The symmetry of the amplified spontaneous emission spectrum incomplex-coupled DFB lasers

We present relations between facet reflections and coupling coefficient for the amplified spontaneous emission (ASE) spectrum of a complex-coupled, an index-coupled, and a gain-coupled distributed feedback (DFB) laser to have a mirror image with respect to the Bragg wavelength. We show that the ASE spectrum of a complex-coupled DFB laser cannot be symmetric in general with respect to the Bragg wavelength. The index-coupled and gain-coupled DFB lasers can have symmetric ASE spectrum for some values of the phase of the facet reflection coefficient that are determined     

A new method for the calculation of the emission spectrum of DFBand DBR lasers

A method based on transmission matrices that allows the emission spectra of arbitrarily complicated semiconductor laser structures to be computed below and above threshold has been developed. These can include active and passive periodic or uniform sections. As examples, the authors compute the emission spectra of a normal distributed feedback (DFB) laser, a DFB laser with a λ/4 phase shifter, and a surface-emitting distributed Bragg reflector (DFB) laser. To do that, Petermann's method for calculating the spontaneous emission coupling coefficient has been extended to the case of a periodic waveguide. It is shown how the spontaneous emission, when treated correctly, can be used to measure the coupling coefficient of the grating in a DFB laser with a λ/4 phase shifter     

Spontaneous emission model of surface-emitting DFB semiconductorlasers

A general spontaneous emission model is developed for surface-emitting (SE) distributed feedback (DFB) semiconductor lasers. The frequency distribution of spontaneous emission noise below lasing threshold and the spontaneous emission rate in lasing operation are formulated by using a transfer matrix method combined with the Green's function method. The effective linewidth enhancement factor is obtained from this model in terms of the elements of the transfer matrix. By way of example, the author applies the formulation to a standard SE DFB laser, and a SE λ/4-shifted DFB laser with a distributed Bragg reflector (DBR) mirror. In particular, the author analyzes the below-threshold spectrum, the threshold current density, the differential quantum efficiency, and the spectral linewidth of these lasers     

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     

Improved selectivity and decreased spontaneous emission from anAR-HR coated SL-MQW DFB semiconductor laser amplifier

It is shown that the performance of a DFB filter/amplifier can be improved considerably with respect to selectivity and amplified spontaneous emission by applying a high reflective coating to the output facet. To illustrate this a strained-layer multiple quantum well DFB filter/amplifier with an output facet reflectivity of 97% is compared with a conventional, AR-coated phase adjusted DFB filter/amplifier. Peak fiber-to-fiber gains for these devices are 21 and 18 dB, respectively, when biased at 98% of their threshold current. The transmission gain of these DFB filter/amplifiers has been measured over a wavelength span of 30 nm. For the AR-HR coated SL-MQW DFB filter/amplifier the selectivity is improved with 11 dB resulting in an extinction ratio for interfering channels of better than 35 dB and the amplified spontaneous emission is reduced by 16 dB down to -37 dBm compared to the conventional DFB filter/amplifier     

Transfer matrix analysis of the amplified spontaneous emission ofDFB semiconductor laser amplifiers

Analytical expressions are derived for the amplified spontaneous emission of a DFB (distributed-feedback) semiconductor laser amplifier with reflective cavity ends. The analysis is extended to a multisection DFB structure including a phase-shifted DFB semiconductor laser amplifier. It is shown that the spontaneous emission power per unit frequency bandwidth emitted from one facet is proportional to the transmission gain and to a quantity which at threshold becomes the inverse of the differential quantum efficiency of the other facet. The analysis is applied to two practical cases: (1) calculation of emission spectra of a DFB semiconductor laser biased below the threshold, and (2) assessment of the signal-to-noise ratio performance of DFB semiconductor laser amplifiers     

Tunable dual-mode operation in a chirped gratingdistributed-feedback laser

We report on the tunable dual-mode operation of a chirped grating distributed-feedback (DFB) laser device with two integrated modulators which act as tuning sections. A transfer-matrix model is used to simulate the amplified spontaneous emission spectrum for a chirped grating DFB laser. Several types of dual-mode operation are observed for wavelength spacings of 0.5 nm and 1.4 nm corresponding to frequency detunings of 63 GHz and 175 GHz     

Coupled phase-shift distributed-feedback semiconductor lasers fornarrow linewidth operation

Mode properties of a coupled phase-shift distributed-feedback (DFB) structure are analyzed and the feasibility of narrow-linewidth emission is shown theoretically. The structure consists of a multiple number of phase-shift DFB laser units which are arranged in tandem and coupled with each other through additional phase shift of corrugation. Optimum structure parameters were determined for two coupled laser units so that the frequency detuning is zero and the mode pattern is the flattest. The mode analysis shows that the intensity distribution is flatter and the normalized coupling constant can be larger than those for the conventional DFB laser with a single phase shift. This indicates that the cavity length can be extended with less influence from the longitudinal spatial hole burning effect     

Dynamic analysis of radiation and side-mode suppression in asecond-order DFB laser using time-domain large-signal traveling wavemodel

In this paper, we have developed a relatively simple algorithm to calculate the large-signal dynamic response of DFB lasers by solving the time-dependent coupled wave equations directly in the time domain. The spontaneous emission noise, longitudinal variations of carrier (hole burning) and photon densities as well as that of the refractive index are taken into consideration. To demonstrate the power of this straightforward algorithm, the model shows how the side-mode suppression ratio in devices with high κL and a λ/4: phase shift is significantly affected by the radiation in the second-order DFB laser. The time-dependent radiation pattern in grating-coupled surface-emitting lasers is also calculated for the first time     

