The duration of energetic ultrashort pulses is usually limited by the available gain bandwidth of ultrashort amplifiers used to amplify nJ or pJ level seed to hundreds of μμJ or even several mJ. In the case of Ytterbium-doped fiber amplifiers, the available bandwidth is of the order of 40 nm, typically limiting the pulse duration of high-energy fiber chirped-pulse amplifiers to durations above 300 fs. In the case of solid-state amplifier based on Yb:YAG crystals, the host matrix order restricts the amplification bandwidth even more leading to pulses in the low picosecond range. Both architecture would greatly benefit from pulse durations well-below what is allowed by their respective gain bandwidth e.g. sub-100 fs for fiber amplifier and sub-300 fs for solid-state Yb:YAG amplifier. In this contribution, we report on the post-compression of two high energy industrial ultrashort fiber and thin-disk amplifiers using an innovative and efficient hollow core fiber structure, namely the hypocycloid-core Kagome fiber. This fiber exhibits remarkably low propagation losses due to the unique inhibited guidance mechanism that minimize that amount of light propagating in the silica cladding surrounding the hollow core. Spectral broadening is realized in a short piece of Kagome fiber filled with air at 1 atmosphere pressure. For both amplifiers, we were able to demonstrate more than 200 μJ of energy per pulse with duration <100 fs in the case of the fiber amplifier and <300 fs in the case of the thin disk amplifier. Limitations and further energy scaling will also be discussed.
We present a comprehensive experimental study of the technique of Longitudinal Mode Filling (LMF) applied to the
reduction of Stimulated Brillouin Scattering (SBS), in Ytterbium Doped Fibre Amplifiers (YDFA) at the wavelength of
1064 nm. Pulse durations and Mode Field Diameters (MFD) lie in the ranges of 10 - 100 ns and 10 - 35 μm,
respectively. Input pulse-shaping is implemented by means of direct current modulation in multimode Laser-Diode
seeds. This evidences a number of interests in the development of robust and low cost Master Oscillator Power
Amplifiers (MOPA). Highly energetic, but properly shaped, nanosecond pulses may be produced this way without any
need of additional electro-optical means for in-line phase and amplitude modulation. Seeds consist of Distributed Feed-
Back (DFB) and Fibre Bragg Gratings (FBG) with different fibre lengths. We demonstrate the benefit of LMF with
properly controlled mode spacing, in combination with chirp effects due to fast current transients in the semiconductors,
in order to deal with SBS thresholds in the range of a few to some hundred μJ. The variations of the SBS threshold are
discussed versus the number of longitudinal modes, the operating conditions of the selected seed and pulse-shaping
We present an all-fiber high power tunable femtosecond soliton-based source incorporating a picosecond fiber laser and
an 8 m long piece of hollow-core photonic bandgap fiber. Strongly chirped high energy 5.5 ps pulses produced by fiber
amplification are compressed in the hollow core enabling formation of stable 520 fs-solitons with 77% conversion
efficiency. Wavelength tunability was provided by exploiting Raman self-frequency shift of the solitons yielding 33nm
tuning range. The transform limited output pulses were frequency doubled using a conventional nonlinear crystal with
high conversion efficiency of 60%. Demonstration of a femtosecond green laser tunable from 534 nm to 548 nm with
180nJ pulse energy is also reported.
We report the generation of white light comprising red, green, and blue spectral bands from a frequency-doubled
fiber laser in submicron-sized cores of microstructured holey fibers. Picosecond pulses of green light are launched
into a single suspended core of a silica holey fiber where energy is transferred by an efficient four-wave mixing
process into a red and blue sideband whose wavelengths are fixed by birefringent phase matching due to a slight
asymmetry of the structure arising during the fiber fabrication. Numerical models of the fiber structure and
of the nonlinear processes confirm our interpretation. Finally, we discuss power scaling and limitations of this
white light source.
