Widely tunable erbium-doped fiber ring laser covering both C-bandand L-band

We demonstrate a widely tunable erbium-doped fiber (EDF) ring laser covering both the conventional wavelength band (C-band) and the long wavelength band (L-band). It features a wide tunable range, high output power, low-coherent, and depolarized output. A tunable range over 80 nm (1520-1600 nm) has been achieved by optimizing the length of the EDF and by using an intracavity fiber Fabry-Perot (FFP) filter     

A 380-mW 7-MHz cerium LiLuF laser pumped by the frequency doubledyellow output of a copper-vapor-laser

We report a high average power Ce:LiLuF laser pumped by the second harmonic of the yellow output from a copper vapor laser. This cerium laser yielded up to 380 mW at a pulse repetition frequency of 7 kHz at the peak lasing wavelength of 309.5 nm, with a slope efficiency of 50%. In addition, single prism tunability was obtained from 305.5 to 316 nm and from 322 to 331.8 nm, Preliminary investigation into color center behavior has been performed involving crystal cooling, He-Ne pump probe experiments and antisolarant pumping     

Frequency control characteristics of a single-frequency fiber laserwith an external light injection

Characteristics of a single-frequency erbium-doped fiber laser (EDFL) controlled by an external light source is investigated. The frequency control is achieved by cooperatively induced spatial hole-burning (SHB) formed by the interference between the lasing light and the external light. We evaluate the frequency stability of several cavity designs of the fiber laser and the frequency control characteristics in detail. Tunable operation as wide as 30 nm wavelength range with a good frequency stability is also demonstrated     

A theoretical investigation of dynamic all-optical automatic gaincontrol in multichannel EDFA's and EDFA cascades

We present a detailed theoretical analysis of the gain dynamics of erbium-doped fiber amplifiers (EDFA's) that have been gain-clamped using a ring laser structure and of gain-stabilized EDFA chains. We examine and analyze the effects of attenuator level in the optical feedback path, switching speed, number of channels dropped or added and the choice of lasing wavelength on the stabilization of the individual EDFA. In particular, we look at the transient power excursions and relaxation oscillations experienced by surviving channels when the number of channels passing through an EDFA changes. Using this analysis as a guide, we present and compare two different approaches to chain stabilization. We highlight the robustness of each approach, show some of their limitations and advantages, and comment on the impact on multiwavelength communication systems     

Power Scaling of Ytterbium-doped Fiber Superfluorescent Sources

Power scaling of ytterbium-doped fiber superfluorescent sources based on single-stage and two-stage cladding-pumped fiber configurations is reported. For the single-stage configuration, a novel fiber-end termination scheme was employed to suppress laser oscillation in combination with a simple all-fiber scheme for achieving a predominantly single-ended output. The fiber was cladding-pumped by a diode stack at 976 nm and yielded ~62 W of single-ended amplified spontaneous emission output for 119 W of launched pump power, limited by the onset of parasitic lasing. At pump powers in excess of 40 W, the slope efficiency with respect to the launched pump power was 67%. The emission spectrum spanned the wavelength range from 1030 to 1100 nm and the bandwidth (FWHM) was 12 nm. Scaling to higher power levels was demonstrated using a two-stage cladding-pumped fiber configuration comprising of a low-power fiber superfluorescent seed source and a high-power amplifier. The two-stage source yielded 122 W of amplified spontaneous emission output (limited by available pump power) in a beam with M² ap 2.1. The slope efficiency for the amplifier with respect to the launched pump power was 77%. The prospects for further improvement in performance and output power are considered.     

Miniature erbium:ytterbium fiber Fabry-Perot multiwavelength lasers

We demonstrate stable simultaneous lasing of up to 29 wavelengths in miniature 1- and 2-mm-long Er³⁺:Yb³⁺ fiber Fabry-Perot lasers. The wavelengths are separated by 0.8 (100 GHz) and 0.4 nm (50 GHz), respectively, corresponding to the free spectral range of the laser cavity. The number of lasing wavelengths and the power stability of the individual modes are greatly enhanced by cooling the laser in liquid nitrogen (77 K). The polarization modes and linewidth of each wavelength are measured with high resolution by heterodyning with a local oscillator. The homogeneous linewidth of the Er³⁺:Yb ³⁺ fiber at 77 K is determined to be ~0.5 nm, from spectral-hole-burning measurements, which accounts for the generation of a stable multiwavelength lasing comb with wavelength separations of 0.4 nm     

全光通信网中的L波段光纤激光器研究

本文首先介绍了光纤激光器(特别是掺铒光纤激光器)的工作原理。进而对L波段光纤激光器进行了深入的探讨,并分析了影响激光器输出的因素:谐振腔长、掺铒光纤长度,且做了相应的理论分析。     

Widely tunable polarization-stable fiber lasers

Four different widely tunable polarization-stable lasers, each based on nonpolarization maintaining erbium-doped fiber are presented. We experimentally examine the effect of output coupling on laser performance, and compare the output power measurements with theoretical predictions. We also discuss the relative costs and construction factors of the four lasers     

Widely tunable DS-DBR laser with monolithically integrated SOA: design and performance

We report recent device characterization results for a fully packaged widely tunable digital supermode (DS) distributed Bragg reflector (DBR) laser which has been monolithically integrated with a semiconductor optical amplifier. This new device gives all of the wide tunability and high side-mode suppression ratio performance previously reported for the DS-DBR laser with the added feature of output powers in excess of 14 dBm in fiber. In addition to output power and basic tuning behavior, we report on linewidth and relative intensity noise measurements for this device in order to investigate the noise characteristics of this laser.     

