[Show abstract][Hide abstract] ABSTRACT: A comprehensive investigation of real-time temperature-induced resonance shift cancellation for silicon wire based biosensor arrays is reported for the first time. A reference resonator, protected by either a SU8 or SiO(2) cladding layer, is used to track temperature changes. The temperature dependence of resonators in aqueous solutions, pertinent to biosensing applications, is measured under steady-state conditions and the operating parameters influencing these properties are discussed. Real-time measurements show that the reference resonator resonances reflect the temperature changes without noticeable time delay, enabling effective cancellation of temperature-induced shifts. Binding between complementary IgG protein pairs is monitored over 4 orders of magnitude dynamic range down to a concentration of 20 pM, demonstrating a resolvable mass of 40 attograms. Reactions are measured over time periods as long as 3 hours with high stability, showing a scatter corresponding to a fluid refractive index fluctuation of ± 4 × 10(-6) in the baseline data. Sensor arrays with a SU8 protective cladding are easy to fabricate, while oxide cladding is found to provide superior stability for measurements involving long time scales.
[Show abstract][Hide abstract] ABSTRACT: We present recent advances in the development of a waveguide microspectrometer chip with high spectral resolution in the near-infrared part of the spectrum. The microspectrometer is designed for a high index contrast silicon-on-insulator (SOI) platform, where high number of spectral channels can be obtained with high spectral resolution in a compact device. We present a 100-channel SOI microspectrometer with designed spectral resolution of ~0.08 nm at 1.5 mum wavelength and about 8x8 mm2 in size. A number of critical design issues are discussed, including design of deep-etched tapers near the Rowland circle required for high-resolution performance as well as coupling between closely spaced waveguides. Device fabrication process is discussed in detail, including two-step e-beam patterning and two-level ICP etches, the focus being on achieving deep and smooth vertical etches in silicon with controllable sub-micron waveguide widths and gaps. The potentially available spectral range of the microspectrometer is limited by the transparency of silicon, extending from the band edge of Si at 1.107 mum to the onset of lattice phonon absorption band near 5 mum. Such compact high-resolution multi-channel integrated microspectrometers are promising for a variety of applications, including spectroscopy, telecommunications, optical interconnects, environmental and bio-sensing.
No preview · Article · Jan 2010 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: In this chapter we discuss recent advances in silicon photonics research at the National Research Council Canada. We review
our work on first implementations of subwavelength grating structures in silicon waveguides, including efficient fiber-chip
coupling structures, and anti-reflective and high-reflectivity structures formed at the SOI waveguide facets. Silicon planar
waveguide spectrometer chips are introduced, namely a high-resolution arrayed waveguide grating spectrometer and the first
planar waveguide Fourier-transform spectrometer with a largely increased light gathering capability. Finally, we review our
work in developing silicon-wire biological sensors with excellent surface sensitivity, ultracompact sensor designs, and new
waveguide geometries that allow these sensors to be densely arrayed for compatibility with conventional microarray spotters.
These sensors provide a practical route to the development of label-free micro-array biochips for multi-analyte monitoring.
[Show abstract][Hide abstract] ABSTRACT: We report a SOI ring resonator biosensor array with 1 reference ring and 4 sensing rings, using WDM as the addressing scheme. On-chip referencing and temperature shift cancellation are demonstrated, and the differential signal shows a low temperature sensitivity of ~plusmn0.8 pm/degC.
[Show abstract][Hide abstract] ABSTRACT: A method is developed for extracting the coupling and loss coefficients of ring resonators from the peak widths, depths, and spacings of the resonances of a single resonator. Although the formulas used do not distinguish which coefficient is coupling and which is loss, it is shown how these coefficients can be disentangled based on how they vary with wavelength or device parameters.
[Show abstract][Hide abstract] ABSTRACT: Silicon photonic wire waveguides have a remarkably high response to surface molecular binding. Evanescent field waveguide sensors based on silicon can be interrogated using Mach-Zehnder interferometers, ring resonators, or by probing surface gratings in a reflection geometry. This paper compares these approaches from a theoretical viewpoint and through recent experimental results, with the goal of defining a path from our existing individual sensors to practical biosensor array chips.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate densely folded spiral cavity resonator with Q > 20,000 and an area of 30 μm × 30 μm. We show that extended cavity length increases Q and improves the fabrication robustness of resonators.
