A two-dimensional system model, including the birefringent low-pass filter (BLF), was designed and a cost function was formulated. This model takes optical system into account in designing BLF. Optimization of the parameter of BLF is acquired by this new method. Best performance of BLF is realized when distance d of o light and e light is about half size of a pixel. Moreover, the relation between the optimized distance d and the cutoff frequency of ideal optical system was established. It is proved that the optimized distance d becomes smaller when the cutoff frequency of optical system increases.
Two-dimensional optical low pass filter (OLPF) was designed, fabricated and tested in our lab. The modulation transfer function (MTF) of OLPF shows that cut-off frequency is 96.15lp/mm in x and y direction, which is satisfied with our design. The transmissions in the visible and infrared regions of the spectrum are mostly above 95% and less than 2%, respectively. The error of every plate thickness is tested less than 0.34% by the experiment of pulse response. The spatial frequency test results show that our device has good low filter performance, matches with the solid state image sensor and well restrains the moire effect and false colors distortion.
A new photoelectric model of silicon based position sensitive detector (PSD) is built and the formulas of the photocurrent and spectral response are got with it. The effect of every layer thickness and SiO<sub>2</sub> thickness to the spectral response is analysis and calculation. The spectral response of PSD is affected by the thickness of p layer mainly at short wavelength and by the thickness of the depletion layer mainly at long wavelength. With the results, a new silicon based near infrared two dimensional pincushion PSD is designed and fabricated. Some necessary tests show that the peak spectral sensitivity of our device is 0.626A/W at 920nm wavelength.
Implementation of a 4 by 1 comb-type Position sensitive detector (PSD) array for position sensing applications is presented. Unlike conventional application, we utilize the method of subdivision to increase the resolution of PSD beyond the feature of photosensitive area, which is presented periodically. To obtain output signal of comb-type PSD, classic grating subdivision circuit is used. Resolution of 6.25μm of comb-type PSD is achieved using optical grating array of a 50μm in pitch and signal power of 3mW. The resolution is limited by the spacing of comb-type PSD and the mismatch of position of PSD array and optical grating array.
The fabrication and testing results of a 65-pin ceramic packaged 4×4 arrayed position sensitive detector are presented. The detector, consisting of 16 tetra-lateral sensitive areas, is a p-n-n+ configuration made on 3-in. 111 n-type high resistance crystal silicon substrates. A 100-nm antireflection SiO2 thin film is formed on the surface, along with a multilayer cover glass with transmissivity >98% from 400 to 950 nm. Primary tests of the device show that it has a low dark current, high spectral sensitivity, very fast response speed, and very good linearity. The dark current of an element unit is less than 20 nA, which is the allowable maximum dark current. The peak spectral sensitivity of the sensor is over 505 mA/W at 800-nm wavelength. Its response time is 8 ns at 45-V reverse bias and the nonlinearity of the total sensitive area is less than 1%.
Position sensitive detectors (PSD) use the lateral photo effect to determine the centroid position of an incident light spot focused on it. A 65-pin ceramic packaged 4×4 arrayed position sensitive detector was fabricated first time as a new prototype of Hartmann-Shack wavefront sensor. The detector, consisting of 16 tetra-lateral sensitive areas, is a p-n-n+ configuration made on 3-inch <111> n-type high resistance crystal silicon substrate. A 100nm antireflection SiO<sub>2</sub> thin film was formed on the surface and a multi-layer cover glass with transmissivity > 98% from 400nm to 950nm. The main parameters of the arrayed as wavefront detector, such as reverse voltage, dark current photosensitivity, response time were reported in the paper.