Novel, efficient and compact package of laser diodes
In optical telecommunications links, electronic data signals are converted into light signals which are emitted through optical isolators into an optical fibre. These non-reciprocal optical devices stabilise and protect laser diodes and semiconductor optical amplifiers by allowing light to pass in one direction, but not in the opposite direction. Current commercial isolators are bulk components requiring collimating lenses and expensive alignment techniques when included in a laser diode package. Developing a planar waveguide-based optical isolator - in the form of a chip - was therefore a long-sought goal in photonics. Until recently, all research in this domain concentrated on designing an isolator with waveguide structures of ferromagnetic garnets to induce non-reciprocity. The integration with semiconductor host material, however, remained an issue, as it was possible only by direct wafer bonding without significant cost reduction. The ISOLASER project partners explored a different research approach. This was based on the requirement that for monolithic integration the isolator structure should be very similar to that of the laser it was to be integrated with. More specifically, in a standard semiconductor optical amplifier an adequately magnetised ferromagnetic metal was placed very close to the guiding region. The result was a component which, being transparent or amplifying in only one direction, was isolating. Moreover, it could be monolithically integrated with other active photonic devices. Such a device would greatly reduce the manufacturing costs of laser diode packages by reducing the number of stand-alone optical components needed. Moreover, the need to accurately align the laser beam when using an external isolator in the package would be eliminated.
