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.
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.
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
mask/mold.
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
crystal feedback.
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 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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.