Second-harmonic generation in periodically poled nonlinear polymer waveguides

We demonstrate quasi-phase-matched (QPM) second-harmonic generation (SHG) at the optical communication wavelengths with side-chain polymer waveguides. A ridge waveguide structure is designed to support fundamental mode guiding at both the pump and the second harmonics, leading to a high field overlap integral of the guided modes. The nonlinearity contrast in the +/0 type QPM waveguide is maximized under a QPM poling electrode width of nearly half the coherence length. Using these configurations, we record a normalized SHG efficiency of 2.2% W(-1) cm(-2) in the polymer waveguide.     

Second-harmonic generation in thermally poled chalcohalide glass

Second-harmonic generation in 60GeS(2)-20Ga(2)S(3)-20KBr chalcohalide glass was investigated by the thermal poling method. A large second-order nonlinear susceptibility, as high as 7.0 pm/V, was obtained in a poled sample by Maker fringe analysis. We believe this to be the first time that a clear second-harmonic wave was observed in chalcohalide glasses containing large amount of alkali ions (6.25 at. %). Such observation is of great potential use in all optical waveguide devices.     

Second-harmonic generation of an optical frequency comb at 1.55 microm with periodically poled lithium niobate

To expand the span of the optical frequency comb (OFC), we generated the second harmonics of an OFC at 1.55microm , using a multiperiod periodically poled lithium niobate (PPLN) crystal. A coupled-cavity OFC generator with an average output power of 0.2 mW was amplified and expanded with a fiber amplifier and a dispersion-flattened fiber. The fundamental OFC average power and span were 100 mW and 45 THz, respectively. The second-harmonic comb's span was 3.2 THz; however, we tuned the center frequency over 30 THz by changing the poling period. We also demonstrated that the second-harmonic comb can be used for frequency-difference measurement.     

非线性左手材料中的二次谐波

基于电磁场理论，推导了无耗非线性左手材料中二次谐波的曼利－诺关系，及相位匹配条件下正向基波与逆向二次谐波的能量转换过程及其空间分布.验证了可将无耗非线性左手材料的入射面作为反射镜，把能量以二次谐波的形式反射.同时分别给出有限厚度介质板中基波和二次谐波的场强分布数值结果，验证了结论的正确性.最后从相位失配角度说明了相位匹配是分析非线性左手材料二次谐波的重要条件.这为研究左手材料的非线性理论奠定了基础.     

Second-harmonic generation in Zn-diffused periodically poled LiNbO3 channel waveguides

In this work second-harmonic generation by quasi-phase matching (QPM) in Zn-diffused periodically poled lithium niobate channel waveguides is presented. A stable TM?TE conversion by QPM has been found. The results are in good accordance with theoretical estimations obtained by the phase-matching condition, either for the polarisation character of the second-harmonic wave as well as for the spectral range, taking into account the periodicity of the domains. Received: 16 May 2001 / Revised version: 7 September 2001 / Published online: 30 October 2001     

Second-harmonic generation in resonant waveguide gratings incorporating ionic self-assembled monolayer polymer films

Experimental results on resonantly excited second-harmonic generation (SHG) in a periodic ionically self-assembled monolayer (ISAM) film are reported. A double-layer guided-mode resonance filter (GMRF) structure is coated with 40 bilayers of pyrlium-based chi(2) ISAM thin film and excited with the fundamental of a Nd:YAG laser. Enhanced second-harmonic conversion in the ISAM film is achieved because of the local field enhancement associated with the fundamental resonating leaky mode. This method of SHG is particularly promising, as the ISAM films under investigation exhibit anomalous dispersion that may be applied for phase matching to improve nonlinear conversion efficiency.     

Second-harmonic generation in graded metallic films

We study the effective second-harmonic generation (SHG) susceptibility in graded metallic films by invoking the local field effects exactly and further numerically demonstrate that graded metallic films can serve as a novel optical material for producing a broad structure in both the linear and the SHG response and an enhancement in the SHG signal.     

Control of the polarization dependence of optically poled nonlinear polymer films

We demonstrate the possibility of controlling the symmetry properties of photoinduced chi((2)) macroscopic susceptibility in polymer films. Ellipsometric adjustment of the write beams allows one to monitor the macroscopic chi((2)) symmetry from a dipolar to an octupolar configuration. Experimental results are in agreement with an irreducible spherical tensor-based model jointly applied to the molecular beta hyperpolarizability and field tensors. We found a purely octupolar polarization-independent photoinduced second-harmonic-generation response in a Dispersed Red 1-methyl methacrylate thin film. Such a configuration, as generated by an octupolar tensor write field tensor made up of counterclockwise circularly polarized omega and 2omega beams, is not within the reach of the classical electric-field poling technique.     

Surface second-harmonic generation based on periodically poled LiNb03 nonlinear optical crystal

We have generated a second-harmonic generation （SHG） of a Q-switched microchip Nd：YAG laser on the surface of a periodically poled LiNbO3 （PPLN） nonlinear crystal near the grazing incidence angle. Three individual SHC waves as transmitted homogeneous, kthomogeneous and reflected radiations have been generated and their intensities are measured and characterized within a desirable range of about 10 different incidence angles of the Nd：YAG laser as pump source on the PPLN surface. The basic of surface nonlinear radiation is also investigated and similar results are calculated and extracted from the theory. Comparison between calculated and measured data shows that they are in good agreement with each other.     

Second-harmonic generation in a direct-bonded periodically poled LiNbO(3) buried waveguide

We report the fabrication of a 12-mum -thick periodically poled LiNbO(3) planar waveguide buried in LiTaO(3) by direct bonding of precision-polished surfaces. Frequency doubling of the 1064-nm output of a cw diode-pumped Nd:YAG laser was performed in a 5.5-mm-long device with a 6.50-mum -period grating at an elevated temperature of 174 degrees C. The resultant green second-harmonic output exhibited fundamental-spatial-mode characteristics at a 4.3%W(-1) conversion efficiency.     

