Single-mode fiber, velocity interferometry

Abstract

In this paper we describe a velocity interferometer system (a VISAR) based entirely on single-mode fiber optics. This paper includes a description of principles used in developing the single-mode velocity interferometry system (SMV). The SMV design is based on polarizationinsensitive components. Polarization adjusters are included to eliminate the effects of residual birefringence and polarization dependent losses in the interferometers. Characterization measurements and calibration methods needed for data analysis and a method of data analysis are described. Calibration is performed directly using tunable lasers.During development, we demonstrated its operation using exploding-foil bridge-wire fliers up to 200 m/s. In a final test, we demonstrated the SMV in a gas gun experiment up to 1.2 km/sec. As a basis for comparison in the gas gun experiment, we used another velocimetry technique that is also based on single mode fiber optics: photonic Doppler velocimetry (PDV).For the gas gun experiment, we split the light returned from a single target spot, and performed a direct comparison of the homodyne (SMV) and heterodyne (PDV) techniques concurrently. The two techniques had a negligible mean difference and a 1.5 % standard deviation in the 1 dimensional shock zone.Within one interferometer delay time after a sudden Doppler shift, an SMV unencumbered by multimode-fiber dispersion exhibits two color beats. These beats have the same period as PDV beats --this interference occurs between the "recently" shifted and "formerly un-shifted" paths within the interferometer. We believe that recognizing this identity between homodyne and heterodyne beats is novel in the shock-physics field. SMV includes the conveniences of optical fiber, while removing the time resolution limitations associated with multimode delivery fiber.2

Fiber-optic interferometric sensor for monitoring automobile and rail traffic

“…As each train axle passes the counting head at the start of the section, the counter increments. These devices can detect the direction and speed of a train by the order and time in which the sensors are passed [10,11]. LIDAR technology is a leading technology for 3D surveying and mapping.…”

A simple and reliable implementation of all-fiber velocity interferometer

“…Therefore, VISAR does not terminate its development and application. [6] reported a single-mode velocity interferometer (SMV) like VISAR but with an all-fiber structure. It resolved the adjusting difficulty of VISAR and could achieve very high velocity resolution by changing the length of delay fiber rather than using a large etalon.…”

“…Theoretically, polarization dependent losses in these components can add a significant systematic velocity error if the polarization from the target evolves. Typically, a polarization dependent loss less than 0.15 dB can still introduce errors up to several percent if the polarization from the target significantly evolves [6]. Besides, SMV used four unbalanced detectors, and then did not get rid of the influence of rapid changes in light intensity on data acquisition and phase analysis.…”

Diagnostics for Kinematics on MTF at NRL

“…Optical techniques can measure velocity more directly and accurately. Laser velocimetry [3], [4] and laser Doppler-shift interferometry [5] are optical techniques and can measure position on optical wavelength scales. Doppler radar [6], [7] it is a technique that is more immune to the excess light produced during launch, whether it is from burning aluminum behind the armature or shock compressed gas ahead of the armature.…”