Inkjet printing is a versatile method to apply surface modification procedures in a spatially controlled, cost-effective and mass-fabrication compatible manner. Utilizing this technology, we investigate two different approaches for functionalizing label-free optical waveguide based biosensors: a) surface modification with amine-based functional polymers (biotin-modified polyethylenimine (PEI-B)) employing active ester chemistry and b) modification with dextran based hydrogel thin films employing photoactive benzophenone crosslinker moieties. Whereas the modification with PEI-B ensures high receptor density at the surface, the hydrogel films can serve both as a voluminous matrix binding matrix and as a semipermeable separation layer between the sensor surface and the sample. We use the two surface modification strategies both individually and in combination for binding studies towards the detection of the protein inflammation biomarker, C-reactive protein (CRP). For the specific detection of CRP, we compare two kinds of capture molecules, namely biotinylated antibodies and biotinylated CRP-specific DNA based aptamers. Both kinds of capture molecules were immobilized on the PEI-B by means of streptavidin-biotin affinity binding. As transducer, we use an integrated four-channel silicon nitride (Si3N4) waveguide based Mach-Zehnder interferometric (MZI) photonic sensing platform operating at a wavelength of 850nm (TM-mode).
We present the design of 20-channel, 50-GHz Si3N4 based AWG applying our proprietary AWG-Parameters tool. For the simulations of the AWG layout we used PHASAR photonics tool from Optiwave. The simulated transmission characteristics were then evaluated applying our AWG-Analyzer tool. We studied the influence of one of the design parameters – the separation between input/output waveguides, dx on the channel crosstalk. The results show that there is some minimum waveguide separation necessary to keep the crosstalk between transmitting channels low. The AWGs were designed for TM-polarized light with a central wavelength of 850 nm. They will later be used in a photonic integrated circuit dedicated to medical diagnostic imaging applications.
Label-free optical schemes for molecular biosensing hold a strong promise for point-of-care applications in medical research and diagnostics. Apart from diagnostic requirements in terms of sensitivity, specificity, and multiplexing capability, also other aspects such as ease of use and manufacturability have to be considered in order to pave the way to a practical implementation. We present integrated optical waveguide as well as magnetic nanoparticle based molecular biosensor concepts that address these aspects. The integrated optical waveguide devices are based on low-loss photonic wires made of silicon nitride deposited by a CMOS compatible plasma-enhanced chemical vapor deposition (PECVD) process that allows for backend integration of waveguides on optoelectronic CMOS chips. The molecular detection principle relies on evanescent wave sensing in the 0.85 μm wavelength regime by means of Mach-Zehnder interferometers, which enables on-chip integration of silicon photodiodes and, thus, the realization of system-on-chip solutions. Our nanoparticle-based approach is based on optical observation of the dynamic response of functionalized magneticcore/ noble-metal-shell nanorods (‘nanoprobes’) to an externally applied time-varying magnetic field. As target molecules specifically bind to the surface of the nanoprobes, the observed dynamics of the nanoprobes changes, and the concentration of target molecules in the sample solution can be quantified. This approach is suitable for dynamic real-time measurements and only requires minimal sample preparation, thus presenting a highly promising point-of-care diagnostic system. In this paper, we present a prototype of a diagnostic device suitable for highly automated sample analysis by our nanoparticle-based approach.
We present our developments on integrated optical waveguide based as well as on magnetic nanoparticle based label-free
biosensor concepts. With respect to integrated optical waveguide devices, evanescent wave sensing by means of Mach-
Zehnder interferometers are used as biosensing components. We describe three different approaches: a) silicon photonic
wire waveguides enabling on-chip wavelength division multiplexing, b) utilization of slow light in silicon photonic
crystal defect waveguides operated in the 1.3 μm wavelength regime, and c) silicon nitride photonics wire waveguide
devices compatible with on-chip photodiode integration operated in the 0.85 μm wavelength regime. The nanoparticle
based approach relies on a plasmon-optical detection of the hydrodynamic properties of magnetic-core/gold-shell
nanorods immersed in the sample solution. The hybrid nanorods are rotated within an externally applied magnetic field
and their rotation optically monitored. When target molecules bind to the surfaces of the nanorods their hydrodynamic
volumes increase, which directly translates into a change of the optical signal. This approach possesses the potential to
enable real-time measurements with only minimal sample preparation requirements, thus presenting a promising point-of-
care diagnostic system.
