The Research On The Single Photon Transmission And Locking On F-P Cavity

The single-photon detection has been widely used for precise measurements, bioluminescence, astrophysics and quantum information application because of its extremely sensitive detection for ultra weak optical signals even to single photons. The single-photon quantum state makes it possible to achieve quantum information and quantum computation. Particularly, the absolute secrecy of transmit information can be guaranteed by use of single photon could be applied in quantum key distribution. However, the ideal single-photon states are difficult to be prepared in practice. Generally, we use attenuated laser pulses which obey Poissonian statistics to replace the ideal single photon source, with the mean number μ of photons source being so low (that is, μ,<<1) to reduce multiphotons emission. In quantum key distribution, multiphoton states represent a security’loophole’ which can be exploited by eavesdroppers and limit the security distance transmission. So the photon number determination is crucial for reducing errors. In addition, we achieve information code in the single photon phase by use of the acousto-optic modulator, the voltage characteristics have very important effects on information encoded and decoded. Therefore, two problems need to be resolved, one of which is the photon number resolution, and the other is the FP cavity locking at single photon level.In this paper, we make following research considering those problems: First, we investigate the response time function characteristic of avalanche photodiode single-photon detector for different incident photons which based on the first photon arrival time and the different response probability of the different photon number, and then present a method to distinguish the incident photon number based on the response time for different photons. An accurately measurement is achieved for the response time of one photon, two photons and three photons in the wavelength of1550nm respectively. The dependence of detection time on pulse response time is also analyzed.Second, the photon number of the modulated laser intensity by the acousto-optic modulator is detected. When modulation signal intensity is below the threshold (0.4v here), the photon counts depend linearly on the modulation pulse intensity. On the contrary, when it is higher than the threshold the acousto-optic modulator works in nonlinear area for single photons.Third, we have homemade a high-finesse FP cavity, with the free spectral range, finesse and line width are750MHz,1173,0.64MHz respectively, using the glass ceramics with the much low thermal expansion coefficient for the cavity body. We use wavelength modulated and demodulated techniques to lock the FP cavity on its transmission frequencyat single photon level.