A novel switch configuration for an optical add/drop multiplexer is proposed. By utilizing a certain Mach-Zehnder interferometer both as a component of a double-gate switch and as a level equalizer, we reduced the number of Mach-Zehnder interferometers from five in a conventional switch configuration to three. The add/drop switch simultaneously provides high-isolation switching and polarization-independent automatic level control. The use of planar lightwave circuit (PLC) technology enables this switch to be fabricated with three thermooptic switches (TOSW's) and a monitor tap. High isolation of more than 44 dB and automatic level control accuracy of better than 0.3 dB are achieved. Bit error rate (BER) measurements confirmed switch's usability in the optical add/drop multiplexer.
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