We present a microfluidic system suitable for parallel label-free detection of several biomarkers utilizing a compact imaging measurement system. The microfluidic system contains a filter unit to separate the plasma from human blood and a functionalized, photonic crystal slab sensor chip. The nanostructure of the photonic crystal slab sensor chip is fabricated by nanoimprint lithography of a period grating surface into a photoresist and subsequent deposition of a TiO2 layer. Photonic crystal slabs are slab waveguides supporting quasi-guided modes coupling to far-field radiation, which are sensitive to refractive index changes due to biomarker binding on the functionalized surface. In our imaging read-out system the resulting resonance shift of the quasi-guided mode in the transmission spectrum is converted into an intensity change detectable with a simple camera. By continuously taking photographs of the sensor surface local intensity changes are observed revealing the binding kinetics of the biomarker to its specific target. Data from two distinct measurement fields are used for evaluation. For testing the sensor chip, 1 μM biotin as well as 1 μM recombinant human CD40 ligand were immobilized in spotsvia amin coupling to the sensor surface. Each binding experiment was performed with 250 nM streptavidin and 90 nM CD40 ligand antibody dissolved in phosphate buffered saline. In the next test series, a functionalized sensor chip was bonded onto a 15 mm x 15 mm opening of the 75 mm x 25 mm x 2 mm microfluidic system. We demonstrate the functionality of the microfluidic system for filtering human blood such that only blood plasma was transported to the sensor chip. The results of first binding experiments in buffer with this test chip will be presented.
For absorbing media the concentration may be calculated directly from the optical transmission following the logarithmic dependence given in the Lambert-Beer law. Due to multiple scattering events in oil-water emulsions (e.g. milk, cream, etc.), these exhibit a nonlinear relationship between the attenuation and the oil concentration. We demonstrate that for increasing oil content in oil-water emulsions the attenuation first increases, then levels out, and finally even decreases for a fat content of 60%. Single-wavelength optical transmission measurements are found to be well suited for the in-line monitoring of oil-water emulsions of fat contents below 20%, e.g., for the in-line fat content monitoring of milk. Using experiments and ray-tracing simulations we evaluate system optimization.
Apertures are basic elements which can be found in many optical systems. Since optical systems are continuously being miniaturized and integrated, there is a need for small and inexpensive apertures to control beam shape and light intensity. Current aperture concepts for the micrometer regime rely on moving MEMS lamella or controlling fluids by capillary or electrostatic forces. We demonstrate an aperture concept for single-wavelength operation based on thermal tuning of a segmented thin film resonator. Thermal tuning changes the optical thickness of the elastomer cavity. This allows for adjusting the intensity to any level between constructive and destructive interference in a specific aperture segment. In order to demonstrate aperture operation we simulate thermal, mechanical and optical properties using finite element method and transfer-matrix method. We confirm our simulation results by experimental beam shape measurements and spatially-resolved spectral transmission and light intensity measurements.
Guided mode resonance biosensors are of emerging interest as they allow integration on chip with fabrication on mass scale. The guided mode resonances (GMRs), observed in the transmission or reflection spectrum, are sensitive to refractive index changes in the vicinity of the photonic crystal (PhC) surface. Standard measurement setups utilize a collecting lens, focusing the extracted light intensity onto a single-point photo detector. In order to achieve highly miniaturized devices, we consider the integration of planar emitting and detector structures, such as organic light emitting diodes (OLEDs) and organic photo detectors (OPDs), together with the PhC based biosensors, on a single chip. This approach, however, consequently leads to a broadband, multi-angular light excitation as well as to a broadband and multi-angular contribution to the OPD photon count. While GMR effects in PhC slabs with directional light sources have been widely studied, this lens-less scenario requires a deep understanding regarding the broadband and the angular influence of both incident and reflected or transmitted light. We performed finite-difference time-domain (FDTD) calculations for GMR effects in two-dimensional (2D) PhC slabs. We study the effects for broadband emission in the visible spectrum, together with an angular incident beam divergence of up to 80°. We verified the simulated results by performing angle-resolved spectral measurements with a light emitting diode (LED) in a macroscopic, lens-less setup. We further utilize this numerical setup to provide a deeper understanding of the modal behaviour of our proposed OLED and OPD-based integrated biosensor concept.
