Experiments Towards the Realisation of a Monolithically-Integrated Optical Isolator Incorporating Quasi-Phase Matched Ma
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Experiments Towards the Realisation of a Monolithically-Integrated Optical Isolator Incorporating Quasi-Phase Matched Magneto-Optical Effects
Barry. M. Holmes, David. C. Hutchings and Josef. J. Bregenzer Department of Electronics and Electrical Engineering, The University of Glasgow, Glasgow, G12 8LT, Scotland, UK, ABSTRACT Experiments towards the realisation of the necessary components for future integrated waveguide optical isolators have been conducted. The design, fabrication and characterisation of GaAs/AlGaAs reciprocal mode converters, realised through the use of three novel approaches, is reported. These devices have been tested at λ=0.9µm and 1.3µm, producing TE-TM conversion efficiencies up to 70%. Initial investigations into the inclusion of magneto optic materials with III-V semiconductor structures for non-reciprocal mode conversion are also discussed. INTRODUCTION When coupling laser diodes to optical waveguides, fibres or components, the inevitable back reflections that arise from the connection interface, travel back into the laser cavity resulting in what’s known as reflection noise or injection noise [1]. This causes instabilities, leading to restrictions on the operational speed, and reduced lifetime, of the devices. Currently, in order to prevent these back reflections, bulk isolators based upon the Faraday effect are introduced into the laser-waveguide-fibre assembly, requiring high precision component alignment. This introduces complexity in the arrangement of the components, leading to a reduction in production throughput and an increase in costs. Increased integration results in the reduction of dimensions and costs, whilst at the same time introducing improved functionality and lifetime of photonic devices. Consequently, the development of a monolithically integrated laser/optical isolator (MIOI) is probably one of the most important and desirable objectives in the field of integrated optics. However, the realisation of such a device is far from simple and each potential design has inherent problems associated with it. Recently, various architectures and designs of MIOI were reviewed [2] and potential solutions to the remaining obstacles to the realisation of such a device were proposed. The design consisted of a passive reciprocal mode converter (RMC) based upon asymmetric shaped waveguide, first reported by [3] coupled to a nonreciprocal polarisation rotation stage (NPRS) using the quasi-phase matched Faraday effect. We report here the principles of operation of the Faraday isolator, the difficulties associated with successful incorporation of these principles into waveguide based devices, and the novel solutions we are applying in order to overcome these problems. Traditional bulk Faraday isolators operate by polarising incident light, rotating it by +45 deg through the use of a Faraday rotator, before passing it through another polarising element whose transmission axis is aligned at +45deg to the first. Due to the nonreciprocity of the Faraday effect, upon reflection this light
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