Modulation response of quantum-well lasers with carrier transport effects under weak optical feedback

We theoretically investigate the influence of optical feedback on the modulation response of quantum-well lasers. Controlled weak optical feedback is shown to be useful to improve the high frequency performance, compensating the limitations imposed by carrier-transport effects.     

Spectral linewidth reduction in semiconductor lasers by an external cavity with weak optical feedback

The linewidth narrowing of a semiconductor laser due to weak optical feedback is analysed, taking into account both phase condition and threshold change for the feedback-induced modes. The achievable linewidth reduction lies in between two limiting cases, 1/(1 + X ?(1 + ?2))2 and 1/(1 + X)2, where ? and X are the linewidth enhancement factor and the feedback parameter, respectively.     

Mode partition in semiconductor lasers with optical feedback

The authors point out that random noise processes induce mode partition fluctuations in semiconductor lasers. Mode partition depends on laser parameters and modulation current. However, external optical feedback can also increase mode partition noise. Here, a numerical solution of multimode noise-driven rate equations with time-delayed terms is utilized to investigate mode partition in semiconductor lasers with reflecting feedback. Photon statistics of the main and side modes in semiconductor lasers under both CW operation and dynamic operation are considered. Probability-density curves for the main and side modes are shown. The feedback-induced change of photon statistics of the main and side modes is clearly seen. Numerical results indicate that, if the laser used is exposed to reflections, a more stringent mode discrimination requirement for suppressing the buildup of laser-cavity longitudinal side modes may result. If mode discrimination is insufficient for avoiding the excitation of side modes, the feedback-induced power penalty depends on the fiber dispersion     

Equivalent circuit of semiconductor lasers with weak coherentoptical feedback

The equivalent circuit modelling of semiconductor lasers makes simulation of direct modulation of semiconductor lasers extremely simple through the use of circuit simulators such as SPICE. The authors extend the circuit model to incorporate the effect of weak coherent optical feedback into the laser cavity. Results from circuit simulation of the model are compared with results reported earlier as well as results obtained from direct numerical analysis of rate equations     

Spectral characteristics of semiconductor lasers with optical feedback

Optical feedback-induced changes in the output spectra of several GaAlAs lasers operating at 0.83 μm are described. The feedback radiation obtained from a mirror 60 cm away from the laser is controlled in intensity and phase. Spectral line narrowing or broadening is observed in each laser depending on the feedback conditions. Minimum linewidths observed with feedback are less than 100 kHz. Improved wavelength stability is also obtained with optical feedback resulting in 15 dB less phase noise. An analytical model for the three-mirror cavity is developed to explain these observations.     

Subharmonic modulation distortions in semiconductor lasers with optical feedback

Experimental studies of subharmonic modulation distortions of semiconductor lasers with optical feedback are described. These distortions were found to exhibit almost resonant frequency characteristics and threshold behaviour against the modulation frequency and its depth, respectively. It was inferred that they would be excited by parametric interactions caused by some laser diode parameter changes due to modulation.     

Noise characteristics in line-narrowed semiconductor lasers with optical feedback

Effects of optical-feedback-induced line-narrowing on low-frequency amplitude and phase noise of semiconductor lasers are reported. Free-running laser noise is compared with that of lasers operating with external mirror feedback. While less than 1 dB difference in the amplitude noise with and without feedback is observed, line-narrowed lasers exhibit 15?20 dB reduction in low-frequency wavelength instability, or phase noise.     

Estimating the parameters of semiconductor lasers based on weak optical feedback self-mixing interferometry

The paper presents a practical approach for measuring the linewidth enhancement factor /spl alpha/ of semiconductor lasers and the optical feedback level factor C in a semiconductor laser with an external cavity. The proposed approach is based on the analysis of the signals observed in an optical feedback self-mixing interferometric system. The parameters /spl alpha/ and C are estimated using a gradient-based optimization algorithm that achieves best data-to-theoretical model match. The effectiveness and accuracy of the method has been confirmed and tested by computer simulations and experiments, which show that the proposed approach is able to estimate /spl alpha/ and C with an accuracy of 6.7% and 4.63%, respectively.     

Analysis of DFB semiconductor lasers with external optical feedback

A theoretical analysis of the sensitivity of DFB semiconductor lasers to external optical feedback is presented. Numerical simulations allow the authors to determine the optimum facet reflectivity, for a given κL value, to minimise the sensitivity to external optical feedback     

弱光反馈对半导体激光器AM和FM噪声谱的影响

一、引言 相干光通信系统具有灵敏度高,选择性好及可采用波分复用等优点。为了实现相干光通信系统,一个首要的问题便是抑制作为发射机振荡器与接收机本地振荡器的LD的噪声。光反馈是抑制LD噪声的有效手段,近年来人们对此进行了大量研究。然而,这些研究一般都局限于LD的线宽。由于LD的场功率谱通常不是洛伦兹型的,因此,必须研究LD的FM和AM噪声功率谱才有实际意义。     

Chaos in semiconductor lasers with optical feedback: theory andexperiment

The authors present a detailed theoretical and experimental investigation of the nonlinear dynamics of a semiconductor laser with optical feedback. The results show that the coherence collapsed state is a chaotic attractor and that chaos is reached for increasing feedback level through a quasi-periodic route interrupted by frequency locking. Furthermore, the coexistence of two attractors, associated with the same external cavity mode, but having different relaxation oscillation frequencies, is demonstrated and explained     

Simple method for feedback parameter determination in optical feedback controlled semiconductor lasers

A simple method is proposed to measure the X parameter which determines the optical feedback influence on the semiconductor laser spectral characteristics. Experimental results are in good agreement with high spectral resolution measurements.     

