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Passive Waveguide

Sandia develops High-performance passive waveguide technologies for sensing and communication applications critical to our nation. Several planar lightwave circuit (PLC) technologies have been developed at Sandia that are ideally suited to applications where low-loss waveguides, thermo-optic switches, and high-Q resonators are needed.

Sandia's strengths in modeling, design, fabrication, and testing have successfully produced ultra low loss, planar lightwave circuit (PLC) technologies with record low loss and high manufacturability in a fully operational CMOS fabrication line.

Lateral mode interference (LMI) 3 dB splitter: simulation (top) and fabricated device (middle), measured results (bottom)


Our Low Loss Silicon Nitride waveguide technology consists of a patterned Silicon Nitride optical waveguide core sandwiched between silicon dioxide cladding materials fabricated on a standard 6-inch silicon wafer. Process development efforts have demonstrated a polarization maintaining, single mode, optical waveguide, with record low attenuation of 0.1 dB/cm.

The index of refraction difference between the silicon nitride core material and the silicon dioxide cladding (2.01 vs. 1.45) makes this an ideal material system for designing small radius bends and complicated device geometries. Polysilicon heaters, metallized bondpads and mode expanding taper interfaces have been monolithically integrated and delivered with this principal PLC technology, and future micro-system integration efforts are under way for multi-material, multiple technology integration. For applications, such as resonant ring gyros where lower attenuation losses are desirable, accelerated process development is currently being executed to produce a (SiON/SiO2) technology with an attenuation goal of 0.05dB/cm or less.  

Evanescent Wave Microring Biochemical Sensor

The transmission of a waveguide coupled high-Q microring resonator is sensitive to the perturbation of its optical path. A slight change of either the mode index or the microring physical size can cause a significant change in the transmission near its resonances. The high-Q integrated microring resonators can be used as ultra sensitive photonic transducers for a variety of sensor applications such as biochemical, gravity, acceleration, pressure, and electromagnetic sensing.

Microring biochemical sensor with a reference microring resonator

Fabricated Microring

Ring resonance for water

Ring resonance for methanol


Based on the evanescent wave and the high-Q microring resonator, Sandia demonstrated a liquid phase chemical sensor that can sense the small change of index of refraction of liquid phase chemicals. The on-chip evanescent wave microring biochemical sensors have the intrinsic capability and potential for large array multi-channel device integration and low cost mass production. Two parallel rings are used in transmission with separate input and output waveguides. One ring is the sense ring while the other is a reference ring embedded in a thick cladding and is not exposed to any biochemical liquids. On the top of the sense ring a window is etched to thin the cladding layer so that the evanescent wave can penetrate through it to reach the liquid. The input light is first coupled into the input waveguide and then split equally into two waveguides which are coupled to the reference ring and the sense ring. Two additional waveguides are used to couple the light out from the reference ring and the sense ring. A beam combiner is used to combine the light from the rings. As the input wavelength is scanned, we expect to see two distinct transmission resonances, one for each ring. The difference between these resonance frequencies is a direct measure of the refractive index of the liquid in the sense region.

Sandia has developed multiple passive waveguide technologies in combinations of the following materials:

Silicon Dioxide
Doped Silicon Dioxide
Silicon Nitride
Silicon Oxynitride
Silicon on Insulator



Contact MEMS at Sandia: memsinfo@sandia.gov

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