Second-harmonic generation taking into account dispersion of nonlinear susceptibility

Second-harmonic generation in the field of an ultrashort pulse and the propagation of extremely short pulses in a medium with quadratic nonlinearity are analyzed. Second-harmonic generation is analyzed taking into account the effect of second-and third-order group velocity dispersion and dispersion of nonlinear susceptibility up to the second order. Corrections, whose order of smallness is determined by the parameter (ω_L t _p)^?1, where t _p is the pulse duration and ω_L is the carrier frequency of the pump wave, are obtained. For a large phase mismatch, two new solutions are found that describe the stationary evolution of solitary pump and second-harmonic waves in the regions of both anomalous and normal group velocity dispersions.     

Second-order nonlinear optical properties of poled coumaromethacrylate copolymers

Second-order nonlinear optical properties of newly designed and synthesized coumaromethacrylate side-chain polymers are reported. The optimum poling conditions were determined experimentally. The optimum poling temperature for these side-chain polymers is well above the glass transition temperature. The second harmonic coefficient of films poled by coronaonset at elevated temperature and the linear electro-optic coefficient of films poled by contact electrodes were measured. The stabilized value of the second harmonic coefficient, d ₃₃, at 1064nm fundamental wavelength was found to be 13 pm/V. The linear electro-optic coefficient, r ₃₃, exhibits strong dispersion ranging from 2 to 12pm/V in the wavelength range 477 to 1115 nm.     

Coupled multiwave interactions in aperiodically poled nonlinear optical crystals

A new type of coupled nonlinear optical interactions that can be implemented in crystals with an aperiodic modulation of the nonlinear susceptibility is studied. The quasi-phase matching condition is satisfied simultaneously for several conventional three-frequency processes involved in the interaction due to the aperiodic variation of the nonlinearity in space. A simple method for designing aperiodically poled nonlinear optical crystals is proposed and analyzed. The method is based on the superposition of nonlinearity modulations produced by several periodic functions simultaneously so that each of these functions individually corresponds to its own quasi-phase-matched nonlinear process. The dynamics of energy exchange during interaction of five waves with different frequencies that involves three coupled three-frequency parametric interaction processes is investigated thoroughly. The ratio between the effective nonlinear wave coupling coefficients and the amplitudes of pump waves is determined for the case in which the initial stage of the interaction is characterized by the parametric instability. It is demonstrated that the secondary simplification of the coupled differential equations with spatially modulated nonlinear coefficients, which leads to the system of equations with constant nonlinear coefficients, correctly describes the dynamics of interaction of the waves at distances of the order of 50 characteristic nonlinear lengths.     

Second-order nonlinear optical properties from poled silicate channel-waveguide

Thin film waveguides of germanosilicate glass are fabricated byrf-sputtering. Second-order nonlinearity ofd ₃₃=3.2 pm/V is obtained from electrically poled film, and the lifetime of the nonlinearity is found to be310 years. The poled channel-waveguide is prepared and the Cerenkov-type phase-matched frequency doubling is successfully observed.     

Second-harmonic generation in surface periodically poled lithium niobate waveguides: on the role of multiphoton absorption

Second-harmonic generation is investigated in lithium niobate channels realized by proton exchange and quasi-phase matched by surface periodic poling. The reduction in conversion efficiency at high powers is interpreted in terms of multiphoton absorption via two-color terms, yielding an estimate of the dominating three-photon process.     

Surface second-harmonic generation based on periodically poled LiNbO3 nonlinear optical crystal

We have generated a second-harmonic generation(SHG) of a Q-switched microchip Nd:YAG laser on the surface of a periodically poled LiNbO3(PPLN) nonlinear crystal near the grazing incidence angle.Three individual SHG waves as transmitted homogeneous,inhomogeneous and reflected radiations have been generated and their intensities are measured and characterized within a desirable range of about 10 different incidence angles of the Nd:YAG laser as pump source on the PPLN surface.The basic of surface nonlinear radiation is also investigated and similar results are calculated and extracted from the theory.Comparison between calculated and measured data shows that they are in good agreement with each other.     

Second-harmonic generation circular dichroism spectroscopy from tripod-like chiral molecular films

The second-harmonic generation (SHG) circular dichroism in the light of reflection from chiral films of tripod-like chiral molecules is investigated.The expressions of the second-harmonic generation circular dichroism are derived from our presented three-coupled-oscillator model for the tripod-like chiral molecules.Spectral dependence of the circular dichroism of SHG from film surface composed of tripod-like chiral molecules is simulated numerically and analysed.Influence of chiral parameters on the second-harmonic generation circular dichroism spectrum in chiral films is studied.The result shows that the second-harmonic generation circular dichroism is a sensitive method of detecting chirality compared with the ordinary circular dichroism in linear optics.All of our work indicates that the classical molecular models are very effective to explain the second-harmonic generation circular dichroism of chiral molecular system.The classical molecular model theory can give us a clear physical picture and brings us very instructive information about the link between the molecular configuration and the nonlinear processes.     

Second-harmonic generation in Langmuir Blodgett waveguide overlays on single-mode optical fiber

Second-harmonic radiation has been obtained from Langmuir-Blodgett films of E-N -octadecyl-4-[2-(4-dibutylaminophenyl)ethenyl]quinolinium octadecylsulfate, deposited as a waveguide overlay upon optical fiber that is single mode at the pump wavelength (lambda=1064 nm) . A quadratic relationship between the pump power and second-harmonic intensity was observed.