LiDAR應用於車輛為近年趨勢，其獲得的影像可輔助駕駛而加強安全性。然而，因雷射光的高度同調性，LiDAR獲得的影像受到雷射光斑雜訊的嚴重影響。雷射光斑為在取得的影像上疊加隨機變化的光強度。光斑雜訊會使影像細節消失並大幅下降影像的清晰度。
本論文將一創新雷射光斑抑制架構系統，設計於車用LiDAR。並與其它既有雷射光斑抑制系統進行模擬分析比較。模擬顯示該創新雷射光斑抑制系統之光斑相干面積為目前較優異的商用系統之10^(-6)。因此驗證該創新雷射光斑抑制系統的優異性。此系統優異的雷射光斑抑制能力亦諭示雷射照明與其他雷射影像擷取應用的可能性。

LiDAR for vehicle application is becoming a trend recently. In addition to the range finding feature, LiDAR can provide images to enhance driving safety. However, due to the highly coherence of laser light, images acquired by LiDAR suffer from laser speckle noise severely.
Laser speckle noise is randomly overlapped to the observed images, and reduces image clarity. In this paper, an innovative laser speckle suppression method is adopted to design a vehicle LiDAR system. The innovative system is compared with other existing laser speckle suppression systems. Simulations show that the speckle coherence area of the innovative laser speckle suppression system is 10^(-6) times smaller than that of the premier commercial system. The excellent speckle suppression ability of the innovative system is thus verified. It implies the possibility of clear images for laser lighting and other laser image acquisition applications.

[1] U. Wandinger, “Introduction to Lidar,” in: C. Weitkamp(Eds.), “Lidar Range-Resolved Optical Remote Sensing of the Atmosphere,” Springer New York, NY, USA, 2005, pp.1-18.
[2] M. Hartwig, “Self-driving and Cooperative Cars,” Bayerische Motoren Werke AG, München, Germany, Jan. 2020.
[3] Velodyne Lidar, “A Guide to Lidar Wavelengths for Autonomous Vehicles and Driver Assistance,” Velodyne Lidar, https://velodynelidar.com/blog/guide-to-lidar-wavelengths/, Mar. 2021 (accessed Jul. 2023).
[4] E. Jakeman, “Speckle Statistics With a Small Number of Scatterers,” Proc. SPIE 0243, Applications of Speckle Phenomena, Dec. 1980.
[5] S.W. James, R.P. Tatam, “Principle of Shearography and ESPI,” OpenOptics, Engineering Photonics, England, UK (accessed Jul. 2023).
[6] Fan Xu, Jia-xing Wang, Dai-yin Zhu, Qi Tu, “Speckle Noise Reduction Technique for Lidar Echo Signal Based On Self-Adaptive Pulse-Matching Independent Component Analysis,” Optics and Lasers in Engineering, vol. 103, pp. 92-99, Apr. 2018.
[7] Jin-ni Geng, Zhe-jun Feng, Chang-qing Cao, Song-meng Feng, Xiang-kai Xu, Ya-jie Shang, Zeng-yan Wu, Xu Yan, “Spatial Decoherence Compensation Algorithm for a Target Speckle Field in Heterodyne Detection Based on Frequency Analysis and Time Translation,” Optics Express, vol. 29, issue 24, pp. 39016-39026, Aug. 2021.
[8] Tao Ma, Xi-hua Liu, Yun-fei Liu, Lin-lin Du, Chun Wang, Shuang-quan Ge, “Denoising Method for LiDAR Intensity Image via Combining Adaptive Non-local Means and Exponential Soft Thresholding,” in: 2021 China Automation Congress (CAC), Beijing, China, Oct. 2021.
[9] M.W. Bowers, J. Cooke, J. Benterou, “Speckle Reduction for LIDAR Using Optical Phase Conjugation,” in: Proceedings of IEEE conference on lasers and electro-optics (CLEO), San Francisco, CA, USA, May 2000.
