Lithium Niobate (LN) based electro-optic modulators are well known in the optical communications field, due to their
high bandwidth and deep rejection ratio . These performances could be used in the field of astronomy for stellar
interferometry in the mid-infrared domain . With our partners from Photline Technologies, we have conceived,
developed and characterized a 2T ABCD  beam combiner in the near-infrared (1.5μm, the H-band in astrophysics).
The modulation scheme, presented below in Figure 1, allows to determine the fringe characteristics in a single shot
measurement, without the need to externally scan the optical phase delay. Fine adjustment of the relative phase can be
achieved using the electro-optic properties of the lithium niobate waveguides. In particular, the phase on each output can
be electrically controlled and locked by using appropriate electrodes. These devices have to ensure modal filtering to
reject optical aberrations of the wavefront and thus optimize the fringes contrast, which means that they have to be single
mode through all the spectral range of interest. This also means that the couplers should be achromatic and balanced in
order to optimize the fringe contrast. We will present results on global transmission, performance of the couplers and the
electro-optic behavior of the device using monochromatic as well as wide spectral sources in the H-band.
In the astrophysical context of the search for Earth-like extrasolar planets, an important research effort has been done for
the realization of single-mode integrated optics devices for mid-infrared space-based interferometry. Preparatory projects
like FKSI , where rejection of high order modes is required to a level better than 40dB, will need photonic devices
that achieve modal filtering and beam combination in the mid-IR band. In this context, we present results on midinfrared
planar integrated optic beam combiners characterized at LAOG using chalcogenide and silver halide materials.
We show results on FTS measurements, allowing to determine the single mode spectral domain, as well as interference
fringes obtained from Y-junctions realized on these materials.
In this paper we present the performances of a modulator, realized by proton exchange, achieving a moderate rejection
ratio in the K-band (2.2μm). The device consists on a simple Mach-Zehnder beam combiner, developed by our partners
from Photline Technologies®, pushing forward their proton exchange technique in order to achieve single mode optical
guiding above 1.9μm in Lithium Niobate X-cut substrates. Applying low modulation voltages (Vπ=3.4V), and by a Fast
Fourier Transform obtain the spectrum of the source with a moderate resolution, due to the reduced length of the active
part (32mm). A white light interferometer is also shown, using a band-pass filter, from 1.8 to 2.6μm.
We present three different techniques for single-mode waveguide realization in Lithium Niobate at the 3.39μm
atmospheric transmission band, named L-band. These methods include Titanium diffusion, Ion Beam Implantation and
Photo-inscription. After describing the fabrication process and waveguide characterization, we will present an integrated
interferometer based on the Young's double slit experiment. From the recorded interferogram we recover information
about the source, namely, its peak emission lines.
The optical damage behaviour of different LiNbO3 optical waveguides has been experimentally studied by measuring the intensity output of a single beam as a function of the intensity input. Parallel measurements of photovoltaic currents have been carried out as a function of the input intensity and they have been correlated with the optical damage data. The following LiNbO3 guides have been studied and compared: proton exchanged (PE) belonging to the phases alpha, beta1, beta2 and reverse proton exchanged (RPE), and Zn in-diffused waveguides. The greatest intensity thresholds for optical damage, about 2x103 times greater than that of the substrate, have been obtained in RPE guides (they support ordinary polarization and have similar nonlinear optic activity as the substrate) and beta2 guides which support extraordinary polarization (they have no nonlinear optic activity). On the other hand, the lowest photovoltaic currents have been measured in beta1,2-phases. As a function of the light intensity, the photovoltaic current exhibits a superlinear behaviour, strong in alpha-phase and weaker in Zn in-diffused and RPE guides. The results for optical damage are discussed in connection with those of photovoltaic currents, paying particular attention to the main mechanisms involved.
Conductivity phenomena affecting fixed devices in photorefractive PE:LiNbO3 waveguides are studied at room and higher temperatures. Contribution from ionic surface charges to charge compensation of photorefractive gratings has been observed. The grating recording/erasing method and current measurements have been used.