A kind of full-function two-sided optical bench interferometer (OBI) is designed to meet the practical requirements of the Taiji Program for space gravitational wave detection. The main optical paths are arranged on the A-side for transmission and interference, and other optical paths and electronic devices are placed on the B-side. According to the design scheme, we successfully constructed two OBIs by using hydrogen–oxygen catalytic stress-free bonding technology. When the OBI is installed and adjusted, the position and Angle error of the interference beam are controlled within 30 μm and 50 μrad through the self-designed precision mechanical clamping mechanism and beam position measuring device. The built OBI was placed on the vibration isolation platform in the vacuum tank for the stability test. The test results show that the noise of the OBI is less than 10 $\mathrm{p}\mathrm{m}/\surd \mathrm{H}\mathrm{z}$ in the frequency band of 0.1 Hz to 1 Hz, which meets the noise budget requirements of the Taiji Pathfinder in the middle- and high-frequency band.

A photonic integrated interference imaging system (PIIIS) is a computational imager based on Michelson interference and photonic integrated circuits (PICs). In this paper, a PIIIS based on a compact sampling lenslet array that can sample the zero spatial frequency through a single lenslet, densely sample the frequency in the azimuth direction through the configuration of a hierarchical multistage lenslet array, and continuously sample the frequency in the radial direction through a Langford sequence is proposed. We introduce the design process of the compact sampling lenslet array in detail and simulate the imaging of the system. The simulation results demonstrate that the lenslet array can effectively improve the imaging quality of a PIIIS. In addition, we design a silicon PIC and a silicon nitride transition PIC that match the compact sampling lenslet array and simulate the imaging of the system under the influence of the on-chip optical loss of PICs (the average interference baseline loss is 15.4 dB at 1550 nm). The results show that on-chip optical loss mainly affects the brightness and contrast of the reconstructed image but has little effect on the structure.

The telescope is the core device for space gravitational wave detection. It is responsible for receiving signal light and emitting outgoing light simultaneously. When the high-energy outgoing laser passes through the telescope, it would produce stray light, which would interfere with the phase measurement and generate phase noise. Therefore, it is necessary to analyze and suppress the stray light of the telescope. In this paper, the requirement of point source transmittance (PST) of the Taiji telescope is obtained through theoretical derivation, which is less than $4\times {10}^{-10}$. Through a complete analysis of stray light, we determined that the M4 was the largest source of stray light under the condition that the roughness of each optical surface is equal, which accounted for 67.22%. We also determined the most lenient requirements for surface roughness ${\sigma }_{\lambda }$, and found that when ${\sigma }_{\lambda }$ of the M1, M2, M3, and M4 were 20 Å, 4 Å, 1 Å, and 1 Å, respectively, the PST was $3.89\times {10}^{-10}$, which met the PST requirement. Next, we calculated the effect of particulate contamination on the PST, and based on the results of our analysis, we determined that the cleanliness level of the testing and storage environment of the Taiji telescope was better than 300. Finally, we evaluated the changes in the PST caused by the damage of micrometeoroids, and the analysis results showed that the stray light level would not change significantly during the service period of the Taiji Telescope.

The support structure between payloads is an important part of a space gravitational wave detection satellite, and its thermal stability will directly affect the interferometer’s measurement accuracy. However, due to temperature changes, the connecting structure between the loads will generate deformation, and a support structure with the coefficient of thermal expansion (CTE) of −1 × 10⁻⁶/K will thus need to be designed to counteract this thermal deformation. In order to solve this problem, this paper adopts the method of mutual offsetting of the thermal deformation of different materials to design a thermally stable support structure satisfying this negative CTE. The structure was optimized by the arithmetic of non-linear programming by the quadratic Lagrangian hybrid algorithm (NLPQL), and the structural parameter satisfying the CTE of −1.008 × 10⁻⁶/K was obtained. Meanwhile, the effect of the change in the thermal expansion coefficient of each material on the overall structure under this parameter was sampled and calculated. Moreover, the experimental results show that the CTE of the support structure under the optimized parameters was −1.114 × 10⁻⁶/K, which differs from the simulation results by 9.5%.