Electro-optic polymer-based monolithic waveguide devices with multi-functions of amplification switching and modulation
Electro-optic (EO) polymer materials have become a promising option for high-performance integrated optics due to their high nonlinearity, small velocity mismatch for traveling wave devices, and flexible monolithic integrated capability on any interested substrates. Based on waveguides fabricated with EO polymers, our research objectives were (1) to design and fabricate amplifiers, switches, and modulators and (2) to investigate the possibility of integrating these devices into a monolithic module. By co-doping rare-earth ions and EO chromophores into photolime gel, a well-known backbone for holographic materials, we present here a dual-functional planar waveguide demonstrating the capability of amplification and modulation. Complete device-fabrication processes, including wafer preparing, polymer coating and curing, adhesion enhancing of film interfaces, waveguide RIE etching, electrode patterning and plating, wafer dicing, waveguide polishing, and wire bonding, have been investigated in depth. All these techniques can be applied to make not only electro-optic polymeric devices, but thermal-optical polymeric devices as well. Straight channel array, Y-coupler array, and X-junction have been demonstrated successfully, all made from polyimides. With a thermal-setting EO polymer PU-FTC, both corona poling and contact poling were investigated. A novel domain-inversion poling technique was developed. We demonstrated an electro-optic modulator based on a 1x2 Y-branch directional waveguide coupler. The symmetric geometry of this coupler provides the modulator with the unique characteristics of an intrinsic 3dB operating point and two complementary output ends. The design, fabrication, and testing of the modulator are discussed in the dissertation. A highly linearized Y-coupler modulator is presented lastly. The high linearity is achieved by suppressing its IMD3 with the ∆β−inversion method. The operation principle of the device is analyzed here. Substantial suppression was achieved for a ∆β−inverted modulator in a wide dynamic range up to 70% optical modulation depth. An IMD3 suppression of 47.29dB was observed for this modulator, as opposed to a conventional one.
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