This paper describes color printing on nanoimprinted plasmonic metasurfaces by laser post-writing, for flexible decoration of high volume manufactured plastic products. Laser pulses induce transient local heat generation that leads to melting and reshaping of the imprinted nanostructures. Different surface morphologies that support different plasmonic resonances, and thereby different color appearances, are created by control of the laser pulse energy density. All primary colors can be printed, with a speed of 1 ns per pixel, resolution up to 127,000 dots per inch (DPI) and power consumption down to 0.3 nJ per pixel.
A highly sensitive distributed feedback (DFB) dye laser sensor for high frame rate imaging refractometry without moving parts is presented. The laser sensor surface comprises areas of different grating periods. Imaging in two dimensions of space is enabled by analyzing laser light from all areas in parallel with an imaging spectrometer. Refractive index imaging of a 2 mm by 2 mm surface is demonstrated with a spatial resolution of 10 μm, a detection limit of 8 10-6 RIU, and a framerate of 12 Hz, limited by the CCD camera. Label-free imaging of dissolution dynamics is demonstrated.
An optical two-beam trap, composed from two counter propagating laser beams, is an interesting setup due to the ability of the system to trap, hold, and stretch soft biological objects like vesicles or single cells. Because of this functionality, the system was also named "the optical stretcher" by Jochen Guck, Josep Käs and co-workers some 15 years ago. In a favorable setup, the two opposing laser beams meet with equal intensities in the middle of a fluidic channel in which cells may flow past, be trapped, stretched, and allowed to move on, giving the promise of a high throughput device. Yet, single beam optical traps, aka optical tweezers, by far outnumber the existing optical stretchers in research labs throughout the world. The ability to easily construct an optical stretcher setup in a low-cost material would possibly imply more frequent use of the optical stretching technique. Here, we will outline the design, the production procedures, and results obtained in a fiber-based experimental setup built within an injection molded microfluidic polymer chip. The microfluidic chip is constructed with a three layer technology in which we ensure both horizontal and vertical focusing of the cells we wish to trap, thereby preventing too many cells to flow below the line of focus of the two counter propagating laser beams that are positioned perpendicular to the direction of flow of the cells. Results will be compared to that from other designs from previous work in the group.
In this paper, we present a route for making smart functionalized plastic parts by injection molding with sub-micrometer
surface structures. The method is based on combining planar processes well known and established within silicon micro
and sub-micro fabrication with proven high resolution and high fidelity with truly freeform injection molding inserts.
The link between the planar processes and the freeform shaped injection molding inserts is enabled by the use of
nanoimprint with flexible molds for the pattern definition combined with unidirectional sputter etching for transferring
the pattern. With this approach, we demonstrate the transfer of down to 140 nm wide holes on large areas with good
structure fidelity on an injection molding steel insert. The durability of the sub-micrometer structures on the inserts have
been investigated by running two production series of 102,000 and 73,000 injection molded parts, respectively, on two
different inserts and inspecting the inserts before and after the production series and the molded parts during the
Structural colors are optical phenomena of physical origin, where microscale and nanoscale structures determine the reflected spectrum of light. Artificial structural colors have been realized within recent years. However, multilayer structures require substantial fabrication. Instead we considered one-layer surface textures of silicon. We explored four patterns of square structures in a square lattice with periods of 500, 400, 300, and 200 nm. The reflectivity and daylight-colors were measured and compared with simulations based on rigorously coupled-wave analysis with excellent agreement. Based on the 200-nm periodic pattern, it was found that angle-independent specular colors up to 60 deg of incidence may be provided. The underlying mechanisms include (1) the suppression of diffraction and (2) a strong coupling of light to localized surface states. The strong coupling yields absorption anomalies in the visual spectrum, causing robust colors to be defined for a large angular interval. The result is a manifestation of a uniformly defined color, similar to pigment-based colors. These mechanisms hold potential for color engineering and can be used to explain and predict the structural-color appearance of silicon-based textures for a wide range of structural parameters.
