| dc.description.abstract | Silicon-on-insulator (SOI) material has received much attention as a platform for planar lightwave circuits (PLCs) due to the compatibility with complementary metal oxide semiconductor (CMOS) technologies and high possibility to integrate other optoelectronic devices within a single chip. SOI’s intrinic high index contrast between silicon and oxide/air causes single-mode core size less than 0.3 μm for a simple slab-type waveguide, and then serious coupling loss from fibers is inevitable. Therefore, rib-type waveguide is usually adopted not only to provide a larger core size but also to maintain single-mode operation. Furthermore, PLCs-related devices such as bends, beam splitters, or filters based on SOI-based rib waveguide have become essentional research issues in these years. In this thesis, we focus on both waveguide bending and filtering applications with ultra-compact and monolithic characteristics. The individual detail for both devices is briefed as follows:
Ultra-compact waveguide bend is very important to achieve devices with high-density integration. SOI-based rib waveguide is a great platform to perform a wild-angle bending with high bending efficiency via reflection mirror, corner mirror technologies. However, these technologies for waveguide bends are short of an efficiently optimal design rule for arbitrary bending angles. Here, a compact SOI rib waveguide bends with benzocyclobutene (BCB) microprisms are proposed. The microprism is designed by using the phase compensation rule and monolithically integrated in the bending area of an optical waveguide to correctly tilt the wavefront of eigen-mode and suppress the radiation loss. The microprism can be realized by dry-etching an air trench in the bent corner and filling it with the BCB polymer material. A very compact bending radius of 10.46 μm is implemented to various bending angles including 10, 30, 40, 48, 55, and 60 degrees with averaged experimental bending loss of 10.48 dB. In addition, the core size of this rib waveguide can be expanded to 2.5 × 2 μm2, resulting in coupling loss less than 4.2 dB.
Wavelength-Division Multiplexer plays an important role in optical communication, which converge signals carried by different wavelength, and then separates it into different terminations. Different kinds of optical filters such as thin film filters and grating filters were broached to serve the demand of multiplexer. However, these technologies are deficient in large working area or the huge packaged size. Therefore, a compact SOI-based rib waveguide with distributed-Bragg-reflector (DBR) structures are also proposed, the DBR layers from one to three pairs are designed for incident wave to resonate and filter through a narrow bandwidth and high transmission efficiency of transmitted wave. The transmission efficiency is as high as 0.96 with FWHM (full width half maximum) of 5 nm, which is achieved by two-pair air trench of DBR filter.
According to the bending and filtering technique as mentioned above, the approach to a compact intra-chip wavelength division multiplexer would be expected, and makes the research more applicable.
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