Dichroic mirror embedded in a submicrometer waveguide for enhanced resonant nonlinear optical devices

We report the design, fabrication and characterization of novel dichroic mirrors embedded in a tightly confining AlGaAs/Al(x)O(y) waveguide. Reflection at the first-harmonic wavelength as high as 93% is achieved, while high transmission is maintained at the second-harmonic wavelength. The measured cavity spectrum is in excellent agreement with finite-difference time-domain simulations. Such a mirror is essential for achieving resonant enhancement of second-harmonic generation.     

Enhanced second-harmonic generation in AlGaAs/AlxOy tightly confining waveguides and resonant cavities

We demonstrate second-harmonic generation (SHG) from sub-micrometer-sized AlGaAs/AlxOy artificially birefringent waveguides. The normalized conversion efficiency is the highest ever reported. We further enhanced the SHG using a waveguide-embedded cavity formed by dichroic mirrors. Resonant enhancements as high as approximately 10x were observed. Such devices could be potentially used as highly efficient, ultracompact frequency converters in integrated photonic circuits.     

Large second-harmonic generation at 1.55 μmin oxidized AlGaAs waveguides

We report on CW second-harmonic generation in selectively oxidized AlGaAs multilayer waveguides. Frequency doubling of a 1.55 μm pump is observed with 2.8% W(-1) conversion efficiency and a maximum second-harmonic power around 0.3 mW. This is the strongest second-harmonic generation ever reported in semiconductor waveguides and an encouraging result toward integrated spontaneous parametric downconversion in the telecom range.     

Quadratic phase matching in slot waveguides

We analyze phase matching with reference to frequency doubling in nanosized quadratic waveguides encompassing form birefringence and supporting cross-polarized fundamental and second-harmonic modes. In an AlGaAs rod with an air void, we show that phase-matched second-harmonic generation could be achieved in a wide spectral range employing state-of-the-art nanotechnology.     

双Lloyd镜数字全息显微测量术

提出了一种双Lloyd镜数字全息显微测量技术.其基本思想是将Lloyd镜的共光束自干涉特性与双波长光学相位解包裹方法相结合,使用两个Lloyd镜调节参考光与物光夹角以形成共光束自干涉,从而获得一张双波长复合全息图,再通过角谱法再现得到每个波长对应的包裹相位,利用两波长的相位差求得解包裹后的相位图和三维高度分布图.采用532和632 nm两波长记录全息图,通过数值再现重构被测物体的振幅和相位信息.与标定值相比,实验值的误差小于5%,证明了该方法的有效性.     

Enhanced second-harmonic generation from planar photonic crystals

Strongly enhanced second-harmonic generation is observed from a two-dimensional square lattice GaAs/AlGaAs photonic crystal waveguide when the fundamental beam, the second-harmonic beam, or both beams resonantly couple to a leaky eigenmode. P-polarized second-harmonic spectra are obtained for s-polarized, 150-fs pump pulses that are tuned from 5000 to 5600 cm(-1) and directed along the gamma-chi direction of the crystal for various angles of incidence. Compared with off-resonant conditions, enhancements of >1200x in the second-harmonic conversion are observed for resonant coupling of both the fundamental and the second-harmonic fields to leaky eigenmnodes. The angular and spectral positions of the peaks are in good agreement with simulations.     

Enhanced Second-Harmonic Generation with Structured Light in AlGaAs Nanoparticles Governed by Magnetic Response

JETP Letters - We employ structured light for the second-harmonic generation from subwavelength AlGaAs nanoparticles that support both electric and magnetic multipolar Mie resonances. The vectorial...     

Simultaneous dual-wavelength Q-switched Nd:YAG laser operating at 1.06 μm and 946 nm

Considering the reabsorption loss of the quasi-three level system and the unsaturable loss of the saturable absorber, we obtained the operating condition of a diode-pumped simultaneous dual-wavelength Q-switched Nd:YAG laser operating at 1.06 μm and 946 nm. The dual-wavelength pulsed laser was realized successfully through adaptive coating design of the cavity mirrors. As much as 1.6 W total average output power of the dual-wavelength at 1.06 μm and 946 nm was achieved at the incident pump power of 14.2 W with an optical conversion efficiency of 11.3%.     