The current autostereoscopic projection system is accomplished by array projectors. It is easy to realize optically but
has a drawback with size. Another type is to place the shutter on the screen. It saves the volume but reduces the
efficiency depending on how many views are produced. The shutter in the lens aperture has the same efficiency
problem, too. To overcome these problems, a full HD autostereoscopic projector based on the lens aperture switching
type is proposed. It has RGB laser sources and can produce 16-views or even higher stereoscopic images.
This system removes the shutter in the lens aperture by the opti-mechanism itself. The specific light on the lens
aperture coming from the point on the DMD is reflected to different angles. The proper angle of light is generated in
the object side by the relay and folding system. The UHP lamps or the LED rays are difficult to constrain in a relative
small cone angle. For this reason, the laser is applied to the design. The very small etendue of the laser is good for
this architecture. The rays are combined by dichroic filter from RGB laser sources then forming and expanding to the
mirror. The mirror is synchronized with DMD by the DSP control system. The images of different views are
generated by DMD and specific position of the mirror. By the double lenticular screen, the lens aperture is imaged to
the observer’s viewing zone and the 3D scene is created.
Virtually imaged phased arrays (VIPA) offer high dispersion compared to conventional gratings and have been proposed as buildings blocks for several photonic devices, including wavelength multipliers, chromatic dispersion compensators, waveformgenerators and pulse shapers. We introduce an elastomer-based tunable VIPA, providing an additional degree of freedom for these devices. In particular, we investigate its capability to implement reconfigurable optical interconnects. In a wavelength demultiplexing setup it allows for both compensation of misalignment as well as reconfiguration of a source wavelength to a target channel. It consists of an elastomer layer sandwiched between two structured silver coatings on a glass substrate forming the resonator cavity. Using Joule heating of the top silver layer a thermal expansion and a thermo-optic effect of the elastomer cavity is induced allowing for tuning the effective optical resonator cavity. We report a tuning span of one free angular range by a temperature increase of less than 10K induced by a power change in the low mW regime. Both resonance quality and tunability of the device are investigated.
We report on polymer light-emitting diodes (PLEDs) with embedded SiO2 nanoparticle interlayers. We fabricated PLEDs with a rather thick (180 nm) SiO2 interlayer between the hole injection layer and a 50-nm thin emission layer. We also made devices, where the interlayer was embedded inside the emission layer. The devices were characterized by electroluminescence and photoluminescence measurements and compared to the respective reference devices. We achieved an enhancement factor of 1.74 for the luminous efficacy and 2.13 for the current efficiency at 4000 cd/m2 for the PLED with the interlayer between the hole injection layer and the emission layer compared to the reference device. For PLEDs with the interlayer between the two emission layers, we obtained an enhancement factor of 1.68 for the luminous efficacy and 1.45 for the current efficiency at 4000 cd/m2 compared to the corresponding reference device. This surprising enhancement can be explained by a superposition of increased internal quantum efficiency and an increase in the extraction efficiency.
We investigated guided mode extraction in organic light-emitting diodes and compare the experimental findings to transfer matrix (T-matrix) and finite difference time domain (FDTD) simulations. To this end, we patterned the indium tin oxide anode with Bragg gratings with lattice constants from 300 to 600 nm and varied the depth of the grating structures. The structuring was done by laser interference lithography and plasma etching. Both techniques allow for a rapid large area processing. We measured angle resolved electroluminescent spectra of the nanostructured devices and reference devices. To obtain the mode distribution in the devices we made use of T-matrix simulations. In addition we performed FDTD simulations of the emission characteristics of the patterned devices. The simulations are in agreement with our experimental findings and give insight into the outcoupling mechanisms.
