Imaging spectral device based on multiple volume holographic gratings

A spectral device based on multiple holographic gratings is proposed. Several volume holograms are superimposed into a common volume of photorefractive crystal Fe:LiNbO3 using the wavelength and angular multiplexing method. This device is implemented by only one single wavelength laser using a two-lambda method. The imaging function of the device is realized with convergent recording beams. It can reduce the spectral system because the focusing lens is removed. Because the diffraction efficiency and the spectral resolution of the superimposed volume holographic gratings could be very high, the spectral device could achieve attracting characteristics of the diffraction efficiency and spectral resolution. Theoretical analysis and model design are presented and a discrete spectral device working at four wavelengths is demonstrated. The device has a uniform diffraction efficiency of 10% and the resolution of 1 to 2 nm. In addition, it has the advantages of wide spectral coverage, simple structure, and flexible design.