Abstract Body

Dynamic target tracking involves continuously monitoring and following a moving object or entity over time to determine its position, velocity, and trajectory. This process is crucial in many applications where understanding and predicting the movement of targets is essential. Since position of the object is unknown, a camera equipped with a detector array is used. Conventional detector arrays, such as CCDs or CMOS arrays, operate based on the sequence of readout logic. Thus, the imaging speed, i.e. frame rate, is determined by the clock of readout lines. In single-photon detection regime where the detection event is sparse and random, readout efficiency of conventional frame-based camera is low since most pixels have no photon counting. Therefore, an event camera that can be triggered by each photon detection is required to maximize the imaging speed. Here, we introduce a kilopixel single-photon delay-line imager, which naturally operates in event-driven mode. The imager was fabricated using superconducting nanowires, which was designed in parallel structure and then meandered into a two-dimensional array over an area of 184 μm × 192 μm. It had 32 columns and the equivalent rows were 40 determined by the differential time jitter. Based on this imager, a single-photon event camera for fast target tracking was built. The imager was placed in a 1 K free-space coupling cryostat. An aspheric lens was placed on a cryogenic XYZ-nano-positioner at 4 K to focus the light onto the imager. The maximum system efficiency was 56.2% at 1550 nm and the time jitter was 200 ps. At room temperature, a galvanometer was used to provide feedback control of the tracking process. With this camera, single-photon trajectory tracking at a high speed of 1 kHz was achieved.

References

[1] Zhao, Q.-Y. et al. Single-photon imager based on a superconducting nanowire delay line. Nat. Photonics 11, 247–251 (2017).

Figure 1. (a) SEM images of kilopixel single-photon delay-line imager. (b) Conceptual illustration of photon event readout by the imager. The photon arrival time t_p and position x_p can be obtained by the arrival time of a pair of positive and negative pulses. (c) The imaging of the focused light spot. (d) Single-photon trajectory tracking demonstration.

Keywords: Kilopixel single-photon delay-line imager, Photon-triggered event camera, Fast dynamic target tracking