Nd-doped Fiber Research Articles

Intrinsic strain and temperature characteristics of Yb-doped silica-based optical fibers

An investigation of strain and temperature characteristics of Yb-doped fibers has been carried out in this article. Results obtained are compared with those reported on Nd-doped fibers, showing that the lifetime variation rate of the single mode Yb-doped fiber with increasing strain is temperature independent, and within experimental error similar to that of Nd, although in each case, the fiber modes, the dopant concentration level, and the rare earth ion itself are different. Their stable behavior may form the basis of a dual element sensor with which to obtain stress and temperature information independently in so-called “smart structures.”

High-power Nd-doped fiber amplifier for coherent intersatellite links

Intersatellite optical communication links require laser beams of at least 1 W of power modulated at gigahertz frequencies. They can be delivered by a master oscillator power amplifier system which consists of a stable single-frequency Nd:YAG laser, a high-speed phase modulator, and an optical amplifier. To allow coherent detection, the polarization state must be stable and controllable at the amplifier output and the phase noise must be kept low. We report here the design and the experimental results of a diode laser-pumped double clad Nd-doped fiber amplifier with polarization control, 30-dB gain, and about 1.3 W of output power.

Intrinsic doped fluorescence decay-time based measurements—strain and temperature characteristics for sensor purposes

With current research in “smart” structures driving interest in the development of intrinsic (in-fiber) sensors for simultaneous strain and temperature monitoring, a new sensor approach is presented. In this, the fluorescence decay-time technique, which is familiar as a method of temperature monitoring with a range of materials is extended to investigate the strain sensitivity of an important temperature probe using Nd-doped fiber, in both single and multimode form. For these fibers, strain and temperature sensitivities are presented, “stress annealing” effects are investigated and the potential for compact, multiparameter intrinsic sensors using Nd-doped fiber is discussed.

Control of Chaos in Lasers by Feedback and Nonfeedback Methods

Analytical approaches of the theory of chaos control in class B lasers are presented in the cases of continuous delayed feedback and of subharmonic modulation. They are compared with experimental findings on a CO 2 laser and a Nd-doped fiber laser with modulated loss and pump respectively. In both cases, analytical theory allows one to predict the shift of the first period-doubling bifurcations, Numerical simulations show that subharmonic modulation may induce shifts, crises and new attractors in a laser with modulated parameters and that its phase relative to the main modulation allows one to control the laser dynamics. These results agree well with the experimental observations on control of chaos in CO 2 and fiber lasers.

Optical and spectroscopic characterization of Nd-doped aluminosilicate fiber preforms made by the MCVD method using chelate delivery

F3/2 level of Nd3+ in aluminosilicate optical fiber preforms after 807-nm excitation are reported in the temperature range from 15 °C to 500 °C for Nd2O3 concentrations in the range from 0.2 to [%wt]0.9 and Al2O3 concentrations of between [%wt]3.8 and [%wt]8. At room temperature it is observed that for concentrations of less than [%wt]0.6 Nd2O3 the fluorescence decay is approximately exponential; for the higher Nd2O3 concentrations the decay is increasingly bi-exponential. We have identified a “slow” (≈500 μs) and a “fast” (≈100 μs) decay time; the slow decay is attributed to isolated ions and the faster decay to energy transfer between homogeneously dispersed ions. The measured 1/e folding fluorescence decay time τ decreases slowly at a constant rate of -0.08±0.007 μs/K for [%wt]0.9 Nd2O3. It is shown that increasing the Al2O3 concentration tends to suppress this temperature quenching effect. A radiative decay time of 640 μs is obtained by Judd–Ofelt analysis.

Correction To The Journal Of Lightwave Technology April 1998 Table Of Contents

Summary form only, as follows. The topical heading of "Fibers" was omitted from JOURNAL OF LIGHTWAVE TECHNOLOGY's April 1998 Table of Contents. The following papers, which were included under "Systems" should have been listed under "Fibers." 1) "Corrections to Fixed Analyzer Measurements of Polarization Mode Dispersion" by P.A. Williams and C.M. Wang. 2) "Signal-Induced Refractive Index Changes in Erbium-Doped Fiber Amplifiers" by M. Janos and S.C. Guy. 3) "Generating Mechanism of Maintaining Force for Optical Fiber Installed in Ferrule Hole" by M. Takahashi. 4) "Simulation and Characteristics of Long-Period Fiber Bragg Grating Coherence Spectrum" by Y. Zhao and J.C. Palais. 5) "Nd-Doped Double-Clad Fiber Amplifier at 1.06μm" by T. Miyazaki, K. Inagaki, Y. Karasawa, and M. Yoshida. 6) "Improved Design of APC Optical Connectors with Slanted Angle of 12° for Dispersion Shifted Optical Fiber" by M. Takahashi.