In this numerical study, we investigate the light trapping mechanism in silicon solar cells with backside diffraction gratings. In order to obtain a clearer view on the physical mechanisms underlying the light trapping we employ a simulation scheme that combines ray tracing with rigorous coupled wave analysis (RCWA). This combined simulation approach treats the light propagation inside the silicon absorber layer incoherently and averages out Fabry-Perot resonances, which otherwise would obscure characteristic humps in the absorption spectra that are directly related to light trapping effect of the diffraction gratings. We provide an in-depth explanation for the origin of these characteristic humps and their interrelationship with the silicon absorber thickness. A major benefit of this combined RCWA/ray tracing approach compared to the fully electromagnetic simulation methods RCWA and finite difference time domain (FDTD) is the more efficient use of computational power accompanied by a gain in simulation precision, in particular for cells with an absorber thicker than 10 μm.
Light trapping by means of backside diffraction gratings can strongly increase the efficiency in silicon solar cells. However, the optimization of the grating geometry involves comprehensive multiparameter scans, which necessitates an efficient simulation method. In this study, we employ a simulation approach that combines ray tracing with rigorous coupled wave analysis. As an additional benefit, this approach provides a much better physical insight into the light trapping mechanism in contrast to fully electromagnetic simulation methods. The influence of the ray tracing simulation settings in terms of recursion depth and diffraction order on the simulation results is investigated. We show that the choice of a proper recursion depth and a sufficient number of diffraction orders is essential for obtaining fully optimized grating parameters and that the minimum recursion depth required for obtaining the correct optimized grating parameters depends on the silicon thickness. Furthermore, we investigate the influence of the angle of incidence on the optimized grating parameters. As major result, we find that the optimum grating structure does not depend on the angle of incidence on the solar cell.
We present a novel wavelength multiplexing concept for an integrated label-free biosensor array employing silicon
photonic Mach-Zehnder interferometers as sensors. Microring resonators act as wavelength selective elements in
the near infrared wavelength region. The radii of the microring resonators differ to obtain resonance wavelengths
that are allocated equally within the free spectral range. By choosing a wavelength where a certain microring is
in resonance, an individual interferometer is addressed. Wire Bragg gratings terminate the interferometer arms
and reflect the light back. The ring resonator, which dropped the light, now couples the light back into the input
waveguide, where it propagates in opposite direction. A standard fiber optic circulator between the tunable laser
source and the in/output separates the incoming from the outgoing light. In this work, the characteristics of the
entire device are discussed. The design based on FEM and 3D-FDTD simulations as well as measurements of the
nanophotonic key components namely micro ring resonators, Mach-Zehnder interferometers, and photonic wire
Bragg gratings are presented. Measurements of combinations of the key components demonstrate the applicability
of the reflectors in photonic circuits. Finally, for proof-of-concept, we successfully performed experiments with
fluids of different refractive index differences rinsed over the sensor array.
In this work, we optimize Bragg gratings covered with SU-8 for TM polarized light at a center wavelength
of 1550 nm with respect to high reflectivity and large wavelength range employing 3D FDTD simulations.
Three different types of lateral grating modulation were studied: I) complete interruption of the waveguide, II)
corrugation within the waveguide width, and III) corrugation exceeding the waveguide width. The wavelength
response was analyzed with a discrete Fourier transformation algorithm for a Gaussian pulse source. The
investigations resulted in a grating structure providing a reflectivity of >70% over a wavelength range of 50 nm.
The transmission and the radiation losses amount both to approximately 1015% each. Corresponding samples
of these three Bragg grating structures with lengths of ~10 μm were fabricated employing e-beam lithography
and reactive ion etching. In order to enable the experimental verification of the reflectivity a Y-branch separates
the light paths of incoming and reflected light directly on the chip. The measured reflection and transmission
spectra match well with the simulations and demonstrate the good performance of the optimized Bragg grating
Various nanostructures with a feature sizes down to 50 nm as well as photonic structures such as waveguides or grating
couplers were successfully replicated into the thermoplastic polymer polymethylpentene employing an injection molding
process. Polymethylpentene has highly attractive characteristics for photonic and life-science applications such as a high
thermal stability, an outstanding chemical resistivity and excellent optical transparency. In our injection molding process,
the structures were directly replicated from 2" silicon wafers that serve as an exchangeable mold insert in the injection
mold. We present this injection molding process as a versatile technology platform for the realization of optical
integrated devices and diffractive optical components. In particular, we show the application of the injection molding
process for the realization of waveguide and grating coupler structures, subwavelength gratings and focusing nanoholes.
The design of optimized V-groove waveguides for evanescent surface sensing as well as for the exploitation of
nonlinear optical effects in low index materials is presented. Morever, the leakage behaviour of horizontal ribtype
slot waveguides is discussed, which has been calculated employing MaxWave, a novel simulation package of
electromagnetic mode solvers for the computation of the optical field in integrated optical waveguide devices.
An integrated all-polymer Mach-Zehnder interferometer based biosensing concept is presented. We show
that efficient coupling of light into thin low index contrast single mode waveguides via surface gratings becomes
feasible by applying a high index coating on the grating. We provide an experimental verification of this effect
as well as homogeneous sensing results.
