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.     

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     

三区DFB激光器高速自脉动的研究

全光信号再生技术是超高速大容量全光网络中的核心技术,其中全光时钟提取是全光再生技术的关键,基于多区DFB激光器件自脉动进行时钟提取是最佳选择方案。基于双区DFB激光器件自脉动研究的基础上,对三区DFB激光器件的自脉动特性进行了讨论和数值模拟分析,并对提高自脉动频率的方案进行了研究。     

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.     

Dispersive self-Q-switching in self-pulsating DFB lasers

Self-pulsations reproducibly achieved in newly developed lasers with two distributed feedback sections and with an additional phase tuning section are investigated. The existence of the dispersive self-Q-switching mechanism for generating the high-frequency self-pulsations is verified experimentally for the first time. This effect is clearly distinguished from other possible self-pulsation mechanisms by detecting the single-mode type of the self-pulsation and the operation of one section near the transparency current density using it as a reflector with dispersive feedback. The operating conditions for generating this self-pulsation type are analyzed. It is revealed that the required critical detuning of the Bragg wavelengths of the two DFB sections is achieved by a combination of electronic wavelength tuning and current-induced heating. The previous reproducibility problems of self-pulsations in two-section DFB lasers operated at, in principle, suited current conditions are discussed, and the essential role of an electrical phase-control section for achieving reproducible device properties is pointed out. Furthermore, it is demonstrated that phase tuning can be used for extending the self-pulsation regime and for optimizing the frequency stability of the self-pulsation. Improved performance of the devices applied as optical clocks thus can be expected     

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     

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.     

An Ultralow Noise and Narrow Linewidth λ/4-Shifted DFB Er-Doped Fiber Laser With a Ring Cavity Configuration

We report a polarization-maintaining lambda/4-shifted distributed feedback (DFB) Er-doped fiber laser with a ring cavity configuration. The ring cavity suppressed the self-pulsation of the stand-alone Er-doped DFB fiber laser. The laser with a 57-m-long ring cavity achieved single-longitudinal-mode operation, a linewidth as narrow as 6 kHz, and relaxation-oscillation-free noise characteristics.     

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     

Distinction between multimoded and singlemoded self-pulsations-inDFB lasers

DFB lasers with split contacts are shown, by large signal dynamic modelling, to self-pulsate at gigabit frequencies. Two different self-pulsation schemes are discussed: where the laser switches between the higher and lower stop band modes, and where the laser pulsates around a single mode. The second scheme can yield self-pulsation frequencies beyond 20 GHz. Comparisons are made with experimental results     

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 multielectrode distributed feedback lasers

Measurements on multielectrode distributed feedback (DFB) lasers without a saturable absorber reveal the existence of a self-pulsation (SP) regime. In this regime, the laser remains in the same single-longitudinal mode with simultaneous intensity and frequency modulation. The laser spectrum is similar to that of a current-modulated single-mode laser. At the up-limit of the SP regime, the behavior between the output power and the injection current becomes bistable. In one branch of the bistable loop, the SP laser presents a very large spectrum without distinguishable peaks, a kind of chaotic state with coherence collapse. A qualitative explanation based on the effective differential gain is given for the origin of SP and associated phenomena in these lasers     

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     

Harmonic Millimeter-Wave Generation and Frequency Up-Conversion Using a Passively Mode-Locked Multisection DFB Laser Under External Optical Injection

We demonstrate that a passively mode-locked multisection distributed-feedback (PML-MS DFB) laser can perform both harmonic millimeter-wave generation and harmonic frequency up-conversion under the external optical injection. Optical multiple modes generated by a PML-MS DFB laser produce harmonic millimeter-waves by mode-beating in a photodiode (PD), and the phase quality and stability are enhanced by the injection of external optical signal modulated at f_LO. In addition, if the external optical signal is modulated simultaneously by f_LO and f_IF, the PML-MS DFB laser performs all-optical frequency up-conversion producing sidebands at f_LOplusmnf_IF when detected by a PD. Using this method, we demonstrate generation of stable harmonic millimeter-waves at 30.42 and 60.84 GHz with f_LO of 15.21 GHz, and up-conversion of 10-Mb/s quadrature-phase-shift keying data at 150 MHz f_IF into the 60-GHz band. These functions of a PML-MS DFB laser can be useful for radio-over-fiber applications in which a compact optical source is needed for processing high-frequency radio signals in optical domain     

