Study of wavelength shift in InGaAs/InAlGaAs QW DFB lasers based onlaser parameters from a comparison of experiment and theory

Experimental data of InGaAs/InAlGaAs quantum well distributed feedback (DFB) lasers such as spectra, under continuous and pulsed biasing, relative intensity noise and linewidth, are compared with the results of model calculations based on a transfer matrix method. Using experimental data of different lasers, a set of physical DFB laser parameters was determined. We succeeded in describing all the experimental data of different lasers by the same set. The determined parameter set was further applied to study the influence of facet properties on the wavelength shift of DFB lasers. We found a very strong dependence of the wavelength tunability on the end facet phases. The wavelength shift varies by a factor up to three between different end facet phases and coatings. This is crucial for the yield of, for example, tunable multisection DFB lasers with an envisaged large tuning range     

Group theory and realization of a helical distributed feedback laser

This study is devoted to theory and first realization of a helical distributed feedback (DFB) laser. The theory emphasizes the group theoretic aspects of helical and linear periodic DFB lasers. It is demonstrated that the dispersion relations of the helical DFB modes are neither periodic nor necessarily symmetric with respect to the propagation constant. Nevertheless, DFB effects exist in helical as well as in linear periodic laser structures. Finally, the first experimental realization of a helical DFB laser is described.     

Analysis of the carrier-induced FM response of DFB lasers:theoretical and experimental case studies

A comprehensive analysis of the carrier-induced FM response of DFB lasers is given. Experimentally it is found that the FM response can sometimes vary strongly from chip to chip. In a number of cases anomalies either as a function of frequency or as a function of bias are observed. Theoretically, a dynamic model which includes spectral as well as longitudinal spatial hole burning is presented. The main feature of the model is that local variations of the Bragg wavelength caused by hole burning are rigorously and self-consistently taken into account. By comparing the experimental results with theoretical calculations, it is shown that in DFB lasers, spatial hole burning is an important phenomenon. The model confirms that the dynamic (FM) behavior can vary from DFB chip to DFB chip. The model shows that spatial hole burning is indeed the dominant factor which induces the anomalies that are found experimentally in the FM response     

Fabrication and operation of first-order GaInP/AlGaInP DFB lasersat room temperature

The fabrication and operation properties of first-order distributed-feedback (DFB) GaInP/AlGaInP double quantum well lasers are reported. The lasers with DFB grating periods between 106 and 109 nm show stable single-mode operation in the visible range from 694.0 to 709.5 nm at room temperature     

Analysis of wavelength conversion using highly nondegeneratefour-wave mixing in λ/4-shifted DFB lasers

We present a theoretical analysis of terahertz-range wavelength conversion using highly nondegenerate four-wave mixing in λ=1.55 μm, medium-coupling λ/4-shifted distributed feedback (DFB) lasers. Based on the coupled-wave approach, our model predicts up to ~2 THz probe-pump detuning with a -20 dB or higher conversion efficiency for quantum-well λ/4-shifted DFB. The influences of pump power and DFB coupling strength (κL) on wave mixing as well as the Bragg reflection effects are discussed. The predictions of the model are found to be in good agreement with recent experimental observations     

Analysis of optical-injected distributed feedback lasers using complex optical low-coherence reflectometry

A theoretical and experimental investigation of reflectograms obtained for a distributed feedback (DFB) semiconductor laser using a phase-controlled high-resolution optical low-coherence reflectometer was carried out, yielding the effective group refractive index and its variation above threshold, the cavity internal loss, as well as the grating coupling factor of a multiquantum-well DFB laser. In addition, direct measurements of the injection-induced complex-modal index changes are presented for the first time.     

Chirped gratings for DFB laser diodes using bent waveguides

The authors propose a method capable of providing arbitrarily chirped DFB (distributed feedback) gratings using bent waveguides on homogeneous grating fields and report the first realization as well as preliminary experimental results     

Chirp reduction of directly modulated semiconductor lasers at 10Gb/s by strong CW light injection