Inspired by nature, nano-textured surfaces have attracted much attention as a method to realize optical surface functionality. The moth-eye antireflective structure and the structural colors of Morpho butterflies are well- known examples used for inspiration for such biomimetic research. In this paper, nanostructured polymer surfaces suitable for up-scalable polymer replication methods, such as imprinting/embossing and injection-molding, are discussed. The limiting case of injection-moulding compatible designs is investigated. Anti-reflective polymer surfaces are realized by replication of Black Silicon (BSi) random nanostructure surfaces. The optical transmission at normal incidence is measured for wavelengths from 400 nm to 900 nm. For samples with optimized nanostructures, the reflectance is reduced by 50 % compared to samples with planar surfaces. The specular and diffusive reflection of light from polymer surfaces and their implication for creating structural colors is discussed. In the case of injection-moulding compatible designs, the maximum reflection of nano-scale textured surfaces cannot exceed the Fresnel reflection of a corresponding flat polymer surface, which is approx. 4 % for normal incidence. Diffraction gratings provide strong color reflection defined by the diffraction orders. However, the apperance varies strongly with viewing angles. Three different methods to address the strong angular-dependence of diffraction grating based structural color are discussed.
We present a method for homogeneous deposition of sol-gel sensor materials, which enable fabrication of sensor spots
for optical pH and oxygen measurements inside plastic containers. A periodic pattern of posts is imprinted into a
polycarbonate substrate and, using the principle of hemi-wicking, a deposited droplet spreads, guided by the posts, to
automatically fill the imprinted structure, not being sensitive to alignment as long as it is deposited inside the patterned
area. Hemi-wicking is an effective method to immobilize a low viscosity liquid material in well-defined spots on a
surface, when conventional methods such as screen- or stamp-printing do not work. On length scales of the order of the
microstructure period, surface tension will govern the shape of the liquid-air interface, and the liquid will climb up the
pillars to keep a fixed contact angle with the sidewalls. The surface to volume ratio is therefore constant all over the
surface of the liquid spread by hemi-wicking, when considering length scales larger than the microstructure period.
Material redistribution caused by solvent evaporation, i.e., the "coffee ring effect", can therefore be avoided because the
evaporation rate does not vary on length scales larger than the periodic pattern.
We report on lasing in conical microcavities, which are made out of the low-loss polymer poly (methyl methacrylate)
(PMMA) doped with the dye rhodamine 6G, and directly fabricated on silicon. Including a thermal reflow step during
fabrication enables a significantly reduced surface roughness, resulting in low scattering losses of the whispering gallery
modes (WGMs). The high cavity quality factors (above 2·106 in passive cavities) in combination with the large oscillator
strength gain material enable lasing threshold energies as low as 3 nJ, achieved by free-space excitation in the quasistationary
pumping regime. Lasing wavelengths are detected in the visible wavelength region around 600 nm. Finite
element simulations indicate that lasing occurs in fundamental TE/TM cavity modes, as these modes have - in
comparison to higher order cavity modes - the smallest mode volume and the largest overlap with the gain material. In
addition, we investigate the effect of dye concentration on lasing wavelength and threshold by comparing samples with
four different concentrations of rhodamine 6G. Observations are explained by modifying the standard dye laser model.
