A programmable optical demultiplexer using a 32–element photodiode array

This paper describes the design and performance of a programmable optical demultiplexer which can compensate the influence of: (1) scattering in the wavelength of an optical source; and (2) wavelength fluctuation of the optical source caused by temperature change, by controlling the branching characteristics in accordance with the wavelength of the optical source. In this multiplexer, a 32‐element Si photodiode array was used to carry out programmable control of the branching characteristics. This optical demultiplexer has the following merits: (1) a wide channel passband is not needed; and (2) since the passband‐center wavelength of this multiplexer is adjusted to the wavelength of the optical sources, fine tuning of the branching characteristic in fabrication is not needed. The fabricated programmable optical demultiplexer has a channel wavelength spacing of 4.0 nm, an insertion loss of 8.0 dB which includes a loss of 3.9 dB due to the detection loss caused by the gap between two photodiodes composing the PD array, and a passband width of 2.8 nm. It was confirmed also by a digital transmission experiment (32 mB/s, RZ signal) that this demultiplexer can maintain its optimum branching characteristics for any wavelength deviation in the optical sources.