Hiring Institution
Université Grenoble Alpes (UGA)

PhD-Awarding Institutions
Université Grenoble Alpes (UGA)
Macquarie University (MQ)

Download the full Position Description in PDF

Option 1

Design and Fabrication of Multi-Telescopes Visible Beam Combiners by Ultrafast Laser Inscription

Design and Fabrication of a 9T Visible Beam Combiner by ULI, for the FIRST/SUBARU instrument FIRST (Fibered Imager foR a Single Telescope instrument) is an astronomical instrument, installed at the Subaru telescope that enables high contrast imaging and spectroscopy by using a unique combination of sparse aperture masking, spatial filtering by single-mode waveguides and cross-dispersion in the visible. In order to increase the instrument’s stability and sensitivity, it is compulsory to increase the number of input waveguides and ideally achieve on-chip phase modulation. The proposed project aims the development of a thermo-optically tuned photonic beam combiner, where the waveguides will be fabricated using Ultrafast Laser Inscription (ULI). The device will enable the interferometric combination of 9 sub-apertures.

Three main activities related to fabrication using ULI are identified:
a) Input Splitters: Each of the N inputs must be split into N-1 single mode waveguides, with identical flux distribution.

b) Thermo-Optic phase modulation: Thanks to the versatility of ULI, waveguides will be inscribed close to the surface, where micro-heaters will interact with the waveguide, slightly modifying the refractive index, and therefore the phase of the optical beam.

c) Recombination stage: Finally, all the inputs will be combined by pairs using c.1) reversed Y-junctions or c.2) directional couplers.

The student will have to optimize each of the basic functions (Y-junction for splitting, reversed Y-junctions and combiners for beam combination), ideally ensuring achromatic behaviour over the spectral band of interest (600-900nm). Also, an optimization of micro-heaters in order to achieve hundreds of Hz phase modulation will be studied.

During the PhD, the student will acquire the knowledge and skills to locally modify the optical material using ULI, in order to define the waveguiding structures. After a 12 months period of training at Macquarie Univ. the student will move to UGA in order to use the optical bench and characterize the optical chips in terms of interferometric performances. The student will also be formed to simulations tools such as Beamprop, in order to model the fabricated waveguides and study propagation, transmission and interferometric expected behaviour of the beam combiners.

If the optical waveguide chips perform as desired, a secondment at the Subaru Telescope is expected, in order to conduct astronomical observations using the FIRST instrument and test the prototypes in a real environment.

Finally, valorisation will be developed through our collaboration with TeemPhotonics, a French company, based near UGA, that develops laser and photonic chips using classical ion indiffusion fabrication methods. Thanks to ULI, more dense and complex circuits can be obtained, that have an interest for Teemphotonics, in order to develop Visible spectro-interferometers. It is also expected that the student makes shorts secondments at FIRST/SUBARU telescope, in order to test the optical chips in the real instrument, if the targeted performances are reached.

Option 2

Design and Fabrication of near IR mode selective Photonic Lanterns for high efficiency flux collection, coupled to SWIFTS spectrometers

Design and Fabrication of near IR mode selective Photonic Lanterns for high efficiency flux collection, coupled to SWIFTS spectrometers Astrophotonic applications (interferometry, spectrometry) are linked to the development of single-mode waveguides that, by definition, have low numerical apertures and therefore collect a reduced amount of light, which translates into a reduced sensitivity. In order to improve the collection efficiency, an interesting approach is the use of photonic lanterns.

These systems allow for high efficiency flux collection due to their multimode input, which then is split in a loss-less manner into a number of single-mode waveguides. A lantern can be made mode-selective by introducing asymmetry. As a result, phase information is preserved which extends its application to interferometry.

The main objectives of this project are:
a) To develop and optimise near IR mode selective photonic lanterns using Ultrafast Laser Inscription
b) To couple the lantern to an integrated optics spectrometer

In order to achieve the complete prototype, the student will have to optimize the photonic lantern for maximum flux collection efficiency.

Also, a detailed study on the phase distribution among the different outputs will be done.

During the PhD, the student will acquire the knowledge and skills to locally modify the optical material using ULI, in order to define the waveguiding structures and lanterns for the near IR. After a 12 months period of training at Macquarie Univ. the student will move to UGA in order to use the optical bench and characterize the optical chips in terms of transmission and temporal stability. The student will also be formed to simulations tools such as Beamprop, in order to model the fabricated waveguides and study propagation, transmission and interferometric expected behaviour of the lanterns.

Finally, valorisation will be developed through our collaboration with TeemPhotonics, a French company, based near UGA, that develops laser and photonic chips using classical ion indiffusion fabrication methods. Thanks to photonic lanterns developed by ULI, more complex circuits can be obtained, that have an interest for Teemphotonics, in order to develop near IR spectrometers. The idea will be to couple the photonic lantern to the optical waveguides developed by Teem. These waveguides contain near IR spectrometers, which sensitivity could be increased by the use of photonic lanterns to improve flux collection.

Option 3

Mid IR beam combiners for Nulling Interferometry in novel optical materials

The ASGARD-NOTT instrument is a nulling beam combining instrument that is proposed for the VLTI. Its heart is currently based on a photonic circuit capable of interfering the light coming from the four telescopes operating in the 3-4 microns regime. The aim of the project is to develop low-loss, laser written waveguides and components in novel mid IR materials, passive but also active electro-optic materials such as lithium niobate.

The goals of the project are:
a) Develop and characterise low loss mid-infrared waveguides in novel materials
b) Investigate bend losses experimentally and via simulations
c) Develop basics components such as Y-junctions and directional couplers
d) Develop electro-optic or thermo-optical phase shifters
e) Develop and characterise a fully integrated 4 telescope beam combiner

During the PhD, the student will acquire the knowledge and skills to locally modify the optical material using ULI, in order to define the waveguiding structures and couplers for the mid infrared. After a 12 months period of training at Macquarie Univ. the student will move to UGA in order to use the optical bench and characterize the optical chips in terms of transmission and temporal stability. The student will also be formed to simulations tools such as Beamprop, in order to model the fabricated waveguides and study propagation, transmission and interferometric expected behaviour of the mid IR beam combiners.

If the optical chips are performant, they will be tested at KU Leuven (D. Defrère) who is PI of the ASGARD-NOTT instrument in order to see if they are suitable for the key scientific objectives of the instrument.

Finally, valorisation will be developed through our collaboration with TeemPhotonics, a French company, based near UGA, that develops laser and photonic chips using classical ion indiffusion fabrication methods. Thanks to 3D waveguides developed by ULI, more complex circuits can be obtained, that have an interest for Teemphotonics, in order to develop mid IR photonic devices.

Guillermo Martin
Simon Gross

Physics, Optical Engineering, Optics, Lasers & Matter Interaction