Recently, the phones with high screen-to-body ratio are popular in the market, and it leads to the demand of in-display fingerprint recognition. The optical fingerprint sensor is based on frustrated total internal reflection (FTIR), and the camera type independent on the panel process is cost-effective and with high yield rate. To meet the volume constraint of the smart phone, a miniaturized compact lens is designed. For maximizing the sensing area in the limited space, the field of view can reach 128°. To increase the accuracy and speed of the recognition, the design has extremely small distortion and low f-number. Mostly importantly, the resolution should be sufficient for the fingerprint extraction algorithm. To achieve the specifications, the lens is designed with three aspheric plastic lenses using injection molding. In this paper, the procedure of optical design, mechanical design, lens fabrication and assembly of the prototype is presented. Finally, the prototype is employed for fingerprint identification.
Since the beginning of this year, the full screen mobile phone has been more and more popular. Because the traditional capacitive fingerprint sensor cannot work under the display, it should be placed on the side or back of the phone. However, it is unfavorable to the consumer experience. Therefore, the demand for in-display fingerprint recognition technology has arisen. The in-display fingerprint identification technology can be divided into optical and ultrasonic fingerprint identification. Because the ultrasonic fingerprint identification is limited by low yield rate and high cost at present, the optical fingerprint identification is more popular in market. The optical fingerprint identification is advantageous for the identification not affected by dry or greasy fingers, higher yield and lower cost. In this study, the miniature wide angle lens under the display is developed for the OLED panel. For optical fingerprint identification, the illumination is inevitable. In comparison with the LCD panel, the OLED panel needs not the backlighting because each pixel has its own light. The optical sensor is based on the principle of the frustrated total internal reflection (FTIR). The ridge of the finger destroys the total internal reflection (TIR), and then the dark pattern appears. On the contrary, the valley of the finger satisfies the TIR condition, and then the bright pattern generates. Because the camera is implemented in the narrow space of the mobile phone, the ultra-wide field of view and extremely short total track length are necessary. In this study, the optical design can successfully meet the requirement for fingerprint recognition.
In this paper, we present a novel optical design to overcome the over-exposure problem without increasing the specifications of sensors. A spatial light modulator (SLM), which is commonly used for modulating light intensity, is used in our design. In projector systems, SLM is commonly used in conjunction with DMD to modulate the intensity of the projected images. In our design, reverse of this design concept is employed. Intensity modulation is performed on object space, instead of image space. This paper shows two optical designs, one is image system, which image the outside object to SLM. This system has F/8 and Field of View (FOV) 40 degree Hyperfocal image design. The other is a relay image system, which relay the image from SLM to sensor. This relay system has F/4 and magnification of 0.5 times. Our design has successfully reduced over-exposure problems.
Solar concentrators are often used in conjunction with III-V multi-junction solar cells for cost reduction and efficiency improvement purposes. High flux concentration ratio, high optical efficiency and high manufacture tolerance are the key features required for a successful solar concentrator design. This paper describes a novel solar concentrator that combines the concepts, and thus the advantages, of both the refractive type ad reflective type. The proposed concentrator design adopts the Etendue-cascading concept that allows the light beams from all the concentric annular entrance pupils to be collected and transferred to the solar cell with minimal loss. This concept enables the system to perform near its Etendue-Limit and have a high concentration ratio simultaneously. Thereby reducing the costs of solar cells and therefor achieves a better the per watts cost. The concentrator demonstrated has a thing aspect ratio of 0.19 with a zero back focal distance. The numerical aperture at the solar cell immersed inside the dielectric concentrator is as high as 1.33 achieving a unprecedented high optical concentration ratio design.
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