Characteristics of Gain-Guided Laser Diodes with Cylindrical-Mirror Cavity

We have developed highly reliable etched-mirror laser diodes using a dry etching method. The lasers without facet-coating have been operating stably over 2500 h under automatic-power control (APC) at a power of 3 mW/facet at 50°C. The gain-guided laser diodes with a cylindrical-mirror cavity (CMC) have coaxial mirrors and a fan-shaped stripe structure. By decreasing the curvature radius of the inner facet or increasing the stripe width of the inner facet, the beam waist parallel to the junction plane can be moved outside of the laser diode, while the beam waist perpendicular to the junction plane stops at the mirror facet. A particular CMC laser has a low astigmatism of 4.1 μm and a low relative intensity of noise (RIN) less than –134 dB/Hz at 4 mW under 0–1% optical feedback without high frequency current superposition.     

大光腔小垂直发散角InGaAs/GaAs/AlGaAs半导体激光器

提出并实现了新型隧道再生耦合大光腔半导体激光器，近场光斑宽度达到1μm，较普通半导体激光器提高了一个数量级，有效地解决了普通半导体激光器由于发光面积狭窄而导致的端面灾变性毁坏和垂直发散角大的问题. 采用低压金属有机物化学气相沉积方法生长了以C和Si分别作为掺杂剂的AlGaAs隧道结、GaAs/InGaAs应变量子阱有源区和新型半导体激光器外延结构，并制备出器件，其垂直发散角为20°，阈值电流密度为277A/cm2，斜率效率在未镀膜时达到0.80W/A. 关键词： 半导体激光器 大光腔 隧道再生     

Fourier transform method for self-mixing interference signal analysis

Self-mixing interferometry (SMI) has been used to measure the distance and displacement. Although the principle of self-mixing interference is different conventional interference, we concluded that FFT analysis technique could also be used to detect the signal phase and increase the measurement precision of self-mixing interferometry.First the SMI signal is obtained by feeding the light from the target to cavity of laser diode, then it is pre-processed by an analog subtraction circuit to remove the overlapped output intensity due to the injection current modulation. Finally, SMI signal is analyzed by FFT phase detection method. Theoretical analysis and simulation calculations are presented. Experimentally, displacement of a PZT-driven target was measured with a precision of λ/50.     

Characteristics of Multi-Beam Module Using Waveguides for Laser Scanning Optical Systems

A multi-beam module using optical waveguides has been studied for a laser scanning optical system. Laser diodes with a wavelength of 780 nm are assembled on a silicon substrate. The beams emitted from the laser diodes are directly coupled into waveguides. This multi-beam module is assembled on a metal substrate with a photodiode. The photodiode controls the power of each laser diode on the silicon substrate. The multi-beam module is able to increase the output speed of high-density image printings, and the speed for high-speed color printings. We have developed the four-beam module with beam divergence angles of 11 degrees and spatial beam interval of 24 μm. Additional heat sink and optimizing tip-bonding between the laser diode and solder pad on the silicon substrate is useful to stabilize laser power against rising temperature.     

Output characteristics of right angle cone mirror cavity laser

The anti-misalignment stability and output characteristics of the right angle cone cavity laser are experimentally studied. When the misalignment angle of the cone mirror turns to 46.8 minutes, the single-pulse output energy of the plano-cone cavity laser decreases 24% and the near-field beam patterns have little change; as for the beam directional stability, when the measuring place stands 3.12 m in front of the output mirror, the near-field beam patterns of the plano-cone laser are located at the primary places until the misalignment angle of the cone mirror turns to 18 minutes. These results show that the plano-cone cavity laser has better performances in comparison with the plano-concave cavity laser. The analytical results of the mode instrument are also obtained, which show that the near-field beam intensity distribution of the plano-cone mirror cavity laser is near to the plane wave.     

A travelling-wave beam deflector cleave-coupled to a diode laser

A new technique for scanning a diode laser beam is introduced where the beam is deflected in a current-injection-type travelling-wave beam deflector integrated with a diode laser. The deflector, which is formed outside the laser cavity, is cleave-coupled to the cavity. An anti-reflection coating on the deflector output facet suppresses the light returning to the laser. As a result, very smooth deflection of the radiation peak with low background intensity is realized in this device, while retaining high efficiency and low threshold current.     

