Balanced photodetectors

Abstract

As telecommunication systems require greater amounts of data to be transferred, communication links and hardware must evolve to use higher frequency radio frequency waves with wavelengths on the order of a millimeter. Traditional fully RF systems meet challenges when trying to meet this goal. For example, coaxial cables become increasingly lossy as operating frequency increases, leading to decreased SNR, and are also bulky, leading to a degraded size, weight, and power specification. ☐ Achieving point-to-point signal routing in the optical domain provides a low loss solution to this problem. However, this cannot be achieved without the development of high-performance photonic devices such as electrooptic modulators and photodetectors. High-power, wide bandwidth, and high-linearity MUTC photodetectors developed at the University of Virginia provide an efficient conversion from the optical domain to the RF domain before feeding a transmitting antenna. ☐ The presence of noise in any communication link is omnipresent. For an analog photonic link, the greatest contributors of noise are Relative Intensity Noise (RIN) from the laser and Amplified Spontaneous Emission (ASE) from the optical amplifier, which amplifies the signal before coupling into a photodetector. Balanced photodetectors (BPDs) employ a balanced detection method that very significantly mitigates RIN and ASE noise. A 40 $\mu m$ BPD was fabricated and tested for its bandwidth and common mode rejection ratio (CMRR) parameters. ☐ These photodetectors have enabled the creation of an antenna array architecture in which the current source for each antenna element is a photodetector [2,29]. The main engineering challenge to be overcome in utilizing these designs is optical integration. In this thesis, a new method of optically coupling fiber light into an array of photodetectors is theorized, simulated, and presented.