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A compact random fiber laser based on a short artificial Rayleigh reflector and heavily-doped Er fibers (custom-made and commercial as a reference) has been proposed, characterized and optimized in terms of efficiency, linewidth and noise level. A 10-cm artificial Rayleigh reflector with mean scattering level of +41.3 dB/mm relative to the natural Rayleigh scattering of the host fiber and low insertion loss level (~0.05 dB/cm at 1535 nm) was fabricated using a femtosecond direct writing technique. Its implementation as a distributed output mirror in a half-open cavity of a 980-nm diode pumped Er-doped fiber laser results in random lasing at 1535 nm in single- and few-mode regimes with power up to 100 mW, slope efficiency up to 16.5%, and signal-to-noise ratio up to 60 dB. A single-frequency regime with ~10 KHz linewidth was observed at output power up to 2.5 mW. Tunability potential of such random lasers is also demonstrated.

For the first time, radiation-induced absorption (RIA) of light is compared in two types of polarization-maintaining PANDA fibers having 1) undoped-silica core and F-doped-silica cladding, or 2) N-doped-silica core and undoped-silica cladding. RIA at λ = 1.55 μm is compared under γ-irradiation and post-irradiation recovery at room temperature (RT) and −60 °C. The post-irradiation RIA decay at RT is used to extrapolate RIA to the postulated end of the PANDA space mission (15 years) with the help of the “nth-order kinetic” model. The RIA extrapolation values for both PANDA types are found to be comparable. RIA spectra are measured in the PANDAs in the spectral range ∼0.5–4 eV in the process of both γ-irradiation and recovery; then the spectra are deconvolved into Gaussians components. The RIA spectra of both PANDA types are found to be composed of inherent and strain-assisted self-trapped holes (STHs), some undoped PANDAs demonstrating, in addition, a long-wavelength RIA tail affecting λ = 1.55 μm. No N-related color centers are revealed. Finally, RIA at λ = 1.55 μm is compared upon pulsed-X-ray irradiation. Undoped PANDAs are found to feature much smaller RIA at RT at post-pulse times larger than ∼40–1000 μs, whereas at smaller times, an N-doped PANDA proved to be superior. At −60 °C and at t > 1 ms, both PANDA types demonstrate approximately equal RIAs. Thus, the experiments showed that the two PANDA types are quite comparable, each type having its own advantages and disadvantages.

We demonstrate selective excitation and coherent amplification in the multicore fiber of the out-of-phase supermode that has equal intensities but interleaved 0/π phases in the neighboring cores. The out-of-phase supermode is beneficial due to its stability at arbitrary high powers, whereas the fundamental supermode becomes unstable at relatively high powers. We fabricated a double-clad all solid silica fiber with six highly Yb-doped coupled cores arranged in a ring structure. We obtained amplification of 50 picosecond chirped pulses up to ∼1 μJ energy with measured content of the out-of-phase mode of >80%. The experimental results were supported by 3D numerical simulation demonstrating the possibility of the out-of-phase supermode amplification in the multicore fibers with real parameters without degradation of supermode composition for powers up to damage threshold in silica glass.

The results of the numerical analysis of a new design of birefringent microstructured fibres containing three rings of identical air holes around an elliptical core with different distances between the rings of holes are presented in this study. The first ring contains two pairs of holes, which are more widely spaced than others. The study shows that the proposed design makes it possible to obtain single-mode guidance of fibres in the spectral range of 0.2 – 2.3 microns.

We experimentally demonstrate spatial beam self-cleaning in an Yb-doped graded-index multimode fiber taper, both in passive and active configurations. The input laser beam at 1064 nm was injected for propagation from the small to the large core side of the taper, with laser diode pumping in a counterdirectional configuration. The Kerr effect permits to obtain high-beam quality amplification with no accompanying frequency conversions. As a result, our nonlinear taper amplifier may provide an important building block for multimode fiber lasers and amplifiers.

