Hypersensitization of rare-earth-doped waveguides for distributed-feedback amplifier and laser applications

Deterioration of the gain coefficient as a result of UV processing of hydrogen-loaded Er(3+) - and Er(3+)/Yb (3+) -doped silicate optical waveguides can be reduced by initial hypersensitization of the waveguide prior to bulk irradiation. This allows improved performance in active-grating devices such as distributed-feedback fiber amplifiers and lasers.     

双频激光泵浦光纤放大器中的原子相干效应

用密度矩阵的方法从理论上分析了不同频率的两个激光场混合泵浦的光纤放大器中，由光场诱导的原子相干效应。并由此引入相干修正因子，通过修正的速率方程讨论了两光场与原子的相干作用对放大器增益的影响。     

Low‐wavelength emission of Nd‐doped lasers

This paper gives an overview of the results obtained with diode‐pumped Neodymium‐doped crystals operating below 900 nm. Operation at such low wavelengths requires considering the strong thermal population of the lower level of the laser transition. Based on a theoretical study and simulations, the paper presents the challenges related to the design of these three‐level lasers. Experimental results are given with Nd:YAG and Nd:vanadate crystals. It is explained how to deal with the line competition with emission at 946 nm or 912 nm. Finally, intracavity second‐harmonic generation is presented. The output powers reach a few hundred mW at wavelengths below 450 nm. Hence, the paper demonstrates the potential of Nd‐doped diode‐pumped solid‐state lasers for applications in the blue range, in replacement of gas lasers such as helium‐cadmium lasers.     

Q‐switched and modelocked all‐fiber lasers based on advanced acousto‐optic devices

The interest in all‐fiber lasers is stimulated by the inherent advantages they have over bulk lasers in aspects such as heat dissipation and robustness. The performance of Q‐switched and modelocked fiber lasers can benefit enormously from the development of all‐fiber configurations. A fiber laser with strictly all‐fiber components can fulfil the requirements of mechanical stability, low maintenance, enhanced power efficiency, simplified assembly process, and low cost. In this framework, recent developments infiber acousto‐optic devices are reviewed that have demonstrated new possibilities for actively Q‐switched distributed feedback fiber lasers, modelocking lasers and doubly active Q‐switched modelocked lasers. The aim is to demonstrate the great potential of infiber devices for the active control of different types of fiber lasers.     

Er掺杂和Er/Yb双掺杂光电陶瓷PLZT的上转换发光

研究了Er掺杂和Er/Yb双掺杂的锆钛酸铅(PLZT)光电陶瓷的上转换发光特性,观测到Er掺杂的PLZT样品在540,566nm附近的绿色发光峰,且随着掺杂浓度的增大而增强;Er/Yb双掺杂的PLZT样品除540,566nm附近处的绿色发光峰外,还有一个较弱的668nm的红色发光峰。另外,上转换发光强度与激发强度的对数关系曲线表明样品的绿光发射和红光发射皆为双光子过程,并且利用喇曼光谱进一步分析讨论了其上转换发光的机制。实验和理论分析表明该材料有望制成电光调Q的双功能上转换激光器件。     

Tm3+/Ho3+共掺碲酸盐微结构光纤激光器

用棒管法拉制了Tm³⁺/Ho³⁺掺杂的碲酸盐微结构光纤,并获得了2 μm的激光输出。以1 560 nm的Er³⁺掺杂石英光纤激光器作为泵浦源,在22 cm长的微结构光纤中,得到了最大功率为8.34 mW、波长为2 065 nm的连续激光输出,泵浦光功率为507 mW,斜率效率为2.97%。研究结果表明,Tm³⁺/Ho³⁺共掺碲酸盐微结构光纤是一种用于研制2 μm激光器的理想材料。     

Flat supercontinuum generation covering C-band to U-band in two-stage Er/Yb co-doped double-clad fiber amplifier

Supercontinuum generation in the gain fiber in two-stage nanosecond pulse Er/Yb co-doped double-clad fiber amplifier had been demonstrated for the first time to our knowledge instead of the conventional method in which nonlinear fiber was pumped by lasers. The Er/Yb co-doped double-clad fiber acts as the gain media and nonlinear media. This route reduces the splice between fiber laser and nonlinear fiber. The supercontinuum was achieved with spectrum range from 1530 nm to beyond 1700 nm at 6 W output power covering the total C-band to U-band. From the analyzing of the spectra at different stages in the amplifiers, it can be found that it is the modulation instability in the anomalous dispersion regime that initiates the supercontinuum gereration.     

