Design Of Mode Converters With Long-Period Gratings Formed In Polymer Waveguide

With the increasing need for transmission capacity of modern communication, people are constantly looking for ways to increase the transmission capacity of optical networks, such as time-division multiplexing(TDM), frequency-division multiplexing(FDM), wavelength-division multiplexing(WDM), mode-division multiplexing(MDM) and so on. Especially MDM with few- mode fibers has attracted much attention in recent years as a promising technology to further enhance the transmission capacity of optical fiber links.In an MDM system, a number of fiber-compatible components are needed to generate, switch, and(de)multiplex fiber modes. O ne of the basic components is a mode converter for coupling light between the fundamental mode and a selected high-order mode. Mode converters have been demonstrated with different technologies, which include, for example, bulk phase plates, liquid-crystal spatial light modulators, and mechanically induced long-period fiber gratings(LPFG). In this pape r, we demonstrated a mode converter based on forming a long-period grating in a polymer channel waveguide. The main work is as follows:First, a brief overview has been provided about MDM, and it has intronduced several common mode converters and analyzed their principle and advantages. O n this basis of the LPFGs, it had the low complexity and the effective conversion. In order to solve the geometry and materials of constrains of a fiber, the long-period waveguide grating(LPWG) has been proposed.Secondly, the mode of waveguide with Maxwell equations has been introduced, and then the basic theory of the channel waveguide has been analyzed. The coupling coefficient and transmission spectrum of LPWG were described on the basis of coupled-mode theory. Finally, as for the materials, it was widely known that the polymer was easy to fabricate, low cost and have a large thermal-optical coefficient..Then, our work has been introduced. First, the two ways were used to determine the dimensions of the channel waveguide. Until a range has been determined, we calculated the period and the depth of the LPWG on the basis of coupled- mode theory and phase- matching condition. Through analyzing the structure and characteristics, the waveguide patterns and grating patterns have been designed to make a mask.Finally, the device has been fabricated with our in-house photolithography and reactive-ion etching(RIE) facilities. Through the experiments and the tests, we demonstrated that the LPWGs could complete the conversion from the fundamental mode to higher order mode, and the test result had been gotten about the coupling efficiency. Additionally, the polarization insensitivity of the LPWGs has been demonstrated. More importantly, our LPWGs could offer a widely tunable operation wavelength by control of the temperature.