Holographic recording of sub-micron period gratings and photonic crystals in the photoresist SU8

SU8 is a commercial negative photoresist, which is highly transparent in the visible and near-infrared and extremely resistant to many organic solvents. Here we show that sub-micron period diffraction gratings, and 2D photonic crystal structures, can be readily formed holographically over extended areas. By coating the SU8 layer with a suitable gain medium, such structures may be used as feedback and output-coupling gratings for organic waveguide lasers. Thin films of SU8, were initially deposited by spin casting onto glass substrates. These films were then mounted in one arm of a Lloyd's mirror interferometer and exposed with the expanded beam of a HeCd laser, operating at 325 nm. Subsequent baking and developing steps lead to both volume gratings with index contrast of 0.014, and surface gratings with corrugation depths of up to 140 nm. By varying the incidence angle of the HeCd laser beam to the SU8 film we have tuned the microstructure period from 500 nm down to 200 nm. Using multiple exposures, both doubly-periodic diffraction gratings and square-lattice crystal structures have been produced

Holographic recording of sub-micron period gratings and photonic crystals in the photoresist SU8

SU8 is a commercial negative photoresist, which is highly transparent in the visible and near-infrared and extremely resistant to many organic solvents. Here we show that sub-micron period diffraction gratings, and 2D photonic crystal structures, can be readily formed holographically over extended areas. By coating the SU8 layer with a suitable gain medium, such structures may be used as feedback and output-coupling gratings for organic waveguide lasers. Thin films of SU8, were initially deposited by spin casting onto glass substrates. These films were then mounted in one arm of a Lloyd's mirror interferometer and exposed with the expanded beam of a HeCd laser, operating at 325 nm. Subsequent baking and developing steps lead to both volume gratings with index contrast of 0.014, and surface gratings with corrugation depths of up to 140 nm. By varying the incidence angle of the HeCd laser beam to the SU8 film we have tuned the microstructure period from 500 nm down to 200 nm. Using multiple exposures, both doubly-periodic diffraction gratings and square-lattice crystal structures have been produced

Novel diffractive feedback structures for semiconducting polymer lasers

Semiconducting conjugated polymers have recently attracted significant interest as amplifying media for solid-state lasers due to their functional photo-physical properties and simple fabrication. Distributed feedback (DFB) cavities are proving to be the most attractive for polymer lasers, since they can combine the properties of transverse optical pumping, low threshold and practical output beams. To date, in most polymer DFB lasers the feedback is provided by second order diffraction. This has the advantage of surface emission, though it also imposes extensive scattering losses. In this work, we present the use of alternative structures that attempt to reduce the threshold of polymer DFB lasers, and also achieve dual wavelength operation. The former was addressed with cavities formed by alternative symmetries of the Brillouin zone of a square lattice. Using the diagonal ΓM symmetry first order feedback was attained. The threshold energy was thus reduced by almost an order of magnitude as compared with the more commonly used ΓX symmetry of second order square gratings. Finally, we show that two lasing wavelengths may be set independently in a semiconducting polymer laser by using a doubly periodic (i.e. MoirÁ½) DFB grating

Modular Polymer Biosensors by Solvent Immersion Imprint Lithography.

We recently demonstrated Solvent Immersion Imprint Lithography (SIIL), a rapid benchtop microsystem prototyping technique, including polymer functionalization, imprinting and bonding. Here, we focus on the realization of planar polymer sensors using SIIL through simple solvent immersion without imprinting. We describe SIIL's impregnation characteristics, including an inherent mechanism that not only achieves practical doping concentrations, but their unexpected 2-fold enhancement compared to the immersion solution. Subsequently, we developed and characterized optical sensors for detecting molecular O2. To this end, a substantially high dynamic range is reported, including its control through the immersion duration, a manifestation of SIIL's modularity. Overall, SIIL exhibits the potential of improving the operating characteristics of polymer sensors, while significantly accelerating their prototyping, as it requires a few seconds of processing and no need for substrates or dedicated instrumentation. These are critical for O2 sensing as probed by way of example here, as well as any polymer permeable reactant

Modular Polymer Biosensors by Solvent Immersion Imprint Lithography.

We recently demonstrated Solvent Immersion Imprint Lithography (SIIL), a rapid benchtop microsystem prototyping technique, including polymer functionalization, imprinting and bonding. Here, we focus on the realization of planar polymer sensors using SIIL through simple solvent immersion without imprinting. We describe SIIL's impregnation characteristics, including an inherent mechanism that not only achieves practical doping concentrations, but their unexpected 2-fold enhancement compared to the immersion solution. Subsequently, we developed and characterized optical sensors for detecting molecular O2. To this end, a substantially high dynamic range is reported, including its control through the immersion duration, a manifestation of SIIL's modularity. Overall, SIIL exhibits the potential of improving the operating characteristics of polymer sensors, while significantly accelerating their prototyping, as it requires a few seconds of processing and no need for substrates or dedicated instrumentation. These are critical for O2 sensing as probed by way of example here, as well as any polymer permeable reactant