Study On Sample Integral Theory And Photon Counting Theory In OTDR

Sample integral is a special technology which is used to renew the weak signal waveform covered by noise.It samples the periodic or repeated signal repeatedly to improve the signal-to-noise ratio(SNR). The effect of SNR is improved by the integral number increases.But the effect is not improved obviously after a number of integral times. And the time of running delays much more.Photon counting is a method which detects ultraweak light.It uses the characteristic when photon detector exports the discrete electronic signal after the irradiation by weak light.And it includes the technology of pulse secerning and digital count.It has many advantage about good stability and SNR compared with the simulant exploration technology.This paper uses the OTDR as the experiment platform.After discussing the theory of the key tache briefly, we design and implement the software and the hardware which include the LD driving circuit, the APD bias control circuit, high voltage power circuit, amplifying circuit and data acquisition card.And There show their key parameters and waveform diagrams.We also summarize the virtual instrument, design the programmes which include the function of digital BOXCAR integrator and photon counter by the LabVIEW software. They are all achieve the design require.At the last part of this paper,we compare the digital BOXCAR integrator with the photon counter, based on the effect of data acquisition with different temperatures,the effect of SNR with different integral number, and dispersion characteristic and positioning accuracy, at last we point out photon counting is advantaged than sample integral in this aspects.