Valery N. Filippov

Cw-pumped erbium-doped fiber laser passively Q switched with Co 2+ :ZnSe crystal: modeling and experimental study

A novel scheme of an all-solid-state low-threshold passively Q-switched erbium fiber laser with a Co2+:ZnSe saturable absorber is demonstrated experimentally and simulated numerically.

Fiber-optic voltage sensor based on a Bi 12 TiO 20 crystal

A fiber-optic voltage sensor based on the longitudinal Pockels effect in a Bi(12)TiO(20) crystal is described. The use of a special backreflecting prism as a phase-retarding element is shown to improve the sensitivity and temperature stability of the sensor. A comparison between the temperature properties of the glass backreflecting prism and that of a quarter-wave plate is derived. The sensor demonstrates temperature stability of +/-1.5% from -20 degrees C to 60 degrees C and sensitivity of 0.145% per 1 V(rms) at 850 nm without the use of an additional temperature control channel.

Fiber sensor for simultaneous measurement of voltage and temperature

We report a new configuration of the fiber-optic voltage sensor based on the Bi/sub 12/TiO/sub 20/ crystal, which allows simultaneous measurements of both voltage and temperature. In our scheme, a quarter-ware plate, being an inherent element of voltage sensor, serves simultaneously as a phase-shifting element and as a temperature sensitive element. The sensor operates at two wavelengths (633 and 976 nm). The sensor has a linear temperature characteristic within the range of 10/spl deg/C-70/spl deg/C, providing the accuracy of temperature measurements of 0.3/spl deg/C. As a voltage sensor, this device has a linear amplitude characteristic up to 1000 V/sub rms/ and the excellent temperature stability of 0.1% within the temperature range of 10/spl deg/C.-70/spl deg/C.

Optically controlled fiber voltage sensor

We describe a fiber optic voltage sensor with optically controlled sensitivity. The sensor operates at two widely separated wavelengths (633 and 976 nm), one of which is a control signal (976 nm). We show that at a properly chosen wavelength of the control signal and of the phase-retarding element, variations of the power of the control signal allow increases or decreases in the sensitivity of the sensor. A theoretical analysis of sensitivity as a function of the optical power of a control signal is presented. We have demonstrated experimentally variation of the sensors sensitivity from 0.01% to 0 per 1 V/sub rms/ of control power changes in the range of 0-7 /spl mu/W.

Ground-state absorption saturation and thermo-lensing effect as main sources of refractive index non-linear change in Cr4+:YAG at CW 1.06 μm excitation

Non-linear change of refractive index in Cr 4þ :YAG is investigated experimentally by the Z-scan technique (CW case) at wavelength 1.06 lm. Theoretical analysis of the processes resulting in non-linear refraction in Cr 4þ :YAG allows one to conclude that the main contributions in non-linear change of the crystal refractive index are the effect of Cr 4þ centers population perturbation due to ground-state (GS) absorption saturation and the thermo-lensing effect. 2002 Published by Elsevier Science B.V.

Application of CdSe-nanocrystallite-doped glass for temperature measurements in fiber sensors

A temperature fiber sensor based on CdSe-nanocrystallite- doped phosphate glass as a sensing element is reported. This glass is shown to exhibit a reversible temperature-induced absorption edge shift at temperatures less than the annealing temperature of the glass (,370°C). A dual-wavelength detection scheme based on a reflective grating and bi-cell photodiode is employed to eliminate the effects of variable signal losses in the intensity-dependent sensor. A sensor proto- type, tested in the temperature range of 220 to 1120°C, is shown to exhibit a linear response to temperature variations.

Stress distribution and birefringence measurement in double-clad fiber

Abstract Modal birefringence and stress distribution measurements in a single-mode double-clad Nd +3 -doped fiber are reported. The contribution of different mechanisms, such as stress-induced birefringence, bending and core ellipticity, to the total birefringence is determined for a fiber wound onto a drum. A stress distribution pattern in the cross-section of the fiber is presented. The stresses are shown to be applied to a fiber core along the cladding minor axis.

Fiber optic voltage sensor with optically controlled sensitivity

Abstract A fiber optic voltage sensor operating at two widely separated wavelengths (633 nm – probe radiation and 976 nm – control laser) with optically controlled sensitivity is presented. The modulation depth of the sensor is calculated as a function of the probe-to-control laser power ratio, orientation angle and thickness of a phase plate. We have demonstrated experimentally the continuous changes of sensitivity from 0.01 to 0 and back to 0.008% per V rms varying the control power from 0 to 55 μ W.

Birefringence measurement in double-clad fiber lasers with large cross section

We report on birefringence measurements in double-clad fibers with large cross section, doped with neodymium and ytterbium. The experimental results for rectangular double-clad fibers are compared with those for single-clad circular neodymium-doped fibers, taking into account existing models of stress- and geometry-induced birefringence. We demonstrated that the ellipticity of an outer silica cladding has no effect on birefringence in large-area double-clad fibers. The stress-induced birefringence is shown to depend on the ratio between the diameter of an internal silica support and the linear dimensions of the rectangular outer cladding. The stress-distribution pattern is derived to prove the experimental results.

Raman effect contribution to cross-phase modulation in nonpolarization-preserving fibers

The contribution of the Raman effect to the cross-phase modulation (XPM) strength in fibers with randomly varying birefringence is calculated taking account of different symmetry rules for the Kerr and Raman susceptibilities. The averaging factors for the Kerr contribution to the nonlinear index are shown to be different from those for the parallel and perpendicular Raman contributions. The XPM strength is calculated as a function of a frequency shift between pulses, and a fiber core composition for a randomly polarized and depolarized light. In pure silica fibers, the XPM coefficient is shown to decrease more than 27% at the peak of the Raman gain compared to the case of co-polarized waves in polarization-preserving fibers.