Influence of strain on lasing performances of Al-freestrained-layer Ga(In)As(P)-GaInAsP-GaInP quantum-well lasers emitting at0.78<λ<1.1 μm

The influence of strain on lasing performances of Al-free strained-layer Ga(In)As(P)-GaInAsP-GaInP quantum-well lasers is investigated for the first time over a large emission range of 0.78<λ<1.1 μm. GaAsP and InGaAs are used for tensile and compressive-strained quantum-well layers, respectively, while GaAs and GaInAsP lattice-matched to GaAs are applied for unstrained quantum wells. The laser structures were prepared by using gas-source molecular beam epitaxy, and broad-area and ridge waveguide Fabry-Perot laser diodes were fabricated. This study shows that applying both tensile and compressive strains in the quantum well reduces threshold current density for the Al-free strained-layer quantum-well lasers. However, it was found that the lattice relaxation set a limitation of maximum compressive strain (i.e., maximum lasing wavelength) for the compressive strained InGaAs lasers while the carrier confinement determined the acceptable maximum tensile strain (i.e., minimum lasing wavelength) and lasing performances for the tensile strained GaAsP lasers. Threshold current density as low as 164 A/cm² has been obtained for 1.4% compressive-strained InGaAs-GaInAsP-GaInP lasers having a 12-nm thick quantum well. However, excellent characteristics, such as low threshold current, high efficiency low internal loss, and high output power, have been achieved for the Al-free strained-layer quantum-well lasers     

The Rising Power of Fiber Lasers and Amplifiers

The first rare-earth-doped fiber lasers were operated in the early 1960s, and produced a few milliwatts at a wavelength around 1 mum. Since the beginning of the decade, an enormous increase of fiber laser output power has been reported, the realm of kilowatt power has been entered, and power levels as high as 100 kW are envisaged. Apart from the power, fiber laser systems are renowned for their inherent compactness, monolithic architecture, and a power-independent beam quality. This paper reviews the challenges, achievements, and perspectives of high-power continuous-wave (CW) laser generation and amplification in fibers.     

Recent advances in DFB lasers for ultradense WDM applications

State-of-the-art distributed feedback (DFB) laser modules integrated with a wavelength monitor are presented that provide excellent wavelength stability. By adopting unique and compact configuration, wavelength deviations of as small as a few picometers have been achieved. The laser modules are improved also in the scope of high power, high reliability, and wavelength tunability. Reliability test results of the DFB laser diodes and modules confirm a sufficiently long lifetime of more than 25 years and a small wavelength drift of less than /spl plusmn/3 pm. The developed laser modules are fully applicable to ultradense wavelength-division multiplexing applications with the current narrowest channel spacing of 25 GHz.     

Long-wavelength-band Er3+-doped fiber amplifierincorporating a ring-laser as a seed signal generator

A novel dual-stage architecture for long-wavelength-band (L-band) erbium-doped fiber amplifier, which incorporates a gain-clamped amplifier based on a ring-laser feedback as a seed signal generator in the first stage is described. This technique has elevated the intensity of a short-wavelength amplified spontaneous emission (ASE) by 29%, from 11.3 mW of ASE power to 14.6 mW with a feedback lasing at 1560 nm. This strong laser then improves the L-band gain enormously, as large as 17.1 dB and noise figures are lower than 4.8 dB for the entire signal range in the flat-gain operation. The seeding signal reduces pump-to-ASE losses in the second stage to 38% compared to a conventional amplifier without feedback. Noise figure penalties are negligible due to efficient low-noise characteristics in the first stage. The proposed amplifier provides 25 dB gain for 50 wavelength-division-multiplexed signals at -30 dBm/ch with gain flatness less than 1.1 dB with only 980 nm pumping     

High-power continuous-wave 3- and 2-μm cascadeHo3+:ZBLAN fiber laser and its medical applications

A new medical fiber laser oscillating at two useful wavelengths (3 and 2 μm) is reported. We have demonstrated highly efficient and high-power continuous-wave cascade oscillation at room temperature with a holmium ion-doped fluoride glass fiber laser pumped with a 1.15-μm fiber Raman laser. The simultaneous oscillation wavelengths were 3 and 2 μm, and their combined output power was 3.0 W with a slope efficiency of 65%. To our best knowledge, this is the first achievement of watt-level-output power in the mid-infrared region with ZrF₄-BaF₂-LaF₃-AlF₃-NaF (ZBLAN) glass fiber. In experiments to evaluate potential for medical applications, we tested the two wavelength beam as a laser surgical knife on soft rabbit tissues and demonstrated that it had strong cutting capability, and that the coagulation layer thickness could be controlled by varying the power ratio of the two-wavelength laser     

