H.J.W.M. Hoekstra

H.J.W.M. Hoekstra
University of Twente | UT · Department of Electrical Engineering

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273
Publications
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Publications

Publications (273)
Article
Full-text available
The fundamental lower size limit in wavelength selecting structures is explored with the aid of the Heisenberg uncertainty principle. The analysis shows that for a given wavelength selectivity resonating structures with optical feedback have the smallest dimensions. Experimental results obtained with integrated optics microring resonators (Q ~ 3.4...
Article
DNA sequencing by microchip capillary electrophoresis (CE) enables cheap, highspeed analysis of low reagent volumes. One of its potential applications is the identification of genomic deletions or insertions associated with genetic illnesses. Detecting single base-pair insertions or deletions from DNA fragments in the diagnostically relevant size r...
Article
Full-text available
The device principle of a prism-based on-chip spectrometer for TE polarization is introduced. The spectrometer exploits the modal dispersion in planar waveguides in a layout with slab regions having two different thicknesses of the guiding layer. The set-up uses parabolic mirrors, for the collimation of light of the input waveguide and focusing of...
Conference Paper
Full-text available
In this talk, we report theoretically study on ring-resonator based CROW for a photonic refractive index sensor employing Mach-Zehnder interferometer readout. We include study for many-ring CROW as well as single-ring resonator circuit. The transfer matrix method and the complex transmission coefficient approach have been used for such study. Enhan...
Article
A general applicable theory is presented for group delay (GD) in nonabsorbing photonic structures, for which the structural boundaries consist of longitudinally invariant waveguides. It is shown that the sum of the GDs of the various outgoing modes weighted by their transmittances is, in general, approximately equal to the ratio of timeaveraged opt...
Conference Paper
Full-text available
Single mode and single polarization waveguides are preferred in many applications, e.g. those related to sensing [1] or interference [2]. To get a single mode and single polarization waveguide, one can play e.g. with the cross-sectional geometry and inducing leakage loss using high-index materials in the vicinity e.g. the high-index substrate [3] i...
Article
DNA sequencing in a lab-on-a-chip aims at providing cheap, high-speed analysis of low reagent volumes to, e.g., identify genomic deletions or insertions associated with genetic illnesses. Detecting single base-pair insertions/deletions from DNA fragments in the diagnostically relevant range of 150-1000 base-pairs requires a sizing accuracy of S < 1...
Article
A novel type of integrated optical sensor has been evaluated theoretically. The sensing is based on the large effect of the refractive index of the measurand (generally a liquid) to the mode profile of a guided mode close to the cut-off. A special type turns over into a leaky mode-based sensor. The sensor has small size and is simple to fabricate....
Patent
The invention relates to an optical sensor comprising an optical waveguide (1) and a light-sensitive element (4) for detecting light coupled out of the waveguide (1) and also various ring resonators (2), the ring resonators (2) being coupled optically to the mentioned waveguide (1) and, with the exception of at most one of the ring resonators (2),...
Article
Full-text available
The relevance of our definition for sensitivity in refractometric sensing, being the relative change in the transmittance of a certain output channel of an optical device over the change in the refractive index of the probed material, is discussed. It is compared to one based on spectral shift per refractive index unit change. Further, there is dis...
Article
Full-text available
The non-normal incidence of semi-guided plane waves on step-like or tapered transitions between thin film regions with different thicknesses, an early problem of integrated optics, is being reconsidered. As a step beyond the common effective index picture, we compare two approaches on how this problem can be tackled—at least approximately—by nowada...
Article
Full-text available
For hybrid integration of an optical chip with an electronic chip containing photo-diodes and processing electronics, light must be coupled from the optical to the electronic chip. This paper presents a method to fabricate quasi-total-internal-reflecting mirrors on an optical chip, placed at an angle of 45° with the chip surface, that enable 90° ou...
Conference Paper
Full-text available
Due to the limited size of the holey cladding, the structures of practical photonic bandgap fibers (PBFs) can be treated as leaky defect resonance structures [1]. The electromagnetic modal field equation of the structures can be solved by mode solvers that take care of field leakage by proper boundary conditions. In this work, we report computation...
Conference Paper
Full-text available
Due to the limited size of the holey cladding, the structures of practical photonic bandgap fibers (PBFs) can be treated as leaky defect resonance structures [1]. The electromagnetic modal field equation of the structures can be solved by mode solvers that take care of field leakage by proper boundary conditions. In this work, we report computation...
