Sam Werquin

Integrated interferometric approach to solve microring resonance splitting in biosensor applications

Silicon-on-insulator microring resonators have proven to be an excellent platform for label-free nanophotonic biosensors. The high index contrast of silicon-on-insulator allows for fabrication of micrometer-size sensors. However, it also limits the quality of the resonances by introducing an intrinsic mode-splitting. Backscattering of optical power at small waveguide variations lifts the degeneracy of the normal resonator modes. This severely deteriorates the quality of the output signal, which is of utmost importance to determine the performance of the microrings as a biosensor. We suggest an integrated interferometric approach to give access to the unsplit, high-quality normal modes of the microring resonator and experimentally show an improvement of the quality factor by a factor of 3.

Measurement of small molecule diffusion with an optofluidic silicon chip

In this work we explore the micro-ring resonator platform to study the diffusion-driven mass transport of small molecules within microfluidic channels. The micro-ring resonators are integrated on a silicon-on-insulator photonic chip and combined with microfluidics in poly(dimethylsiloxane) (PDMS). We apply a strong initial gradient in the solute concentration and use the micro-ring resonators to observe how this concentration evolves over time and space. This can be achieved by tracking the optical resonances of multiple micro-rings as they shift with changing solute concentration. Experiments are performed for both glucose and NaCl and at different temperatures. The measured concentration profiles are used to calculate the diffusion coefficient of both glucose and NaCl in water. The good agreement between measurement and theoretical prediction demonstrates the relevance of this method.

Ring Resonators With Vertically Coupling Grating for Densely Multiplexed Applications

Silicon-on-insulator photonic microring resonators are ideal components for applications that require a high degree of multiplexing because of their small size. However, when very high numbers of microrings are used in parallel, grating couplers and waveguide routing quickly take up more chip space than the actual rings. Therefore, we suggest to combine microring resonators with local weak gratings to read out light directly from the microring while still maintaining high-quality factors of 19 000. We demonstrate simulation results and an experimental analysis of different grating parameters. The resonance spectrum is recovered from the vertical emission of the microring grating, without using a traditional output waveguide.

Silicon photonics biosensing: different packaging platforms and applications

We present two different platforms integrating silicon photonic biosensors. One is based on integration with reaction tubes to be compatible with traditional lab approaches. The other uses through-chip fluidics in order to achieve better mixing of the analyte.

Silicon-on-insulator microring resonators for photonic biosensing applications

Silicon-on-insulator microring resonators have proven to be an excellent platform for label-free nanophotonic biosensors. The high index contrast of the silicon-on-insulator waveguides allows for fabrication of micrometer size sensors. Their small size combined with high sensitivity make them ideal candidates for integration in sensing arrays as a multiplexed DNA detection platform. By chemically modifying the sensor surface, the microrings can provide sequence selective DNA detection. However, the high index contrast also limits the quality of the resonances by introducing an intrinsic mode-splitting by coupling the degenerate resonator modes. This severely deteriorates the quality of the output signal. The quality of the resonances is of utmost importance to determine the performance of the microrings as a biosensor. We will suggest an integrated interferometric approach to give access to the unsplit, high-quality normal modes of the microring resonator.

Improved performance of highly multiplexed silicion-on-insulator microring sensor chips by surface structure implementation

Silicon-on-insulator microring resonators have proven to be an excellent platform for label-free nanophotonic biosensors. The high index contrast of the silicon-an-insulator platform allows for fabrication of micrometer size sensors and a high degree of multiplexing. To enable robust, low-noise performance of a microring resonator sensor chip in a lab-on-a-chip setting, flood illuminating an array of vertical grating couplers is a promising approach to couple input light into the chip. This technique provides a very high alignment tolerance while at the same time exciting multiple sensors simultaneously for rapid parallel read-out. We demonstrate this technique to obtain a highly multiplexed chip output combined with real time sensor information. However, parasitic reflections on the chip surface can deteriorate the sensor signal and limit the performance. We investigate the use of surface structures to limit these parasitic signals and show a significant improvement of the sensor operation.

Implementation of Surface Gratings for Reduced Coupling Noise in Silicon-on-Insulator Circuits

Coupling light into a silicon-on-insulator photonic chip has always been the first hurdle to overcome when using photonic integrated circuits. For applications that require robust, low-noise performance, and high degree of multiplexing, flood illuminating an array of vertical grating couplers is a promising approach to couple input light into the chip waveguides. This technique provides a very high alignment tolerance and allows simultaneous excitation of multiple waveguides for rapid parallel readout. However, parasitic reflections of the coupled light on the chip substrate introduce interferences and limit the device performance. We investigate the use of grating structures implemented on the chip surface to limit these parasitic signals and demonstrate a significant reduction of the coupling noise.

Ring resonator based SOI biosensors

In this paper, two recent advances in silicon ring resonator biosensors are presented. First, we address the problem that due to the high index contrast, small deviations from perfect symmetry lift the degeneracy of the normal resonator mode. This severely deteriorates the quality of the output signal. To address this, we discuss an integrated interferometric approach to give access to the unsplit, high-quality normal modes of the microring resonator. Second, we demonstrate how digital microfluidics can be used for effective fluid delivery to nanophotonic microring resonator sensors fully constructed in SOI.

Silicon Ring Resonator-Based Biochips

This chapter discusses the use of silicon photonics biochips incorporating ring resonator sensors. After an introduction to the ring sensor, we will discuss other aspects like peak splitting compensation, the exploitation of the Vernier effect for increased sensitivity, and the use of dual-polarization rings to determine conformational information.