Abstract

The transition from 10GB/s to 40GB/s fiber optic systems will trigger numerous changes in photodetector structures and receiver architectures. To date, most photodiodes have employed normal-incidence input coupling. This approach is, however, limited by the tradeoff between bandwidth and responsivity, which limits the bandwidth to < 12GHz for acceptable efficiencies. For very high-speed operation this has been circumvented with waveguide structures. While very high speed have been achieved with waveguide photodiodes, this approach given rise to new issues such as input coupling efficiency and sensitivity to polarization. An additional consideration is the ability of the photodiode to handle high input optical power levels in systems that utilize optical preamplifiers. This is particularly important for “amplifierless” receiver architectures, in which optical amplification is utilized to provide signal levels sufficient to directly drive logic circuitry. At moderate power levels the photodiode may exhibit bandwidth saturation and optical nonlinearities. Hence, a new figure of merit, the bandwidth-current product, has become an important device characteristic. Further improvements in performance and functionality can be anticipated with monolithic integration. Examples include integration of the photodiode with a semiconductor optical amplifier or combining detectors in a balanced receiver.

© 2004 Optical Society of America