自锁定半导体激光器中强度压缩及位相噪声的减小

采用外部F-P腔自锁定单模量子阱半导体激光器，观察到强度噪声的压缩现象，并同时大幅度降低了位相起伏.在35MHz附近观察到19.3%的强度压缩，对应激光输出的压缩度为37.8%，在9kHz-100MHz范围内观察到约3个数量级的位相噪声降低.获得了近最小测不准态. 关键词：     

Laser diode beam shaping by optical interference

We recently proposed a novel beam shaping technique that employs Lloyd’s mirror interference. In this study, we apply this technique to three commercial laser diodes: laser diodes used for optical pumping of solid-state lasers, for laser beam printers, and for laser displays. The elliptical output beams from these laser diodes could be transformed into nearly circular beams by inserting a mirror-polished GaAs substrate below the active layer of each laser diode and adjusting its height. The experimentally observed far-field patterns were predicted fairly well by numerical calculations based on Huygens’ integral. We confirmed that our beam shaping technique is applicable to laser diodes with various wavelengths and vertical beam divergence angles. We also describe the monolithic configuration of the beam shaping system, which can be fabricated by dry etching.     

Optimal design for a diode-pumped high-power high-efficiency high-beam-quality laser

We have demonstrated and analyzed a high-power high-efficiency high-beam-quality continuous-wave (cw) Yb:YAG laser, which is directly pumped into the upper lasing level by a fiber-coupled laser diode with a center wavelength of 969 nm. To achieve high efficiency and high beam quality simultaneously, we carried out a series of comparing experiments by changing the laser-medium length and pump-beam waist radius. From the cw Yb:YAG laser with a 5.0-at.%-Yb³⁺-doped and 5-mm-long crystal, an output power of 19.0 W has been obtained for a pump-beam waist radius of 138 μm. The maximum slope efficiency and optical-to-optical conversion efficiency are 78.9% and 55.3%, respectively. The M² factors of the laser beam are 1.33 in the vertical direction and 1.82 in the horizontal direction.     

Efficient 1.8 μm KTiOPO4 optical parametric oscillator pumped within an Nd:YAG/SrWO4 Raman laser

A 1.8?μm optical parametric oscillator (OPO) based on a noncritically phase-matched KTiOPO4 crystal is demonstrated. OPO and stimulated Raman scattering techniques are successfully combined in an acousto-optically Q-switched Nd:YAG/SrWO4 Raman laser. The device efficiently realizes three steps of conversion: from a laser diode wavelength of 808?nm to the fundamental wavelength of 1064?nm; next, to the Stokes wavelength of 1180?nm; and finally to the OPO signal wavelength of 1810?nm. With an incident diode power of 7.2?W and a pulse repetition rate of 15?kHz, an average signal power of 485?mW is obtained with a diode-to-signal conversion efficiency of 6.75%. The beam quality factors (M2) of the signal wave in both horizontal and vertical directions are measured to be 1.7±0.2. The numerical output power results of the system, the thermal lensing, and the stability parameter of the cavity are also discussed.     

980nm半导体激光器腔面膜钝化新技术

研究了不同腔面钝化方法对980 nm渐变折射率波导结构InGaAs/AlGaAs半导体激光器输出激光功率的影响.将980 nm半导体激光器管芯前后腔面不蒸镀钝化膜与蒸镀Si钝化膜和蒸镀ZnSe钝化膜的方法进行了对比.结果表明,蒸镀ZnSe钝化膜比蒸镀Si钝化膜的半导体激光器输出光功率提高了11％,比不蒸镀钝化膜的半导体...     

HLSⅡ干涉法测量储存环横向尺寸与发射度

为了满足合肥光源升级改造后测量小束流尺寸的需求,设计了干涉法测量束团尺寸与发射度系统。简要介绍了在可见光波段利用干涉法测量束团横向尺寸的原理,详细介绍了该系统的光路与软硬件系统和图像处理算法。为了消除CCD的本底噪声对测量的影响,建立了本底噪声图像与束流流强的查找表,最终得到了多束团模式下的在线实验结果。测量得到的水平尺寸为265μm,测量误差为5.78μm;垂直尺寸为114μm,测量误差为4.89μm。     