Growth of highly strained GaInAs-GaAs quantum wells on patterned substrate and its application for multiple-wavelength vertical-cavity surface-emitting laser array

We carried out the growth of highly strained GaInAs-GaAs quantum wells (QWs) on a patterned substrate for extending emission wavelength on a GaAs substrate. We examined the shift of photoluminescence wavelength of the QWs and showed a large wavelength shift due to the spatial modulation in well thickness and indium composition. We demonstrated a single-mode multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) array on a patterned GaAs substrate covering a new wavelength window of 1.1-1.2 /spl mu/m. By optimizing pattern shape, we achieved multiple-wavelength operation with widely and precisely controlled lasing wavelengths. The maximum lasing span is as large as 77 nm. We carried out a data transmission experiment through 5-km of single-mode fiber with a 2.5 Gb/s/channel. The total throughput reaches 10 Gb/s. The VCSEL-based wavelength-division-multiplexing (WDM) source would be a good candidate for WDM-LAN beyond 10 Gb/s.     

Fiber Design For High-Power Low-Cost Yb:Al-Doped Fiber Laser Operating at 980 nm

We investigated an Yb:Al-doped depressed-clad hollow optical fiber (DCHOF) for cladding-pumped 980-nm laser operation. With a careful design, the nonzero fundamental-mode cutoff characteristics of a DCHOF allows the competing 1030- 1060 nm emission to be filtered out, despite being quite close to 980 nm. The laser yielded over 3 W of output power in a diffraction limited beam (M²~1.09) from a DCHOF with an inner-cladding diameter of 120 mum. This is large enough for pumping with standard fiber-coupled multimode diode sources. By reducing the inner-cladding size to 90 mum, and hence, lowering the 980-nm threshold, the output power was scaled up to 7.5 W. However, we believe that the M²-parameter degrades to 2.7, as a result of increased cladding-mode lasing, as the cladding thickness is reduced.     

Fiber amplifiers for coherent space communication

We report on the application of double-clad doped fiber amplifiers for coherent space communication systems using a master oscillator power amplifier (MOPA) design at 1.06 μm. The master oscillator is either a single-frequency Nd:YAG solid-state laser or a distributed-feedback fiber laser. The power amplifier is a diode-laser-pumped double-clad Nd doped fiber with polarization control, 20 dB gain, and about 1.3 W output power. A dual stage configuration using a solid-state Nd:YAG amplifier as second stage is presented as well, increasing the output power to 3.5 W with 28 dB gain. We also report on the possibility to integrate a single-frequency fiber laser, an all-fiber phase modulator, and a fiber amplifier to build an all-fiber phase-modulated MOPA. Up to 1 W continuous-wave output phase-modulated with a bandwidth of 196 MHz has been achieved     

半导体激光器温度控制电路设计及实验研究

DFB可调谐二极管激光器是激光光谱测量系统中的最主要部件之一,它的输出波长与辐射功率的稳定性决定测量系统的稳定性.影响DFB可调谐二极管激光器输出波长和输出功率的因素主要为激光器的注入电流和工作温度,而工作温度对输出特性的影响更大.设计了激光器温度控制电路,并实验分析了PI参数对温度控制稳定性的影响以及温度控制的短期稳定性;将设计电路应用在DFB可调谐二极管激光器上进行激光器输出波长与输出功率的长期监测,得到激光器输出波长的标准偏差为0.2×10-6,输出功率的标准偏差为0.02 mW.     

Design and modeling of laser-controlled erbium-doped fiberamplifiers

This paper presents a comprehensive theoretical analysis of erbium-doped fiber amplifiers (EDFAs) which use lasing to achieve automatic gain control. We have derived, for the first time, the explicit analytical expressions for the calculation of optical gain and noise spectra, critical input signal power, and optimum amplifier length for the laser-controlled EDFAs. Based on these expressions, the design of this type of EDFA becomes a simple and straight-forward task. Two amplifier design criteria, one maximizing the critical input signal power and the other optimizing gain spectra flatness, are discussed. Two examples are given to illustrate the design of gain controlled amplifiers with maximum critical input power and optimum gain spectra flatness, respectively     

An output power stabilized erbium-doped fiber amplifier withautomatic gain control

Based on the cross-saturation between two different-wavelength optical signals in an erbium-doped fiber amplifier (EDFA), we have developed an output power stabilized EDFA system with automatic gain control. The developed system shows 18.5-dB dynamic range of the output power limitation with the ability to set the output power level arbitrarily. When a temporally varying optical signal is input, the system works as a fluctuation remover for the input signal modulated at low frequency up to 1 kHz and does not have any deteriorative effect on high-frequency modulated optical signals. The degree of modulation in the fluctuated optical signal can be reduced down to as low as 0.003