Wavelength Tuning Characteristics of a Vertival Cavity Surface Emitting Laser Diode with an External Short Cavity

The characteristics of a wavelength tunable vertical cavity surface emitting laser diode (VCSEL) with an external short cavity are analyzed, in which the oscillation wavelength can be changed over several tens of nanometers with a nearly constant optical power by slightly altering the external cavity length. Analysis is based on rate equations for the optical power and carrier density, taking the effect of carrier-induced refractive index change into consideration, together with the study of behaviors of a complex resonator. The reflection coefficient r₂ of a laser facet facing the external mirror is shown to affect notably the characteristics of wavelength tuning, optical power and carrier density for a change of the external cavity length. It is also noticed that the wavelength change for this length becomes slower with relatively larger r₂ due to an increasing contribution of the effect of carrier-induced refractive index change, within the optical gain spectrum of the laser diode.     

Laser-diode wavelength tuning based on butt coupling into an optical fiber

An extremely short external cavity that is realized when a Fabry-Perot laser diode is butt coupled to a waveguide or a fiber produces feedback that is effective for controlled wavelength tuning. We used butt coupling to tune a high-output-power laser diode over a wide range (as great as 15 nm) while maintaining constant driving current and temperature. Single-mode or multimode operation repeatedly occurred at specific points throughout the tuning range. An analytical model that includes the effect of multiple reflections from the external cavity, each attenuated by a modal overlap integral, and which is based on phenomenological principles, shows good agreement with the experimental results.     

Spectral properties of edge-emitting semiconductor laser subject to optical feedback from extremely short external cavity

We experimentally and theoretically study the impact of optical feedback from an extremely short external cavity (tens of μm) on the spectral behavior of edge emitting lasers (EELs). We are able to investigate a broad range of external cavity lengths and feedback strengths, by using a nanometer precision movable mirror attached to a fiber facet. A discrete modulation of the wavelength of operation is observed and its amplitude depends on the external cavity length and the external mirror reflectivity. We show that it is possible to optimize the tuning range of such a discrete wavelength tunable laser with respect to the external cavity and laser parameters.     

Resonance amplifier model describing diode lasers coupled to short external resonators

A model of a regenerative resonance amplifier has been used to describe Fabry-Perot GaAs diode lasers coupled to short external resonators. The optical gain and the equivalent input of the resonance amplifier are controlled by means of appropriate rate equations. Homogeneous line-broadening and proportionality between gain and electron density have been assumed in this approach. The model was applied to a diode laser coupled to an external plane mirror placed at a variable distance from one diode mirror. A numerical evaluation of the coupling coefficient between laser and external cavity enables to predict the measured power output and mode selective properties of the coupled system. A similar analysis was done for diode lasers coupled to external hemispherical resonators. The model calculation confirms the previously demonstrated mode selective properties of the hemispherical configuration which permitted stable single mode operation.     

Tunable single-mode Fabry-Perot laser diode using a built-in external cavity and its modulation characteristics

A tunable single-mode laser is obtained by using a weakly coupled cavity structure involved in a coaxially packaged Fabry-Perot laser diode. The cleaved end facet of the coupling fiber becomes an optical reflector and forms an external cavity with a laser facet. The single-mode oscillation condition is controlled and stabilized by tuning the operating temperature. The tuning range is about 10 nm with the side-mode suppression ratio of more than 27 dB when the temperature changes from 11.5 degrees C to 25 degrees C. Direct modulation characteristics were investigated, and our results show that a shorter external cavity can bear deeper modulation depth.     

Extension of the mode-hop-free tuning range of an external cavity diode laser based on a model of the mode-hop dynamics

We report on a universal method to achieve and sustain a large mode-hop-free tuning range of an external cavity diode laser based on a model of its mode-structure dynamics. Using this method, we were able to scan 73 GHz mode-hop free by using an uncoated off-the-shelf laser diode with a central wavelength of 785 nm. Our model applies to any laser system requiring synchronization of more than one optical element.     