Nd-doped double-clad fiber amplifier at 1.06 μm

We propose and demonstrate a double-clad neodymium (Nd)-doped fiber amplifier (IVDFA) at 1.06 /spl mu/m for a compact configuration of a high-power optical amplifier. The proposed 125 /spl mu/m first cladding diameter in the double-clad fiber, provides the single-mode propagation of the signal lightwave into its doped core without misguiding the signal lightwave into the outer core (first cladding), by simply splicing with a standard single-mode fiber. Furthermore a fiber grating in a single-mode core of the double-clad fiber allows the double-pass configuration for the signal lightwave at 1.06 /spl mu/m and also allows the pump lightwave coupling at 0.81 /spl mu/m into the first cladding without employing a bulk dichroic mirror. We demonstrate the signal output power of 110 mW for a 550-mW pump input from a multimode fiber coupled pump source. Theoretical results predict an efficient high-power operation of the amplifier by improving the signal scattering loss in the double-clad fiber.

Polarization dynamics of a fibre Fabry-Perot laser with feedback

Experimental results on the low-frequency polarization dynamics of a free-running Nd-doped optical fibre laser and a fibre laser with derivative feedback are presented. It is found that the power spectrum of each polarization mode reveals three relaxation peaks. Using the combined (negative and positive) derivative feedback it is possible to suppress noise in the region of the in-phase relaxation oscillations and to excite noise in the region of one of the two antiphase relaxation oscillations. The model developed of a class B laser with two orthogonal elliptically polarized modes is checked and explains the main experimental features of relaxation oscillation peaks.

Bipolarized Nd-doped fibre laser: effects of localized and distributed dichroisms

We present a static analysis of a general model for a bipolarized Nd-doped fibre laser including the slow longitudinal variations of the dynamical variables. Approximate analytical results are derived for the thresholds and the output intensities. A good agreement with the numerical simulations is achieved over a large range of parameters. The combined effects of pump-induced, distributed and localized dichroisms are studied versus the fibre length. In particular, the evolution of the thresholds versus the pump-input polarization angle, for different fibre lengths, is thoroughly investigated.

Bipolarized Nd-doped fibre laser: isomorphism between the two-site ion distribution and the truncated multi-site approaches

This paper presents a synthetic formulation of the dynamical equations of a fibre laser in which vectorial properties of the field as well as longitudinal aspects are preserved. The model is shown to reduce to previous and more restricted models which thus become linked together through a simple linear transformation we call isomorphism.

Spectral characteristics and effects of heat treatment on intrinsic Nd-doped fiber thermometer probes

A detailed investigation of the practical spectroscopic features and the effect of prolonged exposure to elevated temperatures of an intrinsic Nd:doped fiber optic thermometer probe using the fluorescence decay time technique has been carried out. Results have shown the optimum length for the doped fiber and a maximum operating temperature of 750 °C, beyond which a range of high-temperature “annealing” effects are seen. These are discussed in light of the operation of the thermometers over the range from −196 to 750 °C and potentially above.

Fiber amplification in the 940-nm water vapor absorption band using the /sup 4/F/sub 3/2/ /sup 4/I/sub 9/2/ transition in Nd

The measurement of atmospheric water vapor in the 940-nm absorption band may be accomplished using fiber amplifiers based on the /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 9/2/ transition in Nd. We report initial experimental results on the effects codopants have on the characteristics of this transition in Nd-doped fiber, and present modeled and experimental results of a fiber amplifier. To our knowledge, this is the first reported fiber amplifier employing this transition.

