Periodic Microbending Induced Coherent Mode Coupling in Multicore Optical Fibers
Mode coupling due to periodic index perturbation is a phenomenon which has many applications in optical fiber communications. Coherent coupling between co-propagating modes is one of the most important outcomes of this index perturbation. This property has been utilized to create frequency selective filters, sensors and frequency shifters just to name a few of the applications. This index perturbation is created by a periodic microbending along the longitudinal direction of the optical fiber. Two of the most commonly utilized methods are Fiber Bragg Gratings (FBG) and Long Period Fiber Gratings (LPFG). LPFGs can be utilized to couple forward propagating core and cladding modes.
In this work, we have investigated how to generate LPFGs by using acoustic vibrations and utilize these vibrations to facilitate mode coupling in newly developing multicore optical fibers. The hypothesis of this work states that the presence of acoustic vibrations can couple core modes to cladding modes, and then couple that cladding mode to the adjacent core mode. This thesis investigates the optimum coupling conditions based on magnitude and frequency of acoustic vibrations and measures potential core-to-core crosstalk.
In our analysis, we used commercial simulation tools to simulate multicore optical fiber core and cladding modes and to calculate coupling coefficient for various modes. As a result, we got the coupling length and crosstalk values between multiple modes under periodic perturbation conditions for two different multicore fiber configurations and concluded that the amount of crosstalk between adjacent cores is not significant in terms of practical optical communications purposes.