Study On The Silica Immersed Grating For The Short-Wave Infrared

Due to the addition of immersion medium, when the diffraction happens in high refractive index medium, the optical path difference and angular dispersion will increase proportionally. Therefore, when immersed grating is used in imaging spectrometer, it will have higher resolution, higher angular dispersion and more compact instrument structure. In this sense the immersed grating is one of the key elements in greenhouse gas hyperspectral spectrometers. In this paper, we have designed the immersed grating with high diffraction efficiency for the atmosphere methane spectral band (the short-wave infrared). The diffraction characteristics of the immersed grating have been investigated by using rigorous coupled wave theory. The simulation showed: the groove depth and duty cycle of the immersed grating must be controlled within the range of 1050nm-1100nm and 0.3-0.36 respectively, in order to guarantee the 1 order diffraction efficiency would be over 80% at wavelength 2300nm. The immersed grating with the period of 1319nm in a silica substrate of 120 mm x 95mm will be fabricated by holographic lithography - ion beam etching in late 2020.