Field enhancement in polymer waveguides fabricated by UV imprinting
Polymers are applicable materials for photonic device fabrication due to their good optical properties and versatile processability at low temperatures, and therefore, provide possibility for low-cost fabrication. For waveguide device fabrication, the most critical requirement is the selection of the patterning method for the ridge that is bounding the optical mode in the waveguide. In this paper, we review our UV-imprinting achievements for fabricating polymer-based single-mode waveguides: ridge, inverted ridge and layered composite waveguides. In addition, we show simulation results for polymer-based slot waveguides. The ridge waveguide consists of a strip waveguide core superimposed onto a slab waveguide made of the core material. When patterning a ridge by imprinting technique, a residual layer is formed underneath the imprinted ridges. The residual layer might cause propagation loss due to power leakage into the slab guide, and therefore, a subsequent etching step is required. In the inverted ridge waveguide configuration, a groove of cladding material is patterned by imprinting, and followed by the filling of the groove with the core material. From the imprint fabrication point of view, the fabrication tolerances can be relaxed due to the fact that the residual slab layer underneath the waveguide can have arbitrary thickness. Besides fabrication of above mentioned waveguide structures, we review the possibility to fabricate composite waveguide devices by depositing inorganic thin films with high-refractive index on UV-imprinted polymeric structures with low-refractive index. The aim to use composite structures is to manipulate the optical field distribution in the waveguides and to enhance the interaction of the optical field with the surface, which is desirable especially in waveguide sensor applications. The polymer-based slot waveguide, which is analyzed theoretically, is an ultimate approach for optical field enhancement.