Four-channel wavelength division multiplexers and bandpass filters based on elliptical Bragg reflectors

Four-channel multiplexers and four-wavelength bandpass filters based on elliptical Bragg reflectors (EBRs) are discussed. The channel spacing is 50 Å near 1.56 μm. The EBRs are narrowband elliptical mirrors that can refocus light from an input waveguide to any one of a number of output waveguides. Spectrally, they perform similarly to Bragg reflectors. The devices were fabricated on silicon using silica-based waveguide technology. The elliptical gratings with 0.53-μm periods were patterned using deep UV spatial frequency doubling photolithography. Multiplexers with single filtering and double filtering were demonstrated. With single filtering, the fiber-to-fiber insertion loss was 3.0±0.5 dB, and the crosstalk was -20 dB; with double filtering, the insertion loss was 4.0±0.5 dB, and the crosstalk was -30 dB. About 2 dB of this loss was due to coupling between the fibers and the waveguide. The additive loss associated with the EBR, including propagation, Bragg reflection, and coupling between input and output waveguides, was about 1 dB