[Show abstract][Hide abstract] ABSTRACT: In this invited paper we introduce several types of waveguide spectrometers. We present a high-resolution 50-channel AWG spectrometer, including its use to interrogate a fibre Bragg grating sensor with a high wavelength accuracy of 1 pm. A 40-channel AWG operating in a broad wavelength range of 1250-1550 nm is introduced. We present a new 15-channel CWDM demultiplexer using a single curved Si-wire waveguide with an etched sidewall grating and chip size of only 90 μm × 140 μm. Finally, the first planar waveguide Fourier-transform spectrometer is presented, with a greatly increased light gathering capability and a static design.
[Show abstract][Hide abstract] ABSTRACT: A new interferometer-based optical sensing platform with nanostructured thin films of ZrO2 or TiO2 as sensing environment has been developed. With the application of an IC compatible Si(3)N(4) waveguide technology, Mach-Zehnder interferometer devices have been fabricated. The application of the glancing angle deposition technique allowed fabrication of nanostructured thin films as the optical sensing environment. Sensing ability of fabricated devices has been demonstrated through the refractive index measurement of a known gas. The transmission spectra and time response measurements have demonstrated a maximum phase shift of Delta phi=pi/10 and a |Delta P(out)|=0.65 dBm. Devices with TiO2 film on the sensing region performed much better than devices with ZrO2, with sensitivity twice as high.
[Show abstract][Hide abstract] ABSTRACT: The spectral characteristics of a ring resonator made of Si photonic
wires are modeled using mode expansion of supermodes of the directional coupler.
The influence of the coupling coefficient, loss factor and waveguide dispersion
on the spectral features are analyzed in detail. The model is then compared
with the experimental data of a ring resonator designed for sensing purposes.
The model that includes a wavelength dependence on coupling length reproduces
the large variations of the envelope of the experimental spectrum, when coupling
coefficient cover its full range from 0 to 1. Fitting parameters explain the
details of the experimental spectrum and contribute to the sensor optimization,
as well as illustrating general guidelines for ring resonator design.
[Show abstract][Hide abstract] ABSTRACT: We report a compact high-resolution arrayed waveguide grating (AWG) interrogator system designed to measure the relative wavelength spacing between two individual resonances of a tilted fiber Bragg grating (TFBG) refractometer. The TFBG refractometer benefits from an internal wavelength and power reference provided by the core mode reflection resonance that can be used to determine cladding mode perturbations with high accuracy. The AWG interrogator is a planar waveguide device fabricated on a silicon-on-insulator platform, having 50 channels with a 0.18 nm wavelength separation and a footprint of 8 mmx8 mm. By overlaying two adjacent interference orders of the AWG we demonstrate simultaneous monitoring of two widely separated resonances in real time with high wavelength resolution. The standard deviation of the measured wavelength shifts is 1.2 pm, and it is limited by the resolution of the optical spectrum analyzer used for the interrogator calibration measurements.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a method of canceling the temperature dependence of ring resonator sensors using a double ring configuration. Temperature calibration curves are provided for SOI photonic wire ring sensors with air and SU8 polymer cladding.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate folded waveguide ring resonators for biomolecular sensing. We show that extending the ring cavity length increases the resonator quality factor, and thereby enhances the sensor resolution and minimum level of detection, while at the same time relaxing the tolerance on the coupling conditions to provide stable and large resonance contrast. The folded spiral path geometry allows a 1.2 mm long ring waveguide to be enclosed in a 150 microm diameter sensor area. The spiral cavity resonator is used to monitor the streptavidin protein binding with a detection limit of approximately 3 pg/mm(2), or a total mass of approximately 5 fg. The real time measurements are used to analyze the kinetics of biotin-streptavidin binding.
