Design for a high dense wavelength division multiplexer based on volume holographic gratings

The design of a 2048-channel dense-wavelength division multiplexer (DWDM) with channel spacing of 0.05 nm (a 3-dB bandwidth) using reflection holograms in LiNbO₃ is reported. We use an innovative approach to combine angular multiplexing with wavelength multiplexing to keep the bandwidth constant within the S, C, and L band of the fiber transmission window. The key to the design is to calculate the half width at first zero (HWFZ) for the Bragg selectivity of reflection holograms derived from the VOHIL model. Thus, one can enable the channel spacing for each center wavelength of the diffraction peak to be constant and maximize the number of channels in DWDM accordingly.