School of Engineering

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. Another difficulty is the phase velocity mismatch as a consequence of the inherent structural birefringence associated with waveguide geometries.

Our approach to the integration of an optical isolator with a III-V semiconductor laser involves combining a nonreciprocal mode converter with a reciprocal mode converter, based on an asymmetric profiled rib waveguide, fabricated by Reactive Ion Etching. 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 III-V 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.

SEM of quasi-phase-matched nonreciprocal mode converter and the measured polarisation conversion 

We are currently developing a lift-off process for garnet films in collaboration with Prof. Beth Stadler at the University of Minnesota. This will allow 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.

SEMs of patterned garnet film after annealing, and after deposition of a silica mask for subsequent III-V waveguide etch 

MRS Fall Meeting 2010 Presentation 

Our ongoing collaboration with Prof. Beth Stadler has been enhanced with the recent award of an EPSRC/NSF joint-funded project Materials World Network: Complex oxides for heterogeneous optoelectronic integration. This project proposes to bring new functionalities to semiconductor systems by using materials research to identify paths of integration for complex oxide claddings onto semiconductor structures, such as waveguides. As the US PI, Stadler from Minnesota brings to the collaboration an expertise in oxide integration with recently proven processes for controlling thermal strain to achieve high-quality oxides on semiconductor platforms. As the UK PI, Hutchings from Glasgow brings to the collaboration an expertise in III-V semiconductor fabrication and processing, including design of quasi phase matching to enable cancellation of structure birefringence effects. Together, this team will add new materials to the palettes of designers interested in electronics, photonics, sensors, and unimagined future areas. To begin, this collaboration will focus on adding magneto-optical (MO) and electro-optical (EO) properties that are orders of magnitude greater than currently available to semiconductors by integrating both doped yttrium iron garnet (YIG) and lithium niobate (LNO), respectively, onto III-V structures.

People

Publications

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