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A new design of a single-frequency fibre laser at a wavelength of 1.55 μm with linearly polarised output radiation is developed and investigated, in which a uniform Bragg grating written in an SMF-28 fibre is used as one mirror and the other mirror is a grating written in a Panda fibre with a small overlap of reflection spectral bands of mirrors and the possibility of fine tuning of the lasing spectral line. The length of the active part of the laser cavity formed by a fibre doped with the low-concentration Er3+ erbium ions is 10 cm. At a pump power of 60 mW and a wavelength of 1.48 μm, the lasing power reaches 100 μW and the width of the spectral line is less than 100 kHz.

A single-mode fibre based on bismuth-doped germanosilicate glass with a high germanium concentration is considered as an active medium of a laser continuously tunable within the range 1.65 – 1.8 μm. The laser scheme included a broadband ring cavity, and the laser wavelength was controlled by an external plane diffraction grating in the Littrow configuration. For a pump power of 300 mW at a wavelength of 1.564 μm, the maximum output laser power was 15 mW in the zero diffraction order and 6 mW at the fibre output.

An experimental setup with a laser fiber optic probe has been developed, and the vibration dynamics of the vocal folds (VFs) in the larynx of rabbits have been studied. VF vibrations were excited by a variable pressure air stream. We found that, at an air flow pressure of 50 to 60 mm Hg, VFs generate a white vibration noise in the frequency range of 100 Hz to 10 kHz. The spectrum of excited vibration frequencies becomes narrower when the air flow pressure decreases from 10 to 20 mm Hg, and three discrete lower fundamental frequencies of intrinsic mechanical vibrations of individual VFs are excited at about 360, 750, and 1100 Hz, simultaneously with narrow peaks in the high-frequency region at about 3, 6, and 8 kHz, respectively. The characteristic discrete vibration frequencies of VFs are most efficiently excited near the air flow exhaustion at a pressure of 1 to 5 mm Hg. We detected a difference in the fundamental frequencies of the excited vibrations between intact VF and those treated for a scar defect in one of the VFs. The frequencies of the lowest intrinsic excited modes of the treated VF are slightly higher compared with untreated (intact) VF. The increase in the vibration frequencies may be explained by the growth of VF’s stiffness related to the formation of scar tissue. The mentioned frequency difference was registered with confidence and may serve as a basis for a mildly invasive instrumental diagnostics in the therapy of VF disorders as an aid to a traditional examination and subjective assessment of VF states.

A Bismuth-doped fiber laser tunable in the new wavelength range 1360-1510 nm with the output power 50 mW has been developed for the first time. The tuning of the laser was carried out by rotating diffraction grating.

Raman-fiber source emitting 1450 nm with a power of 1 W was realized. The application of the commercially available pump source with an output power of 35 W allows one to increase the output power up to 5 W. The emission wavelength corresponds to the water absorption band therefore it is promising laser for the surgery and other medical applications.

In this work we present results on the amplification of narrow-linewidth nanosecond pulses in a recently developed ytterbium-free erbium-doped large mode area fiber cladding pumped at 980 nm. At first, a co-propagating all fiber amplifier scheme was used. Using 1 m of active fiber length in such configuration a peak power of 4 kW limited by instabilities caused by stimulated Brillouin scattering (SBS) was achieved. To the best of our knowledge this is the highest peak power ever reported for single-frequency single mode silica-based fiber sources near 1550 nm. Then all fiber counter-pumped configuration with 6 m of active fiber was used and peak power of 900 W was obtained. In this case peak power was limited by SBS generation in a passive fiber at the laser output. Slope electrical-to-optical conversion efficiency of 8 % demonstrated in such scheme is a record value for kW-level single mode single-frequency Er-doped nanosecond fiber lasers.

We have realized ytterbium fiber laser emitting at 1160 nm. To avoid a competition with a spontaneous lasing at shorter wavelengths we pumped laser into the core at wavelength of 1070 nm. Cladding pumped Yb-laser was used as a pump source. Also, the active fiber was heated up to 70°C to increase the absorption of the pump power and suppress the spontaneous emission. The lasing efficiency slope of 45% was measured. A maximum output power of 3.2 W was achieved.

