Measurement of gain saturation coefficient of a DFB laser forlasing mode control by orthogonal polarization light

The frequency response of a 1.55-μm distributed feedback (DFB) laser is measured by injecting light which has an orthogonal polarization to the laser's lasing mode. The injected light, termed as orthogonal polarization light, is carefully selected to not couple to the lasing mode by adjusting its polarization to be orthogonal to that of the lasing mode and by setting its wavelength slightly different from that of the lasing mode. The wavelength of the orthogonal polarization light, however, is set within the range where the laser's active layer has a gain. The gain saturation coefficients for the lasing light are estimated to be 4.7×10^-23 cm² and that by the injected orthogonal polarization light (almost the same wavelength as the lasing mode) are 3.7×10^-23 cm², respectively     

Cavity-induced antiguiding in a selectively oxidizedvertical-cavity surface-emitting laser

Cavity-induced antiguiding of a lasing mode is demonstrated in a vertical-cavity surface-emitting laser (VCSEL). Selective oxidation of a distributed Bragg reflector (DBR) layer is used to generate a spectrally red-shifted cavity region cladding the lasing mode, with a second selectively oxidized aperture used to form the current confinement to the antiguided mode. Near-field, far-field, and spectral measurements are used to characterize lasing in both the antiguided mode and the antiguiding region     

Short-term wavelength changes in 1.5-/spl mu/m InGaAsP-InP distributed feedback semiconductor lasers

We report short-term lasing wavelength changes in 1.5-/spl mu/m InGaAsP-InP distributed feedback (DFB) lasers. The lasing wavelengths after biasing the lasers have been changed upto 1.2 /spl Aring/ at 20/spl deg/C while maintaining the constant output power. It takes over 700-2000 s, to stabilize the lasing wavelengths in many lasers. The annealing effects could be partially responsible for the wavelength change. It certainly affects the initial performance of cold-start frequency-division-multiplexed systems.     

Tunable multiline distributed feedback dye laser based on the phenomenon of excitation energy transfer

Tunable multiline distributed feedback (DFB) lasing has been observed in the mixture of dyes rhodamine 6G (R6G) and cresyl violet (CV). The dye-pair is pumped by the two pairs of the pump beams derived from a common source at two different angles. A variation in DFB geometry up to seven orders suggests that the third order Bragg diffraction is suitable for such studies. A detailed study at high dye concentrations has been done by steady-state and ps time-resolved spectroscopy. The energy transfer phenomenon and the self-absorption mechanism both, are found to be responsible for the observed tunability and multiline lasing. The threshold energies required for the DFB lasing are also given here.     

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     

Reduced Temperature Dependence of Lasing Wavelength in Membrane Buried Heterostructure DFB Lasers With Polymer Cladding Layers

An athermal operation of the lasing wavelength in a membrane buried heterostructure distributed feedback (BH-DFB) laser was demonstrated by adopting a polymer (benzocyclobutene) cladding layer which has a negative temperature coefficient of refractive index. Membrane BH-DFB lasers of core thickness 65 nm were operated under room-temperature continuous-wave conditions. The temperature dependence of the lasing wavelength was measured to be 2.45times10^-2 nm/degC, which is about 20%-30% of that for conventional semiconductor lasers     

Effects of layer thickness variations on vertical-cavitysurface-emitting DBR semiconductor lasers

A theoretical analysis of the influence of layer thickness variation in vertical-cavity surface-emitting lasers with distributed Bragg reflectors (DBRs) on lasing wavelength is presented. It is shown that changing the active region length of one of the layers in the DBR mirror by only one unit cell (0.56 nm) is sufficient to produce shifts in the lasing wavelength up to 0.12 nm (for an AlGaAs laser). This could limit the precision with which a desired wavelength, its reproducibility, and its uniformity across a large wafer can be obtained. Possible influences on the linewidth of broad area devices are also discussed     

