Abstract
In recent years, as promising alternatives to all-electrical coaxial cable systems, optical radio-frequency (RF) which can provide benefits in large bandwidth, high-power handling capability, low loss, immunity to electromagnetic interference (EMI), and reduced size and weight, have been a widely investigated in tremendous number of microwaves applications in both defense and civilian areas such as radio-over-fiber, antenna remoting, and communications. As the optical-to-electrical converter in optical links, high performance photodiodes (PDs) are a key component in these applications. In this dissertation, three different high performance photodiodes are developed and demonstrated for applications in microwave photonics and communications.
First, for high-gain analog optical links and photoacoustic signal detection applications, a large-area modified uni-traveling-carrier (MUTC) photodiode with a high RF output power and high responsivity at 1550 nm is designed, fabricated and characterized. In this work, surface normal MUTC PDs with diameters of active areas from 100 μm to 600 μm were fabricated. A 100-µm-diameter photodiode achieved an RF output power of 23 dBm at 2 GHz and a dark current of 20 nA at -8 V. The 3-dB bandwidth and responsivity were 1.8 GHz and 0.63 A/W, respectively.
Furthermore, a waveguide photodetector with high speed and high responsivity at zero bias which has applications in radio over fiber links, dense photonic integrated circuits and PD arrays is developed and characterized. A bandwidth of 66 GHz under zero-bias operation and 102 GHz bandwidth at -1 V have been successfully demonstrated for a PD with an active area of 4×4 μm2. Larger PDs (5×7 μm2) have 56 GHz bandwidth and an internal responsivity of 0.48 A/W at 0 V. This performance is among the highest reported for all zero-bias photodiodes and, to the best of our knowledge, represents a new record for waveguide photodiodes.
In addition to PDs designed for 1550 nm, I also have designed, fabricated, and characterized high performance waveguide MUTC PDs at 1310 nm that are successfully integrated on a Si photonic platform by using micro-transfer-printing technology. To the best of our knowledge, this is the first waveguide MUTC photodiode transfer-printed on Si for 1310 nm. At -3 V, the waveguide photodiodes on Si achieved 54 GHz bandwidth, 0.29 A/W internal responsivity, and 5.7 dBm output power at 30 GHz measured from bar-level PDs. Based on its high-speed, high-power and compatibility with micro-transfer printing, these PDs can be used in Si photonic chips such as photonic integrated circuits for integrated microwave photonics.
