光學雷達(Light Detection And Ranging, LiDAR)是一種起源於1960年代的光學遙測技術，自輔助駕駛系統等應用(Advanced Driver Assistance Systems)逐漸普及後更成為光學感測器的重點研究項目之一，其和傳統光學相機相比，具有生成包含深度之三維影像的特點，使其在工業工程，自駕車，機器視覺等領域具有強大的應用潛力，為光學感測技術中的關鍵項目之一。
目前市面上主流的LiDAR系統依照工作原理不同可分為飛時測距光學雷達(Time of Flight LiDAR, ToF LiDAR)以及連續波調頻光學雷達(Frequency-Modulated Continuous-Wave LiDAR, FMCW LiDAR)兩種，和ToF LiDAR相比，FMCW LiDAR具有高的解析度以及更長的工作距離等特點，且在環境抗噪能力與精準度上具有比飛時測距光達更為優異的表現，然而其龐大的系統體積限制以及更高的調頻光源要求，使其在消費性電子產品上的應用受到侷限而難以商業量產，因此，縮小FMCW LiDAR的系統體積將會是提升其競爭力的關鍵之一。
為了能縮小FMCW LiDAR的系統大小，本論文提出基於光纖的數位輔助干涉儀(Digital Auxiliary Interferometer)應用於雙光路的FMCW LiDAR的設計，利用希爾伯特轉換(Hilbert Transform) 修正連續波調頻光學雷達中光源非線性掃頻造成的量測誤差，搭配使用內插法倍數增加插值點數的方式符合奈奎斯取樣定理(Nyquist theorem)，能在校正雷射非線性調頻導致的計算誤差外，也能在滿足取樣定理的條件下大幅縮短輔助干涉儀需要的光纖長度達到縮小體積的目的，同時免去需使用價格昂貴的線性掃頻雷射以及使雷射調頻線性化的回授電路，達到降低 FMCW LiDAR 系統成本同時進一步優化量測精準度之目的。
在本論文實驗量測中，我們使用上述方法將輔助干涉儀光纖長度從類比輔助干涉儀的12公尺大幅縮減至數位輔助干涉儀的10.5公分，分別量測了固定距離10cm至100cm，每公分各10筆數據，以及速度從1cm/s至5cm/s，每公分/秒各10筆數據，和光纖型數位輔助干涉儀用於對反射鏡的二維影像量測，與輔助干涉儀晶片的51筆一維影像量測等，從結果顯示數位輔助干涉儀在重取樣的表現上進一步改善了類比輔助干涉儀存在的實驗誤差，同時在公分等級的距離與速度量測產生的絕對誤差更進一步縮減至43μm與87μm。

Light Detection And Ranging (LiDAR) has become one of the vital research projects for related sensing systems. Compared with traditional optical cameras, LiDAR has been highly valued in recent years to generate three-dimensional images with depth, resulting in a strong potential for applications in industrial engineering, self-driving vehicles, and medical and scientific industries.
Typically, the major LiDAR systems can be divided into Time of Flight LiDAR (ToF LiDAR) and Frequency-Modulated Continuous-Wave LiDAR (FMCW LiDAR), depending on their operating principles. Compared with ToF LiDAR, FMCW LiDAR has a higher resolution and longer working distance, but its bulky system footprint and higher requirement for frequency-modulated sweeping light source limit its application in commercial electronic products and make it challenging to be mass-produced. Therefore, reducing the system size of FMCW LiDAR will be one of the keys to improve its competitiveness further.
To reduce the system size of FMCW LiDAR, we proposed the fiber-based digital auxiliary interferometer that can be conducted in the design of dual-path FMCW LiDAR, calibrating the measurement error caused by non-linear frequency tuning through Hilbert-Transform. Since the Nyquist theorem can be satisfied by shortening the sampling interval, the size of the digital auxiliary interferometer can be significantly reduced without affecting the resampling and measured results. Without an expensive linear swept source or calibrating feedback circuits, the FMCW LiDAR accuracy can be further optimized.
The above method could reduce the auxiliary fiber length from 12 m to 10.5 cm . Ten datum per 10 cm from 10 cm to 100cm for fixed distance, and 10 datum per cm/s from 1cm/s to 5cm/s comparison datum were measured and resampled using both analog auxiliary interferometer and digital auxiliary interferometer. Two-dimensional image of a reflection mirror and 51 points measurement resampling from auxiliary interferometer chip were also measured. Results showed with improved absolute errors in distance and velocity measurements from the centimeter scale to 43 μm and 87 μm, respectively.

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