This paper summarizes the recent progress of improving optical fiber sensor interrogation technique by introducing
acitve fiber loop into demodulation system. Various types of sensors including multimode interferometer chemical vapor
sensor and etc are implemented in the active fiber loop interrogation system. The experiments show an improved signal
to noise ratio by active fiber loop.
This paper reports a long-period fiber gratings(LPFG) fabricated on a double-clad fiber (DCF) by the
laser point-by-point technique. The LPFG is tested by measuring temperature and refractive
index (RI) of different liquids. The results show that the LPFG inscribed on the DCF has no
measurable sensitivity to external RI but has a high sensitivity for temperature. The measured
temperature sensitivity is ~0.11 nm/<sup>o</sup>C, about 10 times higher than that of conventional FBGs. Such
LPFGs can be used as a modulator in fiber lasers or temperature/strain sensors in applications where
the surrounding RI is prone to variation, such as simultaneous measurement of the temperature and
RI of chemical reactions.
Long-period fiber gratings have been used for refractive index measurements under different conditions. Normally, this
kind of sensor is based on measuring resonance wavelength shift with respect to different refractive index environments.
As high order mode long period fiber gratings are attracting more attention, a new methodology based on intensity
measurement of turning points is introduced, which involves simple experiment setup and straightforward demodulation
process compared with wavelength shift based method. By using CO<sub>2</sub> laser point by point irradiation method, high order
mode gratings working at turning point can be easily fabricated. This type of grating has a very high sensitive response
to surrounding refractive index, which can be used in chemical, medical and bio applications. In this paper, high
sensitive refractive index sensor is demonstrated based on high order mode using intensity measurement. Phase match
curve and couple mode theory are combined to analyze the intensity response to refractive index change at turning point
of LPFG. This sensor is also demonstrated as an effective refractive index based glucose sensor with a range from 0 to
40 mM concentration of glucose solution, which can fulfill the medical requirement.
In this paper, we present a new theoretical model for the design of acoustical waveguides in the guided acousto-optic devices. The electromechanical coupling coefficient and the velocity in the acoustical in the acoustical waveguide are analyzed for different waveguide thicknesses. Some valuable results for the design of acousto-optic devices are obtained.
The doughnut beams with charges of 1 to 3 are generated by one and stacking two and three Liquid crystal(LC) spiral
phase plates with cell gaps of 7 μm respectively. Theoretically, any charge number can be obtained by the stacking
method. High efficiency and flexibility are the advantages of generating doughnut beams by stacking liquid crystal spiral
phase plates. The interference of doughnut beam generated by LC spiral phase plate and plane wave has been studied.
The numerical simulation results agree with the experiment.
In this paper, a numerical method is presented to design a biconical waveguide. We use this method to calculate the transmitted and radiated power of the biconical waveguide in an integrated acousto-optic modulator, then we plot the normalized power loss curves versus the taper length and get the optimum design.
An efficient shooting algorithm based on the simple-shooting method and the modified Newton-method for fiber Raman amplifier design is proposed. By introducing the Broyden's rank-one method, the time-consuming calculation of the Jacobian matrix is dramatically relieved. Numerical simulation results show that the simulation efficiency of the proposed method has been improved more than 70 percent compared with the conventional shooting method.
A new numerical optimization method assisted by functional model and improved Newton's iterations is proposed. The method would be applied to the pump power configure optimal design for the gain flatness optimization in the laser-diode discrete Fiber Raman amplifier (FRA). Compared with other optimization algorithms, the proposed improved Newton's iteration has fast convergence speed and good stability. So the method can exploit better solutions and greatly shorten the amount of run time. Two samples show the feasibility of the method with different initial variables. The comparison with Genetic algorithm (GA) is obtained.
In this paper the parameters of a CW double-clad fiber laser are theoretically analyzed, which is of important references to designing the kindred double-clad fiber lasers. This paper also offers a personalizing design scheme of double-clad fiber lasers, with the influence of some important parameters on the output power clarified.
The overlap integral of guided acousto-optic interaction is investigated theoretically. The overlap integral of YZ-LiNbO3 (Y-cut crystal, Z-propagating surface acoustic wave) is discussed with different penetration depths for TE- and TM-polarized light. Some valuable results are obtained for the design of acousto-optic devices.
A Q-Switched All-Fiber Cladding-Pumped Ytterbium-Doped Fiber Lasers using an acoustic-optic waveguide Q-switched (AOW-Q) with a pigtail fiber are studied. For AOW Q-switched, Ti-diffused YX-lithium niobate substrate was applied as optical waveguide, a SiO<sub>2</sub>/In<sub>2</sub>O<sub>3</sub> film of thickness ~150nm as acoustic waveguide and an acoustic aperture of width 110 μm, in conjunction with N=9 finger pairs.
A new method of gain adjustment of multipump Raman fiber amplifier is proposed and numerically demonstrated. The method utilizes the areas under the pump power evolution curves along the gain fiber as a criterion and the Newton-Raphson method is used to find the appropriate power combination of the pumps to realize the desired gain profile. The proposed method has two merits: First, it can maintain the gain profile while changing the gain magnitude to the desired value; second, it is independent of the actual scheme of the amplifier, i.e. it can be used in Raman fiber amplifiers with all kinds of pumping schemes including co-, counter-, or bi-directional pumping. Numerical simulation results are also provided to verify the proposed method and demonstrate its effectiveness.
Raman gain in various optical fibers G652, G653, G655 and DCF (dispersion compensating fiber) and the selection of fibers in discrete broadband Raman fiber amplifiers (RFA) are studied. Using the experimental results from references, we have obtained a polynomial formula of the SRS (stimulated Raman scattering) Stokes spectrum and the effective area of the fibers by sampling and digital fitting. The effective Raman gain coefficients are calculated using the formula. Based on the formula, Raman gains of multi-wave pump RFA in different fibers are obtained with the consideration of arbitrary interaction between pump waves and signal waves. Comparing the pump power distributions and the lengths in the four optical fibers, we propose appropriate selections of optical fibers in Raman fiber amplifiers.
We have demonstrated an effective method for suppression of coupling from a guided mode to cladding modes in a fiber grating. The UV light pulse energy, repeated frequency and exposure time are controlled and optimized during writing process of Bragg grating. We can write advanced Bragg grating using optimum UV light parameters.