Study On Mode Division Multiplexing Technology Based On Two-mode Fiber Bragg Grating

With the rapid development of computers, big data, cloud computing, networkingand mobile Internet and other emerging industries come to rise. Data traffic has grownexponentially, so the bandwidth of optical fiber transmission network put forwardhigher requirements. To meet the rapid growth of data traffic, people study timedivision multiplexing, wavelength division multiplexing technology, higher ordermodulation formats, polarization multiplexing and other new technologies, build thegrowing fiber transmission capacity on single-mode. However, due to the nonlineareffects of single mode fiber, transmission capacity is severely limited. Against thisbackground, mode division multiplexing which has a huge potential transmissioncapacity emerged. Mode division multiplexing is based on few-mode fiber as atransmission medium, and the limited orthogonal of few-mode mode in fiber is usedto carry different signals. At the same time, these signals transmitted information inparallel. Meanwhile, the few modes in fiber can effectively reduce mode coupling,and the large mode area can effectively limit the impact of nonlinear effects, whichwill help to improve the transmission capacity of the system. In this paper, we deeplystudy the mode division multiplexing, and propose an experimental system with atwo-mode fiber Bragg grating and an optical circulator. We successfully build a2×2mode division multiplexing system to achieve two different rates digital signaltransmission. The main efforts in this paper are as follows:Firstly, we introduce the mode division multiplexing system theory and the keytechnologies in detail. From Maxwell equations to study the theory of few-mode fiberThrough the wave equations of the few-mode fiber, we analyze the transmissioncharacteristics of optical fiber and the distribution of the pattern mode. And we havedesigned a four-mode fiber. The four-mode fiber mode field distribution wassimulated.Secondly, using the coupled-mode theory, the theory of the few mode fiber Bragggrating is analyzed. We also study the relationship between the propagation constantand the working wavelength of the few-mode fiber Bragg grating. By theRunge-Kutta method, we solve the coupled-mode equations to calculate the reflection spectrum of the few-mode fiber Bragg grating. Meanwhile, by the case of thereflection spectrum of the few-mode fiber Bragg grating, the transmissioncharacteristics of the few mode fiber Bragg grating are analyzed. And we design atwo-mode fiber Bragg grating. We also simulate the reflection spectrum of thetwo-mode fiber Bragg grating changes under different mode power ratio. Next, atwo-mode fiber Bragg grating is etched by the phase mask and the reflection spectrumis measured. The experimental result is consistent with the theoretical analysis.Thirdly, using the two-mode fiber Bragg grating etched, we propose a way to studythe coupling of LP11mode peak transmission characteristic that the experimentalstructure is based on the two-mode fiber Bragg grating and optical circulator. We alsomake an circular cavity structure light source, making light work wavelengthcorresponds to the coupling of LP11mode of the two-mode fiber Bragg grating. By thecharacteristic peaks of LP11mode of the two-mode fiber Bragg grating, we obtain theLP11mode and LP01modes in reflecting and transmission of the two-mode fiberBragg grating, respectively. And by CCD imaging system, the electric fielddistribution pattern was observed. Meanwhile, the other coupling peaks of thetwo-mode fiber Bragg grating are deeply analyzed.Finally, using the LP01and LP11mode, we designed a2×2mode divisionmultiplexing system based on the two-mode fiber Bragg grating, and successfullybuild the experimental system. In the experiment, LP01mode and LP11mode arecarrying different rates of digital signal. Then the receiving end of the signal eyediagram and other relevant parameters for different transmission distances weremeasured. The results is comparative analyzed. Finally, we summarize the full textand the mode division multiplexing system based on the two-mode fiber Bragggrating is evaluated. At the same time, we analyze the problems and put forwardopinions and suggestions for future research.