Spontaneous emission characteristics are not an inherent property of an emitter, but may be modified by a nanostructured environment surrounding the emitter. The use of one-, two-, and three-dimensional photonic crystals allows for significant and practical control of the spontaneous emission properties in optoelectronic communications devices. Particularly, one-dimensional photonic crystal structures, which are also known as microcavities, already are used in commercial devices. Two- and three dimensional photonic crystals permit a more comprehensive control of the spontaneous emission properties. By employing photonic crystals the device efficiency is enhanced, the angular radiation pattern can be engineered, and faster devices are achieved by decreasing the radiative lifetime. Photonic-crystal defect structures allow further engineering of the emission properties. Important applications for spontaneous emission control are light-emitting diodes, lasers, and single-photon sources.
We introduce a thin-film spectrometer that is based on the superprism effect in photonic crystals. While the reliable fabrication of two and three dimensional photonic crystals is still a challenge, the realization of one-dimensional photonic crystals as thin-film stacks is a relatively easy and inexpensive approach. Additionally, dispersive thin-film stacks offer the possibility to custom-design the dispersion profile according to the application. The thin-film stack is designed such that light incident at an angle experiences a wavelength-dependent spatial beam shift at the output surface. We propose the monolithic integration of organic photo detectors to register the spatial beam position and thus determine the beam wavelength. This thin-film spectrometer has a size of approximately 5 mm2. We demonstrate that the output position of a laser beam is determined with a resolution of at least 20 μm by the fabricated organic photo detectors. Depending on the design of the thin-film filter the wavelength resolution of the proposed spectrometer is at least 1 nm. Possible applications for the proposed thin-film spectrometer are in the field of absorption spectroscopy, e.g., for gas analysis or biomedical applications.
We demonstrate the feasibility of organic semiconductor lasers as light sources for lab-on-a-chip systems. These lasers
are based on a 1D- or 2D-photonic crystal resonator structure providing optical feedback in the active laser material that
is deposited on top, e.g. aluminum tris(8-hydroxyquinoline) (Alq3) doped with the laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). We investigated different fabrication methods for the resonator
structures, like thermal nanoimprint, UV nanoimprint, and laser interference lithography. Different substrate materials
commonly used in lab-on-a-chip systems, e.g. PMMA, Topas, and Ormocer were deployed. By changing the distributed
feedback grating periodicity, we demonstrate a tuning range for a single material system of more than 120 nm.
The investigated organic semiconductor lasers are optically pumped. External optical pumping provides a feasible
way for one-time-use chips. Our recent success of pumping organic lasers with a low-cost laser diode also renders hand-held
As a further step towards the integration of organic lasers in sensor systems, we demonstrate the coupling of an
organic laser into polymeric waveguides which can be combined with microfluidic channels. The integrated organic
lasers and the waveguides are both fabricated on the same polished PMMA substrate using thermal nanoimprint
lithography and deep-UV modification, respectively. We could demonstrate the guiding of the laser light in single-mode
Photonic crystal superprism structures exhibit a rapid change in the group propagation direction with wavelength. For a fixed wavelength, a small change of the refractive index in a superprism structure also results in a rapid change of the group propagation direction. We present a theoretical investigation of switching in active one-dimensional photonic nanostructures with coupled defects (cavities). This switch can be realized as a multilayer thin-film stack or alternatively in a planar waveguide geometry. The device will allow the switching of an incident laser beam to one of N output positions using either electro-optical or all-optical effects. We consider organic optically nonlinear layers, since organic materials show large nonlinear effects and fast switching times. The proper design of the layer structure is a key component for optimizing the performance of the device. We investigate the most effective position for the integrated nonlinear layers. The active layers can be placed inside the cavities or they can serve as coupling layers between cavities. Both approaches are evaluated with respect to performance parameters such as switching energy and necessary number of layers.
