Suspended animation: The researchers suspended two waveguides (the horizontal blue cables) to allow them to move freely under the influence of attractive and repulsive optical forces. The vertical blue structures are photonic crystal waveguide supports.
The Yale group’s approach demonstrates the possibility of manipulating one beam of light with another, right on the chip, without the need for slow, bulky heaters or external crystals. And because of their ability to harness both positive and negative forces, they can now effectively double the range of control over photonics circuitry.
The group used two identical waveguides–the optical equivalents of electronic wires, encasing the light beams moving through them–and suspended them in a central coupling region to allow them to move freely under the influence of the optical force. Then the researchers sent in a beam of laser light, split it in half, and forced one half through a longer path than the other. When the two halves of light recombined, they were out of phase because of having traveled different path lengths. The researchers found that when the light beams were out of phase, their waveguides repelled each other, but when the light was in phase, the waveguides pulled closer together. Because they could change the phase difference between the beams just by tweaking the wavelength of the input laser light, the researchers ended up with a new “knob” to control the optical force in a very simple step.
Though they weren’t transferring information or even turning switches on and off, the group successfully demonstrated the existence of–and easy flipping between–both sides of the force. Their next steps, says Tang, will be to build more complex circuits and improve the efficiency of their technique. They’ll also try to make the force stronger. “The bigger the force, the better,” Tang says.
The benefit of the Yale work, according to Caltech’s Painter, is that the researchers demonstrated the forces used for switching, but they also did it in a silicon system. That shows promise for future integration with microelectronics structures that are already processed on silicon chips. With the flexibility to control the forces right on the chip, key functionality would be added to the silicon microphotonics toolkit. The ultimate goal would be all-optical switches and devices, such as an optical bus that transfers information through a CPU with no electronic parts at all.