Wavelength demultiplexing with volume phase holograms in photorefractive lithium niobate

The concept is discussed of wavelength demultiplexing with volume-phase holograms that are superimposed in a photorefractive lithium niobate crystal, and first experimental results are presented. From theoretical considerations, it turns out that in the telecommunication wavelength region around 1550 nm, simultaneous and polarization-independent demultiplexing of 40 channels can be achieved with losses of less than 1 dB, a channel spacing of 0.8 nm and a cross-talk of less than -35 dB. Superposition of many holograms with high diffraction efficiency requires thermal fixing. Proof-of-concept experiments at room temperature are performed where holographic gratings are written by plane waves of green light. Rotation stages enable precise adjustment of orientation and spatial frequency of the gratings. Demultiplexing of a beam with light of the wavelengths 1558.0 and 1558.8 nm is demonstrated, where the losses are about 15 dB and cross-talk suppression up to 20 dB is achieved.