Measurement of the modal reflectivity of an antireflection coating on a superluminescent diode

A method for measuring the modal reflectivity of the antireflection coating applied to a laser diode is described and demonstrated. It is based on measurements of the Fabry-Perot modulation depth of the resulting superluminescent diode (SLD) output spectrum at the threshold current of the original laser. A modal reflectivity of less than2 times 10^{-4}has been obtained.     

Bistability in grating-tuned external-cavity semiconductor lasers

Bistability has been observed in the tuning characteristic and power versus current relation of a 1.3 μm grating-tuned external-cavity semiconductor laser. Tuning-direction reversal, current variations, and feedback interruption can change the output power and threshold current at a given wavelength. These effects are shown theoretically to be due to the coupling of the semiconductor gain and index of refraction. From measurements of the semiconductor chip facet reflectivity, solitary laser diode mode spectrum, and tuning curve in the presence of external feedback, the analysis yields values for the external feedback strength, semiconductor modal loss, and linewidth enhancement factor. Using an InGaAsP double-channel-planar-buried-heterostructure laser diode with a 4 percent reflectivity antireflection-coated facet inside an external cavity consisting of a 0.60 numerical aperture lens and a 1200 line/mm diffraction grating, we found 22 percent external feedback, 60 cm^-1modal loss, and a linewidth enhancement factoralpha = -7.1.     

Modal noise reduction of laser diodes with specific thickness coating

A low facet reflectivity laser diode is able to oscillate in multilongitudinal modes, and has a high relative intensity noise (RIN) and reduces mode hopping noise. By introducing the electron-cyclotron-resonance (ECR) plasma deposition method, a good facet coating film has been obtained. We have demonstrated that a specific coated laser has very low modal noise characteristics even under direct analogue intensity modulation.     

Reflection-induced changes in the optical spectra of 980-nm QWlasers

High-power 980-nm strained quantum well diode lasers having low reflectivity facet coatings are sensitive to weak reflections that affect the laser emission spectrum. In devices having 0.2% output facet reflectivity, 2% reflections from an external plane mirror shifted the output spectrum from 970 to 1000 mn. Wavelength stabilization and improved immunity to spurious reflections were demonstrated using bulk grating and fiber-grating reflectors. Continuous laser tuning from 958 to 1011 nm was achieved with 1% net grating reflectivity     

Accurate measurement of reflectivity over wavelength of a laserdiode antireflection coating using an external cavity laser

A method for measuring laser diode facet antireflection coating over wavelength is presented. The laser diode is coupled to a wavelength-selective external cavity, and laser threshold current over the wavelength region of interest is measured. The coating reflectivity over wavelength is derived from the threshold current data. Reflectivities as low as 1×10^-5 have been measured with good fit over wavelength to an ideal single layer coating. The net external cavity feedback is also determined. An estimate of the accuracy of the reflectivity measurement is made     

Noise and longitudinal mode characteristics of (GaAl)As TS lasers with reduced facet reflectivities

The AM noise in operation of index-guided (GaAl)As lasers is found to be strikingly reduced by the antireflection (AR) coating of cavity facets. This effect is shown to result from the longitudinal multi-mode operation due to the reduced facet reflectivity. It is observed that the width of the envelope of a laser spectrum depends on the facet reflectivity as well as the laser output power. The AM noise in the low-frequency range of the reduced reflectivity lasers is shown to be nearly constant with respect to temperature change. In contrast, the AM noise in a laser without the AR facet coating is characterized by a number of spikes occurring over a wide temperature range.     

