Optimized sub-wavelength grating mirror design for mid-infrared wavelength range

Several designs of sub-wavelength grating mirrors adapted to mid-infrared operation are reported with several percents of tolerance for the grating fabrication. These designs have been automatically optimized by the use of a genetic-based algorithm to maximize a quality factor defined to meet the requirements of a VCSEL cavity mirror. These mirrors are devoted to integration in VCSEL operating near λ=2.3 μm, with a large bandwidth, very high reflectivity coefficient for transverse magnetic mode only, polarization selectivity and a thickness as low as 2 μm.     

一种具有低折射率的高对比度光栅反射镜的设计

设计并研究了一种工作于2 μm波段的GaSb基亚波长高对比度光栅反射镜,其具有低折射率光栅层结构。通过严格耦合波理论优化结构,以最大限度地满足VCSEL腔面反射镜对反射率带宽的要求。反射镜对2 μm波段的TM模式具有优良的反射效率,带宽与设计波长之比达15%（反射率R>99%）,在反射率R>99.9%的部分Δλ/λ₀>9.5%,带宽中心波长为2.003 μm,与此同时TE模的反射率不超过70.20%。该反射镜结构中几个参数的制作容差较大,且厚度低于1.1 μm,有利于在垂直腔面发射半导体激光器上的单片集成。     

Thermal analysis of high-index-contrast grating (HCG)-based VCSEL

A 3-D thermal analysis of 870 nm high-index-contrast grating (HCG)-based vertical cavity surface emitting laser (VCSEL) by using finite volume method (FVM) is presented in this paper. The HCG-based VCSEL is modeled by applying a steady-state 3-D heat dissipation model. Temperature distribution profile and thermal resistance (R_th) of the device are investigated by inserting the heat source value into the thermal simulation. Also, this analysis is performed for a conventional VCSEL operating at the same wavelength and under the same injected current as well as the same geometric sizes. The analysis shows that the maximum temperature inside the HCG-based VCSEL is lower than that inside the conventional VCSEL.     

基于亚波长光栅的VCSEL偏振控制研究

为了确定亚波长光栅在微电机械系统(MEMS)波长可调谐VCSEL不同位置(上DBR上表面、上DBR下表面以及内腔)中实现TE和TM偏振控制的光栅参数范围以及光栅在哪个位置时实现偏振控制最稳定,通过MATLAB建立MEMS波长可调VCSEL的模型,然后计算光栅在3种位置时上反射镜(包括空气隙和光栅)随光栅参数变化的反射率,以此来确定它们实现TE/TM稳定偏振的光栅参数范围(即高反射范围内的参数)。将各自的高反射所对应反射率减去相同光栅参数范围内TM/TE低反射对应的反射率,通过反射率差值确定光栅在哪种位置时MEMS波长可调谐VCSEL实现偏振是最稳定的。最后得出的结论是光栅在上DBR下表面几乎无法控制TM偏振,而将光栅放置于内腔中,无论是在TE偏振控制上还是TM偏振上都是最稳定的。在实现TE偏振稳定的参数范围内,TE的阈值增益比TM最小少10 cm~(-1);而在实现TM偏振稳定时,在TE偏振稳定的参数范围内,TE的阈值增益比TM最小少5 cm~(-1)。     

Surface texturing of Si, porous Si and TiO2 by laser ablation

Excimer laser ablation at 308 nm has been used to texture the surfaces of a variety of materials of interest for optoelectronic and biotechnological applications. Using a range of pre- and post-processing methods, we are able to produce nano-, micro- and meso-scale features over large areas rapidly in materials such as crystalline Si, porous silicon and TiO₂. Texturing of porous silicon leads to the growth of crystalline dendritic structures, which distinguishes them dramatically from the conical pillars formed from crystalline silicon. Regular arrays of Si microdots are formed by irradiating a Si surface pre-covered with a Cr thin film grating. Nano-crystalline porous TiO₂ films are easily ablated or compacted with laser irradiation. However, at low enough laser fluence, surface roughening without complete loss of porosity is possible.     

