Paraxial-misalignment insensitive external-cavitysemiconductor-laser array emitting near-diffraction limited single-lobedbeam

We present a novel easy-to-align external cavity configuration for efficiently obtaining a near-diffraction limited single-lobed beam from gain-guided laser diode arrays. The external cavity has an external mirror (EM) in the image plane of the array. Two bulk-optics experimental setups are evaluated and a compact GRIN lens design is discussed. There are several advantages for the present geometry, including orders of magnitude lower misalignment-sensitivity and superior mode discrimination. Both experimental setups deliver near-diffraction limited single-lobed beams (of width ~0.8° at the rated output power of 100 mW of the array) in the entire current range. The light-current (L-I) characteristic is linear and kink-free and one of the setups shows higher efficiency than the free-running array. The broad-area laser (BAL) mode theory is discussed, introducing radiation losses to the analysis. Several aspects of amplification in laser arrays are theoretically explained, such as why the optimum angle of the far-field lobe is always greater than the tenth mode angle (for a uniform 10-stripe array). It is shown that the gain of the amplifying medium broadens the far-field profile. The width of the far-field lobe increases with gain and decreases with the lobe angle. An analytical expression for the broadened far-field profile of BAL modes is presented. The theory compares very well with the experiments     

角锥棱镜阵列谐振腔输出模式研究

为了研究角锥棱镜阵列谐振腔的输出特性,利用角锥棱镜阵列作为后腔镜,与平面镜构成角锥棱镜阵列谐振腔,模拟计算了角锥棱镜阵列谐振腔输出模式的近场及远场分布,理论分析了谐振腔的相干输出,实验获得了采用该腔型的钕玻璃激光器的输出模式的近场及远场分布.结果表明,模拟计算与实验得到的模式分布相吻合,近场光斑外形为六边形,与角锥棱镜...     

Influence of external mirror on modal behavior of twin-stripeindex-guided injection lasers

The coupled-mode theory of parallel waveguides is used to calculate the influence of an external mirror on the modal behavior of the AR-coated laser array. The case of twin-stripe index-guided injection lasers with separate contacts is treated in detail. It is shown that for asymmetrical current injection, the external cavity couples the laser's guided array modes and creates new laser-cavity modes with a better mode discrimination in favour of the one having a single far-field pattern. These results imply that multiple laser arrays might benefit from an additional external mirror     

Characterization of the array modes of high-power gain-guided GaAssingle-quantum-well laser arrays

The characteristics of gain-guided GaAs single-quantum-well laser arrays, using proton bombardment to confine the current flow to 11 stripes on 9-μm centers, are described. The longitudinal-mode spectrum, the spectrally resolved far-field, and the near-field of this laser array were studied experimentally up to three times threshold current. The laser arrays are found to emit at ~10 longitudinal modes corresponding to the Fabry-Perot modes of the laser. The longitudinal spectrum is current dependent. Near threshold current, the spectrum consists of a number of longitudinal modes where only the fundamental mode of the array laser. At larger current, each of the longitudinal modes is broadened and the spectrum of each longitudinal mode consists of many individual emission lines of the array modes. For each longitudinal mode, the lowest order array mode emits at the longest wavelength and the highest order array mode emits at the shortest wavelength. The wavelength separation between neighboring array modes increases with increasing mode order. Fourteen array modes are found to emit simultaneously at three times threshold current. The experimental results are in good agreement with direct array-mode analysis based on the finite-difference method     

Finite-aperture waveguide-laser resonators

A general theory of finite-aperture waveguide-laser resonators is developed which represents the external reflectors by matrices which couple linearly polarized waveguide modes having the same azimuthal symmetry. The theory allows the determination of resonator efficiency, resonator frequencies, and laser near- and far-field patterns. Computations of the coupling loss for the fundamental waveguide mode as a function of mirror curvature, separation, and aperture are in good agreement with recent infinite-aperture calculations in the limit of large apertures and indicate three low-loss configurations: 1) large radius of curvature mirrors close to the guide; 2) "large" radius of curvature mirrors centered at the guide entrance: and 3) generally smaller curvature mirrors separated by half their curvature from the guide entrance. The importance of higher order waveguide modes in determining laser output power and far-field patterns is demonstrated experimentally and compared to theoretical predictions. Design guidelines for the construction of high-efficiency CO2, CO, and He-Ne waveguide-laser resonators are summarized in tabular form.     

