A Wavelength Monitor Based on Electroabsorption in Quantum Well Waveguide Photodetectors

The responsivity of quantum well photodetectors exhibits a very sharp transition for wavelengths near the absorption band edge. By varying the reverse bias voltage applied to such a detector the precise location of this transition can be tuned over several nm due to the quantum confined Stark effect. This effect has been used to make wavelength selective detectors for use in optical communications1,2 and sensitive wavelength monitors3,4. In this paper we report on a p-i-n quantum well photodetector in which two electrically isolated segments are fabricated in-line on a single rib waveguide. The first detector in the series filters the light that reaches the second. The ratio of the second detector’s photocurrent to that of the first is a rapidly increasing function of wavelength near the band edge. It can be used as a sensitive wavelength monitor in applications such as optical fiber Bragg grating sensors.