  A novel technique is presented for realising programmable silicon photonic
circuits. Once the proposed photonic circuit is programmed, its routing is
retained without the need for additional power consumption. This technology
enables a uniform multi-purpose design of photonic chips for a range of
different applications and performance requirements, as it can be programmed
for each specific application after chip fabrication. Therefore the cost per
chip can be dramatically reduced because of the increase in production volume,
and rapid prototyping of new photonic circuits is enabled. Essential building
blocks for programmable circuits, erasable directional couplers (DCs) were
designed and fabricated, utilising ion implanted waveguides. We demonstrate
permanent switching between the drop port and through port of the DCs using a
localised post-fabrication laser annealing process. Proof-of-principle
demonstrators in the form of generic 1X4 and 2X2 programmable switching
circuits were then fabricated and subsequently programmed, to define their
function.
