Combined volume phase holographic gratings used as a beam splitter in near-infrared waveband

摘要

With the intrinsic advantages of high diffraction efficiency, signal to noise ratio, wavelength and angle selectivity, and low scattering and absorption, volume phase holographic gratings (VPHGs) have been widely used for spectroscopy, telecommunications, astronomy and ultra-fast sciences. In this paper, a novel kind of beam splitter which is consisted of a transmission VPHG and a reflection VPHG as core components and used in near-infrared waveband is proposed. The design idea of the device is described in detail. Based on the Bragg condition and the rigorous coupled wave analysis (RCWA), diffraction properties in near-infrared waveband of the transmission and reflection VPHGs recorded in dichromated gelatin (DCG) are studied theoretically. As an example, two wavebands that need to be separated in near infrared spectrum region are taken into account. One that from 1.574μm to 1.617μm centered at 1.596μm will be diffracted by the reflection grating, and the other that from 1.636μm to 1.682μm centered at 1.659μm will be diffracted by the transmission grating. The diffraction efficiencies of the gratings are calculated and optimized by applying Kogelnik's coupled wave theory and G-solver software, respectively. The recording setup is also designed for further experiments. The effects of the recording and reconstruction setup parameters, the amplitude of the index modulation {An) and the thickness of the gelatin layer (d), and the polarization state of reconstruction beams on the diffraction efficiency properties of the gratings are calculated and analyzed. This kind of beam splitter is prospected to be used in spectrometers for greenhouse gases monitoring.