带前置光学系统的软X射线透射光栅光谱仪

软Ｘ射线检测是激光等离子体诊断中最复杂而又是最重要的一项工作。本文简要介绍了带有前置光学系统的软Ｘ射线大面积透射光栅光谱仪和用它获得的铝和铜靶激光等离子体的光谱图。     

氧化光栅型垂直腔面发射激光器的研究

通过分析矩形出光孔径和亚波长金属光栅结构,发现大孔径高功率垂直腔面发射激光器(VCSEL)的偏振控制的难点在于横模非常复杂。因此提出一种新型的氧化光栅型VCSEL结构,不仅能够很好地在有源区内引入各项异性的增益结构,并且最大的优势还在于能够完美地控制大孔径VCSEL的横模。通过有限元软件对器件有源区的电流分布进行了模拟,发现当光栅脊的宽度为1.8 μm时,载流子在光栅两端聚集的现象基本上可以消除,而且其电流密度分布差可以达到很高。     

High-speed vertical-cavity surface-emitting laser (VCSEL) absorption spectroscopy of ammonia (NH<Subscript>3</Subscript>) near 1.54 μm

A single-frequency VCSEL has been used for the first time for high-resolution spectroscopy near 1.5 μm. The incorporated buried-tunnel-junction technology enabled the realization of a long-wavelength InGaAlAs/InP VCSEL with low threshold current (0.925 mA), high output powers (0.576 mW) and low series resistance (60 Ω). The high-speed tuning capability of the long-wavelength VCSEL was investigated and used to conduct high-speed absorption spectroscopy. The peak tuning speed was measured to be 3.4 cm^-1/μs and a 4.5-cm^-1-wide NH₃ spectrum was recorded in 2 μs. The VCSEL was used to measure highly resolved low-pressure spectra for pressures ranging from 9.6 mbar to 1 bar. The measured Doppler-broadened linewidth of 0.02 cm^-1 agrees within 3% with the theoretical calculations. The availability and various advantages of 1.3–2-μm single-frequency VCSELs as compared to edge-emitting diode lasers, such as a large current tuning range even at very high tuning frequencies, and low production costs, should significantly expand the application fields for near-infrared laser gas sensors. Received: 17 July 2002 / Revised version: 4 December 2002 / Published online: 12 May 2003 RID="*" ID="*"Corresponding author. Fax: +43-1/58801-15999, E-mail: Gerhard@Totschnig.com     

Wave mixing in nominally undoped Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> at high light intensities

The intensity dependence of the photorefractive response of Sn₂P₂S₆ is studied for the Kr⁺-laser wavelength of 647 nm and pump-beam intensities of up to 10 W/cm². A considerable enhancement of the two-beam coupling gain factor with increasing intensity at a grating spacing of ≃1 μm is attributed to a light-induced increase of the effective trap density. The large gain reached at high intensities is applied for the build up of a double phase conjugate mirror with a sub-millisecond switch-on time.     

凹(平)面衍射光栅稳定共振腔的近似分析

本文从自洽的费涅耳衍射积分方程出发,利用费涅耳数近似趋于无穷,计算了凹(平)面锯齿形和截端锯齿形衍射光栅稳定共振腔的共振模特性。结果指出:当光栅槽很浅,满足光栅自准直条件,在一定的角度范围内,腔内的场振幅分布近似与光栅的闪耀角无关。垂直于光栅槽方向(x方向)的场分布由m阶厄米-高斯函数和微扰项(m+1阶和m-1阶厄米-高斯函数)表示。微扰项随光栅倾角的增大而增大。当微扰项可以忽略不计时,倾斜的光栅可以和垂直于光轴、曲率半径为Γ₁cos³θ(x方向)和Γ₁cosθ(y方向,平行于栅槽方向)的长条凹镜等效。文中给出了栅、镜面上的场分布、稳定性条件、频谱分布及输出场特性。 关键词：     

