The “Universal Optical Breadboard” (UOB) concept, in its most general form, is a template structure from which microfluidic integration is used to define form and function (Figure 1).  By utilizing different UOB substrates, from passive silicon based materials to active III-V semiconductor heterostructures, and integrating them with micofluidic circuits capable of delivering nanolitre fluid volumes of varying optical character, a much richer (and denser) suite of optical functionality can be obtained. 

In this project we envision the UOB breadboard to consist of a highly dispersive planar photonic crystal formed into a silicon-on-insulator (SOI) wafer. The strong curvature in the photonic bands of the SOI photonic crystal near high-symmetry points at the first Brillouin zone (IBZ) boundary result in an effective mass (group index dispersion) for photons which can be extremely heavy, and both positive or negative.  This allows one to trap light on the wavelength scale, forming resonators or waveguides by simply lowering (acceptor-like states) or raising (donor-like states) the local refractive index. Microfluidically injected fluids into the UOB may then be used to define the optical functionality, fundamentally integrating the fluid into the optics.  As an example of this, we show schematically in Figure 2 a tunable guided wave coupler that allows fluid-selectable wavelengths of light to be transferred from a “fiber-like” waveguide layer into the underlying silicon photonic crystal.

Figure 1: Schematic concept of the Universal Optical Breadboard, with a microfluidic, optical fiber, and optical substrate layer integrated together.

Figure 2: Schematic of a fluid tunable guided wave coupler.  Light may initially be coupled from standard optical fiber into the middle PECVD deposited “fiber-like” waveguide layer, where it can then be transferred into the underlying semiconductor (silicon in this example) photonic crystal layer.  The top fluid layer, manipulated through soft-lithography microfluidics, is used to control/trim the wavelength of the coupler by interacting with the evanescent tail of the “fiber-like” guided mode.

Research Group