Investigation On Polymeric Electro-and Thermo-Optical Hybrid Integrated Optical Switch

With the publication of national broadband strategy, the development of opticalcommunication in China enters a new era. Therefore, the whole industry chain ofoptical communication is being promoted from the fiber optic cable manufacturers,optical module suppliers to system integrators. And the year of2012will alsobecome the first year of commercial100G optical communication application. Thereare keen competitions in the domestic optical module market of2.5G products.Limited by the chip costs,10G,40G,100G optical module products are limited bythe expensive chip price. In such a circumstance, study on high speed optical switchis in line with the national strategic deployment and it has an important practicalsignificance.Optical switch is the core device of the optical communication network, and themajority of commercial optical switch still bases on inorganic materials. Thepolarized polymer material theoretical bandwidth is up to100G or more. There is asignificant difference between polymeric materials and inorganic materials. Fullusing of the properties of polymeric material may be complementing the deficienciesin the inorganic materials. Based on all the points above, low cost and high speedpolymer optical switching devices are studied in the following four aspects: materialproperties, device structure, processing and device characterization.(1) Characterization of high cost performance material propertiesDispersed Red1(DR1) doped poly(methyl methacrylate)(PMMA) and PMMAare selected as the core and cladding materials respectively.First, the ellipsometry experimental result shows that the index of material is1.507(@1550nm). Second, the TGA test result indicates that the temperature with5%weight lossof DR1/PMMA is over200℃. This result shows that the DR1/PMMA has a goodthermal stability. The glass transition temperature of DR1/PMMA is102.6℃tested by DSC method. Based on these two results, the poling temperature is chosenas110℃.(2) Design of hybrid integrated optical switchFirst, theory of optical switches is demonstrated. Because of the polymer has abig thermo-optical coefficient and a good thermo collection ability, a thermo-andelectro-hybrid integrated optical switching device with Mach–Zehnder structure isproposed. And in this structure, there is a thermo-optical bias which is designed toadjust device working point. And it guarantees that this optical switch is a currentdrive device and its driving voltage can stay in a low level.Second, the waveguide properties are analyzed by the Effective Index Method(EIM). For different lower-cladding materials, the power confined factor iscomputed. The power confined factor of the waveguide with SiO2lower claddingis3.18%bigger than the one with PMMA lower cladding. Optical field propagationprogress under different biases is analyzed by the Beam Propagation Method.(3) Design and set-up of special fabrication instrumentsAt the device fabrication aspect, non-linear polymer poling system and thereflection method electro-optical (EO) coefficient characterization system aredesigned and set up.Design a new type non-linear polymer poling system.The polymer film is fabricated by the method of spin-coat. After the process ofmetal evaporation, lithograph, wet etch, dry etch etc. the device containingwaveguide and electrode is obtained. The non-linear polymers do not have the EOcoefficient. There is a process called poling which is demonstrated by the followingstatements: rising the device temperature a little higher than the glass transitiontemperature of DR1/PMMA, applying a direct current electric field across the filmfor minutes, keeping this electric field, cooling the device. But there is not acommercial equipment to perform this process, so a PM-II is designed to polarize devices.Design and set up a new type programmable EO coefficient characterizationsystem.An EO coefficient test system is designed and set up to characterize the indexchanging ability of DR1/PMMA under the electric field. The experimental resultshows that the EO coefficient of DR1/PMMA is9.3pm/V.(4) Device performance characterizationComparing with the inorganic material device the polymeric one is softer. Themicrowave probe can induce permanent damage to device electrodes. For aboveconcern, a new test fixture is designed. This fixture can provide protection forelectrodes and ports of devices.The large signal test result shows that the rise time and the fall time of thedevice are12.5ns and10.0ns respectively. The thermo-optical spectrum test resultshows that the device extinction ratio is over21dB under the driving power of13mW.