Study Of Polymer Waveguide Bragg Grating Filter

The all-optical communication systems has a good prospects because its wide bandwidth and high speed. The huge demand for faster and more efficient data exchange (internet, video remote control, video private telecommunications,etc.) pushes toward the photonic devices, which potentially offer much faster performances with respect to traditional interconnection and data processing based on electronics. Bragg grating optical filters are one kind of key elements in optical communication systems such as wavelength-division multiplexing (WDM), optical fibre sensors, gain flattening filters, optical couplers, resonators, and modulators. Because of its advantages in material, structure and fabrication process, polymer waveguide grating is supposed to have a wide range of applications in all-optical communication systems and integrated optical sensors. In this thesis, the operating principle, design, several fabrication methods of the polymer waveguide grating are studied and the characteristics of the device are measured.According to optical waveguide theory and coupled-mode theory, the operating principle of waveguide Bragg grating is presented. By using the ultraviolet curable material ZPU46 and ZPU44 as the core and cladding materials, a polymer waveguide Bragg grating filter with the center wavelength near 1550nm was designed and fabricated. To fabricate the waveguide Bragg grating, two methods were used: (1) Based on the interferometric lithography, we designed, built and optimizated the two-beam interference exposure optical system and a setup for testing the grating period. The shipley s1805 photoresist was used for the two beam interference exposure to form the grating structure. The parameters of the spin coating of photoresist, lithography parameters (exposure time, development time) were studied and optimized.Then the polymer waveguide Bragg gratings (WBG) was fabricated using the traditional micro-fabrication techniques. A transmission dip of-4dB at 1622nm and 3dB bandwidth of 0.3nm were observed. The experimental results agree well with the theroy. (2) The enlarging of the period of the higher-order Bragg grating can reduce the difficulty of the process. And we can use the traditional contact lithography to achieve a large area of the high order grating structure. A surface grating with a period of 1.6μm and height of 680nm was fabricated on single mode rectangular waveguides with 4um thickness by traditional contact lithography and reactive ion etching. Experimental results show that with the waveguide cross section size of 4 x 4.2μm (5 x 4.2μm), the center wavelength of the fabricated third-order polymer waveguide grating is 1549 nm (1550.5 nm), side mode rejection ratio is 19 dB (18dB),3 dB bandwidth is 0.4 nm (0.6 nm), and the insertion loss is 7 dB. The measurement results are accordance with the simulation well.In this thesis, after the study of a uniform grating structure, we studiedtwo kinds of non-uniform grating. We design a third-order sampled waveguide Bragg grating and a third-order apodizated waveguide Bragg grating. And the sampled waveguide Bragg grating was fabricated and tested.The measurement results of the third-order sampled waveguide Bragg grating are accordance with the simulation well.