Velocity-matched Distributed Photodetector Research Articles

Theory and design of a tapered line distributed photodetector

We present the theory and design of a tapered line distributed photodetector (TLDP). In the previously demonstrated velocity-matched distributed photodetector (VMDP), high electrical bandwidth is achieved by proper termination in the input end to absorb reverse traveling waves, sacrificing one-half of the quantum efficiency. By utilizing the tapered line structure and phase matching between optical waves and microwaves in our analyzed structure, a traveling-wave photodetector is more realizable and ultrahigh bandwidth can be attained due to removal of the extra input dummy load that sacrifices one-half of the total quantum efficiency. To investigate the advantages of TLDP over VMDP, we calculate their electrical bandwidth performances by using an analytic photodistributed current model. We adopted low-temperature-grown (LTG) GaAs-based metal-semiconductor-metal (MSM) traveling-wave photodetectors as example unit active devices in the analytic bandwidth calculation for their high-speed and high-power performances. Both VMDP and TLDP in our simulation are assumed to be transferred onto glass substrates, which would achieve high microwave velocity/impedance and make radiation loss negligible. The simulated bandwidth of a properly designed LTG GaAs MSM TLDP is /spl sim/325 GHz, which is higher than the simulated bandwidth of the LTG GaAs MSM VMDP with an open-circuit input end (/spl sim/240 GHz) and is almost comparable to the simulated bandwidth of an input-terminated LTG GaAs MSM VMDP (/spl sim/330 GHz). This proposed method can be applied to the design of high-bandwidth distributed photodetectors for radio-frequency photonic systems and optoelectronic generation of high-power microwaves and millimeter waves.

Generation of millimeter waves by photomixing at 1.55 /spl mu/m using InGaAs-InAlAs-InP velocity-matched distributed photodetectors

Millimeter-wave generation by photomixing at 1.55 μm in long-wavelength velocity-matched distributed photodetector (VMDP) is experimentally demonstrated. The VMDP exhibits a dc responsivity of 0.25 A/W, a breakdown voltage of 7-9 V, and up to 15-mA dc photocurrent without damage. Millimeter-wave output powers of -21 dBm at 75 GHz and -24 dBm at 95 GHz were measured.

DISTRIBUTED BALANCED PHOTODETECTOR FOR RF PHOTONIC APPLICATIONS

A novel velocity-matched distributed balanced photodetector operating at 1.3 and 1.55 μm wavelengths has been proposed and experimentally demonstrated. Distributed absorption and velocity matching of the optical and microwave signals are employed to achieve high saturation photocurrent. The velocity matching between the incident optical wave and the output microwave signal allows the detector length and effective absorption volume to increase without penalizing the bandwidth. A common-mode rejection ratio greater than 27 dB has been achieved over a wide range of photocurrents. More than 24-dB suppression of the relative intensity noise of the laser source and EDFA added noise has been achieved in a broadband RF link experiment. Shot-noise limited performance has been achieved with significant improvements in the signal-to-noise ratio over a wide range of frequencies and phase mismatch of input RF signals. The experimental results indicate that the distributed balanced photodetector will have a major impact on most RF photonic systems with its superior potential of reaching very high power levels.

Distributed Balanced Photodetector for RF Photonic Applications

A novel velocity-matched distributed balanced photodetector operating at 1.3 and 1.55 μm wavelengths has been proposed and experimentally demonstrated. Distributed absorption and velocity matching of the optical and microwave signals are employed to achieve high saturation photocurrent. The velocity matching between the incident optical wave and the output microwave signal allows the detector length and effective absorption volume to increase without penalizing the bandwidth. A common-mode rejection ratio greater than 27 dB has been achieved over a wide range of photocurrents. More than 24-dB suppression of the relative intensity noise of the laser source and EDFA added noise has been achieved in a broadband RF link experiment. Shot-noise limited performance has been achieved with significant improvements in the signal-to-noise ratio over a wide range of frequencies and phase mismatch of input RF signals. The experimental results indicate that the distributed balanced photodetector will have a major impact on most RF photonic systems with its superior potential of reaching very high power levels.

Long wavelength velocity-matched distributed photodetectors for RF fibre optic links

An InP-based long wavelength velocity-matched distributed photodetector with metal-semiconductor-metal photodiodes is experimentally demonstrated. A 3 dB bandwidth of 18 GHz and an external quantum efficiency of 0.42 A/W have been achieved.

High-power high-speed photodetectors-design, analysis, and experimental demonstration

A novel velocity-matched distributed photodetector (VMDP) is proposed to simultaneously achieve high saturation photocurrent and broad bandwidth. Theoretical analysis on the tradeoff between saturation power and bandwidth shows that the VMDP offers fundamental advantages over conventional photodetectors. A comprehensive theoretical model has been developed for the design and simulation of the VMDP. Experimentally, the VMDP with very high saturation (56-mA) photocurrent and instrument-limited 3-dB bandwidth (49 GHz) has been demonstrated. The theoretical analysis and experimental results show that the VMDP is very attractive for high-performance microwave photonic links and high-power optical microwave applications.

Velocity-matched distributed photodetectors with high-saturation power and large bandwidth

A high-power, high-bandwidth photodetector is experimentally demonstrated using a novel velocity-matched distributed photodetector (VMDP). The distributed photodetector structure can achieve large absorption volume and high-saturation power while maintaining the high-speed performance of the fast photodiodes. The VMDP with 56 mA saturation photocurrent and an instrument-limited 3-dB bandwidth of 49 GHz is achieved. The results show that VMDP is ideal for high-performance microwave fiber-optic links and high-power optical-microwave applications.