We report an optical cavity based biosensor using a novel differential detection method for point-of-care applications. Two laser diodes allow for multiplexing capability along with the ability to enhance the responsivity using differential detection. The laser wavelengths are chosen so that the optical intensities of two lasers change monotonically with opposite slopes upon the adsorption of desired biomarkers. The cavity width, PMMA thickness, and silver thickness have been optimized to achieve a large change in scaled differential value. We chose biotinylated BSA detection with Avidin as a receptor molecule to demonstrate the proposed design. Avidin is attached directly to the PMMA layer by physisorption. Then, biotinylated BSA is introduced to the sample and the intensities of the laser diodes are measured by a sCMOS camera. A change in the scaled differential value will correlate to the binding of biotinylated BSA. In this presentation, we will discuss simulation results, fabrication procedures, and preliminary measurement results.
We proposed a low cost optical cavity based biosensor with a differential detection for point-of-care diagnosis. Two lasers at different wavelengths are used for the differential detection. This method enhances the sensitivity through higher responsivity and noise cancelation. To reduce noise further, especially due to the unstable low cost laser diode output, we employed a referencing method in which a reference pixel value in each CMOS image frame is subtracted from all other pixels. To validate the designed structure and demonstrate the sensitivity of it, we perform refractive index measurements of fluids with our design. In this presentation, we will discuss our design, simulation results, and measurement results.
We propose an optical cavity based biosensor with chained differential detection. A three laser diode sensing mechanism provides multiplexing capability and is used to enhance the responsivity and improve fabrication tolerance using a chained differential detection approach. The differential calculation enhances the sensitivity through (1) increased responsivity compared to the actual optical power changes of the individual laser diodes and (2) noise reduction by canceling out some uncontrollable variations along the path of light since all wavelengths of light used for the differential calculation propagate through the same path. However, the responsivity dies off quickly due to even small variations from the designed cavity width. To correct for this and to improve fabrication tolerance, we introduce another wavelength and employ a chaining approach. In this presentation, we will present simulation results of an optical cavity based biosensor with chained differential detection and progresses toward experimental demonstrations.
We report the integration of a nanomechanical sensor consisting of 16 silicon microcantilevers and polydimethylsiloxane
(PDMS) microfluidics. With our recently developed in-plane photonic transduction method we routinely achieve
microcantilever transduction responsivities in the range of 0.5-1.1 μm-1, which is comparable to the best reported for the
laser reflection readout method used in atomic force microscopy (AFM). Prior work has established that differential
surface stress as low as 0.23 mN/m is readily measurable with our arrays. In this paper we show biotin-streptavidin
sensing with a differential surface stress of ~2.3 mN/m as a first step toward characterizing integrated microcantilever
array/microfluidic sensors.
We demonstrate a compact trench-based silicon-on-insulator (SOI) rib waveguide ring resonator comprised of trench-based bends and splitters. It has a perimeter of 50 µm and occupies an area of only 25×25 µm. The measured free spectral range (FSR) is 13.2 nm, which the largest reported for an SOI rib waveguide ring resonator. The measured FSR, full width at half maximum, and quality factor match reasonably well with analytical calculations. Further calculation shows that a FSR of 50.8 nm is achievable for an SOI rib waveguide ring resonator with a perimeter of 15 µm.
A fabrication process for PFCB waveguide air-trench bends with scanning electron microscope (SEM)-based electron
beam lithography (EBL) and autoalignment has been developed and high efficiency air-trench bends (97.2% for TE
polarization and 96.2% for TM polarization) have been demonstrated. We have successfully developed a high aspect
ratio (18:1) anisotropic PFCB etch using a CO/O2 etch chemistry in an inductively coupled plasma reactive ion etcher
(ICP RIE) for PFCB waveguide air-trench splitter fabrication. The fabricated splitters show a 90.1% overall efficiency
and ~ 85-to-15 (85:15) splitting ratio for 950 nm wide splitter trench, which closely matches 2D-FDTD simulation
results. Using air-trench bends, an ultracompact PFCB arrayed waveguide grating (AWG) 8 x 8 wavelength
demultiplexer for Wavelength Division Multiplexing (WDM) application had been designed. Compared to a
conventional AWG in the same material system, the air-trench bend AWG reduces the area required by a factor of 20.
