This paper presents a miniaturized fringe projection system that only uses two fibers to potentially achieve superfast (e.g.,
MHz to GHz) 3D shape measurement speeds. The proposed method uses two optical fibers that carry the same wavelength
of laser light with polarization and phase information properly modulated to generate high-quality sinusoidal fringe patterns
through interference. The high-speed phase shifting is achieved by employing a high-speed Lithium Niobate (LN) electrooptic
phase modulator. Since only two optical fibers are used to generate sinusoidal patterns, the system has a great
potential of miniaturization for applications where the sensor size is critical (e.g., 3D endoscopy). Principle of the proposed
techniques will be introduced, and preliminary experimental results will be presented in this paper to prove the success of
the proposed method.
Laser Doppler velocimetry has the ability to measure speed and surface vibrations non-intrusively with high precision. In
this study the Doppler spectrum shift and spectrum broadening of echo signals by moving targets are investigated. The
interaction between moving object and the laser beam of laser Doppler velocimetry have been described by varying
rotating velocity, the angular velocity, distance and incident facula. By using different scattering surfaces, such as
Polytetrafluoroethylene (PTFE) and sandpaper with different grain sizes, the characteristics of echo signals' Doppler
spectra have been studied experimentally in detail. The results show that Doppler spectrum distribution is changed with
different scattering surfaces. Meanwhile, in order to get a high measuring accuracy, the moving object's scattering
characteristics must be considered carefully.
The design, component selection, fabrication, testing, and evaluation of an optically-switched, binary, fiber optic
programmable delay line are discussed. The basic building blocks, including laser diode which is based on a rate
equation model, external modulated transmitter, transmission fiber and receiver, are explained. The system comprises
eight delay stages, has a maximum delay of 6.4μs with a 100ps step and operates over the 1-18 GHz band. This computer
controlled prototype used low-cost commercially available components in conjunction with graded-index, single-mode
fiber. Its overall performance is satisfied with the simulation result.
An eye-safe, coherent Doppler Light Detection and Ranging (CDL) system for speed measurement under development at
BUAA's School of Instrument Science and Opto-electronics Engineering is introduced in this paper. It consists of a
1.55-μm Er-doped fiber laser transmitter, a monostatic optical antenna, a single-mode fiber (SMF) interferometer, an
InGaAs photodiode detector, and signal processing equipments. All devices of optical circuit are connected by SMFs
making the system reliable and setup arrangement flexible. The goal is to give the evaluations of the Doppler frequency
shift and platform speed. Since the speed accuracy is time-independent, the CDL system can be used for integrated
navigation system. The quality of Doppler-shift estimation by a spectrum analysis technique, fast Fourier transform (FFT)
algorithms, ameliorates as the signal-to-noise ratio (SNR) increases. For the developed CDL system incorporating with
SMF interferometer, only the light beam of mode LP<sub>01</sub> is permitted to propagate, therefore the SNR is improved greatly.
Experiments were performed on a moving hard target with the CDL system and the results were presented.
It is common to use Yb-doped double-clad fibers as gain medium of high power fiber lasers. These fibers are similar
to the so-called "un-doped" telecommunication fiber. Because of small core size, only from several microns to tens of
microns, there are easier causing self-pulsing affects in the fiber lasers. In the first part it is reported the several kinds of
self-pulsing according to the reported papers, like relaxed oscillation, saturated absorption effect, stimulated Brillouin
scattering and stimulated Raman scattering. Then it is presented the experimental study and the different self-pulsing
phenomena. The result shows that under the high power condition, although ytterbium ions without concentration effect,
but large core Yb-doped double-clad fiber are the same to three-level ion systems that self-pulsing behavior was the
result of relaxed oscillation. To Yb-doped fiber laser, saturated absorption effect, stimulated Brillouin scattering and
stimulated Raman scattering cannot be ignored.