Random distributed feedback fibre lasers

The concept of random lasers exploiting multiple scattering of photons in an amplifying disordered medium in order to generate coherent light without a traditional laser resonator has attracted a great deal of attention in recent years. This research area lies at the interface of the fundamental theory of disordered systems and laser science. The idea was originally proposed in the context of astrophysics in the 1960s by V.S. Letokhov, who studied scattering with “negative absorption” of the interstellar molecular clouds. Research on random lasers has since developed into a mature experimental and theoretical field. A simple design of such lasers would be promising for potential applications. However, in traditional random lasers the properties of the output radiation are typically characterized by complex features in the spatial, spectral and time domains, making them less attractive than standard laser systems in terms of practical applications. Recently, an interesting and novel type of one-dimensional random laser that operates in a conventional telecommunication fibre without any pre-designed resonator mirrors–random distributed feedback fibre laser–was demonstrated. The positive feedback required for laser generation in random fibre lasers is provided by the Rayleigh scattering from the inhomogeneities of the refractive index that are naturally present in silica glass. In the proposed laser concept, the randomly backscattered light is amplified through the Raman effect, providing distributed gain over distances up to 100 km. Although an effective reflection due to the Rayleigh scattering is extremely small (∼0.1%), the lasing threshold may be exceeded when a sufficiently large distributed Raman gain is provided. Such a random distributed feedback fibre laser has a number of interesting and attractive features. The fibre waveguide geometry provides transverse confinement, and effectively one-dimensional random distributed feedback leads to the generation of a stationary near-Gaussian beam with a narrow spectrum. A random distributed feedback fibre laser has efficiency and performance that are comparable to and even exceed those of similar conventional fibre lasers. The key features of the generated radiation of random distributed feedback fibre lasers include: a stationary narrow-band continuous modeless spectrum that is free of mode competition, nonlinear power broadening, and an output beam with a Gaussian profile in the fundamental transverse mode (generated both in single mode and multi-mode fibres).     

GaAs distributed Bragg reflector lasers

An equivalent cavity approach is used to derive the oscillation condition of a distributed Bragg reflector laser. The oscillation frequencies and thresholds are determined graphically. The effect of lossy reflectors is discussed. Several advantages and potential applications of distributed Bragg reflector structures are pointed out. Experimental results on optically pumped GaAs lasers are presented.     

Raman fiber distributed feedback lasers

We demonstrate fiber distributed feedback (DFB) lasers using Raman gain in two germanosilicate fibers. Our DFB cavities were 124 mm uniform fiber Bragg gratings with a π phase shift offset from the grating center. Our pump was at 1480 nm and the DFB lasers operated on a single longitudinal mode near 1584 nm. In a commercial Raman gain fiber, the maximum output power, linewidth, and threshold were 150 mW, 7.5 MHz, and 39 W, respectively. In a commercial highly nonlinear fiber, these figures improved to 350 mW, 4 MHz, and 4.3 W, respectively. In both lasers, more than 75% of pump power was transmitted, allowing for the possibility of substantial amplification in subsequent Raman gain fiber.     

Offset quantum-well method for tunable distributed Bragg reflector lasers and electro-absorption modulated distributed feedback lasers

A two-section offset quantum-well structure tunable laser with a tuning range of 7 nm was fabricated using offset quantum-well method. The distributed Bragg reflector (DBR) was realized just by selectively wet etching the multiquantum-well (MQW) layer above the quaternary lower waveguide. A threshold current of 32 mA and an output power of 9 mW at 100 mA were achieved. Furthermore, with this offset structure method, a distributed feedback (DFB) laser was integrated with an electro-absorption modulator (EAM),which was capable of producing 20 dB of optical extinction.     

面发射分布反馈半导体激光器

本文详细阐述了面发射分布反馈半导体激光器(SE-DFB-LD)的基本工作原理、结构设计及其工作性能,针对国内外研究最新进展与发展现状进行了总结和评述,并在此基础上,对面发射半导体激光器的研究工作和发展趋势做出了进一步的讨论和展望。随着面发射分布反馈半导体激光器各性能指标的不断优化提升和后期加工、装调技术的逐渐成熟,其将不断满足科学研究及工业、军事等实际应用领域对半导体激光器的需求,具有很大的发展潜力。     

Relaxation oscillations in distributed feedback lasers

Using approximate solutions for over-coupled (KL > 1) distributed feedback lasers above threshold and a small-signal perturbation analysis, the frequency and damping of DFL relaxation oscillations are calculated.     

Two-photon-pumped distributed feedback zirconia waveguide lasers

Distributed feedback laser action of narrow line-width output was demonstrated in zirconia waveguides doped with trans-4-[p-(N-hydroxyethyl-N-methylamino) styryl]-N-methylpyridinium p-toluene sulfonate, a compound of strong two-photon up-converted emission near 620 nm. Single-beam pumping at 1.06 m led to intense up-converted amplified spontaneous emission at 620 nm. Transient gratings for coherent scattering were generated in the waveguides by crossing two 1.06-m beams. Narrow line-width distributed feedback laser emission was observed at 627 nm. PACS 42.55.Mv; 42.70.Jk; 42.79.Gn     

Dynamics of lasers with two-dimensional distributed feedback

A model of a laser exploiting two-dimensional (2D) distributed feedback is developed. A new feedback mechanism can be realized using a dielectric structure with the width having double-periodical sinusoidal or chessboard modulation. It is shown that 2D Bragg resonator possesses high selectivity over both the longitudinal and the transverse indices. Within semi-classical approach nonlinear dynamics of 2D distributed feedback laser (DFL) is studied and spatial synchronization of radiation from extended active medium is demonstrated.     