Stable, continuously tunable operation of a diode-pumped doubly resonant optical parametric oscillator

We demonstrate, for what is the first time to our knowledge, long-term stable, continuously tunable operation of a doubly resonant optical parametric oscillator (OPO) pumped by a single-stripe diode laser without the use of an external semiconductor amplifier. The OPO is based on periodically poled lithium niobate and is pumped by a 150-mW distributed Bragg grating diode laser. 18-mW total output power is generated at 1.3- and 2.3-mum wavelengths. A cavity-length servo system allows continuous signal tuning of 17 GHz and idler tuning of 10 GHz, limited only by the range of a piezoelectric cavity mirror mount. OPO tuning is demonstrated from 1.1 to 1.4 mum and from 2.2 to 3.7 mum.     

Determine locking range of coherently combined fiber lasers joined by fiber couplers

When the wavelength difference of two fiber lasers, sharing a common reflection mirror with the aid of an optical coupler, is tuned to fall into a certain range, the array lasers can be locked to generate coherent radiation with a wavelength somewhere between the two constituent field wavelengths. Based on the fact that the laser should oscillate at the wavelength with the lowest losses and the band widths of the reflection curves of the laser tuning elements are finite, the locking range of the laser array has been quantified. For the tuning element (i.e., fiber gratings) selected in this work, the calculations show that the locking range is mainly dependent on the coupling coefficients of the gratings which ever is smaller.     

改善外腔半导体激光器调谐特性的新方法

基于原有的Littman结构外腔半导体激光器,提出采用一种新的光学方法来实现波长调谐。该方法采用了包含一个旋转楔形棱镜的“光杠杆”系统来降低调谐的机械要求,提高波长选择精度。通过选择不同的楔形棱镜顶角和光线入射角,机械要求可以降低1～2个数量级,波长选择精度也得到相同量级的提高。该方法使Littman结构外腔半导体激光器的调谐特性得到极大的改善,并大大降低了震动的敏感性。     

激光器型全光波长转换器的小信号分析

当外部光子注入到激光器有源腔中时 ,载流子把被注入光子消耗的一部分放大 ,进而激光器自身的输出功率将降低。基于此 ,可以实现全光波长转换。理论上基于载流子消耗机制 ,对激光器型波长转换器进行了小信号分析 ,给出了频率响应函数。理论分析表明 ,激光器型全光波长转换器的转换速度取决于激光器光子寿命以及激光器腔内的光子密度。     

基于飞秒光频梳的压电陶瓷闭环位移控制系统

利用飞秒光频梳、外腔可调谐半导体激光器和法布里-珀罗干涉仪建立了一套压电陶瓷亚纳米级闭环位移控制系统. 将可调谐半导体激光器锁定至光频梳, 通过精确调谐光频梳的重复频率, 实现了半导体激光器在其工作频率范围内的精密调谐. 利用Pound-Drever-Hall锁定技术将带有压电陶瓷的法布里-珀罗腔锁定至半导体激光器, 进而通过频率发生系统控制压电陶瓷产生亚纳米级分辨率的位移. 实验研究发现锁定至光频梳后可调谐半导体激光器1 s的Allan标准偏差为1.68×10^-12, 将其在30.9496 GHz范围内进行连续闭环调谐, 可获得压电陶瓷的位移行程约为4.8 μm; 以3.75 Hz的步长扫描光频梳的重复频率, 实现了压电陶瓷的450 pm闭环位移分辨率并测定了压电陶瓷的磁滞特性曲线. 该系统不存在非线性测量误差, 且激光频率及压电陶瓷位移均溯源至铷钟频率源. 关键词： 光频梳 压电陶瓷 法布里-珀罗腔 可调谐半导体激光器     

External cavity quantum dot tunable laser through 1.55 μm

The optical performance of InAs/InGaAsP quantum dot (QD) lasers grown on (1 0 0) InP was studied for three different material structures. The most efficient QD laser structure, having a threshold current of 107 mA and an external differential quantum efficiency of 9.4% at room temperature, was used to form the active region of a grating-coupled external cavity tunable laser. A tuning range of 110 nm was demonstrated, which was mainly limited by the mirror and internal losses of the uncoated laser diode. Rapid state-filling of the QDs was also demonstrated by observing the evolution of the spectra with increasing injected current.     