列阵射频CO2激光器研制

本文介绍一种三列阵射频CO2激光器。采用藕合隙技术,获得相干光输出功率35W,效率约10%。测试了光斑远近场分布。     

A coherent all-solid-state laser array using the Talbot effect in athree-mirror cavity

Lateral mode coupling in a diode-pumped Nd:YAG microchip laser array is demonstrated with a Talbot cavity for the first time. The relatively low laser gains of solid-state lasers compared with diode lasers and CO₂ lasers, to which the Talbot cavity has already been applied successfully, are solved by employing a novel auxiliary Talbot cavity configuration. A brighter twin-peak far-field pattern indicating an out-of-phase array mode, whose spot is 9.3 times smaller than that obtained by incoherent superposition of the individual microchip laser outputs, is obtained from the phase-locked microchip laser array with a mode-selecting slit. Without the mode-selecting slit, a far-field pattern with a single narrow peak is obtained, showing that the array is locked in an in-phase mode, presumably because of multiple reflections in the auxiliary Talbot cavity     

增益导引(1×10)列阵波导CO_2激光器的实验研究

1 引言 列阵波导激光器的发展旨在提高激光功率的同时使器件的几何尺寸更加紧凑。以往的实验表明,空心脊波导结构在三列阵以上时便难以获得波导间相位的完全锁定,而交叉波导结构除外加相移波片外,也只能获得反对称模输出。 本文报告一种新结构的列阵波导CO_2激光器。其基本思想与增益导引半导体激光器列阵是一样的,即在波导中通过空间上为周期分布的增益区来获得列阵激光束,由相邻光束间辐射场的耦合来实现相位的同步锁定。     

基于激光相控阵原理的相位调制器半波电压测量方法

半波电压是电光相位调制器的一个重要指标, 针对现有半波电压测量方法存在的测量误差大、测量装置复杂等问题, 提出了基于激光相控阵光束扫描原理的半波电压测量方法.通过理论分析, 得到了远场主光束的偏移量和相位调制器半波电压的关系表达式.搭建了12 全光纤激光相控阵光路, 对铌酸锂波导相位调制器的半波电压进行了实验测量, 改变相位调制器的加载电压, 记录多幅远场光强分布图, 通过求平均值减小测量误差, 而且根据远场光强分布的变化得到了相位调制特性曲线.结果表明, 该方法测量装置简单, 不仅可以精确地测量半波电压, 还可以对相位调制线性度进行分析, 具有重要的工程应用价值.     

Coupled mode analysis of wavefront properties of phased array diode lasers

A coupled mode analysis of phased array diode lasers is used to calculate the far-field wavefront properties of the array modes. It has been found that phase variation across a far-field lobe of the array is less than that of the single emitter.     

Supermodes of hermite tapered arrays of vertical-cavitysemiconductor lasers

Two-dimensional arrays of vertical-cavity semiconductor lasers were prepared by mirror patterning. The size of the laser elements of the array was tapered according to the Hermite polynomial zeros, in order to achieve a multilobed far-field pattern, e.g., for applications as an array illuminator. Injecting short current pulses (~100 ns) to the N×N Hermite tapered vertical-cavity semiconductor laser array resulted in the lasing of anti-phase supermodes, similar to supermodes of uniform size but (N+2)×(N+2) laser arrays. Excitation by a long pulse resulted in a supermode localized on the larger elements of the array-exhibiting the desired multilobed far-field intensity pattern     

Array-mode far-field patterns for phase-locked diode-laser array: Coupled-mode theory versus simple diffraction theory

A simple, closed-form expression is derived for the far-field patterns corresponding to the modes of a phase-locked array ofNidentical elements. That allows a comparison between the correct array-mode far-field patterns (i.e., coupled-mode theory) and the heuristic, diffraction-grating-like far-field patterns generated by using simple diffraction theory. The correct diffraction-limited lobewidth is determined as a function of array-element number.     