A nanoimprinted polymer chip with a thin near-infrared absorber layer that enables light-induced local heating (LILH)
of liquids inside micro- and nanochannels is presented. An infrared laser spot and corresponding hot-spot could be
scanned across the device. Large temperature gradients yield thermophoretic forces, which are used to manipulate and
stretch individual DNA molecules confined in nanochannels. The absorber layer consists of a commercially available
phthalocyanine dye (Fujifilm), with a narrow absorption peak at approximately 775 nm, dissolved in SU-8 photoresist
(Microchem Corp.). The 500 nm thick absorber layer is spin-coated on a transparent substrate and UV exposed. Microand
nanofluidic channels are defined by nanoimprint lithography in a 1.5 μm thick layer of low molecular weight
polymethyl methacrylate (PMMA, Microchem Corp.), which is spin coated on top of the absorber layer. We have used a
previously developed two-level hybrid stamp for replicating two V-shaped microchannels (width=50 μm and height =
900 nm) bridged by an array of 200 nanochannels (width and height of 250 nm). The fluidic channels are finally sealed
with a lid using PMMA to PMMA thermal bonding. Light from a 785 nm laser diode was focused from the backside of
the chip to a spot diameter down to 5 ..m in the absorber layer, yielding a localized heating (Gaussian profile) and large
temperature gradients in the liquid in the nanochannels. A laser power of 38 mW yielded a temperature of 40oC in the
center of a 10 μm 1/e diameter. Flourescence microscopy was performed from the frontside.
Nanoporous liquid core waveguides are fabricated by selectively UV modifying a nanoporous polymer. The
starting point is a diblock polymer where 1,2-polybutadiene (PB) molecules are bound to PDMS. When the PB
is cross linked it self-assembles into PB with a network of 14 nm diameter PDMS filled pores. When the PDMS
is etched, the hydrophobic PB is left with a porosity of 44%. The polymer is subsequently UV exposed through
a shadow mask. This renders the exposed part hydrophilic, making it possible for water to infiltrate these areas.
Water infiltration raises the refractive index, thus forming a liquid core waveguide. Here we present both the
fabrication scheme and characterization results for the waveguides.
This paper reports on-chip based optical detection with three-dimensional spatial resolution by integration of
an optofluidic microscope (OFM) in a microfluidic pinched flow fractionation (PFF) separation device. This
setup also enables on-chip particle image velocimetry (PIV). The position in the plane perpendicular to the
flow direction and the velocity along the flow direction of separated fluorescent labeled polystyrene microspheres
with diameters of 1 μm, 2.1 μm, 3 μm and 4μm is measured using the OFM readout. These results are bench
marked against those obtained with a PFF device using a conventional fluorescence microscope as readout. The
size separated microspheres are detected by OFM with an accuracy of ≤ 0.92μm. The position in the height
of the channel and the velocity of the separated microspheres are detected with an accuracy of 1.4 μm and
0.08mm/s respectively. Throughout the measurements of the height and velocity distribution, the microspheres
are observed to move towards the center of the channel in regard to its height.
Optically pumped polymer photonic crystal band-edge dye lasers are presented. The photonic crystal is a rectangular
lattice providing laser feedback as well as an optical resonance for the pump light. The lasers are defined in a thin film of
photodefinable Ormocore hybrid polymer, doped with the laser dye Pyrromethene 597. A compact frequency doubled
Nd:YAG laser (352 nm, 5 ns pulses) is used to pump the lasers from above the chip. The laser devices are 450 nm thick
slab waveguides with a rectangular lattice of 100 nm deep air holes imprinted into the surface. The 2-dimensional
rectangular lattice is described by two orthogonal unit vectors of length a and b, defining the ΓP and ΓX directions. The
frequency of the laser can be tuned via the lattice constant a (187 nm - 215 nm) while pump light is resonantly coupled
into the laser from an angle (θ) depending on the lattice constant b (355 nm). The lasers are fabricated in parallel on a 10
cm diameter wafer by combined nanoimprint and photolithography (CNP). CNP relies on a UV transparent quartz
nanoimprint stamp with an integrated metal shadow mask. In the CNP process the photonic crystal is formed by
mechanical deformation (imprinting) while the larger features are defined by UV exposure through the combined
In this paper, we investigate the capacitance tuning of nanoscale split-ring resonators. Based on a simple LC
circuit model (LC-model), we derive an expression where the inductance is proportional to the area while the
capacitance reflects the aspect ratio of the slit. The resonance frequency may be tuned by the slit aspect
ratio leaving the area, the lattice constant Λ, and nearest-neighbor couplings in periodic split-ring resonator
structures invariant. Experimental data as well as numerical simulation data, verify the predictions of the simple
We report on the fabrication of a metal-dielectric composite material with tunable optical properties. The developed
fabrication method relies on simultaneous DC sputtering of a metal and a suitable dielectric, creating an isotropic
material with optical properties that can be controllably varied over a wide range of wavelengths. Currently the research
is focusing on a combination of Ag and ZnO that is suitable for applications at the visible and telecommunication
frequencies. The material combination is well suited for the deposition method chosen, and physical characterizations
using AFM and SEM measurements show that the mixture forms homogeneous films with low surface roughness. In
order to test the validity of this approach films are deposited with a variety of deposition parameters, focusing mainly on
the relative deposition rates basically controlling the filling factor. Optical properties found from experiments using
spectroscopic ellipsometry as well as farfield reflection-transmission measurements are compared to those predicted by
the effective medium theory.
