01 Introduction
Recently, the team of researcher Kun Huang and Prof. Heping Zeng at the State Key Laboratory of Precision Spectroscopy Science and Technology of East China Normal University has made progress in mid-infrared single-photon ranging, and developed a mid-infrared up-converted laser ranging system with single-photon sensitivity, high ranging resolution, and large dynamic range. The system utilizes nonlinear asynchronous optical sampling technology to achieve high precision, high rate, large range of optical time scanning, combined with time stretching photon correlation detection scheme, obtaining a highly sensitive, high resolution single-photon ranging performance for the mid- and far-infrared single-photon ranging and imaging provides an effective way.
The results were published in Photonics Research recently under the title of “High-resolution mid-infrared single-photon upconversion ranging”, with East China Normal University (ECNU) as the first author, research student Jiang Shuhong as the first author, and Kun Huang and Prof. Heping Zeng as the co-corresponding authors. The research student Jiang Shuhong was the first author of the paper, and Kun Huang and Prof. Heping Zeng were the co-corresponding authors. The work was supported by the Ministry of Science and Technology, China Foundation, Shanghai Municipality, Chongqing Municipality and East China Normal University.
Figure 1: First page of the paper
02 Research Context
Single-photon laser ranging technology has a wide range of applications in the fields of long-range remote sensing, satellite tracking and microlight detection. For a long time, the technology has been mainly limited to the visible or near-infrared band. The mid-infrared band covers multiple transmission windows of the atmosphere, has good anti-scattering ability, and is located in the fingerprint spectral region of many molecules, which has important applications in environmental atmospheric spectral monitoring. In view of this, the extension of single-photon ranging techniques to the mid-infrared band has become a research frontier in this field. However, the existing mid-infrared detectors have large dark noise at room temperature and limited detection bandwidth, and it is still challenging to realize ultra-sensitive and high-resolution distance measurement. Therefore, there is an urgent need to develop novel infrared photon measurement and control techniques to overcome the long-term difficulties of infrared optical fields in terms of high detection sensitivity and high time resolution, so as to meet the urgent needs of high-precision ranging and imaging in the mid-infrared under sparse photon scenarios.
To this end, nonlinear upconversion detection technology is expected to provide a solution by upconverting the mid-infrared optical field to the visible or near-infrared wavelength bands through a nonlinear sum-frequency process and then utilizing high-performance silicon-based detectors to accomplish sensitive and accurate capture of the signal. Currently, in the upconversion ranging scheme of continuous optical pumping, the axial resolution is limited by the time jitter of the detector, which is usually on the sub-centimeter scale. The upconversion ranging scheme with synchronized pulse pumping, although eliminating the limitation of detector time jitter, can improve the axial resolution to the micron level, but it adopts mechanical scanning as the means of optical delay, which is difficult to meet the needs of large-range and high-rate measurements.
In recent years, dual optical comb ranging technology has been widely used in the field of ranging with its advantages of high accuracy and large range. Currently, this technique is mainly used in the near-infrared band, and its expansion to the mid-infrared faces many challenges. In terms of light source, it is still difficult to prepare a mid-infrared light source with high power and high coherence; in terms of detection, highly sensitive room-temperature infrared detectors with large bandwidths are not yet available; and in terms of data processing, it is necessary to carry out the Fourier transform or the Hilbert transform to extract the time information, which increases the complexity of the data processing. Therefore, the application of double optical comb technology in mid-infrared distance measurement still needs to be further explored.
03 Innovative Research
Recently, the research team proposed and developed a high-resolution mid-infrared single-photon ranging system based on asynchronous up-conversion sampling, realizing a high-performance mid-infrared laser ranging performance with single-photon sensitivity, picosecond temporal resolution, and wide scanning range. The core of the method lies in the nonlinear upconversion detection of asynchronous pulse pumping, and its basic principle is shown in Fig. 2.
Figure 2: Schematic diagram of mid-infrared ranging based on asynchronous upconversion sampling
Specifically, a mid-infrared pulse carrying distance information is sampled in a nonlinear crystal by a near-infrared pump pulse with a 1 kHz difference in reclocking and converted to the visible band. Thanks to the reclocking difference between the two, the two pulses can spontaneously scan in the time domain and generate a sum frequency signal with a period of 1 ms. The maximum delay obtained by the all-optical scanning process can be up to 46.45 ns (determined by the repetition frequency), which is equivalent to a 7 m-long delay line in free space, and overcomes the insufficiency of the limited scanning range of the mechanical delay line in the synchronous pulse-pumped up-conversion scheme (usually several tens of centimeters), enabling high-speed ranging in the mid-infrared over a wide range. In addition, this process stretches the inter-correlation trajectory in the time domain by a factor of 2 × 104, which enables highly sensitive and accurate detection of mid-infrared signals using a low-bandwidth silicon-based single-photon detector. The experimental setup used is shown in Fig. 3.
Figure 3: Diagram of the mid-infrared upconversion single photon ranging experiment setup
Further, the combination of time-dependent single-photon counting technique can realize highly sensitive and accurate measurement of mid-infrared photons. In order to simulate the less-photon scenario, the experiment uses a neutral filter to attenuate the mid-infrared light, and Fig. 4(a) shows the histogram of the mid-infrared up-conversion signal when the corresponding photon count at the detection end is 8×10-5 photons/pulse, with a pulse time width of 213 ns, which is much larger than that of the single-photon detector's own time jitter of 830 ps in Fig. 4(b).Using the amplification factor of asynchronous sampling, an effective ranging resolution of 9.9 ps can be obtained, which is far greater than that of the single photon detector itself in Fig. 4(b). effective ranging resolution of 9.9 ps can be obtained, which is two orders of magnitude lower than the time jitter of the single-photon detector itself. The ranging accuracy is represented by the Allen variance in Fig. 4(c), which can reach 4 μm when the averaging time is 64 s. The adopted time-stretched single-photon counting technique overcomes the inherent time jitter of the single-photon detector, and an accuracy that cannot be achieved by the conventional time-of-flight single-photon ranging system can be obtained.
Figure 4: Highly sensitive mid-infrared ranging based on time-dependent single-photon counting. (a) Histogram of mid-infrared upconversion signal; (b) single-photon detector own time jitter; (c) Allen's variance of the energy at the detector end at 8 × 10-5 photons/pulse.
04 Summary and Outlook
This work innovatively combines asynchronous optical sampling and upconversion detection techniques to realize high-precision and high-sensitivity detection of infrared photons, and solves the long-term problems faced by expanding single-photon ranging technology to the mid-infrared band. In the future, shorter pump pulses can be used to improve the ranging resolution, while the repetition frequency and re-frequency difference of the two-color laser can be increased appropriately to obtain higher refresh rate and finer scanning step. In addition, the method is expected to be extended to the long-wave infrared or terahertz bands to meet the demand for highly sensitive and high-resolution distance or depth measurements, which will provide support for the fields of infrared remote sensing, photonics mapping, and topographic characterization.
Source: High-resolution mid-infrared upconversion single-photon ranging
Link to paper: High-resolution mid-infrared single-photon upconversion ranging
