Rod-type Fiber Research Articles

Robust single-mode all-solid multi-trench fiber with large effective mode area.

We experimentally demonstrate all-solid 30 and 90 μm core diameter multi-trench fibers. Measurements ensure an effective single-mode operation over a wide range of bend radius in the case of 30 μm core fiber, making it suitable for applications like beam delivery and compact fiber lasers. On the other hand, a 90 μm core fiber ensures an effective single-mode operation and shows good potential for rod-type fiber laser applications. Both fibers were fabricated by the conventional modified chemical vapor deposition process in conjunction with the rod-in-tube technique, hence making them suitable for mass production.

Effect of repetition rate on gain-switched fiber laser output pulses

We investigate the influence of repetition rate on the operation and output of a gain-switched fiber laser. We derive an equation relating pump pulse duration to repetition rate, which provides insight into the parameters of the operating laser such as absorbed pump power and internal losses. The change in laser pulse duration with varying repetition rate is measured and found to be negligible. Finally, the derived theory is compared to experimental results obtained using a ytterbium-doped rod type fiber laser.

High power fiber laser system for a high repetition rate laserwire

We present the development of a high power fiber laser system to investigate its suitability for use in a transverse electron beam profile monitor, i.e., a laserwire. A system capable of producing individual pulses up to $165.8\ifmmode\pm\else\textpm\fi{}0.4\text{ }\text{ }\ensuremath{\mu}\mathrm{J}$ at 1036 nm with a full width at half maximum of $1.92\ifmmode\pm\else\textpm\fi{}0.12\text{ }\mathrm{ps}$ at 6.49 MHz is demonstrated using a master oscillator power amplifier design with a final amplification stage in a rod-type photonic crystal fiber. The pulses are produced in trains of 1 ms in a novel burst mode amplification scheme to match the bunch pattern of the charged particles in an accelerator. This method allows pulse energies up to an order of magnitude greater than the steady-state value of $17.0\ifmmode\pm\else\textpm\fi{}0.6\text{ }\text{ }\ensuremath{\mu}\mathrm{J}$ to be achieved at the beginning of the burst with a demonstrated peak power of $25.8\ifmmode\pm\else\textpm\fi{}1.7\text{ }\mathrm{MW}$ after compression. The system is also shown to demonstrate excellent spatial quality with an ${M}^{2}=1.26\ifmmode\pm\else\textpm\fi{}0.01$ in both dimensions, which would allow nearly diffraction limited focusing to be achieved.

Leakage channel fibers with microstuctured cladding elements: A unique LMA platform

We present a novel design of leakage channel fiber (LCF) that incorporates an air-hole lattice to define the modal filtering characteristics. The approach has the potential to offer single-mode, large mode area (LMA) fibers in a single-material platform with bend loss characteristics comparable to all-solid (LCFs) whilst at the same time providing significant fabrication benefits. We compare the performance of the proposed fiber with that of rod-type photonic crystal fibers (PCFs) and all-solid LCFs offering a similar effective mode area of ~1600μm(2) at 1.05μm. Our calculations show that the proposed fiber concept succeeds in combining the advantages of the use of small air holes and the larger design space of rod-type PCFs with the improved bend tolerance and greater higher order mode discrimination of all-solid LCFs, while alleviating their respective issues of rigidity and restricted material design space. We report the fabrication and experimental characterization of a first exemplar fiber, which we demonstrate offers a single-mode output with a fundamental mode area ~1440µm(2) at 1.06µm, and that can be bent down to a radius of 20cm with a bend loss of <3dB/turn. Finally we show that the proposed design concept can be adopted to achieve larger mode areas (> 3000µm(2)), albeit at the expense of reduced bend tolerance.

Generation of 150 W average and 1 MW peak power picosecond pulses from a rod-type fiber master oscillator power amplifier

We report on the direct amplification of picosecond pulses to megawatt peak power and 150 W average power using a Yb-doped rod-type fiber master oscillator power amplifier. 3 ps pulses at 50 MHz repetition rate are amplified in a 55 cm rod-type fiber amplifier to produce linearly polarized pulses with 3 μJ pulse energy and 1 MW peak power. These results extend megawatt picosecond fiber amplifiers to the 100 W average power regime for the first time. Frequency doubling of the pulses yields 70 W green average power, 1.4 μJ pulse energy, and 500 kW peak power.

Energy scaling of a nonlinear compression setup using passive coherent combining

Passive spatial and temporal coherent combining schemes are implemented to scale the output energy of a nonlinear temporal compression setup. By generating 32 replicas of the incident femtosecond pulses, the output of a high-energy fiber chirped-pulse amplifier can be compressed using self-phase modulation in a large-mode-area rod-type fiber at peak-power levels well beyond the self-focusing power. We demonstrate the generation of 71 fs 7.5 μJ pulses at 100 kHz repetition rate, corresponding to a peak power of 86 MW.

