部分端面抽运板条激光器腔镜倾斜问题研究

部分端面抽运的板条激光器是一种新型固体激光器．配合混合腔可以实现在大功率下保持高光束质量的激光振荡输出。谐振腔的腔镜倾斜是影响激光器输出特性的重要因素，快速傅里叶方法是一种快捷有效的计算方法，利用此方法模拟了腔镜倾斜对近场相位分布和远场光强分布的影响，并分析了光束质量的变化。理论分析表明，腔镜的小角度倾斜对近场相位影响较大，但对远场光强空间分布影响不大；随着倾斜角度不断增大，远场发散角和光束腰宽度也增大，光束质量虽然存在恶化的趋势，但光束质量因子肝值仍然较小，离轴非稳腔仍能保持高光束质量的输出。

新型板条激光器的离轴混合腔模场计算

报道了一种新型双板条离轴混合腔激光器。这种激光器结构通过改变传统的冷却方式和采用特殊的谐振腔设计，将使从第一块介质板条高温一侧出射的激光对称地进入另一块板条的低温一侧，从而可对由于温度分布不均匀造成的波面畸变进行一定程度的自校正，减少热效应的影响，可望提高激光器的输出功率和光束质量。利用快速傅里叶变换（FFT）对这种激光器的近场、远场以及相位等模场特性进行了数值计算。分析了波面畸变对输出光束质量的影响，并与常规双板条激光器进行了比较，结果表明这种新型双板条离轴混合腔激光器可以实现一定程度的波面畸变自补偿，

Propagation properties of off-axis Hermite-cosh-Gaussian beam combinations through a first-order optical system

Based on the Collins integral formula, the analytic expressions of propagation of the coherent and the incoherent off-axis Hermite-cosh-Gaussian (HChG) beam combinations with rectangular symmetry passing through a paraxial first-order optical system are derived, and corresponding numerical examples are given and analysed. The resulting beam quality is discussed in terms of power in the bucket (PIB). The study suggests that the resulting beam cannot keep the initial intensity shape during the propagation and the beam quality for coherent mode is not always better than that for incoherent mode. Reviewing the numerical simulations of Gaussian, Hermite-Gaussian (HG) and cosh Gaussian (ChG) beam combinations indicates that the Hermite polynomial exerts a chief influence on the irradiance profile of composite beam and far field power concentration.

填充因子对激光组束远场功率分布的影响

根据Collins积分公式对激光组束后的远场分布进行了理论分析和模拟计算，着重讨论了参与组柬激光的填充因子对组束后的远场分布的影响。

InnoSlab混合腔输出光束质量的理论研究

对InnoSlab Laser用混合腔的输出光束质量问题从热透镜效应和腔镜的不对准两个方面的影响进行理论分析,并从远场光强分布、远场发散角、光腰半径、光束质量因子M2值和桶中功率曲线等几个角度进行了讨论,特别是离轴非稳腔方向上腔镜倾斜对光束质量的影响,利用M2值和PIB曲线两个参数共同评价非稳腔的光束质量,对目前并无统一标准的非稳腔光束质量评价问题提供了有意义的参考.

Propagation of flat-topped beams

The propagation of flat-topped beams passing through paraxial ABCD optical system is investigated based on the propagation formulas of Gaussian beam. The focal shift of focused coherent flat-topped beam is also studied in detail. Analytical expressions of the M-2 factor and the far-field intensity distribution for flat-topped beams are derived on the basis of second-order moments. (C) 2007 Elsevier Ltd. All rights reserved.

Nonparaxial propagation of vectorial hollow Gaussian beams

Based on the vectorial Raleigh-Sommerfeld diffraction integral, the nonparaxial. propagation of vectorial hollow Gaussian beams (HGBs) in free space is studied. The far-field and paraxial cases can be treated as special cases of our general results. The typical numerical examples are given to illustrate our analytical results and comparisons between the different approximations present that the f parameter still plays an important role in determining the nonparaxiality of vectorial diffracted HGBs. (c) 2007 Optical Society of America.

A Single-Fundamental-Mode Photonic Crystal Vertical Cavity Surface Emitting Laser

Single-fundamental-mode photonic crystal (PhC) vertical cavity surface emitting lasers (VCSEL) are produced and their single-fundamental-mode performances are investigated and demonstrated. A two-dimensional PhC with single-point-defect structure is fabricated using UV photolithography and inductive coupled plasma reactive ion etching on the surface of the VCSEL's top distributed Bragg-reflector. The PhC VCSEL maintains single-fundamental-mode operating with output power 1.7 mW and threshold current 2.5 mA. The full width half maximum of the lasing spectrum is less than 0.1 nm, the far field divergence angle is less than 10 degrees and the side mode suppression ratio is over 35 dB. The device characteristics are analyzed based on the effective index model of the photonic crystal fiber. The experimental results agree well with the theoretical expectation.

Fabrication and Characterization of High Power InGaN Blue-Violet Lasers with an Array Structure

InGaN/GaN multi-quantum-well-structure laser diodes with an array structure are successfully fabricated on sapphire substrates. The laser diode consists of four emitter stripes which share common electrodes on one laser chip. An 800-mu m-long cavity is formed by cleaving the substrate along the < 1 (1) over bar 00 >. orientation using laser scriber. The threshold current and voltage of the laser array diode are 2A and 10.5 V, respectively. A light output peak power of 12W under pulsed current injection at room temperature is achieved. We simulate the electric properties of GaN based laser diode in a co-planar structure and the results show that minimizing the difference of distances between the different ridges and the n-electrode and increasing the electrical conductivity of the n-type GaN are two effective ways to improve the uniformity of carrier distribution in emitter stripes. Two pairs of emitters on a chip are arranged to be located near the two n-electrode pads on the left and right sides, and the four stripe emitters can laser together. The laser diode shows two sharp peaks of light output at 408 and 409 nm above the threshold current. The full widths at half maximum for the parallel and perpendicular far field patterns are 8 degrees and 32 degrees, respectively.

