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.
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.
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.
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.