Transmission characteristics of Fabry-Perot (F-P) filter based on silicon substrate with different transmissivity of high reflection (HR) coatings, incident angle, and interference orders are investigated. The results show that the transmissivity of HR coatings has great effect on full width at half maximum (FWHM) of transmission spectrum, the FWHM of F-P filter reduced from 209 nm to 3.4 nm with the reflectivity of HR coatings increased from 84.7% to 99.6%. The peak wavelength shifts from 1546.3 nm at 0° to 1542.6 nm at 5°, indicating that the FWHM of transmission spectrum broadens as the incident angle increases. The 1st, 2nd, 3rd, and 4th order interference are 3.4 nm, 2.3 nm, 1.8 nm, and 1.5 nm, respectively. Thus, in the applications tuning in a narrow wavelength range, F-P filter can be designed to operate in high-order mode to achieve a narrow transmission spectrum.
A mesa-type normal incidence separate-absorption-charge-multiplication (SACM) Ge<sub>0.95</sub>Sn<sub>0.05</sub>/Si avalanche photodiode (APD) was fabricated. The 60-μm-diameter avalanche photodiode achieved a responsivity of ~5A/W (gain=24) and ~3.1A/W (gain=20) at 98% breakdown voltage (-14.2V) under 1310nm and 1550nm illumination respectively with a low dark current of 10μA. The −3 dB bandwidth for a 60-μm-diameter APD is about 1-1.25GHz for gains from 5 to 20, resulting in a gain-bandwidth product of 25GHz for a C-band communication wavelength of 1550nm.
The photonic crystal structure can be utilized for improving the transmission within a broadband, and suppressing the dark current of detector efficiently as well. Considering such an advantage, the study on the multi-level profile photontrapping structure is performed; meanwhile, the enhancement of HgCdTe mid-wavelength infrared detector based on such a structure is analyzed. With the help of FDTD model and FEM model, via optimizing the structure, a multi-level profile photon-trapping detector scheme with a quantum efficiency enhancement of 20% is established. The proposed simulation results and structure are crucial for further acquiring HgCdTe detector with enhanced SNR.
The reflected or radiated electromagnetic wave from natural objects exhibits different polarization characteristics. By detecting the polarization properties of light waves, more information from the target can be obtained, as well as the target recognition capability can be strengthened. In this paper, the research progress of the image processing method for infrared polarization detection is introduced. The traditional extraction methods of polarization components and the theory of polarization information processing are initially demonstrated. The fabricated 128×128 integrated polarization infrared detector, whose extinction ratio is 10:1, is also proposed. By using of the image reconstruction method, polarization images captured from this detector, which can acquire four polarization components simultaneously, are processed. Further, the degree and angle of polarization of natural scene images are obtained as well.