Measurement of high-birefringent spun fiber parameters using short-length fiber Bragg gratings.

Spectral polarization characteristics of short-length fiber Bragg gratings UV-written in a highly-birefringent spun-fiber have been investigated. Based on the analysis of the characteristics the technique for measuring the built-in linear phase birefringence as well as the spin period in this fiber type has been suggested. In this method the birefringence dispersion is excluded and therefore the built-in linear phase birefringence can be measured with an improved accuracy.

Cascaded gain fibers for increasing output power and the stimulated Brillouin scattering threshold of narrow linewidth fiber Raman amplifiers.

We show both experimentally and theoretically a method to increase the stimulated Brillouin scattering (SBS) threshold and output power of narrow linewidth fiber Raman amplifiers. This method employs two or more fibers with varying concentrations of the Raman gain material dopant such as GeO2 or P2O5 in silicate-based glasses. These fibers are then cascaded to form an amplifier gain stage, disrupting the buildup of SBS that normally occurs in single continuous fibers. The numerical model shown is applicable to arbitrary amplifier systems for gain stage optimization and increased power scaling. We give experimental results for phosphosilicate fibers that agree well with simulation predictions that support the numerical model used.

Watt-level, continuous-wave bismuth-doped all-fiber laser operating at 1.7 µm.

A watt-level all-fiber laser radiating at the wavelength of 1.7 µm in a continuous-wave regime was developed by using bismuth-doped high-germania optical fiber. A maximum slope efficiency of 33% with respect to the launched pump power was achieved. The dependencies of the slope efficiencies of bismuth-doped fiber laser versus the length of active fiber and reflectivity of the output mirror were obtained.

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 1.05-1.22 even though the fiber was multimode at the lasing wavelength.

High-efficiency cascaded Raman fiber laser with random distributed feedback.

Cascaded lasing provided by Raman gain (at 1115-nm pumping) and random distributed feedback (via Rayleigh backscattering) in a 1.65-km phosphosilicate fiber is studied. Output power for the second Stokes component (1398 nm) exceeds 5 W at pump power of 11 W. In contrast to conventional cascaded Raman laser with high-Q cavity for the intermediate first Stokes component, there is no cavity here and no cavity losses, correspondingly. Longitudinal power distribution is shown to be quite different also. As a result, the efficiency of pump to 2nd Stokes wave conversion is not influenced by the intermediate stage and depends only on the integral attenuation in the fiber. Herewith, the number of generated 2nd Stokes photons at the output may even exceed the absorbed pump photons due to the lower attenuation of Stokes waves.

Effect of absorption recovery in bismuth-doped silica glass at 1450 nm on soliton grouping in fiber laser.

Saturable absorption in bismuth-doped glasses was found to have a noticeable influence on soliton interaction and group formation. This phenomenon, observed in 1450 nm mode-locked bismuth-doped fiber laser, shows the distinct feature of the multiple pulse regime, which appears as a stationary pulse group whose length can be spread over the whole cavity length by variation of the pump power and polarization. Pulse positioning within the ensemble depends on the saturation fluence and the relatively fast recovery dynamics of bismuth fiber.

Hybrid mode-locked erbium-doped all-fiber soliton laser with a distributed polarizer.

A soliton-type erbium-doped all-fiber ring laser hybrid mode-locked with a co-action of arc-discharge single-walled carbon nanotubes (SWCNTs) and nonlinear polarization evolution (NPE) is demonstrated. For the first time, to the best of our knowledge, boron nitride-doped SWCNTs were used as a saturable absorber for passive mode-locking initiation. Moreover, the NPE was introduced through the implementation of the short-segment polarizing fiber. Owing to the NPE action in the laser cavity, significant pulse length shortening as well as pulse stability improvement were observed as compared with a SWCNTs-only mode-locked laser. The shortest achieved pulse width of near transform-limited solitons was 222 fs at the output average power of 9.1 mW and 45.5 MHz repetition frequency, corresponding to the 0.17 nJ pulse energy.

Excited-state absorption in various bismuth-doped fibers.

Excited-state absorption (ESA) in various bismuth-doped fibers (BDFs) was investigated. No significant ESA in IR emission bands of Bi-doped germanosilicate and phosphosilicate fibers was found. Considerable ESA was observed in Bi-doped aluminosilicate fibers at 800-1700 nm. The ESA spectra of the aluminosilicate BDFs with different bismuth concentration were measured at room and 77 K temperature. Significant dependence of the ESA on the bismuth concentration and the fiber temperature was found.

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.

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. Due to high doping level of the phosphate core optimal length was several times shorter than that of silica core fibers.

Mid-infrared Raman-soliton continuum pumped by a nanotube-mode-locked sub-picosecond Tm-doped MOPFA.

We demonstrate a mid-infrared Raman-soliton continuum extending from 1.9 to 3 µm in a highly germanium-doped silica-clad fiber, pumped by a nanotube mode-locked thulium-doped fiber system, delivering 12 kW sub-picosecond pulses at 1.95 µm. This simple and robust source of light covers a portion of the atmospheric transmission window.