Dynamic regimes in semiconductor lasers subject to incoherent optical feedback

The dynamics of a semiconductor laser subject to polarization-rotated (incoherent) optical feedback in the long cavity limit has been numerically and experimentally investigated. The results show that the induced dynamics can be grouped into four regimes (stable, chaotic, pulsed, and two state) and that the transverse-magnetic mode of the laser never lases in the ring cavity configuration studied. In addition, unlike the earlier short-cavity work, the boundaries between the regimes in the long-cavity case were found to be independent of the external-cavity delay time.     

Suppressing mode hopping in semiconductor lasers by orthogonal-polarization optical feedback

Mode hopping is characterized by a stochastic exchange of power between two longitudinal modes of a laser, inducing a high-level intensity noise in the laser's output. This investigation proposes an orthogonal-polarization optical feedback (OPF) method to suppress mode hopping in semiconductor lasers. Experimental results indicated that, under some operating conditions, mode hopping could be completely suppressed by an OPF of around -29.3 dB in feedback ratio while the laser was conducted into a single-mode state. Moreover, the mode-hopping region was significantly reduced, enabling the laser's wavelength to be tuned continuously over a wider range. These results can be used to greatly improve the performance of semiconductor lasers.     

Chaos synchronization and chaotic signal masking in semiconductor lasers with optical feedback

Theoretical and experimental investigations of chaos synchronization and its application to chaotic data transmissions in semiconductor lasers with optical feedback are presented. Two schemes of chaos synchronization-complete and generalized synchronization-are discussed in the delay differential systems. The conditions for chaos synchronization in the systems and the robustness for the parameter mismatches are studied. The possibility of secure communications based on the chaos masking technique in semiconductor lasers with optical feedback is also discussed, and message transmission of a 1.5-GHz sinusoidal signal is demonstrated. The method of bandwidth enhancement of chaotic carriers is proposed for broad-band chaos communications.     

Noise properties of semiconductor lasers due to optical feedback

It has been recognized for some time that reflections back into the cavity of an injection laser from a mechanically unstable external mirror cause noise in the output of the laser (reflection noise). In this paper, noise measurements are presented for index-guided lasers as functions of the output power, the degree of optical isolation and external cavity length (5-15 cm), while current modulation (using 2-4 mA at 50-200 MHz) has been used to reduce the noise levels by as much as 20 dB. It is demonstrated that the mechanism of noise reduction by modulation is the frequency modulation of the laser's spectrum and its interaction with the modes of the external cavity. It is shown that using an optical isolator can give a relative intensity noise of -110 dB while using modulation in addition can reduce this to -125 dB; the bandwidth performance of optical storage systems is discussed in terms of these two schemes.     

Quantifying optical feedback into semiconductor lasers via thermal profiling

We show that thermal profiling can be used to monitor optical feedback into semiconductor lasers in photonic integrated circuits, where direct optical access is impractical. The optical output power of a laser, both free-running and when exposed to optical feedback, can be quantitatively determined from thermal measurements alone, without recourse to direct optical measurements. Furthermore, the shift in threshold current resulting from optical feedback can be determined from the thermal measurements, enabling quantitative determination of the feedback coupling efficiency into the laser.     

Emission frequency stability in single-mode-fibre optical feedback controlled semiconductor lasers

A newly designed semiconductor laser emitter with adjustable linewidth by controlling the coupling to a single-mode fibre is described with emphasis on thermal requirements to obtain a high-frequency stability. A stable operation has been achieved during more than 1 h using an AlGaAs laser diode with optical feedback from a 50 cm-long single-mode fibre resulting in a 50-fold reduction of the spectral linewidth.     

Theoretical analysis of external optical feedback on DFB semiconductor lasers

The effect of external optical feedback on resonant frequency, threshold gain, and spectral linewidth of distributed feedback (DFB) semiconductor lasers is theoretically analyzed. The analysis applies to any type of laser cavity formed by a corrugated waveguide limited by partially reflecting facets. It is shown that the sensitivity to optical feedback on a facet is closely related to the power emitted through this facet. Numerical results on wavelength selectivity and on sensitivity to optical feedback are given for conventional DFB lasers having an AR-coated facet and for quarter-wave-shifted (QWS) DFB lasers with AR-coatings on both facets. Both laser types are found to be more sensitive to optical feedback on their AR-coated facet than Fabry-Perot lasers for lowkL. On the other hand, QWS-DFB lasers are found to be relatively insensitive to optical feedback for largekL.     

基于半导体环形激光器的光反馈动力学研究

为了研究半导体环形激光器在外部交叉光反馈情况下的非线性动力学特性, 基于环形激光器的速率方程, 采用数值仿真的方法, 得到了各种反馈参量下的时间序列及功率谱, 并研究了反馈系数对混沌带宽及时间延迟特性的影响。结果表明, 在各种不同外部反馈参量的情况下, 环形激光器展现了单周期、多周期、低频反相波动以及混沌态等丰富的动力学态; 在对称光反馈时, 可得到最大为3.7GHz的混沌带宽; 在时间不对称光反馈时, 产生的混沌信号的时延特征被很好地抑制。该研究结果可为环形激光器的实际应用提供一定的理论参考。