Silicon photonic integrated circuits: From devices to integration

Silicon Photonics taps on the volume manufacturing capability of traditional silicon manufacturing techniques, to provide dramatic cost reduction for various application domains employing optical communications technology. In addition, an important new application domain would be the implementation of high bandwidth optical interconnects in and around CPUs. Besides volume manufacturability, Silicon Photonics also allows the monolithic integration of multiple optical components on the same wafer to realize highly compact photonic integrated circuits (PICs), in which functional complexity can be increased for little additional cost. An important pre-requisite for Si PICs is a device library in which the devices are compatibly developed around a common SOI platform. A device library comprising passive and active components was built, which includes light guiding components, wavelength-division-multiplexing (WDM) components, switches, carrier-based Si modulators and electro-absorption based Ge/Si modulators, Ge/Si photodiodes and avalanche photodiodes, as well as light emitting devices. By integrating various library devices, PIC test vehicles such as monolithic PON transceivers and DWDM receivers have been demonstrated. A challenge with Si PICs lies with the coupling of light into and out of the sub-micrometer Si waveguides. The mode size mismatch of optical fibers and Si waveguides was addressed by developing a monolithically integrated multi-stage mode converter which offers low loss together with relaxed fiber-to-waveguide alignment tolerances. An active assembly platform using MEMS technology was also developed to actively align and focus light from bonded lasers into waveguides.