HOBAN (Development of Hard Optical Fiber BrAgg GratiNgs Sensors) is an European H2020 project granted by Kic InnoEnergy and aiming the development of fiber-based temperature and strain monitoring systems that can withstand harsh nuclear environment (350°C temperature and MGy dose levels). The objective will be achieved by employing ‘ad hoc’ fiber Bragg grating (FBG) sensors and their associated instrumentation system which will bring to the market new tools for optimizing the running and the services in current and future nuclear power plants. We’ll present the challenges associated with this project and recent advances at the OFS conference.
Modal filtering is based on the capability of single-mode waveguides to transmit only one complex amplitude function to
eliminate virtually any perturbation of the interfering wavefronts, thus making very high rejection ratios possible in a
nulling interferometer. In the present paper we focus on the progress of Integrated Optics in the thermal infrared [6-20μm] range, one of the two candidate technologies for the fabrication of Modal Filters, together with fiber optics. In
conclusion of the European Space Agency's (ESA) "Integrated Optics for Darwin" activity, etched layers of chalcogenide
material deposited on chalcogenide glass substrates was selected among four candidates as the technology with the best
potential to simultaneously meet the filtering efficiency, absolute and spectral transmission, and beam coupling
requirements. ESA's new "Integrated Optics" activity started at mid-2007 with the purpose of improving the technology
until compliant prototypes can be manufactured and validated, expectedly by the end of 2009. The present paper aims at
introducing the project and the components requirements and functions. The selected materials and preliminary designs,
as well as the experimental validation logic and test benches are presented. More details are provided on the progress of
the main technology: vacuum deposition in the co-evaporation mode and subsequent etching of chalcogenide layers. In
addition, preliminary investigations of an alternative technology based on burying a chalcogenide optical fiber core into a
chalcogenide substrate are presented. Specific developments of anti-reflective solutions designed for the mitigation of
Fresnel losses at the input and output surface of the components are also introduced.
Ion-exchange technology on glass has been successfully used for more than twenty years to manufacture dependable and
low cost integrated optics active and passive devices on silicate or phosphate glasses substrates in the telecommunication
wavelengths operation range (from λ = 0.8 to 1.7 μm). However, the recent developments of integrated optics
instruments for astronomical interferometers or biological sensors have lead to an increase of the devices operation range
towards the mid-infrared. For these reasons, we present in this paper the realization of both surface and buried
waveguides by means of ion-exchange on a glass which is transparent until λ = 5 μm. In this study, the choice of
germanate glass BGA-G115 from Kigre Inc. has been made because of both its similarity with silicate glass, its content
of Na+ ions and its excellent transparency in the considered operation range. A complete study of the silver ion diffusion
on this new glass matrix has been performed allowing the determination of silver and sodium ion-diffusion coefficients
at working temperature and silver concentration. Using theses data, simulations have shown that an ion-exchange of
90 min in a 0.03AgNO3-0.97NaNO3 molten salt at a temperature of 330°C can lead to the realization of surface single
mode channel waveguides at either λ = 1.55 μm or λ = 3.39 μm depending on the diffusion window width. To
demonstrate channel waveguides on BGA-G115, a specific technological process based on the deposition of a
polycrystalline silicon masking layer has been implemented. Single-mode channel waveguides, with a 2.5 μm diffusion
window width, have thus been realized and characterized at the wavelength of 1.55 m. Modal size has been measured to
be 10 μm ± 1 μm x 7 μm ± 1 μm for propagation losses of 1.2 dB/cm ± 0.5 dB/cm for a 2 cm ± 0.1 cm long device. As
for buried waveguides, their feasibility has been demonstrated on multimode ones where a burying depth of 25 μm ± 2
μm has been measured.
Ion-exchange on glass has been successfully used for more than twenty years to realize integrated optics devices such as
wavelength multiplexers, splitters, optical amplifiers, lasers or sensors. One of the major issue is today to integrate more
functions on a single chip which is usually realized be reducing the dimensions of the waveguides. Nonetheless this
reduction is intrinsically limited by the maximum index variation achievable. For this reason, we propose and investigate
in this article the realization of 3D structures where waveguides are integrated vertically instead of horizontally. Based
on the selective burial of ion-exchanged waveguides and the cascading of multiple ion-exchanges, the realization of
"vertical" asymmetric and symmetric Y-junctions have been investigated theoretically.
Broadband wavelength (de)multiplexers play a key role in different fields of integrated optics. In particular, the development of Erbium Doped Waveguide Amplifiers (EDWA) requires efficient integrated pump/signal multiplexers. In this article, the design and the realization of a 980 nm/1550 nm wavelength multiplexer based on a segmented asymmetric Y junction made by silver/sodium ion exchange on glass is discussed. We first present the behavior of an asymmetric Y junction, in order to describe its use as a wavelength (de)multiplexer. Then, the index averaging principle of a segmented waveguide is detailed, as well as its application in the design of one of the asymmetric Y junction branches. The design of a segmented asymmetric Y junction is then described, as well as its BPM simulations results. They show isolation of 33 dB at 980 nm and 25.6 dB at 1550 nm with excess losses of 2.6 dB at 980 nm and 1.3 dB at 1550 nm. In a second time, we present the realization of this component using a Silver/Sodium ion-exchange on glass. For λ = 980 nm, the isolation measured is (31 ± 1) dB, and in the third communication window, the isolation increases from (11.5±0.25) dB at λ = 1500 nm to (15.5±0.25) dB at λ = 1600 nm. The broadband operation is only limited by the modal characteristics of the waveguides composing the junction and ranges from 1500 nm to 1650 nm. Total insertion losses measured at 980nm are (2.63±0.1) dB. Around 1550 nm, losses vary from (3.6 ± 0.1) dB at the 1500 nm wavelength to (4.6 ± 0.1) dB at 1600 nm.
In this paper, the realization and characterization of periodic segmented waveguides made by ion-exchange on glass is presented as well as their application to polarizers and wavelength duplexers. Segmented waveguides are of major interest for integrated devices because they allow tailoring the refractive index without changing the technological parameters. Indeed, a segmented waveguide, which is composed of a periodic succession of guiding and non-guiding zones, can be considered as a classical waveguide with a core refractive index that ranges from the segmented core to the substrate ones, depending on the segmentation ratio. Through this way, it is thus possible to avoid the use of more complex techniques that require a double-step lithography process.
In the first part of the article, surface segmented waveguides made by ion-exchange on glass are studied and a linear relationship between the segmentation duty cycle and the maximum core refractive index of an equivalent continous waveguide is demonstrated.
A simple correction on the duty cycle is needed to take into account the longitudinal diffusion.
After a presentation of its principle of operation, in the second part of the article, we propose the realization and characterization by means of segmented waveguide of a polarizer with more than 30dB of extinction ratio at λ=1550nm. Finally, the design and first results obtained on a duplexer based on an asymmetric segmented Y-junction are presented.
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