20 W single-mode Yb3+ -doped phosphate fiber laser.

We report the demonstration of the first, to our knowledge, cladding-pumped continuous-wave Yb(3+)-doped phosphate-glass fiber laser. Phosphate hosts are of interest because they can be much more heavily doped than silica, and because of the possibility that they may have a higher photodarkening threshold. In an 84.6 cm double-clad fiber doped with 12 wt. % of Yb(2)O(3) and laser-diode pumped at 940 nm, nearly 20 W of single-mode 1.07 microm output power was generated with 60.2 W of absorbed pump power. The measured dependence of the output power on pump power is in excellent agreement with simulations.

Tunable mechanically induced long-period fiber gratings.

We report the experimental characterization of mechanically induced long-period fiber gratings (LPFG's) made by pressing a plate with periodic grooves against a short length of fiber. This filter, which is simple and inexpensive, exhibits transmission spectra and temperature stability similar to those of photoinduced LPFG's. It also offers the unique advantages of being tunable, erasable, and reconfigurable. Its polarization dependence also makes it useful as a polarizer, although it can also be eliminated with simple mechanical designs.

Absolute measurement of the second-order nonlinearity profile in poled silica.

Measurement of the thin nonlinearity profile of poled silica by the Maker fringe technique has been impossible because of total internal reflection (TIR) at the back surface of the sample. We demonstrate that this limitation can be removed by placing a prism against each face of the sample, thus avoiding TIR. This novel technique allows, for the first time to our knowledge, the nonlinearity profile of a thin film to be inferred by the Maker fringe technique. Applied to a silica sample thermally poled under standard conditions (275 degrees C and 5.3 kV for 30 min), it suggests a Gaussian profile with a 1/e width of 8 mum and a maximum d(33) of 0.34 pm/V.

Phase-sensitivity measurement of a 10-sensor array with erbium-doped fiber amplifier telemetry.

We report what are believed to be the first measurements of the phase sensitivity of a fiber sensor array using multiple low-gain remotely pumped amplifiers with an interferometric sensor inserted. The measured phase sensitivities for individual rungs average 5.7 microrad(rms)/ radicalHz and exhibit no dependence on rung number, in agreement with predictions.

Polarized superfluorescent fiber source.

We report the demonstration of a polarized superfluorescent fiber source (SFS) that increases the power output in the desired linearly polarized component by a factor of 1.76 over that of a standard, unpolarized SFS that uses the same pump power. This increase in efficiency is accomplished by insertion of a low-loss polarizer at an optimum point in the erbium-doped fiber of a standard SFS.

Large-scale interferometric fiber sensor arrays with multiple optical amplifiers.

We report what we believe to be the first laboratory prototype of a fiber sensor array using multiple low-gain (5dB) remotely pumped amplifiers in a 10-rung ladder structure. Incorporating amplifiers improves the system noise figure to less than 20dB, compared with 32dB in an optimized passive array of the same size. Scalability to more than 300sensors per fiber pair while a high dynamic range (1microrad/ sensitivity) is maintained is demonstrated.

Basis for a polarized superfluorescent fiber source with increased efficiency.

We propose to produce a superfluorescent fiber source (SFS) with a linearly polarized output by inserting a discrete polarizer near the middle of a polarization-maintaining Er-doped fiber. We show that with a relatively low-loss polarizer (<0.5 dB) the output power of the polarized SFS is predicted to approach that of a standard, unpolarized SFS, i.e., the power of the desired polarization mode is nearly doubled. The efficiency of this source depends weakly on the polarizer location and extinction ratio, although it depends strongly on its insertion loss.

Modeling of ion pairs in erbium-doped fiber amplifiers.

The effects of Er-Er pairs on the characteristics of Er-doped fiber amplifiers are analyzed theoretically. Pairs are found to have little effect on the amplifier optimum length, signal saturation power, and noise figure (at constant gain) but to cause significant reduction in the gain, even at residual levels, quantitatively consistent with fiber laser measurements. A maximum tolerable fraction of paired ions near 8%, corresponding to approximately 400 mole parts in 10(6) Er(2)O(3), is predicted for near-optimum gain efficiency in Al-Ge silica fibers.

