InP-Based Polarization-Insensitive Planar Waveguide Concave Grating Demultiplexer with Flattened Spectral Response

Abstract

ABSTRACT ⎯ InP-based planar waveguide 48-channel concave grating demultiplexers with a channel spacing of 0.8 nm (100 GHz) are described and demonstrated. Polarization insensitivity and flattened spectral response are successfully achieved by the introduction of a polarization compensator and a two-focus grating, respectively. The fabricated device shows a polarization-dependent wavelength shift of less than 20 pm and a -3 dB spectral width of about 0.55 nm (68.75 GHz) over all channels. Keywords ⎯ Planar waveguides, demultiplexer, concave grating, polarization, wavelength division multiplexing. Planar waveguide grating devices have been widely used for wavelength (de)multiplexing, switching, and optical add-drop applications in dense wavelength-division multiplexing optical communication systems. Among the various types of devices to implement a demultiplexer (demux) [1]-[4], the InP-based planar waveguide concave grating (CG) has shown great potential due to its compactness [2] and monolithic integration with laser diodes (LDs), photodetectors (PDs) [3], and semiconductor optical amplifiers [4]. However, compared to silica- or polymer-based CGs, it is difficult to achieve desirable performance in such areas as high channel-spacing accuracy, low polarization dependence, and flat-top spectral response over all channels due to its high refractive index dispersion,