Design of Long-Wavelength Vertical-Cavity Surface-Emitting Lasers with Resonant Optical Pumping

An optically pumped long-wavelength vertical-cavity surface-emitting laser (VCSEL) with resonant optical pumping has been proposed. The proposed structure enables the dual-resonance of pump light (1300 nm band) and output light (1550 nm band) at the same time. It is shown that high pumping efficiency of ∼99% can be obtained by adjusting the top mirror reflectivity and the cavity length. This dual-resonance VCSEL (DR-VCSEL) may have great advantages of high efficiency pumping, low power consumption and can be fabricated by using conventional VCSEL fabrication techniques with reasonable fabrication tolerances.     

Theoretical calculation of turn-on delay time of VCSEL and effect of carriers recombination

It is known that the turn-on delay time, t_d, for semiconductor lasers depends on the functional form of the recombination rate. Previously, an analytic expression for t_d had been obtained, following simple approximations. In this paper, on the basis of the rate equations for quantum well vertical cavity surface emitting lasers (VCSEL), an explicit analytical expression for the turn-on delay of the VCSEL has also been deduced for the general case. The time evolution of the carrier density within the turn-on period of VCSEL has been derived for the case, where the Auger effect is considered as a term proportional to the cube of the carrier density.     

Analysis of anticipated performance of 650-nm GaInP/AlGaInP quantum-well GaAs-based VCSELs at elevated temperatures

The possibility of application of the 650-nm oxide-confined GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers (VCSELs) at elevated temperatures as sources of the carrier 650-nm wave in the fibre optical communication using POFs has been investigated with the aid of the comprehensive self-consistent model. An increase in the VCSEL threshold current at higher temperatures has been found to be mostly associated with both the carrier leakage from the valley of the Ga_0.43In_0.57P quantum-well material to the X-valley of the (Al_0.67Ga_0.33)_0.52In_0.48P barriers and the band-to-band absorption within the Ga_0.52In_0.48P layer of the band-gap comparable with the energy of emitted radiation. Nevertheless, the AlGaInP VCSELs exhibit encouraging thermal behaviour with the characteristic temperature T₀ equal to as much as 134 K for the active-region temperatures up to 357 K. For the 5-μm devices, the maximal achievable output has been determined to decrease from a quite high value of 1.0 mW for 293 K to 0.6 mW for 320 K and to still high 0.33 mW for 340 K. However, an efficient operation of the above VCSEL at elevated temperatures requires still some structure modifications leading to a reduction of both the above effects, the electron leakage from the valley and the band-to-band absorption within GaInP layers.     

单发实验测量软X射线多层膜反射镜反射特性

提出了一种单发实验测量软X射线波段多层膜反射镜反射特性的简易方法。实验采用激光等离子体软X射线源作为光源,用平焦场光栅谱仪分光,在光路中引入掠入射镜以消除高级次谱的影响,用软X光CCD记录,在一发激光打靶实验中,测量了设计中心波长为13.9 nm的Mo/Si多层膜反射镜的反射特性。     

Line Narrowing of a Tunable High Pressure CO2 Laser by Means of an Improved Non-Littrow Cavity

A model is reported to foresee ,for different mirror choices, the spectral properties of a high pressure, frequency tunable, CO₂ laser, operating with a non-Littrow grating mounting. The calculations show a larger frequency selectivity for not collimated plane cavities. The model is experimentally verified in a suitable high pressure laser. In particular narrowed linewidths less than 300MHz ( FWHM) are obtained.     