TW-SLA AR膜剩余反射率实时监控新方法

介绍一种实时监控行波半导体激光放大器(TW-SLA)抗反膜(AR)超低剩余反射率的新方法。从理论和实验上分析了剩余反射率与SLA的输出光功率关系及温度对其输出功率的影响。在1.3μm InGaAsP/InP掩埋异质结(BH)激光二极管(LD)上镀单层SiOx或SiOx1/SiOx2膜获得了低于5×10-4的超低反射率。     

半导体激光器端面剩余模式反射率测量结果的分析

本文分析了单色仪出射狭缝宽度对半导体激光器镀膜端面反射率测量的影响,理论预言了调制度和反射率的测量值以及测量谱中波峰和波谷的位置随缝宽周期性变化的规律。实验结果证实了理论预测的正确性。     

腔面低反射大功率半导体激光器阵列

光束质量问题是制约半导体激光器应用的主要因素,采用出光面蒸镀低反膜LD阵列半导体激光器阵列锁相技术较好地解决了这个问题.本文设计并制作了高反膜系和极低反膜系,获得了高阈值的LD阵列.本文的低反膜系有大的带宽和小于0.2%的剩余反射率,易于工艺实现,LD阵列的阈值电流密度达到480A/cm2.     

体布拉格光栅反射率对外腔半导体激光阵列输出光谱的影响

采用记录在光致热敏折射率玻璃中的反射型体布拉格光栅作为反馈元件构成外腔半导体激光阵列,对其输出光谱特性进行了实验研究,分析了快轴准直透镜的位置对外腔反馈耦合效率的影响。实验结果表明,在体布拉格光栅外腔反馈作用下,半导体激光阵列输出光谱中心波长得到锁定,同时输出线宽显著变窄。重点研究了体布拉格光栅的反射率对外腔反馈半导体激光阵列输出光谱特性以及激光器效率的影响。实验结果表明,体布拉格光栅反射率的增加可提高半导体激光阵列内腔模式的抑制效果,提高输出光谱对比度,减小输出光谱线宽。使用反射率为30%的体布拉格光栅,可将半导体激光阵列的输出波长锁定在808nm附近,输出光谱线宽压缩至0.18nm。外腔半导体激光器的输出功率达24.8W,效率为82.6%。     

Continuous-wave cavity ring-down technique for accurate measurement of high reflectivity

A continuous-wave cavity ring-down (CWCRD) technique employing a broadband diode laser is developed for high reflectivity measurement. The theory of square-wave modulated CW-CRD is presented. The spectrum of the broadband CW diode laser covers numerous free spectral ranges (FSRs) so that sufficient laser power is coupled into the cavity. Both amplitude and phase-shift of the first harmonic of the CRD signal,measured at an appropriate frequency range, are detected by a lock-in method and fitted to obtain the ring-down time and reflectivity. The measurements are repeated with five different cavity lengths and all the fitted reflectivities are in excellent agreement, indicating a high reliability of the CW-CRD technique. The reflectivity of the cavity mirror is determined statistically to be 99.70%,with an uncertainty of 0.01%.     

端面反射率对半导体激光器微分功率特性的影响

从理论和实验上研究了端面反射率对半导体激光器微分输出功率等特性的影响。研究表明,用镀膜方法适当地降低半导体激光器输出端面反射率,有助于增大输出功率和提高外量子效率。     

Measurement of the facet modal reflectivity spectrum in highquality semiconductor traveling wave amplifiers

We demonstrate that the Hakki-Paoli technique, commonly used for measuring single pass gain in semiconductor lasers, can be modified to measure facet modal reflectivity down to 10^-6 in semiconductor laser amplifiers. We also introduce a new technique based on Fourier and Hilbert transformations of the spontaneous emission spectrum (the SET method) which enhances the signal-to-noise ratio and permits modal reflectivity measurements down to 10^-1     

腔面反射率对超辐射发光二极管输出特性的影响

本文用耦合速率方程,从理论上分析研究了超辐射发光二极管(SLD)的功率输出特性。主要讨论了腔面反射率对其功率输出特性的影响。研究结果表明,半导体激光器(LD)存在一最佳输出功率腔面反射率,随腔面反射率的降低,SLD的功率曲线斜率减小,输出功率降低,光谱调制深度减小。增大后腔面反射率可以提高SLD的输出功率,减小其工作电流。由于腔面反射率的降低,前后传输的光子在有源区内的分布的对称性发生了变化,表现为非均匀性,后向传输波大于前向传输波。最后,把理论计算结果同我们研制的1.3μm徐层结构超辐射发光二极管的实验结果作了比较,得到了较好符合。     

