Digital optical switch using an electro-optic polymer

Abstract

Digital optical switch(DOS) is a promising guided-wave switching device due to the following advantages. They are polarization-independent and wavelength-insensitive operation, digital switching characteristics, and relaxed fabrication tolerance. In this thesis, several types of DOS``s using an electro-optic(EO) polymer are proposed and fabricated. The proposed devices are designed by empolying the finite difference beam propagation method(FD-BPM) combined with the effective index method. Two fabrication methods, photobleaching(PB) and reactive ion etching(RIE), are utilized to fabricate the polymeric waveguides. The propagation characteristics of the waveguides are investigated for various fabrication parameters including the PB time, the ething depth, and the poling voltage. First, a wavelength-insensitive and polarization-dependent DOS with photobleached waveguides and a self-aligned electrode is designed and fabricated. To improve its switching performance that is determined by the mode coupling behavior in the branch, the guided mode profiles of photobleached waveguides are controlled by the PB time. The self-aligned electrode is employed to achieve an efficient overlap between the optical and the electric fields and to smoothly introduce the tapered electrodes. The measured crosstalk is better than -21dB at 1.32㎛ and 1.55㎛, and the extinction ratio of each output port is greater than 20 dB. Second, an EO polymer DOS with rib waveguides is designed and fabricated by using the RIE method. Polarization-independent and wavelength-insensitive operation is demonstrated at the wavelengths of 1.3㎛ and 1.55㎛, for the first time in EO polymer-based devices. The rib waveguides have been designed to achieve good guiding properties for both TE and TM polarizations, by controlling the etching depth as well as its aspect ratio. Especially the etching depth is controlled to change the guided mode profiles of the rib waveguide and thus to achieve an optimum coupling in ...