Low-loss polymeric optical waveguides with large cores fabricated by hot embossing.

A simple low-cost method of fabricating polymeric optical waveguides with large core sizes for plastic optical fibers is presented. The waveguides are fabricated by hot embossing with an ultraviolet-cured epoxy resin stamper. The stamper is fabricated by replication of a rectangular groove mold that is made from silicone rubber replicated from a ridged original silicon master. The master is fabricated by anisotropic etching of (110) single-crystal silicon. Optical waveguides with large core sizes of 100-500 microm have been fabricated, and a low propagation loss of 0.19 dB/cm at 650 nm was achieved.

Non-optically probing near-field microscopy with illumination of total internal reflection.

We have developed a non-optically probing near-field microscope with illumination of total internal reflection. Because the illumination light does not pass through the specimens, it is possible to observe thick specimens or highly absorptive materials. It reduces the background noise because the decay length of the evanescent wave is a few hundred nanometres. We found that although in the total internal reflection illumination system the light passed through the photosensitive film and illuminated the specimen, it did not affect the photosensitive film severely and did not limit the resolution. The imaging properties of reflection illumination and transmission illumination are analysed using a finite-differential time domain method.

Simultaneous process of embossing and poling at elevated temperatures: a simple technique for nonlinear grating formation in polymer films.

A simple technique for fabrication of nonlinear gratings in polymer films, based on simultaneous embossing and poling, is proposed and demonstrated. A master grating consisting of a metal electrode with a dielectric die was fabricated and used for repeated embossing of the grating structures into nonlinear optical polymers at elevated temperatures. At the same time, we applied high voltage to the polymer films to induce second-order nonlinearity. The grating profile and the nonlinearity were estimated, as well as the mass productivity of nonlinear gratings.

Single-pulse ultraviolet laser recording of periodically poled structures in polymer thin films.

A simple fabrication technique for nonlinear polymeric optical waveguide patterns is introduced based on the two-beam interference method. We determined that the second-order nonlinearity of poled polymer films is erased by single-pulse ultraviolet (UV) laser irradiation. The erasure mechanism for second-order nonlinearity is discussed. To form a periodic structure in an optical polymer waveguide, two types of optical configuration of two-beam interference were arranged, and a single-pulse UV laser was exposed directly onto poled films. We prove that this method provides a simple way to fabricate volume-type and ridge-type periodically poled structures, i.e., chi(2) gratings, from the submicrometer to the millimeter range.

Polarization-multiplexed optical memory with urethane-urea copolymers.

We present a polarization-multiplexed optical memory with urethane-urea copolymers. The side chains of the urethane-urea copolymers induce cis-trans isomerization by illumination of blue or green light, and they align perpendicular to the linear polarization of the illuminated light, thus producing optical anisotropy. We found that the material showed selective anisotropy for the particular direction that was perpendicular to that of the recording beam polarization. By use of the anisotropic property three different data pages were multiplexed at the same spot of the medium. Erasure of the recorded bit data is also demonstrated.

Reflection-type confocal readout for multilayered optical memory.

We present a multilayered optical memory for use in reading data with a confocal reflection microscope system. We use a recording medium in which photosensitive thin films and nonphotosensitive transparent films are stacked alternately. Since the photosensitive films are thinner than the depth of focus of the recording beam, the spatial frequency distribution of the recorded bit data is extended in the axial direction. The extended distribution overlaps the coherent optical transfer function of the reflection-type confocal microscope. Urethane-urea copolymer film is used as a photosensitive material. The recording and reading of two layers are demonstrated.

Ultraviolet photobleaching process of azo dye doped polymer and silica films for fabrication of nonlinear optical waveguides.

We describe the effect of UV photobleaching of poled polymer and silica films and the application of UV photobleaching to waveguide-type optical devices. Disperse Red 1-doped poled polymer and silica films with large and stable second-order nonlinearity were used as nonlinear optical materials. We investigated the mechanism of UV photobleaching of poled films by the changes in absorption spectrum and nonlinearity and refractive index. Moreover, simple fabrication of both the channel waveguide and the chi((2)) diffraction grating based on UV photobleaching is demonstrated.

Fabrication Technique of a Nonlinear Optical Structure Using Optical Polymeric Films by Direct Electron-beam Irradiation.

A simple fabrication technique of nonlinear optical structures for use with dye-doped polymer is described. Polymethylmethacrylate, U-100 polymer, and polystyrene were used as the host matrices to fabricate the nonlinear optical waveguide. The periodically poled nonlinear optical polymer structures and ridge-type channel structures were fabricated by direct electron-beam irradiation. The electron beam with 25 kV of energy was exposed directly onto the polymer films containing the nonlinear optical chromophores. We can also demonstrate the fabrication technique of the domain-inverted grating of dye-doped polystyrene film.

Self-adaptive spatial filtering by use of azo chromophores doped in low glass-transition-temperature polymers.

We report on self-adaptive spatial filtering by combination of the self-adaptive polarization-rotation property of Disperse Red1-doped polymers with low glass-transition-temperature and Fourier-transform operation. Our system can be operated with only an action beam with object information and without a probe beam for image readout. Edge enhancement by the action beam-probe beam is demonstrated as an example of the system's application to spatial filtering.

Direct electron-beam irradiation: a new technique for the erasure of second-order nonlinearity and the fabrication of channel waveguides by use of optical polymeric films.

We demonstrate a novel and simple technique for fabrication of a nonlinear-optical polymeric waveguide device by direct electron-beam irradiation. To form a periodically poled nonlinear-optical polymer waveguide, we exposed dye-doped polymer films directly to electron beams with an energy of 25keV. It became clear that irradiation with electron beams erased the second-order nonlinearity of poled polymer film. We could also confirm that a ridge-type channel waveguide was realized by means of this simple technique.

Phase-matched second-harmonic generation in a four-layer 2-methyl-4-nitroaniline waveguide with grating couplers.

A four-layer 2-methyl-4-nitroaniline (MNA) crystal waveguide device with grating couplers is fabricated. Second-harmonic generation is observed under phase-matching conditions using the mode dispersion curves of the optical waveguide. A second-harmonic generation conversion efficiency in the waveguide of 0.71% is obtained with a grating coupling efficiency of 11.4% and a decoupling efficiency of 43.2%. The MNA single crystal is never damaged mechanically, and it has been kept stable for nine months.

Phase-matched second harmonic generation in poled dye/polymer waveguide.

Poled film of 2-methyl-4-nitroaniline (MNA) and poly(methyl methacrylate) is prepared. Poling effects of MNA molecular alignments are observed by reducing the absorption spectrum and increasing the refractive index of the film. Phase-matched second harmonic generation (SHG) is achieved using the mode dispersion relation of the optical waveguide with an estimated SHG conversion efficiency of 7.4 x 10(-3) % in the waveguide.