Laser wireless power transmission (LWPT), which can realize long-range power transmission, has been received widespread attention in recent years. The influence of high-power laser nonuniform irradiation on the output power and conversion efficiency of photocells has attracted much attention. This article conducted simulations and experiments on nonuniform irradiation with a constant power density and on nonuniform irradiation with constant incident power. The current I, voltage V, output power PL, conversion efficiency ηL, internal resistance R0, and maximum power point resistance RLmax of a 1 cm × 1 cm single-junction gallium arsenide photocell under nonuniform irradiation were studied. Under the condition of nonuniform irradiation with a constant laser power density, the conversion efficiency of the photocell remained constant, but R0 increased nonlinearly from 0.5 to 5 Ω. The ηL decreased from 45% to 5% when the load resistance is constant. Under the condition of nonuniform irradiation with constant laser power, the photoelectric conversion efficiency and R0 changed little, and the ηL remained about 45%, for it is not affected by nonuniform irradiation. The output characteristics of the photocells under uniform irradiation were also studied, and the results were consistent with the above conclusions. When the photocells with constant temperature were irradiated in-homogeneously, it was also revealed that the internal resistance increased and that the conversion efficiency decreased due to the irradiation power variation. The empirical formula was derived through circuit transformation and curve fitting.
A single-channel encryption method for color images is proposed using chessboard grating and a phase-retrieval algorithm in the Fresnel domain. The pixel sampling operation is introduced to convert the color image to be encrypted into a Bayer image. Thereafter, with a single channel, the Bayer image is encoded by the chessboard grating before being sent into a diffractive-imaging-based encryption scheme. The cryptosystem is simple owing to only one single intensity pattern being required during encryption. In the decryption procedure, the phase-retrieval algorithm and the chessboard grating are combined to extract the plaintext from the intensity pattern. This proposal not only can successfully encrypt a color image into a single diffractive intensity pattern but also can recover the primary color image with high quality from the one single diffraction pattern with a compact optical setup. Numerical simulations are carried out to prove the feasibility and validity of the proposal.
In this paper, we proposed a novel optical encryption and decryption method of gray image based on the computer-generated hologram (CGH), the chaos theory and the logical modulation. In the encryption process, the hologram, which is gotten by Fresnel diffraction from the gray image, is modulated with the chaotic sequence, and the output is encryption image. The decryption is an inverse process of encryption. Experiment results verified the security and robustness of the proposed approach. Moreover, the proposed encryption method could be applied in where requires more security and more flexibility as the field of national defense science and technology.
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