The Research Of Polymeric MZI Planar Optical Waveguide Devices And Integrated Technology

With the development of microelectronics, optoelectronics and microfabricationtechnology, in the research area of optical communication and biosensing, PhotonicIntegrated Circuit (PIC) is the development trend of planar optical waveguide.Because the polymer material can be processed by molecular engineering, it cansatisfy the requirements of preparation of high-performance optoelectronic integrateddevice. What’s more, the polymer material has a wide variety, simple process, lowcost and strong ability of anti-electromagnetic interference, etc, which make themtake an important position in the fabrication and research of planar optical waveguideand integrated devices.Mach-Zehnder interferometer (MZI) type waveguide structure is one of the mostbasic, but also indispensable waveguide structure in the integrated optical devices. Inthis thesis, a series of research work about the design and fabrication of MZI typewaveguide devices and integrated technology by using polymer material has beendemonstrated. The main contents and innovation points of the work are as follows:1. Combing the electro-optical (EO) effect and thermo-optic (TO) effect, theworking principle of MZI waveguide was analyzed. And based on the opticalwaveguide theory, by using effective index method, the mode characteristics of thethree layer planar waveguide, rectangle waveguide, ridge waveguide and strip-loadedwaveguide were analyzed, which laid a theoretical foundation for the design andpreparation of the following devices. At the same time, experimental materials andapparatus were introduced in this paper.2. Two kinds of doped EO polymer materials with good polarization stabilitywere synthesized, and the EO modulators based on MZI structure were designed andfabricated by using these materials. First of all, the hybrid organic/inorganic EOmaterial Disperse Red1(DR1)/TiO2-SiO2was synthesized by using sol-gel method,and the poled polymer film was fabricated by the spin-coating process and the coronapoling technique. The characteristics of the film, such as the refractive index andthickness, the chromophores molecular orientation before and after poling, and thesurface morphology, were characterized in detail by using spectroscopic ellipsometry,ultraviolet-visible spectrum analyzer, atomic force microscope(AFM), respectively. The EO coefficient and polarization stability of the film have been characterized byusing the reflection method. The EO coefficient of20pm/V and the polarizationstability of only10%attenuation in2000hours were obtained. Because the EO filmwas too thin, the strip-loaded EO modulator was designed and fabricated. In thefabrication process, the ICP etching technology and UV-bleaching technology wereintroduced to optimize the performance of the devices. The modulation efficiency wasimproved by about40%. The guest-host EO material DR1/PC was also synthesizedfor EO modulator. And the three layer planar waveguide was prepared with NOA73asthe under/upper cladding, DR1/PC as the core material. The EO properties of singlelayer and triple layer were characterized by using the reflection method. The resultsproved that the material had good polarization stability and good physical andchemical compatibility with NOA73material. Finally, a kind of inverted-rib EOmodulator based DR1/PC polymer was fabricated, and the response signal at10KHzwas observed.3. The polymeric MZI type optical switch based on EO effect and its integratedtechnology were studied. A SU-8-based inverted-rib EO switch with good groovewaveguide and sidewall topography was prepared by using all-wet etching technology.The design of inverted-rib waveguide structure effectively reduced the coupling lossand transmission loss. The rise and fall time of the switch is322ns and294ns,respectively. In order to prepare a monolithic multifunctional and high-speedintegrated chip, a kind of passive-active integrated EO waveguide was designed basedon the photosensitive property of SU-8material. At the same time, the MSL electrodewas introducd. These design made the insertion loss of the device reduce by2.8dBand the switch speed increase50%. An EO switch based on the cladding modulationwas designed and fabricated with DR1/PMMA as the cladding and SU-8as the corelayer. The optical field was simulated and optimized through the COMSOL software,and combining with the molecular engineering, the refraction index of the materialand waveguide size were optimized. Finally, the EO switch based on the claddingmodulation was prepared. The switching time of the device is about100ns level, andthe insertion loss is about12.6dB.4. The polymeric MZI type optical switch based on TO effect and its integratedtechnology were studied. First of all, the effect of hard-baking temperature on SU-8film with or without UV exposure were studied in detail. And a kind of thermalUV-bleaching technique for polymer waveguide fabrication was proposed. Thistechnology greatly reduces the experimental steps and the cost. The refractive index, characteristic absorption peak, surface morphology and the hydrophilic/hydrophobicproperties of the film were characterized by using spectroscopic ellipsometry, fouriertransform infrared spectrometer, optical microscope, AFM and contact angle tester,respectively. And the chemical mechanism of the refractive index changing wereanalyzed. Then a1×1MZI type TO switch was fabricated based on the thermal UV-bleaching technology, and the rise and fall time of the switch is149μs and139μs,respectively. According to the hydrophilic/hydrophobic properties of the exposure andunexposure area on the film, the integration feasibility of this structure with themicrofluidic channel for the biosensing application was analyzed. Secondly, a kind of1×2TO switch based on PMMA material operating650nm wavelength was designedand fabricated. The rise and fall time of the switch is464μs and448μs, respectively,and the driving power consumption is about4.6mW. This kind of TO switch can beused in visible light communication system because the PMMA material has arelatively low absorption loss in650nm wavelength resign. At the same time, anintegrated chip with this structural TO switch and waveguide delay line was designedand simulated. Finally, a polymer/SiO21×1MZI TO switch was fabricated, and thecross section of the waveguide was polished. At the same time, the optical andelectronic packaging of the TO switch were finished, which laid a foundation for thepractical application of the polymer TO switch device.5. The optofluidic technology was studied by combining the microfluidic andoptical technology organically which with the polymer waveguides as the medium.Firstly, a kind of biosensing chip with liquid as the cladding materail of the MZIwaveguide was designed. By optimizing the etching process, the sensing window withlarger contact area was fabricated according to the different etching rate betweenSU-8and PMMA material. With this method, the detection sensitivity of the chip wasenhanced by a factor of2.8. Secondly, in order to make the chip adapt therequirements of the biological, electrochemical and enzyme engineering, a compactoptofluidic chip was designed by integrating optical testing and microfluidic channel.At the same time, the thermal field and electric field was introduced into theoptofluidic chip to achieve dynamic control on-chip, and then realize a kind ofelectro-optofluidic technology. Finally, a kind of all-polymer electro-optofluidic chipwas fabricated by using standard semiconductor technology.In this thesis, based on EO effect, TO effect and microfluidics, a series of workhave been research by using polymer material, which were mainly about MZI typeplanar waveguide devices and integrated technology. Taking account of the excellent characteristics of polymer materials, such as materials variety, easy machining andcutting, and combining the microfluidic technology and optical technology, it isexpected to integrate optical components, such as lasers, optical waveguide,modulator, switches and sensors, and microfluidic channel into a chip. Then a Lab ona chip (LoC) system can be constituted, which lays a foundation for the preparation ofthe integrated chip applied in optical communication systems and sensor system.