40 W of supercontinuum generated by a self-pulsed pump-sharing oscillator-amplifier.

We demonstrate an all-fiber supercontinuum (SC) source delivering up to 40 W of average power ranging from 750 to 2200 nm. The laser source is based on a self-Q-switched pump-sharing oscillator-amplifier. The self-Q-switched master oscillator generates giant pulses, amplified in the high-power stage. Finally, a passive fiber acts as a nonlinear stage, improving the spectrum flatness as well as the spectral broadening. To the best of our knowledge, this is the first time that a pump-sharing oscillator-amplifier is used for SC generation and is based on the use of a submeter Ytterbium-doped fiber length inside the oscillator.

Noise analysis in a seeded four-wave mixing process generated in a photonic crystal fiber pumped by a chirped pulse.

Four-wave mixing is investigated when chirped pump and signal pulses are injected in a photonic crystal fiber. The shot-to-shot stability of the amplified coherent signal was measured by using the dispersive Fourier transform method and compared with numerical simulations. We highlight that the signal-to-noise ratio (SNR) of the pulsed signal increases with the injected power and show that it is not deteriorated through the amplification when the fiber optical parametric amplifier is strongly saturated. The SNR of the signal remains nearly constant after the amplifier.

Design and fabrication of dispersion controlled highly nonlinear fibers for far-detuned four-wave mixing frequency conversion.

We report on the conception, fabrication and characterization of a new concept of optical fiber enabling a precise control of the ratio between the 2nd and 4th-order of chromatic dispersion (respectively ß2 and ß4) at 1.55 µm which is at the heart of the Four-Wave-Mixing (FWM) generation. For conventional highly nonlinear fiber the sensitivity of this ratio to fiber geometry fluctuations is very critical, making the fabrication process challenging. The new design fiber reconciles the accurate control of chromatic dispersion properties and fabrication by standard stack and draw method, allowing a robust and reliable method against detrimental fluctuations parameters during the fabrication process. Experimental frequency conversion with FWM in the new design fiber is demonstrated.

Few-cycle all-fiber supercontinuum laser for ultrabroadband multimodal nonlinear microscopy.

Temporally coherent supercontinuum sources constitute an attractive alternative to bulk crystal-based sources of few-cycle light pulses. We present a monolithic fiber-optic configuration for generating transform-limited temporally coherent supercontinuum pulses with central wavelength at 1.06 µm and duration as short as 13.0 fs (3.7 optical cycles). The supercontinuum is generated by the action of self-phase modulation and optical wave breaking when pumping an all-normal dispersion photonic crystal fiber with pulses of hundreds of fs duration produced by all-fiber chirped pulsed amplification. Avoidance of free-space propagation between stages confers unequalled robustness, efficiency and cost-effectiveness to this novel configuration. Collectively, the features of all-fiber few-cycle pulsed sources make them powerful tools for applications benefitting from the ultrabroadband spectra and ultrashort pulse durations. Here we exploit these features and the deep penetration of light in biological tissues at the spectral region of 1 µm, to demonstrate their successful performance in ultrabroadband multispectral and multimodal nonlinear microscopy.

Pre-compensation of thermally induced refractive index changes in a depressed core fully aperiodic large-pitch fiber for high average power operation.

To prevent the thermally induced spatial beam degradation occurring in high-power fiber lasers and amplifiers, index-depressed core "fully aperiodic large-pitch fibers" (FA-LPFs) have been designed and fabricated. In contrast to previous experimental works performed on FA-LPFs, in which the active core and the surrounding cladding material are quasi-index-matched, the core refractive index is in slight depression compared to the surrounding material (Δn≈-3×10-5). Thus, the index-depressed fiber core tends first to behave as an anti-guide, preventing light from being properly guided into it. However, by increasing the absorbed pump power, the thermal load induces a parabolic refractive index change sufficient to compensate for the -3×10-5 index depression in the core, enabling a robust single-mode amplification at high average power. As a proof of concept, using a 110 µm depressed core FA-LPF, M2 values of 1.3 were demonstrated in amplifier configuration from 60 W to a maximal value of 170 W of emitted average power only limited by the available pump power.

