High Power Fiber Lasers: A Review Zervas, Michalis N.; Codemard, Christophe A.
IEEE journal of selected topics in quantum electronics,
09/2014, Letnik:
20, Številka:
5
Journal Article
Recenzirano
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.
Optical microfibres have recently attracted much attention for nonlinear applications, due to their tight modal confinement. Here, we report broadband third harmonic generation based on the ...intermodal phase matching technique in silica microfibres of several centimetres. The third harmonic signal is predominantly generated from the taper transition regions (rather than the waist), wherein the range of diameters permits phase matching over a wide bandwidth. Microfibres up to 4.5 cm long were fabricated with waist diameters below 2.5 μm to allow a λ = 1.55 μm pump to phase match with several higher order third harmonic modes; conversion rates up to 3 × 10⁻⁴ were recorded when pumped with 4 ns pulses at a peak power of 1.25 kW. Analysis of the third harmonic frequencies generated from the nonlinearly broadened pump components indicate a 5 dB conversion bandwidth of at least 36 nm, with harmonic power detected over a 150 nm range.
We theoretically detail and explain how to control unwanted excess gain for higher order modes in cladding-pumped large-core ytterbium-doped fiber amplifiers operating on the fundamental mode by ...using a small inner cladding and pumping close to the emission wavelength in a so-called tandem-pump configuration. Such excess gain can otherwise limit the core size. We study this experimentally by comparing the level of amplified spontaneous emission at the edge of the core in a conventional diode-pumped and tandem-pumped large-core ytterbium-doped multimode fiber. We also discuss the potential benefits of tandem pumping in reducing fiber photodarkening.
The influence of the core diameter and the fiber length on the beam quality of the transmitted beam was investigated theoretically and experimentally for highly multimode step-index fibers with a ...numerical aperture of 0.22 using a fully monolithic setup. We show that it is possible to maintain a nearly diffraction-limited beam quality (M 2 ≈ 1.3) through 100 m long multimode fibers. For a core diameter of 60 μm and a fiber length of 380 m one can still deliver a beam with an M 2 value of 2.1. The high-power suitability of this approach was shown by transmitting 1 kW of power through a 100 m long fiber with a core diameter of 60 μm without the onset of stimulated Raman scattering while maintaining a nearly diffraction-limited beam quality (M 2 ≈ 1.3).
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•New class of fiber-optic humidity sensors.•Light-sheet precision excitation of optimum group of skew rays for higher sensitivity to humidity.•Fast, temperature insensitive, highly ...robust and inexpensive (commercial optics, multimode fiber and power meter).
The measurement of humidity provides valuable information to a range of industries. Existing hygrometers lack the combination of high sensitivity/low detection-limit, temperature insensitivity, fast response, high robustness and low cost. We present a new design of humidity sensors based on the combination of a polymer-coated multimode fiber interrogated by a light sheet (i.e. thin plane of light) designed to precision excite the optimum group of skew rays for enhanced sensitivity. The sensing mechanism is water absorption of light via evanescent-wave interaction mediated by a polymer-coated multimode fiber. For a 10.0 bilayer poly(diallyldimethylammonium) (PDDA)/poly(styrenesulfonate) (PSS)-coated sensing fiber, we demonstrated a sensitivity of up to 0.14 dB/%RH/cm, a detection limit of 0.007%RH, a temperature cross-sensitivity of less than ˜0.13%/°C, and response/recovery times of 115 ms and 200 ms. The tested dynamic range is between 10%RH and 94%RH. The dependence on the total optical power rather than the phase of light makes such sensors relatively insensitive to temperature while remaining sensitive to humidity. The PDDA/PSS functional coating inherently offers fast response. The use of multimode fibers and power meters make such fiber-optic sensors highly robust and relatively inexpensive, easing the translation to practical applications.
Fresnel reflection equations (4)–(8) are displayed incorrectly in the main text. One of the Goos-Hanchen shift equations (Eq 19) is displayed incorrectly in the main text. On (page 5211, first ...column, second paragraph), the numerical aperture equation is displayed incorrectly. On (page 5216, second column, second paragraph), the conversion of the loss coefficient to loss in decibels is incorrect. In all cases simulations used the correct equations. There are no changes to the key results or conclusions of the paper, only corrections to display errors.
We present a new sensing technique exploiting light-sheet excitation of skew rays in a multimode fiber, which can be applied to enhance the sensitivity of a range of sensing mechanisms such as pump ...absorption. The underlying principle is that a light sheet (i.e., thin plane of light) can selectively concentrate the optimum ray group, giving rise to enhanced interaction between light and matter (e.g., fluorophores). We compared this excitation method with others in terms of attenuation of pump light through Rhodamine B. It was observed that the attenuation experienced by light-sheet skew rays can be up to one order of magnitude higher than that of collimated skew rays, and three orders of magnitude higher than that of normal-incidence rays.
We propose a model and then demonstrate a technique that can be used to optimize pump absorption in active multimode fibers with different cladding geometries, by varying the angle of pump light ...excitation. The analysis of the contribution of different ray groups at different wavelengths enables the design optimization of active and passive fiber components in fiber lasers.
Given the increasing demands for quality assurance in the food industry, a significant challenge emerges in the form of expensive integration of food sensors into packaging. This integration is ...crucial for strengthening food safety measures and ensuring the impeccable quality of food products. Official laboratory food safety testing heavily relies on expensive and bulky equipment. This article presents a new chemical sensing platform and a comparative study of in-house built novel designs for a robust multimode chemical sensor head probed by highly sensitive light-sheet skew rays for addressing cost and footprint issues. The sensing mechanism is the interaction between evanescent field mediated by refined skew rays propagating through a structured coreless multimode fiber and external chemicals, resulting in probe light absorption. The sensitivity is enhanced by the controlled excitation of skew rays using a light sheet and four specially engineered coreless multimode fiber structure, including uniform, tapered, microstub and microbubble designs. The sensitivity was demonstrated to be as high as 0.046 (dB/cm) / dB(1 ng/ml) and the limit of detection as low as 1.028 ng/ml for the microbubble structure. The results of our research pave the groundwork for a new range of chemical sensors suitable for food safety monitoring.
•Demonstrated automated sensing platform based on skew rays excitation of multimode fiber.•New sensing fiber structures based on multimode coreless fiber: taper, microstub and microbubble.•Performance comparison between uniform fiber and the 3 new fiber structures.•Simulation and experiment demonstration of sensing platform using Rhodamine B test chemical.
We investigate the Raman gain spectra produced from pulse-pumping a highly nonlinear fiber with shaped optical pulses delivered from a Yb-doped fiber MOPA pump source. Cascaded Raman wavelength ...shifting up to seven Stokes orders is demonstrated and the counter-propagating gain is measured across all seven Stokes orders. Step-shaped optical pulses with varying instantaneous powers are then used to pump the highly nonlinear fiber, generating a controllable gain spectrum across multiple Stokes orders. Furthermore, we extend this work by using multiple pump wavelengths along with step-shaped pulses to increase the bandwidth of the Raman gain spectrum.
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