A mathematical model of the diffraction efficiency change with the ambient temperature for the double-layer harmonic diffractive elements (HDE) is presented, and its effects are analyzed in this paper. The double-layer HDE structure is investigated and the optimization procedure is based on the equation of diffraction efficiency of the double-layer HDEs. By selecting appropriate design wavelength, the average diffraction efficiency of the system is reaching 99% in working wavelength and working temperature, which improves the image contrast and the image quality significantly. A set of dual-wavelength infrared optical system is designed based on dual-wavelength 320x240 element cooled thermal IR focal plane arrays detector. By introducing double-layer HDEs and aspheric surfaces, the chromatic aberration and the off-axis aberration are well corrected and the system structure is simplified. The system working in the wave band of 3.7~4.8μm and 7.7~9.5μm and with the F number of 2 is consisted of 8 elements and has 100% cold shield efficiency. The image quality evaluating results show that the performance of the dual-wavelength infrared optical system is very well in
temperature from -40C° to +60C°.
Coherent optical RF receivers constructed in self-homodyne configurations have gained considerable attention due to its simplicity and cost-efficiency. Rigorous symmetry is required in such system to suppress the laser phase noise. A method for evaluation of the un-eliminated laser phase noise in self-homodyne coherent optical RF receivers has been presented in this paper. In our proposed scheme, the un-eliminated laser phase noise is acquired by simply inserting an FBG in the in-phase arm and is found to be dependent on the interferometer asymmetry, i.e., the path imbalance of the interferometer arms. With series of simulations, the variance of the un-eliminated laser phase noise obtained by our method becomes larger when the path imbalance is increasing. The simulation results show that, variance increases with the asymmetrical time delays of two interferometer arms. Therefore, this method is very helpful in obtaining further insight into the system symmetry and is also a good guidance for the adjustment of the interferometer architecture to achieve the optimized path equality.
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