Self-Pulsating Amplified Feedback Laser Based on a Loss-Coupled DFB Laser

Monolithic self-pulsating semiconductor lasers called amplified feedback lasers (AFLs) can generate high-frequency self-pulsations according to the concept of a single-mode laser with shortly delayed optical feedback, which consist of a distributed-feedback (DFB) laser, a phase control, and an amplifier section. Since mode degeneracy of the DFB section, which should operate as a single-mode laser, affects the self-pulsation, single-mode characteristics of the DFB section are critical for the self-pulsation. The effect of a complex coupling in the DFB section on the self-pulsation is numerically analyzed to reveal that the complex coupling provides a wide operation range for the self-pulsation. Also, self-pulsating AFLs based on a loss-coupled DFB laser are experimentally demonstrated to verify the self-pulsation characteristics and the capability for all-optical clock recovery.     

High-frequency pulsations in DFB lasers with amplified feedback

We describe the basic ideas behind the concept of distributed feedback (DFB) lasers with short optical feedback for the generation of high-frequency self-pulsations and show the theoretical background describing realized devices. It is predicted by theory that the self-pulsation frequency increases with increasing feedback strength. To provide evidence for this, we propose a novel device design which employs an amplifier section in the integrated feedback cavity of a DFB laser. We present results from numerical simulations and experiments. It has been shown experimentally that a continuous tuning of the self-pulsation frequency from 12 to 45 GHz can be adjusted via the control of the feedback strength. The numerical simulations, which are in good accordance with experimental investigations, give an explanation for a self-stabilizing effect of the self-pulsations due to the additional carrier dynamic in the integrated feedback cavity.     

Controllable self-pulsations in multi-section DFB lasers with anintegrated phase-tuning section

1.55-μm InGaAsP-InP multi-section DFB lasers with an integrated phase tuning section have been fabricated. It is shown for the first time that the self-pulsation can be electrically switched on and off by adjusting the phase current. Reproducible self-pulsation characteristics from device to device are achieved in this way     

Optical generation and sideband injection locking of tunable 11-120GHz microwave/millimetre signals

It is shown that two-section gain-coupled DFB lasers with large section lengths and weak distributed feedback coupling exhibit a self-pulsation tuning range greater than reported previously. The phase noise of a sideband injection locked self-pulsation is measured and the jitter introduced by the self-pulsing laser found to be negligible     

Gigahertz self-pulsation in 1.5 μm wavelength multisection DFBlasers

Self-pulsation in InGaAsP/InP multisection distributed feedback (DFB) lasers was generated reproducibly by adjusting appropriate injection conditions. Frequencies of up to some gigahertz were achieved. It was demonstrated that-in contrast to Fabry-Perot (FP) elements-no selective treatment of one section is required for creating the self-pulsation. It is concluded that the self-pulsation in DFB elements is of a different type than in FP elements     

Modeling self-pulsating DFB lasers with an integrated phase tuningsection

A theoretical model of a self-pulsating three-section DFB laser with an integrated phase tuning section is established. It is based on traveling wave equations and the standard carrier rate equations. Parameters of an existing device are used for applying the model. Key conditions and characteristics of self-pulsations (SPs) are modeled and compared with experimental results. The important role of phase tuning for turning on the SP is pointed out. The dependence of the SP regime on the detuning between the Bragg wavelengths in the laser and reflector is determined and the essential role of phase-readjustment is identified. Frequency tuning via the laser currents, as well as the pulse shape at various frequencies, is investigated. This allows us to identify the mechanism for frequency tuning. The model turns out to be a good tool to improve our knowledge of the self-pulsation effect and to design optimized devices     

Self-pulsation in multisection laser diodes with a DFB reflector

A novel self-pulsation regime is observed in multisection laser diodes which consist of a loss-coupled distributed-feedback (DFB) section, a phase control section, and gain sections, where 10-GHz self-pulsation due to compound cavity mode beating has been reported with the DFB section operated as a single-mode laser. When the DFB section is below threshold current, the devices give the self-pulsation in a very wide operating range. We attribute the pulsation to passive mode-locking and also confirm that this structure is applicable to 40-GHz operation.     

