Narrow-band vertically stacked filters in InGaAlAs/InP at 1.5 μm

A narrow-band wavelength filter in InGaAlAs/InP has been modeled, fabricated, and tested. A highly asymmetrical, vertically coupled directional coupler operating near the band-edge is formed by a narrow ridge and a wide strip-loaded waveguide. The results of numerical simulation, performed by employing the spectral index method, effective-index method, and a modified coupled-mode theory, are used to fabricate a filter structure with a prescribed filter response. Operation at a center wavelength around 1.5 mu m with a bandwidth of 18 angstrom and transfer efficiency of approx.46-48% is achieved. Excellent agreement between the designed and measured bandwidth is demonstrated. A multichannel filter device based on an array of individual filters that is capable of extending the usable spectral range is analyzed.