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sony cmos polarization image sensors
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Four directional polarizer is formed on the image sensor
Sony Semiconductor Solutions' polarization sensor can capture a four directional polarization image in one shot by the four directional polarizer. It can calculate the direction and degree of polarization (DoP) based on the intensity of each directional polarization. Together with subsequent signal processing, it can capture the polarization information in real time.
Polarizer is formed on chip under the on-chip lens layer
With conventional types of polarization sensors, the polarizer is attached on top of the on-chip lens layer. However with Sony Semiconductor Solutions' polarization sensor, the polarizer is formed on chip under the on-chip lens layer.
A shorter distance between the polarizer and the photodiode improves the extinction ratio* and the incident angle dependence.
Since the polarizer is formed during the semiconductor process, form and formulation of polarizer, uniformity, mass productivity and durability are excellent compared to conventional polarization sensors.
Furthermore, Sony Semiconductor Solutions' polarization sensor is covered with an anti-reflection layer, which helps to reduce reflectance and avoids poor flare and ghost characteristics.
Figure 1: Structure
Figure 2: Structure of a conventionnal polarization sensor
Figure : Structure of Sony Semiconductor Solutions' polarization sensor
*Extinction ratio
The extinction ratio is a specification to measure polarization. The extinction ratio of polarization image sensor is the ratio between the sensitivity of transmission axis light and the sensitivity of extinction axis light. The higher the number, the better the specification and performance.
Light has physical elements: brightness (amplitude), color (wavelength) and polarization (vibration direction). Lights from the sun or fluorescent lamps vibrate in various directions and is called unpolarized light.
Figure 4
What is polarization?
Sony Semiconductor Solutions' polarization sensor has wire-grid polarizers. Parallel light against polarizer passes through it, while perpendicular light is cut off at the polarizer.
Degree of Polarization and polarization direction
Polarization has two physical information, which are the degree of polarization and the direction of polarization. This information can be used for various applications such as surface scratch detection, particle inspection, distortion and shape recognition which, traditionnally, has been difficult to detect.
Example of Degree of Polarization (DoP)
The light is reflected by the surface of the object in polarized and unpolarized lights. The degree of polarization of the reflected light depends on the surface condition (material, color, roughness, etc...) and the angle of reflection.
In the degree of polarization image, the white is high polarization and block is low polarization. As an example, the stitch is easily visible due to the difference in the degree of polarization of the thread and leather.
Figure 5: Normal image
Figure 6: Degree of polarization image
Example of Polarization Direction
Figure 7: Normal image
Figure 8: Polarization direction image
Polarization direction provides the direction information of reflected plane of an object.
The direction of polarization iage shows the angle of polarization direction in color using HSV color mapping. In this example, the upper side of the cube is highlighted in light blue meaning that the angle of the polarization direction is 90 degree.
Figure 9: HSV color mapping