Compact ring resonators using these splitters and bends has been designed and fabrication and improvements are
currently underway.
Microcantilevers show significant promise in sensing minute quantities of chemical and biological analytes in vapor and
liquid media. Much of the reported work on microcantilever sensors has made use of single functionalized
microcantilevers, usually derived from commercially available atomic force microscope (AFM) cantilevers. However,
arrays with hundreds to thousands of microcantilevers on a single chip are required to create sophisticated, broad
spectrum chemical and biological sensors in which individual microcantilevers have different bio- or chemoselective
coatings. Unfortunately, the most sensitive microcantilever readout mechanisms (such as laser beam reflection as used in
atomic force microscopy) are not readily scalable to large arrays. We therefore introduce a new microcantilever
transduction mechanism for silicon-on-insulator (SOI) microcantilevers that is designed to scale to large arrays while
maintaining a very compact form factor and high sensitivity. This mechanism is based on in-plane photonic transduction
of microcantilever deflection in which the microcantilever itself forms a single mode rib waveguide. Light from the end
of the microcantilever is directed across a small gap to an asymmetric receiving waveguide with two outputs that enables
differential detection of microcantilever deflection. Initial noise and optical power budget calculations indicate that
deflection sensitivities in the 10's of picometer range should be achievable.
Silicon-on-insulator (SOI) is a widely recognized as a very promising material for high-index integrated photonic chips
because of its compatibility with complementary metal oxide semiconductor (CMOS) technologies. One challenge in
integrating many photonic devices on a single chip is to realize compact waveguide bends and splitters, particularly for
rib waveguide geometries. We report compact SOI rib waveguide 90° bends and splitters with SU8-filled trenches based
on total internal reflection (TIR). We use the two-dimensional finite difference time domain (2D-FDTD) method to
numerically calculate bend and splitter efficiencies. The maximum bend efficiency is 98.0%. The splitter efficiency is
49.0% for transmission and 48.9% for reflection with an 80 nm wide SU8-filled trench. Electron beam lithography
(EBL) is used to accurately position the trench interface relative to the waveguides and to pattern the 80 nm wide trench.
Inductively coupled plasma reactive ion etching (ICP RIE) is used to achieve a vertical sidewall. For fabricated bends
the measured bend loss is 0.32±0.02 dB/bend (93% bend efficiency) for TE polarization at a wavelength of 1.55 microns,
which is the lowest SOI rib waveguide 90° bend loss reported in literature. The initial measured splitter efficiency is
54.6% for transmission and 29.2% for reflection. This can be improved by avoiding defects in fabricated structures.
We discuss the design of a compact ring resonator (RR) and Mach-Zehnder interferometer (MZI) in a low-refractive-index-contrast waveguide material system through the use of air trenches. A narrow air trench at the intersection of one input and two output waveguides can function as a high-efficiency splitter, while wider air trenches operate as waveguide bends. We first discuss the design of individual splitters and bends and then show how they can be used to realize a compact MZI and RR. The RR has a footprint of only 70×100 µm, and its optical efficiency at the drop wavelengths is 86%. The free spectral range and full width at half maximum are 7.2 and 0.5 nm, while the Q factor is >3,000. The MZI occupies only 165×130 µm, and its calculated optical efficiency is 90%.
Compact waveguide bends and splitters are important components to enable dense integration of many functions on a single photonic chip. A common approach is to use a waveguide material system in which a large refractive index contrast between the core and clad materials is available. This permits a small bend radius to be used while still achieving high optical efficiency for the bend. However, such material systems generally have higher propagation loss than is possible with low refractive index contrast material systems such as silica. In this presentation we examine an approach to make the bend size essentially independent of the core/clad refractive index contrast using total internal reflection from a planar interface. We show through both 2D and 3D finite difference time domain (FDTD) simulation that very high bend efficiencies are possible when the correct bend design principles are adhered to. We illustrate this in practice with single air interface bends (SAIBs) in a PFCB material system with approximately 1% refractive index contrast. We experimentally demonstrate 45 degree bends with 0.3 dB loss per bend, and discuss the effects of fabrication issues such as misalignment, etch undercut, and etch roughness.
