The efficiency of integrated acousto-optic (AO) modulators with different optical penetration depths fabricated on 128-deg-rotated Y-cut X-propagation lithium niobate (128-deg YX-LiNbO3) is analyzed theoretically for the first time by determining the overlap integral between the optical and acoustic field distribution. The results show that the smaller the optical penetration depth is, the higher the optimum surface-acoustic-wave (SAW) frequency and diffraction efficiency and the larger the bandwidth will be. Compared with TM-polarized light, TE-polarized light offers better performance for modulation. However, for a well-concentrated optical waveguide, TM-polarized light is attractive for AO modulators, which employ a single SAW.
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.
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.
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.
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 SiO2/In2O3 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.
The thermal effect in the laser diode (LD)-side-pumped solid-state laser is studied. The pump power, the temperature distribution figures and the laser beam parameters are obtained. The thermal effects under different cooling conditions are numerically calculated, as well as those in diode-end-pumped solid-state laser. The calculation results are compared with those in diode-side-pumped solid-state laser.
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.
The effect of liquid-crystal spiral phase plates on the generation of doughnut laser beams is studied. Several parameters of the liquid-crystal (LC) are analyzed and carefully selected including birefringence of the LC, thickness, cell gap, type, topographic charge number, and applied voltage. The LC spiral phase plates have been fabricated.
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.
A novel 16-channel 50-GHz spacing interleaver for dense wavelength-division multiplexing (DWDM) systems has been realized using Ti:LiNbO3 waveguides with the corrugated Si overlays. High refractive-index Si layer on LiNbO3 waveguide enables a large index perturbation to strongly affect the mode index of the composite structure. The reflection spectra strength of each peaks and bandwidths of the individual channels are increased by interleaving several sampled gratings together. The modal characteristics have been analyzed by employing vectoric finite element method. The reflectivity has been obtained by formulating the transmission matrix of the structure. An odd-even channel
separator with a gratings length of approximately 11 mm has been fabricated and its reflection spectrum has been
measured. The -1-dB channel bandwidth is ≥ 0.2 nm and the sidelobes are < -20 dB.
TE/TM mode converter is a key element of integrated acoustooptical tunable filter (AOTF). Employing SiO2/In2O3 film as acoustical waveguide can suppress sidelobes effectively and simplify fabrication technique in integrated quasi-collinear AOTF. In this report, the eigenvalue equation and the field solution of such configuration has been obtained by using modified Wenzel-Kramers-Brillouin (WKB) method. The results are compared with those by using vector finite element method (VFEM). When the optical waveguides are covered by such oxide film, the difference of mode indices of both polarizations and the effective propagation velocity of surface acoustical wave (SAW) will decrease, and these decreases lead the shift of optical wavelength, which mainly results in the change of the former.
Compact and efficient blue light source are attractive for numerous and technical applications such as laser-based metrology, data storage, medicine, xerography, and biotechnology. Nonlinear frequency conversion remains an attractive route to achieving blue light sources. In this paper we show that 915nm laser diode pumped Yb-doped double clad fiber lasers (YDCFL) can provide efficient 978nm light. Frequency doubling ofthe 978nm line ofYDCFL can else generate blue (489nm) light. We setup theoretical model of Yb-doped double clad blue fiber laser. The threshold and Output powers at 978nm and 489nm versus the fiber length, the core diameter, the size and numerical aperture (NA) of the inner cladding, and pumped power are studied through theoretical simulation. The optimum parameters are obtained. In the design of three-level double-clad fiber lasers, we consider two main considerations: high pump brightness and an optimum balance between spectral filtering and modal gain discrimination. Atype I phase—matched BBO crystal is used to generate second harmonic light(489nm).
A dynamic gain control (DGC) technique for the multi-wavelength-pumped fiber Raman amplifier (FRA) is presented. It introduced an all-optical feedback to inject a portion of the signal power into the system by using a variable attenuator. The stable performance of the proposed gain-clamped FRA was simulated and the noise performance was also discussed.
The generation of the third harmonic for quasi-continuous laser diode(QCWLD) pumped Nd:YAG laser are studied. We compute numerically relations between light wavelength and phase-match angle, and effective nonlinear coefficient, and walk-off angle for third harmonic generation (THG) in BBO crystal. Frequency tripling experiment is done using electric-optic and acoustic-optic Q-switching Nd:YAG laser pumped by high power QCWLD. We use type II KTP crystal to generate the second harmonic(532nm) , and type I BBO crystal to generate third harmonic (355nm). Inner cavity frequency and out-cavity tripling are done. Maximum pulse energy of 1 .5mJ for 355nm is achieved.
Quasi-continuous wave titanium-doped sapphire laser pumped by frequency doubled YAG laser was investigated. The maximum average output power is 2.7 W with 11.2 W pump power, and the tuning range is 750 to 870 nm by using one set of cavity mirrors. The rate equations of this type of laser were also developed. Theoretical predictions are confirmed by experimental measurements.
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