New method for residual amplitude modulation control in fibered optical experiments.

When locking the frequency of a laser to an optical cavity resonance, the residual amplitude modulation (RAM), which accompanies the phase modulation necessary to build the error signal, is a major limitation to the frequency stability. We show that the popular method demonstrated by Wong and Hall to cancel this effect, based on the measurement of the RAM using an auxiliary detector, is limited in the case of optical setups exhibiting polarization dependent losses and an imperfect polarizer at the modulator output, such as guided-wave optical systems.We propose and demonstrate a new method, using a single photodetector, to generate the two error signals and demonstrate its usefulness in the case of fibered systems.

Rotation measurements using a resonant fiber optic gyroscope based on Kagome fiber.

We build a resonant fiber optic gyro based on Kagome hollow-core fiber. A semi-bulk cavity architecture based on an 18-m-long Kagome fiber permits achieving a cavity finesse of 23 with a resonance linewidth of 700 kHz. An optimized Pound-Drever-Hall servo-locking scheme is used to probe the cavity in reflection. Closed-loop operation of the gyroscope permits reaching an angular random walk as small as 0.004°/h and a bias stability of 0.45°/h over 0.5 s of integration time.

Experimental demonstration of a dual-frequency laser free from antiphase noise.

A reduction of more than 20 dB of the intensity noise at the antiphase relaxation oscillation frequency is experimentally demonstrated in a two-polarization dual-frequency solid-state laser without any optical or electronic feedback loop. Such behavior is inherently obtained by aligning the two orthogonally polarized oscillating modes with the crystallographic axes of a (100)-cut neodymium-doped yttrium aluminum garnet active medium. The antiphase noise level is shown to increase as soon as one departs from this peculiar configuration, evidencing the predominant role of the nonlinear coupling constant. This experimental demonstration opens new perspectives on the design and realization of extremely low-noise dual-frequency solid-state lasers.

Thickness dependent sensing mechanism in sorted semi-conducting single walled nanotube based sensors.

Single walled carbon nanotube (SWCNT) networks present outstanding potential for the development of SWCNT-based gas sensors. Due to the complexity of the transport properties of this material, the physical mechanisms at stake during exposure to gas are still under debate. Previously suggested mechanisms are charge transfer between gas molecules and SWCNT and Schottky barrier modulation. By comparing electrical measurements with an analytical model based on Schottky barrier modulation, we demonstrate that one mechanism or the other is predominant depending on the percolation of metallic carbon nanotubes. Below the metallic SWCNT percolation threshold, sensing is dominated by the modulation of the Schottky barrier, while above this threshold, it is only attributed to a charge transfer between SWCNT and gas molecules. Both mechanisms are discussed in terms of sensitivity and resolution leading to routes for the optimization of a gas sensor architecture based on highly enriched semiconducting carbon nanotube films.

Solid-state ring laser gyro behaving like its helium-neon counterpart at low rotation rates.

Nonlinear couplings induced by crystal diffusion and spatial inhomogeneities of the gain have been suppressed over a broad range of angular velocities in a solid-state ring laser gyro by vibrating the gain crystal at 168 kHz and 0.4 microm along the laser cavity axis. This device behaves in the same way as a typical helium-neon ring laser gyro, with a zone of frequency lock-in (or dead band) resulting from the backscattering of light on the cavity mirrors. Furthermore, it is shown that the level of angular random-walk noise in the presence of mechanical dithering depends only on the quality of the cavity mirrors, as is the case with typical helium-neon ring laser gyros.

Single-frequency external-cavity semiconductor ring-laser gyroscope.

We report for the first time (to our knowledge) the experimental achievement of a single-frequency ring-laser gyroscope using a diode-pumped half-vertical-cavity semiconductor-emitting laser structure as a gain medium. Thanks to the control of mode competition by an active feedback loop, we observe a beat signal from recombined beams that has a frequency proportional to the rotation rate as predicted by the Sagnac effect. This promising result opens new perspectives for rotation sensing.

Suppression of nonlinear interactions in resonant macroscopic quantum devices: the example of the solid-state ring laser gyroscope.

We report fine-tuning of nonlinear interactions in a solid-state ring laser gyroscope by vibrating the gain medium along the cavity axis. We demonstrate both experimentally and theoretically that nonlinear interactions vanish for some values of the vibration parameters, leading to quasi-ideal rotation sensing. We eventually point out that our conclusions can be mapped onto other subfields of physics such as ring-shaped superfluid configurations, where nonlinear interactions could be tuned by using Feshbach resonance.

Mode-coupling control in resonant devices: Application to solid-state ring lasers.

We report the theoretical and experimental investigation of the effects of mode coupling in a resonant macroscopic quantum device, in the case of a solid-state ring laser. This is achieved by introducing an additional coupling source whose interplay with the already-existing nonlinear effects ensures the coexistence of two counterpropagating cavity modes yielding a rotation-sensitive beat note. The determination of the condition for rotation sensing, both theoretically and experimentally, allows a quantitative study of the role of various mode-coupling mechanisms, in particular, the gain-induced mode coupling. We point out the connection between our work and the theoretical work on mode coupling in superfluid devices. This work opens up the possibility of new types of active rotation sensors.