Micro-Molded High Q Polymer Resonators for Optical Loss Determination
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Micro-Molded High Q Polymer Resonators for Optical Loss Determination Andrea L. Martin, Akil Srinivasan, Deniz K. Armani, Bumki Min, and Kerry J. Vahala Department of Applied Physics, California Institute of Technology, 1200 E California Blvd, M/C 128-95 Pasadena, CA 91125, U. S. A. ABSTRACT Replica molding of ultra-high-Q toroidal microresonators can produce polymer microresonators with material-limited quality factors (Q). This was demonstrated previously using polymers which cure thermally. In this work, high Q polymer microresonators were fabricated using the replica molding technique from previously uncharacterized polymers which require either a thermal or UV cure. The quality factor and effective refractive index of whispering gallery modes was measured at wavelengths ranging from the visible (680nm) through the near-IR (1550nm). The optical absorption coefficient (material absorption) of these previously uncharacterized polymers was determined from the quality factor and effective refractive index of the polymer. INTRODUCTION Low optical loss polymers have recently demonstrated a wide range of applications in telecommunications, finding use in structures such as optical resonators and single mode waveguides [1,2]. An important property of an optical polymer is material or optical loss. A common method used to characterize optical loss is through waveguiding within thin films of the polymers. Alternatively, by fabricating the polymer into a microresonator, the optical loss can also be determined because the quality factor (Q) of the resonator is directly related to optical loss. This latter technique, however, requires resonators that have exceptionally low scattering loss so that Q factor is determined by material loss. Recently, a micro-molding-based method of fabricating nearly absorption-limited polymer microresonators was demonstrated using thermally cured polymers [3]. Because the silicone molding material accurately replicates a silica ultra-high-Q microtoroid with an extremely smooth surface, the periphery of the polymer resonator is also extremely smooth endowing the resonator with very low scattering loss. While in the previous work, this method was applied only to polymers that cure thermally, it can also be applied to other classes of polymers, such as epoxy resins which cure upon exposure to UV light. This is because, in addition to the flexibility of silicone, it is also fairly transparent in the UV range, allowing the epoxy resin to cure. In the present work, replica molding was applied to two polymers, Crystal Cast 9024 (Industrial Polymers) and Efiron WR-509 (Luvantix). These polymers represent two distinct classes of polymers that cure by either thermal (Crystal Cast) or ultra-violet (Efiron) exposure. Luvantix developed the Efiron WR line as a material for molding optical waveguides in the nearIR wavelength regime. However, WR-509 was never fully characterized by Luvantix. Crystal Cast is currently used to make artificial glass-looking vases and water. Since Crystal Cast appears cle
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