Horseshoe templates with global torsion in a driven laser

We perform a topological analysis of chaotic signals from a Nd-doped fiber laser with pump modulation at different values of the modulation frequency. In this experiment, the system displays chaotic behavior in three regions ${\mathrm{C}}_{1\mathrm{/}4}$, ${\mathrm{C}}_{1\mathrm{/}3}$, and ${\mathrm{C}}_{1\mathrm{/}2}$ of parameter space, located around the subharmonics ${\mathrm{\ensuremath{\omega}}}_{\mathrm{r}}$/4, ${\mathrm{\ensuremath{\omega}}}_{\mathrm{r}}$/3, and ${\mathrm{\ensuremath{\omega}}}_{\mathrm{r}}$/2 of the relaxation frequency ${\mathrm{\ensuremath{\omega}}}_{\mathrm{r}}$. We observe that the topological structures of the chaotic regimes inside a given region ${\mathrm{C}}_{1\mathrm{/}\mathrm{n}}$ are described by the same template. However, templates corresponding to different regions display different global torsions ${\mathrm{\ensuremath{\theta}}}_{\mathrm{g}}$, which we find to be related to the order of the subharmonics by ${\mathrm{\ensuremath{\theta}}}_{\mathrm{g}}$(${\mathrm{C}}_{1\mathrm{/}\mathrm{n}}$)=n-1.

Fabrication of LiNbO3 Microfiber Core/Clad Structure by Liquid Phase Epitaxy

Fabrication of a LiNbO3 microfiber core/clad structure consisting of a Nd-doped core fiber grown using the micro-pulling-down method and a Mg-doped cladding layer formed using liquid phase epitaxy is discussed. Etching experiments revealed an inverted ferroelectric domain structure of the cladding layer grown on the core fiber surface oriented toward the +z direction.

Nonlinear-optical modulator for high-power fiber lasers

We propose a novel nonlinear-optical fiber modulator for high-power (>1-W) single-mode fiber lasers. The device is based on transferring the amplitude modulation from a low-power signal at the Stokes frequency onto a high-power beam through stimulated Raman scattering. The efficiency and limitations of the Raman modulator when highly Ge-doped fiber is used is considered. An insertion loss of less than 0.4 dB and an extinction ratio of 20 dB are predicted for modulation of a 10-W single-mode Nd-doped fiber laser.

Optical Fiber Amplifiers and Their Applications. Nd-Doped Fiber Amplifier at 1.06.MU.m.

A key point to develop the Nd-doped fiber amplifier (NDFA) at 1.06pm, the Al co-doping in the Nd-doped fiber, is introduced at first. After reviewing its basic amplification and noise characteristics, various possible application systems are discussed, such as fiber sensing, gravitational wave detection, free-space laser communication and laser radar, for both a booster amplifier and a preamplifier to improve the optical handling power in the transmitter and the sensitivity in the receiver. Finally, results of the fiber transmission and the tunable fiber ring laser source experiments, as examples of the application, are reported.The NDFA will offer a compact, high efficient, polarization independent and beam-distortion-free amplifier in stead of solid-state laser amplifiers at 1.06μm.

Analysis of the efficiency of a third order cascaded Raman laser operating at the wavelength of 1.24 μm

We report a comparative numerical study of the performances of different linear configurations of a third order cascaded Raman laser CW pumped at the wavelength of 1.064 m by a Nd-doped double clad fibre laser. We compare the maximum conversion efficiencies, slope efficiencies and thresholds of various configurations characterized by different parameters of the fibre, different fibre lengths and third Stokes output couplings to give indications towards Raman laser system optimization.

Optimization of Oscillator of Clad-Pumped Fiber Lasers and High Brightness-Compressibility.

An Nd-doped rectangular double-clad fiber (DCF) laser pumped with a 10W fiber coupled LD is demonstrated. Furthermore, the two ends of the fiber are bundled together to achieve efficient matching with the LD. With such a configuration, about 5.4 W of the pump light is launched into the first-cladding and 2.8W laser output is obtained. A slope efficiency of 58% with respect to launched pump power has been achieved. The brightness compressibility of source to laser emission reaches to 700. It is found that the open-cavity is an optimal resonator for clad-pumped fiber lasers.

Propagation of Waves in the Spectrum of a Multimode Laser.

We show that the longitudinally multimode class- $B$ laser can behave as a chain of locally coupled oscillators, each being associated to one mode. Propagation of waves in the laser spectrum is demonstrated theoretically and experimentally in the case of a Nd-doped fiber laser. By extracting the dispersion curves, we show that the group and phase velocities always have opposite signs. This property is a direct consequence of the mode coupling nature (cross saturation), and does not seem to depend on the model details.

Rectangular double-clad fibre laser with two-end-bundledpump

The two ends of an Nd-doped rectangular double-clad fibre are bundled together to achieve efficient matching with a 10 W fibre coupled LD. With such a configuration, ~5.4 W pump light is launched into the first-cladding, and 2.5 W laser output is obtained. A slope efficiency of 51% with respect to launched pump power has been achieved.