外腔锁模多量子阱二极管激光器

报道一种用作光通讯光源的外腔锁模多量子阱结构半导体激光器，其脉冲宽度２～５ｐｓ，波长调谐范围为１．５２～１．５７μｍ，锁模频率０．５～１．０ＧＨｚ平均输出光功率为１ｍＷ。     

Nanometer-scale displacement sensing using self-mixing interferometry with a correlation-based signal processing technique

A self-mixing interferometer is proposed to measure nanometre-scale optical path length changes in the interferometer’s external cavity. As light source, the developed technique uses a blue emitting GaN laser diode. An external reflector, a silicon mirror, driven by a piezo nanopositioner is used to produce an interference signal which is detected with the monitor photodiode of the laser diode. Changing the optical path length of the external cavity introduces a phase difference to the interference signal. This phase difference is detected using a signal processing algorithm based on Pearson’s correlation coefficient and cubic spline interpolation techniques. The results show that the average deviation between the measured and actual displacements of the silicon mirror is 3.1 nm in the 0–110 nm displacement range. Moreover, the measured displacements follow linearly the actual displacement of the silicon mirror. Finally, the paper considers the effects produced by the temperature and current stability of the laser diode as well as dispersion effects in the external cavity of the interferometer. These reduce the sensor’s measurement accuracy especially in long-term measurements.     

A Wavelength and Spectrum Measurement of an Extremely-Short-External-Cavity Laser Diode by Precisely Controlling Slider Flying Height

In this paper we propose a measurement method that uses a laser diode (LD) attached to a flying slider and a semi-transparent rotating disk mirror for an extremely-short-external-cavity configuration. Not only the wavelength, but also the spectrum and the light output are measured at room temperature with the external cavity length, the reflectivities of the LD facets and the external mirror, and the drive current as parameters. We have confirmed wavelength variation as great as 30 nm by changing the external-cavity length for a 1.3-$mUm wavelength laser diode with an antireflection coating on the LD facet facing the external mirror.     

Widely tunable diffraction limited 1000 mW external cavity diode laser in Littman/Metcalf configuration for cavity ring-down spectroscopy

We report on recent progress on external cavity diode lasers (ECDL) using a new concept of a Littman/Metcalf configuration. Within this concept one facet of the diode laser chip is used for coupling to a high quality Littman/Metcalf resonator whereas the other side of the diode laser chip emits the output beam. The alignment of the external resonator is independent from the alignment of the output beam and there is no need for any compromise in the alignment. This results in an improved behavior of the external resonator with the benefit of a drastic increase in power and single mode tuning.We investigated this light source for high resolution spectroscopy in the field of cw-cavity ring-down spectroscopy (CRDS). The monitoring of environmental and medical gases from vehicles or human breath requires a suitable radiation source in the mid-infrared (MIR) between 3 and 5 μm that is frequency stable and can be widely tuned. Since this wavelength cannot be reached via direct emitting room temperature semiconductor lasers, additional techniques like difference frequency generation (DFG) are essential. Tunable difference frequency generation relies on high power, small linewidth, fast tunable, robust laser diode sources with excellent beam quality.With our new compact, alignment-insensitive and robust ECDL concept, we achieved an output power of 1000 mW and an almost Gaussian shaped beam quality (M²<1.2). The coupling efficiency for optical waveguides as well as single mode fibers exceeds 70%. The wavelength is widely tunable within the tuning range of 20 nm via remote control. This laser system operates longitudinally in single mode with a mode-hop free tuning range of more than 150 GHz without current compensation and a side-mode-suppression better than 50 dB. This concept is currently realized within the wavelength regime between 750 and 1080 nm.Our high powered Littman/Metcalf laser system was part of a MIR-light source which utilizes DFG in periodically poled lithium niobate (PPLN) crystals. At the wavelength of 3.3 μm we were able to achieve a high-resolution absorption spectrum of water with four different isotoplogues of H₂O components. This application clearly demonstrates the suitability of this laser for high-precision measurements. PACS 07.57.Ty; 42.55.Px; 42.62.Fi     

