The Basic Research On Polymer/Si Planar Optical Waveguide Devices

Human society is entering into an information age powered by rapidly evolving technologies in areas of microelectronics, optoelectronics, computing and communications. However, as the result of the rapid increase of information, continuous requests have been made for the increase of speed, the enlargement of capacity and the decrease of cost of communications, some traditional communication technologies and devices could not fulfill the demands of applications. Therefore, it is imperious demand to enlarge the speed and capacity for the current fiber network. In recent years, many research groups have been attracted in development of optical integrated devices system densely with the rising of optical network. In order to achieve new functions, optical waveguide can joint light-emitting device, optical receiver and modulator/switch and so on. It is the key component in optical integrated devices. At the same time, there are also structures of waveguide in insides of optical receiver, and optical modulator.The material which can be used for fabricating planar optical waveguide may choose the inorganic material such as silicon dioxide, LiNbO₃ and semiconductor, and also adopt organic/polymeric material. Recently, considerable attention and great efforts have been focused on the development of polymer optical waveguide devices, because of their excellent particular features, such as easy fabrication, low propagation loss, small birefringence, and easy control of the refractive index, which is on a good wicket compared to inorganic devices. The new technique will be well suited for fabricating optical integrated circuits (OICS). At present, many developed countries such as Japan, America and Germany have put abundant researchers and money into the study on those devices, and have made great progress. The fabrication of polymer optical waveguide may not need high temperature equipment, the optical waveguide devices with excellent performance can be fabricated by spun coating and RIE etching equipment. So the polymer optical waveguide material and devices with great predominance have been international forward hotspot. The research of polymer array waveguide grating (AWG), polymer waveguide delay line and polymer high-speed electro-optic (EO) modulators and switches have been taken more and more attention with exploring polymer integrated waveguide devices by many research groups. The low cost, high-powered polymer optical integrated waveguide devices in high-speed, great capability optical communication network, especially for the optical local area network, also imperious demand of city area and user network, possess wide market application foreground. The main work of this thesis focuses on the design, fabrication and testing of polymer array waveguide grating (AWG), polymer waveguide delay line and polymer high-speed electro-optic (EO) modulators and switches. The content and innovations of the thesis are listed as follows:1. The AWG consists of input/output channel waveguides, input/output concave slab waveguides composed of many channel waveguides with a constant path difference between adjacent waveguides. It can work as grating and complete the function of multiplexing and de-multiplexing for light with different wavelength. In this thesis, the configuration, principle, and key parameters are introduced. The characteristics of the polymeric SU-8 2005(MicroChem, MA, USA) are analyzed. By scanning electron microscope (SEM) and microscope photographs, the surface profiles show that the ridge wall is smooth and almost vertical. The characteristic can reduce the scattering loss greatly. The core size can be controlled well. The optimal parameters of single-mode polymeric 41-channel arrayed waveguide grating (AWG) multiplexer are analyzed and simulated by Matlab programming. The performances of the device are also simulated by Rsoft (BeamPROP AWG Utility) and Optiwave (BPM-WDM) software. The near-field guided-mode pattern of the 41 channel AWG device and propagation loss (2.03dB/cm) of optical waveguide by cut-method are measured. The 41 channel AWG device can achieve multiplex/de-multiplex functions well by polishing. By simulating performance parameters, the important parameters of the device can be obtained. The demand designed can be satisfied well, the rate of the finished product can be ensured, this technique is very suit for commercial application.2. Ultra long compact optical polymeric array waveguide true-time-delay line devices are demonstrated in the thesis. Cross-linkable poly-methyl-methacrylate–co-glyciclyl methacrylate P(MMA-GMA) as cladding material has been synthesized. The core material