We report on experimental realization of the Fang Ag superlens structure  suitable for further processing and
integration in bio-chips by replacing PMMA with a highly chemical resistant cyclo-olefin copolymer, mr-I T85 (Micro
Resist Technology, Berlin, Germany). The superlens was able to resolve 80 nm half-pitch gratings when operating at a
free space wavelength of 365 nm.
Fang et al. used PMMA since it enables the presence of surface plasmons at the PMMA/Ag interface at 365 nm and
because it planarizes the quartz/chrome mask. If the superlens is to be integrated into a device where further processing
is needed involving various organic polar solvents, PMMA cannot be used. We propose to use mr-I T85, which is highly
chemically resistant to acids and polar solvents.
Our superlens stack consists of a quartz/chrome grating mask, a 40 nm layer of mr-I T85, 35 nm Ag, and finally 70 nm
of the negative photoresist mr-UVL 6000 (Micro Resist). A 50 nm layer of aluminium on top of the quartz/chrome mask
reflected all light that did not penetrate through the mask openings thereby reducing waveguiding in the top resist layer.
The exposures took place in a UV-aligner at 365 nm corresponding to the excitation wavelength of the surface plasmons
at the mr-I T85/Ag interface. Supporting COMSOL simulations illustrate the field intensity distribution inside the resist
as well as the presence of surface plasmons at the mr-I T85/Ag boundary. AFM scans of the exposed structure revealed
80 nm gratings.
Dye doped polymer photonic crystal band edge lasers are applied for evanescent wave sensing of cells. The lasers
are rectangular shaped slab waveguides of dye doped polymer on a glass substrate, where a photonic crystal
is formed by 100 nm deep air-holes in the surface of the 375 nm high waveguides. The lasers are fabricated
by combined nanoimprint and photolithography (CNP) in Ormocore hybrid polymer doped with the laser dye
Pyrromethene 597. The lasers emit in the chip plane at a wavelength around 595 nm when pumped with 5 ns
pulses from a compact frequency doubled Nd:YAG laser. We investigate the sensitivity of photonic crystal band-edge
lasers to partial coverage with HeLa cells. The lasers are chemically activated with a flexible UV activated
anthraquinone based linker molecule, which enables selective binding of cells and molecules. When measuring in
Phosphate Buffered Saline (PBS), which has a refractive index close to that of the cells, the emission wavelength
depends linearly on the cell density on the sensor surface. Our results demonstrate that nanostructured hybrid
polymer lasers, which are cheap to fabricate and very simple to operate, can be selectively chemically activated
with UV sensitive photolinkers for further bioanalytical applications. This opens the possibility to functionalize
arrays of optofluidic laser sensors with different bio-recognition molecules for multiplexed sensing. The linear
relationship between cell coverage and wavelength indicates that the slight refractive index perturbation from
the partial coverage of the sensor influences the entire optical mode, rather than breaking down the photonic
Organic dye doped polymer photonic crystal band-edge lasers, fabricated by combined nanoimprint and photolithography,
are applied as evanescent-wave refractometry sensors. The emission characteristics of the lasers
are altered in two ways, when the refractive index of the cladding is changed. Not only does the emission wavelength
change, with a sensitivity of 1 nm per 10-2 refractive index units, but also the relative emission intensity
along the two symmetry directions of the rectangular device. The latter phenomenon is caused by the interplay
between the symmetry of the triangular photonic crystal lattice and the rectangular device shape. This causes
two of the three emission axes expected from the photonic crystal geometry to collapse into one. The optical
losses of these two modes are influenced in different ways when the refractive index of the cladding is altered,
thus also causing the emitted intensities along the symmetry directions to change. This suggests an integrated
sensing scheme, where intensity is measured rather than emission wavelength. Since intensity measurements are
simpler to integrate than spectrometers, the concept can be implemented in compact lab-on-a-chip systems.