Monolithically integrated InGaAsP/InP composite-cavity distributedfeedback lasers

Linewidth reduction to 1 MHz for monolithically integrated extended-cavity DFB lasers that are designed to achieve high optical coupling to a low-loss extended cavity is described. Since a high-efficiency extended cavity at the same time degrades the frequency-modulation (FM) response, an active gain section is integrated at the end of the extended cavity, and its use as a modulator section that maintains a flat FM response at 0.7 GHz/mA is shown. The linewidth and FM characteristics of this DFB extended-passive/active-cavity laser are compared to those of the conventional DFB extended-passive-cavity laser and a two-section DFB laser     

Transfer-matrix formulation of spontaneous emission noise of DFBsemiconductor lasers

A unified formulation of the spontaneous emission noise in semiconductor DFB (distributed feedback) lasers is presented by using a transfer-matrix approach. Analytical expressions for the noise power per unit frequency bandwidth below threshold and the spontaneous emission rate into the lasing mode are obtained based on the Green's function method. Three DFB laser structures are analyzed: (1) a standard DFB structure with facet reflectivities, (2) a multisection DFB structure composed of n sections which models a phase-shifted DFB laser and a multielectrode (tunable) DFB laser, and (3) a periodic layered DFB structure which models a surface-emitting DFB laser. It is shown that the spontaneous emission noise of a complicated DFB laser structure can be calculated easily by the transfer matrix of each section of the structure and its derivative to frequency     

New integrated buried laser-ridge modulator with identical active layer

Integrated laser modulators are attractive devices for wavelength-division-multiplexing optical systems due to their compactness, high output power, and low cost. Their fabrication simplicity is a way to decrease further the transmitter cost and address new opening markets of short range and metropolitan networks. We report a new integration scheme electroabsorption-modulator distributed feedback (DFB) laser based on well-established industrial solutions for discrete buried ridge (BRS) DFB lasers and discrete shallow ridge modulators. Processing simplification with an identical active layer has been possible due to a good behavior of strongly positively detuned BRS lasers. The integrated devices demonstrated 30-dB extinction ratio with 10-GHz bandwidth and P/sub out/=10 dBm for emission in 1.55-/spl mu/m range.     

Modeling of distributed feedback semiconductor lasers withaxially-varying parameters

A numerical model that is capable of predicting important laser characteristics such as the threshold gain and the gain margin between the main and side modes for a distributed-feedback (DFB) semiconductor laser of arbitrary complexity is described. The method consists of solving the coupled-mode equations with axially varying parameters iteratively until the boundary conditions at the two facets are satisfied. The numerical model is applied to two DFB laser structures. In the case of a multiple-phase-shift DFB laser the results show that such devices can have a more uniform axial distribution than that of a conventional quarter-wave-shifted DFB laser while maintaining sufficient gain margin between the main and side modes. In the case of a dual-pitch DFB laser it is shown that the incorporation of a slightly different grating period (~0.1%) over a small section can provide a gain margin that is comparable to that achieved in quarter-wave-shifted DFB lasers     

100-GHz soliton pulse train generation using soliton compression oftwo phase side bands from a single DFB laser

A 100-GHz soliton pulse train, with the potential of very low timing jitter, is generated using soliton compression of the beat signal between two optical carriers. The optical carriers are obtained by optically filtering out the third-order sidebands generated from a single DFB laser and a LiNbO₃ electro-optic phase modulator driven at 16.9 GHz     

High-speed 1.5-μm compressively strained multi-quantum wellself-aligned constricted mesa DFB lasers

A great improvement in the high-speed characteristics for compressively strained multi-quantum-well (MQW) distributed-feedback (DFB) lasers with self-aligned constricted mesa structures is described. Negative wavelength detuning is an important factor in making possible the extraction of potential advantages for the compressively strained MQW DFB lasers. A 17-GHz bandwidth, which is the highest among the 1.5-μm MQW DFB lasers, is demonstrated. A wavelength chirp width of 0.42 nm at 10 Gb/s is obtained due to a reduced linewidth enhancement factor that has a magnitude of less than 2. Nonlinear damping K factor in a DFB laser with 45-nm negative detuning has drastically decreased to 0.13 ns, about half of that for unstrained MQW lasers. This is mainly due to an enhanced differential gain as large as 6.9×10 ^-12 m³/s. The estimated intrinsic maximum bandwidth is 68 GHz