Fiber Bragg gratings for optical telecommunications

Bragg gratings photoimprinted in optical fibers have become essential for flattening the gain of amplifiers, stabilizing the wavelength of pumps or sources, and for fiber lasers. Advantages are low insertion loss, very low polarization sensitivity and an extremely flexible design. Those advantages make gratings also very attractive candidates for applications of complex filtering or precise chromatic dispersion compensation. This article briefly describes the different types of Bragg gratings as well as several examples of applications in optical telecommunications. To cite this article: I. Riant, C. R. Physique 4 (2003).     

Quasiparity‐Time Symmetric Microdisk Laser

Recent developments in parity‐time (PT) symmetric systems have ushered in unique photonic devices with enhanced functionalities. While single‐mode laser emission has been demonstrated in such systems, the current designs face severe challenges in applications, either due to their stringent requirement on fabrication precision or nonscalability to larger devices. Here, we demonstrate a general mechanism to achieve single‐mode lasing in coupled cavities, which relies on external mode coupling and overcomes these drawbacks. We find significant gain enhancement for selected modes by external coupling, and our experiments have confirmed the resulting single‐mode laser emission in size‐mismatched photonic molecules (PMs), when only one constituent cavity is pumped. This behavior persists for a wide range of pump power, from transparent threshold to gain saturation, and it is highly tolerant of fabrication imprecisions. In addition, the output intensity of such single‐mode lasers also displays enhancement when compared with the same PMs under uniformly pumping. We believe our results will both advance the understanding of different coupling scenarios in coupled cavities and improve the characteristics of onchip laser sources for practical applications.     

Blue‐green light generation using high brilliance edge emitting diode lasers

A review about second harmonic generation using edge emitting diode lasers and nonlinear crystals to obtain laser radiation in the blue‐green spectral range is presented. Therefore, pump laser radiation with high brightness and narrow bandwidth is necessary. Thus, this review gives an overview of the advances made with distributed feedback and Bragg reflector lasers, tapered lasers and amplifiers as well as external cavity diode lasers and master oscillator power amplifier schemes to achieve high brilliance emission. Since periodically poled materials have enabled high second harmonic conversion efficiencies with low and moderate pump powers, the review is focused on frequency doubling using those materials. The most commonly used materials, their properties and limitations are discussed briefly. Single pass and resonant SHG setups with waveguide and bulk nonlinear crystals are discussed and an emphasis on building compact and integrated devices is made.     

Yb3+:Er3+共掺氟磷酸盐玻璃的发光和激光性能

稀土掺杂氟磷酸盐玻璃是可以满足波分复用系统及超短脉冲系统对带宽和平坦增益要求的激光材料之一。研究了其中一种增益带宽宽,发光谱线平坦的镱铒共掺氟磷酸盐玻璃,其计算半峰全宽为51nm。对反映宽带性能的有效增益截面的研究表明,该镱铒共掺氟磷酸盐玻璃在1530～1580nm之间有一平坦的有效增益截面谱线,证明其宽带特性明显优于掺铒磷酸盐玻璃。对Yb^3 离子敏化效率的研究显示,在镱铒比为10：1时,Er^3 离子的吸收截面和发射截面达最大值,分别为0．6601pm^2和0．7325pm^2,表明此比值下Yb^3 对Er^3 的能量传递效率最高。实验结果显示Yb：Er氟磷酸盐玻璃可用作带宽宽,增益平坦,可实现高能输出的激光器和光纤放大器的基质玻璃材料。     

Enhanced mid-infrared emissions of Er3+ at 2.7 μm via Nd3+ sensitization in chalcohalide glass

Nd(3+) sensitized Er(3+):(4)I(13/2) mid-IR emissions around 2.7 μm were investigated in the transparent Ga(2)S(3)-GeS(2)-CsCl chalcohalide glasses for the first time. Remarkably, it is found that Nd(3+) greatly enhances Er(3+) 2.7 μm emission by a maximal 20 times, and depopulates the lower level of Er(3+):(4)I(13/2) for population inversion. Based on Judd-Ofelt theory, the 2.7 μm emission cross section is calculated (as high as 0.66×10(-20) cm(2)) and the gain property of the Er(3+):(4)I(11/2)→(4)I(13/2) transition is discussed. Hopefully, the materials studied here may find potential applications in the fields of fiber amplifiers and mid-IR lasers.     