We present a nanoimprint lithography based method for the fabrication of plasmonic waveguides in the form of V-grooves
in a metal surface which support propagation of channel plasmon polaritons (CPPs). The developed method is
compatible with large scale production, easily adaptable to different device designs and offers wafer-scale parallel
fabrication of plasmonic components. The metal quality is improved in terms of surface roughness when compared to
previous demonstrations where grooves were made by direct milling of metal, and the design allows easy fiber access at
both ends of the waveguide. We demonstrate the design, fabrication and scanning near-field optical characterization of
channel plasmon polariton waveguides at telecom wavelengths. Optical characterization of the fabricated waveguides
shows low-loss (propagation length ~ 120 μm) CPP guiding.
We report on experimental realization of different metal-insulator geometries that are used as plasmonic waveguides
guiding electromagnetic radiation along metal-dielectric interfaces via excitation of surface plasmon polaritons (SPPs).
Three configurations are considered: metal strips, symmetric nanowires and nanowire pairs embedded in a dielectric, and
metal V-shaped grooves. Planar plasmonic waveguides based on nm-thin and μm-wide gold strips embedded in a
polymer that support propagation of long-range SPPs are shown to constitute an alternative for integrated optical
circuits. Using uniform and thickness-modulated gold strips different waveguide components including reflecting
gratings can be realized. For applications where polarization is random or changing, metal nanowire waveguides are
shown to be suitable candidates for efficient guiding of arbitrary polarized light. Plasmonic waveguides based on metal
V-grooves that offer subwavelength confinement are also considered. We focus on recent advances in manufacturing of
nanostructured metal strips and metal V-grooves using combined UV, electron-beam and nanoimprint lithography.
Optofluidic dye lasers have recently attracted much interest as potentially efficient light sources for integration
on lab-on-a-chip micro-systems. However, dye bleaching resulting in limited life-time could limit the applications
of such devices in lab-on-a-chip technology. Typically, the problem of dye bleaching is addressed by employing a
continuous convective flow of liquid-dissolved dye molecules, compensating the bleaching caused by the external
optical pump. In previously reported optofluidic light sources the required convective dye replenishing flow has
been achieved by external fluid handling apparatus (syringe pumps), on-chip microfluidic pumps, or by means
of capillary effect. We have investigated the bleaching dynamics that occur in optofluidic light sources where a
liquid laser dye in a micro-fluidic channel is locally bleached due to optical pumping. A simple one-dimensional
diffusion model is used to explore the characteristic evolution of the local un-bleached dye concentration in the
optically pumped or bleached volume of the device. In the absence of convective flow, the decay of the local
dye concentration in the optically pumped volume is governed by the diffusion rate and the resulting lifetime
of the device is mainly limited by the capacity of the fluidic reservoirs. Generic microfluidic platforms typically
allow for device layouts with a large volume ratio between the fluidic reservoir and the region being optically
pumped. These conclusions drawn from the simple model are supported by basic experiments. Our investigations
reveal the possibility that such optofluidic dye laser devices may potentially be operated for days by diffusion
without the need for a convective flow. Relying on diffusion rather than convection to generate the necessary
dye replenishment significantly simplifies optofluidic dye laser device layouts, omitting the need for cumbersome
and costly external fluidic handling or on-chip microfluidic pumping devices.
