Rare-earth Doped Optical Fibers Research Articles

Temperature eigenfunction basis for accelerated transverse mode instability simulation.

This work presents a model for the simulation of transverse mode instability (TMI) in rare earth doped optical fiber amplifiers. The model evaluates the internal temperature of a fiber using a superposition of a finite number of thermal eigenmodes. This simplification greatly enhances the speed of calculation with negligible impact on calculation accuracy. This new method is described and quantitatively compared to an older model that uses standard, spatially resolved FDTD to integrate the heat diffusion equation. When tested over a range of spatial and temporal resolutions, this model reduces runtime by a factor of ∼13.9 on average relative to identical simulations using the spatially resolved model.

Modeling and numerical simulation optimization for minimizing the gain spectrum of bismuth-doped broadband fiber amplifiers at 1200-1800 nm

Research on optical fiber amplifiers has gotten much more in-depth in recent years as a direct result of the emergence of the information age. The most effective of these materials are optical fibers that have been doped with rare earth elements. Lasers that have gain media composed of rare-earth doped optical fibers find widespread use in fields such as optical communication, medicine, and the processing of materials. For different rare earth ions, especially for bismuth-doped fiber amplifiers, bismuth-doped fiber has a good prospect in fiber amplifiers and lasers due to its unique luminescence characteristics and ultra-wideband near-infrared luminescence of bismuth. Therefore, for bismuth-doped fiber amplifiers, in this paper, the pump wavelength is designed for the signal wavelength range, energy level structure, and electron transition process. The corresponding rate equation and power equation are established. At the same time, the gain spectrum changes with the fiber length and doping concentration are calculated using Matlab programming, and the maximum and minimum gain differences are minimized using Matlab calculations.

Reducing the refractive index by replacing an [AlPO4]° unit with [BPO4]° in fused silica

The radiation resistance of rare-earth doped optical fibers is critical to applications in space-based environments such as laser radars, optical communications, and laser altimeters. Usually, doping various elements, such as aluminum (Al), phosphorus (P), and boron (B), is necessary to fine-tune the structural, electronic, and optical properties, but often results in degraded radiation resistance. Thus, achieving both excellent optical and radiation properties remain a challenge. Here, we theoretically investigate and compare the electronic, structural, and optical properties of [BPO4]° and [AlPO4]° units in silica glass. We prove that both [BPO4]° and [AlPO4]° units are stable in the SiO2 matrix. As the radiation resistance of [SiO4/2]° is excellent, inferring from the material's structure, the SiO2-BPO4 and SiO2-AlPO4 should have good radiation resistance. From the calculation, the SiO2-BPO4 is structurally and electronically similar to the SiO2-AlPO4. Importantly, the refractive index of SiO2-BPO4 is lower than SiO2-AlPO4, achieving refractive index tuning while maintaining its radiation resistance. Our results provide some guidance for the design of BPO4-based radiation-resistant active fibers.

Ultrashort pulse train in rare earth doped bimodal optical fiber

Here, we present and analyze the nature of a wide class of exact nonlinear wave solutions for a bimodal optical fiber doped with a three level lambda ( Λ ) type system and delineate the parameter regimes for their occurrence. Solutions that are non-resonant with the transition frequencies of the doped system are found to undergo stable propagation under numerical evolution for the small strength of atomic coherence. Higher values of coherence lead to two different behaviors of these solutions: a bound state of pulse trains for sn and cn type cnoidal waves, and amplification of pulse trains for dn type nonlinear excitations. The corresponding power spectra results in an enhanced frequency comb structure in the dominance of atomic coherence.

Mid-IR Rare Earth Doped Tellurite Glass and Optical Fiber

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Role of rare earth on the spectral properties of chalcogenide glassy alloys: A review

In this paper, recent results regarding rare earth element doped with chalcogenide glasses for optical gain media such as amplifiers and lasers are reviewed. Rare earth Chalcogenide glasses are formed when chalcogen elements (S, Se, Te etc.) are mixed with new additive elements (Ge, Ga, Sb, As etc.) and also with rare earth elements (Er, Dy, Pd, Pr etc.) from periodic table and prepared by melt quench technique (MQT). Rare earth element doped with chalcogenide glasses has been emerged as a suitable candidate for applications in the numeral passive and active. Among various materials, chalcogenide glasses show significant improvement in their emission properties in the optical communication range and spectroscopic properties. Finally, rare earth doped chalcogenide and optical fibers show potential for high power mid-infrared gain medium and their spectroscopic properties as well.

