Single-photon imaging inspired by human vision

Single photon detectors are regarded as a key enabling technology in a wide range of medical, industrial, and military applications. However, the existing single photon detectors that can operate at or near room temperature have poor efficiency and high noise. Interestingly, the counterparts of these devices in nature, namely the rod cells, have amazingly high efficiency and low noise. In particular, the noise performance of the rod cells is five to six orders of magnitude better than the semiconductor based single photon detectors at room temperature. At Bio-inspired Sensors and Optoelectronics Laboratory, we explored the origin of such a high noise performance, and designed and implemented a novel semiconductor device based on the underlying detection mechanism in the rod cells. Our device shows very promising properties including orders of magnitude higher gain and lower noise compared with the existing devices. More interestingly, the low operating voltage of the device combined with high gain uniformity should allow, for the first time, realization of large imaging arrays with a high internal gain. Such imagers would open new opportunities for novel applications such as quantum ghost imaging. Keyword: Single Photon Detectors, Infrared Detector, Nano-processing, Single Electron Transistor, Bio-inspired BACKGROUND Compact solid-state single photon detectors are regarded as enabling components in a wide range of applications such as biophotonics, tomography, homeland security, non-destructive material inspection, astronomy, quantum key distribution, and quantum imaging. However, these devices are quickly becoming the bottleneck in many applications due to their limited stable gain of less than a few hundreds, low quantum efficiency Bookmark not , high excess noise, and long deadtime. These problems have encouraged research on alternative detection methods based on superconductors, and quantum dots. Although these methods can potentially alleviate a large number of problems associated with avalanche-based SPDs, they require extremely low operating temperatures, usually below 4°K, which prevent their practical utilization in many applications. Inspired by the amazing sensitivity of the rod cells, we designed and implemented a novel semiconductor base detector detailed in this paper. Rod cell is an extremely sensitive light sensor, and is capable of detecting a few photons. Rod cells are made of inner and outer segments, among which a steady current flow due to Na and K transport in dark. 0-a shows the overall detection mechanism in the rod cells schematically. Outer segment is very rich in photosensitive rhodopsin molecule, which is a strong absorber of photons with peak sensitivity in blue-green spectrum. Upon light reception rhodopsin is triggered with structural changes and acts as a catalyst. Activated rhodopsin triggers a chain of reactions that lead to the destruction of chemical messenger cyclic guanosine monophosphate (cGMP). Finally, the transport channels for Na and K respond quickly to any change in cGMP concentration by closing the ion channels, and significantly changing the current passing through the rod cell. The significance of this detection mechanism is that it can provide both high efficiency and high sensitivity at room temperature; a condition that is very difficult to achieve in conventional single photon detectors. Simply put, the energy of a single photon in the visible or short infrared is extremely small, less than one atto Joule, and the only reliable way to sense this small energy is to use a very small volume, for example a quantum dot. However, the wavelength of light is significantly larger than such a sensor, and hence the interaction between the photon and the sensor, or quantum efficiency, is extremely small. Any attempt to enhance the efficiency by increasing the volume would simply reduce the sensitivity. Rod cell’s detection mechanism Keynote Paper Human Vision and Electronic Imaging XIII, edited by Bernice E. Rogowitz, Thrasyvoulos N. Pappas, Proc. of SPIE-IS&T Electronic Imaging, SPIE Vol. 6806, 680604, © 2008 SPIE-IS&T · 0277-786X/08/$18 SPIE-IS&T/ Vol. 6806 680604-1 0 = -' __ __ _ __ __ _