Article
By employing lab-on-a-chip devices, integrated DNA sequencing and genetic diagnostics have become feasible. We combine capillary electrophoretic separation with integrated waveguide laser excitation and ultrasensitive fluorescence detection in an optofluidic chip. In this manner, we demonstrate a high spatial resolution of 12 μm for laser excitatio...
Article
A theoretical and experimental evaluation is given of a principle of direct, label-free opto-chemical sensing. According to this principle, which is applicable in compact planar optical sensors, measurand-induced wavelength shifts of the sharp fringes in the transmission spectra near the stop band edges of a resonant grating-based cavity are monito...
Article
Full-text available
We demonstrate the versatility of a silicon nitride grated waveguide optical cavity as compact integrated optical sensors for (bulk) concentration detection, label-free protein sensing, and – with an integrated cantilever suspended above it – gas sensing.
Article
Full-text available
For hybrid integration of an optical chip with an electronic chip with photo diodes and electronic processing, light must be coupled from the optical chip to the electronic chip. This paper presents a method to fabricate metal-free 45° quasi-total internal reflecting mirrors in optical chips that enable 90° out-of-plane light coupling between flip-...
Article
The design of fully integrated prism spectrometers and polarization splitters in adiabatically connected slab waveguides with two different thicknesses, using principles of geometrical optics, is presented. In addition, the design of mirrors to connect these devices to input and output waveguides is discussed. The proposed structures will be fabric...
Article
Full-text available
Experimental Observation of Superluminal Phenomenon in Electrical Engineering Superluminal or faster-than-light (FTL) is a phenomenon of propagation of faster than light speed in vacuum (c). This phenomenon often causes controversy as sometimes assumed to be inconsistent with special relativity theory. This paper reports two experimental observatio...
Article
We demonstrate the versatility of a silicon nitride grated waveguide optical cavity as compact integrated optical sensors for (bulk) concentration detection, label-free protein sensing, and — with an integrated cantilever suspended above it — gas sensing.
Article
We demonstrate a proof of concept of a novel and compact integrated mechano-optical sensor for H(2) detection based on a microcantilever suspended above a Si(3)N(4) grated waveguide. The fabricated devices are mechanically and optically modeled and characterized. Sensing operation of the sensor is demonstrated with 1% H(2) in N(2). The error in det...
Conference Paper
A proof-of-concept study is reported on fabrication and characterization of a novel and compact integrated mechano-optical sensor based-on a micro-bridge suspended above a Si<sub>3</sub>N<sub>4</sub> grated waveguide.
Article
Full-text available
A numerical study has been carried out by means of the Green's function method to explore possible performance improvements of a simple grated waveguide (GWg) by the variations of its grated structure. It is shown that a GWg featuring symmetric two-sided grated structure of 16 teeth with a 60 nm groove depth and having a symmetric refractive index...
Article
A new method is proposed for hybrid integration of optical waveguides and CMOS photo-detectors. Simulation results show that the coupling efficiency is 45 % including the losses induced by dielectric layers on the detectors.
Article
This paper provides an overview of the rather new field concerning the applications of femtosecond laser microstructuring of glass to optofluidics. Femtosecond lasers have recently emerged as a powerful microfabrication tool due to their unique characteristics. On the one hand, they enable to induce a permanent refractive index increase, in a micro...
Article
A grated waveguide (GWG), which is a waveguide with a finite-length grated section, acts as an optical resonator, showing sharp fringes in the transmission spectrum near the stop-band edges of the grating. These oscillations are due to Fabry-Perot resonances of Bloch modes propagating in the cavity defined by the grated section [1]. Any small struc...
Article
We present an all-numerical method for post-processing of the fluorescent signal as obtained from labeled molecules by capillary electrophoresis (CE) in an optofluidic chip, on the basis of data filtering in the Fourier domain. It is shown that the method outperforms the well-known lock-in amplification during experiments in the reduction of noise...
Article
We present results related to the fabrication of a novel and potentially highly sensitive mechano-optical sensor for hydrogen gas, based on microcantilevers, provided with a selectively gas-absorbing palladium layer, suspended above a Si<sub>3</sub>N<sub>4</sub> grated waveguide (GWG). Integrated microcantilever-GWG devices have been fabricated suc...
