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]

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

The authors report a new approach to obtain single-transverse-mode operation of a multimode fiber amplifier, in which the gain fiber is coiled to induce significant bend loss for all but the lowest-order mode. They have demonstrated this method by constructing a coiled amplifier using Yb-doped, double-clad fiber with a core diameter of 25 {micro}m and NA of {minus}0.1 (V {approx} 7.4). When operated as an ASE source, the output beam had an M{sup 2} value of 1.09 {+-} 0.09; when seeded at 1,064 nm, the slope efficiency was similar to that of an uncoiled amplifier. This technique does not require exotic fiber designs or increase system complexity and is inexpensive to implement. It will allow scaling of pulsed fiber lasers and amplifiers to significantly higher pulse energies and peak powers and cw fiber sources to higher average powers while maintaining excellent beam quality.

/pdf/single-mode-operation-of-a-coiled-multimode-fiber-amplifier-3gz9g90s11.pdf

Single-mode operation of a coiled multimode fiber amplifier

https://publikationen.bibliothek.kit.edu/1000010981/754615

Periodic nanostructures for photonics

The investigation of nonlinear wave phenomena has been one of the main direc tions of research in optics for the last few decades. Soliton concepts applied to the description of intense electromagnetic beams and ultrashort pulse propagation in various media have contributed much to this field. The notion of solitons has proved to be very useful in describing wave processes in hydrodynamics, plasma physics and condensed matter physics. Moreover, it is also of great importance in optics for ultrafast information transmission and storage, radiation propagation in resonant media, etc. In 1973, Hasegawa and Tappert made a significant contribution to optical soliton physics when they predicted the existence of an envelope soliton in the regime of short pulses in optical fibres. In 1980, Mollenauer et al. conducted ex periments to elucidate this phenomenon. Since then the theory of optical solitons as well as their experimental investigation has progressed rapidly. The effects of inhomogeneities of the medium and energy pumping on optical solitons, the interaction between optical solitons and their generation in fibres, etc. have all been investigated and reported. Logical devices using optical solitons have been developed; new types of optical solitons in media with Kerr-type nonlinearity and in resonant media have been described.

Optical Solitons

We report the amplification of 10-100-pJ semiconductor diode pulses to an energy of 158 microJ and peak powers >100 kW in a multistage fiber amplifier chain based on a single-mode, large-mode-area erbium-doped amplifier design. To our knowledge these results represent the highest single-mode pulse energy extracted from any doped-fiber system.

/pdf/158-microj-pulses-from-a-single-transverse-mode-large-mode-42al7um18w.pdf

158-microJ pulses from a single-transverse-mode, large-mode-area erbium-doped fiber amplifier.

We report, for the first time to our knowledge, the experimental observation of quasi-cw nonlinear switching and multiple gap-soliton formation within the bandgap of a fiber Bragg grating. As many as five gap solitons with 100-500-ps durations were generated from a 2-ns pulse at a launched peak intensity of approximately 27 GW/cm(2). A corresponding increase in the grating transmission from 3% to 40% of the incident pulse energy was observed.

/pdf/nonlinear-self-switching-and-multiple-gap-soliton-formation-4gbt9oh590.pdf

Nonlinear self-switching and multiple gap-soliton formation in a fiber Bragg grating.

We experimentally demonstrate an all-optical 'AND' gate based on coupled gap soliton formation in an unchirped fibre Bragg grating. A switching contrast of better than 17dB was otained with an incident pulse peak power of 2.5kW.

/pdf/all-optical-and-gate-based-on-coupled-gap-soliton-formation-49axwujnm5.pdf

All-optical AND gate based on coupled gap-soliton formation in a fiber Bragg grating.

We report the first experimental demonstration of the optical pushbroom - a novel type of all-optical pulse compression. In the optical pushbroom high intensity pump pulses, tuned well away from the resonance of a Bragg grating, modify the transmission of a weak probe tuned near to the grating's photonic bandgap. The clarity of the experimental results and their close agreement with numerical simulations highlight the tremendous potential of the fiber environment for the detailed study and practical application of nonlinear Bragg grating effects.

/pdf/optical-pulse-compression-in-fiber-bragg-gratings-1ns3ju5in4.pdf

Optical pulse compression in fiber Bragg gratings

Recently, femtosecond erbium fibre lasers have been used with periodically poled lithium niobate(PPLN) to demonstrate frequency doubling with up to 25% conversion efficiency, and using the second harmonic, to pump an Optical Parametric Generator (OPG). However, for many applications e.g. pumping of nanosecond Optical Parametric Oscillators (OPOs) pulses with greater energies are required, for which diode-pumped, large mode-area erbium doped fibre amplifiers (LA-EDFA) and lasers are ideally suited. The combination of diode-pumped, LA-EDFA sources with periodically poled lithium niobate creates an extremely attractive technology for the development of a wide range of practical wavelength tuneable sources. In this work both diode-seeded LA-EDFA chains and Q-switched sources were used to demonstrate extremely high second and third harmonic single pass conversion efficiencies in PPLN. Continuously tunable operation over the erbium gain bandwidth was demonstrated with pulses from 2 to 50ns, repetition rates from 1kHz to 150kHz, and pulse energies of up to 50µJ. Output pulses at a fundamental wavelength of 1536nm were frequency doubled in PPLN, to produce 768nm light with internal conversion efficiencies as high as 83% in a single pass for a peak power of 1.2kW. A second PPLN crystal was used to mix the second harmonic with the remaining fundamental to generate green light at 512nm, with up to 34% internal conversion efficiency. Both PPLN samples were 16mm long and fabricated in 0.5mm thick z-cut lithium niobate by electrical poling. The periods were 18.05µm for SHG and 6.5µm for sum frequency generation.

/pdf/highly-efficient-second-harmonic-and-sum-frequency-1ari73wrk8.pdf

Highly efficient second-harmonic and sum-frequency generation of nanosecond pulses in a cascaded erbium-doped fiber:periodically poled lithium niobate source.

D. Taverner

Papers

158-microJ pulses from a single-transverse-mode, large-mode-area erbium-doped fiber amplifier.

Nonlinear self-switching and multiple gap-soliton formation in a fiber Bragg grating.

All-optical AND gate based on coupled gap-soliton formation in a fiber Bragg grating.

Optical pulse compression in fiber Bragg gratings

Highly efficient second-harmonic and sum-frequency generation of nanosecond pulses in a cascaded erbium-doped fiber:periodically poled lithium niobate source.