A. N. Starodumov

All-fiber absolute temperature sensor using an unbalanced high-birefringence Sagnac loop

We demonstrate a highly sensitive temperature sensor based on a stress-induced high-birefringence-fiber Sagnac loop that uses a Nd-doped-fiber amplified spontaneous emission source. Relative temperature sensing is done in the spectral domain by shifts of a resonant wavelength lambda(r) and absolute temperature sensing by changes in separation between resonances Dlambda . The measured relative change of these parameters with temperature in the range 15-110 degrees C, is (1/lambda(r))(deltalambda(r)/deltaT) = -(1/Dlambda)(deltaDlambda/delta T) approximately (1/Dn)(delta Dn/deltaT)(-0.94 +/- 0.02) x 10(-3)/K, with measured fiber birefringence Dn = 8 x 10(-4) . This gives a wavelength-shift sensitivity of -1.00 nm/K at 1.065 microm and a resonance separation sensitivity of 0.006 nm/K for Dlambda = 6.8 nm . This telemetric point sensor has a loop length of 80 m, an operational bandwidth of more than 50 nm, and a temperature accuracy of better than 1 degrees C.

Blue and infrared up-conversion in Tm3+-doped fluorozirconate fiber pumped at 1.06, 1.117, and 1.18 μm

We report up-conversion in a fluorozirconate Tm3+-doped fiber pumped by the first and second Stokes components of a Raman-shifted Nd3+:YAG laser. Relative fluorescence in the ultraviolet, blue, red, and near-infrared regions is analyzed as a function of the intensity ratio between the Stokes components. It is demonstrated that side fluorescence in the blue at 480 nm strongly dominates over other transitions when pumping with the two Stokes components. This suggests that high-efficiency blue up-conversion lasing is possible by using this pumping scheme with double-clad, Nd3+- or Yb3+-doped fiber laser pumps.

Experimental demonstration of a Raman effect–based optical transistor

We demonstrate optical pulse switching and amplification based on simultaneous Raman and Kerr effects in a fiber-loop mirror. Stimulated Raman scattering is shown to play a dominant role in the transfer function of the loop with highly germania-doped fibers, in agreement with theoretical predictions. Optical switching of a 100-ps signal pulse with an amplification factor of 10 was demonstrated in a 20-mol.% GeO(2)-doped fiber.

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.

Continuous-wave measurement of the fiber nonlinear refractive index

We propose a technique for measuring the nonlinear refractive index of fiber based on transmission-coefficient measurements in a fiber Sagnac interferometer. In contrast with traditional methods, the proposed method uses a single optical source operating in cw mode and direct intensity measurement, enabling one to avoid the errors caused by fiber dispersion and uncertainty of spectral peak difference measurements that occur with pulse-based methods. The nonlinear refractive index in 20-mol. % GeO(2) fiber was measured to be (3.1 +/- 0.2) x 10(-16) cm(2) W(-1) at 1064 nm.

Application of the Z-scan technique to a saturable photorefractive medium with the overlapped ground and excited state absorption

Abstract Z-scan technique is applied to a saturable medium described by a generalized three-level scheme of photoexcitation in the condition of overlapping spectra of the ground and excited states. Correctness of the Z-scan data interpretation is analyzed in the framework of the model. The approach is applied for measuring the refractive indices Δn0 and n2 in polymer films containing bacteriorhodopsin.

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.

Temperature fiber sensor based on semiconductor nanocrystallite-doped phosphate glasses

We propose a temperature fiber sensor based on a CdSe semiconductor nanocrystallite-doped phosphate glass. For 6 nm semiconductor particles the reversible temperature-induced absorption edge shift is demonstrated in the range of 0 °C–150 °C. The prototype of the fiber sensor with sensitivity of 0.12 nm/K and a simple direct intensity detection scheme are reported.

NONLINEAR-OPTICAL MODULATOR FOR HIGH-POWER FIBER LASERS

We propose a novel nonlinear-optical fiber modulator for high-power (>1-W) single-mode fiber lasers. The device is based on transferring the amplitude modulation from a low-power signal at the Stokes frequency onto a high-power beam through stimulated Raman scattering. The efficiency and limitations of the Raman modulator when highly Ge-doped fiber is used is considered. An insertion loss of less than 0.4 dB and an extinction ratio of 20 dB are predicted for modulation of a 10-W single-mode Nd-doped fiber laser.