Maximal Oxygen Consumption Requirements in Professional North American Ice Hockey.

ABSTRACT: Ferland, P-M, Marcotte-L'Heureux, V, Roy, P, Carey, V, Charron, J, Lagrange, S, Leone, M, and Comtois, AS. Maximal oxygen consumption requirements in professional North American ice hockey. J Strength Cond Res 35(4): 1586-1592, 2021-This study was designed to measure preseason on-ice relative V̇o2max of professional ice-hockey players (n = 101 National Hockey League [NHL], 42 American Hockey League [AHL], 4 East Coast Hockey League [ECHL], and 15 Canadian Hockey League [CHL]) throughout 17 years and compare it between generations, league level, and position, and to verify if it was related to season and NHL career statistics. Relative V̇o2max was measured on ice with a portable metabolic analyzer (K4b2, Cosmed, Rome) with full hockey equipment, except for the helmet with either the Skating Multistage Aerobic Test or the 30-15 intermittent ice test tests. Relative V̇o2max results from both tests were compared between players of the same generation with an independent-samples T-test and were not significantly different. A one-way analysis of variance and post hoc pairwise tests were performed to detect significant differences between groups. Pearson correlations (two-tailed) were also performed between selected variables. All statistical significance was set at p < 0.05. Results show that there are no significant differences for relative V̇o2max between generations (2001-2003 vs. 2006 vs. 2015-2017), league level (NHL vs. AHL vs. ECHL vs. CHL), and position (winger, center, and defense), other than the ECHL being lower. There are also no significant relationships between V̇o2max values and hockey season and NHL career statistics. Thus, the results show that there is a minimal relative V̇o2max requirement to play North American ice hockey at the elite level (55.9 ± 5.2 ml·kg-1·min-1; n = 162). Future research should be directed toward comparing V̇o2max of elite and amateur ice-hockey players to confirm the minimal relative V̇o2max requirement to play North American ice hockey at the elite level.

Spectral correlation of four-wave mixing generated in a photonic crystal fiber pumped by a chirped pulse.

We report the spectral distribution of the parametric process generated in a photonic crystal fiber pumped by a chirped pulse. The spectral correlation of four-wave mixing has been measured using the dispersive Fourier transform method. From statistical analysis of multiple shot-to-shot spectral measurements, the spectral correlation between the signal and idler photons reveals physical insights into the particular portion of the pump spectrum responsible for generating the four-wave mixing. Therefore, the shape of the correlation map indicates directly the temporal and spectral links between the signal and the pump, which are highly important to design a four-wave mixing based amplifier.

Widely tunable Q-switched dual-wavelength synchronous-pulsed Tm-doped fiber laser emitting in the 2 µm region.

We demonstrate a widely tunable Q-switched dual-wavelength fiber laser emitting synchronized pulses in the 2 µm spectral range. Owing to the use of a Tm-doped rod-type fully aperiodic large pitch fiber, together with an acousto-optic modulator and two volume Bragg gratings (VBGs), the wavelength separation was shown to be continuously tunable from 1 to 120 nm (∼0.1-10 THz). A peak power higher than 8 kW was demonstrated over the whole tuning range for a repetition rate (RR) of 1 KHz and a 26 ns pulse duration. The RR was modulated from 1 to 30 kHz, and the laser pulse duration measured between 23 ns and 130 ns, depending on the RR and the wavelength separation.

High-power widely tunable ps source in the visible light based on four wave mixing in optimized photonic crystal fibers.

We present a detailed study on the generation of widely tunable visible light through four wave mixing in specifically designed micro-structured fibers. The fiber's properties are optimized for an efficient conversion to the visible and near infrared with a combined tunability from 620 to 910 nm of a picosecond Yb-doped tunable source for biomedical applications.

Polarization-maintaining Yb-doped large-mode-area fully aperiodic large-pitch fibers.

