Wavelength stabilized 980 nm uncooled pump laser modules for erbium-doped fiber amplifiers

We review the development of wavelength stabilized 980 nm pump laser modules without active temperature stabilization for applications in erbium-doped fiber amplifiers. Operation over a wide temperature range with an output power exceeding 400 mW at an ambient temperature of 70°C is demonstrated. The overall reliability of uncooled modules is estimated to be well below 500 FIT at all operating conditions. Such devices are made possible by continuous development and steady improvement of the pump laser chip, the optimization of the fiber Bragg grating stabilization scheme, careful design of the module package, and extended reliability analysis on the basis of stress tests as well as field data.     

Frequency stabilization of a 214.5-nm ultraviolet laser

An improved method for stabilizing a frequency-quadrupled 214.5-nm tunable diode laser system is reported. Improvements to the method include a homemade logic circuit and the use of a Fabry-Perot optical spectrum analyzer as a transfer cavity. Lasers locked with this method exhibit megahertz-level frequency stability measured with an optical frequency comb referenced to a cesium atomic standard. The laser can be locked for hours to days, depending on experiment requirements. Being relatively inexpensive, stable, and robust, the control method can be applied to stabilizing essentially all lasers of deep ultraviolet wavelengths.     

Single-frequency operation of a high-power, long-wavelength semiconductor disk laser

An optically pumped, high-power, single-frequency semiconductor disk laser is demonstrated. A thin (50 microm) diamond bonded to an InGaAsP gain chip provides the combined functions of heat removal and spectral filtering, thus eliminating the need for the additional intracavity etalons that are usually employed for single-frequency operation. In a short cavity (4 mm) configuration we obtained a maximum output power of 470 mW at 0 degrees C and 170 mW at 20 degrees C in a near-diffraction-limited beam (M2 < 1.2). The emission wave-length was 1549 nm and the linewidth was less than 200 MHz.     

大功率780 nm半导体激光器的设计与制备

设计并制备了一款780 nm半导体激光器,并进行了外腔反馈锁模研究。利用金属有机化学气相沉积技术制备了激光器外延层,采用GaAsP/GaInP作为量子阱/波导层有源区,限制层采用低折射率AlGaInP材料。采用超高真空解理钝化技术,在激光器腔面蒸镀无定形ZnSe钝化层。未钝化器件在输出功率2.5 W时发生腔面灾变损伤（COD）,钝化后器件未发生COD现象,电流在10 A时输出功率10.1 W,电光转换效率54%。体布拉格光栅（VBG）外腔锁定前后,器件的光谱半峰全宽分别为2.6 nm和0.06 nm,VBG变温调控波长范围约230 pm。     

Wavelength stabilization and spectrum narrowing of high-power multimode laser diodes and arrays by use of volume Bragg gratings

Spectral line narrowing (by a factor of 8) and stabilization of the emission wavelength (by a factor of 30) of multimode high-power laser diodes and arrays is demonstrated by use of volume Bragg gratings fabricated in high-stability inorganic photorefractive glasses. Applications include stabilization of pump laser diodes and arrays for solid-state lasers and metal-vapor lasers, spin hyperpolarization of noble gases used in medical imaging, and others.     

机载大功率半导体激光信标系统设计

为配合地面探测跟踪系统对飞行目标的探测,设计了一种以４０ Ｗ 紧凑型半导体激光器为光源、具有一定发散角的机载式单色信标系统。由于系统要满足机载平台加装体积小、质量轻、散热好的要求,设计了一体成型的鳍片式壳体结构,解决系统散热问题的同时,控制了整体质量。为实现在有限体积内,４０ Ｗ 单阵列光纤耦合半导体激光器模块所需的６０A 大电流恒流驱动,采用叠相调制技术和同步ＢUＣＫ 变换电路结构;为解决激光器在高空低温环境下输出光功率和中心波长能够稳定控制的难题,设计了数模混合双向温控系统。利用ＺEMAX 软件设计了双凹透镜组结构的扩束装置,实现了对激光发散角的发散和可调节。通过环境考核测试,系统在０℃～１５℃的低温环境下,输出光功率稳定度和波长控制精度均能满足要求。     

Wavelength tuning characteristics of a fabry-perot semiconductor laser with an external short cavity

Wavelength tuning characteristics of a Fabry-Perot semiconductor laser with an external short cavity are analyzed, in which the oscillation wavelength can be changed by slightly altering the external cavity length. Analysis is based on rate equations for an optical power and carrier density. It is shown that the wavelength tuning range is dominated by a change of carrier density through the effect of carrier-induced refractive index change in the active layer of a laser diode. This depends on effective coupling coefficients of the optical field iteratively reflected back to the laser diode by the external mirror, and on reflection coefficients of an anti-reflection coated laser facet and the external mirror which compose the external cavity. The effective coupling coefficient is also derived using the waveguide theory and Kirchhoff ’s theory. Finally, an unstable condition which may limit a stable wavelength tuning range is shown by results of a linear stability analysis of rate equations.     