Trace-gas analysis using diode lasers in the near-IR and long-path techniques

Room-temperature, near-infrared, semiconductor diode lasers continue to gain importance for gas monitoring applications owing to their compactness, ease of use, reasonable cost and compatibility with telecommunications-grade optical fiber components. They may probe overtone or combination vibrational bands for a large variety of atmospheric relevant molecular species. These spectral bands exhibit line strengths orders of magnitude lower than those of fundamental vibrations, occurring in the mid-infrared. As a consequence, they are often used in conjunction with long-path techniques, enabling one to perform high sensitivity local measurements through long absorption path-lengths. At this purpose, resonant optical cavities can be fruitfully employed. This paper is devoted to a discussion of the main features of cavity-enhanced absorption spectrometers, operating with near-infrared diode lasers. We report on the operating principle as well as the achievable performance of these devices, also compared to more traditional apparatus, based on the multiple reflection cells. Experimental results on water vapour and oxygen detection are reported.     

The erbium-doped fiber amplifier: Technology and applications

The basics of active fiber technology and their application to optical amplifiers and lasers are reviewed, with particular reference to the activities of the Italian groups involved in this research. The main uses of optical amplifiers in telecommunications and the perspective of ultrafast soliton fiber lasers are presented and discussed.     

Semiconductor amplifiers and lasers with tapered gain regions

Semiconductor amplifiers and lasers with tapered gain regions provide the highest-brightness all-semiconductor sources of near infrared continuous wave (CW) power and have many useful applications. Simple models of these devices are described. Their applications, device performance and brightness limitations are reviewed.

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The spectroscopic and energy transfer characteristics of the rare earth ions used for silicate glass fibre lasers operating in the shortwave infrared

The continuing growth in the research and development of high power diode‐pumped fibre lasers relates to the exceptional thermal management provided by the extended geometry of the fibre and the small quantum defect associated with the 1 μm emitting Yb³⁺ ion. Lengthening the emission wavelength of diode‐pumped fibre lasers further into the infrared is important for many applications ranging from medicine to defence; however, extending the emission wavelength remains a challenge. This review will examine in detail the spectroscopy and the energy transfer processes that impact Tm³⁺‐doped and Ho³⁺‐doped silicate glasses that are used for fibre lasers in the 1.9 μm to 2.1 μm region of the shortwave infrared spectrum. We will explore a number of important applications that function in the shortwave infrared region that will benefit from using these light sources and I will suggest the reasons for choosing silicate glass over other glasses as the host material for this wavelength range.     

Silicon photonics: from a microresonator perspective

Silicon photonics leverages the optical, electrical and material properties of silicon and the mature complementary metal‐oxide semiconductor (CMOS) nanofabrication technique to develop on‐chip photonic integration, which has been making significant impacts in various frontiers including next‐generation optical communications networks, on‐chip optical interconnects for high‐speed energy‐efficient computing and biosensing. Among many optical structures fabricated on silicon chips, microresonators due to their high‐Q resonances and small footprints play important roles in various devices including lasers, filters, modulators, switches, routers, delays, detectors and sensors. This paper reviews from a microresonator perspective some of the latest progress in the field, summarizes design considerations in various applications and points out key challenges and potentials.     

熔锥型侧面泵浦耦合器的研究

 现在高功率光纤激光器和光纤放大器采用的双包层掺杂光纤,相对于从半导体泵浦激光器发射出的多模泵浦光束的大发散角,其内包层的直径很小,因此把泵浦光有效地耦合到双包层掺杂光纤的内包层是一个急需解决的难题。研制一种熔锥型侧面泵浦耦合器,可以大幅度提高泵浦光功率,实现增益光纤的多点泵浦,在双包层光纤放大器中使用良好,安全稳定,实现了较高的耦合效率,达到了70%,信号光通过率98%,信号输入与泵浦输入的隔离度大于50 dB,泵浦输入对输出端反向传输光的隔离度27 dB。通过对比结构紧凑性、耦合效率、系统稳定性等相关指标发现,熔锥型侧面泵浦耦合器完全可以满足高功率光纤激光器和光纤放大器的使用要求。     

Functional organic single crystals for solid‐state laser applications

Because of long‐range order and high chemical purity, organic crystals have exhibit unique properties and attracted a lot of interest for application in solid‐state lasers. As optical gain materials, they exhibit high stimulated emission cross section and broad tunable wavelength emission as similar to their amorphous counterpart; moreover, high purity and high order give them superior properties such as low scattering trap densities, high thermal stability, as well as highly polarized emission. As electronic materials, they are potentially able to support high current densities, thus making it possible to realize current driven lasers. This paper mainly describes recent research progress in organic semiconductor laser crystals. The building molecules, crystal growth methods, as well as their stimulated emission characteristics related with crystal structures are introduced; in addition, the current state‐of‐the‐art in the field of crystal laser devices is reviewed. Furthermore, recent advances of crystal lasers at the nanoscale and single crystal light‐emitting transistors (LETs) are presented. Finally, an outlook and personal view is provided on the further developments of laser crystals and their applications.