条形半导体激光器光束质量因子M2的理论计算

通过一个二维半矢量模型求得纯折射率导引脊形波导和掩埋波导这两种常见平面条形半导体激光器波导结构的模式光场分布，现通过描述光束传播的非傍轴矢量二阶矩，通过平面波谱的方法获得激光器出射光束在横向和侧向上的束腰、远场发散角和M^2因子。讨论了波导结构参量变化对M^2因子的影响，并对两种波导结构光束的性质与波导参量的关系进行了比较。     

GRINSCH—SQW激光器波导特性的数值分析

采用折射率台阶近似法将梯度折射率分别限制异质结单量子阱(GRINSCH—SQW)激光器波导结构中的缓变折射率层离散成折射率近似为常数的亚层,从而推导出此波导的近似本征方程,并用数值计算求解出波导对于基模的等效折射率。在此基础上,通过计算波导中垂直于激光器结平面方向上的光强近场分布,计算出与激光器的阈值电流有密切关系的光学常数——激光器有源层的光限制因子P以及各种波导结构参数对P的影响,同时计算了激光器的远场图形。计算结果可用于GRINSCH-SQW激光器波导结构参数的优化设计。     

带有多孔二氧化硅间隔层的导模共振光栅实现染料激光器发射增强

导模共振光栅是一种典型的平面波导共振结构,可在光栅表面或波导层内形成较强的局域电场,能增强光与物质的相互作用.本文在导模共振结构的光栅层和基底层之间,引入低折射率的多孔二氧化硅间隔层,显著增强了局域电场与增益介质的接触度.结果表明,引入多孔二氧化硅后,共振产生的电场增强区域上移至激光染料层,增加了激光染料与电场的相互作用,实现了激光出射增强.本文基于时域有限差分法,对结构参数进行分析优化,研究了820 nm共振波长激发下的出射激光特性,得到了连续的激光出射,其能量阈值约为2.5 mJ/cm^2,线宽约为0.3 nm.本文提出的结构实现了对表面局域电场的有效调控,增强了激发光与增益介质的相互作用,不但可应用于激光器,还为其它发光器件的设计提供了参考.     

平面波导衍射特性分析

从电磁波的瑞利－索末菲标量衍射积分公式出发，利用罗兰圆结构特殊的光学性能，在平面坐标系中简化标量衍射积分公式，推导出横截面折射率阶跃分布的平面波导端口衍射场分布的计算公式，并导出常用的对称结构介质平面波导和金属平面波导端口衍射场的空间频谱，阐明平面波导端口衍射场就是驻波衍射场的本质。     

Ta2O5平面波导湿度传感器的研究

本文从应用的角度介绍平面波导传感器的概念及制备方法，在实验的基础上分析和讨论了Ｔａ２Ｏ５平面波导湿度传感器的原理，结构与特性测试方法，为开展集成光学平面波导传感器研究提供理论与技术依据。     

高亮度锥形半导体激光器

介绍了由双量子阱非对称波导结构外延片刻蚀成的带有脊形波导结构的锥形半导体激光器。该激光器有效抑制了p型区域对激光的影响,减小了半导体激光快轴方向的发散角,同时采用脊形结构和锥形结构的组合获得了高亮度激光。实验中,在电流7 A时获得了中心波长963 nm、连续功率4.026 W的激光输出。测得慢轴方向和快轴方向激光光束参数乘积分别为1.593 mm·mrad和0.668 mm·mrad。     

平板波导谐振腔的耦合损失和模式特征

相应于方波导或圆波导的三种低耦合损失的谐振腔结构，即平行平面、半共心、半共焦结构、计算了不同纵横比的平板波导内各种模式的耦合损失，讨论了平板波导激光器谐振腔的设计和模式特征。     

微纳光纤及其锁模激光应用

微纳光纤是一种直径接近或小于传输光波长的纤维波导,由于纤芯和包层折射率差较大,具有强光场约束、强倏逝场、低损耗、反常波导色散、表面均匀性好和机械性能高等特性。近年来,以纳米材料作为饱和吸收体的被动锁模激光器成为超短脉冲激光技术方向的研究热点。得益于微纳光纤的强光场约束能力及大比例倏逝场,纳米材料与微纳光纤的复合结构能显著增强光与物质的相互作用,进而降低该复合结构的饱和吸收阈值,为超短脉冲产生和非线性动力学等研究提供一个新颖而灵活的平台。同时,微纳光纤因具有反常波导色散、光谱滤波、饱和吸收和偏振敏感等特性,在激光器的色散调控、偏振锁模等方面获得应用。介绍了微纳光纤的制备和特性以及在锁模激光方面的典型应用和相关技术的最新进展,并就未来的发展方向进行了展望。     