Electro-optic phase modulation in a silica channel waveguide.

We report what is to our knowledge the first demonstration of electro-optic phase modulation in a fused-silica channel waveguide. The nonlinearity is induced through elevated temperature poling of an electron-beamirradiated waveguide. A phase shift of 32 mrad was measured at lambda = 633 nm for a device interaction length of 4.8 mm and an applied electric field of 7.3 V/microm.

Wavelength stability of a high-output, broadband, Er-doped superfluorescent fiber source pumped near 980 nm.

We report the dependence of the mean wavelength of Er-doped superfluorescent fiber sources on temperature, pump wavelength, and pump power. In particular, we measure an intrinsic temperature coefficient of between -2 and +8 parts in 10(6) (ppm) per degree Celsius depending on pump wavelength, pump power, and fiber length. Additionally, we report a pump wavelength dependence that is symmetrical about the peak pump absorption wavelength (near 976 nm) and a decrease in mean wavelength with pump power with a slope of between 0 and -93 ppm/mW.

Photorefractive-damage-resistant Zn-diffused waveguides in MgO:LiNbO(3).

Planar waveguides were fabricated by diffusing Zn into MgO:LiNbO(3) and LiNbO(3). Zn-diffused waveguides in MgO:LiNbO(3) guide both the ordinary and extraordinary polarization and have propagation losses at 633 nm in the range of 0.4-1.2 dB/cm. Single-beam-induced in-plane scattering due to photorefractive damage was not observed at 515 nm up to intensities of as much as 90 kW/cm(2).

Electronically tunable, 1.55-microm erbium-doped fiber laser.

An erbium-doped, silica-based fiber laser was electronically tuned over two ranges from 1529.6 to 1533.3 nm and from 1543.8 to 1563.0 nm with more than 13 mW of maximum power. The tuning element was an intracavity acousto-optic modulator (Bragg cell) configured to feed back the first-order, frequency-shifted deflected beam. The maximum optical/acoustic tuning coefficient was -15 nm/MHz.

Broad-spectrum, wavelength-swept, erbium-doped fiber laser at 1.55 microm.

We describe an argon-ion-laser-pumped erbium-doped fiber laser at 1.55 microm that incorporates low-rate frequency modulation of an intracavity acousto-optic modulator to provide repeated, continuous tuning of the output spectrum. The spectral width of this wavelength-swept fiber laser is as large as 20 nm with 9 mW of output power, even though erbium in silica has a mostly homogeneously broadened gain. The time-averaged visibility curve for a 14-nm-wide source indicates a short (160-microm) coherence length, which is of interest for fiber-optic gyroscopes that operate with long integration times and short-coherence-length sources.

Stable fiber-source gyroscopes.

We describe two new configurations of fiber gyroscopes that use superfluorescent fiber laser sources. In the first configuration we introduce a backward-pumping technique that achieves an order-of-magnitude increase in the power that can be launched into the gyroscope without instabilities. In the second configuration we employ the optical gain of the superfluorescent fiber laser source to amplify the signal returned from the gyroscope, obtaining an additional three-orders-of-magnitude increase in the optical power incident upon the detector, with an implication for simplification of the electronics. In both configurations, source beat-noise-limited rotation sensitivity is achieved.

Nd:MgO:LiNbO(3) continuous-wave laser pumped by a laser diode.

Diode-pumped laser oscillation was achieved in Nd:MgO:LiNbO(3). The absorbed pump power thresholds were as low as 1.9 mW for the high-gain or pi polarization and 8 mW for the low-gain polarization. A cw output power of 2 mW was obtained for the pi polarization at lambda = 1.085 microm for 9 mW of absorbed pump power. A slope efficiency of 37% was achieved. The diode-pumped Nd:MgO:LiNbO(3) lasers operated for extended periods of time without exhibiting any reduction in output power.