Handbook of Modern Coating Technologies

Microphotonics and microoptics

The scope of applications of micro- and nanostructures produced using PBW includes microoptics and microphotonics. Processing light signals is possible with the use of chip- integrated optical elements, such as emitters, waveguides, detectors, modulators, and large arrays of microlenses to ensure high-speed data processing. There are basically two ways in which PBW technology can be applied. The first involves the formation of small structures by directly forming a pattern of polymers, layered by centrifugation on a suitable substrate, such as a silicon wafer with a thermooxide layer or glass. The optical fiber core material should have a higher refractive index whose sheath and substrate are for use as an optical fiber. For the production of waveguides, the SU-8 resist is the most suitable material because of its low loss of light signal, high transparency, and smooth walls (Fig. 5—12B). In addition, the refractive index of the SU-8 is only slightly higher than that of thermal silicon oxide and glass substrate. Microlens arrays can be manufac­tured utilizing structures composed of a layer of a resistive material laid centrifugally on a transparent substrate (e.g., glass is most frequently applied in optical microscopy). To produce microlenses of the desired diameter, the next step is to form a pattern. Due to the heating of the entire structure to the glass transition temperature, the polymer is thermally fused after development. The surface tension will aid in forming hemispherical lenses (Fig. 5—12C). The focal length depends on the combination of the resist thickness and the lens diameter. By direct drawing, other structures can be fabricated which include Fresnel and lattice plates. The second method of forming waveguides in quartz glass or bulk polymer using PBW involves modifying an ion beam without a direct recording development step [132]. This is achieved by utilizing the process proceeding at the final stage of ion motion in the sample when a buried waveguide channel is created in a substrate. As shown above, the peculiarity of ion beams is that the amount of energy input into the substrate increases rapidly with decreasing velocity. The probability that the ion will create a vacancy closer to the end of the range is rapidly increasing. The local increase in the refractive index occurs due to the local increase in the density of the material due to the creation of a hidden area of damage. This damaged area can serve as the core of a waveguide.