Output coupling for closely confined Pb1-xSnxTe double-heterostructure lasers

The output coupling of an idealized, symmetric model of a double-heterostructure (DH) laser is analyzed theoretically using parameters suitable to Pb1-xSnxTe. For the TEOmode incident at the laser mirror and for thin optical guiding regions such that only the TEO, TE1, TMO, and TM1modes may propagate, an exact formulation of the coupling problem is obtained including mode coupling at the mirror into the continuum of unguided radiation modes. Using this formulation, the power reflection and transmission coefficients, the fraction of incident power coupled into the radiation modes, the mirror illumination, and the far-field pattern are calculated for typical parameters. Significant mode coupling can occur, limiting the maximum external efficiency of such lasers. This and other potentially undesirable characteristics resulting from close optical confinement, such as large output beam divergence, must be considered in design criteria for DH structures in this alloy system.     

Y-Junction semiconductor laser arrays: Part I--Theory

A general formulation for theY-junction semiconductor laser array is developed and analytic solutions are obtained for the important special case of identical waveguides. Modal thresholds, resonances, near-field, and far-field patterns are derived for the array modes. We show that the minimum threshold mode has identical modal intensities (except in the outermost waveguides) and the modal amplitudes are all in-phase. Thus the dominant mode radiates in a centered, narrow, single-lobe beam. Because the injected charges are utilized uniformly and efficiently, the mode is predicted to remain stable above threshold. All other array modes are shown to resonate at the same wavelength as the dominant mode, hut at increased thresholds.     

射频激励增益波导CO2激光器的光强分布

提出了一种新的射频(RF)激励增益波导阵列CO2激光器技术。为了提高输出激光光束质量,增强多个波导通道之间模式的耦合,通过在上电极刻上等距离的凹槽,形成一个个并列的子电极,使增益在电极横向具有周期分布特征。同时使用表面刻有周期性凹槽的相移全反射镜,实现了远场光束的极强相干叠加。研究了其近场和远场的光强分布情况。在气压为10.0 kPa,10.7 kPa的情况下,近场为长20 mm的若干个尖峰分布,远场为中心压窄的极锐尖峰。随着时间变化,只有光强峰值变化,相对强度分布保持不变。     

Two-segment cavity theory for mode selection in semiconductor lasers

A simple three-mirror composite laser cavity is analyzed and optimum structures proposed in terms of the position of the central reflector and the value of its reflectivity in order to give single longitudinal mode operation. Two optimum structures are discussed, the first corresponding to relatively long cavities where a large period in the gain modulation is required in order to avoid a jump to the next mode with a high effective reflectivity, usually in a second mode group (as defined by a neighboring period of the gain modulation). The second corresponds to shorter lasers where jumps to neighboring modes should be avoided, since the spectral gain variation prevents jumps to other mode groups. The effects of mode discrimination due to external feedback have been analyzed and minimum values of reflectivity for the third mirror derived in order to preserve the internal mode selectivity.     

Far-field distribution of semiconductor phase-locked arrays with multiple contacts

Experimental results of far-field patterns of semiconductor laser arrays with multiple contacts are reported. It is found that, by tailoring the distribution of the currents through the array elements, narrow single-lobe patterns?which are more useful in most applications?can be obtained from arrays that usually operate in a double-lobe mode. A diffraction-limited 1.8°-wide far-field pattern was obtained from a three-element array.     

Single-mode characteristics of short coupled-cavity semiconductor lasers

The characteristics of single-longitudinal-mode selection in short coupled-cavity (SCC) semiconductor lasers with a plane reflector are analyzed theoretically. It is found that the power ratio of the main mode to other side modes can be increased significantly by reducing the reflectivity of a laser diode facet adjacent to the external mirror. Based on the theoretical results, a new type of SCC laser is developed; single-longitudinal-mode output with 35-40 dB side mode suppression ratio is obtained under CW and 150 MHz modulation conditions.     

Focused phased array measurements

Measurements describing the patterns of a linear phased array antenna which has been electronically focused to a point in the Fresnel region, located a few aperture widths distance from the array face are given. The measurements were taken inside a building with no effort made to reduce extraneous reflections. A comparison of the results with patterns taken on a conventional far-field range reveals that the estimated measurement accuracy of the level of the first few sidelobes is on the order ofpm1dB. The technique provides a good performance monitor check, is easily implemented, permits an indoor measurement, and offers the advantage of simplicity over far-field measurements.