We present the design and operation of low-threshold and widely tunable polymer-based nanofluidic distributed
feedback (DFB) dye lasers. The devices rely on light-confinement in a nanostructured polymer film embedded
between two substrates. An array of nanofluidic channels forms a Bragg grating DFB laser resonator relying on
the third order Bragg reflection. The lasers are fabricated by Combined Electron beam and UV Lithography
(CEUL) in a thin film of SU-8 resist and polymer mediated wafer bonding. The devices are operated without the
need for external fluidic handling apparatus. Capillary action drives the liquid dye infiltration of the nanofluidic
DFB lasers and accounts for dye replenishment. The low Bragg reflection order yields: (i) low out-of-plane
scattering losses, (ii) low coupling losses for the light when traversing the dye-filled nanofluidic channels due to
the sub-wavelength dimensions of the resonator segments, and (iii) a large free spectral range (FSR). Points
(i)+(ii) enable a low threshold for lasing, point (iii) facilitates wavelength tuning over the full gain spectrum of
the chosen laser dye without mode-hopping. By combining different grating periods and dye solution refractive
indices, we demonstrate a tuning range of 45 nm using a single laser dye and obtain laser threshold fluences
down to ~ 7 μJ/mm2. The lasers are straightforward to integrate on lab-on-a-chip microsystems, e.g. for novel
sensor concepts, where coherent light in the visible range is desired.
We demonstrate wafer-scale fabrication of integrated polymer optics, comprising nm to mm features, by combined
nanoimprint and photolithography (CNP). Active and passive polymer optical components are integrated:
Distributed feed-back (DFB) polymer dye lasers and polymer waveguides. The laser devices are defined in SU-8
resist, doped with Rhodamine 6G laser dye, shaped as planar slab waveguides on a Si/SiO2 substrate, and with
a 1st-order DFB surface corrugation forming the laser resonator. In the CNP process, a combined UV mask
and nanoimprint stamp is embossed into the resist, which is softened by heating, and UV exposed. Hereby
the mm to (micron)m sized features are defined by the UV exposure through the metal mask, while nm-scale features
are formed by mechanical deformation (nanoimprinting). The UV exposed (and imprinted) SU-8 is crosslinked
by a post-exposure bake, before the stamp and substrate are separated, and the un-exposed resist is dissolved.
Polymer waveguides are added to the system by an additional UV lithography step in a film of un-doped SU-8,
which is spincoated on top of the lasers and substrate. When optically pumped at 532 nm, lasing is obtained in
the wavelength range 559 nm - 600 nm, determined by the grating period. Our results, where 20 laser devices are
defined across a 10 cm diameter wafer substrate, demonstrate the feasibility of CNP for wafer-scale fabrication
of advanced nano-structured active and passive polymer optical components.
We have investigated the bleaching dynamics that occur in opto-fluidic dye lasers, where the liquid laser dye
in a channel is locally bleached due to optical pumping. Our studies suggest that for micro-fluidic devices, the
dye bleaching may be compensated through diffusion of dye molecules alone. By relying on diffusion rather
than convection to generate the necessary dye replenishment, our observation potentially allows for a significant
simplification of opto-fluidic dye laser device layouts, omitting the need for cumbersome and costly external
fluidic handling or on-chip micro-fluidic pumping devices.