Based on a special large-pitch architecture that has already proved its single-mode single-polarization behavior in a passive configuration, two ytterbium-doped versions of such large-mode-area fibers have been fabricated and tested in both laser and amplification configurations for high-power laser source applications. Due to the high sensitivity of large-pitch fiber design to the active-core-to-passive-cladding index mismatch, the realization of a single-polarization structure is highly challenging. However, we report on the preservation of a polarization-maintaining feature. A linear polarization with an extinction ratio of 17 dB is demonstrated for mode field diameters reaching up to 58 µm as long as the single-modeness of the emitted signal is preserved.

Comparison between Different Structures of Suspended-Core Microstructured Optical Fibers for Volatiles Sensing.

In this paper, different core structures of microstructured optical fibers (MOFs) for low-finesse Fabry⁻Pérot (FP) sensors are experimentally compared to get the highest sensitivity. These devices are designed for volatile organic compounds (VOCs) measurements. Indium tin oxide (ITO) thin films were deposited by sputtering on the MOFs and different optical fast Fourier transform (FFT) phase responses from the FP were measured for saturated atmospheres of ethanol. It has been demonstrated that the sensitivities of the developed sensors depend strongly on the geometry and the dimensions of the MOF-cores. The sensors show recovery times shorter than 100 s and the baselines are fully recovered after every exposure to ethanol vapors.

Broadband single-mode single-polarization passive fully aperiodic large-pitch fibers.

Two evolutions of fully aperiodic large-pitch fiber designs employing few stress-applying parts are presented. The induced elasto-optic stress discriminates the two orthogonal polarization modes (LP01x and LP01y) of the fundamental mode, selectively delocalizing one of them into the cladding via a suitable coupling to one or several cladding modes. This ensures the propagation of a single linear polarization mode. For the largest core dimensions, however, the applied stress can strongly influence the intensity distributions of core modes, and a tailored design process must thwart this. The polarization properties are investigated experimentally with core scalability over a large spectral bandwidth into passive structures, leading to the evidencing of a single-mode single polarization over a large span from 1 to 1.6 µm with a core dimension of 80 µm and, notably, at 1400 nm for a core dimension of 140 µm. The polarization extinction ratio is also determined.

Experimental study of the mode instability onset threshold in high-power FA-LPF lasers.

We report here on an experimental investigation of the temporal behavior of transverse mode instabilities into "fully aperiodic large-pitch fibers" (FA-LPFs) operated in high-power continuous-wave laser configuration. To ensure an effective transverse single-mode emission into FA-LPFs, a perfect index matching between the active core and the background cladding materials (Δn=0) is required. The original design of such fibers enables an effective transverse single-mode emission by strengthening the higher-order mode delocalization out of the gain region, even for high heat load levels, consequently leading to the improvement of the beam spatial quality. The study was conducted over fibers of various gain region diameters, from 58 to 100 µm, for a refractive index mismatch Δn of about +8×10-5. The emitted beam is characterized using both M2 measurements and time traces to study the changeover of a stable temporal behavior to an unstable one.

140 µm single-polarization passive fully aperiodic large-pitch fibers operating near 2 µm.

In this paper, we demonstrate a single-polarization feature out of passive very-large-mode-area fully aperiodic large-pitch fibers. It has been previously shown theoretically that one of the two polarizations of the fundamental mode is selectively coupled to a cladding mode. This coupling does not require fiber bending, which permits us to avoid any decrease in mode effective area. The coupling is achieved owing to boron-doped silica inclusions implemented into the microstructured cladding and acting as stress-applying parts. This mechanism has been assessed experimentally in this work using fibers of two different core diameters: 60 µm and 140 µm, providing mode field areas of 3637 µm2 and 14,590 µm2, respectively, at 1942 nm. The tested fibers have a length of 45 cm and an outer diameter exceeding 1 mm, yielding rod-type fibers. Each sample has been characterized using an unpolarized laser source emitting at 1942 nm. This laser, based on a thulium-doped large-mode-area step-index fiber, has a spectral bandwidth of about 0.5 nm. After passing through a piece of the passive fiber, a polarization extinction ratio higher than 16 dB has been achieved.

Study of Optical Fiber Sensors for Cryogenic Temperature Measurements.