We have realized and studied the fiber laser based on 4-core Yb-doped fiber and multimode Bragg grating as the input reflector. The lasing efficiency slope of 55% was measured. An investigation of the output emission has shown that the far-field pattern constitutes an interference picture. That allows us to conclude that the multimode Bragg grating provides phase locking of 4 lasers utilizing the different active cores. A coherent length of laser is longer than possible difference between optical ways of different active cores.

A two-stage Raman fibre converter (1.089/1.273/1.533 μm) based on a P2O5-doped silica fibre is fabricated and studied. The spectral broadening of the first Stokes component is investigated. The Raman converter is simulated numerically. By using the experimental data, the method of Raman converter simulation is improved by taking into account the additional power loss of the first Stokes component. The results of calculations by the improved method are in good agreement with the experiment. It is shown that the additional power loss of the first Stokes component results in a change in the region of the optimal resonator length from 300–600 m to 600–800 m.

A fibre Raman amplifier operating at a wavelength of 1.65-μm is fabricated. A two-stage phosphosilicate fibre Raman converter of 1.53-μm radiation for pumping the Raman amplifier is designed and tested. The amplifier pumped by a phosphosilicate fibre Raman converter can operate with a maximum of the gain band ranging from 1.6 to 1.7 μm. A fibre with a core of a high (25%) molecular content of GeO2 serves as an active medium for the Raman amplifier. The gain obtained for different powers of the input signal is 22 — 25 dB. Our calculations show that the use of a standard telecommunication fibre (with a lower content of GeO2) allows one to increase the gain in this scheme by reducing fibre splicing losses.

We present an experimental test of a recently published model that describes a nested fiber Raman cavity taking into account all interactions between forward and backward traveling waves. The experiment consists in the realization of a one-stage fiber Raman laser, pumped at 1090 nm, using one Stokes shift to produce output radiation at 1150 nm. The conversion efficiency measured as a function of input power and fiber length is successfully compared with the numerical results. We also apply the model to the comparison between the performance of phosphosilicate (PS) and germanosilicate (GS) fibers. We have considered a five-step Raman laser using a GS fiber with a 1117 nm pump, and a two-step Raman laser using a PS fiber with a 1061 nm pump, both emitting at 1480 nm. In the optimum configuration, the simpler PS fiber laser presents a conversion efficiency about 15% lower than that of the GS fiber laser and uses a fiber length 40% larger.

We have designed and implemented a new fibre-optic phase-sensitive coherent reflectometer configuration, which allows one to avoid signal fading owing to the use of a two-fibre scattered-light interferometer.

We present a single-frequency nanosecond all-fiber amplifier based on a specially developed single-mode large mode area double-clad Erbium-doped fiber. We have demonstrated a record peak power of 3.5 kW before the onset of SBS.

Yb-doped cladding-pumped fiber laser with linearly-polarized output emission was realized. To obtain linear-polarization operation we have applied Bragg grating written in the fiber with high birefringence as the input reflector. The polarization extinction ratio was of 17 dB. A maximum output power of 12 W was achieved with an efficiency slope of 69%. The laser linewidth was less than 0.1 nm even for maximum output power.

All-fiber Raman fiber source emitting at 1254 nm was realized. For the first time to pump Raman converter we have applied Yb:Bi pulsed fiber laser. The P-doped fiber was used as an active medium of the Raman converter. The conversion slope efficiency of 70% and the peak power of 12 W were observed.

A model of a sensor of an external action on a fibreoptic cable used in extended-perimeter security systems with localisation of the action site is developed. The detection principle is based on phase-sensitive reflectometry with the use of a narrowband pulsed radiation source. The model has a high sensitivity inherent in interference sensors. The maximum detection range and spatial resolution are 35 km and 5 m, respectively.

We have realized a compact Bragg grating based Ho3+ fiber laser emitting at 2.1 μm with a CW output power of 2 W. The laser is pumped by an Yb3+ fiber laser at 1.12 μm, the latter laser being based on a GTWave active fiber pumped by two semiconductor modules with a maximum power of 25 W at 0.98 μm.