Article
Full-text available
We introduce a principle of parallel optical processing to an optofluidic lab-on-a-chip. During electrophoretic separation, the ultra-low limit of detection achieved with our set-up allows us to record fluorescence from covalently end-labeled DNA molecules. Different sets of exclusively color-labeled DNA fragments-otherwise rendered indistinguishab...
Article
Full-text available
We demonstrate the versatility of a silicon nitride grated waveguide optical cavity as compact integrated optical sensors for (bulk) concentration detection, label-free protein sensing, and – with an integrated microbridge suspended above it – gas sensing. A grated waveguide (GWG), which is a waveguide with a finite-length grated section, acts as a...
Article
Full-text available
Sorting and sizing of DNA molecules by capillary electrophoresis (CE) within the human genome project have enabled the genetic mapping of various illnesses. By the use of miniaturized lab-on-achip devices, on-chip-integrated DNA sequencing and genetic diagnostics have become feasible. The inherent advantages of microfluidic CE separation of differe...
Article
Full-text available
At the Integrated Optical Microsystems (IOMS) Group of the University of Twente, we are working towards setting the basis for the future of on-chip nanophotonics. In the following sections, our work on on-chip lasers and amplifiers, optical waveguide devices for different applications such as medical imaging and sensing as well as photonics-electro...
Article
We report the label-free, sensitive detection of PepN enzyme using a Si3N4 grated waveguide optical cavity covered with an immobilized, selective (antibody) receptor layer. The receptor-enzyme reaction was monitored in real-time.
Article
Use of optical principles for the detection and analysis of biomolecules and biotissue has a long-standing tradition, and highly sensitive optical methods have been developed. Integration on a microchip offers cost reduction and instrument miniaturization, thus enabling novel applications, but also allows reduced biosample volumes, higher sensitivi...
Article
A grated waveguide (GWG), which is a waveguide with a finite-length grated section, acts as an optical resonator, showing sharp fringes in the transmission spectrum near the stop-band edges of the grating. These oscillations are due to Fabry-Perot resonances of Bloch modes propagating in the cavity defined by the grated section. Small changes in th...
Article
Full-text available
A new method is proposed for hybrid integration of SiON optical waveguides and standard CMOS photo-detectors based on anisotropic etching of 45° facets in a Si substrate. After removal of anisotropically etched Si structures in cladding SiO2, the fabricated total-internal-reflection mirrors can direct the output of the waveguides to photo-detectors...
Article
We introduce a principle of parallel optical processing: modulation-frequency-encoded multi-wavelength laser excitation, fluorescence detection with a single detector, and Fourier analysis decoding. As an example, we demonstrate simultaneous detection of DNA fragments from different origins.
Article
Integrated optics is a rapidly advancing research field, enabling the miniaturization of a variety of optical functions and their implementation on a single chip. We discuss several technologies and devices for the realization of on-chip amplifiers, lasers and optical sensors. Recent research results comprise high-speed (170 GBit/s) amplifiers and...
Article
Full-text available
An efficient numerical scheme developed on the basis of Green’s function method is applied to the investigation of structural effects on the performance of planar grated waveguide at the first resonance wavelengths next to the band-edges. Restricting ourselves to the transverse-electric waves, this study is focused on the effects induced by variati...
Conference Paper
We present recent progress in the field of sensing fluorescently labeled biomolecules, as separated by micro-chip capillary electrophoresis, being a method to improve the detection limit of the fluorescence signal by numerical post-processing and a way for parallel detection of differently labeled sets of molecules using en-coded excitation.
Article
After electrophoretic separation of dye-labeled DNA molecules of 17 different sizes, integrated-waveguide laser excitation and physical or numerical lock-in amplification enables a limit of detection down to 8-9 DNA molecules in an optofluidic chip.
Article
Full-text available
We present a simple approach in electrophoretic DNA separation and fluorescent monitoring that allows to identify the insertion or deletion of base-pairs in DNA probe molecules from genetic samples, and to perform intrinsic calibration/referencing for highly accurate DNA analysis. The principle is based on dual-point, dual-wavelength laser-induced...
Article
By applying integrated-waveguide laser excitation to an optofluidic chip, fluorescently labeled DNA molecules of 12 or 17 different sizes are separated by CE with high operating speed and low sample consumption of approximately 600 pL. When detecting the fluorescence signals of migrating DNA molecules with a PMT, the LOD is as low as 2.1 pM. In the...
