提高二极管激光阵列外腔锁相效率的实验研究

采用1/4 Talbot外腔实现宽条二极管激光阵列的锁相,在工作电流是35 A时,获得7.56 W的锁相输出功率,输出光束的远场图像是多瓣结构,锁相前后输出光的光谱宽度从2.0 nm压缩到0.2 nm。腔内插入焦距大约为5倍腔长的柱透镜,在相同电流下获得8.75 W的锁相输出功率,输出光的远场图像是多瓣结构,输出超模的数目有所减少,能量向中部集中,输出光的光谱宽度是0.2 nm。     

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     

Effect of mirror imperfections on phase-locked semiconductor laser arrays

Phase-locked semiconductor laser arrays normally have far-field-radiation patterns broader than that predicted by theory. We propose a possible broadening mechanism caused by steps on the cleaved mirror facets and by misalignment of the laser guide with respect to the laser facet. In the presence of facet steps, supermodes are coupled upon reflection. To satisfy the round-trip threshold condition, a laser cavity mode has to be an admixture of supermodes. This results in a broader far-field pattern (FFP) than that of a single supermode. Asymmetry of the pattern can also be predicted by this model. For an array of 10 lasers with center-to-center spacing of 8μm, the FWHM angle in the FFP of the lowest cavity mode is broadened by 1.5 and 2.5 folds, respectively, for random steps of average heights 17 and 90 Å between adjacent lasers. The broadening factor is 2.3 when a single 204 Å step exists between the third and the fourth laser. If the laser cavity is not aligned perpendicular to the facet, significant change in the FFP occurs only for a civity length not much shorter than the coupling length. A general consequence of the supermode mixing is the diminution of the threshold gain difference among the cavity modes, encouraging their simultaneous excitation.     

法布里－珀罗干涉仪外腔半导体激光器的选模和锁模特性研究

报道了法布里－珀罗干涉仪用作半导体激光器外腔的选模原理和选模及锁模实验。通过压电陶瓷调节Ｆ－Ｐ干涉仪的间距，实现了半导体激光器本身的静态及动态单纵模运转，在调制频率为６５６ＭＨｚ的情况下，获得了近变换极限的外腔锁模高斯形超短脉冲，脉宽为１３ｐｓ，时间带宽乘积为０．４６。最后讨论了Ｆ－Ｐ干涉仪对半导体激光器的模式特性的影响。     

Modeling of a linear array of hollow dielectric square waveguide CO2 lasers phase coupled by Talbot effect

The author develops the theory and numerically analyzes the capability of a linear array of hollow dielectric square waveguide CO ₂ lasers phase coupled by the Talbot effect. The author used a Rigrod-like analysis for computing the power supplied by the phased array versus the insertion losses induced by both the filling factor and the finite number of lasers. The result is compared to the one obtained with an identical device in incoherent mode. This makes it possible to define a coupling efficiency. An arrangement able to improve this coupling efficiency using a three-mirror cavity is presented     

Characteristics of single- and two-dimensional phase coupled arraysof vertical cavity surface emitting GaAs-AlGaAs lasers

Two-dimensional arrays of 3×3 vertical cavity surface emitting GaAs-AlGaAs lasers with 7-μm center spacing are described. The lasers were grown by molecular beam epitaxy and contain one grown GaAs-AlAs mirror under the active layer and a second, thermally deposited, high-reflectivity, SiO₂-Si mirror on top of the epitaxial layer. The array has a 295-K threshold of 90 mA, corresponding to 10 mA per laser. The individual lasers in the array have Gaussian beam profiles both spatially in the near field and angularly in the far field. When all the lasers in the array are operating in a coupled manner, the emission exhibits a lobed far-field pattern with a 5° separation in the direction parallel to the contact edge and a 2.5° separation perpendicular to the contact edge     

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.     

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     

In-phase emission from index-guided laser array up to 400 mW

Phased-array lasers with real-refractive-index waveguides have been grown by metalorganic chemical vapour deposition. The index guides are coupled via `Y?-type coupling regions and the laser array emits with all elements in phase. Powers of over 400 mW are obtained with no indication of a change in the far-field pattern.     

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     

Extremely small vertical far-field angle of InGaAs-AlGaAs quantum-well lasers with specially designed cladding structure

We report on a very small vertical far-field angle achieved by lasers with a specially designed structure. For an InGaAs-AlGaAs quantum-well laser with a 2.5-/spl mu/m-wide ridge waveguide, the far-field pattern has a vertical far-field angle of 13/spl deg/ and a lateral far-field angle of 8/spl deg/. Meanwhile, the threshold current remains acceptably low (/spl ap/36 mA for a 500-/spl mu/m-long cavity). The slope efficiency of the L-I characteristic is high (>0.9 W/A) compared to that of the conventional laser.     