Two-electrode DFB laser filter used as a wide tunable narrow-bandFM receiver: tuning analysis, characteristics and experimental FSK-WDMsystem

Characteristics of a two-electrode DFB laser filter are studied both theoretically and experimentally. Using a matrix analysis of spontaneous emission, a continuous tuning range of 6.7 Å is achieved by changing both net field gains of the two electrodes. A total discontinuous tuning range of over 10 nm comprising alternating mode jumps and continuous tuning range of 4 Å are measured experimentally. The laser filter presents a FWHM bandwidth of 5 GHz which depends on the optical input power. In addition, it is demonstrated that a DFB laser filter can act as a frequency discriminator/photodetector, i.e., a narrow-band FM receiver, with a uniform bandwidth of 1.5 GHz. Using the two-electrode DFB laser for both transmitter and receiver, a two-channel FSK-WDM transmission system utilizing the discontinuous tuning range is reported. The advantage of such a device is the simplicity as compared to the heterodyne technique     

Theory and experiment on the amplified spontaneous emission fromdistributed-feedback lasers

The amplified spontaneous emission (ASE) of a strained quantum-well distributed feedback (DFB) laser biased below laser threshold is used to extract the gain and refractive index spectra in a systematic manner. A modified Hakki-Paoli method is used to obtain the gain and differential gain spectra. The refractive index change due to carrier injection is obtained from the shift of the Fabry-Perot peaks in the ASE spectrum. The measured ASE spectrum, gain, refractive index change, and linewidth enhancement factor are then compared with our theoretical model for strained quantum-well lasers. Our model takes into account the realistic band structure and uses the material and quantum-well dimensions directly in the calculation of the electronic and optical properties. The theory agrees very well with the experiment     

Axial profile of grating coupled radiation from second-order DFBlasers with phase shifts

Axial profiles of the grating-coupled radiation field emitted in a direction normal to the surface of distributed-feedback (DFB) lasers with phase-shifted second-order corrugation are theoretically analyzed. The profiles are calculated for nonreflecting DFB lasers with the following phase shifts: λ/4 shift, two λ/8 shifts, and two 3λ/8 shifts. It is demonstrated that the radiation field can be controlled by changing the phase shifts. This result suggests a new method for modulating the surface emission of a DFB laser     

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.     

EAM-DFB集成光源典型参数特性的电路级分析

针对电吸收型调制器和分布反馈激光器集成光源(EAM-DFB)的光电混合特征,建立了包含自发辐射、俄歇复合、寄生效应以及隔离电阻的等效电路模型。分析了在不同驱动电流和自发辐射因子下,该模块的输出、调制及噪声特性,并与直接调制DFB作了对比。结果表明,EAM-DFB可生成超短脉冲(小于25 ps);随着驱动电流的增加,输出功率增大、脉冲展宽,噪声增强且峰值点向高频移动;减小自发辐射因子和增加驱动电流均使其调制带宽增加;与DFB相比,EAM-DFB增加了少量噪声,但具有更陡峭的功率-电流特性和更大的调制带宽。     

Computer simulation of FSK laser spectra and of FSK-to-ASKconversion

The performance of binary frequency shift keyed (FSK) modulated two-segment semiconductor injection lasers is simulated by generating a 64-b pseudorandom step-function bit pattern. This signal, superimposed on a DC bias, is used to drive a two-segment distributed feedback (DFB) laser. To obtain the optical laser spectrum, the input signal is passed through the laser's small-signal transfer function. The resulting spectrum is passed through a Fabry-Perot filter that rejects one of the two principal peaks of the wide-deviation optical spectrum and converts the FSK modulation to amplitude shift keying (ASK) modulation. This simulation determines how different system parameters influence the performance of a laser system used for signal transmission by means of FSK-to-ASK conversion     

Modeling the static and dynamic behavior of quarter-wave-shiftedDFB lasers

High-coupling (grating coupling constant=3.0) phase-shifted distributed-feedback (DFB) lasers are studied using a transmission-line laser model (TTLM) which includes spatial hole burning (SHB), the material gain spectrum, refractive index dependence on carrier concentration, and random spontaneous emission. Good agreement for CW spectra is shown with other models and experimental results. Dynamic simulation of laser transients shows SHB-induced deterministic mode hopping and chirping at moderate output powers. The effects of mode hopping and chirping on system performance are studied using a laser model combined with a fiber model     

Amplified spontaneous emission model for quantum-well distributedfeedback lasers

An amplified spontaneous emission model for quantum-well (QW) distributed feedback (DFB) lasers is presented, which takes into account local spontaneous emission, stimulated emission, and real refractive index change which are calculated from the Fermi-Dirac occupancy functions in a self-consistent manner. The local-normal-mode transfer-matrix method is used, which allows a coupling of the local DFB effect with the local QW spontaneous emission and gain. As an example, an analysis is given of a partly gain-coupled DFB laser with periodically etched QWs, which has a large discontinuity of spontaneous emission and gain in high- and low-corrugation regions. It is shown that the side-mode suppression improves with the increase of the number of etched QW's, due to the carrier-density-dependent gain-coupling     

Effective linewidth enhancement factor and spontaneous emissionrate of DFB lasers with gain coupling

A field rate equation governing the noise and dynamic properties of a DFB (distributed feedback) laser with gain coupling is presented. Analytic expressions for the effective linewidth enhancement factor and spontaneous emission rate are derived. It is shown numerically that the linewidth contribution from spontaneous emission can be substantially reduced in DFB lasers with gain coupling     

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.     

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。