Basic Research On Electro-Optic Switch Based On Poled Polymer DR1/SU-8

Recently, with the development of large capacity optical fiber communication systems, optical network has become the first choice of next generation high speed broadband network for its large capacity, good transparency, wavelength routing features, compatibility and scalability. Optical fiber communication devices have been used widely as well. The array of optical switch is one of the key devices of optical multiplexing and optical cross connect. Its performance is the key to decide the node performance and network performance. The materials commonly used in the fabrication of optical switches are semiconductor materials, LiNbO3 and polymer materials. We notice that in the materials above, the polymer material has aroused wide attention and covered almost all aspects of integrated optics because of its simple processing technology, low price, easy integration, and small applied voltage. The polymer optoelectronic devices have become the research hotpot in recent years. Therefore, polymer EO switch has wide range research and application value.Firstly,the concept, classification and application of optical switch were introduced in this thesis. The character, research significance and progress were described in domestic and abroad of polymer electro optic switch, then basic research focused on a kind of cross linked polymer electro optic material DR1/SU-8 and the application of DR1/SU-8 in polymer electro optic switch were carried out. The main work was focused on the following three aspects:1,Independently synthesized a kind of cross linked poled polymer material DR1/SU-8 which could be used for the preparation of electro optic switch. The material performances were studied more systematically for the first time. SU-8 is negative, epoxy resin based UV photoresist, which is widely used in the field of micro machining and also applied to the fabrication of polymer optical waveguide in recent years. There are many advantages of SU-8 such as simple processing technology, smooth lateral wall of lithography pattern, low absorption near UV band, good self smooth ability and good thermal stability. In order to make the material show the second order nonlinear optical effects to be applied on the electro optic switch, we doped small organic molecules chromophore DR1 into the mixed solution of SU-8 and SU-8 dilution, forming homogeneous blend system DR1/SU-8. The polymer film formed by this doping system is different from that formed by the conventional guest host doped polymer. As the bulk material SU-8 was cross linked after exposure and post exposure bake, the orientation polarization of DR1 molecular was "frozen" in the cross linked network, forming a cross link poled polymer. The electro optic coefficient and polarization stability of cross linked material were larger than that of non cross linked doped polymer, and the performances of the electro optic switch prepared by cross linked polymer were better than that prepared by doped polymer.It is the foundation for waveguide design and fabrication that accurate measuring the refractive index and film thickness of polymer materials used for waveguide. The refractive indexes of SU-8 and DR1/SU-8 under different exposure time were measured by large number of experiments, and the relationship of refractive index changing with the exposure time was got. That is, when the exposure time increased, the refractive index decreases, until the exposure time was above 5min. The relationship lays the foundation for the design of single mode waveguide. I analyzed the UV visible near infrared absorption spectra of DR1/SU-8 and found that in optical communication window department 1310nm and 1550nm, the absorption coefficient were lower. Because of this, the absorption loss brought with the material would be smaller when the material was used for preparation of waveguide. By analyzing the TG curves of DR1/SU-8 before and after cross linking, it was indicated that the initial thermal decomposition temperature of post crosslink DR1/SU-8 was 217.8℃, and the temperature of 5% weight loss was 297.9℃, which were both higher than that of before cross linking. This material had good thermal stability, which could stand a higher temperature. By measuring electro optic coefficients of DR1/SU-8 before and after cross linking, we found that the EO coefficients after cross linking were significantly higher than that of non cross linking. And the polarization stability was also improved.2,Two types of electro optic switch waveguides using DR1/SU-8 as the electro optic material was fabricated: the rectangle waveguide and the inverted ridge waveguide. Then, theoretical analysis and experimental fabrication of these two types of waveguides were respectively made.The single mode conditions of four types of rectangle waveguides was respectively calculated which used PMMA(polymethyl methacrylate),SU-8,BCB (benzocyclobutene),CYTOP (cyclized transparent optical polymer) as cladding. The rectangle waveguide with DR1/SU-8 as the core material was fabricated using reactive ion etching for the first time. In the beginning, a lot of experimental exploration focusing on some key processes such as lithography and etching had to be done. At last, the problem of photoresist folding was solved, which made me can not get neat edge graphics, by sputtering SiO2. We successfully fabricated the rectangle waveguide with SU-8 as cladding, and DR1/SU-8 as core material, and got the near field output beam of straight and MZ waveguides. But, because of large power in reactive ion etching, the scattering loss was large. The input optical power reached to 4.6mw.Therefore, we fabricated another type of electro optic switch waveguide, the inverted ridge waveguide. First, 5 m grooves with mask in combination with UV light exposure was fabricated using SU-8 as under cladding. Then, DR1/SU-8 material was filled in the SU-8 grooves. After being sputtered SiO2, at last, PMMA was coated as cladding. The performance of straight ridge waveguide, Y branch, 1×4 waveguide branch, 1×8 waveguide branch and MZ waveguide were better than that of rectangle. When the input optical power reached to 0.05mw, the near field output beam could be seen. 3,The complete polymer electro optic switch based on poled polymer DR1/SU-8 was fabricated for the first time.Aluminum electrode was loaded on the ridge waveguide which transmission loss was smaller. When the polymer electro optic switch using DR1/SU-8 as electro optic material was used for modulation, the frequency of ac signal can reach to 100 kHz, and the frequency of square signal can reach to 1 kHz.In this thesis, we did basic research focusing on cross linked polymer poled material DR1/SU-8 and its application in electro optic switch, and finally successfully fabricated inverted ridge waveguide electro optic switch. This work laid a foundation for fabricating electro optic switch of high performance which used this material.