Research On Polymer/Si Waveguide Thermo-Optic Switch And Integrated Technology

In recent years,with the rapid development of Internet business and information technology,optical fiber communication has become one of the cornerstones supporting our rapid development of information-driven society,and people's dependence on information has become higher and higher.Some emerging business such as Internet of Things,big data and cloud computing also put forward higher requirements for optical communication systems.Optical switches and optical switch arrays are the important devices for constructing the optical communication networks.Whether in visible light communication systems or in the mode division multiplexing(MDM)systems used to improve communication capacity,complex network topology requires reliable and flexible network management.Optical switches and optical switch arrays play the functions of optical domain optimization,routing,protection and self-healing in optical networks.Therefore,it is very important to develop optical switching devices with low power consumption,high integration,good stability and simple fabrication process.Waveguide-based optical switch is the most widely used in optical communication network at present,which has the advantages of simple structure and good long-term stability.At present,the materials used to fabricate waveguide-based optical switches are mainly divided into inorganic materials and organic polymer materials.Compared with inorganic materials,organic polymer materials have the advantages of wide variety,simple fabrication process,low cost,adjustable refractive index,easy three-dimensional integration,and high thermo-optic coefficient and electro-optic coefficient.It is of great significance to explore and study thermo-optic switches with high performance,low power-consumption,miniaturization and integration by using organic polymer materials.What's more,it has broad application prospects in the realization of all-optical communication networks and on-chip optical interconnect technology.This paper is based on organic polymer materials to study the thermo-optic switches by using the thermo-optic effect of materials and combining with the hybrid integration of organic/inorganic materials.With the aim of reducing the power consumption of devices and improving the transmission capacity of optical communication systems,the low-power-consumption thermo-optic switch based on triangular waveguide at 532 nm for visible light communication system,mode-insensitive thermo-optic switch and polymer/SiO₂hybrid three-dimensional integrated waveguide thermo-optic mode switch for MDM system are designed respectively.The main contents are as follows:1.The optical waveguide mode theory and coupled mode theory are analyzed,and the mode characteristics of three-layer planar waveguide and the rectangular waveguide are also analyzed by using the effective refractive index method.Based on these theories,combined with thermal field and thermo-optic modulation theory,the working principle of the thermo-optic switch based on Mach-Zehnder Interferometer(MZI)and directional coupler structure studied in this paper are analyzed,which lays a theoretical foundation for the subsequent structure design,simulation and optimization and fabrication of the devices.2.A low-power-consumption polymer MZI thermo-optic switch operating at the wavelength of 532 nm is proposed.The polymer/SiO₂hybrid integrated waveguide is introduced to improve the performances of the device.At the same time,a triangular waveguide is adopted to replace the traditional rectangular waveguide,thereby achieving a further reduction in power consumption.Compared with the rectangular waveguide,the triangular waveguide can easily achieve single-mode transmission in a large-dimension waveguide.In addition,due to the upward squeezing effect of the two oblique sides of the triangular waveguide on the optical field,the change of the effective index caused by the thermal field generated by the heating electrode is larger than that of the switch with rectangular waveguide.It is further confirmed that the electrode located directly above the triangular waveguide has higher heating efficiency under the same conditions,resulting in a lower driving power of the device.The triangular waveguide is fabricated by thermal photobleaching and spaced exposure,which reduces the transmission loss of the device and simplifies the fabrication process.Compared with the thermo-optic switch with the traditional rectangular waveguide,the driving power of the proposed polymer MZI thermo-optic switch based on triangular waveguide is reduced by 3.3 m W.The power consumption of the device is 2.2 m W,and the rise/fall time of the switch is of110/130?s.3.A polymer waveguide MZI mode-insensitive thermo-optic switch based on directional coupler is proposed.Mode-insensitive power splitter is the premise and basis for realizing the mode-insensitive switch.However,the Y-branch in the traditional MZI waveguide structure is usually mode sensitive.Therefore,a few-mode waveguide power splitter based on the directional coupler is firstly proposed and demonstrated.By optimizing the coupling gap and coupling length of the symmetric directional coupler,a dual-mode waveguide power splitter that supports both LP₀₁and LP_11amodes and a three-mode waveguide power splitter that supports LP₀₁,LP_11aand LP_11bmodes are designed,respectively.The two devices are verified experimentally by using polymer materials Epo Core and Epo Clad,which are sensitive to ultraviolet light and have a good thermal and optical stability.At 1550 nm,the splitting ratio of each mode in the two proposed few-mode waveguide power splitters is about 0.5:0.5.Based on above design,a polymer waveguide MZI mode-insensitive thermo-optic switch based on directional coupler is proposed and experimentally demonstrated by using polymer materials.By introducing mode-insensitive phase shifters into two interference arms of MZI,the insensitive transmission and control of LP₀₁and LP_11amodes can be realized.With the driving power applied to one of the heating electrodes,the two modes can be simultaneously switched between Core 1 and Core 2.The total length of the fabricated device is 30 mm and the driving power is 9.0 m W.Within the C-band,the extinction ratios of the device are higher than 17.2 d B and16.2 d B for LP₀₁and LP_11amodes,respectively,and reach 17.5 d B and 16.4 d B at1550 nm.The switching time of the device is?1.30 ms.4.A polymer/SiO₂hybrid waveguide thermo-optic mode switch based on asymmetric directional coupler is proposed.The monolayer graphene is buried in the polymer waveguide as a heating electrode to improve the heating efficiency of the device,so as to reduce the power consumption of the device.The loss characteristics of graphene film in the polymer waveguide are analyzed by using the interface model theory and a ultra-broadband TM-pass polarizer based on graphene-buried polymer waveguide is proposed.The influence of the buried position of graphene film and the dimension of waveguide core layer on the device performance is studied in detail.The mode loss and wavelength-dependent characteristics of the device under TE and TM polarization are simulated and calculated.Taking advantage of the simple and flexible processing technology of polymer materials,two polarizers are fabricated with the graphene film buried on the surface and in the center of the waveguide core,respectively.Theoretical and experimental results show that these two polarizers have low loss under TM polarization,and the extinction ratios in the bandwidth range of110 nm are higher than 22.9 d B and 41.9 d B respectively.Furthermore,a polymer/SiO₂hybrid waveguide thermo-optic mode switch based on asymmetric directional coupling structure is proposed,and the monolayer graphene is integrated into the polymer optical waveguide as a heating electrode.The device is based on the polymer/SiO₂3D hybrid integrated waveguide structure,which combines the advantages of high thermal conductivity of SiO₂and high thermo-optic coefficient of polymer materials.This structure not only significantly improves the performance of thermo-optic mode switch,but also solves the difficulty of 3D integration of SiO₂waveguide.The theoretical results show that the coupling efficiencies of LP₀₁-LP_11aand LP₀₁-LP_11bmodes in C-band are higher than 93.4%and 92.8%,respectively,and the extinction ratio is higher than?28 d B.Compared with traditional switch with metal electrode,the power consumption is reduced by?30%,and the response speed is also significantly improved.