Light-driven mechanism of a photothermal conversion infrared image generation chip

Abstract

An infrared image generation chip (IR-IGC) based on the photothermal conversion effect was developed. It can transform visible light images into infrared (IR) images. However, full 256 IR grayscales of an 8-bit IR grayscale image cannot always be completely captured due to the short integral time of the IR imaging devices. In this paper, we propose a novel light-driven mechanism of the IR-IGC to break the limitation on the integral time of IR imaging devices. A digital micro-mirror device (DMD) working in its binary mode was adopted for generating a light-driven image sequence including 8 binary images. The IR-IGC was driven by these 8 binary images in turns circularly during a heating period. The heating period was divided into a rising period and a holding period. The temperature of the IR-IGC gradually rised during the rising period and then stabilized during the holding period. After the heating period, the IR-IGC entered a cooling period to dissipate heat and got ready for generating the next frame of IR image. The IR imaging device can capture full 256 grayscales by integrating the IR radiation during the holding period of the IR-IGC. The thermal response curves of the IR-IGC under different light-driven waveforms were simulated. The heating period was set to 20 ms. For the grayscale of 255, the rising period was about 5.89 ms, the holding period was about 13.84 ms, and the cooling period was about 8.32 ms. The maximum temperature rise corresponding to the grayscale of 255 was about 123.71 K. The temperature change caused by unit grayscale was 0.36–0.61 K. We also experimentally tested the performance of the IR-IGC under the light-driven mechanism. Clear IR images with 256 grayscales were captured. And the measured thermal response curve of the IR-IGC conformed to the simulation curve. The light-driven mechanism proposed in this paper can also be extended to generate IR images with a grayscale greater than 8-bit, such as 12-bit and 16-bit.