基于液晶/聚合物光栅选频的高效率有机半导体激光器

报道了一种基于液晶/聚合物光栅选频的高效率有机半导体激光器的制备方法。首先在一片玻璃基板上旋涂有机半导体荧光薄膜MEH-PPV作为增益介质,然后在其上通过光场中的定域光聚合制备液晶/聚合物光栅,形成分布式反馈(DFB)有机半导体激光器。激光出射阈值0.32μJ/pulse,斜率转化效率高达7.8%,呈现良好的s偏振特性。采集了激光束的光斑,轮廓清晰,呈现扇形结构。通过改变光栅周期,实现了53.4nm激光出射范围。本工作为新型有机激光器的制备提供了有益的指导和借鉴意义。     

GaxIn1-xAsyP1-y/InP injection laser partially loaded with first-order distributed Bragg reflector

GaInAsP/InP distributed Bragg reflector (DBR) lasers with a first-order grating were demonstrated experimentally for the first time at a wavelength of 1.3 μm. Single longitudinal mode oscillation was obtained at low temperature, and the temperature dependence of the lasing wavelength was 0.7-0.8 Å/deg. The equivalent refractive index of GaInAsP at the lasing wavelength of 1.3 μm was 3.50 at 186 K.     

Control of lasing wavelength in distributed feedback lasers byangling the active stripe with respect to the grating

We proposed and demonstrated a new and very simple technique of varying the lasing wavelength of distributed feedback (DFB) lasers with the need for fabricating gratings with different pitches. This is accomplished by angling the active stripe at an oblique angle with respect to the axis of the grating lines. This technique should be particularly suitable for fine tuning of lasing wavelength, and it eases the stringent demand on precise control of absolute grating pitches. It should be useful and important for dense (wavelength division multiplexing (WDM) applications and monolithic integration of multi-wavelength DFB lasers     

基于氮化镓的通信波段可调DFB激光器的研究

为了利用悬空的周期可调光栅控制激光器的波长输出,采用了微机电系统技术中微驱动器与分布反馈激光器光栅相结合的结构,根据严格耦合波理论和介质平板波导理论,针对光通信的C波段,利用有限元软件COMSOL,建立了基于氮化镓的波长可调分布反馈激光器2维稳态模型。分析了1550nm处2维电场模式图以及激射波长线宽图,得到了激射波长与光栅周期的对应关系。结果表明,在光栅厚度、高度以及增益层厚度等结构参量一定的情况下,激射波长与光栅周期呈现与理论分析基本一致的似线性关系。该研究为该器件设计以及制备的后期工作开展提供了理论指导意义。     

Lasing in the vertical direction in InGaN/GaN/AlGaN structures with InGaN quantum dots

InGaN/GaN structures with dense arrays of InGaN nanodomains were grown by metallorganic chemical vapor deposition. Lasing in vertical direction occurs at low temperatures, indicating ultrahigh gains (～ 10⁵ cm^?1) in the active region. Fabrication of an effective AlGaN/GaN distributed Bragg reflector with reflectivity exceeding 90% enables vertical lasing at room temperature in structures with a bottom distributed Bragg reflector, despite the absence of a well-reflecting upper mirror. The lasing wavelength is 401 nm, and the threshold excitation density is 400 kW/cm².     

Current-injection efficiency in semiconductor lasers with a waveguide based on quantum wells

A dynamic distributed diffusion-drift model of laser heterostructures, which takes into account carrier capture by quantum wells, is developed. The leakage currents in the lasing mode are calculated for different laser structures without wide-gap emitters: InGaAs/GaAs (lasing wavelength λ = 0.98 μm), InGaAsP/InP (λ = 1.3 μm), and InGaAs/InP (λ = 1.55 μm). It is shown that consideration of the finite carrier-capture time is of major importance for calculating structures with deep quantum wells. The ratio of the leakage currents to the total current in the structures with deep quantum wells (InGaAsP/InP and InGaAs/InP) increases with an increase in the injection current and may reach a few percent when the lasing threshold is multiply exceeded.     

Continuously tunable organic solid-state DFB laser utilizing molecular reorientation in molecular glasses

We report a facile way for continuously tuning the lasing wavelength of an organic thin-film distributed feedback (DFB) laser after device fabrication by varying the effective refractive index seen by the one-dimension DFB laser structure. Varying the effective refractive indices of the organic gain medium and thus the effective refractive index of a one-dimension DFB laser structure after device fabrication is made possible with reorientation of molecules in a molecular glass at elevated temperatures. Distributions of molecular orientations can be fine controlled by annealing temperatures and times, permitting continuous tuning of optical properties and lasing wavelengths. Molecular reorientation can be conducted after devices are made, thus giving one the freedom to set or tune the lasing wavelength to meet a particular purpose with a common structure.     