Amplification and compression of temporally shaped picosecond pulses in Yb-doped rod-type fibers

We report on a new technique to produce high power sub-picosecond pulses from a fiber amplifier. We use parabolic pulse shaping of 27 ps transform-limited pulses in order to control nonlinear effects in the fiber amplifier. 63 MW, 780 fs pulses with 25 W average power were obtained, and ways to scale the technique to higher peak powers were identified.

SBS-managed high-peak-power nanosecond-pulse fiber-based master oscillator power amplifier

We report on a compactly packaged Yb-doped fiber-based laser architecture featuring an actively pulse controlled, single-longitudinal-mode seeder and multistage amplifier chain terminated by a "folded" rod-type photonic crystal fiber. In this laser source, stimulated Brillouin scattering (SBS) is the power-limiting factor, but is managed by phase modulating the seeder with a pseudo-random noise signal. Pulse energy/peak power of ~2 mJ/1.5 MW at 10 kHz repetition rate are thus obtained within ~1.55 ns pulses of peak spectral brightness >20 kW cm(-2) sr(-1) Hz(-1).

Picosecond to femtosecond pulses from high power self mode–locked ytterbium rod-type fiber laser

We have designed an ytterbium rod-type fiber laser oscillator with tunable pulse duration. This system that delivers more than 10 W of average power is self mode-locked. It yields femtosecond to picosecond laser pulses at a repetition rate of 74 MHz. The pulse duration is adjusted by changing the spectral width of a band pass filter that is inserted in the laser cavity. Using volume Bragg gratings of 0.9 nm and 0.07 nm spectrum bandwidth, this oscillator delivers nearly Fourier limited 2.8 ps and 18.5 ps pulses, respectively. With a 4 nm interference filter, one obtains picosecond pulses that have been externally dechirped down to 130 fs.

High-gain amplification in Yb:CaF2 crystals pumped by a high-brightness Yb-doped 976 nm fiber laser

We report on high single-pass gain in Yb:CaF2 crystal longitudinally pumped with a 40 W high-brightness fiber laser source based on an ytterbium-doped ultra-large core photonic crystal rod-type fiber operating at 976 nm. A single-pass small-signal gain of 3.2 has been achieved in a 6 % Yb-doped 10-mm-long CaF2 crystal at room temperature, outperforming any CW-diode-pumped scheme and paving the way towards very promising innovative lasers and amplifiers schemes merging the Yb-doped solid-state and fiber technologies.

Amplification of nanosecond pulses to megawatt peak power levels in Tm^3+-doped photonic crystal fiber rod

We report amplification of sub-10-100 ns pulses with repetition rates from 1 to 20 kHz in a rod-type thulium-doped photonic crystal fiber with 80 μm core diameter. The rod is pumped with a 793 nm laser diode and produces the highest peak power at 1 kHz repetition rate with 6.5 ns pulse duration and more than 7 W average output power. This result exemplifies the potential of this fiber design to scale pulse peak powers and pulse energies to the megawatt and multi-millijoule range in the 2 μm wavelength regime.

Mode area scaling with multi-trench rod-type fibers.

We propose a novel all-solid rod-type fiber structure that presents a cylindrical symmetry and low refractive-index contrasts. Effectively single-mode propagation for the fundamental mode is ensured thanks to resonant couplings between Higher Order Modes (HOMs) and cladding modes. Numerical simulations demonstrate the possibility of achieving a fundamental mode effective area as large as 5000 µm² at a wavelength of 1.06 μm in fibers ensuring a high leakage loss ratio (>100) between the HOMs and the fundamental mode while keeping the fundamental mode leakage losses at a level lower than 0.2dB/m. Further scaling to an effective area of 12,200 µm2 at 1.06 μm in an effectively single-mode fiber is also presented by exploiting the power delocalization of several HOMs on top of the high-leakage loss filtering.

High Peak Power, Single-polarized, Sub-nanoseconds Pulses Generation of a Yb-doped Rod-type Photonic Crystal Fiber Amplifier

We report a high-peak-power, single-polarized master oscillator power amplification system employing polarization- maintaining Yb-doped rod-type photonic crystal fiber. The MOPA system comprises of a Q-switched microchip laser generating ~630ps pulses at 8.6 kHz repetition-rate and two amplification stages employing double cladding fiber and rod-type PCF respectively. The MOPA system obtains narrow spectral bandwidth, single-polarized pulses of 9W maximum output average power, corresponding to peak power of 1.7MW.

Low-repetition rate, nanosecond, high-power pulse amplifier system based on Yb-doped rod-type fiber

We report a nanosecond-pulse amplification system based on an Yb-doped, 100-μm core, rod-type photonic crystal fiber. Up to 10W of average power with pulse energy of 1 mJ and peak power of 450 kWis obtained at the repetition rate of 10 kHz. The high-power nanosecond pulse has a good pulse shape and spectral characteristics. The usage of rod-type fibers provides a novel structure for nanosecond pulse amplification.

