Infrared Single-photon Detectors Developed

As an important technique for detecting weak light, single photon detection technique is widely applied in many fields, such as physics, astronomy, chemistry, biology and medicine. Recently, with the development of quantum mechanics and information science, it is produced a new subject: quantum information. Quantum information has been a focus in physics and information science. Also, single photon detection technique is very important in quantum information.In quantum information, it is usually used single photons to transmit information. Single photon detectors can detect these photons, and then extract information on these photons by some methods, such as coincidence measurement and count. To satisfy the requirements of quantum information, the single photon detectors should have stable performance, high detection efficiencies and low dark count rates.With the development of quantum communication and quantum cryptography on telecom wavelengths (including 850 nm, 1310 nm and 1550 nm), Single photon detectors for telecom wavelengths are active demand. In 1990s, commercial single photon detectors for 400 - 1000 nm were produced. Recently, research on single photon detectors for 1310 and 1550 nm has been made good progress in. InGaAs/InP avalanche photodiodes (APDs) are always used to detect 1310 and 1550 nm photons. Since the limits of the semiconductor technology, special APDs for single photon detection are not mature, now it is usually used commercial APDs for telecom communication to detect single photons. In this way, it should change the APDs operating mode and design special circuits for these APDs to realize single photon detection.The main content of this dissertation is the research on infrared single photon detectors. We can draw the outline of this dissertation as follows:1. We have introduced some methods and their principles to detect infrared single photons. On the telecom wavelengths, Most of the single photon detectors are based on InGaAs/InP APDs. When these APDs are used for single photon detection, it should be operated in a so-called Geiger mode. Under this condition, the APDs will generate a self-avalanche, and the gain can reach above 10⁶. We have discussed these APDs structures and operating modes. In single photon detection, some important techniques and problems should be solved. Also we have introduced the single photon avalanche photodiodes and the main structure and performance of the InGaAs/InP single photon detectors.2. We have established an infrared single photon detecting system by using Fujistu InGaAs/InP APDs. In this system, a magic-T network is used to cancel the spikes noise, which is generated by the APDs capacitance. The detection efficiency and dark count rate of this system are both increased with the APDs bias voltage. We got that the minim value of the ratio of the detection efficiency to the dark count rate is about 0.035.3. We have established an infrared single photon detecting system by using JDSU InGaAs/InP APDs. In this system we used two coaxial cables with the same length to cancel the spikes noise. Since the performance of the JDSU APDs is better than that of the Fujistu APDs, we obtained better results in this system. The dark count rate per pulse is less than 5×10^-5 when the detection efficiency is about 10%. Based on this system, we produced a practical single photon detector for quantum key distribution. This single photon detector has stable performance and it is very simple to operate it.4. We have proposed a method of two APDs in series to cancel the spikes noise. This method uses two gate voltages with opposite polarities. So the spikes of the two APDs are opposite and are canceled by the circuit itself. In the other similar methods, two gate voltages with same polarities are used and it must have some elements or devices to cancel the spikes with same polarities. Actually, these elements or devices will attenuate the avalanche signals and then decrease the signal to noise ratio. So the method of two APDs in series is better than other similar methods in theory. Based on this method, we established an infrared single photon detecting system. In this system, JDSU APDs are used to detect single photons. When the detection efficiency of this system is about 10%, the dark count rate is less than 3×10^-5.