Electrically switchable self-pulsations in integratable multisection DFB-lasers

An integratable version of a self-pulsating AR-coated multisection DFB-laser with a phase-tuning section integrated between two DFB sections is presented. It is shown that the phase current can act as an electrical switch for turning ON and OFF the self-pulsations. In addition, the frequency stability can be improved by properly adjusting the phase current. The frequency of the self-pulsations is electrically tunable over more than one octave continuously.     

Self-pulsation in two-section DFB semiconductor lasers and itssynchronization to an external signal

A model of self-pulsation in two-section distributed feedback (DFB) lasers without a saturable absorber is developed by using generalized rate equations. The introduction of an effective differential gain in our model allows us to take into consideration both material and structural effects. The self-pulsation conditions are derived from a linear stability analysis. A mechanism based on a negative effective differential gain is proposed to explain the origin of self-pulsation in such lasers. By considering an injected optical signal, the optical synchronization of self-pulsating lasers is studied using nonlinear simulations. This leads to the determination of some locking-range properties, which are then compared to experimental and analytical results     

混合光栅型的三段式自脉动DFB激光器

制作了1.55μm InGaAsP-InP三段式混合光栅型DFB激光器.观察到了20GHz左右的自脉动信号.讨论了自脉动的产生机制,并且对调相区所起的作用进行了研究.     

Optical feedback on self-pulsating semiconductor lasers

Weak optical-feedback effects on the statistical properties of self-pulsations in narrow-stripe semiconductor lasers are analyzed using Lang-Kobayashi-type equations. The self-pulsation features are compared with the characteristics of excited relaxation oscillations. We determine the operating regime in which the randomizing effect of spontaneous-emission noise destroys pulse coherence. In this regime, only phase-insensitive effects of optical feedback are possible, and optimum jitter reduction is achieved with delay times of the order of an integer-odd multiple of the free-running pulsation period. In the high-pump operating regime, interpulse coherence is retained and the optical-feedback phase is shown to be instrumental for pulse-jitter control. Our results show that for cavity lengths up to 10 cm, variations on the order of half an optical wavelength induce jitter variations of one order of magnitude     

两节分布反馈激光器的性能

详细讨论了两节(两电极)分布反馈(DFB)激光器的重要特性,其中包括调谐理论、频率调制响应以及频率交换速率。两节DFB激光器的调谐机理可根据波导光栅反射特性的基本相位和幅度来解释。波长调谐由不均匀电流注入的纯电子效应所引起。激光器的调制带宽由有源区中受激载流子寿命所决定。在激光器红移和蓝移静态调谐状态下,FM响应和频率交换是不同的。对高速FSK调制,激光器应偏置于蓝移状态下工作。FM响应的大小和相位变化影响激光器的高速频率交换。     

Wavelength tuning mechanism in three-electrode DFB lasers

The wavelength tuning mechanism is investigated for three-electrode distributed feedback (DFB) InGaAs-InGaAsP lasers. It is shown that the side and center sections play different roles in wavelength tuning: the former determines the effective Bragg wavelength and the latter contributes through the round-trip phase condition. The lasing wavelength is expressed in a simple form that renders the wavelength shift behavior exceedingly understandable. The indispensability of the thermal contribution to continuous broad range tuning is also clarified both theoretically and experimentally     

Analysis of oscillation characteristics of separated-electrode DFBlaser diodes

The oscillation characteristics of separated-electrode distributed feedback (DFB) lasers are analyzed by a numerical approach. In the calculation, coupled-mode equations are used including the carrier-density nonuniformity along the laser axis, which is introduced by the spatial hole burning and/or the nonuniform current injection. When the center section of a DFB laser, with three equally separated electrodes, is more strongly pumped than the side sections, high performance is achieved: the mode stability is maintained in the high-power state, resulting in a narrow linewidth. This is because the spatial hole burning is compensated by the larger current injection into the center region. The wide tunable range is also obtained under this bias condition     

Static, dynamic, and noise analysis of multisection DFB lasersusing frequency-domain transmission line model

