Most current advanced optical systems employ low-temperature optical technology to cool the optical lens to a lower temperature level to reduce optomechanical radiation and enhance the detection sensitivity and dynamic range of remote sensing instruments, which helps to enhance the detection performance of optical remote sensing instruments. This research focuses on the packaging technologies that are required for the engineering application of multiband long-wave infrared detectors for cryogenic optics, including multimodule splicing and multiband integrated filter low-temperature registration, support and heat insulation of low-temperature optical windows of modules, and coupling stress between detectors and refrigerators. Through systematic investigation, the multiband long-wave infrared detector’s Dewar for low-temperature optics has been successfully developed, and it has been confirmed by a series of space environment adaptability tests.
1. Low-temperature module splicing registration and four three-band integrated filters. The filter was designed based on the imaging optical path. The closer the filter was to the chip, the smaller the non-uniformity, stray radiation energy, and the detector image surface’s stray ratio. To enhance the detector image plane’s uniformity, the filter in the Dewar package should be as close to the chip as possible (Fig. 5). Detectors and filters were packaged as follows: 1) four three-band detectors were spliced and cemented on the ceramic substrate, and the flatness of the cemented surface of the ceramic substrate detector’s gemstone was controlled to be less than 5 μm; 2) the four integrated filters were preliminarily bonded to the filter holder, and the splicing accuracy was controlled in the range from -3 μm to + 3 μm; 3) the filter holder was aligned with the detector’s center, ensuring the alignment accuracy was in the range from -5 μm to + 5 μm.
2. The design of the flexible bellows shell’s thermal insulation structure. We proposed a Dewar flexible bellows shell structure for the infrared detector assembly employed in the low-temperature optical system. By increasing the heat transfer path, reducing heat leakage, and increasing thermal insulation, the heat transfer area of the transfer link can be reduced.
3. The design of a cold platform for physical isolation of coupled stress. In this research, based on the detector’s coupling characteristics and the refrigerator’s cold finger, an arc-shaped isolation groove of a specific shape was designed and processed on the cold platform. The groove width is H1 (Fig. 8). On the heat transfer capacity’s premise needed by a certain heat load, the heat conduction link’s physical isolation and the coupling stress transfer channel were achieved.
Through the positioning and integration design of four three-band integrated filters, the alignment error between three-band integrated filter and detector back cover is less than 10 μm. By implementing the Dewar flexible bellows shell structure, the thermal isolation between the infrared detector Dewar refrigeration assembly’s low-temperature shell and the refrigerator expander or pulse tube is achieved, as well as the infrared detector Dewar assembly flexible corrugated shell’s 101 mW thermal insulation (Table 1). During the thermal vacuum test, at the operating temperature of 55 K, the temperatures of the compressor’s cooling surface and the pulse tube’s cooling surface increased immediately, and there was no visible response to the Dewar temperature (Fig. 7). We measured the cold platform’s surface deformation after slotting and compared it with the cold platform’s surface deformation without slotting (Fig. 9). During the implementation of the Dewar’s full coupling and the refrigerator, the unslotted cold platform’s surface deformation increases sharply and stabilizes at around 40 μm/m, while the cold platform’s surface deformation after grooving does not change, and stabilizes at about 8 μm/m, and the deformation decreases by about 80%. From this, it can be deduced that the cold platform’s surface stress is reduced by 80% after grooving.
The challenges of packaging multiband long-wave infrared detectors are examined to meet the requirements of spliced multiband long-wave IRFPA in cryogenic optics. It is proposed that the three-band integrated filter and the detector’s back cover can be aligned with a misalignment of fewer than 10 μm, and the Dewar flexible corrugated housing 101 mW heat insulation is realized. Simultaneously, measures including a multilayer thermal layer structure that physically isolates the coupled stress are designed on the Dewar cold platform. It addresses essential technologies like low light string, low background radiation, low power consumption, high-temperature uniformity of cold platform, and high reliability of multiband long-wave infrared detector components. A 12.5 μm three-band 2000×12 element detector component for cryogenic optics was successfully developed and a series of space environment adaptation tests were implemented, and the test results indicate that the Dewar assembly meets the criteria of engineering application.