光纤光栅外腔半导体激光器改进模型分析

改进了基于耦合腔激光器模型的光纤光栅外腔激光器静态分析模型．在考虑了激光器和光纤光栅之间的耦合效率后．将光从激光器耦合进光纤光栅的耦合系数η1和从光纤光栅反馈回激光器的耦合系数η2推导进描述耦合腔的散射矩阵元中．修正了耦合腔模型的表达式。发现两个耦合系数η1ljη2之积的大小对增益曲线产生具体影响。分析表明短外腔及短的光纤光栅长度决定了损耗曲线最低处单纵模振荡．激光管芯与光纤端面的反射率也对阈值电流、边模抑制比产生明显影响．尤其对于激光器端面反射系数比较大的情况．可以通过仔细设计空气间隙的长度实现外腔模和法布单一珀罗(F-P)模式的匹配。     

Highly reliable 200 mW AlGaAs laser diode with fundamental transverse mode

A highly reliable 200 mW AlGaAs laser diode with a fundamental transverse mode has been developed, by optimising its structure with a 0.8 mu m thick p-cladding layer, a 1200 mu m long cavity length, and a front facet coating with a low reflectivity of 2%. The maximum output power was 500 mW, and stable fundamental transverse mode operation was obtained up to 350 mW. Stable operation under 200 mW and 50 degrees C was confirmed for more than 1200 h. Optical feedback noise was below 3*10/sup -14/ Hz/sup -1/.<>     

An open-resonator model for the analysis of a short external-cavitylaser diode and its application to the optical disk head

Based on the open resonator theory, a model of a complex coupling coefficient suitable for the analysis of an ultrashort external-cavity laser diode is presented. It is shown that the effective reflectivity of the short external-cavity laser diode calculated by using this model is a function of the size of the laser-emitting area and is significantly influenced by the phase-modification factor as well as by the amplitude-reduction factor of the complex coupling coefficient. The calculated output power characteristics show good qualitative agreement with experimental observation. The necessary condition that the optical disk head using an external-cavity laser diode does not fail to detect the recorded signal for a broad range of flying height is also derived     

Reflectivity measurements of intracavity defects in laser diodes

A method for measuring the complex reflectivity associated with a localized defect existing inside a laser diode cavity is presented. It relies on analyzing the magnitudes of resonant peaks in the Fourier transform of a subthreshold laser spectrum. Reflectivities between 0.01 and 0.02 with zero phase have been measured in a laser with a deliberately induced scattering center produced by standard lithographic techniques.     

Closed form theory of multicavity reflectors and the output power of external cavity diode lasers

A closed form solution for the transmission and reflection coefficients of a double cavity Fabry-Perot resonator is given. The explicit expressions for these coefficients are used in a formula to give the output power of diode lasers coupled to multiple external cavities. Analysis of a cleaved or etched coupled-cavity laser shows that stable operation depends on proper choice of the phase length of both the gap and the control section. A study of a diode laser coupled to an external waveguide containing a Bragg reflector shows that for correct choice of grating reflectivity only modestly effective antireflection coatings (5 percent on laser facet and 2 percent on waveguide face) are required to allow the grating to dominate the operating wavelength of the laser diode. A single external cavity with loss coupled to a laser diode is also considered. In this case the theory indicates the necessity of proper control of loss or coupling fraction between diode and cavity for there to be effective control of wavelength.     

高功率850 nm宽光谱大光腔超辐射发光二极管

超辐射发光二极管(SLD)具有不同于半导体激光器和普通发光二极管的优异性能。为提高半导体超辐射发光管的光谱宽度,采用非均匀阱宽多量子阱(MQW)材料拓宽超辐射器件的输出光谱。优化设计器件的波导结构,利用大光腔结构设计出高功率、低发散角850 nm超辐射发光二极管。采用直波导吸收区而后在器件的出光腔面上镀制抗反射膜的方法制作超辐射发光二极管。器件在140 mA时器件半峰全宽(FWHM)可以达到26 nm,室温下连续输出功率达到7 mW。器件的垂直发散角为28°,水平发散角为10°。由于器件具有比较小的发散角,与光纤耦合时具有比较高的耦合效率,单模保偏光纤耦合输出功率达到1.5 mW。