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]

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

Acceleration of relativistic electrons in a dielectric laser accelerator at high electric field gradients is reported, setting the stage for the development of future multi-staged accelerators of this type. Conventional particle accelerators, based on radio-frequency technology, are large-scale installations that are expensive to run. Micro-fabricated dielectric laser accelerators (DLAs) offer an attractive alternative, as they are able to support much larger accelerating fields than current accelerators, while being compact, economical and simple to manufacture using lithographic techniques. This paper presents the first experimental demonstration of a DLA capable of sustained, high-gradient (beyond 250 MeV m−1) acceleration of relativistic electrons. The results set the stage for the development of future multi-staged DLA devices composed of integrated on-chip systems, which would enable compact table-top MeV–GeV-scale accelerators. Applications include security scanners and medical therapy, X-ray light sources for biological and materials research, and portable medical imaging devices. The enormous size and cost of current state-of-the-art accelerators based on conventional radio-frequency technology has spawned great interest in the development of new acceleration concepts that are more compact and economical. Micro-fabricated dielectric laser accelerators (DLAs) are an attractive approach, because such dielectric microstructures can support accelerating fields one to two orders of magnitude higher than can radio-frequency cavity-based accelerators. DLAs use commercial lasers as a power source, which are smaller and less expensive than the radio-frequency klystrons that power today’s accelerators. In addition, DLAs are fabricated via low-cost, lithographic techniques that can be used for mass production. However, despite several DLA structures having been proposed recently1,2,3,4, no successful demonstration of acceleration in these structures has so far been shown. Here we report high-gradient (beyond 250 MeV m−1) acceleration of electrons in a DLA. Relativistic (60-MeV) electrons are energy-modulated over 563 ± 104 optical periods of a fused silica grating structure, powered by a 800-nm-wavelength mode-locked Ti:sapphire laser. The observed results are in agreement with analytical models and electrodynamic simulations. By comparison, conventional modern linear accelerators operate at gradients of 10–30 MeV m−1, and the first linear radio-frequency cavity accelerator was ten radio-frequency periods (one metre) long with a gradient of approximately 1.6 MeV m−1 (ref. 5). Our results set the stage for the development of future multi-staged DLA devices composed of integrated on-chip systems. This would enable compact table-top accelerators on the MeV–GeV (106–109 eV) scale for security scanners and medical therapy, university-scale X-ray light sources for biological and materials research, and portable medical imaging devices, and would substantially reduce the size and cost of a future collider on the multi-TeV (1012 eV) scale.

https://web.stanford.edu/~rlbyer/PDF_AllPubs/2013/Nature%20Final%20Version.pdf

Demonstration of electron acceleration in a laser-driven dielectric microstructure

Fiber lasers have seen progressive developments in terms of spectral coverage and linewidth, output power, pulse energy, and ultrashort pulse width since the first demonstration of a glass fiber laser in 1964. Their applications have extended into a variety of fields accordingly. In this paper, the milestones of glass fiber laser development are briefly reviewed and recent advances of high-power continuous wave, Q-switched, mode-locked, and single-frequency fiber lasers in the 1, 1.5, 2, and 3 μm regions and their applications in such areas as industry, medicine, research, defense, and security are addressed in detail.

Fiber lasers and their applications [Invited]

We describe fundamental measurements of the properties of thulium (Tm)-doped silica and power scaling studies of fiber lasers based on the material. Data on the high-lying Tm:silica energy levels, the first taken to our knowledge, indicate that pumping at 790 nm is unlikely to lead to fiber darkening via multiphoton excitation. Measurement of the cross-relaxation dynamics produces an estimate that, at the doping levels used, as much as 80% of the decay of the Tm level pumped is due to cross relaxation. Using a fiber having a 25-mum-diameter, 0.08 numerical aperture (NA) core, we observed fiber laser efficiencies as high as 64.5% and output powers of 300 W (around 2040 nm) for 500 W of launched pump power, with a nearly diffraction-limited beam. At these efficiencies, the cross-relaxation process was producing 1.8 laser photons per pump photon. We generated 885 W from a multimode laser using a 35-mum, 0.2-NA core fiber and set a new record for Tm-doped fiber laser continuous-wave power.

Tm-Doped Fiber Lasers: Fundamentals and Power Scaling

Disclosed is an optical fiber article for receiving pump radiation of a first wavelength for amplifying or generating radiation of a second wavelength. The optical fiber article includes a core for propagating light of the second wavelength. The core has a first index of refraction and includes a rare earth material. A cladding surrounds the core and has a second index of refraction that is less than the first index of refraction. The outer circumference of the cladding can include a plurality of sections, where the plurality of sections includes at least one substantially straight section and one inwardly curved section. The optical fiber article can also include at least one outer layer surrounding the cladding, where the index of refraction of the outer layer is less than the second refractive index. Methods for producing the optical fiber article are also disclosed, as well as methods for providing a preform for drawing such an optical fiber article.

Cladding-pumped optical fiber and methods for fabricating

Single- and dual-wavelength tunable lasing (around 1552 nm) has been obtained in an Er-doped low-Bi fiber laser with a Bragg grating mirror in a Hi-Bi fiber. Equal output powers for both laser lines and spectral spacing of up to 0.26 mm, larger than the original spacing between the resonance peaks of the grating (0.2 nm), can be easily achieved by employing a polarization controller inside of the laser cavity.

Fiber laser polarization tuning using a Bragg grating in a Hi-Bi fiber

A double-clad optical fiber includes a core, a multimode inner cladding layer disposed about the core, and a second cladding layer disposed about the inner cladding layer. The core includes an active material for absorbing pump radiation received by the inner cladding. The multimode inner cladding includes truncated regions including a first material, where the first material has an index of refraction that is different than the material of the inner cladding that surrounds said truncated regions, for promoting the scattering of pump radiation propagating in the multimode inner cladding for increasing the absorption of the pump radiation by the active material of the core. Particles can be distributed in soot deposited via Outside Vapor Deposition for forming the truncated regions in an optical fiber drawn from the preform.

Double-clad optical fiber for lasers and amplifiers

Optical apparatus including a cladding-pumped optical fiber that includes a core that includes an active material, a multimode inner cladding disposed about the core, and a second cladding disposed about the multimode inner cladding. The cladding-pumped optical fiber can include, disposed about the inner cladding layer, an asymmetrical layer, a layer that includes granular matter, a compressive layer, or a hard layer. External provision can be included for applying stress to the cladding-pumped optical fiber.

Cladding-pumped optical fiber

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