This paper describes a fabrication technique of polymeric distributed-feedback lasers using the photonanoimprint lithography. In devices with a grating structure, which was imprinted directly onto the active layer surface in vacuum, single-mode laser oscillations were easily obtained. The emission color of the distributed-feedback laser can be controlled only by changing doping material and grating period of the master mold. It was demonstrated that the nanoimprint lithography would be a key technology for development of a multicolor light source.
This paper describes an organic dye-doped polymeric laser with a multilayered structure of active waveguides. Using the technique of photonanoimprint lithography, organic active-waveguide layers with distributed-feedback cavities and a polymeric intermediate cladding layer were stacked on a silica substrate. Under optical pumping, lasing oscillations at 427 and 636 nm, which correspond to the Bragg reflection wavelengths in the respective active waveguides, were simultaneously observed. The fabrication scheme presented here is expected to be a promising technology for the development of compact multicolor laser sources.In the past decade, solid-state organic lasers have received much attention for their use as compact light sources 1,2 because of the material advantages of organic compounds for producing various luminescent colors and their flexibility in thin-film fabrications. 3 Actually, lasing oscillations at various wavelengths in the whole visible region have already been demonstrated, 3,4 which is an attractive feature of solid-state organic lasers that inorganic semiconductor lasers do not have. As one of the extensive works, multicolor lasing oscillation in a single device would be a considerable research target. In the case of organic lightemitting diodes ͑OLEDs͒, multicolor emissions have been demonstrated in devices with a blend of luminescent polymers and organometallic complexes or multilayered structures of luminescent thin films. 5,6 Unlike OLEDs, the development of multicolor organic lasers requires new problems to be overcome. Multicolor lasing cannot be expected from a waveguide cavity with a polymer blend because the lasing wavelength will be self-tuned to the wavelength with the maximum gain. Thus, a parallel arrangement of channel waveguide cavities 7 or a stack of slab waveguide layers with various operation wavelengths would be a realistic device configuration. In these two configurations, a multilayered structure of active waveguides is preferable because it requires no microfabrication processes. To fabricate organic lasers with a multilayered structure, however, there are some important problems as follows. First, the emission generated in each active layer must be sufficiently confined to induce the lasing oscillation. Therefore, a thick intermediate cladding layer must be introduced between the active waveguide layers to suppress the power distribution of the guided emission. In addition, an effective optical feedback cavity must be fabricated in each active waveguide using a simple method.We have been attempting to develop a key fabrication scheme to form a multilayered structure of cavity waveguides fabricated by photonanoimprint lithography ͑photo-NIL͒. Using photo-NIL, we have recently fabricated laser devices with distributed-feedback ͑DFB͒ cavities and have demonstrated lasing oscillations with blue, green, and red operation colors. 4 Photo-NIL has advantageous features for the convenient fabrication of organic DFB lasers; it does not require a dry etching process or a severe op...
SUMMARYMeasurement of workload using voice user interface systems is helpful for improving usability. We propose an evaluation method which performs the main task of listening and answering via voice and the subtask of pressing the keyboard responding to signs on the visual display simultaneously. Using this dual-task method, we can find the parts of the voice interface systems where the user experienced problems. These are the parts the developer must improve. Our experiments showed that the proposed method reflected the difference of task difficulties significantly.
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