is the mixture of P(MMA-GMA) and bis-phonel-A epoxy. The relative refractive of the material can be modified by the different content of bis-phonel-A epoxy. According to the parameter demands of the devices, new types of UV curable polymeric 1×2,1×3,1×5,1×9 ultra-long compact array waveguide true-time-delay (TTD) lines for wideband phased array antennas (PAA) are designed and fabricated using direct UV photolithography process. The unique feature of the approach consists of different 1×N waveguide splitters, low-loss S-bend cosine waveguide connectors, and 180°array bend waveguides with a constant spacing differenceΔR between adjacent waveguides. The waveguide delay line can achieve not only basic equal time delay between adjacent waveguides, but also time-delay increments from ps to ns. Taking advantage of the UV curable SU-8 resist as core and P(MMA-GMA) as cladding to fabricate devices, we obtain good profile of the waveguide, analyze and simulate scattering loss, bend loss, the coupling loss of the overlap integral and offset between the input mode and output mode for straight-curve, curve-curve waveguide junction. The new fabricating technique of the resist can provide a simple, rapid, and controllable process. 1×2, 1×4, 1×8 polymeric star coupler devices are also successfully prepared. The delay increments for each element are calculated. The base time delay incrementΔt is 6.6ps, the maximal range of nΔt can be 46.2-ps. Furthermore, the performance of the max delay line between the first channel and 2-9th channel can be up to 1.3 ns. The experimental setup is used for characterization of the time delay circuit. The photograph and near-infrared field patterns of the device are obtained. The insertion loss of the first channel is about -5dB, and other four values of the loss for array channels are in range from -9dB to-12dB.3. EO waveguide modulator based on a new type of organic chromophore group bonded organic-inorganic hybrid material and EO waveguide switch based on host-guest doped polymeric DR1/SU-8 material are researched in this thesis. A new type of organic chromophore group/ SiO2-TiO2 second-order nonlinear optical (NLO) materials has been obtained by sol-gel process from titanium butoxide [Ti(OBu)4] and an alkoxysilane dye (ASD) synthesized by coupling disperse orange-11 (DO-11), disperse red-1(DR1), and disperse red-19(DR19) with (3-glycidoxypropyl) trimethoxysilane ( KH-560). The optics characteristics of the material are investigated. The poled film exhibits good orientation stability by UV-VIS absorbance spectra. A strip-loaded waveguide structure is introduced according to the characteristics of the synthesized organic/inorganic hybrid EO materials. Based on the planar waveguide mode theory, the light field modes are simulated and optimized by OptiBPM software. A polarization-insensitive strip-loaded waveguide structure is obtained by adjusting the propagation constant under different polarization. The optimized sizes and refractive indices of the waveguide are obtained. SU-8 photoresist and P(MMA-GMA) copolymer are selected as the strip waveguide, Aluminum film is utilized as electrode material. By process of spin-coating, photolithography, wet-etching, and corona poling technology, the M-Z poled polymer EO modulator based on strip-loaded waveguide is fabricated. The modulation function is achieved. In order to optimize and enhance the performance of the host-guest doped polymeric DR1/SU-8 material, the appropriate quantity of photoacid generator is added into the material. A new type of single-mode embedded dye-doped polymeric planar waveguide device based on cross-linkable negative photoresist has been successfully designed and fabricated using a thermal UV-bleaching technique. A notable difference in the refractive index of the resist between exposed and un-exposed regions is observed, which is found to be dependent on the curing temperature. The easy-fabricate waveguide structure is suitable for planar light-wave circuit applications. By optimizing the poling temperature and the dopant levels of Disperse Red 1, the material showed excellent photostability and exhibited a electro-optic coefficient,γ33, of 25pm/V. Polymeric EO waveguide switch is fabricated by simulating and optimizing the structure of waveguide, the switch function can be obtained.The successful research and fabrication on polymer/Si array waveguide grating (AWG), waveguide delay line, and EO waveguide modulator and switch may not only accumulate experience for other polymer active/passive waveguide devices, but also establish foundation for investigating integrated optical waveguide devices. The work will promote the development of polymeric waveguide devices greatly.