Article
We propose a Y splitter in a two-dimensional photonic crystal with a triangular lattice of air holes suitable for mechanooptical switching. Full switching between the two output ports can be achieved at a certain wavelength owing to the presence of a resonant central cavity with well-chosen symmetry. Experimental results confirm the operation of th...
Article
Controllable splitting of optical power with a large splitting ratio range is often required in an integrated optical chip, e.g. for the readout of phase-shift in a slow-light sensor. In this work, we report the modeling and design of an integrated optical programmable power splitter consisting of a Y-junction with a programmable phase-shifter casc...
Article
A Mach-Zehnder refractive index sensor is inscribed in a microfluidic lab-on-a-chip by exploiting the unique three-dimensional capabilities of femtosecond laser fabrication. This enables high sensitivity and spatially resolved label-free detection of biomolecules.
Article
Fluorescence from different emitters (labeled biomolecules) with distinct absorption wavelengths is encoded by uniquely modulating each excitation beam. Detection by an ultrasensitive, albeit color-blind photomultiplier and subsequent Fourier analysis reveals the origin of each signal.
Conference Paper
Implementing capillary electrophoresis with high base-pair resolution and integrated multi-wavelength excitation in an optofluidic chip, we separate simultaneously sets of end-labeled DNA fragments from independent human genomic segments, relevant for breast cancer and anemia.
Article
Full-text available
We propose a novel and highly sensitive mechano-optical device for gas-sensing through nano-displacements, based on micro-cantilevers, supplied with a selective gas absorbing layer (Pd), suspended above a Si 3 N 4 grated waveguide (GWG). We present the simulation and preliminary experimental results, which indicate the sensing of nanodisplacements,...
Article
Full-text available
Ultrafast laser writing of waveguides in glasses is a very flexible and simple method for direct on-chip integration of photonic devices. In this work we present a monolithic optofluidic device in fused silica providing label-free and spatially-resolved sensing in a microfluidic channel. A Mach-Zehnder interferometer is inscribed with the sensing a...
Conference Paper
Full-text available
Femtosecond-laser-written integrated waveguides enable multi-wavelength fluorescence sensing of flowing biomolecules in an optofluidic chip. Fluorescence from differently labeled biomolecules with distinct absorption wavelengths, encoded by uniquely modulating each excitation beam, is detected by a color-blind photodetector, and the origin of each...
Conference Paper
Full-text available
Sorting and sizing of DNA molecules within the human genome project has enabled the genetic mapping of various illnesses. By employing tiny lab-on-a-chip devices for such DNA analysis, integrated DNA sequencing and genetic diagnostics have become feasible. However, such diagnostic chips typically lack integrated sensing capability. We address this...
Article
Full-text available
Recently we have proposed and demonstrated a novel and compact read-out principle for cantilever deflection with a grated waveguide optical cavity. The device, consisting of a microcantilever suspended above a Si3N4 grated waveguide (GWG), is a potentially highly sensitive mechano-optical sensor for gas sensing. In this report, we present results o...
Article
We present results related to the fabrication and the proof of concept of a novel and highly sensitive mechano-optical sensor for hydrogen gas, based on microcantilevers, supplied with a selective gas absorption layer, suspended above a Si3N4 grated waveguide (GWG). The presence of a dielectric object, in this case a suspended cantilever, in the ev...
Article
Full-text available
Recent Near-field Scanning Optical Microscopy (NSOM) experiments with slit metal coated probes claim to measure the out-of-plane optical magnetic field around a dielectric sample waveguide [1]. The observations can also be explained by mode overlap calculations.
Conference Paper
Full-text available
We report on the monolithic integration of optical waveguides and microfluidics in a fused-silica lab-on-a-chip. Labeled biomolecules such as double-stranded DNA are flown and separated in the microfluidic channel by capillary electrophoresis and their fluorescent labels are excited by a continuous-wave laser beam through femtosecondlaser-written i...
Conference Paper
Full-text available
Silicon photonics, either in the form of integrated optical chips or fiber, has attracted much interest due to their small foot-print, high refractive-index, high thermal-conductivity, high non-linear-optical coefficient, and compatibility with CMOS and fiber-drawing process technology. Recently, fabrication of well-arranged deeply-etched nanometri...
Conference Paper
Full-text available
Controllable splitting of optical power with a large splitting ratio range is often required in an integrated optical chip, e.g. for the readout of phase shift in a slow-light sensor [‎1]. In this work, we report the design of an integrated optical programmable power splitter consisting of a Y-junction with programmable phase shifter cascaded to a...