We present a technology for miniaturized, chip-based liquid dye lasers, which may be integrated with microfluidic networks and planar waveguides without addition of further process steps. The microfluidic dye lasers consist of a microfluidic channel with an embedded optical resonator. The lasers are operated with Rhodamine 6G laser dye dissolved in a suitable solvent, such as ethanol or ethylene glycol, and optically pumped at 532 nm with a pulsed, frequency doubled Nd:YAG laser. Both vertically and laterally emitting devices are realized. A vertically emitting Fabry-Perot microcavity laser is integrated with a microfluidic mixer, to demonstrate realtime wavelength tunability. Two major challenges of this technology are addressed: lasing threshold and fluidic handling. Low threshold, in-plane emission and integration with polymer waveguides and microfluidic networks is demonstrated with distributed feed-back lasers. The challenge of fluidic handling is addressed by hybridization with mini-dispensers, and by applying capillary filling of the laser devices.
We present the first observation, to our knowledge, of lasing from a levitated, dye droplet. The levitated droplets are created by computer controlled pico-liter dispensing into one of the nodes of a standing ultrasonic wave (100 kHz), where the droplet is trapped. The free hanging droplet forms a high quality optical resonator, which shape can be externally controlled by the ultrasonic field, yielding wavelength tunability and directional control of the emission. Our 700 nL lasing droplets consist of Rhodamine 6G dissolved in ethylene glycol, at a concentration of 0.02 M. In our experiments the droplets are optically pumped at 532 nm light from a pulsed, frequency doubled Nd:YAG laser, and the dye laser emission is analyzed by a fixed grating spectrometer. With this setup we have achieved reproducible lasing spectra in the wavelength range 610 nm - 650 nm. The lasing spectra can controllably be modulated by shaping the droplet. Lasing micro-droplets have been demonstrated earlier, where the droplets in free fall passed the pumping laser beam. The levitated droplet technique has successfully been applied for a variety of bio-analytical applications at single cell level. In combination with the lasing droplets, the capability of this high precision setup can further be applied to create a highly sensitive intra cavity absorbance detection system.
Miniaturized, single mode polymer dye lasers are realized by means of grey scale electron beam lithography (EBL) in functionalized SU-8 2000 resist, doped with Rhodamine 6G laser dye. These devices offer the possibility of easy integration of single mode laser sources in polymer based lab-on-a-chip microsystems. The demonstrated laser
device consists of a planar waveguide with a 1st-order distributed feedback grating (DFB) surface corrugation, which forms an optical resonator. When optically pumped at 532 nm, single mode lasing is obtained in the wavelength range 570 nm - 630 nm, determined by the grating period. Our results demonstrate the feasibility of fabricating advanced nano-structured active optical components in a rapid prototyping process.
We present a polymer lab-on-a-chip (LOC) microsystem with integrated optics, fabricated by thermal nanoimprint lithography (NIL) in a cyclic olefin copolymer, Topas from Ticona. The LOC contains microfluidic channels and mixers, an absorbance cell, optical waveguides, a microfluidic dye laser, and Fresnel lenses to couple light in and out of the waveguides. The polymer structure is embedded between two glass substrates. By this device we exploit the excellent chemical, mechanical and optical properties of Topas, and demonstrate the fabrication of millimeter to micrometer sized structures in one lithographic step. In addition, the NIL approach allows for addition of nanometer-scale features, limited only by the stamp fabrication. The silicon stamp for the imprint process is fabricated by standard UV-lithography and silicon deep reactive ion etching (DRIE). The sidewall roughness of the DRIE process is reduced to below 15 nm by thermal oxidation and subsequent oxide etching. Prior to imprint the stamp is coated with an anti-sticking coating from a perfluorodecyltrichlorosilane precursor by molecular vapor deposition. Topas, in our case grade 8007, dissolved in toluene is spin coated onto a SiO2 substrate. The imprint temperature is 200 °C, at an imprint force of 15000 N on a 4 inch wafer, imprint time is 5 min. Finally the imprinted structure is bonded to a pyrex wafer with a second layer of Topas in our case grade 9506. Bonding temperature is 70 °C, at a bonding force of 5000 N on a 4 inch wafer. Bonding time is 5 min.