双波长垂直腔面发射激光器及特性研究

基于光子晶体技术在一维光子晶体带隙内引入缺陷态模式,并对激光器谐振腔内部电磁场分布和共振波长进行调制,从而将单一波长分裂为双波长输出.最终制备出了一种新的具有双波长光谱输出特性的垂直腔面发射激光器,缺陷层为Al_0.8Ga_0.2As材料,厚度为5λ/4.所得到的双波长输出光谱具有低吸收损耗、输出波长容易控制及同方向垂直输出特性.同时,通过调整一维光子晶体的折射率差和缺陷层厚度可以有效调谐双波长的间距及输出波段.所设计的双波长垂直腔面发射激光器结构同样 关键词： 垂直腔面发射激光器 光子带隙 双波长     

Rapidly tuning miniature TEA CO2 laser – rotating mirror and grating mechanism

In this research, directed toward using differential absorption lidar (DIAL) for measuring concentrations of pollutant gases, a device for rapidly tuning a transversely excited atmospheric-pressure (TEA) CO₂ laser is presented. It is shown that it is possible to utilize a rotating six-sided scanning mirror and a fixed diffraction grating to rapidly switch wavelength over randomly selected lasing transitions in the 9–11 μm region of the spectrum. The scanning mirror and an optical encoder are driven by a hysteresis synchronous motor at a speed of 1500 rpm. A surface-wire-corona preionization was utilized in a cavity. The laser system is highly automated with microprocessor-controlled laser line selection. Single-branch emission at two wavelengths with time interval ⩽10 ms has been obtained from a single cavity TEA CO₂ laser. An accurate line selection has been demonstrated in over 40 transitions at a pulse repetition frequency of up to 100 Hz. The laser energy at first-order couple output was up to 20 mJ per pulse and the pulse width is about 60 ns in an active volume of 36 cm³.     

光泵气体THz激光器用CO2泵浦源腔内光场模式

CO2泵浦源是光泵气体太赫兹激光器的核心器件之一,其性能直接关系到太赫兹激光器的工作稳定性。CO2泵浦源一般由闪耀光栅作为全反射尾镜,构成特殊的光栅腔实现波长的选支输出。采用传输矩阵的特征向量法对光栅谐振腔的腔内光场模式进行了理论分析与数值模拟,计算了光栅腔的一系列本征模式及相应的衍射损耗。结果表明光栅腔的腔内模式特性等效于一个平凹腔,而对于大菲涅尔数的光栅腔, Littrow波长的附近支线也可能具有衍射损耗较低的低阶模,可能优先于Littrow波长的高阶模起振,导致光栅腔的波长选择性降低。     

High power 808 nm vertical cavity surface emitting laser with multi-ring-shaped-aperture structure

The carrier conglomeration effect has been one of the main problems in developing electrically pumped high power vertical cavity surface emitting laser (VCSEL) with large aperture. We demonstrate a high power 808 nm VCSEL with multi-ring-shaped-aperture (MRSA) to weaken the carrier conglomeration effect. Compared with typical VCSEL with single large aperture (SLA), the 300-μm-diameter VCSEL with MRSA has more uniform near field and far field patterns. Moreover, MRSA laser exhibits maximal CW light output power 0.3 W which is about 3 times that of SLA laser. And the maximal wall-plug efficiency of 17.4% is achieved, higher than that of SLA laser by 10%.     

面向微型近红外光谱仪的高效扫描光栅微镜设计（英）

近年来,随着微光机电系统(MOEMS) 技术的快速发展,光谱仪朝着微型化、低成本、高性能方向发展。基于MOEMS技术制作的闪耀光栅可集成于扫描微镜,其作为近红外光谱仪的核心部件,可实现单管探测器代替昂贵的阵列式探测器,以降低近红外光谱仪成本与体积。设计了一种高性能扫描光栅微镜,以提高光谱仪的探测灵敏度。扫描微镜表面集成高衍射效率光栅,背面制作电磁驱动线圈。采用光学软件与有限元方法对器件参数进行优化。仿真结果表明:扫描光栅微镜谐振频率为484.38 Hz,最大扭转角度为4.55,在800~1800 nm工作波长范围内,整体动态衍射效率在54%以上且最大值达90%。