Optical Coherence Tomography System Of Monte Carlo Simulation

In this paper, the Monte Carlo method has been used to simulate the OCT signal of scattering medium. By contrasting simulation results with experimental results, the generating mechanism of OCT signal from scattering medium and the influencing factors on OCT signal were revealed.First of all, being directed at the fact that the existing simulating research on OCT only simulate OCT signal as viewed from the interaction between sampling beam and measured medium, but the influence of the optical structure and parameters of sampling arm on OCT signal were not taken into consideration, a new method to take OCT system and the measured sample as a whole to be simulated was presented. Whether a photon within sampling beam would contribute to OCT signal and how much contribution it would do were determined by tracing its stochastic propagating trajectory through the focusing system and within the measured sample. OCT signal was composed of the contributions of all photons in sampling beam.Secondly, based on analyzing the existing methods to calculate the light-path through an aspheric optical system, a stepping-dichotomy based auxiliary surface to calculate the light-path was presented. The method not only sped up the light-path calculation of a photon going through the sampling focusing system (aspheric optical system), which made it possible to simulate a great deal of photons, but also eliminated such phenomena as light ray "overflow" and "pseudo cross point" that possibly arise in the process of light-path calculation.Thirdly, the beam emitted from the Superluminescent Diode used in OCT system is Gaussian beam. Based on Gaussian beam's characteristic of hyperboloid with one sheet, a new numerical method to simulate Gaussian beam was presented. The method takes the Gaussian beam as a hyperboloid consisting of myriads of co-axis hyperboloids of one sheet, and the propagation direction of a photon launched from the beam-waist section was chosen equiprobably and stochastically between the two generatrices of the hyperboloid that goes through the photon's initial emission point. It not only conforms to rectilinear propagation of photon, but also means that the "average" propagation direction of a lot of photons is in the direction of the Poynting's vector of the corresponding Gaussian beam.Finally, the program to simulate OCT signal from scattering medium was developed with Visual C++6.0 platform, and the simulations to different scattering media and OCT system's parameters were carried out. By contrasting experimental results and simulating results, the influences of such factors as the optical characteristics of measured medium (scattering medium), the numerical aperture of the sampling arm fiber, and the optical characteristics on OCT signal intensity were analyzed. The research in this paper provided basis for applying OCT to measure the optical characteristic of various scattering media and to optimize the design of OCT system.