Marie-Françoise Blanc-Mignon

Magneto-optical properties of yttrium iron garnet (YIG) thin films elaborated by radio frequency sputtering

Thin films of Yttrium Iron Garnet (YIG) are grown by radio frequency magnetron non reactive sputtering system. Thin films are crystallised by heat-treatment to obtain magneto-optical properties. On quartz substrate, the network of cracks observed on the annealed samples can be explained by the difference between the thermal expansion coefficient of substrate and YIG. The Faraday rotation of thin films is measured with a classical ellipsometric system based in transmission which allows us to obtained an accuracy of 0.01°. We studied the variation of Faraday rotation versus the applied magnetic field. The variation of the Faraday rotation is the same that this obtained by VSM (vibrating sample magnetometer) analysis. With a quartz substrate, maximum Faraday rotation is observed to be 1900°/cm at the wavelength of 594 nm for an annealing of 740°C. The variation of the Faraday rotation versus the wavelength is studied. The obtained values are comparable to those of the literature for the bulk material. In order to eliminate the stress due to the heat-treatment, we made some films on Gadolinium Gallium Garnet (GGG) which thermal expansion coefficient is near than the YIG one. The material crystallises with no cracks and the Faraday effect is equivalent.

Development of sol-gel saturable absorber for integrated Q-switched lasers

The diversity of integrated photonic sensors such as LIDARs increased in part thanks to integrated laser sources development. Glass integrated lasers fit well sensing demand because of their high durability and great integration potential. We propose here a new kind of saturable absorber (SA) for glass integrated Q-switched lasers, based on a solgel matrix. This is intended to improve durability and output power of existing lasers, whose SA is often based on plastic materials. While sol-gel is already used for optical limiting devices, its use as a host for SA has not been investigated so far. Due to its interesting properties such as durability, high laser induced damage threshold (LIDT) and coating convenience, it should also be a good candidate to realize a reliable SA matrix. We mixed a hybrid organic-inorganic sol with toluene and (bis(4_dimethylaminodithiobenzil) nickel – BDN I, a SA dye molecule. Drops of this mix have been coated and annealed to obtain a SA sol-gel thick layer. We modeled BDN I with a four energy-level system and measured its absorption over optical input power at the wavelength of 1064nm in order to extract its physical parameters: absorption cross sections and relaxation time. This SA showed good performances with 30% modulation depth. This sol-gel has also been spin coated on ion-exchanged glass integrated waveguide. The characteristics of this waveguide SA have been measured and the evanescent light interaction between the waveguide and the saturable absorber layer has been modeled. This study will allow further integrated Q-switched lasers design.

Design of a waveguide with optics axes tilted by 45° and realized by ion-exchange on glass

The fabrication of on-chip optical isolators to protect integrated optical sources is one of the major challenges of research in integrated optics. Their operation principle is based on the control of the guided-wave polarization and the most common structures are composed of a polarization splitter, a non-reciprocal rotator based on the Faraday effect, and a reciprocal rotator. The reciprocal rotator is a device that rotates the wave polarization by 45°. This can be achieved by creating a relative phase shift between the waveguide’s two polarization eigen states or by twisting its optics axis thanks to an appropriate shaping of its core. In this work, we propose the design and simulation of a waveguide with optics axes tilted by 45° fabricated by two cascaded field-assisted ion exchanges on a glass substrate and an encapsulation. The dependences of the proposed design on process time, temperature, applied voltage and photolithography over-etching are investigated. The final device exhibits a 45.1° rotation of its optical axes and less than 5% variation on the C+L telecommunication band.