The rise in output power from rare-earth-doped fiber sources over the past decade, via the use of cladding-pumped fiber architectures, has been dramatic, leading to a range of fiber-based devices with outstanding performance in terms of output power, beam quality, overall efficiency, and flexibility with regard to operating wavelength and radiation format. This success in the high-power arena is largely due to the fiber’s geometry, which provides considerable resilience to the effects of heat generation in the core, and facilitates efficient conversion from relatively low-brightness diode pump radiation to high-brightness laser output. In this paper we review the current state of the art in terms of continuous-wave and pulsed performance of ytterbium-doped fiber lasers, the current fiber gain medium of choice, and by far the most developed in terms of high-power performance. We then review the current status and challenges of extending the technology to other rare-earth dopants and associated wavelengths of operation. Throughout we identify the key factors currently limiting fiber laser performance in different operating regimes—in particular thermal management, optical nonlinearity, and damage. Finally, we speculate as to the likely developments in pump laser technology, fiber design and fabrication, architectural approaches, and functionality that lie ahead in the coming decade and the implications they have on fiber laser performance and industrial/scientific adoption.

High power fiber lasers: current status and future perspectives [Invited]

The history, fabrication, theory, numerical modeling, optical properties, guidance mechanisms, and applications of photonic-crystal fibers are reviewed

Photonic-Crystal Fibers

Fibre lasers in the mid-infrared regime are useful for a diverse range of fields, including chemical and biomedical sensing, military applications and materials processing. This Review summarizes the different rare-earth cations and host materials used in mid-infrared fibre laser technology, and discusses the future applications and challenges for the field.

Towards high-power mid-infrared emission from a fibre laser

In this paper, we summarize the fundamental properties and review the latest developments in high power fiber lasers. The review is focused primarily on the most common fiber laser configurations and the associated cladding pumping issues. Special attention is placed on pump combination techniques and the parameters that affect the brightness enhancement observed in single-mode and multimode high power fiber lasers. The review includes the major limitations imposed by fiber nonlinearities and other parasitic effects, such as optical damage, transverse modal instabilities and photodarkening. Finally, the paper summarizes the power evolution in continuous-wave and pulsed ytterbium-doped fiber lasers and their impact on industrial applications.

High Power Fiber Lasers: A Review

High-power fibre lasers are in demand for industrial, defence and scientific applications. This review provides an overview of the present state of the art in the field and discusses present challenges and the future outlook.

High-power fibre lasers

Rare-earth doped, laser-diode-pumped, single-mode, double-clad fiber lasers are studied in detail, experimentally and theoretically, with particular attention to properties of scaling to higher output powers. Gain saturation, spontaneous emission, fiber propagation loss, and the optimum output coupler are considered for oscillator design and laser performance. Thermal properties are investigated, including the thermal fracture limit, the decrease of quantum efficiency with increasing pump power through the temperature dependence of multiphonon decay and ion-ion energy transfer, and thermal lensing. Self-focusing and Raman effects are briefly considered. It is shown that output powers in the tens of watts range are readily feasible with available double-clad fiber lasers. >

High-power double-clad fiber lasers

We propose a novel approach of making large effective area laser fiber with higher threshold for the stimulated Brillouin scattering (SBS) using Al/Ge co-doping in the fiber core. The increased SBS threshold is achieved by reducing the acoustic-optic overlap integral while keeping the optical refractive index profile with a step structure. The manipulation of the overlap integral is done by adjusting the relative doping level between Al2O3 and GeO2 in the core. The mechanism is validated by detailed examples of numerical modeling. An Yb-doped double clad fiber with the core co-doped with Al2O3 and GeO2 was fabricated by the OVD process. Measured acoustic velocity profile using a scanning acoustic microscope verified that the acoustic velocity in the fiber core changes with the design. An amplifier utilizing the fiber demonstrated that the proposed fiber yielded 6 dB higher SBS threshold than a fiber without using the co-doping scheme.

Al/Ge co-doped large mode area fiber with high SBS threshold.

According to one example of the invention an optical fiber comprises: (i) silica based, rare earth doped core having a first index of refraction n1; (ii) at least one silica based cladding surrounding the core and having a second index of refraction n2, such that n1> n2 with the following features, alone or in combination: said cladding includes 0.5 to 5 wt% F and 0.5 to 20 wt% B, said optical fiber has less than 8dB/km core background loss at a wavelength of 1280 nm. at least one of the core or cladding is doped with AI203 concentration is less than 2:1.

Optical fiber and method for making such fiber

A modified Sagnac interferometer-based fiber temperature sensor is proposed. Polarization independent operation and high temperature sensitivity of this class of sensors make them cost effective instruments for temperature measurements. A comparison of the proposed sensor with Bragg grating and long-period grating fiber sensors is derived. A temperature-induced spectral displacement of 0.99 nm/K is demonstrated for an internal stress birefringent fiber-based Sagnac interferometer.

Fiber Sagnac interferometer temperature sensor

High power operation of narrow linewidth optical fiber amplifiers is usually limited by the onset of stimulated Brillouin scattering. In this paper, we present results demonstrating over 500 Watts of power in a single mode beam from a fiber designed to suppress stimulated Brillouin scattering through a reduction in the overlap of the optical and acoustic fields. Simulations demonstrate the potential for this fiber to achieve greater than 1000 Watts of output power.

Luis A. Zenteno

Papers

High-power double-clad fiber lasers

Al/Ge co-doped large mode area fiber with high SBS threshold.

Optical fiber and method for making such fiber

Fiber Sagnac interferometer temperature sensor

502 Watt, single transverse mode, narrow linewidth, bidirectionally pumped Yb-doped fiber amplifier