| In Wavelength Division Multiplexing(WDM) optical communication networks, power equalization and adjustment between channels demand Variable Optical Attenuator(VOA) be capable of providing low power consumption, low insertion loss, polarization independence, integration compatibility and flatness in a wide wavelength range. Among the presented VOAs, thermo-optic type owns superior polarization dependence upon electro-optic one, and thermo-optic VOA can be driven with much lower power than Micro-electro-mechanic System(MEMS). Recently, polymeric waveguides became attractive due to its advanced characteristics. The article overviewed first of all the latest techniques realizing VOA, then briefly introduced several polymers used on optical communications. Furthermore, a few typical thermo-optic VOA designs were illustrated and compared.The article set up 2-dementional steady heat conduction model and equations based on buried channel waveguide, and solved the equations by separating variables method. Using MathCAD, 2-D temperature distribution and the influenced refractive index distribution by thermo-optic effect were plotted in waveguide section area. This equation solving method overcomes the shortcomings of simulation software on thermal field analysis, strongly complements the commonly used 1-D temperature distribution to analyze thermo-optic devices in literature. The results avoids complicated form of solutions provided by Fourier Transform method, and thereafter lend itself to analyze the influence of thermo-optic to attenuation characters and power consumption in waveguide.The article introduced a novel thermo-optic VOA based on organic polymer, which used a parabolic profile transition to connect single-mode waveguide and multi-mode waveguide. To illustrate the superiority of this type of transition, the author adapted the Local Normal Mode(LNM) based on couple-mode theory to explain the coupling between two lowest order modes along the transition. For the two important parameters, propagation constants difference between the two modes Apy and mode coupling coefficient Cy, which denoting power coupling between LNMs, the approximation expressions using structure parameters were worked out. Then the author compared three typical different transitions according to the demanding of power coupling, at last concluded that the parabolic-type transition can transport the light in shortest length with lowest loss. Besides this, a bypass multi-mode waveguide were used to improve attenuation efficiency and reduce power consumption. Based on buried channel structure, the simulation software BeamPROP?produced by Rsoft Corp shows some better results than the original device: attenuation range over 20 higher, insertion loss merely 1dB higher and the calculated power consumption is only 25mW. The crosstalk between arrayed VOAs wasalso considered, the best result is -50dB. Simulations shows that the wavelength dependence and polarization dependence are respectively 2dB and 0.2dB.Apart from these, the Mach-Zehnder type VOA was analyzed too. The author deduced directly the relation between attenuation and power consumption, which corrects the faults in literature, utilizing the relation between attenuation and temperature rise and the already presented temperature distribution. From these results, MZ-type VOA based on two 3dB directional couplers was studied further, the characters comparison between single and cascaded MZ-type VOA were given.The reflection leakage VOA don't depend on high temperature stability as MZ-type need, while the latter own much lower power consumption than the former. In a word, the two type of VOA both have valuable applicability and potential market.The author have done numerous processing to work out new processing such as polymer coating and cure and triple-layer-metal film vaporing. Other new processing, polymer ultra-violet(UV) cure and inductively-coupled plasma(ICP) etching were studied.At last, the author developed thermo-optic VOA sample chip in reverse ridge struc... |
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