Collapse and revival of synchronisation of chaotic diode lasers

Synchronisation of a mutually coupled external cavity chaotic diode laser and a solitary laser collapses and revives depending on the optical phase of the external cavity diode laser.     

Highly linear-polarized external cavity lasers hybrid integrated on planar lightwave circuit platform

We propose and demonstrate, for the first time, a highly linear-polarized external cavity laser (ECL) integrated on planar lightwave circuit (PLC) with an in-PLC polarizer designed to improve polarization extinction ratio (PER). The in-PLC polarizer based on a 45/spl deg/-tilted grating was simply formed in the laser cavity composed of a Fabry-Pe/spl acute/rot laser diode and a Bragg grating. The proposed ECL exhibited a PER value as high as 30 dB and single longitudinal mode oscillation with a high sidemode suppression ratio of 50 dB at 1310 nm.     

光纤光栅外腔半导体激光器理论模型分析与选取

为了讨论三腔镜近似或耦合腔近似两种等效腔模型对计算光纤光栅外腔半导体激光器等效反射率等参量的近似程度,挑选出最优的理论模型,采用数值计算的方法进行模拟仿真,得到了两种模型在采用切趾光纤Bragg光栅和非切趾光纤Bragg光栅情况下的阈值增益等特性曲线。结果表明,在采用切趾光纤Bragg光栅,特别是切趾深度较大的情况下,采用三腔镜近似模型更加符合实际情况。此研究结果对分析和设计单纵模光纤光栅外腔半导体激光器具有一定的参考价值。     

外腔半导体激光器的空间模式特性分析

通过对宽发光截面半导体激光器(BAL)输出激光空间特性和远场分布的理论分析,并根据激光振荡的自再现原理,导出了反馈注入外腔宽发光截面半导体激光器输出激光的光场分布。计算表明外腔的反馈作用可以看作是频谱面上引入了一个带通滤波器,通过选择特定模式的频谱分量进行反馈注入,从而实现选模和改善输出激光光束质量的目的。完成了相应的外腔反馈注入宽发光截面半导体激光器的实验,获得了单瓣近衍射极限的激光输出,在工作电流为1.18倍阈值电流时,获得远场发散角为0.074°的输出激光,计算得相应的光束衍射倍率因子M2为1.16,和理论计算的结果基本吻合。     

外腔半导体激光器的单纵模机制

本文建立了一种外腔半导体激光器单纵模机制的模相互作用模型。由于引入四波混频耦合项,模相互作用的效应对次级模的影响是对称的,均使次级模受到增益抑制。     

Facet Reflection Coefficient of Phase—locked Diode Laser Array in an External Cavity

A diode laser array(DLA) positioned in an external cavity can receive the radiations emitted from its neighboring elements (C1)and that of itself(S) after being reflected at the DLA facet as well as from the external mirror(C0).Considering the fact that |C0/S| should be larger than uniity if the external cavity is effective,and |C1/S| should be larger than unity if the phase locking may be established in the external cavity.The requirements on the reflection at the facet of diode laser array have been specified in terms of the cavity length and reflection coefficient of the external mirror.     

Wavelength Selector External Cavity Laser Diode by Fiber Switch

A Fabry–Perot laser diode coupled to a single-mode fiber Bragg grating has the ability to emit a single longitudinal mode. In this paper a wavelength selector source based on a mechanical fiber switch used to change the Bragg grating in front of the laser diode is investigated. The external laser wavelength is changed. Critical coupling exists between the two fiber ends of the switch, which leads to the creation of a parasitic cavity inside the laser cavity. The aim of this work is to optimize the coupling ends of a single-mode fiber switch with respect to coupling efficiency and afterward measure the laser output power variation and spectrum to check their optical feedback characteristics on the relative intensity noise. Typical emission performance is a power of −2.5 dBm with a SMSR of 43 dB and a RIN of −146 dB/Hz.     

