High-performance compact optical WDM transceiver module for passive double star subscriber systems

High-performance transceiver-type optical WDM interface modules with a volume of only 36 cc have been developed for PDS subscriber systems. The new module comprises an optical WDM sub-module, hybrid-integrated transmitter and receiver circuits. In the WDM sub-module, a planar lightwave circuit chip was hermetically sealed together with laser and photodiode chips in order to minimize the size of the transceiver module. The lightwave circuit was formed on an optical-waveguide chip by adopting a high-silica based optical-waveguide technology. The circuit has a 3-dB directional coupler for bi-directional transmission with a 1.3-μm wavelength through a single fiber and a wavelength division multiplexer between both 1.3-μm and 1.55-μm wavelengths. The overall characteristics of the fabricated WDM sub-module achieved were a responsitivity of 0.25±0.05 A/W, an insertion loss approximately 3 dB at 1.55 μm and an isolation of 35 dB between both wavelengths. Optical output power of the fabricated transceiver module was -3.8 dBm. Also, receiver sensitivity of less than -35 dBm with an overload of over -14 dBm were obtained by introducing high-speed automatic gain and threshold control techniques. Thus, an allowable span loss of over 30 dB and an optical dynamic range of over 20 dB were attained. The preamble bit length required to reach stable receiver operation was confirmed to be within three bits