Y.B. Liao

Improving the performance of a FBG sensor network using a genetic algorithm

Genetic algorithm is used to improve the performance of FBG sensors within in a wavelength-division multiplexed sensor network. Simulations and experiments demonstrated wavelength detection accuracy of a few microstrains even when the spectrums of FBGs within the network are partially or completely overlapped.

Enhancement of wavelength detection accuracy in fiber Bragg grating sensors by using a spectrum correlation technique

A digital post-processing technique based on spectrum correlation is developed and applied to determining the Bragg wavelength shift accuracy in fiber Bragg grating (FBG) sensors. Theoretical analysis shows that the enhancement factor is proportional to the square root of the number of the independent sampling points within the 3d B bandwidth of the FBG. A wavelength detection accuracy of better than 1 pm in terms of standard deviation was experimentally demonstrated, representing an enhancement factor of 7.3 over the conventional peak detection technique. This technique may also be used for applications such as white light interferometer sensors where the interferometric pattern shifts with applied measurand while the shape of the pattern remains unchanged.

Nd:YAG slab laser end-pumped by laser-diode stacks and its beam shaping

Abstract An efficient high power cw Nd:YAG slab laser, partially end-pumped by diode laser stacks, and a novel beam shaping technique are reported in this paper. The optical efficiency amounted to 44% and the slope efficiency to 55%. Introducing an intracavity Brewster plate to polarize the laser beam, an optical efficiency of 35% and a slope efficiency of 41% was obtained. The output beam was rectangular and the beam quality asymmetric in two orthogonal directions. To equalize the beam quality, a step mirror beam shaping technique was introduced. The beam shaping technique and the results obtained with it are discussed in this paper.

NEODYMIUM:YAG 30-W CW LASER SIDE PUMPED BY THREE DIODE LASER BARS

A theoretical calculation of pump power deposition in a direct water-cooled Nd:YAG laser rod, side pumped by three diode laser bars is presented. The pumping cavity design provides a nearly uniform pump profile. More than 30-W cw output power with optical-to-optical efficiencies of more than 30% are obtained.

Polarization characteristics of a Nd:YAG laser side pumped by diode laser bars

A detailed experimental investigation of the polarization characteristics of a diode laser side-pumped Nd:YAG laser has been performed. A Brewster plate inserted into the cavity resulted in a decrease of 50% of the output power that is due to depolarization. A thin-film polarizer (TFP) was introduced into the cavity and the depolarization loss served as the output coupling. By introduction of a quarter-wave plate (QWP) the output coupling rate and the beam shape were improved. An analytical expression for the output coupling rate of a cavity containing a TFP and a QWP has been derived. The experimental results are in good agreement with the simplified theoretical analysis.

A digital passive phase demodulation scheme using 3×3 coupler for fiber-optic interferometric sensors

A real-time digital phase demodulation scheme is developed. This scheme, based on cos -1 and channel-choosing techniques, uses the two optical outputs from a 3×3 coupler to overcome the signal fading problem of fiber interferometer.

Novel polarization ellipticity angle modulation scheme for analog optical space communication

A novel polarization ellipticity angle modulation scheme is proposed and analyzed. The scheme shows linear modulation property and negligible phase noise. With this method, analog signal such as microwave sub-carrier can be directly encoded onto light carrier, simplifying the integration of traditional RF system and optical space communication system.

High-efficiency high-beam-quality 38-W Nd:YAG slab laser end-pumped by a stack with three diode bars

A Nd:YAG slab is partially end-pumped by a diode laser stack with three diode laser bars. The pumped volume has a rectangular cross section. A hybrid resonator which is stable in the plane of small dimension and off-axis unstable in the plane of large dimension of the gain cross section was used, in order to obtain highly efficient laser operation at diffraction limited beam quality. In this paper, the laser design and experimental results are reported. 31.2 W output power was obtained with M2 equals 1.3 in the unstable plane and M2 equals 1.7 in the stable plane. 38.6 W output power was obtained with M2 equals 1.7 in the unstable plane and M2 equals 3.9 in the stable plane.

Efficient TEM00 operation of Nd:YVO4 laser end pumped by fiber-coupled diode laser

We have demonstrated efficient TEMoo operation of the Nd:YVO4 rod laser, one-end-pumped by a fiber-coupled diode laser. 11.6-W linearly polarized laser output with an optical efficiency of 54% in a TEMoo mode has been achieved.

Stability of lasers with intracavity second-order nonlinearity

On the basis of the dynamical model for the intracavity frequency-doubled laser we demonstrate a criterion for the stable operation of laser-resonators with intracavity nonlinear elements. This allows the determination of the laser stability from the resonator parameters and material constants.