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.     

Transient and optoelectronic feedback-sustained pulsation of laserdiodes at 1300 nm

We report the observation of self-sustained pulsation and transient self-pulsation in laser diodes at 1300 nm and the effects of optoelectronic feedback on the pulsations. Transient self-pulsation has a lifetime of a few minutes with frequencies up to 7 GHz. The linewidth of self-pulsation is on the order of 0.5 GHz. With optoelectronic feedback, the transient self-pulsation can be sustained and the linewidth significantly reduced to about 20 kHz. The center frequency of feedback-sustained pulsation is dependent on the passband of the bandpass filter in the feedback loop. The feedback sustained pulsation can be frequency modulated for applications in subcarrier multiplexed optical networks such as cable TV distribution and antenna remoting     

Observation of sustained self-pulsation in CW operated flaredY-coupled laser arrays

The time evolution of the near-field radiation patterns of CW operated inphase locked flared `Y' coupled diode laser arrays has been observed with a streak camera. The arrays exhibit sustained self-pulsation at frequencies as high as 4 GHz     

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.     

半导体激光器的自脉动与被动锁模

利用普适GaAlA3双异质结半导体激光器，观察到被动锁模现象。讨论了半导体激光二极管的自脉动、外腔中的诱导自脉动以及被动锁模间的区别与联系。     

All-optical synchronization and multiplication of the frequency ofmode-locked signals

The authors report all-optical synchronized multiplication by rational fractions of the modulation frequency of optical signals in self-pulsing two-section semiconductor laser diodes. The effect is based on the overlap of harmonics of the input signal with harmonics of the self-pulsation. This new generic function is illustrated with mode-locked inputs rich in harmonics, where fractions of 1, 2, and 3/2 are generated, and a number of applications for this effect are identified     

Efficient diode-pumped single-frequency erbium:ytterbium fiberlaser

We report a 7.6-mW single-frequency fiber laser operating at 1545 nm, using for the first time an Er³⁺:Yb³⁺ doped fiber and a fiber grating output coupler. The laser did not exhibit self-pulsation, which is a typical problem in short three-level fiber lasers, and had a relative intensity noise (RIN) level below -145.5 dB/Hz at frequencies above 10 MHz. The linewidth of the laser was limited by the relaxation oscillation sidebands in the optical spectrum and was typically less than 1 MHz     

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。     

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     

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 an InGaN laser-theory and experiment

Room-temperature operation of self-pulsating InGaN lasers was obtained at a wavelength of 395 nm. The laser structure consists of a multiquantum-well InGaN active layer and a p-type InGaN single-quantum-well saturable absorber. The frequency range of the self-pulsation was from 1.6 to 2.9 GHz. The experimental results were well explained with our theoretical analysis. We found that features of the saturable absorber strongly affect the self-pulsation. Influence of device and material parameters on the laser dynamics was also investigated.     

Self-pulsations in strongly coupled asymmetric external cavitysemiconductor lasers

Self-pulsations in asymmetric external cavity semiconductor lasers are studied experimentally and are analyzed using improved rate equations which include multiple reflections. These equations are valid for arbitrary levels of coherent external optical feedback. The dependence of self-pulsation frequencies on injection current, external mirror tilt angle and reflectivity, and external cavity length is explained by small-signal analysis of the rate equations. By numerical integration of the rate equations, self-pulsations are demonstrated theoretically and resonant enhancement of intensity noise is shown to occur when the self-pulsation frequency is an integer fraction of the external cavity resonance frequency     

Effects of intermodulation distortion on the performance of a hybrid radio/fiber system employing a self-pulsating laser diode transmitter

A self-pulsating laser is used to generate a multicarrier (five radio frequency (RF) channels) microwave optical signal for use in a hybrid radio/fiber system. The self-pulsation is achieved by external light injection into the laser diode. By varying the RF channel spacing, we have been able to estimate the degradation in system performance due to intermodulation distortion (caused by the nonlinear dynamic response of the laser). The power penalty on the central RF channel is found to be 3.2 dB for operation at the RF band around the laser self-pulsation frequency of 18.5 GHz. We have also characterized the performance of the multicarrier hybrid radio/fiber system in the frequency band corresponding to the inherent relaxation frequency of the laser.     

