Alignment and packaging of a 1D-array of optical transition edge sensors to an optical fiber array

We present an alignment and packaging technique designed to enable low-loss coupling between an array of single-mode telecommunication fibers and a 1D or 2D array of single-photon transition-edge sensors (TESs). Our approach integrates two or four metal-semiconductor-metal (MSM) photodetectors fabricated at the edges of the TES array. These MSM photodetectors ensure accurate optical alignment of the entire fiber-detector array. The alignment process is performed by adjusting the position of the fiber array relative to the detectors across six degrees of freedom, three translational and three rotational, using a combination of rotational and goniometric stages. The alignment process begins with leveling the fiber array with respect to the detector chip using goniometric adjustments. The translational optical alignment is achieved by moving the fiber array with respect to the detector array, while monitoring the electrical output signals from the MSM photodetectors. This technique allows us to achieve an alignment error better than 2 μm. Once alignment is confirmed, the packaging process begins. A patternable polymer is used as an adhesive to securely bond the fiber array to the device chip. We characterize the alignment process at room temperature and evaluate the robustness of the packaged system through thermal cycling tests.