Germanium-on-silicon planar concave grating wavelength (de)multiplexers in the mid-infrared

Mid-infrared wavelength (de)multiplexers based on planar concave gratings (PCGs) fabricated on a germanium-on-silicon waveguide platform are presented. PCGs with two different types of gratings (flat facet and distributed bragg reflectors) are analyzed for both transverse electric (TE) and transverse magnetic (TM) polarizations. The insertion loss and cross talk for flat facet PCGs are found to be −7.6/−6.4 dB and 27/21 dB for TE/TM polarization. For distributed bragg reflector PCGs the insertion loss and cross talk are found to be −4.9/−4.2 dB and 22/23 dB for TE/TM polarization.