We propose the V-groove waveguide as a novel silicon nanophotonic structure. By anisotropic etching of a
monocrystalline silicon layer, angled photonic wires with isosceles-trapezoidal cross section can be realized.
Placing two such wires side by side results in a waveguiding structure consisting of two highly coupled wires
separated by an acute angled V-shaped nano groove. By choosing proper geometry parameters, the light is
concentrated near the bottom of the groove. In this work, we theoretically study the dependence of the light
confinement characteristics on the waveguide geometry parameters and demonstrate the suitability of the Vgroove
waveguide as a versatile platform for surface sensing, for exploiting nonlinear optical effects in low index
materials, and for realizing nanowire lasers.
Due to the small coupling strength of waveguide grating couplers in low index contrast material systems such
as polymers, the efficient coupling to single-mode waveguides via surface gratings represents a severe challenge.
In this work, we demonstrate that the coupling strength of grating couplers in low-index difference waveguide
systems can be strongly enhanced by the application of a thin high-index coating (HIC) on top of surface gratings.
This allows reducing the grating coupler aperture size without sacrificing efficiency by up to more than an order
of magnitude, which enables low-loss lateral tapering to single-mode waveguides.
In this work, we present optimized rib-type and photonic crystal based horizontal slot waveguide structures which
provide the possibility of electrical wiring while at the same time maintaining minimum mode volume for linear and
Planar-integrated optical biosensors based on the interferometric evanescent wave sensing principle facilitate highly
sensitive label-free detection of biomolecules. In this work, we present a novel polymer waveguide device concept that
allows for cost effective fabrication of disposable sensor chips by utilizing injection moulding and spin-coating. Surface
grating couplers are used in combination with lateral tapers to couple light in and out of the biosensor. The coupling
strength of these polymer gratings is increased by applying a thin inorganic high-index coating, which allows reducing
the grating size and thus achieving efficient lateral tapering into single mode waveguides. The sensor concept, design of
the waveguide components as well as first experimental results of the injection moulding process, the grating couplers
and the Mach-Zehnder interferometers are presented.
In this study, we theoretically investigate the leakage behavior of SOI slot waveguides at a wavelength of 1.55 μm.
First, the dependence of the substrate leakage of vertical and horizontal wire-type slot waveguides on their
geometry is shortly summarized. The main part is devoted to the lateral leakage in perfectly symmetric and
asymmetric rib-type slot waveguides, which is caused by coupling between the TM-like slot mode and the TE
slab modes outside the rib. The influence of the geometry parameters on the leakage behavior and the impact
of structural deviations caused by the fabrication process are studied in depth. A semi-analytical criterion for
the design of leakproof rib-type slot waveguides is derived and compared with full-vectorial numerical methods
employing a commercial FEM solver and a recently developed variational mode-matching 2D eigenmode solver.
We modify the Soref single-mode criterion such that it can be applied also to waveguides with small cross sections. This is verified for highly sensitive silicon on insulator (SOI) rib waveguides with core thicknesses of 60 nm for TE- and 220 nm for TM-polarization, respectively, at a wavelength of 1550 nm by a fully vectorial finite element method (FEM) eigenmode analysis. The semi-analytical criterion enables an efficient design of rib waveguides for evanescent wave sensing devices.
To support the rapid growth of communication traffic in information age, all optical node technology is vitally needed. The present review summarizes the design consideration, the fabrication procedures and the result of the test experiments. Major technical issues toward the realistic development of all optical switching modules are listed and the possible solutions are discussed.
We present a surface emitting GaAs/AlGaAs laser diode beam steering device based on the surface mode emission (SME) technique. The SME-laser diodes operate in a single-mode and show efficient surface emission into a single beam with a minimum beam divergence of 0.11 degree(s). We demonstrate a large digital beam steering from this device, which is achieved by mode switching. The special SME-structure supports two single-mode emission wavelengths, which are spaced by 8.38 nm. Digital switching between these two modes by a proper current pulse sequence leads to a steering of the surface emitted single-beam by 4.9 degree(s). Presently the beam steering frequency is limited to a maximum value of 0.15 MHz. An optimized device design for a continuous steering of the single, surface emitted beam is proposed.
First results from surface mode emitting (SME)-laser diodes utilizing a first-order grating are presented. The use of a first-order grating instead of a third-order grating strongly improves the radiation characteristics of surface emitting SME-laser diodes. Although a real single mode operation from SME-laser diodes is not yet achieved, the tunability of the main emission wavelength by changes of the waveguide thickness is clearly demonstrated. The crucial feature of the SME-technique is that it provides a high flexibility, when processing surface emitting laser diodes with desired radiation pattern and wavelength emission characteristics. These features are discussed to demonstrate the high application potential of the SME-laser diodes.