Bragg Reflector Waveguide and Electro-Optic Modulator Based on Barium Titanate Epitaxial Thin Films
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1014-AA07-01
Bragg Reflector Waveguide and Electro-Optic Modulator Based on Barium Titanate Epitaxial Thin Films Zhifu Liu, Pao-Tai Lin, and Bruce W. Wessels Materials Science and Engineering and Materials Research Center, Northwestern University, 2220 Campus Drive, Evanston, IL, 60208 ABSTRACT We report the nanofabrication of Bragg reflector waveguide structure based on a barium titanate (BTO) epitaxial thin film grown on MgO substrate and characterized its optical transmission. Low pressure nano-lithography was used for the formation of Bragg reflector waveguide structure. We demonstrate that there is sufficient refractive index contrast to form a well-defined stop band by forming gratings in a top strip layer of Si3N4 that was grown on BaTiO3 (BTO) thin film. Simulations of the optical transmission and stop band of TE mode, and electro-optic (EO) modulator tunability are also discussed. The non-linear photonic crystal waveguides are potentially suitable as tunable optical filters and ultra-wide bandwidth modulators. INTRODUCTION Nano-photonic materials and devices will play a key role in next generation fiber-optic communication systems. Optical modulators are essential components of communication network systems. Modulator requirements include: ultra-wide bandwidth, low insertion losses, high extinction ratios and thermal stability. Wide band modulators have been made from bulk LiNbO3 (LNO) ferroelectrics with high bandwidth operation under laboratory conditions [1-3]. Non-linear photonic crystal waveguide structures have been proposed for improving bandwidth of EO modulator [4]. One dimensional photonic crystal Bragg grating structures have been previously proposed for slow wave modulator devices using a ferroelectric material, and subsequently demonstrated using a bulk LiNbO3 waveguide [5-7]. With a Bragg reflector slow light structure for better phase matching between optical wave and microwave, a lithium niobate Mach-Zehnder EO modulator potentially having ~125 GHz bandwidth with a one volt drive voltage potentially could be achieved for devices few centimeters in length [8]. Further improvements can be realized by using other ferroelectrics. The promises of EO modulators based on a BTO platform are higher bandwidth, device ruggedness, low-loss, integration with silicon [9]. BTO is an excellent non-linear optical material with an extremely large EO coefficient [10]. A thin film BaTiO3 EO modulator with a >15GHz modulation bandwidth has recently been demonstrated [11]. To enhance the modulation bandwidth, photonic crystal waveguides based on BTO thin films have been proposed. In this investigation, a 1D photonic crystal Bragg reflector waveguide based on BTO platform was designed, fabricated and tested. The Bragg grating functions as a reflector for a specific wavelength, which satisfies the Bragg condition. By implementing a Bragg grating structure, the EO modulatorís driving voltage can be potentially lowered by an order of magnitude compared to that of a polarization intensity waveguide modulator since fo
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