Analysis of the spectral linewidth of distributed feedback laser diodes

The spectral linewidth of distributed feedback (DFB) laser diodes is theoretically studied. Numerical calculation shows that DFB lasers with long cavity lengths and large coupling coefficients have very narrow spectral linewidth less than 1 MHz, The effects of the phase shift and mirror facets on the spectral characteristics of DFB lasers are also analyzed, It is shown that the phase-shifter further narrows the spectral linewidth of DFB lasers. Its numerical result and physical meaning are also shown.     

Design of widely tunable semiconductor lasers usinggrating-assisted codirectional-coupler filters

The analysis and design of widely tunable semiconductor lasers using grating-assisted codirectional-coupler filtering in a vertical twin-guide structure are considered. An orthogonal coupled mode formalism is applied to obtain the important design parameters for the filter. It is shown that there is a tradeoff between tuning range and spectral purity when using this type of filter as an intracavity mode selector. Practical laser structures are presented, and design considerations and limitations are discussed for GaAs and InP material systems with lasing wavelengths around 0.98 and 1.55 μm, respectively     

Hollow cathode metal ion lasers

A new class of metal ion lasers with significant CW output power in the UV (220-320 nm) and near IR (800-2000 nm) spectral regions is described. In a hollow cathode discharge the upper laser levels are excited via charge transfer collisions between ground state buffer gas ions and ground state metal atoms. At the present stage of development, hollow cathode metal ion lasers are shown to be comparable in UV output power to rare-gas ion lasers but with lower threshold currents by a factor of more than twenty. Visible output powers are lower than rare-gas ion lasers. In the text we present device progress to date, measurements of important plasma parameters, and an outline of potential applications of hollow cathode metal ion lasers.     

Effects of hole burning, carrier-induced losses and thecarrier-dependent differential gain on the static characteristics of DFBlasers

A model solving the steady-state laser equations above threshold is presented. It calculates important laser parameters such as the threshold losses, emitted optical power, gain margin between the main and secondary modes and, spectral linewidth of any index-grating DFB laser structure. A more exact theoretical linewidth calculation considering nonuniform carrier densities and gain saturation is reported. Good agreement with experiments is found on phase-shifted lasers. The model is used to investigate the factors that determine the importance of spatial hole burning, and general design rules are proposed to reduce this effect. Gain compression combined with carrier-dependent losses is shown to limit the differential external efficiency and cause the emission wavelength to decrease and the spectral linewidth to rebroaden at high output power     

Critical design parameters for engineering broadly tunableasymmetric multiple-quantum-well lasers

Asymmetric multiple-quantum-well (AMQW) lasers are MQW lasers with QW's of varying thickness and/or composition in a single active region. AMQW lasers can, if designed properly, exhibit broad spectral tuning ranges more than twice as large as those of conventional MQW lasers. In the paper, it is shown experimentally and theoretically that AMQW lasers only exhibit broad wavelength tuning ranges near a specific cavity length defined as the transition cavity length. The transition cavity length is a critical design parameter for engineering broadly tunable AMQW Lasers     

Laser linewidth requirements and improvements for coherent opticalbeam forming networks in satellites

A coherent optical beam forming network using phase-locked semiconductor lasers as sources is presented. For this scheme the spectral purity of the intermediate frequency derived from mixing the signals from two semiconductor lasers is considered. The relationship between the linewidths of the lasers in a satellite transmitter and the phase error at the detector of a microwave differential quaternary phase-shift keying earth station receiver is analyzed. The demands placed on the linewidths from the point of view of phase stability requirements are calculated using quaternary phase-shift keying modulation at data rates of 33 and 131 Mb/s. It is shown that a substantial improvement in performance can be achieved when phase locking the two lasers to each other is feasible     

半导体激光器谱宽的测量研究

本文从范德玻尔(van der Pol)方程出发,导出了描述延迟自差拍法谱宽测量的公式。讨论了各结构参数对测量的影响。报道了用该法对单频半导体激光器测量的一些结果。     

Raman fiber lasers for optical communication application

We review the principle and characteristics of cascaded Raman fiber lasers in their telecommunication applications. The fundamentals of Raman fiber lasers are described, such as pumping scheme, fiber type and reflectors. We explain simple equations forcw laser operation as well as a possible way to calculate spectral width. We investigate the common issues in the use of Raman fiber lasers: theoretical optimization, control of the linewidth, suppression level of the other Stokes orders and relative intensity noise. Finally the more complex multiple-wavelength Raman fiber lasers are reviewed.     

