Chromatic dispersion characteristics of holographic multiple-channel demultiplexers

We examine and characterize a wavelength demultiplexer using a holographic grating for WDM multiple-channel applications. The holographic grating is a kind of volume grating recorded in a photopolymer, which is different from the general surface relief type diffraction gratings. The holographic grating disperses the wavelength components of incident wave into spatial domain so that through the coupling optics, different wavelength channels can be separated to the different output optical fibers. The characteristics of the polymeric holographic grating are compared to those of the relief type diffraction gratings. Overall demuliplexer characteristics is characterized by applying first order Born approximation with electro-magnetic vectorial analysis. It shows that the amplitude and group velocity (i.e., the chromatic dispersion) characteristics are determined by the holographic grating phase structure and out-coupling optics lens aberrations. The out-coupling lens aberration effect to the chromatic dispersion is examined and classified according to the lens aberration classification. The holographic grating phase perturbation (i.e., chirping) can be used to minimize the lens aberration caused chromatic dispersion to improve the demultiplexer performance. The demultiplexer polarization dependent loss is also examined in relation to the spatial dispersion and diffraction efficiency characteristics.