[Show abstract][Hide abstract] ABSTRACT: First implementations of subwavelength gratings (SWGs) in silicon-on-insulator (SOI) waveguides are discussed and demonstrated by experiment and simulations. The subwavelength effect is exploited for making antireflective and highly reflective waveguide facets as well as efficient fiber-chip coupling structures. We demonstrate experimentally that by etching triangular SWGs into SOI waveguide facets, the facet power reflectivity can be reduced from 31% to <2.5%. Similar structures using square gratings can also be used to achieve high facet reflectivity. Finite
difference time-domain simulations show that >94% facet reflectivity can be achieved with square SWGs for 5 𝜇m thick SOI waveguides. Finally, SWG fiber-chip couplers for SOI photonic wire waveguides are introduced, including design,
simulation, and first experimental results.
Full-text · Article · Jun 2008 · Advances in Optical Technologies
[Show abstract][Hide abstract] ABSTRACT: We demonstrate silicon photonic wire evanescent field sensors formed by folding long photonic wire waveguides into dense spiral paths that occupy spot sizes less than 150 mum in diameter, and are hence suitable for biochip array formats. These sensors are incorporated into both ring resonator and Mach-Zehnder interferometer (MZI) interrogation circuits, and tested by monitoring streptavidin protein adsorption. The level of detection is less than 1% of a monolayer in either configuration. Using a balanced MZI design, we show that the sensors can be insensitive to temperature and wavelength, while retaining a very high sensitivity to molecular adsorption.
[Show abstract][Hide abstract] ABSTRACT: We review the use of the oxide cladding stress-induced photoelastic effect to modify the polarization dependent properties in silicon-on-insulator (SOI) waveguide components, and highlight characteristics particular to this high index contrast (HIC) systems. The birefringence in SOI waveguides has its origin in the electromagnetic boundary conditions at the waveguide boundaries, and can be further modified by the presence of stress in the waveguiding materials. With typical stress levels in SiO2 films, which are often used as the upper cladding, the waveguide effective index can be altered anisotropically up to the order of 10Ã¢ÂˆÂ’3 for ridges with heights ranging from 1Ã¢Â€Â‰ÃŽÂ¼m to 5Ã¢Â€Â‰ÃŽÂ¼m. This effect can be used effectively to counter the waveguide geometrical birefringence, allowing the waveguide cross-section profiles to be optimized for design criteria other than null geometrical birefringence. Design strategies are developed for using stress engineering to achieve a variety of functions. Polarization insensitive arrayed waveguide gratings (AWGs), polarization insensitive ring resonators, and polarization splitters and filters are demonstrated using these design principles.
No preview · Article · Jan 2008 · Advances in Optical Technologies
[Show abstract][Hide abstract] ABSTRACT: Photonics is playing an increasingly important role in the field of medical diagnostics, genomics and drug discovery. With the advances in molecular biology which gives insight to the processes underlying diseases and drug response, there is a need for new biological sensors to rapidly detect and quantify these processes. Sensing of biological events using planar waveguide evanescent field (EVF) detection offers label-free, high sensitivity, and real time monitoring [1-4]. This is a competing technology with the commercially pervasive SPR (surface plasmon resonance) method, but with the advantage of portability and low cost.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate experimentally and by simulations the use of subwavelength grating patterns on the facets of planar waveguides as a means of modifying facet reflectivity over a wide range of values, from antireflective to highly reflective. An antireflective structure can be obtained from a gradient index effect with triangular gratings. Square gratings can be used to obtain either antireflective or highly reflective facets by an interference effect. Finite difference time domain simulations and calculations based on effective medium theory show that reflectivities well below 1% can be achieved with triangular gratings. Experimentally, facet reflectivities as low as 2.0% and 2.4% for the fundamental TE and TM waveguide modes, respectively, are demonstrated for light of 1.55 mum wavelength in silicon-on-insulator ridge waveguides. The experimental results are in good agreement with both effective medium theory and finite difference time domain simulations. The polarization dependence of the effects is also discussed in detail.
Full-text · Article · Oct 2007 · Proceedings of SPIE - The International Society for Optical Engineering