Oscillation conditions of cw simultaneous dual-wavelength Nd：YAG laser for transitions 4F3／2-4I9／2 and 4F3／2-4I11／2

The operating condition of a cw simultaneous dual-wavelength Nd:YAG laser for both {}^4F_{3/2}-{}^4I_{9/2} (quasi-three-level system) and {}^4F_{3/2}-{}^4I_{11/2}(four-level system) transitions is studied. According to this condition, the cw simultaneous dual-wavelength at 1.06μm and 946 nm in Nd:YAG crystal has been realized experimentally through an adaptive coating design of the cavity mirrors. A total power output of 2.5W of the dual-wavelength at 946nm and 1.06μm has been achieved with an optical conversion efficiency 14.3%. The experimental results are in good agreement with the theoretical analysis.     

High-quality lowest-loss-mode lasing in GaAs quasi-stadium laser diodes having unstable resonators

We obtained high-quality lowest-loss-mode lasing in quasi-stadium laser diodes having unstable resonators that consisted of two curved end mirrors and two straight sidewall mirrors. The laser diodes were fabricated by applying a reactive ion etching technique to a metal-organic chemical-vapor deposition-grown graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs structure. The electrode contact area of the laser diodes was formed along unstable periodic orbits, along which the optical beams are localized. Highly directional fan-out beams corresponding to the numerically obtained lowest loss mode were emitted from the end mirrors under CW operation at room temperature.     

Interface magnetization reversal and anisotropy in Fe/AlGaAs(001)

The reversal process of the Fe interface layer magnetization in Fe/AlGaAs heterostructures is measured directly using magnetization-induced second-harmonic generation, and is compared with the reversal of the bulk magnetization as obtained from magneto-optic Kerr effect. The switching characteristics are distinctly different due to interface-derived anisotropy--single step switching occurs at the interface layer, while two-jump switching occurs in the bulk Fe for the magnetic field orientations employed. The angle between the interface and bulk magnetization may be as large as 40-85 degrees. Such interface switching will dominate the behavior of nanoscale structures.     

Quasi-stadium laser diodes with an unstable resonator condition

We have observed lasing in a complicated eigenmode of a quasi-stadium laser diode with an unstable resonator consisting of two curved end mirrors obeying an unstable resonator condition and two straight sidewall mirrors. The laser was fabricated by application of a reactive-ion-etching technique to a molecular beam epitaxy-grown graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs structure. The far-field pattern shows that the lasing mode corresponds to the complicated lowest-loss mode obtained numerically by an extended Fox-Li method.     

Generation of vacuum-ultraviolet light by an optically contacted,prism-coupled KBe2BO3F2 crystal

We have demonstrated the second harmonic of a frequency-tripled Nd:YVO4 laser with 2.5-mW quasi-cw output by using an optically contacted, prism-coupled KBe2BO3F2 crystal. We also achieved the second harmonic with a frequency-doubled single-mode Ti:sapphire laser at 172.5 nm and sum-frequency mixing with a dual-wavelength Ti:sapphire laser at 163.3 nm. These wavelengths are to our knowledge the shortest obtained by use of nonlinear crystals for second-harmonic generation and sum-frequency mixing, respectively.     

Large-area broadband saturable Bragg reflectors by use of oxidized AlAs

Broadband saturable Bragg reflectors (SBRs) are designed and fabricated by monolithic integration of semiconductor saturable absorbers with broadband Bragg mirrors. The wet oxidation of AlAs creates low-index AlxOy layers for broadband, high-index-contrast AlGaAs/AlxOy or InGaAlP/AlxOy mirrors. SBR mirror designs indicate greater than 99% reflectivity over bandwidths of 294, 466, and 563 nm for center wavelengths of 800, 1300, and 1550 nm, respectively. Highly strained and unstrained absorbers are stably integrated with the oxidized mirrors. Large-scale lateral oxidation techniques permit the fabrication of SBRs with diameters of 500 microm. Large-area, broadband SBRs are used to self-start and mode lock a variety of laser systems at wavelengths from 800 to 1550 nm.     

