In this article, We demonstrated an image sensor for detecting changes in polarization with high sensitivity. For this purpose, we constructed an optical system with a two-layer structure, comprising an external polarizer and polarizers on a pixel array. An external polarizer is used to enhance the polarization rotation while reducing the intensity to avoid pixel saturation of the image sensor. Using a two-layer structure, the two polarizers can be arranged under optimal conditions and the image sensor can achieve high polarization-change detection performance. We fabricated the polarization image sensor using a 0.35-µm CMOS process and, by averaging 50 × 50 pixels and 96 frames, achieved a polarization rotation detection limit of 5.2 × 10 −4 • at a wavelength of 625 nm. We also demonstrated the applicability of electric-field distribution imaging using an electrooptic crystal (ZnTe) for weak-polarization-change distribution measurements.
In this study, a polarisation-analysing CMOS image sensor is fabricated for sensitive polarisation modulation detection. Although the image sensor with on-pixel polarisers can image the incident polarisation collectively, its sensitivity to a weak polarisation change is not high. With the proposed method, an external polariser is used to enhance the polarisation modulation sensitivity with a polarisation image sensor. The performance of this highly sensitive polarisation image sensor and imaging experiments are evaluated using a flow channel.
In this paper, we propose an improved on-pixel polarizer structure for an image sensor, which was fabricated using the 0.35 μm standard CMOS process with dual metal layers (Metal 1 and Metal 2), i.e. two layers of gratings with metal-wiring layers were stacked. By designing the line/space ratio as 0.7/0.7 μm, the extinction ratio was significantly improved at a wavelength of 780 nm, which was over 1.4 times higher than that of a single-layer grating, and the detection sensitivity of the polarization change was enhanced by more than 1.8 times. We also demonstrated electro-optical imaging at radio frequency using this image sensor.
In this study, we demonstrate a reflective imaging system in which a dual polarizer structure, consisting of a uniform polarizer and a polarizer on the pixel of a polarization image sensor, enables the detection of weak polarization changes. The uniform polarizer can achieve a high extinction ratio and is used to render the amount of polarization change in a condition that is easily detectable by the polarization image sensor. The polarization image sensor uses two types of polarizers arranged in an orthogonal relationship with each other to obtain complementary signals for polarization rotation. This is also used for differential detection to reduce the in-phase noise components. In the prototype system, the signal characteristics were in close agreement with theoretical considerations. Furthermore, as a demonstration of high-sensitivity polarization rotation imaging, the polarization rotation of a menthol solution in a 150-µm-thick channel was detected.
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