Thermal Effects on the Single-Mode Regime of Distributed Modal Filtering Rod Fiber

Power scaling of fiber laser systems requires the development of innovative active fibers, capable of providing high pump absorption, ultralarge effective area, high-order mode suppression, and resilience to thermal effects. Thermally induced refractive index change has been recently appointed as one major limitation to the achievable power, causing degradation of the modal properties and preventing to obtain stable diffraction-limited output beam. In this paper, the effects of thermally induced refractive index change on the guiding properties of a double-cladding distributed modal filtering rod-type photonic crystal fiber, which exploits resonant coupling with high-index elements to suppress high-order modes, are thoroughly investigated. A computationally efficient model has been developed to calculate the refractive index change due to the thermo-optical effect, and it has been integrated into a full-vector modal solver based on the finite-element method to obtain the guided modes, considering different heating conditions. Results have shown that the single-mode regime of the distributed modal filtering fiber is less sensitive to thermal effects with respect to index-guiding fibers with the same effective area. In fact, as the pump power is increased, their single-mode regime is preserved, being only blue-shifted in wavelength.

Multi-stage ytterbium fiber-amplifier seeded by a gain-switched laser diode

We demonstrated all-fiber amplification of 11 ps pulses from a gain-switched laser diode at 1064 nm. The diode was driven at a repetition rate of 40 MHz and delivered 13 µW of fiber-coupled average output power. For the low output pulse energy of 325 fJ we have designed a multi-stage core pumped pre-amplifier in order to keep the contribution of undesired amplified spontaneous emission as low as possible. By using a novel time-domain approach for determining the power spectral density ratio (PSD) of signal to noise, we identified the optimal working point for our pre-amplifier. After the pre-amplifier we reduced the 40 MHz repetition rate to 1 MHz using a fiber coupled pulse-picker. The final amplification was done with a cladding pumped Yb-doped large mode area fiber and a subsequent Yb-doped rod-type fiber. With our setup we reached a total gain of 73 dB, resulting in pulse energies of &gt;5.6 µJ and peak powers of &gt;0.5 MW. The average PSD-ratio of signal to noise we determined to be 18/1 at the output of the final amplification stage.

High-power Q-switched rod-type photonic-crystal-fiber laser with linear polarization

We have developed a high-power Q-switched laser based on a ytterbium-doped rod-type photonic crystal fiber (PCF) with a 100-µm core size. Thanks to the big core size and the high pump absorption of the rod-type PCF, energetic high-peak-power laser pulses can be generated from a short-length Q-switched rod-type PCF laser. The maximal pulse energy is 3.3 mJ with a pulse duration of 13 ns, yielding a 0.25-MW peak power, and the maximal average power is more than 250 W at a high repetition rate of 150 kHz. With a polarizer installed inside the laser cavity, a high degree of linear polarization is achieved even at the maximal output energy.

Passive coherent combination of two ultrafast rod type fiber chirped pulse amplifiers

Using passive coherent beam combining of two ultrafast fiber amplifiers, we demonstrate the generation of high temporal quality 300 fs and 650 μJ pulses corresponding to 60 W of average power at a repetition rate of 92 kHz. Furthermore, at 2 MHz of repetition rate record coherent combining average powers of 135 W before and 105 W after compression are measured. A combining efficiency higher than 90% is maintained over the whole range of output powers and repetition rates investigated demonstrating the efficiency and robustness of the passive combining technique. The measured pulse-to-pulse relative power fluctuation at high energy is 2%, indicating that the system is essentially immune to environmental phase noise. We believe the passive combining method to be an attractive approach for compact multi-GW peak power femtosecond fiber-based sources.

Maintaining the Polarization, Temperature and Amplification Characteristics of a Ytterbium-doped Rod-type Photonic Crystal Fiber (PCF) Amplifier

Maintaining the Polarization, Temperature and Amplification Characteristics of a Ytterbium-doped Rod-type Photonic Crystal Fiber (PCF) Amplifier

Airclad fiber laser technology

High-power fiber lasers and amplifiers have gained tremendous momentum in the last 5 years. Many of the traditional manufacturers of gas and solid-state lasers are now pursuing the fiber-based systems, which are displacing the conventional technology in many areas. High-power fiber laser systems require reliable fibers with large cores, stable mode quality, and good power handling capabilities-requirements that are all met by the airclad fiber technology. In the present paper we go through many of the building blocks needed to build high-power systems and we show an example of a complete airclad laser system. We present the latest advancements within airclad fiber technology including a new 100 μm single-mode polarization-maintaining rod-type fiber capable of amplifying to megawatt power levels. Furthermore, we describe the novel airclad-based pump combiners and their use in a completely monolithic 350 W cw fiber laser system with an M2 of less than 1.1.