Electroluminescence properties of a whispering-gallery-mode laser with coupled disk cavities

Whispering-gallery-mode (WGM) lasers (emission wavelength λ = 2.1–2.4 μm) with coupled disk cavities connected by a bridge are developed on the basis of a GaInAsSb/GaAlAsSb quantum-well nano-heterostructure and their emission spectra and optical far-field patterns are studied. Almost single-mode lasing in one spatial mode is observed in a wide range of supply currents. The emission wavelength grows with increasing current due to heating of the laser, and this phenomenon can be used in diode-laser spectroscopy. An assumption is made that the flux of generated emission can pass in lasers of this kind from one cavity to the other and back along the cavity-connecting bridge. It is found that strong narrowing of the laser emission pattern occurs with increasing current near the plane separating the coupled cavities.     

Mode locking of individual array modes of a gain-guidedsingle-quantum-well laser array with an external mirror

Mode locking of individual spatial lateral array modes of gain-guided GaAs single-quantum-well laser array with an external mirror is observed. The single-lobe fundamental array mode and several higher order array modes were individually selected by adjusting the external mirror. The array modes were characterized by the far-field patterns of the laser array. The corresponding spectrum consists a number of narrow longitudinal modes indicating that a single array mode was selected. These array modes were mode locked using a combination of feedback from the external mirror and sinusoidal RF modulation. The far-field patterns remained spatially constant when the RF modulation was applied. Autocorrelation pulsewidth measurements showed that the pulses have a Gaussian shape. Pulses as short as 70 ps were obtained for the lowest order array mode, where all the laser emitters were in phase, and increase with increasing array mode order     

阵列光束的偏振方向对其相干合成远场光强分布的影响

理论推导了线偏振光纤激光器阵列相干合成远场光强分布的表达式,详细研究了激光器的偏振方向对相干合成远场图样分布、中心主瓣的角宽度以及相干合成远场条纹可见度的影响.阵列光束偏振方向的不一致会使相干合成远场光强的峰值功率下降,中心主瓣的宽度增加,远场光强分布有本底漂移,远场条纹可见度下降.     

自成像列阵共振腔的分析——Ⅰ.Talbot共振腔

利用自成像效应进行半导体列阵激光器锁相是一种重要的外腔锁相技术,所构成的共振腔可分为Talbot腔和带相位补偿板的Lau腔。我们用Fox-Li方法计算了共振模式。本文给出了Talbot腔的计算结果和分析,表明同相和反相模的损耗随腔长变化存在临界点。     

1.3-μm AlGaInAs-InP buried-heterostructure lasers with modeprofile converter

AlGaInAs buried-heterostructure (BH) lasers with a mode profile converter (MPC) have been successfully fabricated for the first time. The thickness of the multiple-quantum-well (MQW) waveguide was vertically tapered by selective area growth (SAG). The threshold current I_th was 14.6 mA with a 600-μm-long cavity and a high-reflective-coated rear facet. The full-width at half-maximum of the far-field pattern in the perpendicular and horizontal directions were 9.2° and 12.6°, respectively. The optical coupling loss between lasers with MPC and a single-mode fiber was 3.0 dB when the distance between the laser and fiber was 20 μm     

Array mode analysis of two-dimension phased arrays of verticalcavity surface emitting lasers

The modal properties of two-dimensional phase-locked arrays of vertical cavity surface emitting (VCSE) lasers where the spatial coherency across the aperture comes from the evanescent coupling of the optical fields of the lasers were investigated. Typical two-dimensional arrays can be separated into three categories: the periodic array, the circular array and the centered polygonal array (or concentric circular array). It is shown that symmetry plays an important role in determining the array mode, and that the use of VCSE lasers gives a good longitudinal mode selection leading to dynamic single-mode operation. These results can be extended to a quantum box laser array to give better optical beam control     

Room-temperature operation of a transverse-distributed-feedback cavity laser

A new type of transverse-distributed-feedback cavity laser is proposed. A threshold current of a two-dimensional mode is 190 mA, and an output power of 30 mW is obtained at 1.5Ith. The far-field pattern is stable up to a measured current of 2.1Ith.     

Fourier-optical transverse mode selection in external-cavity broad-area lasers: experimental and numerical results

Broad-area lasers (BALs) with external Fourier-optical cavities with spatial filter for transverse mode selection have been studied experimentally and theoretically. The transverse mode structure of BALs is modeled using a three mirror cavity approach. The model accounts for gain saturation, carrier diffusion, and anti-guiding effects. Near- and far-field distributions are calculated and compared to experimental results. Transverse mode selection is achieved for BALs with a residual front facet reflectivity of 10% at low pump currents. For BALs having a very low front facet reflectivity of 0.001%, transverse modes can be selectively excited up to pump currents more than 200% above laser threshold. Calculations show that BALs having a 0.001%-antireflection coating with an external Fourier-optical cavity high above threshold can operate in a self-Q-switched-like mode with pulse durations of 2-4 ns and repetition rates of 100-200 MHz. Experimental results obtained with a hybrid integrated-optical external cavity for transverse mode selection are also presented.     

二极管激光阵列Talbot外腔锁相机理的实验研究

研究了二极管激光器阵列(DLA)独立单元的Talbot外腔锁相和多个单元的Talbot外腔锁相,验证了在大电流情况下单元内部可以实现Talbot外腔锁相,远场图样显示为高阶横模的锁定.多个单元的Talbot外腔锁相实验表明,随着发光单元个数的增加,DLA趋向于局部锁相.