The Research Of Fabrication Technology Based On Polymer Electro-optic Switch

In today's society, optical communication networks occupies the dominant position of the field of communications. The optical switching devices are key components of optical communications networks, which are also the research focus of the communications field in recent years. Optical switch can achieve optical beam in time, space and wavelength. Switches have many applications in optical networks, such as optical switches used in optical cross-connect (OXC), optical add-drop multiplexing (OADM), optical fiber communications device testing, automatic protection switching, optical network monitoring and so on. High-speed and high-performance optical switches play a decisive role for raising the speed of optical communication networks.Optical Switch is divided into mechanical and non-mechanical optical switch. The MEMS optical switch in mechanical light switches is the mainstream programs to solve today's network problems. Non-mechanical optical switches have many types, including those based on thermo-optic, electro-optic, acousto-optic, magneto-optical effect and some other new switching. electro-optical switches become the research hot with a non-centro-symmetric structure of chromophore molecular because of its fast response.Electro-optic effect theory is the basis of electro-optic switching theory. We can find the relationship between the refractive index of electro-optic materials and the external electric field. Electro-optic switch structure types are divided into Mach - Zehnder (MZ) interferometer, directional coupler, multimode interference (MMI) type and digital type. We use the structure of the MZ interferometer. Electrode system is fabricated on the waveguide to form electro-optical switch. The electrode system includes input and output areas, transition zones and interaction zones. Interaction zones include coplanar waveguide (CPW) type and micro-strip line (MSL) type. We use CPW-based interaction zone because CPW electrode can be designed to push-pull structure.The performances of electro-optical switch include optical and electrical parameters. Optical parameters are insertion loss, return loss, isolation, crosstalk, extinction ratio, switching time and so on. Electrical parameters are switching voltage, characteristic impedance, modulation bandwidth, loss factor, driving power and so on. Among them, we need to consider insertion loss, extinction ratio, switching time, switching voltage as the important parameters. These parameters relates to whether the electro-optic switch can be practical.Electro-optical material is divided into inorganic materials, semiconductor materials and poled polymer materials. The studies of electro-optic switches which are made by inorganic materials and semiconductor materials have been more mature to meet the business needs. But the poled polymer electro-optic switches have large electro-optic coefficient, simple process, many kinds of optional materials, fast response, etc, which become the research hot spots. Most polymer materials are amorphous, and have central symmetry, while the electro-optic effect (for the second-order nonlinear effect) exists in the material with a non-centro-symmetric. In order to make polymers with second-order non-linear, we dope a non-centro-symmetric structure of chromophore into polymer. With an electrostatic field, the intramolecular charges of the chromophore molecules begin to move , which make a change in dipole moment, resulting in second-order nonlinear effect.By combination of the different ways between chromophore molecules and polymers, electro-optic polymer materials can be divided into host/guest doping type, side-chain type, main-chain type and cross-linking and so on. The coefficients of Subject-object-type material can not be large, and the stability is not very good. The stability of the side-chain bonding type is well, and the electro-optic coefficient is relatively high. The poling of the main-chain boning type is more difficult, and the solubility is not very good. Cross-linking has higher stability than the side-chain boning type. The light transmitting through material is not very good and electro-optic coefficient is also somewhat reduced. This article made a host/guest doping polymer material DR1/SU-8 and side-chain bonding hybrid materials DR19ASD. The absorption spectrum of the material, refractive index, film flatness and other parameters were measured. By adjusting the material doping ratio, we made the materials fit to the electro-optic switch.The next task is to fabricate the electro-optic switches based on DR1/SU-8 and DR19ASD side-chain bonding hybrid materials. First, the cross-section of the waveguide structure is discussed to find the most suitable for the corresponding material. DR1/SU-8 material can not carry out wet etching. In order to achieve a good waveguide morphology, we make SU-8 groove, and then spin DR1/SU-8 materials, followed by reactive ion etching to remove the flat above in order to achieve a good pass-light results. Finally the inverted ridge waveguide structure is fabricated. For the side-chain bond DR19ASD hybrid material, we can not make a waveguide morphology by wet or dry etching method because its rigid is strong. We adopt the structure of load bar to achieve pass-light results.We fabricate M-Z waveguide based on DR1/SU-8 and DR19ASD side-chain bonding hybrid materials. Good pass-light results are achieved. Followed by aluminum vacuum evaporation, photolithography and other steps, we fabricate coplanar waveguide (CPW) traveling-wave aluminum electrodes on the waveguide. the material has electro-optic effect through linear electrode corona polarization using the polarization equipment . The hole progress is completed.Finally, modulation and switching response of the device is tested. For the DR1/SU-8 switch, the responses under the 100kHz input modulation signal and 10kHz input switch signal have been obtained. The switching speed reach to 6μs.We need further optimize to obtain a higher switching speed. For the electro-optical switch of side-chain bonding DR19ASD hybrid material, the modulation effect of the PMMA loaded strip is slightly better, which can obtain stable modulation output under 10kHz input signal and modulation phenomenon with instability wave under 50kHz. SU-8 loaded strip modulation device has worse modulation phenomenon, only response to 1kHz.Although the performance of the electro-optical switches which we fabricate has a large gap compared to the international advanced level, the electro-optic materials are our synthesis, which has shorter synthetic cycle and lower cost. For the performance of the device, we can further optimize to improve it. The materials' application prospect is very broad.