Polarization independent InP WDM multiplexer/demultiplexer module

We report the design, fabrication, packaging, and characterization of a polarization independent integrated optical InP multiplexer/demultiplexer module. The device is based on a vertically etched diffractive grating and separates four channels with 4 spacing in the 1.55 μm window. An n^-/n⁺-InP layer structure with very low birefringence results in a shift of the passbands between transverse electric (TE) and transverse magnetic (TM) polarization of less than 0.1 nm. With a self-aligned flip-chip mounting technique light is optically coupled from the input and output waveguides to an array of lensed single mode fibers with a coupling efficiency of more than 80%. The packaging includes temperature control that allows fine tuning of the channel passbands over 5 nm. Optical crosstalk is always better than -17 dB and fiber to fiber losses of 15 dB are achieved. The module has been successfully implemented in a 4×2.5 Gb/s WDM transmission system