Coherent propagation of supermodes in a multicore fiber is promising for power scaling of fiber laser systems, eliminating the need for the active feedback system to maintain the phases between the channels. We studied the propagation of broadband pulsed radiation at a central wavelength of 1030 nm in a multicore fiber with coupled cores arranged in a square array. We designed and fabricated a silica multicore fiber with a 5 × 5 array of cores. For controllable excitation of a desired supermode, we developed a beam-forming system based on a spatial light modulator. We experimentally measured intensity and phase distributions of the supermodes, in particular, the in-phase and out-of-phase supermodes, which matched well the numerically calculated profiles. We obtained selective excitation and coherent propagation of broadband radiation with the content of the out-of-phase supermode of up to 90% maintained without active feedback. Using three-dimensional numerical modeling with allowance for a refractive index profile similar to those of the developed fiber, we demonstrated stable propagation of the out-of-phase supermode and collapse of the in-phase supermode at a high signal power.

The copolymers of N-vinyl-2-pyrrolidone (N-VP) and condensation cardo and/or fluorinated condensation polymers (aromatic polyamide, polyimide and polyarylate) were synthesized by free radical in situ polymerization. The partial formation (14–61 wt%) of polivnylpyrrolidone (PVP) homopolymer upon the polymerization of N-VP containing dissolved condensation polymer was stated. Synthesized (co)polymers are differed in heat resistance and solubility from neat PVP. Using relevant copolymers solutions in N-methyl-2-pyrrolidone the optical fiber coatings having good adhesion properties were fabricated. Such coatings demonstrate high stability at elevated temperatures. A substantial number of defects on coatings and a slight decrease in bending strength are observed only on exposure at 200 °C for 72 h. Simultaneously holding for 1 and 24 h at the same temperature leads to hardening of the fibers: bending strength changes from ∼5 up to 6 GPa.

Highly birefringent microstructured fibers (HB MSFs) with similar mode field sizes along the two orthogonal axes have been presented. The core of the HB MSF is surrounded by two or more concentric rings having identical circular air holes. The key feature of this setup is that the first ring contains one or two pairs of holes, which are more widely spaced than others, i.e., they have one or two wider bridges. The shape of the core may be circular or elliptical. The HB MSFs were characterized using the finite element method. Simulation results show that HB MSFs with a certain relationship between the width of the wider bridges and the core ellipticity may have high birefringence (more than 2.7 × 10−3) and equal mode sizes along the two orthogonal axes. We have fabricated and investigated several such fibers, that have birefringence up to 2.9 × 10−3 and almost equal measured mode field sizes along the two orthogonal axes.

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. The target porphyrinoids having stable reactive silane anchors possess the ability to self-assemble on metal oxides and quartz surfaces and optical fibers. Covalent attachment is done in one-step, which makes the bonding process fast and easy. Immobilized chromophores were further converted by on-surface reactions into Zn(II) and Mg(II) metal complexes. The metallation time was found to be as fast as 1 min for Zn ion. Bonding densities calculated from the absorbances of the deposited layers give rough estimations for packing of the molecules on various substrates and evidence for monomolecular layers formation.

We present numerical and experimental investigations of microstructured fibers with high birefringence and low mode asymmetry. Fibers with approximately equal mode sizes along the two orthogonal axes and birefringence up to 2.7×10−3 were fabricated.

In this paper we continue numerical and experimental investigations of highly birefringent microstructured fibers (HiBi MSFs) proposed earlier [1,2]. These HiBi MSFs have an elliptical or circular core surrounded by two or more concentric rings of holes of constant diameter d. The holes in the first ring around the core have equal spacing Λ between the centers, except one or two pairs of holes with increased spacing Λ1. For convenience, we use the following code name characterizing the new HiBi MSF structure: MNKLec, where M is the number of holes in the first ring; N is the number of gaps in the first ring; K is the number of additional holes, which cover the gaps; L is the number of holes in the second ring; e means that the core is elliptical (c, circular); c means that the holes are circular (e, elliptical). To characterize the HiBi MSF shape, we use parameter δ defined as the deviation of the angle between adjacent holes in the first ring from its maximum value.

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. The change in the sign of the core boundary curvature leads to a loss of simplicity of boundary conditions for core modes and to "localization" and limitation of their interaction with the cladding material in space. Such HC MOFs made of different materials can be potential candidates for solving problem of ultra high power transmission including transmission of CO and CO2 laser radiation.

