Optical EngineeringPolarization-independent wavelength-multiplexing using thermally fixed photorefractive gratings in lithium niobate
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We report on the feasibility of a polarization-independent multiplexer for two visible wavelengths region with a spectral separation of 2.4 nm and an angular separation of 4 deg. To construct this device, holographic gratings are recorded in an iron-doped lithium niobate crystal via the photorefractive effect. Thermal fixing is employed to avoid optical erasure and increase the lifetime of the recorded gratings. It is shown that the two polarization modes associated with each wavelength propagate collinearly outside the crystal. Furthermore, it is shown that the signal power depends only marginally on the incident polarization, and its variation is less than 5%. No polarization crosstalk is detected, and the wavelength crosstalk is suppressed by 8 to 11 dB.