Infrared luminescence in bismuth-doped AgCl crystals.

Experimental and computer-modeling studies of the spectral properties of crystalline AgCl doped with metal bismuth or bismuth chloride are performed. The broad near-IR luminescence band in the 0.8-1.2 µm range with time dependence described by two exponential components corresponding to the lifetimes of 1.5 and 10.3 µs is excited mainly by 0.39-0.44 µm radiation. Computer modeling of probable Bi-related centers in the AgCl lattice is performed. On the basis of experimental and calculation data, a conclusion is drawn that IR luminescence can be caused by Bi+ ion centers substituted for Ag+ ions.

Centers of near-IR luminescence in bismuth-doped TlCl and CsI crystals.

A comparative first-principles study of possible bismuth-related centers in TlCl and CsI crystals is performed and the results of computer modeling are compared with the experimental data. The calculated spectral properties of the bismuth centers suggest that the IR luminescence in TlCl:Bi is most likely caused by Bi(+)···V(Cl)(-) centers (Bi(+) ion in thallium site and a negatively charged chlorine vacancy in the nearest anion site). On the contrary, Bi(+) substitutional ions and Bi(2)(+) dimers are most likely responsible for the IR luminescence in CsI:Bi.

Near-infrared luminescence in TlCl:Bi crystal.

Experimental and theoretical studies of spectral properties of crystalline TlCl:Bi are performed. Two broad near-infrared luminescence bands with a lifetime of about 0.25 ms are observed: a strong band near 1.18 µm excited by 0.40, 0.45, 0.70, and 0.80 µm radiation and a weak band at ≳1.5 µm excited by 0.40 and 0.45 µm radiation. Computer modeling of Bi-related centers in TlCl lattice suggests that a Bi(+)…VCl(Cl)(-) center (Bi(+) in Tl site and a negatively charged Cl vacancy in the nearest anion site) is most likely responsible for the IR luminescence.

Thulium-doped mode-locked all-fiber laser based on NALM and carbon nanotube saturable absorber.

We present a thulium-doped fiber laser mode-locked by a carboxymetylcellulose high-optical quality film with dispersed single-walled carbon nanotubes. Laser system based on the nonlinear amplifying loop mirror generates the shortest pulses earlier obtained in SWCNT mode-locked thulium-doped fiber lasers with a duration of 450 fs and 18 mW maximum average power at 1870 nm.

Transform-limited pulse generation in normal cavity dispersion erbium doped single-walled carbon nanotubes mode-locked fiber ring laser.

We demonstrate an erbium doped fiber ring laser mode-locked with a carboxymetylcellulose high-optical quality film with dispersed single-walled carbon nanotubes (SWCNT). The laser with large normal net cavity dispersion generates near bandwidth-limited picosecond inverse modified soliton pulses at 1.56 µm.

Bismuth-doped silica-based fiber lasers operating between 1389 and 1538 nm with output power of up to 22 W.

An efficient CW bismuth fiber laser operating around 1.46 µm with an efficiency of >50% and an output power of >20 W has been developed on a bismuth-doped GeO(2)-SiO(2) fiber. The laser demonstrates weak dependence of the output power on temperature in comparison with bismuth lasers operating near 1.15 and 1.3 µm. The laser generation has been obtained in the range 1.39 to 1.54 µm. The first linearly polarized bismuth-doped fiber laser at 1.46 µm based on a PANDA-type fiber has been demonstrated.

Combined excitation-emission spectroscopy of bismuth active centers in optical fibers.

For the first time, 3-dimensional luminescence spectra (luminescence intensity as a function of the excitation and emission wavelengths) have been obtained for bismuth-doped optical fibers of various compositions in a wide spectral range (450-1700 nm). The bismuth-doped fibers investigated have the following core compositions: SiO(2), GeO(2), Al-doped SiO(2), and P-doped SiO(2). The measurements are performed at room and liquid nitrogen temperatures. Based on the experimental results, the positions of the low-lying energy-levels of the IR bismuth active centers in SiO(2)- and GeO(2)-core fibers have been determined. Similarity of the energy-level schemes for the two core compositions has been revealed.

Laser diode pumped bismuth-doped optical fiber amplifier for 1430 nm band.

A 24 dB gain bismuth-doped fiber amplifier at 1430 nm pumped by a 65 mW commercial laser diode at 1310 nm is reported for the first time (to our knowledge). A 3 dB bandwidth of about 40 nm, a noise figure of 6 dB, and a power conversion efficiency of about 60% are demonstrated. The temperature behavior of the gain spectrum is examined.

Furnace chemical vapor deposition bismuth-doped silica-core holey fiber.

A bismuth-doped-pure-silica holey fiber is fabricated using a fiber preform made by the furnace chemical vapor deposition method. The spectroscopic properties of the fiber are studied, and laser action at λ=1450 nm with an efficiency of 12% is demonstrated.