Research on key technologies for 2μm band of thulium-doped fiber laser

The gain material of 2μm wavelength thulium-doped fiber laser is a thulium-doped fiber doped with rare earth element thulium. Rare earth doped optical fiber as gain medium is the basic structure of optical fiber laser. This type of laser is mainly composed of pump source, coupler, gain optical fiber doped with rare earth elements, cavity and other optical devices. The pump source is generally a combination of one or several high-power laser diodes. The light emitted by the pump source enters the gain optical fiber doped with rare earth elements through a certain pumping mode. The inversion of the number of particles occurs when the doped optical fibers absorb photons, and then the light waves stimulated from the doped optical fibers are emitted by the laser after the oscillation. Since the connection structure and parameters between optical fibers and optical components can be maintained stable over a long period of time, thulium-doped lasers do not need to be maintained regularly and are based on output power. They have smaller volume and weight, lighter weight and longer life than solid-state lasers. However, in general, the power of a 2μm wavelength thumbium-doped fiber laser is not too high, while a high-power 2μm wavelength thumbium-doped fiber laser can meet people’s needs and play a greater role. Therefore, improving the power of 2μm wavelength thumbium-doped fiber laser is an important direction for the development of thumbium-doped fiber laser. The energy level structure of thulium ion is analyzed, the doping concentration of thulium ion is studied, and the method to increase the power of a 2μm wavelength thulium-doped fiber laser is given.

Research on dispersion control technology of thulium-doped fiber laser

Rare earth doped optical fibers have important applications in fiber lasers, amplifiers and sensors. The Tm-doped fiber laser made with Tm-doped fiber as gain medium can be used in optical communication system. Because the fiber itself has a cylindrical waveguide structure and the core diameter of the fiber is very small, it is easy to achieve high energy density pumping in the fiber. Fiber laser has low laser threshold and good heat dissipation performance, and its core diameter matches well with the communication fiber, forming the integration of transmission fiber and active fiber, which can be an important basis for all-optical communication. However, due to the dispersion of Tm-doped fiber laser, it will lead to the broadening of laser pulse and the degradation of laser quality, which seriously affects the quality of laser communication. In this paper, the causes of dispersion are analyzed, and a dispersion adaptive control system is designed. The experimental results show that the proposed dispersion compensation system can compensate the dispersion produced in the optical fiber laser to a certain extent, so that the laser pulse can return to normal state.This is of great significance for optical communication systems.

Rare Earth Doped Optical Fibers with Multi-section Core.

SummaryThe gain bandwidth of a single-mode fiber is limited by the atomic transitions of one rare earth gain element. Here we overcome this long-standing challenge by designing a new single-mode fiber with multi-section core, where each section is doped with different gain element. We theoretically propose and experimentally demonstrate that this configuration provides a gain bandwidth well beyond the capability of conventional design, whereas the inclusion of multiple sections does not compromise single-mode operation or the quality of the transverse modal profile. This new fiber will be beneficial in realizing all fiber laser systems with few-cycle pulse duration or octave tunability.

Gradual-Time Solution Doping for the Fabrication of Longitudinally Varying Optical Fibres

Standard MCVD process and solution doping are commonly used for processing rare-earth doped optical fibers. Since the 1970s, this technique is mainly employed to fabricate homogeneous preforms in the longitudinal direction. A variant is proposed here, by using two doping solutions and by applying a gradual time doping. To demonstrate the validity of this approach, three preforms were prepared with longitudinal gradient of La, Ce, and Al. Preforms were characterized by refractive index profile measurements and concentrations in optical fibers were characterized by EPMA . These results will allow to perform rapid material development in optical-fiber domain. This process is also expected to offer a new way to prepare optical fibers with varying longitudinal characteristics.

