Impact of Air Hole on Crosstalk Suppression and Spatial Core Density of Multi-Core Fiber

We experimentally and theoretically investigate the effect of an air hole between cores in a multi-core fiber (MCF) on the suppression of crosstalk (XT). We clarify that XT decreases in proportion to the air hole diameter and that XT of about 20 dB in an MCF can be suppressed by employing just one air hole between cores. We confirm that the calculated XT suppression value is in good agreement with the measured value. We also clarify numerically that the minimum distance between cores satisfies the required XT without reducing the effective area by using an air hole. Next, we consider the influence of air holes on macro-bending loss and cutoff wavelength. We confirm that none are related to the arrangement of the air holes. Moreover, we discuss the relationship between the effective area and the core multiplicity factor (CMF) against several core arrangements. As a result, we show that the CMF in MCF with air holes can increase by 1 or more compared with that without air holes.