High-Resolution Near-Infrared Micro-Spectrometer With Dual Gratings and a Cylindrical Lens
WU Jing-yi1, ZHOU Zhe-hai1*, ZHAO Shuang1, MIN Kun-long2, LI Hui-yu1
1. Key Laboratory of the Ministry of Education for Optoelectronic Measurement Technology and Instruments, Beijing Information Science & Technology University, Beijing 100192, China
2. Beijing Aerospace Measurement and Control Technology Co., Ltd., Beijing 100041, China
Abstract：Micro-spectrometers have become a significant trend in the development of spectrometer technology because of the advantages of portability, low cost, and integration. The NIR micro-spectrometer is a class of micro-spectrometers operating in the near-infrared band, which has an extensive range of applications in the field of optical fiber sensing and demodulation, fiber-optic communication, etc. However, contemporary NIR micro-spectrometers typically are low resolution, expensive, bulky, and impractical for portability. A unique micro-spectrometer structure with dual gratings and a cylindrical lens is proposed and carriedout theoretically and experimentally. Three major alterations are adopted in the new design compared to the traditional micro-spectrometer structure: optical fibers are used to reduce light energy loss, dual gratings are used to split the beam by secondary diffraction, and the cylindrical lens is used to change the imaging size on the surface of the line-array CCD. The optical path is decreased to a volume of 66 mm×40 mm×24 mm with a spectral resolution of 0.2 nm in the wavelength range from 1 525 to 1 570 nm according to the simulation analysis with Zemax, which is 2.5 times better than that of spectrometers without a cylindrical lens. Based on the theoretical analysis, suitable optoelectronic devices are selected for system packaging and combined with the irmatching circuit module to realize the spectral detection function of the micro-spectrometer.The optical system of the micro-spectrometer can be installed in a volume of 66 mm×40 mm×30 mm, and the spectral resolution is measured to 0.215 nm, which is in agreement with the theoretical results. Furthermore, a Fiber Bragg Grating (FBG) temperature sensing system based on the micro-spectrometer used as a demodulator is built. Four FBG with central wavelengths of 1 534, 1 538, 1 542, and 1 545 nm were selected as sensors. The temperature varies continuously at 1 ℃ intervals in the 0~50 ℃, resulting in real-time temperature measurement and signal demodulation with a system temperature sensitivity of 9.58, 9.68, 9.69 and 9.6 pm·℃-1 respectively. So, the micro-spectrometer with-high resolution and reliability is verified. The subcomponents of the micro-spectrometer can be fixed to the shell, which is small in size, high in resolution and good instability. It is expected to be applied to other occasions requiring high-resolution spectral analysis, such as substance concentration analysis, sensing signal measurement, etc.
Key words：Micro-spectrometer; Dual gratings; Cylindrical lens; High-resolution; Near-infrared band
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