980nm半导体激光器n型波导结构优化

为了提高980nm半导体激光器的输出功率并获得较小的远场发散角,在非对称波导结构的基础上设计了n型波导结构,即在n型波导中引入高折射率的内波导层。采用理论计算和SimLastip软件模拟对常规非对称波导结构和内波导结构进行了研究。利用分子束外延系统生长980nm内波导结构的外延材料,并制作了激光器。对于条宽为100μm、腔长为1000μm的器件,阈值电流为97mA,斜率效率为1.01W/A;当注入电流为500mA时,远场发散角为29°(垂直向)×8°(水平向),与模拟结果相符。理论计算和实验结果表明:较之于常规非对称波导结构,内波导结构可有效降低光场限制因子,提高输出功率,减小远场发散角。     

2600W偏振耦合高效率半导体激光光源

将两个中心波长为808 nm,输出功率为1500W的半导体激光叠阵,经过快慢轴准直后,利用半波片将其中一个叠阵的偏振方向旋转90°,使用偏振分光平板的耦合功能,将两个偏振方向相互垂直的激光耦合到一个光路.扩束后再通过焦距为100 mm的聚焦镜组聚焦,提高激光器的亮度.在工作电流为75 A时,输出功率达到了2600 W,...     

Properties of (InGa)As/GaAs QW (λ ≈ 1.2 µm) facet-coated edge emitting diode laser

In this paper, we report on the design and optical properties of laser diodes with an emission wave-length of ～1170 nm based on an (InGa)As/GaAs double quantum well active layer. The back and front facet of the laser diodes were coated with SiO_x dielectric films that influence the output optical power by enhancing or lowering the facet reflectivity. The measurements show improvement of the facet-coated laser diode properties in the threshold-current-density reduction along with light output power enhancement. Furthermore, a narrow far field pattern and high side mode suppression have been observed.     

Beam concentration and homogenization for high power laser diode bar

A novel optical element is presented and applied for beam concentration and homogenization of laser diode (LD) bar. It consists of a tapered SiO₂-rod with twisted surfaces which is designed and optimized by the optical system design software and fabricated by a curved surface grinder and an optical polishing lathe. Results show that a rectangular output beam spot with uniform intensity distributions both at slow and fast axis is obtained at the output facet of the rod and the beam size is only 1.3 mm ∗ 0.8 mm.     

A diode-laser pump source with small focus diameter for end- pumped systems

A pump source with eight angular multiplexed laser diodes is built. The diode laser emission is collimated and focused using relatively inexpensive aspherical lenses. The maximum output power is 6.3W at 970nm. The overall transmittance of the beam shaping optics is T=85%. The electrical, temporal and spectral properties are studied. The variances of the spatial intensity distribution are r0x=99m and r0y=85m. The beam propagation factors are M2x=38 and M2y=112. The high intensity in the focus makes this system ideal for end pumping of solid state lasers.     

Time-average holographic interferometry with a sinusoidally modulated laser diode

Laser diodes have the features of a single-mode operation and a frequency tunability. Holographic interferometry is described for investigating the vibrating amplitude and phase with a frequency-modulated laser diode. Sinusoidal wavelength change by varying laser injection current produces the sinusoidal phase modulation of relative phase difference between the reference and vibrating object paths. Holograms are made by time-average exposure of three-type recording modes with a laser diode. The phase of vibrating object is extracted from the measurements of Bessel-type fringe irradiances in three kinds of time-average holographic reconstruction. Experimental results of phase and amplitude for a vibrating cantilever object are shown.     

Optimization of facet coating for highly strained InGaAs quantum well lasers operating at 1200 nm

The optical output power of a laser diode can be enhanced by anti-reflection (AR) and high-reflection (HR) facet coatings, respectively, at the front and back facet. AR and HR coatings also serve the purpose of protection and passivation of laser diode facets. In this work, we have designed and optimized a single layer λ/4 thick Al₂O₃ film for the AR coating and a stack of λ/4 thick Al₂O₃/λ/4 thick Si bi-layers for the HR coating for highly strained InGaAs quantum-well edge emitting broad area (BA) laser diodes. Effect of the front and back facet reflectivities on output power of the laser diodes has been studied. The light output versus injected current (L–I characteristics) measurements were carried out on selected devices before and after the facet coatings. We have also carried out the numerical simulation and analysis of L–I characteristics for this particular diode structure. The experimental results have been compared and verified with the numerical simulation.     

Straightness Measurement Using Laser Diode and CCD Camera

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