Modeling of resistance characteristics of a continuously-graded distributed Bragg reflector in a 980-nm vertical-cavity surface-emitting laser

The resistance characteristics of a continuously-graded distributed Bragg reflector(DBR) in a 980-nm verticalcavity surface-emitting laser(VCSEL) are modeled in detail.The junction resistances between the layers of both the p-and n-DBR mirrors are analysed by combining the thermionic emission model and the finite difference method.In the meantime,the intrinsic resistance of the DBR material system is calculated to make a comparison with the junction resistance.The minimal values of series resistances of the graded p-and n-type DBR mirrors and the lateral temperature-dependent resistance variation are calculated and discussed.The result indicates the potential to optimize the design of the DBR reflectors of the 980-nm VCSELs.     

A high-power single-pulse laser with stabilized spectrum and directivity near the diffraction limit

Journal of Applied Spectroscopy -     

大功率半导体激光器光谱合束光栅热效应分析

提出了一种大功率半导体激光器光谱合束光栅仿真模型。该模型针对光谱合束中的核心器件光栅的光-热-应力变化特性进行了分析。数值分析结果表明,当激光巴条功率为200 W,自然对流系数为10 W·(m2·K)?1时,衍射光栅上温度最高点可升高至346.52 K,应力最高点可升高至0.4825 Pa,光栅表面变量最高为52.28 nm/mm,这将会使得反馈光束中心位置发生0.25～0.3 mm的偏移,从而影响激光功率以及合束效率。减少衍射光栅基底厚度,在相同激光光源条件下工作,温度、应力、面形以及应变的变化均能有效抑制,这与实验结果具有较高的一致性。该方法为大功率半导体激光器的结构设计和光学器件的测试分析提供了有效的多物理场分析,为激光器设计和测试提供了综合分析数值模型。     

A stabilized tunable dual wavelength erbium-doped fiber laser with equal output power

Tunable dual-wavelength erbium-doped fiber laser with good stability is experimentally demonstrated. Output power of as high as +5.26 dBm is obtained in dual ring configuration. Both laser output can be tuned to as closed as 0.8 nm spacing between each other, with tuning range of 31.33 nm. The stability of both outputs was tested that results in less than ±0.8 dB and ±0.01 nm in power and wavelength fluctuation, respectively.     

激光系统中半导体激光器温度稳定系统研究与设计

激光器系统中半导体激光器的功率输出稳定度和工作温度有很大的关系,为了使大功率半导体激光器输出功率稳定,需要对激光器实现高精度、快速温度控制。针对现有的激光系统中激光器温度控制系统存在控制精度不够高、控制速度慢等问题,设计了一种温度稳定系统,采用PT-100热电偶测量激光器温度,并使用最小二乘法对温度数据进行拟合,使得温度测量精度达到0.01 ℃;使用改进粒子群算法优化(PSO)的PID控制器实现温度控制。仿真实验和实际测试表明,所设计的温度稳定系统能够很好地控制激光器温度,达到目标温度所需的调节时间小于11 s,达到稳态后温度波动在±0.02 ℃内。与传统的温度控制方式相比,所设计的系统能够实现参数自整定并自动调节温度,对大功率激光系统中激光器温度具有良好稳定效果。     

Ultralow-jitter, 1550-nm mode-locked semiconductor laser synchronized to a visible optical frequency standard

Using high-bandwidth feedback, we have synchronized the pulse train from a mode-locked semiconductor laser to an external optical atomic clock signal and achieved what is to our knowledge the lowest timing jitter to date (22 fs, integrated from 1 Hz to 100 MHz) for such devices. The performance is limited by the intrinsic noise of the phase detector used for timing-jitter measurement. We expect such a highly stable device to play an important role in fiber-network-based precise time/frequency distribution.     