Sequential TE/TM polarization emission from a tunable externalcavity diode laser

A tunable external cavity diode laser that emits in a closely spaced sequence of alternating TE and TM wavelength intervals in the range between 1256 and 1282 nm is reported. In each interval, stable single longitudinal mode TE and then TM emission occurs that can be tuned in wavelength. Two consecutive intervals are separated by a wavelength region where emission instabilities are observed. The wavelength spacing between two successive intervals belonging to the same polarization state corresponds to the mode spacing of the solitary diode laser. As the laser is tuned beyond 1282 nm and up to 1316 nm, the emitted radiation is only TM polarized. The above-mentioned phenomena are based on the composite cavity gain modulation with the wavelength, and on the comparable losses of the system for the TE and TM polarization     

浅析元件参数对外腔半导体激光器输出谱宽影响

半导体抽运碱金属蒸气激光器（DPAL）需大功率窄线宽泵浦源,但市售半导体激光器输出线宽远远大于碱金属原子吸收谱宽,难以实现有效泵浦,因此需采用Littrow 外腔法压窄半导体激光器输出谱宽。Littrow 外腔系统中元件参数的选择直接影响大功率半导体激光器输出谱宽。为此文中沿入射光线方向构建外腔压窄模型,利用球面镜替代柱面镜,分析了微柱透镜阵列、光学系统和光栅元件对外腔输出谱宽的影响,模拟结果为微柱透镜阵列焦距越小、光栅刻线越密、球面镜焦距越大,外腔输出谱宽越窄,实验结果符合理论模型。     

External cavity controlled operation of a semiconductor diode gain element in series with an optical fiber

The series combination of a semiconductor diode gain element (a diode laser whose end facets have been antireflection coated) and an optical fiber has been placed inside an external cavity and the combined system has lased in a single spectral line whose width was less than the1.7 times 10^{-5}-nm (7.5-MHz) resolution of the scanning Fabry-Perot interferometer used in the measurement. This result has been achieved with either a single-mode or a multimode optical fiber in series with the diode gain element and for experiments in which a polarizer, oriented so its polarization is parallel to the diode gain element polarization, was placed at the other end of either fiber. The output of the external cavity is temporally stable as measured both by a 225-MHz-bandwidth detector system and a spectrum analyzer. Over a one minute interval the maximum fluctuation in the output frequency of the external cavity was found to be 2 MHz. Analysis of the threshold behavior of the external cavity for the cases where the multimode or single-mode fiber are in the cavity indicates that the coupling coefficients for either fiber are nearly the same. Without an external cavity, the coupling coefficient from the diode gain element (or from a similar, not anti-reflection-coated, laser) to the multimode fiber is over five times larger than that to the single-mode fiber. These coupling results are explained by postulating that for the multimode fiber, only one or a selected number of the many modes of the fiber can participate in the laser action of the external cavity. It is believed that only these mode(s) are reflected back into the fiber by the spherical mirror in appropriate phase and angle to participate in the laser emission.     

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.     

Widely Tunable GaSb-Based External Cavity Diode Laser Emitting Around 2.3$mu$m

We report on a widely tunable external cavity GaSb-based diode laser (ECL) in Littrow-configuration. The low (44$^circ$full-width at half-maximum) fast axis beam divergence of the quantum-well diode laser employed allowed an efficient coupling to the external cavity, which resulted in a wide tuning range of 177 nm around the central emission wavelength of 2.30$muhbox m$. The maximum output power of the fiber coupled ECL system varied only moderately between 16.5 mW at 2.23$muhbox m$and 9 mW at the long-wavelength limit at 2.39$muhbox m$.     

外腔半导体激光器动态模稳定性的研究

为了研究调谐过程中外腔半导体激光器的模稳定性,采用多光束干涉理论推导Littrow结构外腔半导体激光器的腔增益,并模拟其模结构。分析了光栅面和转臂不在同一平面的情形下,在光栅转动调谐时,通过匹配光栅的反馈波长变化率与外腔波长变化率,推导出最佳的初始外腔长度,并研究了动态模稳定（无跳模调谐）的范围;采用严格的耦合理论和光线变换矩阵分析了准直（耦合）透镜的位置对系统后向耦合效率的影响。结果表明,系统后向耦合效率最大可达99%,极大地压窄了中心波长为780nm半导体激光器的线宽,外腔半导体激光器的理论线宽为未加外腔时的0.96%,动态模稳定范围可达6.8nm。     

外部光反馈对强耦合外腔半导体激光器特性影响的理论分析

本文从理论上分析了外部光反馈对强耦合外腔半导体激光器特性的影响，对相干外部光反馈和非相干外部光反馈两种情形的分析结果均表明强耦合外腔半导体激光器可将半导体激光器所能容忍的临界光反馈强度提高大约２０ｄＢ以上，同时得出了长外腔和强耦合有利于提高外腔半导体激光器抗反馈能力的结论。     

Longitudinal mode-switching dynamics in a dual external-cavitylaser diode [optical neural network]