The use of organic optoelectronic devices such as organic light-emitting diodes and organic photodiodes in micro-optical systems is discussed. Potential applications like optical interconnects and optical sensor systems are examined. Device characteristics including emission spectra, I-V-curves and the dynamic behaviour are analysed. In the combination with a polymeric optical fibre (POF) a transmission line comprising a organic light emitting diodes and organic photodiodes is demonstrated. An important step towards integration is realized by coupling the amplified spontaneous emission of an organic semiconductor material into a single-mode polymethylmethacrylate (PMMA) waveguide.
Compared to well established liquid based dye lasers, amplifying media based on amorphous organic thin films allow the realisation of versatile, cost effective and compact lasers. Aside from that, the materials involved are organic semiconductors, which in principle allow the fabrication of future electrically driven organic laser diodes. A highly promising, low-loss resonator geometry for these lasers is the distributed feedback (DFB) structure, which is based on a periodic modulation of the refractive index in the waveguide on the nanometer scale. By variation of the grating period Λ one may tune the laser emission within the gain spectrum of the amplifying medium. We will demonstrate organic lasers spanning the entire spectral region from 360-715 nm. Tuning ranges as large as 115 nm (λ = 598-713 nm) in the red spectral region and more than 30 nm (λ = 362-394 nm) in the UV render these novel lasers highly attractive for various spectroscopic applications. As the grating period Λ is typically between 100 nm and 400 nm the DFB resonators are fabricated by e-beam lithography. These gratings may, however, be used as masters to obtain an arbitrary amount of copies by nanoimprint lithography into plastic substrates. Therefore these lasers are very attractive even for single-use applications (e.g. in medicine and biotechnology). Today, the key challenge in the field is the realisation of the first electrically driven organic laser. Key pre-requisites are highly efficient amplifying material systems which allow for low threshold operation and charge transport materials that bring about the stability to sustain the necessary current densities, several orders of magnitude higher than in OLEDs. We will demonstrate diode structures operated electrically under pulsed conditions at current densities up to 760 A/cm2 with a product of the current density and the external quantum effciency (J×ηext) of 1.27 A/cm2. Mechanisms deteriorating the quantum efficieny at elevated current densities will be discussed.
Many sensing applications benefit from a wavelength-selective measurement. For integrated sensors it is therefore necessary to realize compact wavelength splitting devices. Here we discuss dispersive devices based on the photonic crystal superprism effect and related spatial dispersion effects in photonic nanostructures. We focus on one-dimensional nanostructures, since these can be realized reliably and cost-effectively as multilayer thin-film stacks. The thin-film stack is designed such that light incident at an angle experiences a wavelength-dependent spatial beam shift at the output surface allowing a wavelength-selective measurement. We introduce different algorithms for designing thin-film stacks with high spatial dispersion and discuss integration approaches. Results are presented showing that it is possible to custom-engineer both the magnitude of the dispersion as well as the dispersion properties with wavelength.
The successful realization of devices based on two-dimensional (2D) photonic crystal structures relies on an accurate characterization of the properties of the fabricated nanostructured surface. Scanning electron microscope (SEM) images allow the verification of geometric parameters of fabricated 2D-photonic crystal structures such as the periodicity or the hole diameter. In order to investigate the optical properties of 2D-photonic crystals we realized an experimental setup for spectrally and spatially resolved transmission measurements at normal incidence. These measurements reveal the allowed modes of the photonic crystal at the Gamma-point. In contrast to transmission measurements in the plane of the photonic crystal, these measurements are independent of the lateral termination of the structure, since only the area of the photonic crystal is probed. The experimental setup allows for the characterization of microscopic structures of dimensions down to 50 micrometers in diameter. The setup can furthermore be utilized to characterize the spatial homogeneity of larger nanostructured surfaces. We present experimental results and compare them to photonic band structure calculations.