Planar refractive microlens arrays in indium phosphide and quartz substrates

Large-area concave refractive microlens arrays, or concave template structures, and then the non-refractive-index-gradient type of planar refractive microlens arrays in InP and quartz substrates, are fabricated utilizing the method consisting of conventional UV photolithography, thermal shaping of concave photoresist microlenses, etching with an argon ion beam of large diameter, and filling or growing optical medium structures onto the curved surfaces of preshaped concave templates. Several key conditions for fabricating concave and also planar microlenses are discussed in detail. The concave structures obtained are characterized by scanning electron microscope and surface profile measurements. The far-field optical characteristics of quartz/ZrO2 planar refractive microlens arrays have been acquired experimentally. (c) 2008 Society of Photo-Optical Instrumentation Engineers.

Continuous-wave operation of GaN based multi-quantum-well laser diode at room temperature

Room-temperature operation of cw GaN based multi-quantum-well laser diodes (LDs) is demonstrated. The LD structure is grown on a sapphire (0001) substrate by metalorganic chemical vapour deposition. A 2.5 mu m x 800 mu m ridge waveguide structure is fabricated. The electrical and optical characteristics of the laser diode under direct current injection at room temperature are investigated. The threshold current and voltage of the LD under cw operation are 110mA and 10.5V, respectively. Thermal induced series resistance decrease and emission wavelength red-shift are observed as the injection current is increased. The full width at half maximum for the parallel and perpendicular far field pattern (FFP) are 12 degrees and 32 degrees, respectively.

Monolithically integrated transceiver with novel Y-branch by bundle integrated waveguide for fibre optic gyroscope

A novel Y-branch based monolithic transceiver with a superluminescent diode and a waveguide photodiode (Y-SDL-PD) is designed and fabricated by the method of bundle integrated waveguide (BIG) as the scheme for monolithic integration and angled Y-branch as the passive bi-directional waveguide. The simulations of BIG and Y-branches show low losses and improved far-field patterns, based on the beam propagation method (BPM). The amplified spontaneous emission of the device is up to 10mW at 120mA with no threshold and saturation. Spectral characteristics of about 30 nm width and less than 1 dB modulation are achieved using the built-in anti-lasing ability of Y-branch. The beam divergence angles in horizontal and vertical directions are optimized to as small as 12 degrees x 8 degrees, resulting in good fibre coupling.

A mini-staged multi-stacked quantum cascade laser for improved optical and thermal performance

In this paper, a mini-staged multi-stacked quantum cascade laser structure with a designed wavelength of 4.7 mu m is presented. By introducing five 0.5 mu m thick high thermal conductivity InP interbuffer layers, the 60-stages active region core of the quantum cascade laser is divided into six equal parts. Based on simulation, this kind of quantum cascade laser with a 10 mu m ridge width gives nearly circular two-dimensional far-field distribution (FWHM = 32.8 degrees x 29 degrees) and good beam quality parameters M-2 = 1.32 x 1.31 in the fast axis (growth direction) and the slow axis (lateral direction). Due to the enhancement of lateral heat extraction through the interbuffer layers, compared to the conventional structure, a decrease of about 5-6% for the maximum temperature in the active region core of the mini-staged multi-stacked quantum cascade laser with indium-surrounded and gold-electroplated packaging profiles is obtained at all possible dissipated electrical power levels.

Mode Analysis for Equilateral-Triangle-Resonator Microlasers with Metal Confinement Layers

Mode characteristics are analyzed for electrically injected equilateral-triangle-resonator (ETR) semiconductor microlasers, which are laterally confined by insulating barrier SiO2 and electrode metals Ti-Au. For the ETR without metal layers, the totally confined mode field patterns are derived based on the reflection phase shifts, and the Q-factors are calculated from the far-field emission of the analytical near field distribution, which are agreement very well with the numerical results of the finite-difference time-domain (FDTD) simulation. The polarization dependence reflections for light rays incident on semiconductor-SiO2 -Ti-Au multi-layer structures are accounted in considering the confinement of TE and TM modes in the ETR with the metal layers. The reflectivity will greatly reduce with a Ti layer between SiO2 and Au for light rays with incident angle less than 30 especially for the TE mode, even the thickness of the Ti layer is only 10 nm. If the ETR is laterally confined by SiO2-Au layers without the Ti layer, the Fabry-Perot type modes with an incident angle of zero on one side of the ETR can also have high Q-factor. The FDTD simulation for the ETR confined by metal layers verifies the above analysis based on multi-layer reflections. The output spectra with mode intervals of whispering-gallery modes and Fabry-Perot type modes are observed from different ETR lasers with side length of 10 m, respectively.

Holographic fabricated photonic-crystal distributed-feedback quantum cascade laser with near-diffraction-limited beam quality

We demonstrate the fabrication and characterization of photonic-crystal distributed-feedback quantum cascade laser emitting at 4.7 mu m. The tilted rectangular-lattice PCDFB structure was defined using a multi-exposure of two-beam holographic lithography. The devices exhibit the near-diffraction-limited beam emission with the full width at half maximum of the far-field divergence angles about 4.5 degrees and 2.5 degrees for stripe widths of 55 mu m and 95 mu m, respectively. Single-mode emission with a side mode suppression ratio of approximate to 20 dB is achieved in the temperature range (80-210 K). The single-facet output power is above 1 W for a 95 mu m x 2.5 mm laser bar at 85 K in pulsed operation. (C) 2009 Optical Society of America