Influence of standing waves on DFB lasers including saturableabsorptive gratings

The influence of standing waves on the performance of distributed feedback (DFB) lasers is investigated, whereby local changes of the wavenumber as induced by gain compression or inhomogeneous saturation of an absorptive grating are incorporated into the coupled wave equations. With the help of this model, it is shown that gain compression ultimatively limits the maximum output power for monomode operation. As compared to in-phase complex-coupled lasers, it is shown that the worse monomode capability of antiphase complex-coupled lasers is related to the better stability properties of these lasers. Additionally, a characteristic interaction between the saturable absorptive grating and the optical field is found, which furthermore reduces the maximum monomode output power of antiphase complex-coupled lasers with saturable absorptive gratings     

Analysis, fabrication, and characterization of 1.55-/spl mu/m selection-free tapered stripe DFB lasers

A new selection-free laser structure for monomode behavior based on an engineering of the stripe geometry is proposed. The structure is designed in order to eliminate facet phase effects and laser to laser variations. The effect of spatial hole burning is simulated and an enhancement of the sidemode suppression ratio (SMSR) with power is predicted and measured. Moreover, the sensitivity to technological fluctuations is theoretically analyzed. Experimentally, lasers having a 47-dB SMSR at 10 mW and an excellent homogeneity from laser to laser is obtained on a two inch wafer.     

窄沟槽衬底条形GaAlAs/GaAs DH激光器特性的测量和分析

本文着重讨论窄沟槽衬底条形GaAlAs/GaAsDH激光器的观察和测量。显示了单模激光器和多丝激光器特性的基本差别,讨论了引起这些差别的基本原因和这两类器件的应用前景。     

多模TEA CO_2激光位相复共轭的实验研究

本文报导了TEA CO_2激光在谐振吸收介质SF_6和增益CO_2介质中的多模位相复共轭效应。实验上我们获得了与单模情况相近的位相复共轭波反射率。     

Low-damage dry-etched grating on an MQW active layer anddislocation-free InP regrowth for 1.55-μm complex-coupled DFB lasersfabrication

A grating dry-etched through the upper wells of a multiquantum-well active layer has been characterized before and after regrowth. TEM observation and carrier lifetime measurements have shown growth-free defects of the epitaxial layers. As a consequence, quasi-100% monomode oscillation on λ+1 mode has been achieved on complex-coupled distributed-feedback GaInAsP QW lasers fabricated with such grating     

Coherence-collapse threshold of 1.3-/spl mu/m semiconductor DFB lasers

The onset of the coherence-collapse threshold is theoretically and experimentally studied for monomode 1.3-/spl mu/m antireflection/high reflection distributed-feedback lasers taking into account facet phase effects. The variation of the coherence collapse from chip to chip due to the facet phase is in the range of 7 dB and remains almost independent of the grating coefficient. Lasers that operate without coherence collapse under -15-dB optical feedback, while exhibiting an efficiency as high as 0.30 W/A, are demonstrated. Such lasers are adequate for 2.5 Gb/s isolator-free transmission without under the International Telecommunication Union recommended return loss.     

New stripe-geometry laser with simplified fabrication process

A new type of GaAs-GaAlAs stripe-geometry laser with an appreciably simplified fabrication process is described. Owing to the excellent lateral current confinement of this structure, low threshold current densities are achieved even for very narrow stripe widths. In addition, the built-in passive wave-guiding stabilises the fundamental horizontal transverse mode, thereby avoiding nonlinearities in the light output against current characteristic. For 3?m wide and 175 ?m long lasers, threshold currents of 30?35 mA are achieved and stable transverse and longitudinal monomode emission has been observed up to more than 5 mW light power output.     

Lasing mode selection in vertical-cavity surface emitting-laserdiodes

A detailed model, including current spreading, carrier diffusion, and corresponding modal gains, is developed for a well-defined vertical-cavity surface-emitting laser structure. Above-threshold-operation (hole burning) is also analyzed by the model to quantitatively demonstrate the influence of injecting contact geometry and size in determining monomode operation. Results from this model demonstrate the importance of modal gain dynamics in establishing stable operation of such devices and hence the model may be used for improved device design     

New method for measuring ultrawide frequency response of optical detectors

We propose a simple method which allows for a direct measure of the frequency response of photodetectors up to very high frequencies and avoids some of the problems inherent in the standard time-domain or frequency-domain measurements. This method is based on the detection of the tunable beat frequency obtained by superimposing the EM fields of two monomode semiconductor lasers.     

MOVPE growth of AlGaAs/GaInP diode lasers

GaAs-based diode lasers for emission wavelengths between 800 nm and 1060 nm with AlGaAs-cladding and GaInP-waveguide layers were grown by MOVPE. For wavelengths above 940 nm broad area devices with InGaAs QWs show state-of-the-art threshold current densities. Ridge-waveguide lasers fabricated by selective etching achieve 200 mW CW monomode output powers. (In)GaAsP QW-based diode lasers with an emitting wavelengths around 800 nm suffer from problems at the upper GaInP/AlGaAs interface. Asymmetric structures with a lower AlGaAs/GaInP and an upper AlGaAs/AlGaAs waveguide not only avoid this interface but also offer better carrier confinement. Such structures show very high slope efficiencies and a high T₀. Maximum output powers of 7 W CW are obtained from 4 mm long devices.     