A unified theory of magnetic bremsstrahlung, electrostatic bremsstrahlung, Compton-Raman scattering, and Cerenkov-Smith-Purcell free-electron lasers

This paper discusses in a comparative way the main operating parameters of various free-electron lasers (FEL's), providing a useful tool for laser design and a comparative evaluation of the various lasers. We show that the various kinds of FEL's satisfy the same gain-dispersion relation and differ only in a single coupling parameterk. The different gain regimes which are common to all FEL's are delineated. We find the small signal gain in all the gain regimes (warm and cold beam, low- or high-gain, single electron, collective or strong coupling interaction). The laser gain parameter, radiation extraction efficiency, maximum power generation, and spectral width are given and compared in the various kinds of FEL's and gain regimes. The maximum power generation of all FEL's (except Compton-Raman scattering) is shown to be limited by an interaction region width parameter. This parameter and, consequently, the laser power are larger in the highly relativistic limit by a factorsim gamma_{0}in all bremsstrahlung FEL's, in comparison to Cerenkov-Smith-Purcell FEL's. Some expressions which were derived earlier for the magnetic bremsstrahlung FEL, like the expression for gain in the low-gain regime with the space charge effect correction and the low-gain expression for efficiency, are shown to be special cases of more general expressions.     

Polarization-Insensitive Low Timing Jitter and Highly Optical Noise Tolerant All-Optical 40-GHz Clock Recovery Using a Bulk and a Quantum-Dots-Based Self-Pulsating Laser Cascade

We report on the experimental assessment of an all-optical clock-recovery scheme at 40-Gb/s cascading a polarization-insensitive bulk-based self-pulsating (SP) laser and a high spectral purity quantum-dots-based SP laser. It is demonstrated experimentally that such a clock-recovery scheme is polarization insensitive, efficient in the jitter filtering, and tolerant for an input optical signal-to-noise ratio (OSNR) as low as 15 dB/0.1 nm. It is shown theoretically that the jitter-filtering function of the cascade is the product of the transfer functions of both lasers. The contributions of the phase noise of these two lasers to the final jitter are also identified and quantified. The influence of the degradation of the OSNR to the total timing jitter is also analyzed. The approach proposed in this paper offers the real opportunity to realize an all-optical clock recovery with a performance compatible for system applications     

Static and dynamic simulation for ridge-waveguide MQW DFB lasers

An efficient and versatile computer-aided simulator for the design and analysis of ridge-waveguide (RWG) multiple-quantum-well (MQW) distributed-feedback (DFB) lasers has been developed and is presented. This simulator combines spectral index method and Green's function-based transfer-matrix method (TMM) to deal with the transverse RWG MQW structure and longitudinal DFB structure, respectively. It is capable of simulating both static and dynamic behaviors for a variety of RWG MQW DFB lasers. The major difference from most of the existing models and analyses is that this simulator is capable of linking important device characteristics with practical material and geometrical parameters directly and self-consistently. For instance, the effects of lateral ridge width, vertical MQW layers and longitudinal nonuniformity are all explicitly included in the simulator. important laser characteristics, such as L-I curve, effective linewidth enchancement factor, static lasing wavelength shift, spectral linewidth, facet-power spectrum, AM and FM modulation responses, dynamic-wavelength chirping, as well as longitudinal photon and carrier distribution, can be predicted based on material and waveguide parameters. Therefore, this simulator may be used as an efficient and versatile tool for the systematic exploitation and optimization of a wide range of practical RWG MQW DFB lasers. Analysis of a λ/4 shifted SCH RWG MQW DFB laser is performed to illustrate the capability of this simulator     

Impedance characteristics of quantum-well lasers

We derive theoretical expressions for the impedance of quantum-well lasers below and above threshold based on a simple rate equation model. These electrical laser characteristics are shown to be dominated by purely electrical parameters related to carrier capture/transport and carrier re-emission. The results of on-wafer measurements of the impedance of high-speed In_0.35Ga_0.65 As/GaAs multiple-quantum-well lasers are shown to be in good agreement with this simple model, allowing us to extract the effective carrier escape time and the effective carrier lifetime, and to estimate the effective carrier capture/transport time     