We present a microcavity solid polymer dye laser based on a single
mode planar waveguide. The all-polymer device is self contained in
the photo definable polymer SU-8 and may therefore easily be
placed on any substrate, and integrated with polymer-based optical
or microfluidic systems. As the active medium for the laser we use
the commercially available laser dye Rhodamine 6G which is
incorporated into the SU-8 polymer matrix. The single mode slab
waveguide is formed by a 3-step spin coating deposition: a buffer
layer of un-doped SU-8, a core layer of SU-8 doped with Rhodamine,
and a cladding layer of un-doped SU-8. The refractive index
increases with Rhodamine concentration, and the difference between
the un-doped buffer and cladding layers and the doped core layer
is fine tuned to 0.001, allowing a large gain volume.
The integration of optical transducers is generally considered a key issue in the further development of lab-on-a-chip microsystems. We present a technology for the integration of miniaturized, polymer based lasers, with planar waveguides, microfluidic networks and substrates such as structured silicon. The flexibility of the polymer
patterning process, enables fabrication of laser light sources and other optical components such as waveguides, lenses and prisms, in the same lithographic process step on a polymer. The optically functionalised polymer layer can be overlaid on any reasonably flat substrate, such as electrically functionalised Silicon containing
photodiodes. This optical and microfluidic overlay, interfaces optically with the substrate through the polymer-substrate contact plane. Two types of integrable laser source devices are demonstrated: microfluidic- and solid polymer dye lasers. Both are based on laser resonators defined solely in the polymer layer. The polymer laser sources are optically pumped with an external laser, and emits light in the chip plane, suitable for coupling into chip waveguides. Integration of the light sources with polymer waveguides, micro-fluidic networks and photodiodes embedded in a Silicon substrate is shown in a device designed for measuring the time resolved absorption of two fluids mixed on-chip. The feasibility of three types of polymers is demonstrated: SU-8, PMMA and a cyclo-olefin co-polymer (COC) -- Topas. SU-8 is a negative tone photoresist, allowing patterning with conventional UV lithography. PMMA and Topas are thermoplasts, which are patterned by nanoimprint lithography (NIL).
The integration of optical transducers is generally considered a key issue in the further development of lab-on-a-chip Microsystems. We present a technology for miniaturized, polymer based lasers, suitable for integration with planar waveguides and microfluidic networks. The lasers rely on the commercial laser dye Rhodamine 6G as active medium, and the laser resonator is defined in a thin film of polymer on a low refractive index substrate. Two types of devices are demonstrated: solid and microfluidic polymer based dye lasers. In the microfluidic dye lasers, the laser dye is dissolved in a suitable solvent and flushed though a microfluidic channel, which has the laser resonator embedded. For solid state dye lasers, the laser dye is dissolved in the polymer forming the laser resonator. The miniaturized dye lasers are optically pumped by a frequency doubled, pulsed Nd:YAG laser (at 532 nm), and emit at wavelengths between 560 nm and 590 nm. The lasers emit in the plane of the chip, and the emitted light is coupled into planar polymer waveguides on the chip. The feasibility of three types of polymers is demonstrated: SU-8, PMMA and a cyclo-olefin co-polymer (COC) - Topas. SU-8 is a negative tone photoresist, allowing patterning with conventional UV lithography. PMMA and Topas are thermoplasts, which are patterned by nanoimprint lithography (NIL). The lasing wavelength of the microfluidic dye lasers can be coarse tuned over 30 nm by varying the concentration of laser dye, and fine tuned by varying the refractive index of the solvent. This is utilized to realize a tunable laser, by on-chip mixing of dye, and two solvents of different index of refraction. The lasers were also integrated with waveguides and microfluidic networks.
The technique utilizes the capacitive coupling between a pair of Corbino electrodes and a conducting layer placed on top of and insulated from the electrodes. Measurements on heterostructures of GaAs/GaAlAs and GaAs/GaInP are reported. The audiofrequency impedance exhibits ShubnikovdeHaas oscillations. These oscillations are used to investigate persistent photoconductiity at 0. 635 tm and 1. 00 jim illumination. The role played by contacts is discussed.