M. I. Belovolov

Record-peak-power all-fiber single-frequency 1550 nm laser

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.

Record peak power single-frequency erbium-doped fiber amplifiers

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.

Stabilisation of a radiation wavelength of a nanosecond fibre laser by a passive nonlinear loop mirror

A method for stabilising the radiation wavelength of a mode-locked fibre nanosecond laser is proposed and realised. Generation of nanosecond laser pulses with a spectral bandwidth of , which corresponds to a transform-limited pulse, is demonstrated.

Pulsed oscillation of a diode-pumped passively Q-switched Ca{sub 3}Ga{sub 2}Ge{sub 3}O{sub 12}:Nd{sup 3+} laser

Pulsed oscillation of a diode-pumped passively Q-switched Nd3+:Ca3Ga2Ge3O12 (Nd:CGGG) solid-state laser is studied. For the absorbed pump power of 0.8 W, the pulse energy was 3.5 μJ and the pulse rise time, duration and decay time were 6, 11 and 13 ns, respectively. The pulse repetition rate varied from 3 to 13 kHz when the absorbed pump power was changed from 0.45 to 1 W. It is shown that all the temporal parameters of the generated pulse decrease with increasing the absorbed pump power. The sensitivities of these parameters and the pulse repetition rate to changes in the absorbed pump power and the laser resonator length are measured. The results of the research are compared with the corresponding results for the pulsed Nd:YAG laser operating under the same conditions.

Diode-pumped solid-state Nd{sup 3+}:Ca{sub 3}Ga{sub 2}Ge{sub 3}O{sub 12} crystal lasers

Spectral, luminescent and laser parameters of Nd3+:Ca3Ga2Ge3O12 (Nd:CGGG) crystals are studied and compared with the corresponding parameters of Nd:YAG crystals. Continuous-wave spatially single-mode lasing in these crystals at a wavelength of 1.064 μm is investigated upon longitudinal diode pumping through an optical fibre and it is shown that the pump geometries being the same, the output power of a Nd:CGGG laser is close to that of a Nd:YAG laser. The effective cross section σ for induced transitions is measured, which is 1.4 × 10-19 cm2 for Nd:CGGG crystals. It is found that the 1.064-μm line of the Nd:CGGG laser is inhomogeneously broadened and has a fine structure of four distinct peaks conforming the spectroscopic data about the existence of four main types of activator Nd3+ ions in Ca3Ga2Ge3O12 crystals. The output power of 700 mW for the absorbed pump power of 2.7 W is obtained for a compact cw solid-state laser with the 1-mm thick active element. It is shown that the thermal distortions of the active element are the main mechanisms limiting the output power of a solid-state Nd:CGGG crystal laser.Spectral, luminescent and laser parameters of Nd{sup 3+}:Ca{sub 3}Ga{sub 2}Ge{sub 3}O{sub 12} (Nd:CGGG) crystals are studied and compared with the corresponding parameters of Nd:YAG crystals. Continuous-wave spatially single-mode lasing in these crystals at a wavelength of 1.064 {mu}m is investigated upon longitudinal diode pumping through an optical fibre and it is shown that the pump geometries being the same, the output power of a Nd:CGGG laser is close to that of a Nd:YAG laser. The effective cross section {sigma} for induced transitions is measured, which is 1.4 x 10{sup -19} cm{sup 2} for Nd:CGGG crystals. It is found that the 1.064-{mu}m line of the Nd:CGGG laser is inhomogeneously broadened and has a fine structure of four distinct peaks conforming the spectroscopic data about the existence of four main types of activator Nd{sup 3+} ions in Ca{sub 3}Ga{sub 2}Ge{sub 3}O{sub 12} crystals. The output power of 700 mW for the absorbed pump power of 2.7 W is obtained for a compact cw solid-state laser with the 1-mm thick active element. It is shown that the thermal distortions of the active element are the main mechanisms limiting the output power of a solid-state Nd:CGGG crystal laser. (active media. lasers)

Novel fiber optic acoustic sensor based on asymmetrically sensitive Sagnac interferometer

A novel configuration of a single-loop Sagnac interferometric acoustic sensor based on asymmetric desensitization of a half of the coil (loop) to phase modulation is presented. Sensitivity as high as 10-5 Pa at a maximum frequency response of ~8 kHz is demonstrated in underwater experiments.

