Daan Martens

Silicon and silicon nitride photonic circuits for spectroscopic sensing on-a-chip [Invited]

There is a rapidly growing demand to use silicon and silicon nitride (Si3N4) integrated photonics for sensing applications, ranging from refractive index to spectroscopic sensing. By making use of advanced CMOS technology, complex miniaturized circuits can be easily realized on a large scale and at a low cost covering visible to mid-IR wavelengths. In this paper we present our recent work on the development of silicon and Si3N4-based photonic integrated circuits for various spectroscopic sensing applications. We report our findings on waveguide-based absorption, and Raman and surface enhanced Raman spectroscopy. Finally we report on-chip spectrometers and on-chip broadband light sources covering very near-IR to mid-IR wavelengths to realize fully integrated spectroscopic systems on a chip.

Compact Silicon Nitride Arrayed Waveguide Gratings for Very Near-Infrared Wavelengths

In this letter, we report a novel high-index-contrast silicon nitride arrayed waveguide grating (AWG) for very near-infrared wavelengths. This device is fabricated through a process compatible with a complementary metal-oxide-semiconductor fabrication line and is therefore suitable for mass fabrication. The large phase errors that usually accompany high-index-platform AWGs are partly mitigated through design and fabrication adaptions, in particular the implementation of a two-level etch scheme. Multiple devices are reported, among which a 0.3-mm2 device which, after the subtraction of waveguides loss, has a -1.2 dB on-chip insertion loss at the peak of the central channel and 20-dB crosstalk for operation

Photonic detection and characterization of DNA using sapphire microspheres

\sim 900

Comparison between Vernier-cascade and MZI as transducer for biosensing with on-chip spectral filter

nm with a channel spacing of 2 nm. These AWGs pave the way for numerous large-scale on-chip applications pertaining to spectroscopy and sensing.

A low-cost integrated biosensing platform based on SiN nanophotonics for biomarker detection in urine

Abstract. A microcavity-based deoxyribonucleic acid (DNA) optical biosensor is demonstrated for the first time using synthetic sapphire for the optical cavity. Transmitted and elastic scattering intensity at 1510 nm are analyzed from a sapphire microsphere (radius 500  μm, refractive index 1.77) on an optical fiber half coupler. The 0.43 nm angular mode spacing of the resonances correlates well with the optical size of the sapphire sphere. Probe DNA consisting of a 36-mer fragment was covalently immobilized on a sapphire microsphere and hybridized with a 29-mer target DNA. Whispering gallery modes (WGMs) were monitored before the sapphire was functionalized with DNA and after it was functionalized with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The shift in WGMs from the surface modification with DNA was measured and correlated well with the estimated thickness of the add-on DNA layer. It is shown that ssDNA is more uniformly oriented on the sapphire surface than dsDNA. In addition, it is shown that functionalization of the sapphire spherical surface with DNA does not affect the quality factor (Q≈104) of the sapphire microspheres. The use of sapphire is especially interesting because this material is chemically resilient, biocompatible, and widely used for medical implants.

Silicon photonics biosensing: different packaging platforms and applications

Abstract The Mach-Zehnder interferometer (MZI) and the Vernier-cascade are highly responsive photonic sensors with large design freedom. They are therefore very suitable for interrogation through a broadband source and an on-chip spectral filter, a sensing scheme that is well equipped for point-of-care applications. In this work, the MZI is shown to outperform the Vernier-cascade through a better minimum detectable wavelength shift as well as a higher power efficiency, indicating its superiority in this sensing scheme. Fabricated MZIs yield bulk detection limits down to 8.8×10−7 refractive index units (RIU) in a point-of-care compatible measuring setup, indicating the potential of the proposed sensing scheme.

CMOS-compatible silicon nitride spectrometers for lab-on-a-chip spectral sensing

We present a low-cost integrated nanophotonic lab-on-a-chip platform suitable for point-of-care (POC) biomarker analysis. The sensor chip included in the platform contains multiplexed Mach–Zehnder interferometers with an on-chip optical spectral analyser consisting of an arrayed-waveguide grating. The sensor chip is fabricated in silicon nitride material, which makes it compatible with consumer-electronics-grade sources and detectors, leading to the possibility of low-cost instrumentation. The nanophotonic sensor chip exhibits a detection limit of 6 × 10−6 RIU (Refractive Index Units), which is in the same order of magnitude as the reported values for state-of-the-art evanescent wave sensors. The sensor chip is biofunctionalised with specific bioreceptors and integrated into a polymer microfluidic cartridge. The POC instrumentation platform contains optical excitation and read-out sub-systems and dedicated on-board software for real-time analysis of patient samples. To demonstrate the versatility of the platform, we present results both on the detection of an antigen related to tuberculosis directly in urine samples using a laboratory prototype and on the detection of a protein biomarker (CRP) related to inflammation using the integrated instrument.

Ring resonator based SOI biosensors

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 Ring Resonator-Based Biochips

We report on miniaturized optical spectrometers integrated on a photonic integrated circuit (PIC) platform based on silicon nitride waveguides and fabricated in a CMOS-compatible approach. As compared to a silicon- on-insulator PIC-platform, the usage of silicon nitride allows for operation in the visible and near infrared. Furthermore, the moderately high refractive index contrast in silicon-nitride photonic wire waveguides provides a valuable compromise between compactness, optical loss and sensitivity to phase error. Three generic types of on-chip spectrometers are discussed: the arrayed waveguide grating (AWG) spectrometer, the echelle grating or planar concave grating (PCG) spectrometer and the stationary Fourier transform spectrometer (FTS) spectrometer. Both the design as well as experimental results are presented and discussed. For the FTS spectrometer a specific design is described in detail leading to an ultra-small (0.1 mm2) footprint device with a resolution of 1 nm and a spectral range of 100nm. Examples are given of the usage of these spectrometers in refractive index biosensing, absorption spectroscopy and Raman spectroscopy.

Spectroscopic sensing and applications in Silicon Photonics

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.