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.