Dual Aperture Single Mode Optical Fiber Laser Doppler Velocimeter

Abstract

Single mode optical fibers and graded index microlenses have recently been utilized in laser light scattering experiments.1,2 The utilization of single mode optical fiber technology offers many advantages over conventional bulk optic arrangements including: ease in alignment, unity heterodyne efficiency, polarization maintaining capability, high angular resolution and small size. A dual aperture single mode optical fiber heterodyne technique has recently been demonstrated which simultaneously measures the angular orientation, radial velocity and angular velocity of a target simulator.3 This technique was demonstrated with an interferometer that utilized the exposed cores of the receiving fibers as the apertures. Presented in this report is a dual aperture heterodyne interferometer that employs pigtailed graded index microlenses as the detection apertures, thereby extending the range and angular resolution of the laser Doppler velocimeter (LDV). Although the velocimeter presented here utilizes microlenses, the results are applicable to lens systems of greater dimensions which are suitably coupled to the single mode fiber. This interferometer may be useful in a number of LDV applications including: particle flow measurements, atmospheric wind sensing, satellite tracking, laser radar and robotic positioning.