Ultra-high-definition (UHD) technologies have recently received attention on account of their practical applications in consumer electronics. UHD devices require uncompressed video transmission at a data rate exceeding 100 Gb/s; thus, an optical fiber connection is essential. In consumer applications, optical fibers are very short. Moreover, their connections must permit variations in the fiber alignment, which accommodates rough handling by consumers. Under this condition, the transmitted signal quality is significantly degraded owing to noise and instabilities that strongly depend on the fiber alignment conditions in optical modules and connectors. Therefore, graded-index plastic optical fibers (GI POFs) are promising optical cables for consumer applications because of their flexibility, safety, and high bandwidth. Recently, the authors experimentally demonstrated that GI POFs can reduce interferometric noise, such as modal noise and multipath interference noise, in a multimode fiber link based on a vertical-cavity surface-emitting laser (VCSEL). This noise reduction effect results from strong mode coupling of GI POFs, which is closely related to microscopic heterogeneous structures of a core polymer matrix. In this paper, a control method of mode coupling using the copolymerization process for fiber core materials is proposed. The formation of composition fluctuations by copolymerization increases the mode coupling in the GI POF core. It thereby enables highly stable and robust data transmission with a large fiber misalignment tolerance in a VCSEL-based multimode fiber link. The proposed method for mode coupling control is expected to contribute to household optical communication systems in the upcoming UHD era.
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