X-rays, γ-rays, electrons and protons radiation-induced changes on the lifetimes of Er3+ and Yb3+ ions in silica-based optical fibers

The evolution of Ytterbium 2F5/2 and Erbium 4I13/2 energy level lifetimes versus doses of various radiation types (40keV X-rays, 480MeV protons, 1.2MeV γ-rays and 6MeV electrons) were investigated on samples of silica-based Rare-Earth Doped optical Fibers (REDFs). For each studied sample (Er-doped and Er/Yb-doped), a strong dependence of the lifetime value on the irradiation dose (for equivalent doses ranging from 10Gy(SiO2) to 10MGy(SiO2)) is observed regardless of the radiation nature. For both fiber types and luminescent ions, complex dose dependences are observed: a limited decrease of the lifetime at the lower doses, whereas a large reduction is reported at doses exceeding 100kGy(SiO2). The results highlighted the vulnerability of REDF based systems, such as optical amplifiers and sources, for space and nuclear applications. In such harsh environments, Radiation Induced Attenuation (RIA) is also a key issue. The positive effect of Ce co-doping on both the RIA and the lifetimes is reported even at the highest dose of 10MGy(SiO2). The basic mechanisms involved during the interaction between radiation and fiber material were also investigated through low temperature spectroscopic measurements that revealed the fundamental role of radiation-induced point defects.

Optical Studies of Erbium and Ytterbium Doped Gd2Zr2O7Phosphor for Display and Optical Communication Applications

The paper reports synthesis, characterization, and luminescence studies of different erbium-ion-doped Gd2 Zr2O7 phosphor with fixed and variable concentration of ytterbium. Herein, pure Gd2Zr 2O7 and Er, Yb doped Gd2Zr2O7 phosphors were synthesized by solid-state reaction method which is suitable for large-scale production and maintained morphology of the phosphor. Phosphor were synthesized for Er (1–2 mol%) with Yb (1 mol%) was fixed. The pure synthesized phosphor shows downconversion (UV to visible converter) having gadolinium dominating peaks covers all visible region and useful for display devices application including solid-state lightening. For Yb used as a sensitized and Er used as an activator having impurity in Gd2Zr2O7 host matrix shows upconversion (IR to Visible) phenomenon and erbium ions are responsible for prominent peaks and transition in Gd2Zr2 O7 host matrix. The upconversion behavior of prepared phosphor is useful for optical communication and it is application for low-power consumption in display applications. Prepared phosphors were characterized by XRD for pure Gd2Zr2O7 host matrix. It is applicable for optical amplifiers through development of improved rare-earth doped optical fibers. We demonstrated the efficiency of codoping with core of Erbium/Ytterbium doped optical fibers to improve their radiation tolerance.

Contributed Review: A review of the investigation of rare-earth dopant profiles in optical fibers.

Rare-earth doped optical fibers have captivated the interest of many researchers around the world across the past three decades. The growth of this research field has been stimulated primarily through their application in optical communications as fiber lasers and amplifiers, although rare-earth doped optical fiber based devices are now finding important uses in many other scientific and industrial areas (for example, medicine, sensing, the military, and material processing). Such wide commercial interest has provided a strong incentive for innovative fiber designs, alternative glass compositions, and novel fabrication processes. A prerequisite for the ongoing progress of this research field is developing the capacity to provide high resolution information about the rare-earth dopant distribution profiles within the optical fibers. This paper constitutes a comprehensive review of the imaging techniques that have been utilized in the analysis of the distribution of the rare-earth ion erbium within the core of optical fibers.

Vapor phase doping process for fabrication of rare earth doped optical fibers: Current status and future opportunities

Emerging application of rare‐earth (RE) doped optical fibers in high power lasers requires preforms with stringent geometrical and optical properties. This in turn demands more versatile and reliable process technology which brought Vapor Phase Doping (VPD) into prominence. This technology has immense potential to overcome fiber fabrication related challenges viz, dopant‐rich phase separation, RE uniformity in radial as well as longitudinal direction, “star‐like” defect elimination from core‐clad boundary and refractive index (RI) adjustment which results in improved beam quality and power stability of fiber laser. Further, high power lasers demand LMA active fibers with large core diameter and low numerical aperture (NA) which is easily producible by VPD method as it permits deposition of multiple RE doped core layers in a reproducible “in situ” manner. So, the prime focus is to optimize process technology to produce low RI, large core fibers. This article gives an overview of the comprehensive effort made by the global researchers to overcome challenges of VPD method and to demonstrate a standardized process technology for RE doping in silica glass preform.

