An approach to the design of highly selective resonant-cavity-enhanced photodetectors

The information capacity of a communication system employing a wavelength-division multiplexing scheme can be increased by reducing the free spectral range between different signals, reducing the full width at half maximum (FWHM), and detecting these closely spaced channels. After critically analyzing the design parameters of existing resonant-cavity-enhanced (RCE) p–i–n photodetectors, we have determined that more closely spaced channels can be detected either by increasing the length of a RCE p–i–n detector or by reducing the stop-band width of the bottom mirror. A masking procedure is described to determine the maximum cavity length attainable for any bottom distributed Bragg reflector (DBR) materials so that photodetector filters and detects only one wavelength, being insensitive to all other wavelengths. The optimized cavity length of single wavelength selective RCE detector operating at 1.3 μm using 42 12 pairs of InAlGaAs/InP as a bottom DBR is 7.5 μm and its theoretical FWHM is 2.5 nm.