We study the potential speed of an optical neural network that uses the longitudinal cavity modes of an external-cavity laser diode as neurons. For this purpose, we used a laser diode coupled to two external cavities, each corresponding to one longitudinal cavity mode. The process of longitudinal mode switching is investigated for the case of intracavity optical modulation. In this experiment, the feedback for the mode in one cavity is modulated, and the length of the other cavity can be controlled. Three limitations are imposed on the switching speed. A number of external-cavity round trips are needed to switch from one mode to the other. It is observed that, depending on the amount of optical feedback in both cavities, between 7 and 21 round trips are needed. When the experimental results for varying cavity length are extrapolated to zero cavity length, a residual delay of a few nanoseconds remains. It is believed that this delay is due to a change in carrier density, needed to switch from one mode to another. Modified rate equations are used to model our experiments. The results of numerical simulations are in good agreement with the experimental results and predict the residual delay. The model also predicts a turn-on delay that is related to relaxation oscillations and imposes a third limitation on the operation speed of our optical neural network. Implications of our findings on the potential operation speed of the optical neural network are discussed and suggestions are made for optimization     

Bandwidth-limited picosecond pulse generation by hybrid mode-locking in a ring cavity GaAlAs laser

Bandwidth-limited picosecond pulses have been obtained using hybrid active/passive mode-locking in an external cavity semiconductor diode ring laser. Active mode-locking by application of sinusoidal RF modulation at the cavity round-trip frequency to a diode laser providing gain is supplemented by passive mode-locking in a second laser which is biased to provide saturable loss. Simultaneous streak camera and scanning Fabry-Perot interferometer measurements show that bandwidth-limited pulses of 25 Ps duration are obtained. Operation is not limited to near laser threshold, and frequency detuning sensitivity is improved when compared to the case of purely active mode-locking.     

体光栅外腔半导体激光器列阵的光谱及调谐

对采用体布拉格光栅作为波长选择器件的外腔半导体激光列阵进行了实验研究。实验表明,在体光栅外腔作用下,高功率半导体激光器输出的线宽得到压窄、波长得到固定。与此同时,从布拉格衍射相关理论出发,分析了体光栅法线方向改变对激光器系统输出中心波长的影响。实验表明改变体光栅法线方向的角度,可以在一定范围内调整列阵的输出波长。     

Stable operation range for laser diodes with an integrated passivecavity in the presence of external optical feedback

It is shown that a laser diode with an integrated passive cavity yields higher tolerable levels of feedback from distant reflections than an equivalent long solitary laser diode. To ensure this high tolerance for external feedback, the internal feedback level in the integrated passive cavity must be of the order of about 10%. Then the laser diode remains stable up to external feedback levels in excess of 1% even if the internal reflection phase is not carefully adjusted. External reflections from a cleaved fiber end are then not sufficient to drive the laser into coherence collapse, if realistic coupling efficiencies between laser diode and fiber are taken into account. The low feedback sensitivity is explained by the combination of the long effective length of the laser and a high relaxation resonance frequency. Therefore, quantum-well laser diodes with a long length and a high relaxation resonance frequency are likewise expected to exhibit low feedback sensitivity     

高亮度半导体激光器无输出耦合镜光栅外腔光谱合束

宽面发射半导体激光器的光谱合束技术对发展高功率直接半导体激光光源具有重要意义。光栅外腔光谱合束基于光栅的波长选择特性和外腔半导体激光技术,实现单个合束单元的光谱锁定和所有合束单元的合束输出,输出光束质量与单个合束单元相当,而亮度和功率得到很大的提高。基于无输出耦合镜光栅外腔光谱合束结构,实现了单个半导体激光短阵列的光谱合束,分析了光谱合束的输出光谱、输出功率和光束质量的特性,获得了70 A工作电流下40.8 W的连续输出功率,快轴和慢轴方向的光束质量分别为0.41 mmmrad和9.16 mmmrad （包含95%能量）,相应的电光转换效率为38.4%,亮度高达67.90 MW/（cm2sr）。     

Dynamical properties of a laser diode with optical feedback from anexternal high-finesse resonator

The effect of coupling optically a laser diode to a high-finesse external resonator is described. The authors take into account multiple roundtrips in the external cavity and the carrier finite life-time in the diode laser. The rate equations are studied analytically. Steady states are obtained and their stability determined. Numerical resolution of the equations leads to predicting self-pulsing modes of operation. To the authors' knowledge, this is the first numerical study of the laser diode rate equations with an infinite number of delay terms. The main result is a stabilization effect due to the high-finesse cavity; neither deterministic chaos nor complicated bifurcation schemes have been found