The elliptical laser beam produced by a laser diode (LD) has asymmetrical divergence angle distribution and limits its application in long-distance space optical communication. In this paper, a double lens freeform miniaturized antenna design method is proposed to collimate, shape, and transmit elliptical beams from a LD. Based on the law of conservation of energy, refraction vector theory, equal optical path principle, and the three-dimensional point-by-point construction iterative method, two freeform surfaces on both lenses are constructed simultaneously. According to the simulation results, the maximum divergence angle of the output light is compressed to 4.92 µrad. The volume of the antenna is 1244.61cm3, which realizes the miniaturization of the antenna. In addition, the performance of the system is evaluated under different wavelength shifts, astigmatism based on the proposed improved line light source model, the offset of the light source, and the offset of both lenses. This paper provides a practical method for designing a simplified antenna that can collimate and shape laser beams and improve transmission efficiency. Furthermore, the proposed improved optimization method can provide a reference for the study of the initial parameters of lens freeform antennas.

A ring focus reflector is proposed for transmitting a perfect vortex (PV) beam, and the transmission characteristics of the PV beam with different topological charges in free space after passing through the reflector are studied. The reflector parameters can be determined by fitting the structural formula, and PV beams of different orders transmit with small spot sizes at the same time. The transmission trajectory calculated by the diffraction formula is consistent with the ray tracing results. The research results show that the reflector can achieve a high level of transmission efficiency of beams with different topological charges, which is conducive to the multiplexing of PV beams.

Dark hollow beams (DHBs) possess great potential for material processing, holography, and vortex beams, and thus designing a high-Q DHB cavity is significant for these applications. In this Letter, a method of designing and optimizing a high-Q DHB cavity based on a one-dimensional topological photonic crystal (TPhC) is proposed. Furthermore, how the structural parameters control the performance of the cavity is analyzed with the help of finite-element-method (FEM) simulation. According to the simulation results, the Q factor of the designed cavity can reach the order of 105 with only 19 periods of layers. It is critical to mention that, although increasing the layers can improve the average Q of the cavity, it will cause serious fluctuation of both the Q factor and the divergence angle of the output beam. The design method proposed in this Letter may not only help designers of future DHB lasers but also promote the applications of DHBs in various fields.

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