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Low-loss coupling of an optical fiber, or an integrated optical source, to high refractive index photonic circuits



The field of microelectronics seeks to integrate photonics in order to improve the performance of current electronic systems. The possibility of enabling optical communication between electronic chips, via an optical bus, will have a major impact on the performance of electronic systems. Research in the field is very active, but sometimes the advanced solutions are poorly adapted and difficult to achieve.

Silicon, mainly used in electronics, limits major advances in this field due to its high light refraction index (i.e. 3.5 for silicon vs 1.44 for fiber optics). It is difficult to directly inject light signals from one material to another. This leads to losses of optical intensity which are mainly generated by the reflections at the injection interface as well as by the excessive difference in coverage between the optical modes. The impact of these two phenomena can be greatly reduced by using an intermediate component.

The present invention addresses the identified problems.


Our new technology applies to the fields of microelectronics and biosensors. It allows the passage of light coming from the exterior (e.g.: optical fiber) or from the interior (e.g.: integrated hybrid optical source) of the chip towards a photonic circuit that has been manufactured from high-index materials of refraction. The reverse is also possible.

The invention is based on two consecutive and distinct steps, starting with the coupling of the fiber in a micrometric resolution guide produced by standard photolithography (with a refractive index comparable to that of the fiber), thus allowing end-to-end coupling simple and efficient. The next step is the alignment of the guide produced by photolithography on the nanostructures of the component with a high refractive index, which is relatively simple thanks to precise control of the thicknesses of the interface layers between the nanometric guide with a high index and the guide. low index micrometer.

Our technology therefore makes use of an intermediate waveguide having a refractive index close to the index of the optical fiber. This makes it possible to minimize the losses due to the reflection and to the covering of the optical modes. Given the lower index difference, the waveguide will be able to have a geometry, therefore dimensions closer to that of the fiber, and thus recover almost all of the signal. Once the signal is in this intermediate guide, the signal is transferred by directional coupling into a high refractive index guide, often silicon, having a geometry specially designed to allow low-loss transfer. The effective refractive indices of waveguide optical modes fabricated from high-index materials, including semiconductors such as silicon, can be greatly lowered when thinned to a few hundred nanometers. This is what allows low-loss coupling with the intermediate guide.



  • Less signal loss when passing light.

  • Simplicity of manufacture: very high injection efficiency in the high refractive index material which can be obtained by using low resolution lithography. The solution is essentially 2D.

  • Insensitive to alignment: major benefit for chip packaging.

  • Variety of materials: The materials used for manufacturing can be very varied.

  • Variety of configurations.

  • Companies targeted: optical telecommunications, microelectronics, biosensors, others such as TeraXion, Teledyne Dalsa, IBM, Texas Instruments, Intel, AMD, ST Microelectronics.


  • Injection by the facets: allows an easier alignment.

  • Less than 1dB of loss per connection for the coupler.

  • Short coupling distance possible (< 100 ?m).

  • Polarization dependent and polarization independent designs are possible.

  • Injection/extraction from edge or center of chip.

  • Compatible with passive fiber alignment schemes (eg V-groove, U-groove).


  • Microelectronics: chip-to-chip interconnections, 3D integration, others.

  • Biosensors.

  • Telecommunications.



  • TRL 3: the proof of concept was carried out by simulation.

  • First generation prototype manufactured and characterized, demonstrating the effectiveness of the concept.


  • US Patent 8,787,712, issued July 22, 2014.

  • Canadian Patent 2,822,685, issued July 4, 2017.


Research or marketing partners. Licenses available.

Project Director: François Nadeau

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