Fabrication and Replication of Polymer Integrated Optical Devices Using Electron-Beam Lithography and Soft Lithography ² Yanyi Huang,* George T. Paloczi, and Amnon Yariv Department of Applied Physics, California Institute of Technology, Pasadena, California 91125 Cheng Zhang Pacific WaVe Industries Ltd., 129 Sheldon Street, El Segundo, California 90245 Larry R. Dalton Department of Chemistry, UniVersity of Washington, Seattle, Washington 98195 ReceiVed: January 19, 2004 Polymeric integrated optical devices, including microring resonator optical filters and Mach-Zehnder interferometer modulators, fabricated by electron-beam lithography and soft lithography are considered in this article. Microring resonator optical filters made of SU-8 (MicroChem, Newton, MA), directly patterned by electron-beam lithography, demonstrate that SU-8 is a good candidate for high-precision, easily fabricated, and good-optical-quality passive integrated optical devices. Due to the electron-beam lithography process, the coupling between the straight waveguide and the microring resonator is precisely controlled, and the critical coupling condition can be achieved. Additionally, films containing several devices patterned by electron- beam lithography are peeled from the silicon substrate, yielding ultrathin all-polymer flexible free-standing microring resonator optical filters exhibiting up to -27 dB filtering extinction. Using a PDMS stamp, molded from these electron-beam-patterned microring resonator optical filters, identical replicas are fabricated by the soft lithography molding technique. Soft lithography is also applied to active polymer materials. A short 2-mm active-section prototype Mach-Zehnder interferometer modulator is made by the replica molding process, using CLD-1/APC electrooptic polymer as the core material. A reasonable intensity-modulation effect is observed by applying voltage to one arm of the interferometer. 1. Introduction In the fields of high-speed telecommunication, optical signal processing, optical computing, and networking, planar integrated optical devices are the key functional devices to carry and manipulate signals. At present, semiconductor, glass-based materials and some inorganic crystals serve as both passive and active materials for making modern integrated optical devices. Polymers have become one of the most promising candidates for new materials with excellent optical performance and functionality. 1-3 Compared with other materials, polymeric materials have several advantages. First, the properties of polymers can be widely tuned by chemically modifying the structure of the monomer, the functional groups or chromo- phores, or the polymer backbones. Second, polymeric materials can be easily manipulated by several conventional or uncon- ventional fabrication techniques such as dry etching, 4 wet etching, 5 embossing, 6 and soft lithography. 7 Third, compared to fragile glass fiber and expensive semiconductor chips, polymeric materials provide for easy, low-cost, and reliable fabrication of optical devices. Fourth, functional polymeric materials also provide an excellent platform for integrating several diversified materials with different functions. Low- optical-loss polymer materials for waveguiding have been studied for more than two decades, and some have been commercialized. Furthermore, several classes of active materials, such as laser-emissive and electrooptical materials, 8 can be either made as polymer or doped within the polymer matrix to become a guest-host polymer system. Electron-beam lithography has been applied as one of the most effective methods for modern micro- and nano-fabrication. Electron-beam lithography utilizes the effect that some materials will undergo chemical changes when exposed to a beam of energetic electrons. This method has been used to fabricate high- precision optical waveguide devices, which are impossible to make by photolithographic techniques. 9 These structures typi- cally have cross-section dimensions on the order of micrometers and minimum features on the nanometer scale. An advantage of this technique is that the waveguiding core structures are directly patterned by the electron-beam. Alternatively, soft lithography, which utilizes a master device to generate several soft molds each used to reproduce identical replicas, has been extensively developed during the past 10 years and has shown promise for improving optical waveguide manufacturing through- put. 10 This simple method has been applied in a number of fields to transfer and reproduce micro- or nanometer patterns and features. The limiting feature size can be on the order of 1 nm, 11 indicating that soft lithography is a competitive technique for producing high-quality polymer integrated optical devices. We demonstrate two types of important integrated optical components in this report: microring resonators and Mach- ² Part of the special issue “Alvin L. Kwiram Festschrift”. * To whom correspondence should be addressed. E-mail: yanyi@caltech.edu. 8606 J. Phys. Chem. B 2004, 108, 8606-8613 10.1021/jp049724d CCC: $27.50 © 2004 American Chemical Society Published on Web 05/01/2004