[10] M.W. Bowers and R.W. Boyd, “Phase Locking via Brillouin-Enhanced Four-Wave-Mixing Phase Conjugation,” IEEE Journal of Quantum Electronics, vol. 34, issue 4, pp. 634-644, Apr. 1998.
[11] C.S. Sambridge, J.T. Spollard, A.J. Sutton, K. Mckenzie, L.E. Roberts, “Detection Statistics for Coherent RMCW LiDAR,” Optics Express, vol. 29, issue 16, pp. 25945-25959, 2021.
[12] I. Florescu, “Probability and Stochastic Processes,” John Wiley & Sons, Inc., Hoboken, New Jersey, USA, 2015.
[13] O. Lux, C. Lemmerz, F. Weiler, U. Marksteiner, B. Witschas, E. Nagel, O. Reitebuch, “Speckle Noise Reduction by Fiber Scrambling for Improving the Measurement Precision of an Airborne Wind Lidar System,” in: 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), Munich, Germany, Jun. 2019.
[14] J.W. Goodman, “Speckle Phenomena in Optics: Theory and Applications,” Roberts & Company, Englewood, Colorado, USA, Apr. 2006.
[15] Optotune, “Laser Speckle Reducers (LSR-4C-L),” 銓州光電股份有限公司, https://www.onset-eo.com/product-category/optics/opto-electric-instrument/laser-speckle-reducers/, 2019 (accessed Jul. 2023).
[16] Chih-Hsiao Chen, “Laser Illumination System and Method for Eliminating Laser Speckle Thereof,” United States Patent 010359692B2, Jul. 23, 2019.
[17] Edmund Optics Inc., “高斯光束計算器,” Gaussian beam calculator, https://www.edmundoptics.com.tw/knowledge-center/tech-tools/gaussian-beams/, 2023 (accessed Jul. 2023).
[18] Chang-Hyeon Ji, Moongoo Choi, Sang-Cheon Kim, See-Hyung Lee, Jong-Uk Bu, “Performance of a Raster Scanning Laser Display System Using Diamond Shaped Frame Supported Micromirror,” IEEE Photonics Technology Letters, vol. 18, issue 16, pp. 1702-1704, Aug. 2006.
[19] Motion Solutions, “Raster Scanning Techniques for Photonics Applications,” Motion Solutions, https://www.motionsolutions.com/raster-scanning-techniques-photonics-applications/, 2023 (accessed Jul. 2023).
[20] L.B. Wolff, “Diffuse Reflection From Smooth Dielectric Surfaces,” Journal of the Optical Society of America A, vol. 11, issue 11, pp. 2956-2968, 1994.
[21] ITF Technologies, “ITF 1550nm Lidar Sources - Kala 2,” ITF Technologies, http://www.itftechnologies.com/files/13/ITF_DataSheet_KALA2_V1_KALA1_V3_2023-01-26-15-07.pdf, 2023 (accessed Jul. 2023).
[22] Edmund Optics Inc., “10mm Aperture VIS/NIR Fiber Optic Collimator, SMA,” Edmund Optics Inc., https://www.edmundoptics.com/p/10mm-aperture-visnir-fiber-optic-collimator-sma/30458/, 2023 (accessed Jul. 2023).
[23] Maradin, “MEMS 2D Laser Scanning Mirror,” Maradin, https://www.maradin.co.il/products/mems-mirrors/mar1110-e-2d-scanning-mirror/, 2023 (accessed Jul. 2023).
[24] Si-jing Chen, Deng-kuan Liu, Wen-xing Zhang, Li-xing You, Yu-hao He, Wei-jun Zhang, Xiao-yan Yang, Guang Wu, Min Ren, He-ping Zeng, Zhen Wang, Xiao-ming Xie, Mian-heng Jiang, “Time-of-Flight Laser Ranging and Imaging at 1550 nm Using Low-Jitter Superconducting Nanowire Single-Photon Detection System,” Applied Optics vol. 52, issue 14, pp. 3241-3245, 2013.