Integrated Magneto-Optics

The incorporation of optical isolators and related non-reciprocal devices such as circulators within standard optoelectronic wafer platforms is exceptionally challenging. Preferred magneto-optic materials cannot be exploited as waveguide core layers on semiconductor wafers due to a lower refractive index. Our approach to the integration of an optical isolator on semiconductor platforms involves combining a nonreciprocal mode converter with a reciprocal mode converter. We demonstrate that suitably tapered waveguides can be employed to connect the mode converter to other sections thereby avoiding problems caused by mode-matching and reflections from the section interfaces.

The nonreciprocal mode converter is formed from a continuation of the semiconductor waveguide core with a magneto-optic upper cladding so that Faraday rotation occurs through the interaction of the evanescent tail. The phase velocity mismatch due to the waveguide birefringence is overcome using a quasi-phase-matching approach. Lithography is used to pattern the top cladding so that the film immediately on top of the waveguide core alternates between magneto-optic and a non-magneto-optic dielectric of a similar refractive index.‌

We developed a lift-off process for garnet films in collaboration with Prof. Beth Stadler at the University of Minnesota. This allows annealing of the film in an oxygen atmosphere to facilitate the crystallisation of the garnet phase and realise the potential of the large Verdet coefficiecients available in YIG and related garnets.‌‌ Our recent work uses substituted Terbium Iron Garnets (TIG) which has the advantage of crystallisation without the requirement for a comprimising garnet seed layer.‌MRS Webinar on Material for Nonreciprocal Photonics, June 2018



Project Support

  • EPSRC/NSF EP/J018708/1: Materials World Network: Complex oxides for heterogeneous optoelectronic integration
  • EPSRC GR/S10599/01: Monolithic-Integrated Optical Devices Containing Magneto-Optic Elements
  • EPSRC GR/S79787/01: PLATFORM: Optoelectronic device integration technologies for the 21st Century