We have made a compact fiber pulsed source based on a self Q-switched Yb-doped fiber laser with an additional amplification. The output pulse energy of 0.17 mJ has been achieved with a pulse duration of several tens nanoseconds. The repetition frequency of 20 kHz and the maximum average output power of 3 W were observed.

A pulsed fibre laser is fabricated which is based on an active fibre with a multielement cladding and an additional single-mode fibre providing nonlinear feedback. The peak output power of the laser is ~1 kW for 20-ns pulses. The emission spectra of the laser with additional fibres having different nonlinear and dispersion properties are investigated.

We have realized a set of multimode lasers based on a double-clad Yb-doped fiber and Bragg gratings written on a graded-index multimode fiber. Efficient laser operation in the spectral range of 1.03-1.09 μm has been observed. Spectral characteristics of the laser emission have been investigated.

A new scheme of a fibre Raman laser emitting at two wavelengths is proposed. The scheme uses a one-stage Raman converter with the output Bragg grating with the reflectivity above 99%. Lasing at two wavelengths is achieved due to the overlap of the output emission spectrum with the reflection spectrum of the output Bragg grating.

A high power erbium-doped fibre amplifier pumped by single-mode radiation at 1478 nm is fabricated and tested. A Raman converter based on a fibre with a phosphosilicate core was used as the pumping source. The maximum output power achieved in spectral ranges C (1.53 — 1.56 μm) and L (1.56 — 1.60 μm) is 28 dBm.

A set of diode-pumped fibre lasers producing a cw output of 4–7.5 W in the range from 1.05 to 1.15-μm is realised on the basis of an ytterbium double-cladded fibre. The output of the ytterbium fibre laser was used to pump a Raman phosphor-silicate fibre converter, resulting in fibre lasers producing a cw output power of more than 3 W at 1.26 and 1.3-μm.

The impact of intra-cavity Stokes wave broadening on the performance of P2O5-doped fibre lasers is investigated. It is shown that nonlinear broadening of the radiation strongly affects laser performance and optimal configuration of the cavity.

A study was made of the use of single-mode fiber ring interferometers in narrowing the emission lines of semiconductor lasers and increasing the optical radiation power. Efficient coupling of radiation, emitted by a multifrequency injection laser with an external resonator, into a fiber ring interferometer was achieved both under cw and mode-locking conditions. Matching of the optical lengths of the external resonator and the fiber interferometer made it possible to determine the mode width for this laser. A method for generation of optical pulses in a fiber ring interferometer from cw frequency modulated radiation was developed.

We present results of the research and development of CW fiber lasers with reflectors based on multimode fiber Bragg gratings. Considered laser schemes used cladding pumped active fibers as an active medium. We have shown that multimode fiber gratings written in the graded index multimode fiber can be used to form the cavity of different types of the fiber lasers. In particularly we have fabricated single mode and multimode lasers based on all-silica and polymer coated double-clad active fibers. The realized lasers were based on Yb-doped fibers having an emission band between 0.98 and 1.1 μm, and based on Er-doped fiber with an emission wavelength near 1600 μm.

We report a development of Raman fiber source potentially operating in 1.6-1.75 /spl mu/m region in which typical rare-earth doped fiber lasers do not cover. The output power of 1.2W at 1.649 /spl mu/m is achieved.

An all-fiber 1.48-/spl mu/m generator based on a LD-pumped Yb-doped double-clad laser with intracavity Raman wavelength conversion has been developed. Second-order Raman Stokes radiation was generated in a phosphorosilicate-resonator formed by two pair of Bragg gratings.

A high output power EDFA, based on the single-mode heavily aluminum co-doped active fiber, pumped at 1.48 /spl mu/m was fabricated and tested. A Raman converter based on single-mode P-doped fiber, having maximum output power equal to 900 mW, was applied as a pump source. A maximum output power as high as 28 dBm was achieved for the C-band signal and L-band signal as well.

