Copyright © 2006 The Institute of Electronics, Information and Communication Engineers
Regular Section -- Papers -- Optoelectronics |
Extended-Range High-Resolution FMCW Reflectometry by Means of Electronically Frequency-Multiplied Sampling Signal Generated from Auxiliary Interferometer
1 The authors are with the Division of Electrical Engineering and Computer Science, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa-shi, 920-1192 Japan. E-mail: iiyama{at}ee.t.kanazawa-u.ac.jp, 2 Presently, with the Hitachi Cable Ltd.
High-resolution FMCW reflectometry is often realized by sampling the beat signal with a clock signal generated from an auxiliary interferometer. The drawback of this system is that the measurement range is limited to less than half of the optical path difference of the auxiliary interferometer to satisfy the Sampling theorem. We propose and demonstrate a method to extend the measurement range of the system. The clock signal gerenerated from the auxiliary interferometer is electronically frequency-multipled by using a PLL circuit. The measurement range is experimentally extended by a factor of 20 while keeping high spatial resolution, and is theoretically extended by a factor of 128. The advantage of the proposed system is that the optical path difference of the auxiliary interferometer can be kept short, which is very effective for obtaining the stable and low time-jitter clock signal.
Key Words: optical fiber sensing, optical ranging system, optical reflectometry, FMCW, OFDR
Manuscript received October 17, 2005. Manuscript revised January 5, 2006.