Contents Introduction
High capacity future all-optical networks based on optical time division multiplexing (OTDM) and wavelength division multiplexing (WDM) will require compact and high speed demultiplexing devices. There have been already reported all-optical demultiplexing of 80−160 Gb/s optical signal using semiconductor optical amplifier (SOA) based interferometric devices [1]–[5] but they have demonstrated only one channel extraction. As suggested in Ref. [1], an SOA-based Mach-Zehnder interferometric (MZI) device with multimode interference coupler (MMI) can extract both the switched and the unswitched states simultaneously into the two output ports. The input signal can be fully utilized without any waste in power if both the output signals have signal qualities well enough for further processing. However, it is difficult to attain equal signal qualities for both the switched and unswitched signals, since a fine balance in phase-shift between the two arms is not easy to realize. On the other hand, a one-arm MZI polarization switch, which is called “an ultrafast nonlinear interferometer (UNI)”, has an assured balance in phase-shift because it consists of only one SOA, therefore it may provide two output signals having equal signal qualities with much less difficulty.
