Abstract
We demonstrate a novel approach to enhance the modal stability between the modes of a few-mode fiber (FMF) by increasing the effective index differences between these modes. Unlike single mode fibers (SMFs), a FMF guides more than one mode with a larger effective mode area. Mode division multiplexing in FMFs has gained significant importance for potentially high data rate transmission. However, with the increase in the number of modes, a FMF encounters possible coupling between the modes. We proposed two designs of a FMF that supports LP01, LP11, LP21 and LP02 modes, which propagate with larger mode spacing, offering reduced mode coupling and thus enhancing mode stability. The modal stability or effective index difference between the modes is enhanced by more than 26% by introducing a ring of air-holes in the first fiber design. Moreover, a second fiber design is also proposed, where a five modes fiber is transformed to a four modes fiber and the modal stability enhancement is calculated to be more than 30% without affecting the mode quality significantly. It is also shown here that such a FMF is more resilient to both bending loss and mode area variation compared to a standard SMF. Our proposed technique is scalable and can be used for fibers with a higher number of modes to increase the transmission capacity along with reduced mode coupling.
Highlights
Recent studies show that the capacity limitation of a single mode optical fiber (SMF) is rapidly approaching the fundamental Shanon limit [1, 2]
The mode division multiplexing in a three-mode fiber using multiple-input multiple-output (MIMO) processing have shown significant transmission capacity improvements over the long distance communication [9]
We have proposed a new few-mode fiber design technique that is used to increase the modal spacing or effective index difference between the different modes of propagation
Summary
Recent studies show that the capacity limitation of a single mode optical fiber (SMF) is rapidly approaching the fundamental Shanon limit [1, 2]. The mode division multiplexing in a three-mode fiber using multiple-input multiple-output (MIMO) processing have shown significant transmission capacity improvements over the long distance communication [9]. A MIMO less elliptical core based three-mode fiber design was proposed to suppress the inter-modal coupling by increasing the effective index difference between LP01, LP11a and LP11b modes [13]. Alexander and Michalis proposed a four-mode fiber with asymmetric refractive index profile that focuses on the enhancement of mode spacing between the LP21 and LP02 This resulted in a significant increase in mode spacing between LP21 and LP02, the initial mode spacing between the LP01, LP11 and LP21 modes was noticeably reduced [14]. In order to increase the effective index difference (∆nef f ) between the modes, we have proposed an innovative approach by introducing an array of air-holes in a FMF. The proposed fiber design can be fabricated by adopting the similar process that of a Photonic crystal fiber (PCF) with nanometer size air-holes [15, 16]
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