The influence of strong light injection on the reduction of the dynamical linewidth broadening of directly current-modulated semiconductor lasers at high bit rates is theoretically investigated and experimentally verified for 10 Gb/s NRZ pseudorandom modulation with a large current swing of 40 mA pp. Significant chirp reduction and single-mode operation are observed for bulk DFB, quantum well DFB lasers at 10 Gb/s and a weakly coupled bulk DFB laser at 8 Gb/s, so that an improvement of the transmission performance using standard monomode fibers in the 1.55 μm low-loss wavelength region can be achieved for all these laser types, where dispersion otherwise causes severe penalties for long-haul transmission. The properties of injection-locked bulk DFB and quantum well DFB lasers with respect to high bit rate modulation have been systematically studied by the use of the rate equation formalism. A dynamically stable locking range of more than 30 GHz under modulation has been found for both laser types with injection ratios higher than 0.5     

Self-consistent Simulation of self-pulsating two-section gain-coupled DFB lasers

The role of cavity conditions in the dynamics of two-section gain-coupled distributed feedback (DFB) lasers is investigated using a self-consistent model. Self-sustained pulsation (SSP) exists only for devices with strongly coupled DFB gratings. As the coupling strength increases, multiple SSP regimes are developed. The SSP frequency tuning range increases as cavity length decreases. The frequency and modulation index predicted by the model agree well with experimental results. The facet condition of each section is found to affect SSP differently because of the asymmetrical behavior of the modes responsible for SSP.     

利用高阶光孤子压缩效应获得4．8ps超短半导体激光脉冲

对有损光纤中高阶光孤子压缩进行了理论分析，利用Ｆ－Ｐ光谱窗和高阶光孤子效应使增益开关ＤＦＢ激光器输出光脉冲脉宽由４４．２ｐｓ压缩至４．８ｐｓ，实验结果与理论结果相一致。     

Stability and dynamic properties of multi-electrode laser diodesusing a Green's function approach

In DFB (distributed feedback) lasers, the shape of the longitudinal intensity and carrier density distributions changes above threshold as a result of spatial hole burning. The longitudinally distributed coupling of spontaneous emission into the lasing mode also plays an important role for the noise properties. The authors demonstrate how both effects can be included in a dynamic analysis. They extend their previously developed theory for multielectrode lasers to enable calculation of stability properties as well as small-signal modulation responses and noise spectra. The theory is used to study global and local stability of the stationary solutions (modes). The numerical results for several laser structures are presented. It is shown that symmetric DFB lasers are likely to exhibit pitchfork bifurcations in their static tuning characteristics as the current is increased. The authors discuss how the presence or proximity of such instabilities can affect the modulation and noise properties, and in particular, the spectral linewidth     

Fundamental Thermal Noise in Distributed Feedback Fiber Lasers

A detailed analysis of fundamental thermal frequency noise in distributed feedback fiber lasers (DFB FL) is presented. An expression relating the laser frequency noise spectrum to the spectrum of thermal (temperature) fluctuations in the fiber, accounting for the nontrivial DFB FL mode shape, is derived. A new expression for the thermal fluctuation spectrum of single-mode optical fiber is derived which predicts high-frequency thermal noise 3 dB higher than previously published results. Theoretical predictions are compared against experimental measurements for a well characterized DFB FL. Anomalous 1/f noise at low frequency is discussed     

Criterion of external feedback sensitivity in index-coupled andgain-coupled DFB semiconductor lasers to be free from excess intensitynoise

Sensitivities of index-coupled as well as gain-coupled DFB semiconductor lasers to external optical feedback are theoretically investigated in this work. The conditions of getting free operation from excess intensity noise in these two types of DFB lasers are obtained. It is found that the sensitivity of external feedback for these two types of DFB laser depends significantly on the structure such as the internal grating, the facet reflection, and the phase relation between the grating and the facet. The condition of making a DFB laser less sensitive to external optical feedback is to adjust the lasing wavelength to the Bragg wavelength in both index-coupled and gain-coupled structures. A phase-adjusting mechanism such as the λ/4 shift region in the index-coupled structure is effective to avoid the external feedback     

Distributed feedback lasers in chiral media

The combined effects of chirality and gain (or loss) on wave propagation and coupling in periodic structures is investigated here. The focus is on distributed feedback (DFB) lasers in a transversely unbounded periodic slab with spatially modulated electromagnetic parameters. The analysis uses a coupled-mode approach employing a canonical physical model of chiral materials to predict the effects of modulated chirality admittance on DFB lasers. Results for DFB laser behavior in chiral media are compared and contrasted to that in achiral media. It is found that, under certain circumstances, the electric and magnetic field coupling, which is characteristic of chiral materials, results in a lower threshold gain for DFB lasers in media with a given index of refraction and characteristic impedance. It is also found that chiral index-coupled or gain-coupled DFB lasers exhibit the same spectral mode properties as achiral DFB lasers     

