© (2006) OSA

When designing integrated optical circuits — the photonic equivalent of electronic integrated circuits low cost and a mature fabrication technology make silicon a tempting material to work with. With passive optical components such as waveguides already well developed, the requirement now is for silicon-based light sources. However, despite its near ubiquity in electronic applications, silicon is particularly poor at creating light. One possible route around this problem is the use of hybrid systems — coupling the light from an optically efficient III–V semiconductor, such as gallium arsenide, into silicon optical components. The drawback is that the cost associated with aligning the components in the two materials negates the savings achieved by using silicon. Now, A. W. Fang and his collaborators from the USA and Israel have created a laser diode that is bonded to a silicon waveguide without the need for expensive alignment1.

In the approach taken by A. W. Fang and colleagues, the two different materials are bonded together at a high temperature and pressure for twelve hours. Etching the laser mesa and the waveguide after bonding ensures that the two components are automatically aligned. The optical mode straddles both the III–V active region, providing the gain required for lasing, and the silicon waveguide region, which acts as the cavity. This hybrid laser was able to produce 1.8 mW of light at a wavelength of 1,577 nm and operated at temperatures up to 40°C. This technique allows several lasers to be fabricated on the same chip, and can be combined with a whole range of existing silicon optical components to produce low-cost integrated optical circuits.