Inline quantum-well waveguide photodetectors for the measurement of wavelength shifts

A two-segment GaAs-InGaP-InGaAs p-i-n quantum-well waveguide photodiode has been fabricated and demonstrated to function as a sensitive wavelength monitor. The ratio of the two segments' photocurrents varies linearly with wavelength in a region near the absorption band edge. A wavelength sensitivity on the order of 1 pm was measured for input optical power levels above 30 /spl mu/W and signal averaging times of 0.2 s. An operating range from 980 to 1020 nm was achieved using electroabsorption tuning of the band edge. The intended application for this detector is wavelength demodulation of Bragg grating fiber optic strain sensors. A strain sensor with resolution of /spl plusmn/6 /spl mu//spl epsiv/ was demonstrated using a superluminescent diode and the inline detectors to monitor strain-induced changes in the reflection wavelength of an in-fiber grating.