大功率全固态激光数控加工机床

工业焊接切割使用的大功率激光器主要经历了CO．激光器、灯泵浦Nd：YAG固体激光器阶段,现在正向全固态激光器的应用方向发展。全固态激光器集半导体激光器和固体激光器的优势于一体,具有体积小、重量轻、效率高、性能稳定、可靠性好、寿命长、光束质量高等优点,近年来已成为激光学科的重点发展方向之一,大功率全固态激光器在工业加工、军事和科研等领域中有着十分重要的应用前景。     

折射率平面波导光栅耦合特性分析

利用波导系统等效网络分析法,分析了折射率平面波导光栅的耦合特性.计算了影响光栅输入输出耦合的重要参数——损耗系数α,并通过数值计算分析了平面波导光栅各参数对损耗系数的影响.     

Epitaxial Nd:YLF linear waveguide laser

We report laser operation in planar and linear Nd:YLF waveguide structures grown by liquid-phase epitaxy (LPE). We could reduce the relatively high threshold of 115-mW incident pump power observed for the planar waveguide to 8 mW in a ridge-type structure that we obtained by mechanical polishing and subsequent growth of a cladding layer. Substantial improvements seem possible with reduction of the losses caused by imperfect end-face reflection and scattering, as well as by use of techniques capable of producing smaller structures than the 40-mum-wide triangular ridge cross section that was obtained with polishing. Since the LPE technique is applicable to other activator ions as well, it might offer a route to development of low-threshold upconversion lasers.     

Formation of the transverse field structure in terahertz planar free-electron lasers

The formation of a transverse structure of the field in terahertz free-electron lasers with a two-mirror Bragg resonator based on the open planar waveguide is analyzed. It is shown that the combination of diffraction effects with radiation channeling effects produced by sleeve electron bunches ensures spatial coherence of the field structure in the relevant coordinate for high values of the Frenkel parameter. The diffraction loss in this case is small on the scale of the power of radiation passing through the mirrors.     

Numerical Analysis of Multilayer Waveguides Using Effective Refractive Index Method

With the help of the effective refractive index method we have numerically analyzed a multilayer planar waveguide structure and calculated the propagation constants, confinement factors, and transverse electric (TE) modes. A five-layer waveguide model has been provided to analyze the electro-magne tic wave propagation process. The analysis method has been applied to the 980 nm laser with active layer of GaInAs/GaInAsP strained quantum wells, GaInAsP confinement layers and GaInP cap layers. By changing the thickness of confinement layers, we obtained confinement factor as high as 95% with higher TE modes TE1 and TE2. The results are in good agreement with the experiment by A. Al-Muhanna et al. and give the new idea to enhance output power of semiconductor lasers. The analysis method can also be extended to any other slab multilayer waveguide structures, and the results are useful to the fabrication of optic-electronic devices.     

Comparative study of asymmetric versus symmetric planar slab dielectric optical waveguides

In this paper we have studied the asymmetric versus symmetric planar waveguide in terms of their usefulness in optical fiber communication systems. We have explored the thin waveguide versus thick waveguide first. Later on usefulness of asymmetric versus symmetric waveguide is carried out to target for WDM optical network application. All kinds of optical network components are fabricated on Si substrate with the point of view of their application. Here asymmetric planar structure may be more useful compared to symmetric waveguide in terms of their non-uniform power confinement properties. However, the symmetric waveguide structure may be more useful for their high power confinement properties. It is well known that the thin symmetric waveguide supports at least one mode. However the thick waveguide may support many even as well as odd modes. We study the power confinement properties for symmetric as well as asymmetric waveguide structure. We conclude that higher order modes show the nonlinear power variations. Mode field profile for various cases is discussed as well. Comparative study between asymmetric versus symmetric waveguide has a lot of significance in optical network area. It has been shown through analysis that in asymmetric waveguide, the power flows more through film region in the case of fundamental mode. Power confinement properties for asymmetric waveguide versus symmetric waveguide have been studied.     