Unified model for analysis of light amplification in rare-earth doped fibers

This paper discusses a unified method for modeling and simulating signal light amplification in rare-earth doped optical fiber amplifiers. The model accounts for gain saturation, spontaneous emission, dispersion, and nonlinear effects along the length of the distributed gain medium. Simulations based on the unified model are shown to compare favorably with experimental results. The new model can be used to provide guidance in the design and construction of a variety of fiber-based optical amplifiers. Furthermore, it is suitable for analyzing the performance of high-power amplifiers in a wide range of operating conditions.

Vapor Phase Doping of Rare-Earth in Optical Fibers for High Power Laser

This letter describes an optimized vapor phase doping technique using modified chemical vapor deposition system to fabricate rare-earth doped optical fibers for a high power laser. The process comprises deposition of aluminium oxide and ytterbium oxide in vapor phase simultaneously in combination with silica during formation of the core layer. The process parameters have been judiciously controlled to deliver aluminium chloride and rare-earth-chelate compounds to the reaction zone without decomposition and/or condensation of the precursor materials prior to the reaction zone. The standardization of the process parameters resulted in a good repeatability with a very low variation of dopant concentrations throughout the length of the preform. The fabricated fibers exhibit good optical properties with lasing efficiency of 76% at 1.06 μm.

Measurement of Pump-Induced Temperature Increase in Doped Fibers Using Whispering-Gallery Modes

Accurate measurement of the pump-induced temperature increase in rare earth doped optical fibers has been carried out based on the excitation of whispering-gallery modes resonances of the doped fiber itself. Variations of fiber temperature are found from the wavelength shift of the resonances. The narrow bandwidth of the resonances (few hundredths of a picometer) provides a temperature resolution better than 10-2°C at room temperature. The technique is all-optical and it does not require processing of the doped fiber.

Progress in the fabrication of rare earth doped optical fiber by standard and Sol-Gel derived granulated oxides

We produced active optical fibers by the doped granulate silica-method. The granulates were derived from the sol-gel technology. We determined volume percentage and distribution of chemical elements in the fabricated glasses fiber by the analytical technique of Energy-Dispersive X-ray (EDX), Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA) and the degree of crystallization by X-Ray Diffraction analysis (XRD). Furthermore we measured fluctuations of the Refractive Index Profile (RIP) and scattering losses of the fiber core. It was observed from the RIP measurement that the average index difference with respect to the undoped silica was 5.3*10-3, and thus the optical fiber has a numerical aperture of 0.12. XRD measurements and investigations with SEM showed that the manufactured optical fiber has an amorphous structure. The dopant and co-dopant elements in the core region were uniformly distributed. Although we found strong isolated scattering centers in the fabricated fiber, the loss of the fibers was determined to be 0.35- 3dB/m for selected fiber pieces. Here we present our progress of improving the optical quality of fibers produced from granulates.

Analysis of absorption property for pumping laser with double cladding rare earth doped fiber

In this paper, a pump laser absorption model for double cladding rare earth doped optical fiber is established by using the finite difference beam propagation method combined with complex refractive index profile, and the absorption properties are analyzed in detail for some typical inner cladding structures by using this model. The results can be used to design the double cladding rare earth doped optical fiber.

Radiation Induced Absorption in Rare Earth Doped Optical Fibers

We have investigated the radiation induced absorption (RIA) of optical fibers with high active ion concentration. Comparing our results to the literature leads us to the conclusion that RIA appears to be only weakly dependent on the rare earth dopant concentration. Instead, co-dopants like Al, Ge, or P and manufacturing processes seem to play the major role for the radiation sensitivity. It is also observed that different types of irradiation cause very similar RIA at the same dose applied, with the exception at very high dose rates. It has been studied how RIA can be efficiently reduced via moderate heating. Recovery of up to 70% of the original transmission has been reached after annealing at 450 K. We conclude that radiation induced color centers have weak binding energies between 20 and 40 meV. This suggests that annealing could become a key strategy for an improved survival of rare earth doped fibers in radiative environments, opening up new possibilities for long-term missions in space.