Pulse generation by distributed feedback dye lasers

Equations describing the pulse generation by distributed feedback dye lasers are derived and solved by analytical methods. The dependence of the laser output on macroscopic parameters is discussed.On leave from the Department of Physics, Friedrich-Schiller-University, DDR-6900, Jena, German Democratic Republic     

Biharmonic pumping in dye lasers with distributed feedback

Conclusions We have shown that biharmonic pumping can effectively excite traveling population gratings in an active medium when m <(W_o/2 +1/T₁), and temperature gratings if m <(₀x_m)^–1. As the order m increases the population-grating excitation efficiency decreases, while that of the temperature gratings may either increase or decrease. The times taken for the thermal and resonance processes which form the gratings to build up are given by the expressions t=₀x_m, t =T₁/(1 +W₀T₁/2), respectively. In this case distributed feedback is formed by a thermal mechanism if (14) is satisfied, and by resonance mechanism if the opposite inequality is satisfied. The self-excitation threshold over a wide range of parameters depends logarithmically on the amplitude of the grating forming the distributed feedback. Hence, for a comparatively small excess of the threshold, self-excitation of a laser with distributed feedback is possible over a wide spectrum. Thus, for double excess of the self-excitation threshold and T₁ =10^–9 sec, =1, and H =8 lasing over a wide spectrum of 10 cm^–1 is possible.Translated from Zhurnal Prikladnoi Spektroskipii, Vol. 40, No. 2, pp. 195–202, February, 1984.We wish to thank A. A. Afanasev and P. A. Apanasevich for useful discussions.     

Laser modes in organic solid-state distributed feedback lasers

We report on the laser modes in optically pumped solid-state lasers using an electroluminescent organic semiconductor as the active medium. Mechanically flexible distributed-feedback lasers are fabricated by depositing a thin film of an active material onto a nano-patterned polyester substrate either via spin-coating of a soluble ladder-type poly(p-phenylene) or via vacuum co-sublimation of small organic molecules. The different surface texture resulting from the fabrication process causes different feedback mechanisms. In both lasers higher lateral modes give rise to a broadening of the laser spectra at higher pumping levels. Received: 7 August 2000 / Revised version: 12 September 2000 / Published online: 8 November 2000     

Energy theory of waveguide distributed feedback gas lasers

In this paper systematic numerical studies of the nonlinear operation of a waveguide distributed feedback gas laser equipped with a metal waveguide of rectangular cross section are presented. An approximate formula relating small-signal gain with the output power and the parameters of the structure for this kind of lasers is derived. Characteristics revealing saturation effects for weak as well as strong coupling regions are presented.Academic guest from the Institute of Microelectronics and Optoelectronics, Technical University, Warsaw, Poland     

具有内部相移的分布反馈半导体激光器电路模型

以耦合波方程为基础,经过适当的近似处理,给出一个比较简单的适用于有内部相移的单模分布反馈半导体激光器电路模型。该模型可用于直流、交流和瞬态分析。适于在开发光电集成回路电路级模拟软件中采用,亦可加入到现有电路模拟软件中。     

Perfectly phase-matched third-order distributed feedback terahertz quantum-cascade lasers

We report a novel laser cavity design in third-order distributed feedback (DFB) terahertz quantum-cascade lasers based on a perfectly phase-matching technique. This approach substantially increases the usable length of the third-order DFB laser and leads to narrow beam patterns. Single frequency emissions from 151 apertures (5.6 mm long device) are coherently added up to form a narrow beam with (FWHM≈6×11°) divergence. A similar device with 40 apertures shows more than 5 mW of optical power with slope efficiency ～140 mW/A at 10 K pulsed operation.     

Mode locked and distributed feedback silicon evanescent lasers

Electrically pumped lasers that can be made on silicon and integrated with other components are important in order to take full advantage of the capabilities of silicon photonics. In this paper we review two specific types of hybrid silicon evanescent lasers that can fulfill these requirements. We discuss recent results of distributed feedback (DFB) lasers and mode locked lasers made on silicon using evanescent coupling to thin films of III‐V material. Device designs and test results are discussed in detail.     

Solgel grating waveguides for distributed Bragg reflector lasers

Solgel grating waveguides and their application to the fabrication of external-cavity distributed Bragg reflector (DBR) lasers are demonstrated. A new composition of aluminosilicate material is developed for the fabrication of single-mode waveguides and Bragg reflectors. An average loss of <0.2 dB/cm is measured in the single-mode waveguides at 1550 nm. The reflectors show filtering greater than 97% near 1530 nm, with a bandwidth of ~0.6 nm . The Bragg reflectors are used as feedback resonators for DBR lasers. Single-mode lasing with a sidemode suppression of better than 25 dB is demonstrated.     

大功率分布反馈激光器中光栅优化及试验

对于分布反馈激光器来说，光栅的耦合系数是一个重要参数. 利用改进的耦合波理论计算了具体器件结构中光栅形貌对二级光栅耦合系数的影响. 在此基础上制作的器件功率达到了单面50 mW，边模抑制比为36 dB. 关键词： DFB激光器 耦合波理论 二级光栅 边模抑制比