# Research on Compressed Sensing Spectrometry Based on Electro-Optical Transmittance Coding
## 3 Experiment  
According to Figure 1, a compressed sensing spectrometry system is built, as shown in Figure 3. The size of the LiNbO\({}_{3}\) electro-optic crystal (\(L_{X}\), \(Ly\), \(L_{Z}\)) is selected as 2 mm \(\times\) 4 mm \(\times\) 40 mm, the light passing surface is the _xoy_ plane, and the size is 2 mm \(\times\) 4 mm. The distance the light travelled is 40 mm. The LiNbO\({}_{3}\) electro-optic crystal (provided by Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences) was grown by the Czochralski method. Its absorption loss is less than 0.1%. The dimensional tolerance of the crystal is \(\pm\)0.1 mm. To uniformly apply the driving voltage to the LiNbO\({}_{3}\) electro-optic crystal plate, a 30 \(\upmu\)m thick aluminum film was plated on the two main sections of the crystal plate--_yoz_ plane. The aluminum film serves as the electrode layer and can evenly distribute the applied voltage on the electrode surface and form a uniform electric field in the LiNbO\({}_{3}\) electro-optic crystal plate. The electric field is provided by a high voltage driving circuit made by ourselves, and the driving circuit is composed primarily of an FPGA and an LC circuit. The FPGA provides a 1 kHz frequency of sinusoidal AC driving control voltage, and the magnitude of the driving voltage can be more than 2000 V  
Figure 2: Spectrum compressed sensing process.  
resonantly amplified by the LC circuit. The voltage will choose all the values in the range of 0-2000 v within 0.25 ms in 1/4 cycles.  
The polarizers are uncoated calcite Gran Taylor polarizers, the light transmission range is 0.35-2.3 \(\upmu\)m, and the extinction ratio is up to 10\({}^{5}\):1. The light transmission aperture is 5 mm \(\times\) 5 mm, which not only meets the light transmission requirements, but also reduces the volume of the spectrum measurement optical system as much as possible. The silicon-based amplified photodetector PDA10 A2 produced by Thorlabs company, with a wavelength response range of 0.2-1.1 \(\upmu\)m and a measurement bandwidth response of DC-150 MHz was selected for photoelectric detection. Both collimating lens f1 and converging lens f2 are K9 glass flat convex lenses, with a focal length f = 6 mm and diameter D = 6 mm. Optical input and output interfaces are equipped with an optical fiber FC/PC adapter. Throughout the entire spectrometry system, the light to be measured is coupled by optical fiber and collimated into parallel light via the collimating lens f1; subsequently, the incident light is collimated into the LiNbO\({}_{3}\) electro-optical transmittance coding modulator composed of polarizer1, the LiNbO\({}_{3}\) electro-optic modulator, and polarizer2. The encoded optical signal is concentrated and emitted through converging lens f2, and finally detected by the photodetector. The dimensions of the entire spectrometry system are only 30 mm \(\times\) 30 mm \(\times\) 90 mm.  
To verify the feasibility of this scheme, the system was selected to be operated in the visible light range of 0.38-0.78 \(\upmu\)m. After the optical transmittance coding was calibrated, the compressed sensing spectrum measurement experiment was performed.