Theoretical analysis of external optical feedback on DFB semiconductor lasers

The effect of external optical feedback on resonant frequency, threshold gain, and spectral linewidth of distributed feedback (DFB) semiconductor lasers is theoretically analyzed. The analysis applies to any type of laser cavity formed by a corrugated waveguide limited by partially reflecting facets. It is shown that the sensitivity to optical feedback on a facet is closely related to the power emitted through this facet. Numerical results on wavelength selectivity and on sensitivity to optical feedback are given for conventional DFB lasers having an AR-coated facet and for quarter-wave-shifted (QWS) DFB lasers with AR-coatings on both facets. Both laser types are found to be more sensitive to optical feedback on their AR-coated facet than Fabry-Perot lasers for lowkL. On the other hand, QWS-DFB lasers are found to be relatively insensitive to optical feedback for largekL.     

DBR几何特性对其反射率和DBR激光器线宽的影响

对DBR几何参量不同的InGaAs-GaAs-AlGaAs DBR半导体激光器样品的输出线宽进行了测量和分析.样品激光器DBR光栅取不同的长度和蚀刻深度以考察其几何特性对耦合系数、反射率以及输出线宽的影响.线宽通过自差频测量系统测量得到.对实验结果与理论计算结果进行了对比.对测得的光学特性参数与几何特性参数之间的联系进行了分析.在此基础上讨论了DBR几何特性对激光器输出线宽的影响.研究结果为该类型DBR半导体激光器的制造提供了有用的信息.     

Effect of DBR Geometry on Reflectivity and Spectral Linewidth of DBR Lasers

对DBR几何参量不同的InGaAs-GaAs-AlGaAs DBR半导体激光器样品的输出线宽进行了测量和分析.样品激光器DBR光栅取不同的长度和蚀刻深度以考察其几何特性对耦合系数、反射率以及输出线宽的影响.线宽通过自差频测量系统测量得到.对实验结果与理论计算结果进行了对比.对测得的光学特性参数与几何特性参数之间的联系进行了分析.在此基础上讨论了DBR几何特性对激光器输出线宽的影响.研究结果为该类型DBR半导体激光器的制造提供了有用的信息.     

Analysis of the spectral linewidth of distributed feedback laser diodes

The spectral linewidth of DFB laser diodes is analysed. DFB lasers with long cavities are shown to have very narrow spectral linewidth, and it is further narrowed if a phase shift is introduced at the centre of the cavities.     

Analysis of diode laser properties

An analytic model of diode lasers applicable to both the lasing and the nonlasing states is described. For these homogeneously broadened devices, spectral envelope widths for TE00and TM00modes are related to power in each modal family and are shown to depend critically on spontaneous emission coupling into the transverse modes. Thus, lasers with real-refractive index waveguiding (and associated weak spontaneous emission coupling) operate single longitudinal mode above threshold, whereas gain-guided devices run multimode. After connecting gain and spontaneous emission, a charge conservation equation, containing optical power in the form of a stimulated emission term, pumping current, spontaneous emission, and spectral width, is derived. These equations are then demonstrated to suffice for determination of the completeLversusIcharacteristic. For lasers in which both charge and mode confinement exist, such as the buried heterostructure (BH) and channelled-substrate narrow stripe (CNS) types, it is shown that both TM00power and spectral envelope width approach limiting values at threshold, whereas TE00mode power grows in conjunction with TE00spectral envelope narrowing.     

Spectral aspect of degradation in 1.55 μm long-cavity MQW DFBlasers

Degradation behaviors, particularly for the increase in spectral linewidth and FM efficiency, in 1.55 μm long-cavity MQW (multiple quantum well) DFB (distributed feedback) lasers, with a spectral linewidth of around 1 MHz, are presented from the viewpoint of coherent system application. Through the clarification of the behaviors, it is shown that highly coherent lasers are sufficiently durable in coherent transmission systems     

Description of laser pulses using Fourier analysis

The output of lasers in various modes of operation is described in a unified way, using Fourier analysis. A novel model for treating an active Fabry-Perot cavity, including the case of high gain, is developed resulting in a more exact expression for the spectral width of the cavity modes. Simple mathematical tools are given to relate the observed pulse length with the average gain and with the initial population inversion in the laser medium. It is shown that lasers with homogeneously broadened spectral lines have cavity modes of equal width and that if the modes are locked together the resulting ultrashort pulses are of equal duration. For lasers with inhomogeneously broadened spectral lines the cavity modes vary in width along the gain curve and, when mode-locked, the ultrashort pulses increase monotonically in duration along the emitted pulse train.