A resonant fiber-optic sensor using a general ring fiber is proposed. A frequency sweep sinusoidal intensity modulated
laser beam is injection locked to the ring fiber sensor using a fiber coupler of low coupling coefficient. The ring fiber is a
resonant ring as well as an extracted carrier. In respect that the resonant ring of difference length has difference resonant
frequency, the systems operating in the length range 0.6-2 meters and resonant frequency range 100-300MHz, frequency
division multiplexing has been used in these sensor systems. Demodulation was achieved by using frequency tracking
demodulator that uniform amplify signals in large bandwidth and a narrow band filter in it, so that it has a high signal to
noise rate(SNR). According to the experiments with a general ring fiber, the method is very easy and inexpensive to
implement, demodulation linearity over 1 decades and minimum relative variation detection ∼0.1% attained. The ring
fiber sensors have certain advantages that include high sensitivity, large bandwidth, and ease in implementing
multiplexed or distributed sensors. Strain, temperature and pressure are the most appropriate measurands in the systems.
Based on the theory of Mueller matrix of optical devices with both polarization dependent loss (PDL) and birefringence, the definition of polarization loss (PDL) is analyzed. The newly formulated equations for PDL are generalized for input light with arbitrary degree of polarization (DOP). Theoretical derivation shows that the overall polarization states should contain all the polarization states with random DOP. The magnitude of PDL has connection with the input DOP. The direction of PDL vector is only decided by the Mueller matrix.
This article reports the surface hardness values, transverse and longitudinal distributions of three kinds of carbon steels treated by laser surface heat treatment. The surfaces of the steel samples hardened by this way are harder than those of steels hardened by normal way. The surface hardness value of low-carbon steel sample, especially, increases a lot after being hardened by laser. This has much significance in the practical use in the future.
We report the experimental study on a intracavity frequency doubling and self-Q-switching phase-conjugation two-rod Nd:YAG lasers, using a KTP crystal as second harmonic generator, and a phase-conjugation mirror based on stimulated Brillouin scattering in acetone. The experimental results show that this kind of lasers not only generate Q-switched laser pulses, with duration about 15 ns, and energy over 90 mJ at 532 nm, but also possess the capacity of stabilizing the laser pulse energy, which the energy fluctuation about 5% are obtained. Theoretical analysis on the experimental results is given.