A tunable cyclic encoder using photopolymer-based holographic grating for optical CDMA application

It is important to have a tunable encoder in optical channel coding for the purpose of coping with varying communication environment. In this paper, a tunable encoder based on the holographic grating (HG) using photopolymer as the holographic medium is described. The system is composed of photopolymer holographic grating as a demultiplexer, spatial light modulator (SLM), and other lens systems. The photopolymer grating acts as a demultiplexer to distribute optical wavelength channels on the SLM through its spatial dispersion property. Then, the SLM produces wavelength-endcoded data but its spatial amplitude/phase modulation. The merits of using the holographic grating are that it has relatively easy fabrication process, and that non-uniform grating structure and multiplexing can be exploited. In this setup, we can additionally change demultiplexing wavelengths by inducing strain gradient on the polymer grating, which is attached on the two XYZ linear stages. Hence a different set of wavelengths is incident to SLM and this enables another type of encoding pattern.