Quasi-self-imaging planar waveguide lasers with high-power single-mode output

We describe high-power planar waveguide laser which can achieve single-mode output from a multi-mode structure. The planar waveguide is constructed with incomplete self-imaging properties, by which the coupling loss of each guided mode can be discriminated. Thermal lens effects are evaluated for single-mode operation of such high-power diode-pumped solid-state lasers.     

Planar waveguide lasers and structures created by laser ablation — an overview

The parameters of planar and channel waveguide lasers fabricated by different techniques are reviewed. Materials and properties of thin films used for creation of planar waveguide lasers are summarized. The parameters of active and passive planar waveguides created by the method of pulsed laser deposition and problems of laser deposition are described. The aspects of laser generation of planar waveguide lasers, resonators and channel waveguides are presented. The results of our experiments of laser deposition of thin Ti:sapphire layers and thin layers of Nd:YAG and Nd:YAP are briefly discussed. This work was supported by the grant of Czech Grant Agency No. 102/96/0429.     

Ti:sapphire rib channel waveguide fabricated by reactive ion etching of a planar waveguide

We report, to our knowledge, the first active channel waveguide in Ti:sapphire. We have created ∼1.4-μm high ribs in a ∼10-μm thick Ti:sapphire planar waveguide by reactive ion etching. Following excitation by an Ar-ion laser, the rib structure showed channel-waveguide fluorescence emission. The mode profiles and the beam-parameter values (M²) were measured. The coupling efficiency of fluorescence emission into a single-mode fiber was an order of magnitude higher than for fluorescence from unstructured planar regions of the waveguide. Such devices are of interest as low-threshold tunable lasers and as broadband light sources in low-coherence interferometry. Received: 22 December 2002 / Revised version: 30 March 2002 / Published online: 8 August 2002     

CO2 laser drives extreme ultraviolet nano-lithography — second life of mature laser technology

It was shown both theoretically and experimentally that nanosecond order laser pulses at 10.6 micron wavelength were superior for driving the Sn plasma extreme ultraviolet (EUV) source for nano-lithography for the reasons of higher conversion efficiency, lower production of debris and higher average power levels obtainable in CO₂ media without serious problems of beam distortions and nonlinear effects occurring in competing solid-state lasers at high intensities. The renewed interest in such pulse format, wavelength, repetition rates in excess of 50 kHz and average power levels in excess of 18 kiloWatt has sparked new opportunities for a matured multi-kiloWatt CO₂ laser technology. The power demand of EUV source could be only satisfied by a Master-Oscillator-Power-Amplifier system configuration, leading to a development of a new type of hybrid pulsed CO₂ laser employing a whole spectrum of CO₂ technology, such as fast flow systems and diffusion-cooled planar waveguide lasers, and relatively recent quantum cascade lasers. In this paper we review briefly the history of relevant pulsed CO₂ laser technology and the requirements for multi-kiloWatt CO₂ laser, intended for the laser-produced plasma EUV source, and present our recent advances, such as novel solid-state seeded master oscillator and efficient multi-pass amplifiers built on planar waveguide CO₂ lasers.     

Multi-layer cladding leaky planar waveguide for high-power applications

We design a multi-layer cladding large-core planar waveguide that supports a single guided mode. The waveguide works on the principle of higher-order mode discrimination. The cladding of the waveguide is formed by alternate low- and high- index regions, which helps leaking out of higher-order modes while retaining the fundamental mode over the entire length of the waveguide. The structure is analyzed by the transfer-matrix method and the leakage losses of the modes have been calculated. We show that a waveguide formed in silica with numerical aperture 0.24 and core width 10 μm can be designed to exhibit single-mode operation at 1550-nm wavelength. Such a structure should find applications in high-power planar waveguide lasers and amplifiers.     

An He-implanted optical planar waveguide in an Nd:YGG laser crystal preserving fluorescence properties

We report the formation of a planar waveguide in an Nd:YGG laser crystal by low-energy He-ion implantation at liquid nitrogen temperature (77 K). The optical properties are measured by the prism coupling and end-face coupling methods, the absorption properties the waveguide and Nd:YGG substrate are obtained. The fluorescence spectrums are investigated by confocal methods. The experimental results revealed that the planar waveguide preserved the absorption and fluorescence properties of the Nd:YGG laser crystal. Thus, the planar waveguide formed by the ion implantation method is a promising candidate in waveguide lasers.