Paper Review Laser & Photonics Reviews, 2009 I. Photodiode - - PowerPoint PPT Presentation

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

Paper Review

Laser & Photonics Reviews, 2009 I. Photodiode review II. Motivations

• III. Principle of UTC PD
• IV. Design of UTC PD

V. Applications

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

Photodetection

• Photodetection
• Produces current when ℎ𝜉 > 𝐹𝑕
• Different absorption coefficient with different material(𝐹𝑕)
• R(Responsivity) =

𝐽 𝑄

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

Phototectors

ℎ𝜉

Photoconductor PN junction photodiode PIN junction photodiode

• Easy to make
• Slow
• Dark current
• Reverse bias
• Small dark current
• Drift in depletion region
• Thin depletion region

 bad efficiency

• Reverse bias
• Solve efficiency problem
• f PN junction PD

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

Demands for High Power RF PD

• Power amp can be followed by PD

Only when amplifier is available at frequencies of interest

• High frequency optical signals

High speed PD required

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

Principle of UTC PD

(a) UTC PD (b) PIN PD

• Light absorption layer(p-type) + Carrier collection layer(transparent)
• Generated hole  respond very quickly within in the dielectric relaxation time
• Generated electron  exhibit velocity overshoot in carrier collection layer

(Condition : quasi-field in the absorption layer by doping grading, bias for overshoot velocity)

• Electron diffusion time mainly determines the operation speed

* UTC : Uni Traveling Carrier

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

Pulse Response

• Current tails observed due to the slow response of holes in PIN PD
• No current tails in UTC PD due to the fast response of holes

(a) UTC PD (b) PIN PD

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

Bandwidth

• Conventional PIN PD
• Trade-off between transit time vs RC time
• UTC PD
• No trade-off in thickness of layer

due to diffusive electron transport in absorption layer Thinner absorption layer increases BW 𝑈𝑠𝑏𝑜𝑡𝑗𝑢 𝑢𝑗𝑛𝑓 𝑚𝑗𝑛𝑗𝑢𝑓𝑒 𝐶𝑋 ∝ 1 𝑒 𝑆𝐷 𝑢𝑗𝑛𝑓 𝑚𝑗𝑛𝑗𝑢𝑓𝑒 𝐶𝑋 ∝ 1 𝑆𝐷 ∝ 𝑒

𝑒: Thickness of absorption layer

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

Output Saturation Current

(a) UTC PD (b) PIN PD

• Photogenerated carriers(electron & hole) are stored in the absorption layer

in conventional PIN PD  Decrease E field  Current saturation

• Only electrons whose velocity at overshoot stored in UTC PD

 Current saturation occurs at much higher intensity

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

Structure Design

Surface(vertical) illuminated PD Refracting Facet(RF) PD Waveguide(WG) PD Waveguide-fed evanescently coupled PD

Improve responsivity while maintaining BW

Distributed Waveguide(WG) PD Distributed Waveguide-fed evanescently coupled PD

Improve responsivity & BW

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

Circuit Design

• Integration with a short-stub matching circuit  Increase output power, bandwidth

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

Applications

Schematic diagram of wireless link

• High-speed wireless communications
• Promising technique for “uncompressed” HDTC broadcasting
• UTC PD can make transmitter core very compact and light-weight
• Spectroscopic measurement systems
• Using photonic LO is best combination due to low noise

Experiment setup for spectroscopic system

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

Conclusion

• High power RF photodetector required in microwave photonics
• UTC PD
• Larger bandwidth
• Higher saturation current
• Better pulse response
• Structure & circuit design

Improvement of responsivity & bandwidth

• Microwave photonics applications