Sergei A. Vasiliev

Laser-diode-pumped phosphosilicate-fiber Raman laser with an output power of 1 W at 1.48 mum.

An all-fiber 1.48-mum generator based on a laser-diode-pumped Yb-doped double-clad laser and a cascaded Raman wavelength converter has been developed. Second-order Raman Stokes radiation was generated in a phosphosilicate-fiber resonator formed by two pairs of Bragg gratings. A slope efficiency of the Raman converter of 48% with respect to the power emitted by the double-clad Yb laser has been achieved. We obtained an output power of 1 W at a slope efficiency of 34% with respect to the laser-diode array power, with a total optical-to-optical efficiency of 23%.

Tunable loss filter based on metal-coated long-period fiber grating

An all-fiber electrically tunable loss filter that is based on photoinduced long-period grating coated by Ti-Pt metal coating was developed and investigated. Maximum wavelength tuning of 11 nm with an applied power of 0.67 W was achieved for the HE17 cladding mode resonance peak.

Postfabrication resonance peak positioning of long-period cladding-mode-coupled gratings

A simple, flexible method of postfabrication positioning of resonance wavelengths of long-period cladding-modecoupled gratings is proposed. This method is based on changing the outer fiber diameter. Reducing the diameter by etching the fiber in HF acid shifts the loss peaks to higher wavelengths. A shift as large as 130 nm after 5 min of HF etching was observed for our strongest grating peak, corresponding to the cladding mode HE19. The experimental results are in excellent agreement with model calculations.

Refractive-index gratings written by near-ultraviolet radiation

This is the first report, to our knowledge, of refractive-index grating side writing in 10 mol.% GeO(2)-doped fiber by the near-UV light of a cw Ar(+) laser (333-364 nm). An induced-index magnitude as large as 1.9 x 10(-4) at 1.7x10(5) W/cm(2) UV power density has been achieved. The observed gratings have exhibited the same temperature stability as gratings written by a KrF excimer laser (248 nm).

Germania-glass-core silica-glass-cladding modified chemical-vapor deposition optical fibers: optical losses, photorefractivity, and Raman amplification

Germania-glass-core silica-glass-cladding single-mode fibers (deltan as great as 0.143) with a minimum loss of 20 dB/km at 1.85 microm were fabricated by modified chemical-vapor deposition. The fibers exhibit strong photorefractivity, with type IIa index modulation of 2 x 10(-3). A Raman gain of 300 dB/(kmW) was determined at 1.12 microm. Only 3 m of such fibers is sufficient for constructing the 10-W Raman laser at 1.12 microm with a 13-W pump at 1.07 microm.

Long-period refractive index fiber gratings: properties, applications, and fabrication techniques

The article overviews the main properties, fabrication techniques and ares of application of long-period fiber gratings. The basic theoretical equations describing spectral properties of the gratings are given. Experimental investigation of the cladding modes excited by long-period gratings, as well as sensitivity of the long-period grating spectrum to external perturbations are discussed. The most common fabrication techniques of long-period gratings are examined with reference to their advantages and disadvantages. The most important applications of long- period gratings are discussed. Particular attention is paid to the recent results obtained with participation of the authors.

Yb3+-doped double-clad fibers and lasers

We present results of the research and development of double-clad Yb3+-doped fibers for high-power fiber lasers. The quality of the fabricated fibers and optimization of reflecting Bragg gratings allowed us to demonstrate fiber lasers with a quantum efficiency close to 90%. These fiber lasers were used in Raman converters emitting at various wavelengths.

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.

Fiber-optic dosimeter based on radiation-induced attenuation in P-doped fiber: suppression of post-irradiation fading by using two working wavelengths in visible range

The design of a fiber-optic dosimeter, which determines the radiation dose from the difference of radiation-induced attenuation (RIA) Δα measured in a P-doped silica fiber at λ = 413 and 470 nm, is presented along with its first test results under gamma-radiation (dose rates 0.00064 and 0.0066 Gy/s, maximal dose ~2Gy). The dose-dependence of Δα as well as of RIA at individual wavelengths is found to be well described by a power law, the exponent lying in the range 0.90-0.94. In contrast to RIA at individual wavelengths, Δα is found not to depend on dose rate and to decay only slightly on termination of irradiation. Therefore, using Δα for dosimetry is argued to be more promising.

Annealing of UV-induced fiber gratings written in Ge-doped fibers: investigation of dose and strain effects

Effects of UV-dose and fiber strain on annealing properties of fiber gratings written in Ge-doped fibers have been experimentally investigated. A new band in the distribution of the activation energy of the grating thermal decay with a center at 2.9 eV has been observed.