Static frequency chirping in λ/4-phase-shifteddistributed-feedback semiconductor lasers: influence of carrier-densitynonuniformity due to spatial hole burning

An experimental and theoretical study of the effect of carrier-density nonuniformity on frequency modulation (FM) characteristics of 1.3-μm λ/4-phase-shifted distributed-feedback (DFB) lasers is discussed. The static frequency chirping is measured using a recently developed method that is free from dynamical chirping as well as thermal frequency shift. The amount of chirping shows a strong dependence on the bias current level. This is explained theoretically by considering the nonuniform carrier-density distribution due to the spatial hole burning effect     

Nondegenerate four-wave mixing in a long-cavity λ/4-shiftedDFB laser using its lasing beam as pump beams

In this paper, we discuss nondegenerate four-wave mixing in a lasing long-cavity λ/4-shifted DFB laser using the laser beams as pump beams. A high conversion efficiency and wide conversion range were experimentally demonstrated without the assistance of Fabry-Perot resonance. Electric field profiles of the pump, signal, and conjugate beam in our λ/4-shifted DFB laser are discussed. The third-order nonlinear susceptibilities of InP-InGaAs MQW's are then estimated from the experimental results. We discuss the saturation characteristics and the ratio of the conjugate power to the amplified spontaneous emission. We show that λ/4-shifted DFB lasers are suitable for wavelength converters using nondegenerate four-wave mixing because of their ability to provide single-device operation     

光纤激光传感技术及其应用

超高灵敏度的信号探测在石油勘探、地震预报和安全监测等领域都具有重要的应用价值.近年来出现了一种以分布反馈(DFB)光纤激光器为传感元件的新一代光纤传感器,它具有尺寸小、输出激光信号极窄的光谱线宽和极低的噪声等优势,与高分辨率波长解调技术结合可以达到极高的探测灵敏度.介绍了在光纤激光传感技术及其应用技术方面的研究进展,包括线宽仅为3 kHz、尺寸仅为3.6 cm的窄线宽低噪声DFB光纤激光器的研制及其测试,波长分辨率达3.5×10~(-7) pm/Hz~(1/2)的超高分辨率波长解调系统,基于密集波分复用的光纤激光传感网络,以及相关技术在水声和地震波探测中的应用研究.     

The effect of die bonding distributed feedback lasers

The effect of die-bonding-induced strain on the output spectra of gain-coupled distributed feedback (DFB) diode lasers was investigated. Bonding strain affects the in situ diffraction grating in DFB lasers and manifests itself as changes in the output spectrum. It is shown in this paper that such changes are observed in DFB lasers by comparing the spectra before and after die bonding. In addition, it was also observed that upon die bonding the lasing mode can, in some cases, flip from one side of the stopband to the other. This flip was modeled using a probability-amplitude transfer-matrix DFB laser model that included a bonding-induced perturbation of the pitch of the Bragg grating along the length of the cavity. The nonuniform strain perturbation of the pitch of the grating was determined from a finite element method simulation of a die bonded laser chip and correlated well with the strain that was deduced from measurements of the degree of polarization of photoluminescence from bonded chips.     

Gain saturation in DFB lasers with end reflectors

Results of an analysis of gain saturation in distributed feedback (DFB) lasers with end reflectors are presented. The dependence of the gain and frequency-shift eigenvalues of DFB lasers on the properties of end reflectors is reduced by gain-saturation effects. The degree of gain saturation is sensitive to the reflector properties if the distributed feedback and the reflections from the ends are of approximately equal strength.     

Spectral properties of angled-grating high-power semiconductorlasers

We study the spectral properties of angled-grating high-power semiconductor lasers, also known as α distributed feedback (DFB) lasers. We have derived a closedform expression to describe the cavity resonance. The results of this model are shown to compare favorably with experimental data. Intrinsic device parameters such as coupling coefficient and grating period are shown to be correlated to spectral and nearfield characteristics. The formulations and insights developed in this paper allow one to calculate these critical design parameters for optimum performance