A Coherent Detection Method With 106 Higher Intensity Response Sensitivity Than Normal Heterodyne Interferometry

• Published in: Journal of lightwave technology 2022-07, Vol.40 (14), p.4649-4654
• Main Authors: Tian, Mingwang, Li, Mingfang, Xu, Xin, Hua, ZiYu, Tan, Yidong
• Format: Article
• Language: English
• Subjects: Aluminum; Feedback; Frequency modulation; Gain measurement; Interference; laser applications; Laser feedback; Lasers; Measurement by laser beam; Microchip lasers; Neodymium lasers; Optical filters; Photonics; Photons; Sensitivity
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2022.3169803

Based on the Nd: YVO 4 microchip laser frequency-shifted feedback system, we carry out the detection of ultra-weak light signals, and verify that the response limit of the proposed system can reach 0.5 photon per second (corresponding to 2.1 × 10 −7 photon's energy per frequency modulation cycle of 0.42 μs), with approximately linear response to weak light. Then, the system is compared with the traditional Mach-Zehnder heterodyne interference system, the comparison results confirm the higher intensity response sensitivity of the laser feedback technology (about six orders of magnitude) when detecting both cooperative and non-cooperative targets. On this basis, a verification experiment is carried out on long-distance weak light imaging, and the "THU" pattern made of unpolished aluminum blocks is successfully reconstruct at 60 m distance (with an additional 10 −7 attenuation provided by the neutral density filter added to the optical path). During the imaging process, the response energy as low as 2 × 10 −5 photon is achieved in each frequency modulation cycle of 0.42 μs. The successful implementation of the laser frequency-shifted feedback detection enables an anti-disturbance and sensitive coherent method in weak light signals detection.