High-power, high-linearity photodiodes and high-power photodiodes as optoelectronic mixers

Even since fibers are proposed to replace conventional coaxial cables to transmit microwave signals, the applications for analog optical link have been rapidly increasing such as phased array antennas, radio over fiber, photonic analog-to-digital converters, etc. Power handling capability is an essential figure of merit for photodiodes that are utilized in analog optical links in order to minimize the loss of the analog optical link. In this dissertation the saturation mechanisms in uni-traveling-carrier (UTC) photodiodes and modified uni-traveling-carrier (MUTC) photodiodes arc investigated, and some guidelines for the design of high-power UTC and MUTC photodiodes arc presented.

Photodiodes are frequently the limiting factor for the linearity performance of an analog optical link. Third-order output intercept point (0IP3), the figure of merit for the linearity of photodiode, needs to be maximized especially at high frequencies. In this dissertation the nonlinear phenomena in Charge-Compensated MUTC (CC-MUTC) photodiodes are quantitatively measured, and the physical origins of those nonlinear phenomena arc explained. An equivalent circuit model is develop that provides excellent fits to the measured 0IP3 of CC-MUTC photodiocles. The equivalent circuit model is used to optimize the operating wavelength for the highest OIP3 of CC-MUTC photocliodes, and a high 0IP3 of 57.5 dBm is achieved for CC-MUTC at 152 MHz. An InGaAs/lnP partially depleted absorber photodiode with highly eloped absorbers (HD- PDA) and a modified uni-traveling-carrier photodiode with highly doped absorber (HD- MUTC) are designed to improve the 0IP3 at high frequencies. For HD-MUTC the 0IP3 starts at a high value of 55 dBm at low frequency and remains as high as 47.5 dBm at 20 GHz.

Radio-over-fiber systems operating at millimeter-wave frequencies have great potential in providing future V-band (50-75 Ghz) wireless networks with larger channel capacity. Photodiodes can be used as V-band optoelectronic mixers, but photodiodes must be able to deliver high up-converted RF power. In this dissertation a high-power MUTC photodiode is presented to work as a V-band optoelectronic mixer. By optimizing the operation condition of the MUTC photodiode, a record high up-converted RF power of -4.7 dBm was achieved at 60 GHz when the photocurrent was 70 mA.

Note: Abstract extracted from PDF file via OCR.