EIT as a tool to observe dual wavelength operation of a semiconductor laser

We propose a simplified technique for dual wavelength operation of an extended cavity semiconductor laser, and its characterization using electromagnetically induced transparency (EIT). In this laser cavity scheme light beam is made converging before it incidences on the cavity grating. The converging angle of the beam creates two longitudinal oscillating modes of resonating cavity. Frequency separation between the longitudinal modes are measured with the help of beat frequency generation in a photodiode and creating pair of EIT spectra in Rb vapor. The pair of EIT dips that are generated due to dual wavelength of this laser (that is used as control laser) can be used to estimate frequency difference between the generated wavelengths. Width of EIT spectra can be used to estimate linewidth of individual wavelength components.     

Harmonically mode-locked laser stabilized by semiconductor saturable absorber modulated with the residual pump

Stabilization of a passive harmonically mode-locked laser is demonstrated by directly modulating a 980-nm pump diode laser used both to provide gain and to optically modulate an intracavity saturable absorber. The results indicate a reduction of the undesired laser modes by more than 55 dB. The timing jitter was decreased by 9 dB. Received: 3 April 2002 / Revised version: 30 April 2002 / Published online: 12 July 2002     

Output characteristics of a simple FP-LD/FBG module

We propose a simple laser diode module that consists of a Fabry–Perot laser diode (FP-LD) and a fiber Bragg grating (FBG) for a compact, stable and low-cost wavelength division multiplexing light source. The spectral bandwidth of the laser output from the FP-LD/FBG module was measured to be 0.024 nm. The side mode suppression ratio (SMSR) was 44.42 dB at the injected electric current of 14 mA and at 25 °C. Both the BER characteristics and the eye diagram were measured, and they confirmed that the present laser diode module could be used as an alternative configuration for a low-cost light source.     

Wavelength stabilization of a distributed Bragg reflector laser diode by use of complementary current injection

We have demonstrated wavelength stabilization in an 821-nm AlGaAs three-section tunable distributed Bragg reflector (DBR) semiconductor laser diode (LD) that consists of active, phase-controlled, and DBR regions. We injected two separate, complementary currents into the active and the phase-controlled regions in the DBR-LD to suppress wavelength shift. This modulation method was applied to the LD fundamental wave in a second-harmonic-generation (SHG) laser, and the oscillating wavelength was maintained within the phase-matching acceptance range of the SHG device during modulation. A peak blue-violet light power of 62 mW was obtained for the ideal modulation waveform.     

Wavelength stabilization of an Ar+ laser with an external129I2 absorption cell

Wavelength stabilization of the green Ar⁺ laser line at 514.5 nm by¹²⁹I₂ absorption was found to be more favourable than by¹²⁷I₂ absorption because the maximum of¹²⁹I₂ absorption is closer to the center of the 514.5 nm gain curve. A simple method for stabilizing a short air cooled laser with only one servo loop is given, yielding a stability of 10⁻⁸ λ.     

Characterization of a high-power tapered semiconductor amplifier system

We have characterized a semiconductor amplifier laser system which provides up to 200 mW output after a single-mode optical fiber at 780 nm wavelength. The system is based on a tapered semiconductor gain element, which amplifies the output of a narrow-linewidth diode laser. Gain and saturation are discussed as a function of operating temperature and injection current. The spectral properties of the amplifier are investigated with a grating spectrometer. Amplified spontaneous emission (ASE) causes a spectral background with a width of 4 nm FWHM. The ASE background was suppressed to below our detection limit by a proper choice of operating current and temperature and by sending the light through a single-mode optical fiber. The final ASE spectral density was less than 0.1 nW/MHz, i.e. less than 0.2% of the optical power. Related to an optical transition linewidth of Γ/2π=6 MHz for rubidium, this gives a background suppression of better than -82 dB. An indication of the beam quality is provided by the fiber coupling efficiency of up to 59%. The application of the amplifier system as a laser source for atom-optical experiments is discussed. Received: 8 May 2000 / Revised version: 21 September 2000 / Published online: 7 February 2001     

Frequency stabilization of a 1319-nm Nd:YAG laser by saturation spectroscopy of molecular iodine

Hyperfine transitions of molecular iodine were observed by use of the frequency-doubled output of a 1319-nm Nd:YAG laser with saturation spectroscopy. The laser frequency was stabilized to the observed hyperfine transition and reached a stability of 6 x 10(-12) for a 1.5-s averaging time, improving toward the 1 x 10(-12) level after 100 s. The iodine-stabilized 1319-nm Nd:YAG laser is an excellent candidate for an optical frequency standard for telecommunication applications.