Self-pulsation dynamics in narrow stripe semiconductor lasers

In this paper, we address the physical origin of self-pulsation in narrow stripe edge emitting semiconductor lasers. We present both experimental time-averaged polarization-resolved near-field measurements performed with a charged-coupled device camera and picosecond time resolved near-field measurements performed with a streak camera. These results demonstrate dynamic spatial-hole burning during pulse formation and evolution. We conclude from these experimental results that the dominant process which drives the self-pulsation in this type of laser diode is carrier induced effective refractive index change induced by the spatial-hole burning.     

Chaotic self-pulsation and cross-modulation in awavelength-selective external-cavity laser diode

Chaotic self-pulsation in a single wavelength external-cavity laser diode is observed. It is shown that the self-pulsation is caused by interdependencies between the optical output power and the compound cavity losses through the refractive index of the laser diode material. Refractive index changes result in a detuning between the externally selected wavelength and the weak internal-mode structure of the anti-reflection coated laser diode. This detuning is directly related to the compound cavity losses. On the one hand, a change in optical output power results in a change of the refractive index via the carrier density. On the other hand, it results in a change of refractive index via temperature changes. Compared to the carrier induced refractive index change, the temperature induced refractive index change is opposite in sign, a factor of ~10² smaller and slower. The switch-on and switch-off time of the self-pulsation is governed by the carrier life time. The repetition rate of the self-pulsation is governed by the thermal time constant and is in the megahertz region. Cross-modulation resulting from the thermal induced refractive index change is demonstrated. In a two-wavelength double external-cavity laser diode, optical power at one wavelength effects the optical power at the other wavelength. This cross-modulation is shown to be related to previous experiments on a laser neural network. A novel technique is introduced to measure the thermal impedance of a laser diode that is based on the cross-modulation     

Direct evidence for laser reabsorption as initial cause for self-pulsing in three-level fibre lasers

The temporal characteristics of a standing wave Tm/sup 3+/-doped silica fibre laser are presented. For uni-directional pumping, the output displays the well-known self-pulsation phenomenon, but with bidirectional pumping, a significant increase in the laser stability is observed. A longitudinally uniform population inversion is shown to be of paramount importance to the stability of three-level lasers.     

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.     

Frequency and wavelength tunable optical microwave source based on a distributed Bragg reflector self-pulsation laser

A frequency and wavelength tunable self-pulsation laser based on DBR laser devices is reported for the first time.This laser generates continuous tunable optical microwave in the range of 1.87-21.81 GHz with 3-dB linewidth about 10 MHz by tuning the injection currents on the front and back gain sections,and exhibits wavelength tuning range from 1536.28 to 1538.73 nm by tuning the injection currents on the grating section.     

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.     

Development of self-pulsations due to self-annealing of proton bombarded regions during aging in proton bombarded stripe-geometry AlGaAs DH lasers grown by molecular beam epitaxy

Experimental observations indicate that the occurrence of optical self-pulsation in proton delineated stripe-geometry double-heterostructure junction lasers is related to the degree of gain guiding inherent in individual lasers. We show that an aging process occurs during lasing operation which has the effect of partially annealing the proton induced carrier removal concentration at the edges of the active stripe of the laser. In some lasers, the magnitude of this annealing effect is sufficiently large to flatten the active stripe carrier concentration profile thus reducing filament stability leading ultimately to optical self-pulsation. It is shown that the carrier concentration profile modification is due to the dual effects of decreasing then = 2nonradiative current component at the active stripe-proton bombarded interface as well as the geometric effect of increasing the laser active stripe width. This latter effect may be also responsible for some portion of laser threshold current increase observed during device operation.