In this project, we investigate the optical non-reciprocal phase shift (NRPS) induced by a magneto-optic material such as Ce: YIG. Further, we wish to utilize the NRPS to design a magneto-optical isolator with high isolation ratio. The wavelength of operation is chosen to be 930 nm (or 1550 nm); hence the choice of waveguide material is Silicon Nitride which is transparent in the wavelength of interest. A possible architecture of the waveguide cross-section is given in Fig. 1.
Fig 1: Geometry of a Silicon Nitride optical isolator. Magnetic field is along the X direction .
The isolator is based on a Mach–Zehnder interferometer (MZI) to provide a high isolation ratio and wide bandwidth. Magnetic field (B) is generated using a metal coil or a bar. Around 200 mA of current is needed to saturate the magnetic material. Further, improvement can be made by bringing the electromagnet closer to the Ce: YIG waveguiding materials. NRPS is maximized for an asymmetric configuration shown in Fig. 1. To achieve NRPS of π, a total length of 1 mm is required for the phase shifter for single arm driving while the length can be as small as 500 µm for the push-pull driving scheme and power consumption of 10 mW. Further reduction can be obtained by using materials with higher magnetization or by using multiple electromagnets.
Since the isolator is required to be operated within a large temperature range, athermal designs  might also be useful to maintain stable isolation ratios. Recent work on athermal isolators has provided stable isolation in the backward direction, but the invariance of spectrum in the forward direction is absent . In this work, we vary the effective index of both the arm to obtain a net zero change in the spectral properties of an unbalanced MZI. Athermal operation between 20-80 ºC will be designed for the proposed isolator. Isolation ratio is mostly limited by the ratio of TE/TM mode present within the waveguide. The goal is to incorporate nonreciprocal devices onto photonic platforms in order to achieve the photonic analog of the integrated electrical diode.
The student can distribute his/ her work load as follow:
- Literature survey: 15%
- Proposing a new design/ architecture of the integrated magnetic material-based isolator as explained above (if any): 15%
- Design, simulation and layout of the proposed design: 40 %
- Feasibility study of the proposed design with the mentor and integration team: 15%
- Thesis/ report writing: 15 %
 Paolo Pintus, Fabrizio Di Pasquale, and John E. Bowers, "Integrated TE and TM optical circulators on ultra-low-loss silicon nitride platform," Opt. Express, 21, 5041-5052 (2013).
 S. Dwivedi, H. D'heer, W. Bogaerts, "A compact all-silicon temperature insensitive filter for WDM and bio-sensing applications", IEEE Photonics Technology Letters, vol. 25 (22), IEEE, pp. 2167 – 2170 (2013).
 Yuya Shoji and Tetsuya Mizumoto 2014 Sci. Technol. Adv. Mater. 15 014602
Type of project: Thesis
Required degree: Master of Engineering Science
Required background: Electrotechnics/Electrical Engineering, Physics