Free-space monolithic reflow-based fused silica fiber-to-fiber couplers

Efficient and robust free-space light coupling in integrated systems is a challenging task for photonic devices. Here we propose a femtosecond laser process combined with CW laser thermal reflow for manufacturing a fiber-to-fiber free-space light-coupling device in fused silica. The monolithic free-space coupler design consists of two fiber holders and two ball lenses, used to achieve both, fiber-output collimation and fiber-injection. The device proved to efficiently work at 633 nm for single mode fiber coupling, which can be extended beyond the whole visible range with a simulated maximum efficiency of up to 90-95% of coupling.