Article
Full-text available
Controllable splitting of optical power with a large splitting ratio range is often required in an integrated optical chip, e.g. for the readout of phase shift in a slow-light sensor. In this work, we report the design of an integrated optical programmable power splitter consisting of a Y-junction with programmable phase shifter cascaded to a direc...
Chapter
Full-text available
Femtosecond lasers enable the fabrication of both optical waveguides and buried microfluidic channels on a glass substrate. The waveguides are used to integrate optical detection in a commercial microfluidic lab-on-chip for capillary electrophoresis.
Conference Paper
Femtosecond-laser-written optical waveguides are integrated into a commercial capillary electrophoresis chip. A fluorescence detection scheme is implemented, resulting in a compact device. Testing is performed by electrophoresis and detection of a 1-nM oligonucleotide plug.
Conference Paper
Femtosecond-laser-written waveguides were integrated with fluidic microchannels in a commercial lab-on-a-chip. High-spatial-resolution monitoring of fluorescently labeled DNA molecules during capillary electrophoresis separation is demonstrated, as an intermediate step toward point-of-care diagnostic bioassays for DNA analysis.
Conference Paper
Full-text available
Electrophoretic separation of fluorescently labeled DNA molecules in on-chip microfluidic channels was monitored by integrated waveguide arrays, with simultaneous spatial and wavelength resolution. This is an important step toward point-of-care diagnostics with multiplexed DNA assays.
Article
Grated silicon photonic wires for refractometric applications have been fabricated using a 248-nm deep UV lithography. It is shown experimentally, that a device with length of only 180 μm has an index sensitivity of 10−6 assuming a detector power resolution of 1%. It is also demonstrated that the device is suitable to monitor index changes in a liq...
Article
A grating mode analysis of the unusually broadband TM reflection from a high contrast binary grating sheds light on the origin of this effect. This interpretation will be submitted to the workshop attendance.
Conference Paper
Full-text available
We report on monolithic optical sensor integration in a lab-on-a-chip toward onchip diagnosis of all kinds of genetic diseases, e.g. breast cancer. Such an analysis of genetic diseases is based on the capillary electrophoresis separation of DNA fragments amplified from diagnostically relevant regions of the concerned gene. This paper presents a pro...
Article
We report on the use of femtosecond laser pulses to fabricate photonic devices (waveguides and interferometers) inside commercial CE chips without affecting the manufacturing procedure of the microfluidic part of the device. The fabrication of single waveguides intersecting the channels allows one to perform absorption or Laser Induced Fluorescence...
Conference Paper
Full-text available
We study pulse transmission across a single optical ring-resonator circuit theoretically. The theory is supported by experimental measurements. From the study, we discuss intuitively the fulfillment of the causality rules in negative delay phenomenon, which occurs when the circuit possesses a negative group velocity.
Article
Full-text available
Silicon photonics, either in the form of integrated optical chips or fiber, has attracted much interest due to their small foot-print, high refractive-index, high thermal conductivity, high non-linear-optical coefficient, and compatibility with CMOS and fiber-drawing process technology. Recently, fabrication of well-arranged deeply etched nanometri...
Article
We have investigated the label-free biosensing properties of grated silicon photonic wire (GSPW) waveguides with cross-sectional dimensions of 350 nm x 220 nm, fabricated using a 248-nm deep UV lithography process. The steep edges of the optical transmission spectrum of the GSPW enable detection of very small spectral shift, hence of small index ch...
Article
We present results related to the simulation and fabrication of a novel and highly sensitive mechano-optical sensor for gas detection (i.e., hydrogen gas) based on microcantilevers, supplied with a selective gas absorption layer, suspended above a Si3N4 grated waveguide (GWG). The presence of a dielectric object, in this case a suspended cantilever...
Article
Full-text available
We present results related to the fabrication of a novel and highly sensitive mechano-optical sensor for hydrogen gas, based on microcantilevers, supplied with a selective gas absorbing layer (Pd), suspended above a Si3N4 grated waveguide (GWG). Integrated microcantilever-GWG devices have been fabricated successfully using MEMS techniques. Several...
Article
Full-text available
We present the simulation and fabrication of a novel and highly sensitive mechano-optical sensor for nano-displacements, based on microcantilevers suspended above a Si3N4 grated waveguide (GWG). The presence of a dielectric object, in this case a suspended cantilever, in the evanescent field region of the GWG may lead to the occurrence of propagati...