Ultra-high-definition applications will be one of the main drivers for emerging 5G communications. 5G supports higher data rate utilizing higher frequency bands than those in existing cellular systems. However, higher-frequency radio waves have higher directionalities, resulting in decreased indoor coverage. Therefore, radio-over-fiber (RoF) systems are needed for indoor distribution of wireless signals. Recently, we developed a graded-index plastic optical fiber (GI POF) that enables higher-quality RoF transmission than conventional multimode fibers for short-distance links (<100 m). The GI POF can reduce noise and distortion in RoF transmission through its strong mode coupling. Here, we demonstrate that the GI POF significantly increases fiber-misalignment tolerance in RoF transmission. The GI POF will realize do-it-yourself optical fiber connections for indoor applications.
The growing demand for high-speed data transmission in consumer applications such as 4K/8K television motivates the development of multilevel modulation. Multilevel modulation can increase bit rate over 2-level modulation for same symbol rate, but is subject to noise and modulation instability in optical link. Recently, we experimentally demonstrated that a graded-index plastic optical fiber (GI POF) significantly improved the transmission signal quality compared with a silica GI multimode fiber (MMF) in the consumer-friendly MMF link without an optical isolator, where laser and optical fiber easily coupled. This high-quality transmission is related to reflection noise reduction because of a strong mode coupling in the GI POF. However, the signal quality also depends on the modulation response of the vertical-cavity surface-emitting laser (VCSEL) coupled with optical fibers. Here, we investigate the influence of the strong mode coupling in the low-noise GI POF on the modulation response of the VCSEL in the consumer-friendly MMF link. We show that the low-noise GI POF can significantly decrease the distortion of the modulation response compared with the silica GI MMF which easily coupled with the VCSEL. This low-distortion performance is related to the strong mode coupling in the low-noise GI POF, which stabilizes the VCSEL owing to the self-coupling reduction of the optical feedback into the VCSEL cavity. This suggests that the novel GI POF allows for highly-stabilized multilevel transmission for consumer-friendly 8K interface. In the conference, we will also discuss the mechanism for the stabilization effects of the low-noise GI POF using theoretical analyses.