Grating-assisted vertical directional couplers can be combined with evanescently coupled absorption layers to realize integrated wavelength-selective photodetectors. The multimode structure of a photodetector including layered waveguides is studied, and mode transfer from the lossless filter section to the absorptive detector section is analyzed. By optimizing the device structure, the background absorption of unselected wavelengths can be suppressed, and, as a result, high crosstalk attenuation can be obtained. The filter bandwidth can be designed to cover a wide range from on the order of 10 nm down to the order of 0.5 nm with a device length that is shorter than 2 mm, which makes it suitable for various types of wavelength-division-multiplexing systems.>
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Hajime Sakata (1993) studied this question.
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