Transient regime of a dynamic distributed feedback laser: Theory and numerical analysis

A semiclassical treatment of transient behavior of a gain-coupled, distributed feedback laser is developed. The nonlinear response of the lasing medium to the spatially periodic pump and the effect of self-induced grating are involved in the theory. The influence of a noise signal value on the generation kinetics is demonstrated. The possibility of practically unidirectional lasing is also shown.     

A unified Green's function analysis of complicated DFB lasers

An efficient full-wave analysis technique for one-dimensional optical domains, known as the recursive Green's function method (RGFM), is presented for evaluation of distributed feedback (DFB) laser cavities with arbitrary material profiles. The method first constructs the Green's function of an inhomogeneous domain and subsequently uses Green's theorem to determine the laser optical field, lasing wavelength, and threshold gain. The technique is applied to investigate the performance of three DFB laser structures: a chirped-grating configuration, a modulated stripe width design, and a reduced duty cycle complex-coupled device. These structures are evaluated in terms of their single-mode lasing behavior and the uniformity of the optical field within the cavity     

Stable Dual-Wavelength DFB Fiber Laser With Separate Resonant Cavities and Its Application in Tunable Microwave Generation

A single-longitudinal-mode dual-wavelength distributed feedback fiber laser with a wavelength spacing of 0.312 nm is proposed and demonstrated. Based on two spatially separated resonant cavities in a single fiber Bragg grating made by a simple method, stable dual-wavelength lasing is established. Then, a 38.67-GHz microwave signal generated by beating the two lasing wavelengths is obtained with a 3-dB bandwidth of ~6 kHz and a frequency drift <5 MHz without any feedback mechanism. As a potential application of this device, a tunable microwave source ranging from 18.67 to 58.67 GHz (with a small discontinuity) is proposed and partially demonstrated     

液晶分子取向对液晶/聚合物光栅电光特性以及激光出射特性的影响

报道了液晶分子不同取向对液晶/聚合物光栅电光特性以及激光出射的影响。通过扫描电子显微镜观察液晶/聚合物光栅的截面,成功观察到了光栅的体光栅结构。液晶分子垂直光栅矢量排列时,由于光栅形貌变差,衍射效率由液晶分子沿光栅矢量排列时的83.2%降低至72%,同时散射损耗由11.8%增加至19.1%。液晶分子垂直光栅矢量时,液晶/聚合物光栅的调谐电场由液晶分子沿光栅矢量时的13.6V/μm下降至3.1V/μm。液晶沿光栅矢量排列时,激光出射阈值更低,为利于激光出射的方向。本文工作为进一步加深对液晶/聚合物光栅以及染料掺杂分布式反馈选频的理解和认识,提供了指导和借鉴。     

DFB-LD在不同温度下的频响测量

利用脉冲注入法测量了分布反馈激光器(DFB-LD)芯片温度与激射波长的关系.基于此关系测量了不同芯片温度下分布反馈激光器的小信号响应曲线、传输眼图和误码率,并讨论了温度、偏置电流对响应曲线、传输眼图和误码率的影响.     

High-performance single-longitudinal-mode operation of InGaAsP/InP DFB-DC-PBH LD's

The lasing performance of InGaAsP/InP distributed feedback laser diodes with double-channel planar buried heterostructure (DFB-DC-PBH LD's) is reported for end-titled and antireflection (AR) coated configuration. High-power CW single-longitudinal-mode (SLM) operation over 55-mW light output at room temperature, high-temperature CW SLM operation over 105°C, as well as stable SLM operation under 2-Gb/s high-speed direct modulation, have been attained for 1.3-μm band DFB-DC-PBH LD's. 1.5-μm band DFB-DC-PBH LD's have also exhibited excellent DFB lasing characteristics, such as high power over 20 mW and high temperature over 75°C CW SLM operation. DFB SLM yield in the laboratory was also examined for 1.3-μm DFB-DC-PBH LD's, giving rise to a good prospect for practical use in optical-fiber communication systems.