We report on the design of a quasi-monolithic fiber chirped pulse amplification (FCPA) system operating at 1040 nm. Chirped-pulse amplification has been achieved using an all-solid step-index PM VLMA Yb-doped fiber, designed and drawn at Photonics Bretagne. The amplifier is integrated to the system through an internally developed mode field adapter (MFA), and bended with a 14 cm diameter, giving a truly single-mode behavior. 540 fs pulses are obtained without any fiber length optimization. An average power of 50 W has been achieved at the fundamental repetition rate of the laser, but also energies up to 41 µJ per pulse at lower repetition rate, pump power limited. The pulses are stretched using a thermally–controlled tunable chirped fibered Bragg grating (CFBG), allowing fine dispersion tuning, and compressed using a chirped volume Bragg grating (CVBG).
Mid-infrared absorption spectroscopy is nowadays considered as a routine analysis and sensing tool providing highly discriminatory information on organic and inorganic molecules. The specific needs of the transport, aerospace or energy industries may involve applications for which the spectroscopic sensor has to withstand high temperatures. This paper reports the design and fabrication of a silica hollow-core anti-resonant fiber with 8 non touching capillaries primarily designed for mid-infrared COx sensing inside engines. Numerical and analytical simulations performed to ensure fiber transparency in the 4-5 µm region are reported. Optical transmission between 3.9 µm and 4.7 µm is observed and demonstrate attenuation below 1 dB/m for single capillary ring fibers in this range. A preliminary scheme for CO2 sensing using a quantum cascade laser operating in one of the fiber’s transmission windows (λ=4.3 µm) is depicted.
Optimal suppression of higher-order modes (HOMs) in hollow-core antiresonant fibers comprising a single ring of thin-walled capillaries was previously studied, and can be achieved when the condition on the capillary-tocore diameter ratio is satisfied (d/D ≈ 0.68). Here we report on the conditions for maximizing the leakage losses of HOMs in hollow-core nested antiresonant node-less fibers, while preserving low confinement loss for the fundamental mode. Using an analytical model based on coupled capillary waveguides, as well as full-vector finite element modeling, we show that optimal d/D value leading to high leakage losses of HOMs, is strongly correlated to the size of nested capillaries. We also show that extremely high value of degree of HOM suppression (∼1200) at the resonant coupling is almost unchanged on a wide range of nested capillary diameter dN ested values. These results thus suggest the possibility of designing antiresonant fibers with nested elements, which show optimal guiding performances in terms of the HOM loss compared to that of the fundamental mode, for clearly defined paired values of the ratios dN ested/d and d/D. These can also tend towards a single-mode behavior only when the dimensionless parameter dN ested/d is less than 0.30, with identical wall thicknesses for all of the capillaries.
We compare, thanks to a Sagnac interferometer, the phase sensitivity to strain of different microstructured
optical silica fibers (MSF) that we design and fabricate. Our results show that when a same elongation is applied
to different MSF, the induced phase change is equal or lower than the one obtained for a standard fiber, showing
no advantage on this parameter for sensing applications.
KEYWORDS: Multimode fibers, Optical fibers, Single mode fibers, Near field optics, Tunable lasers, Modal analysis, Light wave propagation, Near field scanning optical microscopy, Structured optical fibers, High power fiber lasers
We propose and demonstrate two methods for modal decomposition in multi-mode fibres. Linearly polarized modes
propagating in a slightly multi-mode fibre are easily retrieved from intensity measurements at the fibre output surface.
The first method is an improvement of the so-called spectrally and spatially imaging technique, which is limited to largemode-
area optical fibers. The second method is a new, simpler and faster solution for the characterization of any kind of
optical fibre, thus attractive in comparison to previously reported methods, which are cumbersome, time-consuming
and/or limited to large-more-area fibres. Different kinds of multi-mode optical fibres are characterized. A large-modearea
photonic-bandgap fibre, a photonic-crystal small-core non-linear fibre, and a standard index-stepped multi-mode
fibre are characterized successfully.
KEYWORDS: Optical fibers, Birefringence, Dispersion, Near field scanning optical microscopy, Photonic crystal fibers, Near field optics, Optical microscopy, Polarization, Reflectometry, Single mode fibers
We present the structure of photonic crystal fibers and give a characterization results in birefringence and
chromatic dispersion using scanning near field optical microscopy and low coherence interferometry.
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