Monostatic coaxial 15 μm laser Doppler velocimeter using a scanning Fabry-Perot interferometer

Abstract

We present a laser Doppler velocimeter (LDV) in monostatic coaxial arrangement consisting of off-the-shelf telecom-grade components: a single frequency laser (wavelength λ = 1.5 μm) and a high-finesse scanning Fabry-Perot interferometer (sFPI). In contrast to previous 1.5 μm LDV systems based on heterodyne detection, our sFPI-LDV has the advantages of having large remote sensing range not limited by laser coherence, high velocity dynamic range not limited by detector bandwidth and inherent sign discrimination of Doppler shift. The more optically efficient coaxial arrangement where transmitter and receiver optics share a common axis reduces the number of components and greatly simplifies the optical alignment. However, the sensitivity to unwanted backreflections is increased. To circumvent this problem, we employ a custom optical circulator design which compared to commercial fiber-optic circulator achieves ~40 dB reduction in strength of unwanted reflections (i.e. leakage) while maintaining high optical efficiency. Experiments with a solid target demonstrate the performance of the sFPI-LDV system with high sensitivity down to pW level at present update rates up to 10 Hz.

Design and Characteristics of Dual-Core Photonic Crystal Fiber Doppler Differential Velocimeter

“…Xue-feng Huang, 1 Sheng-ji Li, 2 Guang-hua Zheng, 1 Guan-jun Zhao, 1 Jiang-rong Xu, 1 and Wei-chih Wang…”

“…[1][2][3][4][5] As a sensor system, the LDV possesses many advantages, including essentially nonintrusive, good spatial and temporal resolution, high accuracy and easy application to hostile environments. [6,7] The LDV technique relies upon the measurement of the Doppler frequency shift of light scattered from an illuminating laser beam by particles entrained within the flow.…”

CW Direct Detection Lidar with a Large Dynamic Range of Wind Speed Sensing in a Remote and Spatially Confined Volume

“…A CW monostatic (coaxial) DDL using a 1575 nm fiber laser and a scanning FPI (sFPI) as a frequency discriminator was first demonstrated in our previous work [22]. The advantages of the sFPI-DDL in [22] included the following: the optical system was compact, the monostatic architecture resulted in simple alignment and high transmitter-receiver efficiency in comparison to bistatic designs, the system control and the data processing were simple and, moreover, it provided a high dynamic range of wind speed measurement (zero to hundreds of meters per second). However, the system in [22] lacked the ability to measure wind because its sensitivity was limited by noise from its InGaAs detector and the relatively high irradiance of its reference signal.…”

All-fiber upconversion high spectral resolution wind lidar using a Fabry-Perot interferometer

“…Recently, an intracavity upconversion system has been demonstrated for detection of atmospheric CO 2 [25]. A Doppler velocimetry has been demonstrated before by using a scanning Fabry-Perot interferometer and an InGaAs photodetector [26,27]. Although InGaAs detector is commercial available, its high after-pulse probability distorts the raw signal significantly and the time gating operation mode exhibits periodic blind zones [28].…”