Broadband free space 2 × 4 90° optical hybrid for satellite laser communication.

We design a broadband free space 2×4 90° optical hybrid over a spectral window of 1000-1200 nm and 1470-1650 nm and verify the feasibility of the scheme experimentally. The hybrid consists of three broadband polarization beam splitters, an achromatic λ/4 wave plate, and three achromatic λ/2 wave plates. The fabricated hybrid exhibits a good quadrature phase response with an interchannel imbalance of 0.93-1.07 and a low phase deviation of less than 0.2° under the typical communication wavelengths of 1064 nm and C-band. The experimental results of the heterodyne method show that the proposed hybrid can effectively solve the wavelength incompatibility problem in satellite laser communication and realize interconnection at different wavelengths. The designed hybrid (without coupling) has a measured insertion loss of no more than 7.34 dB at 1064 nm and C-band. A high-speed transmission experiment with BPSK format has been conducted to verify the performance of the assembled device.

Sensitivity Deterioration of Free-Space Optical Coherent/Non-Coherent OOK Modulation Receiver by Ambient Light Noise.

In free-space optical (FSO) communication systems, on-off keying (OOK) is a widely used modulation format. Coherent and non-coherent OOK receivers with sensitivities of -54.60 dBm and -51.25 dBm, respectively, were built with a communication rate of 1 Gbit/s and a bit error rate of 10-3. In an FSO communication system, the parameters must be designed to ensure a sufficient link margin. In contrast to optical fiber systems, FSO systems have ambient light (AL) noise such as sunlight. The efficiency of sunlight coupling in the single-mode fiber (SMF) of the receivers was calculated in this study. For a signal light with AL, the change in the main components of noise and the sensitivity deterioration were theoretically analyzed and experimentally verified in conditions of coherent reception and non-coherent reception with a preamplifier. For coherent reception, the theoretical sensitivity deterioration results are consistent with the experimental results which indicate that coherent reception exhibits better anti-AL noise performance than non-coherent reception when the power spectral density of the AL is the same. Coherent and non-coherent receivers coupled with SMF can work in direct sunlight. When the receiver lens diameter is greater than 4.88 × 10-4 m, the anti-AL noise performance of the receiver can be improved by increasing the receiver lens diameter.

Multi-dimensional and large-sized optical phased array for space laser communication.

In this study, we propose a novel multi-dimensional and large-sized optical phased array theory for space laser communication that addresses the theoretical limitations of the conventional optical phased array. We theoretically analyzed the principle of this phased array technology. The results of simulation and laboratory experiment clearly showed it can realize the large scanning angle and high optical gain required for communication. The novel optical phased array theory is of great significance to the revolution of miniaturization and networking in the field of space laser communication.