31%-efficient blue second-harmonic generation in a periodically poled MgO:LiNbO3 waveguide by frequency doubling of an AlGaAs laser diode

We present a method of controlling the shape of the domain-inverted structure in an off-cut MgO:LiNbO(3) crystal by utilizing a two-dimensional high-voltage application. With this technique a periodically domain-inverted structure with a period of 3.2mum and a thickness of 2.0mum was fabricated over a 10-mm interaction length. This structure has made possible sufficient overlaps between propagation modes and domain inversion in the waveguide. Using this structure, we demonstrated cw blue second-harmonic generation of 17.3 mW of power at a wavelength of 426 nm with single-pass 55-mW cw AlGaAs laser diode input, which corresponded to 31% power-conversion efficiency.     

Second-harmonic generation in three-well and bound-to-continuum GaAs-based quantum-cascade lasers

We present efficient second-harmonic generation in state of the art GaAs-based quantum-cascade lasers with nonlinear output powers up to 100 μW. The nonlinear output was significantly improved by applying an AlGaAs waveguide structure, which guides both, the fundamental and nonlinear light. We further show the influence of the doping in the active region on the nonlinear light generation by comparing two similar structures with different doping levels. PACS 42.55.Px; 42.65.Ky; 81.05.Ea     

Second-harmonic generation in asymmetric quantum dots in the presence of a static magnetic field

The second-harmonic generation(SHG) coefficient in an asymmetric quantum dot(QD) with a static magnetic field is theoretically investigated.Within the framework of the effective-mass approximation,we obtain the confined wave functions and energies of electrons in the QD.We also obtain the SHG coefficient by the compact-density-matrix approach and the iterative method.The numerical results for the typical GaAs/AlGaAs QD show that the SHG coefficient depends strongly on the magnitude of magnetic field,parameters of the asymmetric potential and the radius of the QD.The resonant peak shifts with the magnetic field or the radius of the QD changing.     

Laser-excited fluorescence of perylene by using self-induced second-harmonic and sum-frequency radiation emanating from high-power AlGaAs double hetero-type diodes

High-power (12 W) pulse-operated AlGaAs double-heterostructure lasers with a large thickness of the active layer (1.5 µm) are able to produce internal second-harmonic and sum-frequency generation with a peak power of 10 mW. The corresponding portion of the electroluminescence spectra has a maximum at 405 nm. Clearly resolved mode structures of the fundamental and harmonic radiation are analysed in detail. Particular transverse modes exhibit different conversion efficiencies. Violet resonances without modal precursors in the infrared spectrum make a marked contribution to the light intensity. The harmonic signal serves as an excitation source in photoluminescence studies. A technique of single-photon counting is applied in order to perform spectral measurements under weak-intensity levels. Bright fluorescence spectra of saturated solution of perylene ino-xylene are presented. The spectrum obtained when the solution is illuminated with a gas discharge lamp shows no differences with respect to the positions of the intensity peaks. This allows us to suggest that AlGaAs high-power lasers can be used as convenient excitation sources in photophysics, in particular in time-resolved experiments.     

Phase correction in double-pass quasi-phase-matched second-harmonic generation with a wedged crystal

Compensation for dispersive elements is necessary for efficient multiple-pass and intracavity nonlinear frequency-conversion devices. We describe the use of a wedged quasi-phase-matched crystal to compensate for the phase shifts introduced by mirrors in such devices, taking advantage of the periodic variation in the relative phases of the interacting waves in a quasi-phase-matching grating. A representative double-pass second-harmonic generation experiment with a 5-cm -long periodically poled lithium niobate crystal showed the expected conversion efficiency enhancement.     

The second-harmonic generation in parabolic quantum dots in the presence of electric and magnetic fields

The second-harmonic generation (SHG) coefficient for parabolic quantum dots (QDs) subject to applied electric and magnetic fields is theoretically investigated, within the framework of the compact-density-matrix approach and an iterative method. Numerical results are presented for typical GaAs/AlGaAs parabolic QDs. These results show that the radius of QD and the magnitude of electric and magnetic fields have a great influence on the SHG coefficient. And the peak shifts to the aspect of high energy when considering the influence of electric and magnetic fields. Moreover, the SHG coefficient also depends sensitively on the relaxation rate of the spherical QD system.