Over recent years, there has been a tremendous and rapid progress in power scaling Yb-doped fiber-based picosecond sources due to their high efficiency, excellent beam quality and immunity to thermo-optical effects. These remarkable properties are not only very attractive for many scientific and industrial applications but also for frequency doubling to generate green. Besides good beam quality, a high degree of polarization and a narrow linewidth, further increase in conversion efficiency requires high peak power and increased crystal length. High peak power can be obtained by employing a fiber master-oscillator power amplifier design (MOPA) where seed pulses with adequate duty cycle are amplified to high average powers. However in this arrangement minimizing nonlinear effects arising in the fiber amplifiers becomes a challenge. The amplification of picosecond pulses causes linewidth broadening and the spectral bandwidth of the crystal is reduced by a preferred longer length. This trade-off can result in lower frequency doubling efficiency. In this paper, as well as the benefits and limitations of fiber lasers applied to nonlinear frequency conversion, we will review the various design considerations for the development of a high average power picosecond green laser based on single-pass frequency doubling of a fiber MOPA system.
Fiber lasers and amplifiers offer unique characteristics that are derived from the use of a waveguide and the properties
of rare-earth doped silica glass. Their capability for high output power, with high efficiency, has been demonstrated
both in CW and pulsed regimes. Cladding-pumped Yb-doped fiber lasers have now reached beyond kW levels with
good beam quality. Advances in both fiber technology and high-power multimode diode pump sources, and the
inherent power scalability of cladding-pumped fibers, lie behind this power surge. However, there are still many
challenges to overcome in the high-power fiber laser area. These include, for example, single-mode output at higher
powers and power scaling of a three-level laser. This paper reviews novel W-type fiber and depressed clad hollow
optical fiber waveguide structures designed with distributed wavelength filter characteristics to achieve an efficient and
high power cladding-pumped three-level lasers such as Nd-doped fiber laser operating at 930 nm and Yb-doped fiber
laser at 980 nm. Moreover, such fiber geometries enable to scale up the output power in a small and single-mode core
for generating a single-mode output beam in a robust and reliable manner.
We propose a depressed clad hollow optical fiber with fundamental (LP01) mode cut-off suitable for high power short-wavelength, especially three-level, fiber laser operation by introducing highly wavelength dependent losses at longer wavelengths. The cut-off characteristic of such fiber structure was investigated. A Yb-doped depressed clad hollow optical fiber laser generating 59.1W of output power at 1046nm with 86% of slope efficiency with respect to the absorbed pump power was realised by placing the LP01 mode cut-off at ~1100nm.
We review recent advances in Yb fiber lasers and amplifiers for high power short pulse systems. We go on to describe associated recent developments in fiber components for use in such systems. Examples include microstructured optical fibers for pulse compression and supercontinuum generation, and advanced fiber grating technology for chirped-pulse amplifier systems.
We discuss the dramatic development of high-power fiber laser technology in recent years and the prospects of kilowattclass
single-frequency fiber sources. We describe experimental results from an ytterbium-doped fiber-based multihundred-watt single-frequency, single-mode, plane-polarized master-oscillator power amplifier (MOPA) operating at 1060 nm and a similar source with 0.5 kW of output power, albeit with a degraded beam quality (M2 = 1.6) and not linearly polarized. Experiments and simulations aimed at predicting the Brillouin limit of single-frequency system with a
thermally broadened Brillouin gain are presented. These suggest that single-frequency MOPAs with over 1 kW of output power are possible. In addition, the power scalability of a simple single-strand fiber laser to 10 kW is discussed.
We report power-scaling of an ytterbium-sensitized thulium-doped silica fiber laser generating up to 75 W of output power in the 2 μm wavelength range when cladding-pumped by a 975 nm diode stack. The slope efficiency is 32% with respect to launched pump power and the beam quality factor (M2) is 1.3. We also investigate the characteristics of this fiber in a tunable laser configuration, operating at ~10 W of output power with the tuning range extended from 2000 to 2080 nm at a launched pump power of 40 W.
We have developed a material system, a fabrication process, and optical designs that allow for direct integration of patternable optical components onto microelectronics and optoelectronics platforms. The spin-on-glass is a sol-gel platform that has a low waveguide loss with the ability to incorporate a waveguide amplifier. Our material and process includes the ability to fabricate 3-D structures in a single photolithography step. In this paper, we present details of our fabrication process, general materials characteristics, and some optical designs for planar lightwave circuit platforms.
Experimental results on the realization and characterization of microspherical lasers at 1.56 micrometers with Er-doped ZBLAN glasses are presented. The lasers are excited through an evanescent wave coupling. Thresholds of 600 (mu) W have been obtained. Multimode operation has been observed with linewidths of the order of 250 KHz.