In order to study the spatial wavelength division diffraction effect, the Chirped Volume Bragg Gratings (CVBG) based on the Photo-thermo-refractive glass on the oblique incident light was analyzed by the fundamental matrix method. When diffracted by grating, the complex beam would be separated into multiple beams in space by wavelength. The diffraction efficiency of the separated optical wave can reach up to 90%. Furthermore, the diffraction efficiency, increases as the refractive index modulation depth increases and decreases as the chirp rate increases. The diffraction spectrum has the characteristics of flat-top band pass. To increase the spatial separation distance, multiple schemes of CVBGs in parallel combination are designed. By combining a self-focusing lens array, the proposed system can realize wavelength division multiplexing with bandwidth less than 0.4nm.
A collimating system is designed by two orthogonal aspheric cylindrical lenses, which is used to collimate the the output beam of the Laser Diode (LD). The theory of light transmission is used to analyze the optical collimating system. The theoretical expressions are derived and the numerical results are obtained. The nonlinear Levenberg-Marquardt (LM) fitting algorithm based on the trust-region rule is applied to the surface shape evaluation. Residual analysis is used to test the rationality of the model hypothesis, and a simple analysis is made on the source of the error and the data optimization process. And the optical simulation of model optimization results is established. Simulation results show that the semidiverging angles of 20° and 9° for the fast and slow axes of semiconductor laser beam are both reduced to 0.05 mrad after passing the collimation system which is much better than that of a normal cylindrical lens collimating system 3 mrad. A uniform circular spot can be formed in the far field by adjusting the distance between the two aspheric lenses.
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