A high-performance scanning grating based on tilted (111) silicon wafer for near infrared micro spectrometer application

In the near infrared (NIR) micro spectrometer system, a scanning grating is the most critical component which makes spectrometer operate with one single photodiode instead of expensive photodiode array. However, most scanning gratings have low diffraction efficiency and are not integrated with sensor to monitor the state of the scanning grating. To solve these problems, a novel scanning grating for NIR micro spectrometers is presented and designed. The scanning grating consists of grating, electromagnetic actuator and angle sensor, which are integrated in a chip. Based on a tilted (111) silicon substrate, a blazed grating structure can be obtained by wet anisotropic etching the substrate, and the desired blaze angle can be easily realized by choosing the appropriate tilt angle of device silicon. Simulation results show that the efficiency of the grating with grating constant of 4 μm is more than 50 % over the wavelength range from 800 to 1,800 nm and the maximum efficiency reaches to 90 %. In order to satisfy the requirement of the operating wavelength range, an electromagnetic actuator is designed to drive the millimeter-sized (6.96 × 6.36 mm²) grating plate to achieve large scanning angle, and theoretical analysis shows that the maximum optical deflection angle is ± 10.8° at frequency of 600.5 Hz. An electromagnetic angle sensor is designed to detect the state of the scanning grating and supply the feedback signal for close loop control. Theoretical results show that the voltage output of angle sensor is 1.3226 × 10⁻⁴ V/rad/s with magnetic flux density being 400mT.