1.55 micron wavelength indium gallium arsenide/indium aluminum arsenide/indium phosphide velocity-matched distributed photodetectors

High power, high frequency photodetector is a key component for high performance microwave fiber optic links. High optical power in externally modulated links can greatly enhance the link gain, signal-to-noise ratio, and the spurious-free dynamic range. They are also very useful for millimeter-waves generation by photomixing.; In conventional photodetectors, there is a design trade-off between saturation current and bandwidth. Device bandwidth is inversely proportional to RC time and carrier transit time, while saturation photocurrent is proportional to the absorption volume. Thus high speed device usually has a small absorption volume to reduce RC time and carrier transit time, but the small absorption volume limits the amount of photocurrent that can be generated. Conversely, high power device usually has a large absorption volume, which results in large RC and transit time, thus limiting the bandwidth.; The velocity-matched distributed photodetector (VMDP) is a novel type of travelling-wave photodetector which can achieve both high power and high bandwidth. In this dissertation, the principle, design, and experimental results for InP-based VMDP will be discussed. We will present the first experimental results of 1.55 μm wavelength InGaAs/InAlAs/InP VMDP, with a 3-dB bandwidth of 18 GHz, maximum linear photocurrent of 12 mA, and an external quantum efficiency of 0.42 A/W. We will also present the first experimental results of millimeter-wave generation by photomixing at 1.55 μm using high speed, high power W-band VMDP, with millimeter-wave output power of −21 dBm at 75 GHz, and −24 dBm at 95 GHz. To our knowledge, this is the highest CW millimeter-wave power generated by photomixing at 1.55 μm at these frequencies.