All Fiber Coherent Doppler LIDAR for Wind Sensing
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All Fiber Coherent Doppler LIDAR for Wind Sensing Toshiyuki Ando1, Shumpei Kameyama1, Kimio Asaka2, Yoshihito Hirano1, Hisamichi Tanaka3, and Hamaki Inokuchi3 1 Information Technology R&D Center, Mitsubishi Electric Corporation, 5-1-1 Ofuna, Kamakura, 247-8501, Japan 2 Communication Systems Center, Mitsubishi Electric Corporation, 8-1-1 Tsukaguchi-Honmachi, Amagasaki, 661-8661, Japan 3 Aerospace Research Center, Japan Aerospace Exploration Agency, 6-13-1 Osawa, Mitaka, 1810015, Japan -ABSTRACT An 1.5 micron pulsed Coherent Doppler LIDAR system using all fiber optical components has attracted attention for remote wind sensing application because of its eye-safety, reliability and easy deployment. We report on our key technologies such as fiber based MOPA (Master Oscillator Power Amplification) transmitter, high peak power optical amplification and a real-time signal processing. Some performance results and applications are also provided. INTRODUCTION A Coherent Doppler LIDAR (CDL) is an attractive sensor for wind sensing because it offers a method of remote wind speed measurement in the clear atmospheric condition. The CDL involves irradiations of coherent light and detection of weak backscattered from natural aerosols in the distant atmosphere, and provides the line-of-sight component of wind speed via Doppler frequency shifts from backscattered light. This technique was first demonstrated in 1970s, and since then it has been the focus of many research projects for a variety of applications. All-fiber CDL using 1.5 micron wavelength has many advantages including eyesafety, reliability under various environmental conditions, and flexibility for components’ layouts [1,2]. Mitsubishi Electric has been involved in development of a commercial prototype of an all-fiber CDL system since 2004, and has successfully confirmed its highly accurate performance based on simultaneous measurements with a conventional ultrasonic anemometer [3]. In 2005 a commercial product of an all-fiber CDL system (LR-05FC series) was manufactured [4], which successfully achieved reductions not only of its dimensions but also for manufacturing cost less than 50% of the prototype system [5]. Our all-fiber CDL has mainly used fiber-optic components which have largely improved its cost, compactness and reliability in telecommunications industry. However some specific points needed to be considered for the pulsed CDL system: generating optical seed pulses with a high on/off extinction ratio, obtaining high peak power using fiber amplification, and optical heterodyning without any fluctuation in the polarization state. Non-linear optical effects in optical fibers have to be specially considered to improve measurement performances of all-fiber CDL. Stimulated Brillouin Scattering (SBS) is one of the most dominant non-linear effects to limit measuring distance because output peak power has to be kept at SBS threshold to avoid parasitic oscillations imposing damages on fiber components.
High speed signal processing is also an important aspe
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