Single-Mode Segmented Cladding Chalcogenide Glass Fiber With Ultra-Large Mode Area

Small core size in conventional single mode step-indexed chalcogenide fiber could reduce the ability of mid-infrared (mid-IR) laser power delivery due to its limitation of power density. An effective way to solve the problem is to increase mode area with large core size, but this may degrade the beam quality. In this work, a novel mid-IR segmented cladding fiber (SCF) with leakage structure based on chalcogenide glasses was proposed to obtain large mode area, as well as single-mode condition. The leakage loss and effective mode area of the SCF was analyzed by optimizing the segment number
N
, duty cycle
γ
and core radius
r
. The results show that, when
N
= 4,
γ
= 75% and
r
= 33 μm, the mode area is more than 2000 μm
²
in the wavelength range of 3–10 μm and the loss ratio of high order modes (LP
₁₁
) to fundamental mode (LP
₀₁
) is more than 300, indicating the SCF can achieve single-mode operation with a large core. Then, a mid-IR SCF was fabricated via an extrude-and-stack technique based on chalcogenide glasses for the first time. The minimum fiber loss is 3.1 dB/m at 8.6 μm, the bend loss is 3 dB when bend radius is 6 mm. Compared with that in the traditional step-index single-mode fiber, it was found that, the mode area in SCF can be increased over 15 times. All these results demonstrate the SCF possesses the potential of high-power mid-IR laser transmission.