Design, Fabrication and Characterization of a Polymer Electro-Optic Modulator

Abstract

We have designed and fabricated an Electro-optic (EO) polymer Mach-Zehnder modulator for the use at the 1550nm telecommunication wavelength. Structures in polymer are patterned with μm-resolution by laser ablation – a method that hasn’t been widely used in single-mode polymer waveguide production. The core layer of the device is made of a guest-host polymer system, where two chromphores, named Disperse Red1 (DR1) and C10 are doped into polycarbonate, respectively, to serve as the EO system. A 248nm KrF excimer laser machining system provides good surface qualities for the waveguide patterning. The propagation losses are measured to be approximately 2dB/cm. A moisture-curing polyurethane coating product MCL and a UV-curable epoxy UV15 are chosen as the cladding materials for our device, taking into consideration the laser machining performance, curing process, refractive indices, resistivity, solubility, glass transition temperature and other properties. We precisely deposit an Au-electrode to cover one arm of the M-Z structure and pole the device. A modulated signal at 1kHz has been detected from our modulator, and EO coefficients ( 33) of 2.9pm/V and 1.1pm/V were obtained for modulators made of PC/DR1 and PC/C10 EO systems, respectively. Besides the laser ablation technique that we used for the machining of single-mode waveguides, two other novel ideas have been implemented in this study: one is the rayoptics theory in rectangular waveguides – the method is simple but enables the light propagation through a rectangular waveguide to be presented in a visualized way. Based on the ray-optics theory in 1-D slab waveguide, light propagation within a 2-D rectangular waveguide is simplified as reflections within two planes of incidence. By employing the mode equations for different polarizations, one can directly calculate the effective refractive indices for each optical mode in the waveguide. The other new method is for the attenuation measurement of polymer waveguides – we fabricate waveguides of different lengths on one substrate and characterize the attenuation by plotting the output power of these waveguides as a function of the propagation lengths.