Photonic bandgap Bragg fibers are promising for designing large-mode-area structures owing to their high bend immunity. However, at a large core diameter, filtering of high-order modes (mainly, the LP 11 mode) becomes difficult, because the propagation constant of such modes is close to that of the fundamental LP 01 mode. In this paper, we demonstrate the possibility to suppress high-order modes in Bragg fibers by introducing low-index inclusions into the Bragg fiber core. Numerical analysis shows that an appropriate choice of the position and types of such inclusions allows one to increase the LP 11 mode radiation loss without increasing the optical loss of the fundamental LP 01 mode. The Bragg fiber with two B-doped and two F-doped rods in the core was fabricated and studied. The fundamental LP01 mode at 1064 nm had a mode-field area of about 340μm 2 and an optical loss below 0.2 dB/m at a bending radius of 15 cm. The LP 11 mode was not observed in both bent and straight fibers at this wavelength. Only the LP 21 mode was detected in a straight fiber; however, it was completely suppressed after propagating a length of 60 cm in a fiber bent with a radius

We report environmentally stable mode-locked Yb-doped fiber laser with dispersion compensation by index-guided solid-core photonic crystal fiber. The photonic crystal fiber and Faraday rotator in the cavity allow for robust 200-fs operation at 1 μm.

An optical fiber has to be defended by some protective coating from mechanical damage during handling and from environmental factors during its use. In many cases, a polymer coating is appropriate for enough protection. However, there are a number of special applications of optical fibers in which ordinary polymer-coated fibers cannot be used. These applications can be divided into several groups

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. Under experimental conditions, the resonances are broadened and the dispersion coefficient is decreased to 1000 ps/(nm km). However, to the best of our knowledge, this is the largest dispersion coefficient reported using a large mode area fiber.

Photonic bandgap fibers have already proved their huge potential for guiding light in air over kilometric lengths. Nowadays, solid-core bandgap fibers draw considerable attention due to their unusual properties. For instance, the bandgap effect may lead to very large mode area operation, management of the chromatic dispersion curve, spectral filtering or bend loss reduction, all features that could enhance fiber laser performances. Recent results about the design, fabrication and characterization of large mode area solid-core bandgap fibers are presented. Prospects of further development of bandgap fiber lasers are discussed.

Experimentally measured propagation losses and numerical simulation of a realistic depressed core Bragg fiber are presented. The relative contributions of Bragg modes and of modes trapped in the periodic cladding are discussed.

Static fatigue of bare indented fibers in different environments was studied. It was found that the n-value in different pH-solutions did not significantly change and was higher than that for strong fibers and lower than that for bulk samples in similar conditions. All lifetime reduction with a pH increase was due to a change of the B-value. The results obtained were used for evaluation of the lifetime of weak fibers for different service environments.

A brief overview of some possible degradation mechanisms of Raman amplifiers and lasers is presented. It is demonstrated that further investigations are required to clear up all the open questions related with mechanical and optical reliability of such devices and their components.

Photosensitivity and induced losses in phosphosilicate fibers depend on irradiation wavelength. The best induced index/loss relation has been obtained for H2-loaded samples at 157 nm irradiation. Pre-exposure procedure failed to decrease the induced losses.

Stress changes in hydrogenated phosphorous-doped fibers after Bragg grating inscription have been measured. Fibers with three different drawing tensions have been investigated. The core stress was found to increase independently of the initial stress state.

Significant photosensitivity of aluminosilicate fibers (with and without Er codoping) was observed. Effect of photosensitization was demonstrated for the first time for such fibers. Potential to write gratings directly in Er-doped aluminosilicate fibers was demonstrated.

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. The M(2) parameter was measured to be 1.17. A high-power cw laser was built exhibiting 80% slope efficiency above threshold. The robust propagation allows the fiber to be tightly bent. Weak incidence on the slope efficiency was observed with wounding radii as small as 6 cm.

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. It was found that the shift of the resonant wavelengths exhibited a well-defined linear dependence on temperature up to 700 degrees C.