Summary form only. We pump the Ho/sup 3+/-doped fiber laser into the core using a high-power double-clad Yb/sup 3+/-doped fiber laser operating at 1.15 /spl mu/m. This wavelength corresponds to a sufficiently strong absorption band of Ho/sup 3+/ ions due to the laser transition. Also we use a Bragg grating with a resonance wavelength of 2 /spl mu/m as the input mirror of the laser.

In this work we have tested characteristics of EDFA based on a single-mode Er-doped fiber, pumped at 1480 nm by two-stage Raman fiber converter. As an active media of Raman fiber converter a single-mode fiber with phosphorus doped core was used. The conversion efficiency of Raman converter was measured to be 36%. Output power of EDFA as high as 26 dBm was achieved at wavelengths 1554 and 1582 nm corresponding to C and L-band of WDM systems.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper, we present results on the amplification of 2 MHz linewidth nanosecond pulses in a recently developed ytterbium-free erbium-doped large mode area fiber cladding pumped at 980 nm. A record peak power of 4 kW for single-frequency single-mode silica-based fiber sources near 1550 nm is demonstrated. Pulse instabilities arising in an all-fiber laser scheme from stimulated Brillouin scattering are described.

A multicascade femtosecond supercontinuum source based on a holmium-doped fiber amplifier was demonstrated. Maximum average power was approximately 400 mW and concentrated in the range from 1950 to 2150 nm. The shape of the output spectrum was controlled by the pump of the holmium-doped fiber amplifier.

A 1.43 micrometers fiber laser with an output power of 1.4 W is reported. The laser is based on Raman conversion of the Yb- fiber laser emission in a phosphorous doped fiber. The light conversion is based on both phosphorous and silica Raman shifts in the same P-doped fiber. This device can find medical applications, since its emission wavelength coincides with one of the water absorption bands.

We present results of the research and development of double-clad Yb 3+ -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.

A 2-μm broadband radiation source based on a fibre doped with holmium ions, which is pumped by a 1.12-μm ytterbium fibre laser, is developed. The maximum output power of 8 mW is achieved for the emission spectrum width of 45 nm.

A multimode cladding-pumped erbium-doped fibre laser is described. The maximum output power and the slope efficiency of the laser at 1.6 μm are 4.2 W and 30%, respectively.

An efficient cladding-pumped Yb-doped fibre laser with a Bragg grating written in a multimode graded-index fibre is fabricated for the first time. The laser emits one transverse mode with a slope efficiency of 60%. The resonator design proposed in the paper can be used for the development of high-power fibre lasers with an increased fibre core diameter.

A broadband radiation source emitting in the 1.03 — 1.1-μm spectral region is built. The −3-dB level width of the emission spectrum of the source is 47 nm at the maximum output power of 22 mW. An Yb-doped fibre twisted with a passive fibre is used as the active medium in the source. The source is pumped through the passive fibre.

Ytterbium-ion-doped double-clad optical fibres were developed. The differential quantum efficiency of a diode-pumped fibre laser, fabricated on the basis of such optical fibres with a fibre Bragg grating, was 90%.

Parameter optimisation of a two-stage Raman converter based on phosphosilicate-core fibre is presented. The optimal operational regime is determined and its tolerance against variations of laser parameters is examined. Results of numerical modelling are in a good agreement with experimental data.

For the first time an Ho/sup 3+/ silica fibre laser has been realised using a Bragg grating as the input coupler and a fibre pump source at 1.15 /spl mu/m. The output power of 280 mW at 2 /spl mu/m is to the authors' knowledge the highest value reported so far for Ho/sup 3+/ silica fibre lasers.

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%.

A pair of coupled step-index waveguides is analyzed. Characteristic equations are obtained and used to evaluate the cutoff frequencies and coupling constants. Mode transformation at tapers is analyzed. The spectral properties of fused couplers and tapered filters for which cutoff frequencies of higher modes were observed are studied. A fiber polarization splitter is realized. A semiconductor laser with an external dispersive cavity based on the spectral selective coupler is designed. >

A report is given of the fabrication of the first semiconductor laser with an external dispersive resonator in which a loop fiber reflector with a selective fused single-mode coupler is employed as a frequency discriminator. Single-mode emission and tuning of the emission frequency are reported for this laser.