S L Semenov

Optical gain and laser generation in bismuth-doped silica fibers free of other dopants

Luminescence emission and excitation spectra of bismuth-doped silica optical fibers free of other dopants have been obtained to construct an emission-excitation map in a wide wavelength range of 400-1600 nm. The main low-lying energy levels of the bismuth active centers in such fibers have been determined. For the first time (to our knowledge), optical gain and lasing have been obtained in such fibers. A gain of 8 dB has been achieved with a pump power of 340 mW, and a cw fiber laser emitting at 1460 nm with an output power of 40 mW and an efficiency of ≈3% has been created.

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.

Composite laser fiber with Yb, Er co-doped phosphate glass core and silica cladding

This letter is devoted to fabrication and tests of an optical fiber with a phosphate glass core in a silica cladding. The fiber preform was made by melting Yb, Er co-doped phosphate laser glass in a high-purity silica tube. 1.54 μm laser action was demonstrated under 1.06 μm pumping into the Yb absorption band.

High-aperture optical waveguides based on fluorine-doped silica glass

The dependence of fluorine incorporation into silica glass on conditions of the optical waveguide blank manufacture using the method of modified chemical vapor deposition (MCVD) is studied. The degree of fluorine incorporation at constant consumption of a fluoridizer (SiF4) is shown to increase with an increase in the volume of deposited material. Samples of multimode optical waveguides with a core from pure silica glass and a reflective coating made of fluorine-doped silica glass with a numerical aperture of ∼0.18 are obtained. Optical losses in such optical waveguides reach 0.5 dB/km in the long-wavelength region of the spectrum.

Wheat Lectin Possibly Serves as a Signal Molecule in the Azospirillum - Wheat Association

Addition of a wheat lectin (wheat germ agglutinin, WGA) to the Azospirillum brasilense Sp 245 culture was shown to induce not only the previously reported enhancement of N2-fixation, ammonia excretion, and indole-3-acetic acid production, but also protein biosynthesis in the cell. Also, variation in the acidic phospholipid proportion in the membrane was noted. The proposals that the observed effects could occur naturally and that WGA might serve as a signal molecule in the Azospirillum-wheat association are discussed.

MW peak power diffraction limited monolithic Yb-doped tapered fiber amplifier

Chirped pulse monolithic fiber amplifier based on a newly developed tapered polarization maintaining Yb-doped fiber has been developed and optimized. A novel amplification regime in a relatively long (220 cm) tapered fiber of improved design, which has been theoretically predicted, allowed us to achieve an ultimate high peak power. In this regime, the signal propagates most of the fiber without amplification and growths very rapidly only in the last 80 cm of the tapered fiber, which has a mode field area of approximately 1000 μm2 near the output. We have demonstrated amplification of 20 ps chirped pulses centered at 1056-nm with spectral width of 20 nm to 0.7 MW peak power directly from the tapered fiber amplifier. The pulses had a diffraction limited quality (M2 ~ 1.124) and could be compressed down to 350 fs with 50% efficiency. In addition, amplification of narrow-band 9 ps pulses centered at 1064 nm to a peak power of 1.8 MW directly from the tapered fiber amplifier was demonstrated.

Phase Separation and Crystallization of Phosphate–Silicate Glass Cores of Preforms of Fiber Optics

The phase separation and the emergence of nanocrystalline inclusions in phosphate–silicate preforms for optical fibers activated with ytterbium, which are obtained by the powder sintering methods with the vibrational mixing of the melt and the addition of ytterbium-containing nanoparticles into preforms, are studied. Nanocrystals of YbPO4, SiO2, and YbP3O9 are formed in the preforms in the low-temperature areas of the powder sintering process when using either of the methods. It is concluded that the phosphates are crystallized as a result of the phase separation from the glass phase enriched with ytterbium.

1.5 MW peak power diffraction limited monolithic Yb-doped tapered fiber amplifier

High peak power lasers are of great importance for a wide number of applications like material processing, remote sensing and etc. The most impressive, and still record, result has been demonstrated with using of photonics crystal fibers (PCFs), where amplification to more than 1 MW peak power directly from amplifier was demonstrated [1, 2]. However such fiber are difficult in production, handling and requires use of bulk optics, that negates the benefits of truly all-fiber systems. For this reason, the development of alternative LMA design is still very actual task. One of the promising one is the tapered step-index fiber [3, 4]. Such fibers have robust single-mode (SM) input end part (to couple signal) and a very big core and outer diameters output end part. The output signal end is formally highly multi-mode, but slowly increasing diameter along the tapered fiber, ensuring of adiabatic enlargement of fundamental mode and suppress excitation of high order modes. A larger first cladding diameter at the output tapered fiber end makes possible counter-pumping using a low-brightness cheap pump diodes. Recently we have demonstrated chirped pulse amplification system, with final cascade based on Yb-doped PM fiber, generating diffraction limited (M2<1.2) 5-ps pulses at 1057-nm with 0.5 MW of peak power and 7-ps pulses at 1035-nm with 100 kW of peak power, which were compressed down to 130-fs with 60% efficiency [4].

Phosphate glass core and silica cladding laser fiber

The goal of the present work is to develop a composite Yb-Er doped optical fiber that combines the advantages of both phosphate and silica glasses. In the lasing experiment the output fiber of 4W at 1064 nm laser was spliced with high-reflective fiber Bragg grating having resonance wavelength 1535 nm with core diameter corresponding to the Yb-Er fiber. The grating was then spliced with Yb-Er fiber having the length of 0.9 m. The Yb-Er laser resonator was formed by the Bragg grating and cleaved fiber end. Maximum output power of 130 mW and the slope efficiency 4% were obtained. Relatively small efficiency value in the first experiment can be explained by high splice connection losses. Thus an optical fiber with Yb-Er co-doped phosphate glass core in a silica cladding was fabricated. 1.54 μm laser action in it was demonstrated under core pumping into Yb absorption band.

Optical losses in single-mode and multimode fibres heavily doped with GeO{sub 2} and P{sub 2}O{sub 5}

Optical losses in single-mode and multimode optical fibres heavily doped with germanium oxide and phosphorus oxide are studied. Optical losses in multimode fibres in a broad spectral range are found to be much lower than in single-mode fibres with the same concentration of dopants. The study of few-mode fibres showed that the core — cladding interface is the region of excess optical losses. The reasons for the observed relation between optical losses in single-mode and multimode fibres are discussed.