Tuning characteristics of a tunable-single-frequencyexternal-cavity laser

The lasing characteristics of a tunable-single-frequency laser operated in conjunction with a tunable external cavity are investigated. The effect of phase error in the external cavity on the lasing frequency, linewidth, and output power is calculated by deriving the characteristic equation for the FP cavity as a traveling amplifier with an effective mirror concept. The analysis suggests that the diode laser and the external cavity may be successfully tuned open-loop if the feedback strength is appropriate and the tuning nonlinearities in the active and passive cavities are not too severe. This is demonstrated by maintaining a linewidth of 4 MHz while tuning continuously over 34 GHz     

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。     

Experimental stability diagram of a diode laser subject to weakphase-conjugate feedback from a rubidium vapor cell

We report on a systematic experimental investigation of the dynamical behavior of a diode laser subject to delayed feedback from a phase-conjugating mirror based on nearly-degenerate four-wave mixing in rubidium vapor. We present the first experimental stability diagram for this system. In the weak feedback regime, with feedback levels up to -30 dB, me demonstrate locking to the pump frequency with a reduced linewidth smaller than 8 MHz. In contrast to a laser with external injection, and contrary to predictions made for phase-conjugate feedback, the extent of this locking region is found to be limited. For increased feedback rates, the laser leaves the locking region and enters an unstable region through a series of multiple sidebands spectra. This is associated with self-excitation of the relaxation oscillation, and the observed scenario suggests a series of period-doublings after an initial Hopf bifurcation     

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。     

Polarization switching of an er :yb :cr: phosphate glass microchip laser

We show that the light of a commercially available Er:Yb:Cr.-phosphate glass microchip laser end-pumped at 977 nm by an InGaAs laser diode can be switched between two linear polarization eigenstates when it is submitted to a polarized optical feedback. The flip occurs when the feedback phase is scanned by the external cavity length. In our experiments the laser diode light is confined to a fiber which is single-mode at pumping wavelength and the microchip laser operates in a single-longitudinal-and transverse mode. The microchip laser exhibits a self-pulsing behavior.     

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     

Dynamical behavior of a semiconductor laser with filtered externaloptical feedback

We report on a theoretical analysis of the dynamical performance of a semiconductor laser under the influence of delayed weak filtered external optical feedback. The filter widths considered range from 1 to 100 GHz. The analysis concentrates on the well known low-frequency fluctuations (LFFs) regime, in which LFFs occur in the absence of filtering. As expected, filtering the feedback light stabilizes the system in general. LFF can already be suppressed for moderately broad filters (25-50 GHz). In that case, the system was found to operate on the maximum gain mode with a small amplitude limit cycle. We show how the filtering can, in principle, be used for targeting the laser on the maximum gain mode     

External optical feedback effects on semiconductor injection laser properties

Influences on the semiconductor laser properties of external optical feedback, i.e., return of a portion of the laser output from a reflector external to the laser cavity, have been examined. Experimental observations with a single mode laser is presented with analysis based on a compound cavity laser model, which has been found to explain essential features of the experimental results. In particular, it has been demonstrated that a laser with external feedback can be multistable and show hysteresis phenomena, analogous to those of non-linear Fabry-Perot resonator. It has also been shown that the dynamic properties of injection lasers are significantly affected by external feedback, depending on interference conditions between returned light and the field inside the laser diode.     

光栅外腔提高VCSEL微波调制效率实验研究

实验研究了垂直腔面发射激光器(vertical cavity surface emitting laser,VCSEL)在闪耀 光栅作为外腔反馈时的直流和微波调制特性。VCSEL底部端面和外部闪耀光栅组成法布里- 珀罗(Fabry-Perot,FP)腔,由于闪耀光栅的反馈作用,可以提高VCSEL微波调制效率。在VCSEL仅有直流 电流驱动时,实验观察到了频率与FP腔长有关的边带功率,调节FP腔长,使FP腔谐振频率与 微波调制频率耦合,可在相同微波功率下得到2倍的有效边带功率。研究结果表明,闪耀光 栅外腔VCSEL可以在较宽的输入较小微波功率范围内得到较高的有效边带功率。本文研究将 为微波调制VCSEL及其他半导体激光器应用提供一定的参考意义。     

Controling the linewidth of a semiconductor laser withphotorefractive phase conjugate feedback

A novel technique for narrowing the linewidth of a single laser diode using photorefractive phase conjugate feedback is presented. The behavior of this system can be modeled by adapting the previously developed theory to include the phase constraints of the phase conjugate external cavity. The experiments show excellent agreement with the model. This technique produces a stable, narrow linewidth in a semiconductor laser. The comparison to the conventional case is discussed     

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$muhbox m$.     

Characteristics of a grating-external-cavity semiconductor lasercontaining intracavity prism beam expanders

A grating tuned external cavity semiconductor laser incorporating a gradient-index rod lens and a pair of intracavity silicon prism beam expanders was constructed using a configuration aimed at simultaneously achieving the following objectives: the ability to operate at any external cavity longitudinal mode without tuning gaps caused by residual resonances of the laser diode cavity, stable feedback coupling between the diode and external cavities, narrow optical linewidth, and a high degree of external cavity longitudinal sidemode suppression     

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.     

