Low power polymeric thermo-optic digital optical switch

Abstract

Optical switches are essential components in optical network. In order to improve the performance of optical network, the optical switch must address requirements, such as low crosstalk, high extinction ratio, low insertion loss, low power consumption, very fast switching time and insensitive to wavelength and polarization. Digital optical switch (DOS) has become a very attractive component for space switching in multi-wavelength optical communication system application due to its sensitivity for drive power fluctuations, polarization, wavelength, temperature and device geometrical variations. This thesis explores the design of new DOS in order to improve its performance especially in terms of crosstalk and power consumption. Polymeric thermo-optic effect DOS has been developed due to its high thermo-optic coefficient which can support low power consumption devices. Buried square core waveguide is used in this research due to its low fiber to chip coupling loss. In order to ensure the waveguide operates as a single-mode waveguide in the optical communication transmission window, the optimization was done using alternating direction implicit method, finite difference method (FDM) and effective index method. The simulation and optimization of the Y-branch shape are done using finite difference beam propagation method whereas the heater design was optimized by employing FDM to solve the steady state heat transfer equation and scalar Helmholtz equation. The Y-branch shape is a hybrid of modified cosine Sbend branch and linear branch. Effective waveguide heating has been done by using a parabolic heater. With branching angle of 0.299 o and device length of only 5 mm, the simulation shows that the device could exhibit crosstalk of -33 dB at heating power of only 26 mW. In order to further reduce the crosstalk, a variable optical attenuator (VOA) has been designed to be connected to the DOS. The VOA is constructed from cosine S-bend which has low loss (< 0.2 dB) at off state, thus it is suitable to be used in optical switch. The VOA design uses the same material as that of the DOS which is the photo-active ultra violet curable fluorinated resins based on acrylate in order to ensure compatibility. The thermo-optic coefficient of the material is -1.7 ×10 -4 / o C and thermal conductivity is 0.17 W/m o C. The optimized DOS without VOA was fabricated. The crosstalk of -26 dB is achieved at electrical power of 32 mW, and the insertion loss is less than -2.5 dB. In terms of wavelength dependency, the device shows a good performance inside the C-band with fluctuation of the insertion loss value around 0.5 dB.