Supermode lasing and light amplification in multicore bismuth-doped fiber.

Multicore fibers are promising structures with specific light propagation properties, which can be managed to benefit several applications in optical communications, fiber lasers and amplifiers, high-resolution imaging, and fiber-based sensors. The current use of multicore fibers in laser technology is mainly focused on in-phase coherent beam combining in far-field regions (out-cavity) using bulk optical elements. However, this approach is challenging in terms of the power scalability of all-fiber lasers (intra-cavity), particularly with using low-gain media, where it is needed to provide mode-coupling (supermode propagation) stability along relatively long lengths.

Soluble Fluorinated Cardo Copolyimide as an Effective Additive to Photopolymerizable Compositions Based on Di(meth)acrylates: Application for Highly Thermostable Primary Protective Coating of Silica Optical Fiber.

The development of photocurable compositions is in high demand for the manufacture of functional materials for electronics, optics, medicine, energy, etc. The properties of the final photo-cured material are primarily determined by the initial mixture, which needs to be tuned for each application. In this study we propose to use simple systems based on di(meth)acrylate, polyimide and photoinitiator for the preparation of new photo-curable compositions.

Spectrum collapse in a 7-core Yb-doped fiber laser with an array of fs-inscribed fiber Bragg gratings.

Femtosecond inscription of fiber Bragg gratings (FBGs) in each core of a cladding-pumped seven-core Yb-doped fiber enables efficient (≈70%) 1064-nm lasing in a robust all-fiber scheme with ≈33 W power, nearly the same for uncoupled and coupled cores. However, the output spectrum is quite different: without coupling, seven individual lines corresponding to the in-core FBG reflection spectra sum up into a broad (0.22 nm) total spectrum, whereas the multiline spectrum collapses into a single narrow line at strong coupling.

Advanced distributed feedback lasers based on composite fiber heavily doped with erbium ions.

Specially designed composite heavily Er-doped fiber in combination with unique point-by-point inscription technology by femtosecond pulses at 1,026 nm enables formation of distributed-feedback (DFB) laser with ultra-short cavity length of 5.3 mm whose parameters are comparable and even better than those for conventional Er-doped fiber DFB lasers having much longer cavity. The composite fiber was fabricated by melting rare-earth doped phosphate glass in silica tube.

Durable shape sensor based on FBG array inscribed in polyimide-coated multicore optical fiber.

The paper presents a novel three-dimensional quasi-continuous shape sensor based on an FBG array inscribed by femtosecond laser pulses into a 7-core optical fiber with a polyimide protective coating. The measured bending sensitivity of individual FBGs ranges from 0.046 nm/m to 0.

Spatial beam self-cleaning and supercontinuum generation with Yb-doped multimode graded-index fiber taper based on accelerating self-imaging and dissipative landscape.

We experimentally demonstrate spatial beam self-cleaning and supercontinuum generation in a tapered Ytterbium-doped multimode optical fiber with parabolic core refractive index profile when 1064 nm pulsed beams propagate from wider (122 µm) into smaller (37 µm) diameter. In the passive mode, increasing the input beam peak power above 20 kW leads to a bell-shaped output beam profile. In the active configuration, gain from the pump laser diode permits to combine beam self-cleaning with supercontinuum generation between 520-2600 nm.

Distributed Bragg reflector fiber laser directly written in a composite fiber manufactured by melting phosphate glass in a silica tube.

We demonstrate a single-frequency distributed Bragg reflector (DBR) fiber laser based on the novel erbium-doped composite fiber fabricated by melting phosphate glass in a silica tube. The fabricated composite fiber was single-mode at the wavelength of 1.55 μm; the measured cutoff wavelength was 1.

Four-photon absorption cross-section measurements in UV fused silica at 473 nm.

With the use of I- and z-scan techniques, the four-photon absorption cross section in a UV fused silica sample has been measured to be σ=(1.0±0.5)×10  cm s at 473 nm.

Raman fiber laser with random distributed feedback based on a twin-core fiber.

An operation of a linearly polarized Raman fiber laser with random distributed feedback based on a polarization-maintaining twin-core fiber (TCF) is demonstrated for the first time, to the best of our knowledge. The results indicate that the TCF allows one to obtain laser generation with a linewidth that is about five times smaller than that for the random laser based on a conventional fiber with similar parameters. The reasons for narrowing include both the weakening of nonlinear effects due to the power density reduction and the spectrally selective properties of the TCF.

Sub-MW peak power diffraction-limited chirped-pulse monolithic Yb-doped tapered fiber amplifier.

We demonstrate a novel amplification regime in a counter-pumped, relatively long (2 meters), large mode area, highly Yb-doped and polarization-maintaining tapered fiber, which offers a high peak power directly from the amplifier. The main feature of this regime is that the amplifying signal propagates through a thin part of the tapered fiber without amplification and experiences an extremely high gain in the thick part of the tapered fiber, where most of the pump power is absorbed. In this regime, we have demonstrated 8 ps pulse amplification to a peak power of up to 0.

High-beam quality, high-efficiency laser based on fiber with heavily Yb(3+)-doped phosphate core and silica cladding.

We have fabricated and tested a composite fiber with an Yb(3+)-doped phosphate glass core and silica cladding. Oscillation with a slope efficiency of 74% was achieved using core pumping at 976 nm with fiber lengths of 48-90 mm in a simple laser configuration, where the cavity was formed by a high-reflectivity Bragg grating and the cleaved fiber end. The measured M(2) factors were as low as 1.

