R. Le Naour

The inhibition mechanism in polarization bistable semiconductor lasers

The polarization bistability between TE 00 and TM 00 eigenstates in InGaAsP/InP lasers is shown to be due to the mode inhibition mechanism. A theoretical analysis shows that the switching is governed by two current-dependent competing terms. One term represents the self-stabilization for the existing lasing mode to resist the onset of a new mode. The other term is the gain recovering term of the nonlasing mode. The major contribution to the latter is the relative current dependence of the TE and TM gains. By making proper assumptions for the device parameters based on experimental data, the observed hysteresis loops have been successfully modeled. The conditions for the existence of polarization bistability are discussed.

Polarization slaving mechanisms in vectorial bistable lasers

The basic mechanisms of external all-optical control of polarization bistabilities are isolated in one- and two-frequency systems. Induced rotation and induced inhibition mechanisms by vectorial injection in lasers are theoretically predicted and experimentally shown in both systems. The sensitivity of the vectorial systems leads to subfemtojoule switching energies, which correspond to the theoretical threshold values. A reduction by four orders of magnitude compared to the lowest energy demonstrated in scalar passive systems is obtained.

Measurement of small rotations by eigenvector flips in a quasi-isotropic Fabry-Perot

A novel small rotation or small birefringence measurement scheme based on the dynamics of the helicoidal eigenstates of a passive Fabry–Perot cavity with two quarter‐wave plates is described. When the system is inserted between two crossed polarizers, the sensitivity of the method is shown to be proportional to the square of the finesse of the cavity. For a finesse of 50, the observed noise floor corresponds to an estimation of the minimum detectable small rotation of 3×10−8 rd. We discuss possible improvements and potential possibilities of the method.

Lamb dip asymmetry in lasers with plane-parallel resonators

The Lamp dip asymmetry due to linear or nonlinear lenslike effects is investigated in lasers with plane-parallel resonators. The experiments are performed using diffracted light spectroscopy. It is shown that the frequency-dependent diffraction losses are essential in determining Lamb dip asymmetry, regardless of the origin of the lenslike effects.

Critical geometry in multimode-laser spectra

The mode spectra in usual lasers with fundamental Gaussian beams are shown to be correlated to the critical length introduced for a monomode laser with lens or lenslike effects induced by the Gaussian beams. Three typical mode behaviors exist with large asymmetry-mode spectra in different lasers. The bulk of the oscillation energy occurs (1) to the low-frequency side of the gain curve, (2) to the high-frequency side of the gain curve, (3) to the low- or the high-frequency side alternatively. For a given laser, the effective behavior is governed by its geometry relative to the critical geometry, which depends on the cavity parameters, and by the position of the diffracting element.

Direct measurement of induced polarization anisotropies in a gas laser

Abstract A small linearly polarized rotating probe is used to obtain a direct measurement of the induced anisotropic properties occurring in an “atom + linear electromagnetic field” system constituting the active column of a gas laser. The anisotropic processes are isolated from the isotropic ones and lead to a special phase-shifting-collision effect of the Zeeman coherences.

Twofold critical geometry for lasers

Use of a twofold critical cavity is proposed to obtain a symmetrical saturated absorption peak on a symmetrical background. The experimental verification is performed on the CH(4)3.39-microm system. This geometry is expected to provide optical frequency standards with better reproducibility.

Spatial-asymmetry distribution of a saturated-absorption peak.

The amount of asymmetry of saturated-absorption peaks observed outside a cavity with two collinearly counter-propagating Gaussian beams is analyzed at different points in the cross section of the probe beam. Although the total beam exhibits a quasi-symmetric line shape, a spatial distribution of asymmetries with different amounts and signs is obtained versus the distance to the beam axis. A simple model taking account of pure focusing and defocusing effects induced by a saturated Gaussian beam leads to agreement between experiment and theory for the 5944-A neon line in the case of saturated-absorption spectroscopy.

Comparative analysis of a laser frequency stabilization method using a mobile and a fixed Lorentzian

Frequency stabilization using ‘mobile’ resonances is compared with that employing frequency modulation. Analogy with radio-frequency experiments leads to an optimization of the error signal. Offsets occuring in each case are discussed and additional offsets due to asymmetry are evaluated.

Analysis and measurement of the polarization sensitivity of single-mode fiber passive optical components

Abstract The single-mode fiber passive optical component behavior as a function of the input state of polarization changes is investigated. We measure in particular the component attenuation by varying the state of polarization. For this sake we use a polarization controller comprizing a combination of an ideal polarizer, a quarter-wave plate, and a half-wave plate. A state function depending on two variables related to the orientation of the optical plates is defined and allows the convenient description of all states of polarization. The component attenuation function is then depicted by different graphical representations in one, two, or three dimensions. This mapping allows the global visualization of the component behavior as a function of the polarization states, which depends on the conception and the product fabrication quality. The polarization sensitivity parameter is also deduced from these representations.