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To achieve fast location, precise tracking and accurate identification over a large field of view (FOV), we have proposed a heterogeneous compound eye camera (HeCECam), which consists of a heterogeneous compound eye array, an optical relay system and a CMOS detector. However, the current HeCECam can hardly acquire high-precision 3D information of the targets to realize these applications. To solve this challenge, we propose a scheme on optimizing the structure of the HeCECam to improving the detection performance, including the optimization of the distribution uniformity of the sub-eyes with the proposed "Three-direction center-of-gravity subdivision (TGS)" and the enhancement of the compatibility between heterogeneous compound eyes and the optical relay system with the proposed compensation method for tilt. The TGS significantly reduces the distribution unevenness of sub-eyes down to 117% from the previous 152%, and provides symmetry to the heterogeneous compound eye array. The tilt compensation effectively addresses previous imaging defects, such as distortion of sub-images, increased stray light, and support structures being imaged, and it improves the imaging clarity of the system, especially in external FOV. Based on two proposed methods, we re-design and fabricate the heterogeneous compound eye array to obtain a high-performance prototype. To verify the imaging capacities of the optimized HeCECam, a series of comparison experiments are performed, including blank scene imaging, FOV tests, resolution verification and real-world scene imaging. The results show that the previous imaging defects have been well eliminated, and the optimized prototype has stronger resolving power and wider FOV. This allow the HeCECam to perform better in subsequent practical applications, such as wide-area surveillance, forewarning, and navigation.

Programmable hyperspectral imaging is a promising and efficient technique for fast target classification by coding hyperspectral post-processing algorithms as spectral transmittances, which enables such post-processing to be directly performed by special optical dispersive element during the process of optical imaging. Compared with conventional hyperspectral imaging and post-processing techniques, it shows significant advantages of fast image acquisition, post-processing free, and a much lower load of data transmission and storage. However, when multi-target classification tasks are encountered, the speed would decrease seriously due to the requirement of a large number of filters. In this study, a novel splitting strategy is proposed to reduce the number of filters in programmable hyperspectral imaging for fast multi-target classification while maintaining the classification performance. Numerical simulation experiments were performed on six publicly available hyperspectral data sets. Compared with the conventional splitting strategies, the proposed splitting strategy can reduce the number of filters by 25% to 80% and achieve similar classification performance, which is of great significance to improve the speed of multi-target classification with programmable hyperspectral imaging technique.

Yb 3+ /Al 3+ co-doped silica fibers (YDFs) with almost identical core glass compositions were prepared using the sol-gel and modified chemical vapor deposition (MCVD) methods. The photodarkening (PD) and laser performance before and after the PD process were tested under 974 nm pumping. The doping homogeneity of Yb 3+ ions and clusters of Yb 3+ ions in preform slices of these two fibers were investigated via optical absorption spectroscopy, photoluminescence emission spectra, electron probe microanalysis (EPMA), and low-temperature (4 K) electron paramagnetic resonance (EPR). It is known that the PD resistance of YDFs prepared via the sol-gel method is significantly better than that of YDFs prepared via MCVD under the same test conditions. EPMA mapping reveals that the doping homogeneity of Yb 3+ ions in the sol-gel fiber core glass is better than that in the MCVD fiber. The low-temperature (4 K) EPR and cooperative luminescence spectra of Yb 3+ ions indicate that the clustering degree of Yb 3+ ions in the sol-gel fiber is lower than that in the MCVD fiber. In the absorption and emission spectra, small amounts of Yb 2+ ions are observed in the preform slice from the sol-gel method. A model of the color-center generation in the PD process was proposed to explain the mechanism of PD resistance improvement for the YDFs fabricated via the sol-gel method.

Output power scaling of single mode large mode area (LMA) photonic crystal fiber (PCF) amplifiers urgently requires the low refractive index of Yb 3+ -doped silica glasses whilst maintaining high optical homogeneity. In this paper, we report on a promising alternative Yb 3+ /Al 3+ /F - /P 5+ -co-doped silica core-glass (YAFP), which is prepared by modified sol-gel method developed by our group and highly suitable for fabricating high power LMA PCF amplifiers. By controlling the doping combinations of Al 3+ /F - /P 5+ in Yb 3+ -doped silica glass,it not only ensures low refractive index (RI) but also maintains the excellent optical homogeneity and spectroscopic properties of Yb 3+ . The spectroscopic properties of Yb 3+ ions have not deteriorated by the co-doping of F - and P 5+ in YAFP glass compared with that of Yb 3+ /Al 3+ co-doped silica glass. A large-size (⌀5 mm × 90 mm) YAFP silica-core glass rod with low average RI difference of 2.6 × 10 -4 (with respect to pure silica glass), and low radial and axial RI fluctuations of ~2 × 10 -4 , was prepared. A LMA PCF with 50 µm core diameter was obtained by stack-capillary-draw techniques using YAFP core glass. Its core NA is 0.027. An average amplified power of 97 W peaking at 1030 nm and light-light efficiency of 54% are achieved from a 6.5 m long PCF in the pulse amplification laser experiment. Meanwhile, quasi-single-mode transmission is obtained with laser beam quality factor M 2 of 1.4.