Tunable single-frequency diode laser source for gas-analysis applications

This paper deals with development of novel single-frequency tunable diode laser with fiber-optic output for gas-analysis applications. The approach we proposed is convenient, simple and cheap solution for spectroscopy of a single absorption lines of any gases having absorption bands in the optical fiber transparency window (0,7 ÷ 1,7 μm). The presence of fiber-optic output is an additional advantage for remote sensing applications. The laser operation was demonstrated in the case of the line R7 of methane absorption band 2v3 at wavelength λ=1,645 μm. The mode-hop-free tuning range of 35 GHz (1,2 sm-1) was achieved.

High sensitive fiber optic accelerometer with laser readout

Fiber acceleration sensors based on one end fixed fiber sections as an elastic element with own seismic mass are developed and researched. It is shown, that by reading traversal deformations of oscillating fiber sections we are able to increase accelerometers sensitvity by orders in comparison to detection of a longitudinal oscillating fibers configuration changes, as it was taken in a number of works. For precision and non-inertial acceleration detection, it is suggested to apply single frequency laser coupled to Fabry-Perot interferometer. The measuring laser system based on the single frequency semiconductor laser with a narrow linewidth (λ=1.5 μm) and single mode optical fibres was created to demonstrate basic physical properties accelerometers. This system allows to detect one end fixed fiber sections small linear traversal bend deformations, caused by inertial force. Small dielectric 100% reflecting mirror with neglecting mass was fixed on the other fiber section end. The input/output fiber end was used as the second mirror. It could be placed in few centimeters from the first one. It is experimentally approved, that 20 mm length fiber section first resonant frequency is 300 Hz. Sensor is accelerometer at low frequecnies with sensitivity range (10-6 - 10-2) m/s2, and at higher frequencies (≥2 kHz) the sensor is vibrometer, which output is in proportion to sensor case displacement. Gain-frequency characteristic at 10 Hz - 10 kHz is measured. Multiplexed and 3-D sensors are mentioned as the next goal.

Luminescence of Nd-doped epitaxial single-crystal garnet films grown on Gd{sub 3}Ga{sub 5}O{sub 12} substrates

Epitaxial films with the atomic concentration of neodymium varied in the range from 1 to 15 % were grown on Gd3Ga5O12 substrates with the orientation (111) by the method of liquid-phase epitaxy from a PbO — B2O3 overcooled melt solution. The absorption spectra of the films are recorded and their luminescence spectra and luminescence lifetimes of active ions are measured upon diode laser pumping. The concentration dependence of the luminescence lifetime of Nd3+ ions is determined.Epitaxial films with the atomic concentration of neodymium varied in the range from 1 to 15 % were grown on Gd{sub 3}Ga{sub 5}O{sub 12} substrates with the orientation (111) by the method of liquid-phase epitaxy from a PbO - B{sub 2}O{sub 3} overcooled melt solution. The absorption spectra of the films are recorded and their luminescence spectra and luminescence lifetimes of active ions are measured upon diode laser pumping. The concentration dependence of the luminescence lifetime of Nd{sup 3+} ions is determined. (active media. lasers)

Single-mode fibers with an additional ring lightguide for two-channel data transmission

For the first time, two-channel concentric-core optical fibers consisting of a broadband central single-mode lightguide for the wavelength of 1.3 micrometers and a ring multimode lightguide, 10 micrometers in thickness, have been developed. The outer fiber diameter is 125 micrometers . The fibers are meant for two-channel communication systems. Optical losses of less than 1 dB/km for the both cores have been achieved, the channel-to-channel crosstalk being less than -40 dB. A dependence of optical losses in the ring lightguide on the radius of curvature and strain of a coiled fiber has been revealed. The optimal refractive index profile of the ring core has been found to minimize optical losses in coiled and straightened fibers. A fiber-optic communication link, 12 km in length, has been constructed, and the loss distribution along the link has been investigated using the OTDR-technique. It is shown that there is no distributed coupling between the two cores and the channels remain independent even at large distances.