A novel frequency-domain transmission line model for multisection distributed feedback (DFB) lasers is developed. The characteristic impedances of active periodic structures are derived. A multisection DFB laser is described as a transmission line network, with each section represented by a transmission lint segment with a corresponding characteristic impedance. Static, dynamic, and noise analysis of multisection DFB lasers is demonstrated. The reflections at the junctions between sections are evaluated more accurately. The resonant condition of the equivalent transmission line network, instead of cumbersome Wronskian, is used to reformulate the rate equations. The diffusion coefficient of Langevin noise terms of any two different positions is solved for the first time, resulting in a more accurate noise analysis of multisection semiconductor lasers. Analytical expressions of the dynamic responses and noise properties of multisection DFB semiconductor lasers are derived     

Enhanced wavelength tuning range in two-section complex-coupled DFBlasers by alternating gain and loss coupling

A novel tunable two-section complex-coupled distributed feedback (DFB) lasers were demonstrated which exhibited an enhanced wavelength tuning range beyond 7 nm by current injection only. By a simple master-and-slave type of injection current control, either in-phase gain-coupling or antiphase loss-coupling mechanism can be activated, in such a way that one of the two Bragg modes around DFB stopband will become the lasing mode, and its wavelength can be simply and independently tuned by corresponding injection current. More then 45 dB side-mode suppression ratio (SMSR) over entire tuning range were obtained. Good system performance for 375 km transmission with butt-coupled III-V Mach-Zehnder (MZ) modulator at 2.5 Gb/s over nondispersion-shifted fiber was also demonstrated     

Widely frequency tunable amplified feedback laser as 20 GHz optical microwave source

Optical microwave sources are required in optical signal processing. Amplified feedback laser (AFL) which can generate high frequency self-pulsation due to compound cavity modes beating are used as optical microwave sources. In this paper, we fabricate a four-section AFL consisted of a different distribute feedback (DFB) section, a phase control section, an amplifier section, and a transparent section. This AFL generate continuously tunable microwave in the range 19.87–26.30 GHz with 3 dB linewidth about 3 MHz. Microwave with narrow linewidth is obtained by injecting quarter frequency modulated light experimentally.     

Self‐Pulsation in Multisection Distributed Feedback Laser Diode with a Novel Dual Grating Structure

A self‐pulsating multisection distributed‐feedback laser diode (DFB LD) can potentially realize all‐optical clock extraction. This device generally consists of three sections, two DFB sections and one waveguide section. The most important variable in this device is detuning, which is the relative spectral position between the stop bands of two DFB sections. We fabricated a novel structure in which two gratings were located one over and one under the active layers. Each grating structure was independently defined in processing so that detuning, which is the prerequisite for self‐pulsation, could be easily controlled. Observing various self‐pulsating phenomena in these devices under several detuning conditions, we characterized the phenomena as dispersive Q‐switching, mode beating, and self‐mode‐locking.     

基于分布反馈激光器布里渊散射的高精度光谱测量

实现了一种基于光纤中受激布里渊散射(SBS)效应 的高分辨率光谱测量技术。使用连续可调谐分布反馈(DFB) 激光器作为泵浦光,与待测信号光在单模光纤(SMF)中发生受激布里渊放大相互作用,由此 实现对待测光的高分 辨率光谱测量与分析。DFB激光器的波长扫描通过高精度温度调谐来实现。与相关报道 中使用的外腔 可调谐激光器对比,DFB激光器具有体积小、成本低的优势。同时在波长扫描过程中,对DFB 激光器的输出光进行自 拍频处理获得其实时扫描速率,以此校正激光器的实时扫描波长,提高测量准确度。实验 初步验证了本文高分辨率光谱测量技术的可行性,并获得了0.24pm 的光谱分辨率。     

Wide range tunable laterally coupled distributed-feedback lasers based on InGaAs-GaAs quantum dots

The authors have investigated tunable distributed feedback (DFB) lasers based on InGaAs quantum dots grown by molecular beam epitaxy. Two-section tunable DFB lasers were fabricated by patterning laterally gain coupling binary superimposed gratings perpendicular to the ridge waveguide. Side-mode suppression ratios of up to 40 dB have been achieved. The tuning range covers 30 nm.