Laser Processing of Integrated Optic Waveguides for Photonic Applications
Very low loss integrated waveguides of optically transparent materials are desirable for many passive and active photonic waveguide devices. In the past, there have been numerous reports on several waveguide fabrication techniques applied to organic, inorganic and semiconducting materials. This article focuses on laser fabrication of integrated optic waveguides of organic and inorganic materials. Choice of material and laser processing technique are application specific. While inorganic glass waveguides are appropriate for high temperature environments such as space applications, waveguides of organic polymers are not. The flexibility of film deposition and laser processing of organic polymers are however very attractive for photonic applications at moderate temperatures. Waveguide fabrication may be broadly classified under two categories, namely, lithographic patterning and resist-free patterning. Lithographic patterning is usually followed by ion diffusion or some form of etching (wet chemical or dry). Although lithographically patterned waveguides is an established technology, it involves time consuming mask transfer process and use of chemicals that are not environmentally safe. Laser fabrication of integrated waveguide structures is the dominant resist-free patterning technique, which offers flexibility, reproducibility and rapid manufacturing conditions, besides being environmentally safe. Also, as described in a later section, laser fabrication allows variation of film thickness and refractive index across the wafer which may be needed in improving coupling and bending losses. This article will describe pulsed and cw UV laser processing techniques and the inorganic and organic materials commonly used for the fabrication of channel waveguides for photonic applications. Our research effort on a unique laser processing of very low loss (0.08 dB/cm) channel waveguides on polymethylmethacrylate (PMMA) will be given in detail.
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