Optical isolators1 are non-reciprocal devices in which time reversal symmetry is broken for light propagation. They are of great importance in laser and amplifier technology, where they are used to reduce parasitic reflections as well as in optical communication and sensing systems. Traditionally they consist of devices in which magneto-optical interactions are provided by materials exhibiting the Faraday effect2 , which modifies the polarization of light passing through certain materials in the presence of a magnetic field; with the use of suitable polarization and birefringent filters, light can be transmitted through the material in the forward direction while being strongly attenuated in the backward direction. Despite the efficiency in achieving non-reciprocity, this technique presents some drawbacks in on-chip integration for nanoscaled devices such as high costs of materials, difficulties in processing, hardly scalable sizes, emergence of parasitic magnetic interferences and wavelength restrictions. With the ever-growing need of nanoscale technologies, the quest for alternative and more compact isolation schemes has recently garnered an immense impetus and spawned a variety of methods which make use of optical non-linearities, conjunction with resonators, strongly modulated gratings, stimulated Raman and Brillouin effects, thermo- or acousto-optic effects, to name a few. Most of the techniques proposed to-date provide a solution to some of the aforementioned problems but present additional limitations such as high costs, difficult scalability or reproducibility on an industrial level, and are still far from representing an alternative solution to the standard technology. In our group at IMEC we are developing acousto-optic isolators that use acoustic modulation of the optical properties of materials to modify non-reciprocally their interaction with light. We make use of surface acoustic waves, which can be controlled externally, and whose modulation can be enhanced by accurate tailoring of the geometrical, material and physical properties of the devices. The devices that we are developing, are expected to be of interest for both academy and industry. The initial goal of this thesis is to design an acousto-optic isolator in which the acoustic, optic and acousto-optic effects are carefully studied and modelled using multiphysics software. After completion of the design and modelling of the device, the work will be shift to the design and construction of a set up for measuring the fabricated devices and to the (acoustic, optic and acousto-optic) measurements of the prototypes of devices. In addition, a part of the work will consist in reproducing the results proposed by other techniques and to estimate their integrability with our technology. This Master thesis, based in IMEC, offers the possibility to work on a truly multiphysics project which involves both acoustics and optics, and their interaction, as well as the possibility to work in a friendly and multicultural environment with cutting edge facilities, technology and know-how.
In summary the successful candidate will work on:
- Literature study of the Physics of elasto-optics, optical isolation, and of the optical isolation techniques proposed to-date.
- Design and full modelling of an acousto-optic isolator (Ansys, Comsol, Matlab, Python...).
- Design and building of the set-up for optic, acoustic, and acousto-optic measurements of the devices.
- Reproduce and compare the results of other papers which can be of interest for comparison or integration into our device.
- Measurement of the optic isolator.
- Analysis of data and estimation of the performance and figures of merits of our devices.
Examples of nanophotonic devices produced in our group (waveguides coupled through ring resonators)
 D. Jalas, et al. Nature Photonics. 7, 579 (2013).
 B. J. H. Stadler, IEEE Photonics Journal 06, 0600215 (2013).
Type of project: Thesis
Required degree: Master of Engineering Technology, Master of Science
Required background: Electromechanical engineering, Electrotechnics/Electrical Engineering, Nanoscience & Nanotechnology, Physics