Phosphate-core silica-clad Er/Yb-doped optical fiber and cladding pumped laser.

We present a composite optical fiber with a Er/Yb co-doped phosphate-glass core in a silica glass cladding as well as cladding pumped laser. The fabrication process, optical properties, and lasing parameters are described. The slope efficiency under 980 nm cladding pumping reached 39% with respect to the absorbed pump power and 28% with respect to the coupled pump power.

Multicore fiber with rectangular cross-section.

We have fabricated, to our knowledge, the first rectangular cross-section multicore fiber with eight cores arranged in a line. We have shown that the rectangular cross-section remains practically unchanged during the fiber-drawing process. The heterogeneous version of the proposed fiber design could be beneficial for crosstalk reduction because of the low influence of fiber bends on crosstalk between neighboring cores.

Fabrication of Bragg gratings in microstructured and step index Bi-SiO2 optical fibers using an ArF laser.

An ArF excimer laser was used to fabricate Bragg gratings in fibers with Bi-SiO(2) core and microstructured or F-doped claddings without fiber presensitization. Average and modulated refractive index changes of 2.7 × 10(-4) and 1.

Mechanisms of optical losses in Bi:SiO2 glass fibers.

The mechanisms of optical losses in bismuth-doped silica glass (Bi:SiO(2)) and fibers were studied. It was found that in the fibers of this composition the up-conversion processes occur even at bismuth concentrations lower than 0.02 at.

Synthesis of porphyrinoids with silane anchors and their covalent self-assembling and metallation on solid surface.

We have synthesized a set of porphyrin and phthalocyanine compounds with two different silane anchors. Syntheses of the anchor-substituted chromophores have been carried out via hydrosilylation of alkene derivatives, catalyzed by platinum complexes. The reduction side-process was suppressed using specific anchor/catalyst pairs, and the silane-containing compounds were successfully isolated from hydrogenated by-products in pure form with good yields.

Demonstration of a waveguide regime for a silica hollow--core microstructured optical fiber with a negative curvature of the core boundary in the spectral region > 3.5 μm.

We present a numerical and experimental demonstration of a waveguide regime in a broad band spectral range for the hollow core microstructured optical fibers (HC MOFs) made of silica with a negative curvature of the core boundary. It is shown that HC MOFs with the cladding consisting only of one row of silica capillaries allows to guide light from the near to mid infrared despite of high material losses of silica in this spectral region. Such result can be obtained by a special arrangement of cladding capillaries which leads to a change in the sign of the core boundary curvature.

Broadband wavelength conversion in a germanosilicate-core photonic crystal fiber.

A photonic crystal fiber with a germanosilicate core having a nonlinear coefficient of 40 (W km)(-1) near the single dispersion zero at 1.09 microm is fabricated and studied. Broadband parametric wavelength conversion of the Ti:sapphire laser output tunable at 0.

Single-mode all-silica photonic bandgap fiber with 20-microm mode-field diameter.

An all-silica photonic bandgap fiber with a cladding index difference of approximately 2 % and diameter-to-pitch ratio (d/wedge) of 0.12 was fabricated and studied. To our knowledge, this is the first report on the properties of photonic bandgap fiber with such a small d/wedge.

High-power photonic-bandgap fiber laser.

An original architecture of an active fiber allowing a nearly diffraction-limited beam to be produced is demonstrated. The active medium is a double-clad large-mode-area photonic-bandgap fiber consisting of a 10,000 ppm by weight Yb(3+)-doped core surrounded by an alternation of high- and low-index layers constituting a cylindrical photonic crystal. The periodic cladding allows the robust propagation of a approximately 200 microm(2) fundamental mode and efficiently discriminates against the high-order modes.

Highly dispersive large mode area photonic bandgap fiber.

An all-silica photonic bandgap fiber composed of a low-index core surrounded by alternating high- and low-index rings allows us to achieve a large mode area (500 microm(2)) and large chromatic dispersion. Sharp resonances from the even Bragg mode to odd ring modes theoretically lead to 20,000 ps/(nm km) chromatic dispersion when large bends are applied. By nature, sharp resonances are sensitive to inhomogeneities along the fiber length.

Effect of polymer coating on leakage losses in Bragg fibers.

It is found that the reflection of leaky radiation from the interface between the outer silica cladding and the coating polymer greatly modifies the loss spectrum of Bragg fibers. A simple model that describes this effect is proposed and confirmed by measurement and computation.

Low-loss singlemode large mode area all-silica photonic bandgap fiber.

We describe the design and characterization of solid core large mode area bandgap fibers exhibiting low propagation loss and low bend loss. The fibers have been prepared by modified chemical vapor deposition process. The bandgap guidance obtained thanks to a 3-bilayer periodic cladding is assisted by a very slight index step (5.

Arc-induced long-period gratings in aluminosilicate glass fibers.

Permanent long-period gratings were written using arc discharges in two aluminosilicate fibers, one of which was doped with erbium. Reversible gratings were also mechanically induced in both fibers. The thermal behavior of the arc-induced gratings was investigated at up to 1100 degrees C.

Hydrogen loading and UV-irradiation induced etch rate changes in phosphorus-doped fibers.

We show strong changes in chemical etching of phosphorus-doped fiber cores due to hydrogen loading and subsequent UV-irradiation using an atomic force microscope. The etch rate of the fiber core in a low concentration hydrofluoric acid solution (HF) is decreasing after hydrogen loading by as much as 30%. In contrast, UV-irradiation of the hydrogenated fiber increases the core etch rate to values of 27% above the etch rate of the pristine fiber.