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     

掺镱单模石英光纤中放大的自发辐射

描述了掺镱单模石英光纤中正向和反向放大的自发辐射 (ASE)的差异以及ASE谱轮廓随抽运功率、激活光纤长度和抽运波长等量的变化 ,这些结果对于掺镱光纤激光器、放大器的设计有重要的指导意义。     

双模双光子激光连续振荡过程的讨论

本文推广的结果,用约化的光学Bloch方程的稳态解,讨论非简并双光子激光连续振荡过程,得到了双模双光子过程中激光物质的增益、色散和频率牵引等结果。与单模双光子的结果进行了比较,分析了两模之间的耦合对这些特性的影响。     

InGaAs-GaAs-InGaP distributed feedback buried heterostructurestrained quantum-well lasers for high-power operation at 0.98 μm

Data are presented on device results from InGaAs-GaAs distributed feedback buried heterostructure (DFB BH) strained-quantum-well lasers with InGaP cladding layers. DFB BH lasers with a p-n InGaP current blocking junction entirely grown by a three-step MOVPE on GaAs substrates show a low laser threshold of 3.2 mA and a high output power of 41 mW with single-longitudinal-mode operation, both measured CW at RT. The monomode oscillation is obtained even at the injection current of 140 mA (44 times the laser threshold) with the side-mode suppression ratio of 35 dB and the temperature sensitivity of Bragg modes being 0.5 Å/°C measured between 20 and 40°C     

Temperature insensitive 1.3 /spl mu/InGaAs=GaAs quantum dot distributed feedback lasers for 10 Gbit=s transmission over 21km

Long wavelength monomode InGaAs/GaAs quantum dot (QD) distributed feedback (DFB) lasers with emission wavelength around 1325 nm are presented. Threshold currents below 19 mA for operating temperatures up to 70degC and output powers of 10 mW at 25degC (6 mW at 70degC) are observed. Error-free 10 Gbit/s transmission over 21 km fibre with an extinction ratio of 8.5 dB at room temperature (5.1 dB at 70degC) is demonstrated. The low threshold, low temperature sensitivity and high modulation speed were realised using complex coupled DFB lasers with ten stacks of self-organised MBE-grown QD layers and p-type modulation doping     

Realistic monomode air-core honeycomb photonic bandgap fiber with pockets

We present a photonic bandgap calculation of monomode air-core fibers with a realistic treatment of "pocket" interstitials that are formed in a honeycomb cladding. The analytic Fourier transformations of different honeycomb-lattice unit cells are used for plane-wave calculations. The consideration of the true pocket geometry within the cladding shifts the fundamental bandgap to higher frequencies and leads to a hollow-core fiber. The core radius necessary for a monomode fiber is approximated and then proved via the full-vectorial solution. The field distribution and polarization state of the fundamental mode for a real honeycomb photonic-crystal fiber (PCF) are given.     

Progress in monomode transmission techniques in the United Kingdom

The key results obtained from experimental systems studies over monomode fiber and cable links are given for both direct detection and coherent optical systems. Direct detection techniques have been studied at 1300 nm using conventional lasers and at 1500 nm with narrow line transmitters of the injection-locked and external cavity types. In the case of coherent optical systems, developments of the same transmitters have been used in conjunction with amplitude and phase shift key (PSK) modulation techniques to obtain improved performance. Increases in receiver sensitivity of up to 14 and 17 dB have been obtained using, respectively, heterodyne and homodyne detection techniques. These results approach theoretical predictions and offer the possibility of much greater transmission capacity and extended regenerator spacings for monomode systems.     

Thermal resistance and temperature distribution in double-heterostructure lasers: Calculations and experimental results

The thermal resistance and temperature distribution in double-heterostructure lasers have been calculated taking into account the characteristics of the different layers, the internal quantum efficiency, and allotment of the dissipated power, in order to optimize their structure. The influence of the different layers in the heterostructure and of the electrical contact is analyzed. Thermal resistance of CW, shallow proton-implanted lasers has been determined experimentally using the technique that relies upon a null measurement of the wavelength of a single Fabry-Perot mode. Statistical results on some hundreds of lasers with different stripe widths (6-125 mum), mounted on different heat sinks (copper, silicon, beryllium oxide) are given and compared to theoretical values. The model we propose gives good agreement with experimental results. The 6 μm width stripe laser is of special interest because this laser is transverse monomode up to an optical power of 6 mW. A value of 22° C/W has been achieved in a reproducible manner for6 times 300 mum lasers mounted on copper heat sinks. The effectiveness of the bonding technique is demonstrated. Si and BeO heat sinks are suitable for many applications because of their chemical (V grove etching in Si) and thermal properties (better linear expansion coefficient match to GaAs). We show that the increase of thermal resistance so introduced is still compatible with long CW operation.     

Pump source requirements for end-pumped lasers

A simple model is developed to relate laser design and properties of a gain medium to the requirements on a pump source for end-pumped lasers or amplifiers. A novel technique for scaling the pump power or energy for end-pumped lasers is presented and analyzed in terms of this model. The results indicate that power or energy scaling of the pump source for end-pumped lasers is not limited by geometry; however, the results also show that some minimum pump energy or power is required