Side-mode gain in grating-tuned extended-cavity semiconductorlasers: investigation of stable single-mode operation conditions

In semiconductor lasers, nonlinear phenomena inside the active medium change the side-mode gain with respect to the static threshold-gain. For a given side mode, the sign and the magnitude of the change depend on the lasing-mode optical power and on the wavelength detuning from the lasing mode. If the side-mode gain is enhanced, mode-hopping can occur toward a side mode whose loss is higher than the lasing-mode one. Conversely, in the case of side-mode-gain suppression, the side-mode loss can be smaller with no mode-hop. In this paper, effects of carrier-density pulsation, carrier heating, and spectral-hole burning on the conditions of stable single-mode operation in grating-tuned single-mode extended-cavity semiconductor lasers are investigated. Taking into account the external cavity spectral selectivity and mode coupling, we present a theoretical analysis of experimental results. We perform calculations that compare well with the experimental data obtained with a 1.55-μm extended-cavity laser     

Relaxation of the single-mode emission conditions in extended-cavity semiconductor lasers with a self-organizing photorefractive filter

Commercial 1.55-microm extended-cavity semiconductor lasers provide single-mode operation that can be continuously tuned over a range larger than 100 nm without mode hopping. But such performance requires delicate factory adjustment and high mechanical stability of the external cavity. Furthermore, at high emission power the tuning range is limited to small values because of the annoying multimode operations that sometimes occur. We have shown that the alignment constraints can be relaxed by use of an intracavity photorefractive filter. Here we present new results obtained with a crystal with low absorption and high photorefractive gain. We demonstrate that, without inducing excessive additional loss, we can preserve single-mode emission at an output power higher than the maximum power obtained in the absence of a photorefractive crystal over the full tuning range of the laser.     

High-capacity photorefractive neural network implementing a kohonen topological map

We designed and built a high-capacity neural network based on volume holographic interconnections in a photorefractive crystal. We used this system to implement a Kohonen topological map. We describe and justify our optical setup and present some experimental results of self-organization in the learning database.     

Design and implementation of a page-oriented "holographic" memory based on a Lippmann architecture

Optical data storage inspired by Lippmann interference color photography was proposed a long time ago as an alternative to holographic memories. Very high capacities were predicted for a page-oriented approach with wavelength multiplexing, but, up to now, such an architecture has never been implemented. Based on simple conception rules, we build such a page-oriented Lippmann data storage system. Submicrometer resolved data pages recorded in thick materials are evidenced by the experimental results.     

Photorefractive beam-steering system that uses energy transfer in a BaTiO(3) crystal for a fiber-array interconnect

A beam-control system to write gratings on a holographic plane is studied. The arrangement is designed to interconnect two 1024 monomode fiber arrays. The beam-control system is composed of two subsystems: a beam steerer, which deflects one incident beam toward 1024 positions, and a collimating system, which adapts the shape of the deflected beam to the holographic plane. The collimating system was studied only after the beam steerer had been fully built and tested. It is based on the photorefractive amplification of a beamlet selected by a shutter array. The deflection efficiency is enhanced by a factor 1500 with the photorefractive crystal, and the signal-to-noise ratio is larger than 5500. The influence of the optical aberrations on the coupling losses of the infrared beams in the monomode fibers are evaluated.     

Continuous monitoring of a surface slope by real-time shearing interferometry with a photorefractive crystal

We propose and demonstrate a new technique for measuring the temporal variations of the surface slope of an object. This real-time shearometric arrangement takes advantage of the dynamic properties of holograms in photorefractive crystals. The accuracy of the measurements should make this technique suitable for real-time structural intensity determinations.     

Analysis of the build up of oscillations in self-inducedphotorefractive light resonators

The transient behavior of self-induced photorefractive resonators is discussed. An analytical expression for the buildup of oscillations, which clearly shows the influence of the different parameters involved in the resonator, is derived. This theoretical analysis is confirmed by experiments     

Polarization properties of two-wave mixing under an alternatingelectric field in BSO crystals

The coupled-wave theory is extended to analyze the two-wave mixing interaction under an alternating electric field in a sillenite crystal. Within the undepleted pump beam approximation, an analytical expression which allows prediction of the phase, the polarization state, and the amplitude of the amplified beam is derived. It is shown that all these features usually oscillate. These predictions are confirmed by experiments     

Modal competition via four-wave mixing in single-mode extended-cavity semiconductor lasers

An analysis of the wave-coupling phenomena in extended-cavity semiconductor lasers is carried out to investigate the conditions of mode-hop-free single-mode operation. Taking into account the external cavity selectivity and the mode coupling via four-wave mixing in the active medium, we present a theoretical analysis of the modal competition and perform calculations that are in good agreement with experimental results obtained with a 1.55-/spl mu/m extended-cavity laser.