ~70 percent <Effects of increasing optical modulation depth> Special Topics in Optical Engineering II (15/1) Minkyu Kim

Conclusion 𝑂 : carrier density Rate equations 𝑂 𝑝𝑛 : carrier density for transparency 𝑄 : photon density 𝑒𝑂 𝐾 𝑂 𝐾 : pump current density 𝑒𝑢 = 𝑓𝑒 − 𝜐 𝑡 − 𝐵 𝑂 − 𝑂 𝑝𝑛 𝑄 ⑴ 𝑒 : thickness of active layer 𝜐 𝑡 : spontaneous recombination lifetime of carriers 𝑒𝑄 𝑄 𝑂 𝑒𝑢 = 𝐵 𝑂 − 𝑂 𝑝𝑛 𝑄 − 𝜐 𝑞 + 𝛾 ⑵ 𝜐 𝑞 : photon lifetime 𝜐 𝑡 𝐵 : optical gain coefficient 𝛾 : fraction of spontaneous emission entering to lasing mode 𝑈 = 1 𝐵𝑞 0 𝑔 2𝜌 𝜐 𝑞 A ↑, p 0 ↑, τ p ↓  high speed semiconductor laser • Parasitic elements limitations • Intermodulation products • Intensity noise • Large signal effects Special Topics in Optical Engineering II (15/1) Minkyu Kim