Trimming of Athermal Silicon Resonators

Technology #15448

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FIG. 1A is a schematic cross-sectional view of an example waveguide structure including an index tuning cladding layer and a thermo-optic coefficient compensation cladding layer over the waveguide core.  FIG. 1B is a schematic planar top-down view of the waveguide structure of FIG. 1A configured in a racetrack resonator photonic device.FIG. 2 is a plot of the experimentally measured thermo-optic performance of an experimental waveguide having the structure of FIGS. 1A-1B, before and after the refractive index of the waveguide is tuned.FIG. 3 is a plot of the change in the resonant wavelength of a waveguide resonator like that of FIG. 1B as induced by index changes in the refractive index tuning cladding layer for three separate layers of the chalcogenide As2S3 having thicknesses of 20 nm, 30 nm, and 50 nm, respectively.
Professor Lionel Kimerling
Department of Materials Science and Engineering, MIT
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Vivek Raghunathan
Microphotonics Center, MIT
Vivek Singh
Department of Materials Science and Engineering, MIT
Anuradha Agarwal
Materials Processing Center, MIT
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Jurgen Michel
Materials Processing Center, MIT
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Stefano Grillanda
Politecnico di Milano
Andrea Melloni
Politecnico di Milano
Francesco Morichetti
Politecnico di Milano
Managed By
Jim Freedman
MIT Technology Licensing Officer - Chemicals, Instruments, Consumer Products
Patent Protection

Athermal photonic waveguide with refractive index tuning

US Patent 9,110,221
High capacity, photo-trimmable athermal silicon waveguides
Group IV Photonics (GFP), 2012 IEEE 9th International Conference, pp.45,47, 29-31 Aug. 2012


WDM devices, electronic-photonic integrated chip, waveguide, resonator

Problem Addressed

Silicon based ring resonators form an integral part of the WDM architecture of an electronic-photonic integrated chip. However, fabrication variations and temperature fluctuations alter the response of the optical filters. Active tuning involving heaters and thermo-electric coolers of these resonators have been proposed to keep the response within desirable limits, but these solutions prove power inefficient and the number of I/O lines limits the integration density, and thermal tuning energy constitutes a significant portion of the energy cost.

Also, there is a shift in filter response of an athermal ring, which consists of a negative thermo-optic (TO) polymer cladding, which needs to be tuned back to its desired value due to fabrication variations.


This invention is about a Silicon based trimmable athermal ring resonator with energy efficiency driving Moore’s law. The prototype design rule requires encapsulation of a-Si core with a thin layer of As2S3 before the polymer top cladding deposition. Trimmable athermal waveguides leverage the photosensitivity of As2S3 and negative TO coefficient of polymers to address the fabrication and temperature sensitivities of Si based resonators. Constraints of TO resonance shift lower than 1.3 pm/K and trimming window of 5 GHz imposed by a 20 GHz channel spacing can been successfully satisfied by resonators fabricated with these waveguides.


  • Minimum TO peak shift and high trimming resolution
  • Closer channel spacing and higher channel count
  • Bandwidth multiplication due to wavelength division multiplexing (WDM) (incentive for electronic-photonic integration)