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We have developed an ultra-low noise tunable Brillouin fiber laser exhibiting three orders of magnitude better frequency noise performance than the Neodymium-doped fiber laser pump and remarkable optical signal-to-noise ratio exceeding 80 dB suitable for immediate applications in coherent nonlinear conversion, quantum computing and underwater communications. In addition, we have implemented a custom optical phase-locked loop to ensure long-term stable operation and have investigated its impact on frequency noise. We demonstrate the power scalability of the single frequency (Hz-class) Brillouin laser, delivering over 500 mW with tunability across the 900 nm to 930 nm range in an all-fiber fully polarization-maintaining architecture.

An all-fiber polarization maintaining (PM) laser tunable over 170 nm via Raman soliton self-frequency shift (SSFS) delivering sub-100 fs pulses with a central wavelength ranging from 1880 to 2050 nm is presented. The 40 MHz laser emits power ranging from 15 to 34 mW with pulse duration as short as 80 fs. It is based on exclusively commercially available standard fibers and has been designed to produce sub-100 fs pulse durations over the whole spectral range without the need for adjusting neither nonlinearities nor dispersion. The laser is versatile and a robust potential alternative to Tm and Tm:Ho oscillators.

We report here on the development of a multi-Watt power tunable single frequency ultra-low noise laser system emitting around 620 nm. More than 5 W of output power is obtained between 616.5 nm and 630.8 nm using sum frequency generation of 1050 nm and 1550 nm tunable laser sources in a periodic poled lithium niobate crystal. The tunability is achieved through temperature and channel shift, and only limited by the crystal characteristics. An output power of 10.1 W and an optical-optical efficiency of 45% are reached at 624.5 nm. The relative intensity noise properties of the conversion process have been experimentally investigated in different configurations showing excellent agreement with the analytical prediction.

We report herein on the development of a linearly polarized, single-frequency tunable laser system producing more than 10 W in the 1550 nm range, using a two-stage erbium/ytterbium co-doped fiber-based master oscillator power amplifier (MOPA) architecture. The all-fiber MOPA provides an ultralow intensity noise of -160 d B c / H z beyond 200 kHz between 1533 and 1571 nm ( Δ λ =38 n m ) at full output power and a minimum optical signal to noise ratio of 38 dB. A good stability is obtained over 4 h at maximum power for several wavelengths with peak-to-peak fluctuation less than 3% and rms below 0.5%.

Background: The foot is the most complex body's structure; it is highly susceptible to disorders because of its loading pattern. The complexity of the foot structure geometry implies the use of reverse engineering tools to obtain a model that can accurately mimic the biomechanical behavior of the foot., Objective: The objective of this study is to establish a state-of-the-art ankle-foot finite element (FE) model with anatomically realistic geometry and structure in order to get the model that will suit all cases for future studies on stress injuries and foot insole designs under different loading conditions., Material and Methods: In this analytical study, tomography images were imported in DICOM format, after that, the object was exported in the form of three-dimensional structures in STL file format to define and assemble the structures. After that, the computer simulation on numerical model was done. One-way Analysis of variance (ANOVA) test was performed, and a threshold (p<0.05) was used to indicate the significance of results., Results: The results showed no significant differences (P>0.05) between the values of the plantar pressure corresponding to neutral standing condition with other foot models in literature. The stresses transferred to the bone structure show that the relatively higher stress was located in the fifth, fourth and third tarsometatarsal, where the maximum von Mises stress in the bone structure was 2155.4 kPa., Conclusion: The state-of-the-art ankle-foot FE model with anatomically realistic geometry and structure will be very helpful for future studies on stress injuries and foot insole designs under different loading conditions., (Copyright: © Journal of Biomedical Physics and Engineering.)

In this Letter, a low-cost interrogation technique for multiple fiber Bragg gratings (FBGs) is demonstrated. The design utilizes the major advantage of the distributed feedback lasers, which is tuning their emitted wavelength by current modulation and temperature variation. The sensitivity of this method and the influence of optical losses on the measurement have been carefully studied, and an accuracy of 5 pm is achieved.

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.

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.

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 M 2 measurements and time traces to study the changeover of a stable temporal behavior to an unstable one.

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  μm 2 and 14,590  μm 2 , 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.

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 (LP 01x and LP 01y ) 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.

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.

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 M 2 of 1.4 was measured, the emitted power becomes temporally unstable when exceeding 95 W, owing to the occurrence of modal instabilities.

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.