Yasuhisa Ichihashi

Polymer waveguides from alicyclic methacrylate copolymer fabricated by deep-UV exposure

We have investigated the fabrication of waveguides from alicyclic methacrylate copolymer based on refractive-index modification by deep-UV exposure. By optimizing the UV-exposure process, we were able to obtain single-mode waveguides with a propagation loss of 0.8 dB/cm at 1550 nm, which is due only to material losses in this wavelength range. The loss obtained here is comparable with that of poly(methyl methacrylate) (PMMA) waveguides fabricated by deep-UV exposure. The fabricated waveguide is also single mode at 808 nm, and its propagation loss is 0.6 dB/cm. This alicyclic methacrylate copolymer is a promising material for the fabrication of polymer waveguides by use of deep-UV exposure.

Material Investigation of Alicyclic Methacrylate Copolymer for Polymer Waveguide Fabrication

We investigated the physical and chemical properties of alicyclic methacrylate copolymers and their changes under deep-UV exposure. It was shown that alicyclic methacrylate copolymers have a better thermal stability and a higher refractive index than conventional poly(methyl methacrylate) (PMMA). Fourier transform IR (FTIR) spectra show the scission of the carbonyl group of the alicyclic methacrylate copolymers by deep-UV exposure similar to that of PMMA. This structural modification results in a local and controllable increase in refractive index in the exposed areas of the polymer surface. We fabricated polymer waveguides from alicyclic methacrylate copolymers by conventional photolithography using quartz/chromium mask. The minimum propagation loss of the straight waveguide with a 7.5 µm width was 2 dB/cm at 1550 nm.

Enhancement of the evanescent field using polymer waveguides fabricated by deep UV exposure on mesoporous silicon

Polymer integrated reverse symmetry waveguides on porous silicon substrate fabricated by using deep ultraviolet radiation in poly(methyl methacrylate) are presented. The layer sequence and geometry of the waveguide enable an evanescent field extending more than 3 microm into the upper waveguide or analyte layer, enabling various integrated optical devices where large evanescent fields are required. The presented fabrication technique enables the generation of defined regions where the evanescent field is larger than in the rest of the waveguide. This technology can improve the performance of evanescent-wave-based waveguide devices.

Determination of living cell characteristics and behavior using biophotonic methods

This paper describes the development of methods for the determination of the characteristics and the behavior of living neural cells. A technology which is used is the deep ultraviolet (DUV) modification of methylmethacrylate polymers which leads to a new surface chemistry affecting the selective absorption of proteins and the adhesion of living cells in vitro. The bi-functionality of the modified polymer chips supporting waveguides and cell anchorage capabilities at the same time provides the opportunity to monitor protein adsorption, cell attachment and spreading processes by evanescent-field techniques. This allows the defined spatial control of a cell/surface interaction and leads to a combination of desired biological and optical properties of the polymer. Among them are the high sensitivity of cultured mammalian cells to, for example, environmental changes and special features of integrated optical waveguides like their online compatibility, minuteness and robustness. The scientific fields, biology and optics, meet at the polymer surface becoming a cell culture substrate together with an optical waveguide by the application of special patterning and fabrication technologies. In addition to the already mentioned fabrication and immobilization technology, the technique proposed also offers the possibility of being able to couple to microstamping processes and to also incorporate electrical measurements on individual cells. Thus, by extending this method and coupling it to the DUV technique described above the possibility is given of being able to simultaneously optically and electrically interrogate individual cellular processes with spatial resolution.

Photonic Integrated Circuits fabricated by Deep UV and Hot Embossing

We review our work in the field of deep UV modification of methacrylate-based polymers. Planar and rib waveguide structures are presented. A method of integrating polymer waveguides with organic light sources into all-polymer systems is shown.

Monitoring Fluorescence in Cultured Neural Networks using Polymer Waveguide Excitation

We present fluorescence excitation of cultured living neural cells using integrated optical waveguides. The waveguides (width 5, 7, 9 mum) are fabricated in polymethylmethacrylate (PMMA) using deep ultraviolet radiation. The excitation wavelength is 473 nm.

Polymer photonic integrated circuits by DUV-induced modification

Polymer optical waveguide devices will play a key role in several rapidly developing areas such as optical networks, biophotonic and fluidic applications. We have developed a technology which enables the increase of the refractive index of methylmethacrylate based polymers by deep ultra violet (DUV) radiation. The modification of the dielectric properties of polymers by DUV is a useful technique for the realization of photonic integrated optical circuits. The technique presented here has several advantages with respect to common methods because only a single polymer layer is used, which serves as the substrate and waveguide as well and no further etching or development step is required. This method can not only be applied to planar polymer substrates but also to preembossed substrates. This enables the fabrication of ridge waveguide based devices by hot embossing. Nickel stampers with feature heights of about 15-20 μm and aspect ratios usually between 2:1 and 3:1 can be utilized for replication without major effort. Nickel stampers are not only used to replicate optical waveguides, but are also used to realize fluidic channels in the range of several microns. UV modification of methylmethacrylate polymers additionally leads to a new surface chemistry affecting the selective absorption of proteins and the adhesion of living cells in vitro. The bi-functionality of the modified polymer chips supporting waveguides and cell anchorage capabilities at the same time provides the opportunity to monitor protein adsorption, cell attachment and spreading processes by evanescent-field techniques.