The properties of electrically pumped organic laser devices are investigated by the self consistent numerical solution of the spatially inhomogeneous laser rate equations coupled to a drift-diffusion model for the electrons, holes and singlet excitons. By fully taking into account the effect of stimulated emission on the exciton population, we determine the spatial and temporal evolution of the photon density in organic multilayer structures. We apply the model to calculate laser threshold current densities and investigate transient phenomena like the delay of radiation onset. By performing systematic parameter variations, we derive design rules for potential organic laser diode structures.
Thin-film stacks exhibiting a high spatial dispersion similar to the photonic crystal superprism effect can be employed to multiplex or demultiplex several wavelength channels using a single thin-film stack. The phase properties of these stacks are designed such that a small change in the wavelength results in a large change of the effective group propagation angle and therefore of the beam exit position for light beams of oblique incidence angle. Here we demonstrate that such a structure also exhibits a large change in the exit position for a fixed incident wavelength due to a small refractive index variation. We investigate theoretically the introduction of optically nonlinear polymer layers into multilayer thin-film structures for electro-optic switching of the refractive index. Polymers offer a number of advantages as nonlinear materials - they are simple to process, they show high, non-resonant nonlinear coefficients and they posses low refractive indices. A dispersive thin-film stack containing tunable polymer layers is therefore promising as a 1:N spatial beam switch with switching times in the nanosecond range. We developed and simulated different designs for dispersive thin-film stacks consisting of dielectric and polymer layers. The approaches range from Bragg stacks with two alternating materials, one of them the active polymer, over impedance matched Bragg stacks to coupled cavities that contain the active material. The achievable refractive index changes with guest-host polymer systems were evaluated and integrated into our calculations.
In this article, a model to calculate the modal gain in organic
laser diode structures is presented. A single layer design is
considered to investigate the dependence of the gain on power
density, charge carrier mobility and thickness of the active layer.
We show that unequal charge carrier mobilities are detrimental and
that there is an optimum active layer thickness of approximately
200 nm, if different devices are compared on the basis of equal
power density. Neglecting all losses, the highest calculated gain
is 0.7/cm for a power density of P=50 kW/cm2 in our MEH-PPV
like model material. Furthermore, the influence of absorption by
polarons is quantified. We show that the cross section for this
process has to be at least 20 times smaller than the cross section
for stimulated emission in order to achieve net gain in the most
favourable case that was considered.
The high angular dispersion achieved with the photonic crystal superprism effect as well as dispersive non-periodic photonic nanostructures promise compact wavelength division multiplexing (WDM) devices. An important criterion for the usefulness of such WDM devices is the number of channels that a structure can multiplex or demultiplex. Here two different models are developed for calculating the possible number of channels for a given structure. The first model is based on the assumption that different wavelength channels should propagate in mutually exclusive propagation cones within the volume of the dispersive structure. We call these non-overlapping channels "volume modes." The second model assumes that it is sufficient to spatially separate the different wavelength channels on a single output surface, e.g., the plane of the detectors or output waveguides. Since they are only separated along one surface and not in the entire volume, we name these modes "surface modes." As an example it is shown that a dispersive 200-layer non-periodic thin-film stack can be used to multiplex or demultiplex approximately eight WDM channels. The achievable number of channels is not defined by the dispersion alone but by the product of dispersion and wavelength range over which this dispersion is achieved.
We measure the optical properties of turbid media by performing a spatial scan for homogeneous liquid samples and by immersion into a known reference medium for small secondary samples. We demonstrate that both types of measurements have a precision of better than 1% (standard deviation) and an absolute accuracy of better than 3% (mean error). Furthermore we conduct an experiment measuring the absorption and scattering coefficients of a human hand immersed into a reference medium for a changing level of blood oxygenation.
We show that the optical properties of a sample with moderate scatter can be obtained by performing frequency domain measurements in a reflection geometry. In experiments and Monte Carlo simulations we show that absorption and scatter produce opposing trends in the amplitude signal and common trends in the phase signal. Therefore a measured amplitude and phase signal correspond to a unique combination of optical properties for a given phase function.