Distributed balanced photodetectors for high performance RF photonic links.

摘要

In this dissertation, a novel velocity-matched distributed balanced photodetector with a 50Ω coplanar waveguide output transmission line has been designed and experimentally demonstrated in the InP/InGaAs material system. The device can increase the optical saturation power without penalizing the bandwidth. Theoretical models are developed for designing and simulating the performance of the device. Initially, metal-semiconductor-metal (MSM) photodiodes are used to demonstrate the device. A maximum linear DC photocurrent of 33 mA/branch is achieved. This is equivalent to 66 mA in single-ended photodetectors. The receiver exhibits high AC linearity even under high power operation. The bandwidth of the receiver remains unchanged when the effective DC photocurrent is varied from 1 mA to 21 mA. The distribution of photocurrents was also measured. Device length for optimum RF performance is calculated and implemented in the design. The RF link experiment conducted at 4.16 GHz shows that the relative intensity noise (RIN) of the laser has been suppressed by more than 24 dB and shot noise limited performance has been achieved. Significant improvement of signal-to-noise ratio (SNR) has been observed over a wide range of frequencies and phase mismatch of input RF signals.; A correlation between the dark current of the photodiodes and their failure mechanism has been established. Analyzing the failure mechanism, junction diodes such as p-i-n are found to be more suitable for high power applications. Velocity matched distributed photodetectors and distributed balanced photodetectors with p-i-n photodiodes were also demonstrated for the first time. Record high linear DC photocurrent of 45 mA has been achieved without suffering from thermal damage, thanks to the superior power handling capability of p-i-n photodiodes. A novel fiber alignment technique has been developed to achieve high linear photocurrent. In an RF fiber optic link experiment, more than 37-dB of common-mode-rejection ratio with 45-dB suppression of laser relative intensity noise (RIN) over a broad frequency range has been achieved using the p-i-n distributed balanced photodetectors. The frequency response is flat from 1 GHz to 35 GHz. The experimental results indicate that the distributed balanced photodetector will have a major impact on most RF photonic systems.