In this work, the performance of five different fiber optic sensors at cryogenic temperatures has been analyzed. A photonic crystal fiber Fabry-Pérot interferometer, two Sagnac interferometers, a commercial fiber Bragg grating (FBG), and a π-phase shifted fiber Bragg grating interrogated in a random distributed feedback fiber laser have been studied. Their sensitivities and resolutions as sensors for cryogenic temperatures have been compared regarding their advantages and disadvantages. Additionally, the results have been compared with the given by a commercial optical backscatter reflectometer that allowed for distributed temperature measurements of a single mode fiber.

50.4% slope efficiency thulium-doped large-mode-area fiber laser fabricated by powder technology.

We report on a triple clad large-mode-area Tm-doped fiber laser with 18 µm core diameter manufactured for the first time by an alternative manufacturing process named REPUSIL. This reactive powder sinter material enables similar properties compared to conventional CVD-made fiber lasers, while offering the potential of producing larger and more uniform material. The fiber characterization in a laser configuration provides a slope efficiency of 47.7% at 20°C, and 50.4% at 0°C with 8 W output power, with a laser peak emission at 1970 nm. Finally, a beam quality near the diffraction-limit (M(x,y)2<1.1) is proved.

Precompensation of the thermal-induced refractive index changes into a fully aperiodic LPF for heat load resilience.

In this paper, a strategy consisting of precompensating the thermal-induced transverse refractive index changes is undertaken to push further the appearance threshold of a multimode regime. First, a standard air-silica large pitch fiber (LPF) and a fully aperiodic large pitch fiber are confronted in regard to their heat load resilience and capabilities for single-mode emission. Thereafter, slight refractive index depressions are judiciously introduced into the active core area. This approach enhances the delocalization of the high-order modes even under severe heat load levels. This combination of aperiodic cladding microstructuration and index-precompensation theoretically increases the multimode regime threshold while preserving large mode field areas. This investigation is performed at 1.03 and 2 µm operating wavelengths.

Demonstration of a homogeneous Yb-doped core fully aperiodic large-pitch fiber laser.

The first demonstration of a 40 µm core homogeneously ytterbium-doped fully aperiodic large-pitch fiber laser, to the best of our knowledge, is reported here. In this concept, the amplification of unwanted high-order modes is prevented by means of an aperiodic inner-cladding structure, while the core and inner-cladding material has a higher refractive index than pure silica. In a laser configuration, up to 252 W of extracted power, together with an optical-to-optical efficiency of 63% with respect to the incident pump power, have been achieved. While an average M2 of 1.4 was measured, the emitted power becomes temporally unstable when exceeding 95 W, owing to the occurrence of modal instabilities.

Fundamentals on new capillaries inspired by photonic crystal fibers as optofluidic separation systems in CE.

Two prototypes of microstructured capillaries (MSCs) were designed, manufactured, and used to carry out different experiments. MSC-1 consisted of six holes of ≈28 µm id whereas MSC-2 consisted of 85 holes of ≈7.7 µm id. A fundamental study on the hydrodynamic injection through a commercial CE equipment was conducted. Experimental times to flush specific volumes were approximately three times larger than the theoretical values. Then, the detection of starch was carried out by using the MSCs and conventional capillaries, and the electropherograms were compared on the basis of analytical parameters employed in CE. An improvement in peak asymmetry was obtained for the MSC-1 compared to the conventional capillaries. S/N was one order of magnitude increased with the MSC, improving ten times the sensitivity. Considering this advantage, the separation and detection of nitrostarch was performed as a first application of the MSC-1. Minimal sample amounts of nitrostarch (1.7 µg) were detected. Results present a real interest in forensics since this substance had not been previously detected through CE, leading to new investigations in the design of new capillaries capable of enhancing CE performance.

Experimental and numerical characterization of a hybrid Fabry-Pérot cavity for temperature sensing.

A hybrid Fabry-Pérot cavity sensing head based on a four-bridge microstructured fiber is characterized for temperature sensing. The characterization of this cavity is performed numerically and experimentally in the L-band. The sensing head output signal presents a linear variation with temperature changes, showing a sensitivity of 12.5 pm/°C. Moreover, this Fabry-Pérot cavity exhibits good sensitivity to polarization changes and high stability over time.