High efficiency small-area waveguide bends and splitters for perfluorocyclobutane (PFCB) copolymer materials have been designed with air trench structures (ATSs). An air trench at the intersection of one input and two output waveguides can function as a high efficiency splitter. High efficiency small-area waveguide bends are achieved by placing ATSs at the waveguide bend corners and operate through total internal reflection (TIR). In this paper we discuss bends and splitters that are designed specifically for constructing a ring resonator and a Mach-Zender interferometer. Two dimensional (2-D) finite difference time domain (FDTD) analysis has been used for design. In order to further examine the performance of realistic small-area air trench bend structures, we have also employed three dimensional (3-D) FDTD. From 3-D FDTD simulation results, we find that the 2-D designs are representative of actual devices. By combining small-area air trench bends and splitters, we show how a compact ring resonator can be realized. Simulation results show attractive properties for the proposed ring resonator design. Preliminary ATS etch results of PFCB with CO and O2 shows the possibility of fabricating the proposed devices.
The ability to make small-area bends and splitters in low index contrast waveguide materials is a critical enabler to realize densely integrated planar lightwave circuits (PLCs) in such materials. We discuss two approaches, the first based on photonic crystal (PhC) structures of limited spatial extent and the second on single air trenches. In each case, PhC or air trench regions are used to augment conventional waveguides (CWGs) to permit drastic reductions in overall device size while preserving the traditional advantages of CWGs such as straightforward design for single mode operation, low propagation loss, low fiber coupling loss, low dispersion, and mature microfabrication processes. We show how these approaches can be used to realize example devices having a very small footprint, including Mach-Zender interferometers and ring resonators.
We previously proposed the hybrid integration of photonic crystals (PhCs) and conventional index-guided waveguides (CWGs) as a potentially attractive method of realizing compact waveguide elements for large-scale planar lightwave circuits (PLCs). We now examine 90-deg bends and beamsplitters in PhC/CWG structures in which the waveguide core has a high refractive index (3.25) and yet a low refractive index contrast (1.54%) with the clad material. A PhC structure composed of a triangular or square array of air holes is placed at the intersection of input and output waveguides to obtain high efficiency 90-deg bends. We find that diffraction from the boundary of the PhC region with CWG limits the optical efficiency of the bend. To overcome this we use a rigorous design tool based on a microgenetic algorithm (µGA) and a finite difference time domain (FDTD) method to optimize the boundary layer to suppress the unwanted diffraction. We find that this approach yields improvements in the bend efficiency at a wavelength of 1.55 µm from 56.2 to 92.5% (for a triangular PhC structure, TE polarization) and from 72.0 to 97.4% (square PhC structure, TM polarization).
Hybrid photonic crystal (PhC) and conventional waveguide (CWG) structures have been proposed to achieve ultracompact waveguide bends and splitters with very high efficiency (>99.0%). Such elements are enablers to realize large scale planar lightwave circuits (PLCs) with low index contrast waveguide materials such as silica and polymers. In this paper, we first discuss high efficiency 90 degree bends and splitters and then show how these can be used to create compact ring resonators. These in turn can be used as building blocks for add/drop filters, band pass filters, wavelength division multi-/demultiplexers, and all optical switches.
We have proposed the hybrid integration of photonic crystals (PhCs) and conventional index-guided waveguides (CWGs) as a potentially attractive method of realizing compact waveguide elements for large-scale planar lightwave circuits (PLCs). In this paper we briefly review the properties of PhC/CWG 90° bends in low index, low index contrast waveguides and then extend them to waveguides with high index and low index contrast. We find that diffraction from the boundary of the PhC region limits the optical efficiency of the bend. To overcome this we use a rigorous design tool based on a micro-genetic algorithm (microGA) and a finite difference time domain (FDTD) method to optimize the boundary layer to suppress the unwanted diffraction. We find that this approach yields an improvement in the bend efficiency for light at 1.55 micron from 80% to 95%.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.