785nm便携式光栅外腔可调谐半导体激光器的研制和输出特性

针对移频激发拉曼光谱测试系统的小型化需求,在Littrow结构中,采用商用的785nm大功率激光二极管作为增益器件,构建了一款便携式光栅外腔可调谐半导体激光器。该激光器通过采用一种新型的波长调谐方法,即以改变半导体增益器件相对于准直透镜的水平位置来实现波长的连续调谐,实现了尺寸为140mm×65mm×50mm的小型化结构设计。相比于传统的旋转衍射光栅改变光线在光栅上的入射角来实现波长调谐的方式,该方法有效地缩减了增益器件的平移距离,从而有利于便携式外腔激光器波长的快速宽带调谐。实验结果表明,该激光器具有较宽的波长调谐范围,在340~900mA注入电流下均可实现10nm以上的波长调谐,尤其在900mA大注入电流下,其波长调谐覆盖779.40~791.07nm,调谐范围可达11.67nm,且激射线宽小于0.2nm,单波长输出功率最高可达280mW,放大的自发辐射抑制比大于25dB,呈现出较优异的输出性能,满足移频激发拉曼光谱检测系统对光源的基本要求。此外,该激光器可采用一微型压电陶瓷驱动器来实现波长的电动调谐,实验获得了1.35nm的波长调谐范围,证实了所制785nm便携式光栅外腔可调谐半导体激光器适合作为便携式移频激发拉曼光谱检测系统的光源用于减除原始拉曼光谱中的荧光背景。     

Achieving single-lobed far-field patterns of broad area laser diode with external cavity feedback

We demonstrate a technique for single transverse mode operation of high-power broad area laser diode (BAL). In the experiment, the HR mirror is used as an external cavity mirror and the grating is used as a wavelength selective component. By tiling the HR mirror and the grating, the number of transverse modes oscillating in the cavity can be limited and the spectral bandwidth of the laser diode can be reduced. A single-lobed near diffraction-limited laser beam with the beam divergence (FWHM) of 0.43°, the spectral line-width of 0.7 nm and the output power of 350 mW are obtained. With the feedback, the power density of the output laser beam is increased 6 times in comparison with the free running.     

High-power cladding-pumped Tm-doped silica fiber laser with wavelength tuning from 1860 to 2090 nm

A high-power double-clad Tm-doped silica fiber laser, pumped by two beam-shaped and polarization-coupled diode bars at 787 nm, was wavelength tuned by use of an external cavity containing a diffraction grating. The Tm fiber laser produced a maximum output power of 7 W at 1940 nm for 40 W of incident diode power and was tuned over a wavelength range of 230 nm from 1860 to 2090 nm, with >5-W output power over the range 1870-2040 nm. The prospects for further improvement in performance and extension of the tuning range are discussed.     

Development of narrow-linewidth diode lasers by use of volume holographic transmission gratings

We present two diode laser setups that employ volume holographic transmission gratings to provide optical feedback. The advantage of this kind of grating is high diffraction efficiency and the possibility to place optical elements on both sides of the grating. This allows for advanced external cavities and adjustable feedback efficiency. The first setup is a diode laser in the Littman configuration with the transmission grating replacing the conventional reflection grating. The second setup improves the frequency selectivity by substituting the feedback mirror with a passive resonator. This grating-enhanced external cavity diode laser (GECDL) achieves excellent frequency stability. A prototype of the GECDL setup demonstrates an intrinsic linewidth of 7 kHz and an operation range that covers the full amplification profile of the laser diode.