Annapolis, MD-based Little Optics, a company that has invented a glass high-index optical waveguide material system called Hydex for planar lightwave circuit (PLC) fabrication, has now developed 8-bit programmable delay lines based on the technology.
The circuit structure is comprised of a series of crossbar switches that selectively route signals through either a planar time-delay element or a bypass. Applications include true-time-delay signal processors for phased-array antennas, optical-time-domain multiplexing, optical-clock distribution, and optical buffering within all-optical routers.
Little Optics uses a “pick-and-place” stepper lithography strategy to selectively place spirals of arbitrary length onto a common bus structure. A library contains more than 400 long-path-length waveguide spirals ranging from 0.05 to 20 cm (corresponding to time delays from 3 ps to 1.2 ns) that can be integrated onto a chip that is less than 1 cm2.
Using the 8-bit architecture, a device with a maximum time delay of around 2.4 nsec can be realised using standard photonic elements.
Longer delays or devices with specific requirements can be designed if not available in the standard device library. Mode transformers are integrated into the PLC for efficient coupling into conventional single mode fibres.