In U.S. Patent 7,643,714, California Institute of Technology (Caltech) researchers Michael J Hochberg, Tom Baehr-Jones and Axel Scherer reveal a set of tools for concentrating light to a high degree by using silicon or other high index contrast waveguides making a range of silicon nanophotonic devices possible.
The Caltech scientists have fabricated devices that demonstrate some of the many applications that can be contemplated when such nonlinear materials are exploited. While the description were expressed using single crystal silicon, the researchers believe that similar devices, systems and methods can be provided using polycrystalline silicon ("poly silicon") or amorphous silicon (also referred to as "a-silicon" or ".alpha.-silicon"). In particular, by utilizing split waveguides (or slot waveguides), they are able to greatly enhance the optical fields in the cladding of a tightly confined waveguide, without greatly enhancing the optical losses of the same waveguide.
Combining the high field concentrations available from the split waveguides with the high nonlinear activity of nonlinear optical polymers permits the development of nonlinear optical devices operating at much lower optical input power levels than are possible with conventional free space or chip based systems.
They have demonstrated four-wave mixing (which is based upon chi3), as well as optical rectification (based on chi2), in such waveguides. Using these waveguides it is possible to decrease the power levels needed to observe significant nonlinearities to the point where, by contrast with conventional nonlinear optics, it can be done with non-pulsed, continuous wave lasers.
Chi2 and chi3 based optical effects can be used in particular to build on-chip optical parametric oscillator ("OPO") systems, where two input wavelengths can be mixed together to produce sum and difference frequencies. These frequencies can be either higher or lower than the input frequencies, and can be made tunable. These effects work for frequencies from the ultraviolet and X-ray regime all the way out into the far infrared and microwave, and in fact can work down to DC in some cases, particularly with optical rectification.
Systems and methods from the tool kit can be used to construct optical logic functionality, such as optical AND or optical flip-flops. It is believed that Caltech systems can be employed to create optical NAND, OR, NOR and XOR gates, and optical latches, or optical memory. The systems can further comprise pump lasers integrated onto the same chip. The systems can further comprise off-chip feedback or amplification for frequency conversion or pulse generation. In some embodiments, an additional electrical signal is coupled into the structure to provide active mode locking.
Below are two nanophotonic devices made by the Caltech scientists with their new tool set as illustrated in U.S. Patent 7,643,714.
FIG. 7 is a diagram showing an scanning electron microscope (SEM) image of a portion of an oval slot waveguide.
FIG. 8 is a diagram showing a more detailed SEM image showing the coupling region of an exemplary slot waveguide and an input waveguide.
