Research Of Single Polarization Single Mode Fiber Couple

With the rapid development of optical fiber communication technology, transmission rate information has been greatly improved in the past ten years, and the demand for information has also been further expanded. To further enable the transmission rate to achieve a breakthrough, OTDM, WDM, FDM and other multiplexing technology must be used, however, these technologies are inseparable from the optical coupling technology. As an important passive optical device, optical fiber coupler is widely used in the field of optical fiber sensing and signal processing, etc. With conventional polarization maintaining fiber coupler developed more mature, the development of single-mode single-polarization optical fiber coupler based on polarization separation attracted more and more attention.In this paper, through the compare of the past various fiber couplers, a fiber model based on core geometric asymmetry to artificially introduce birefringence has been proposed. Sufficiently high birefringence can be achieved with the introduced of elliptical air hole in the central fiber core, and then the power can be shift with the coupling between two different cores to achieve polarization separation. Based on the theoretical model, we obtain the effective refractive index and coupling length parameters after complete the simulation of the optical fiber coupler mode with Comsol Multiphysics and Matlab, and the analysis of it with coupled-mode theory and supermodel theoretical. Then we investigate its polarization separation condition according the polarization separation qualification, and discuss its single polarization characteristics and operating bandwidth with extinction ratio. The result shows that this optical fiber coupler can achieve narrow-band single-mode single-polarization operate in both two cores with λ=1550nm (±1nm) after transfer182mm, and the highest extinction ratio could be65dB and35dB.On this basis, this paper also presents a single-mode single-polarization optical fiber coupler with rectangular metal wire, which could introduce birefringence with the asymmetry of metal wire and its surface plasma to achieve polarization separation. By analyze its mode field characteristics with supermodel theoretical based on finite element method, we could obtain the best ratio of coupling length of different polarization states. Meanwhile, we discuss its coupling length and single-polarization characteristic through the power transfer situation between two cores and extinction ratio,The study tinds that this optical fiber coupler could achieve single-mode single-polarization operation with bandwidth of1546-1553nm after transfer36.9mm.