激光二极管阵列的窄线宽、可调谐输出

外腔反馈的激光二极管阵列(LDA)可获得窄线宽、可调谐的光谱输出。外腔由快轴准直镜、准直光学系统和闪耀光栅组成。由于阵列中各发光单元的排列弯曲导致不同波长的光原路返回,引起谱线展宽,在输出光路中加入光谱滤波器,使激光二极管阵列的线宽进一步窄化。这样,激光二极管阵列的输出光谱由自由运转时的2 nm压缩到0.12 nm,在恒定温度23℃时,实现了激光在806～818 nm的调谐,调谐范围达12 nm。     

Characteristics of transients among periodic attractors controlledby high-frequency injection in a chaotic laser diode

We numerically studied statistics of the transient response time when switching between periodic attractors obtained through chaos control with a high-frequency injection method in a laser diode that is subject to optical feedback. Each transient response time significantly depends on its position in the starting attractor, whereas the statistical distributions of the response times for many transients are determined almost entirely by the final attractor. The average transient response time is 40 times larger than the round time in the controlled periodic attractors. The transient response time is also strongly affected by the external cavity length. The shortest average transient response time is obtained at a minimum external cavity length and a zero phase difference between the laser field and the feedback light field     

Tunable amplification properties of distributed feedback laserdiodes

The tunable amplification properties of a distributed feedback laser diode (DFB-LD) are described. The performance of the laser diode as an optical filter, its tuning range, amplification gain, crosstalk due to submodes, and signal-to-noise ratio are determined. To achieve maximum amplification with the least noise, the DFB-LD injection current is held at or near the threshold value by feedback from an optical detector. The resonant wavelength is precisely controlled over a range of 2.0 nm (154 GHz) by varying the temperature of the DFB-LD, while at the same time the injection current is kept at the optimum value by the feedback system. By using the tunable amplification properties of a DFB-LD, an optical tunable filter was experimentally observed     

Relative intensity noise for laser diodes with arbitrary amounts ofoptical feedback

A unified study of the noise characteristics of semiconductor lasers with optical feedback and short external cavity length is presented. A new set of nonlinear rate equations that can describe a laser diode with any amount of optical feedback is proposed. The relative intensity noise (RIN) is calculated by using a numerical solution of these equations. This paper concentrates mainly on the moderate and strong feedback regimes. The spectral phenomena observed during the transition from the weak feedback to the “coherence collapse” regime and then to the strong feedback regime are studied and explained. The effect of the variation of some of the laser diode parameters on the RIN characteristics is also investigated     

Compact external cavity diode laser for quantum experiments

We present a compact and practical scheme of building a ~780 nm external cavity diode laser (ECDL) whose wavelength is mainly determined by an interference filter. The Lorentzian linewidth measured by the heterodyne beating between two identical lasers is 60 kHz, and the geometry size of the laser is only 71.5 mm×65 mm×40 mm. The linear cavity design is less sensitive to misalignment induced by mechanical and thermal disturbances, and in comparison to a common grating-based design, the sensitivity to vibration is substantially reduced. Due to its excellent performance, the laser design has already been applied to cold atom trapping experiments. This interference filter ECDL method can also be extended to other wavelengths and widen the application range of diode laser.     

Chaos control and noise suppression in external-cavitysemiconductor lasers

Feedback-induced chaos and intensity noise enhancement in a laser diode with external optical feedback are studied by computer simulations. The enhancement of relative intensity noise (RIN) that is often observed in experiments is considered as a result of the feedback-induced deterministic chaos and the intensity noise suppression is treated from the viewpoint of chaos control. Especially, the conventional noise suppressing technique known as a high-frequency injection modulation is turned into a problem of stabilizing chaos through parameter modulations. We developed an analytical method which allows to optimize the modulation frequency from the linear stability analysis of the dynamical model that describes the laser diode with external feedback. The robustness of the modulation with respect to the modulation frequency and depth is verified and the results suggest the feasibility of applying our method to actual noise suppression. The RIN in the low-frequency region (up to 100 MHz) is shown to be reduced to the solitary laser level when the feedback-induced chaos is effectively controlled with the optimized modulation frequency     

双体光栅外腔二极管激光器光谱特性研究

为了研究双体布喇格光栅外腔二极管激光器的衍射特性,采用一块体布喇格光栅与一块横向啁啾体布喇格光栅组成双体布喇格光栅,理论分析了组合前后体布喇格光栅的衍射特性,实验研究了双体布喇格光栅外腔二极管激光器的输出光谱特性。结果表明,在双体布喇格光栅外腔反馈的作用下,可以实现双波长同时输出,通过横向移动横向啁啾体布喇格光栅,可以在保持其中一个中心波长不变的情况下,使另外的一个波长在800nm~815nm的范围内线性调谐。此研究为基于双体布喇格光栅实现双波长输出的大功率二极管激光器提供了实验指导。