Two-photon direct laser writing of beam expansion tapers on single-mode optical fibers

Abstract

Small misalignments between two standard telecom single-mode fibers in a physical contact connection can lead to large optical losses. It is known that by expanding the mode field diameter of the fiber, the misalignment tolerances can be relaxed. One of the approaches to obtain this beam expansion is to use tapers. We propose an air-clad taper structure to transmit the fundamental mode of a single-mode fiber adiabatically to a 3 times larger mode field area in physical contact expanded beam connectors. This results in a 241.4 µm long linear taper. The taper itself is fabricated on top of a cleaved fiber facet by means of the two-photon polymerization direct laser writing technique. Experimental results for lateral misalignment show excellent agreement with simulated values and give an increase in lateral misalignment tolerance of 1 µm (-1 dB) and 1.8 µm (-3 dB). Total insertion losses down to 0.76 dB are measured, showing the trade-off between achievable insertion loss and misalignment tolerance relaxation. Finally, we show that the use of additive manufacturing techniques in fiber beam expansion applications make it possible to fabricate taper structures with full 3D design freedom and to upscale the process to multi-fiber components.

Optical Fiber Integrated Functional Micro-/Nanostructure Induced by Two-Photon Polymerization

“…Meanwhile, the lenses for fiber-fiber coupling have also been studied. Figure 1F shows a beam expansion taper for SMF-SMF coupling by transmitting the fundamental mode adiabatically from a SMF to 3 times larger mode field area in physical contact expanded beam connectors (Vanmol et al, 2019). The trade-off between achievable insertion loss and misalignment tolerance relaxation was demonstrated by measuring a total insertion loss as low as 0.76 dB.…”

“…(E) Microlens array printed on the top of single-mode and multi-core fiber for free-space light coupling (Dietrich et al, 2017). (F) Beam expansion taper for SMF-SMF coupling (Vanmol et al, 2019). multiplexer for OAM fiber communication.…”

Mode-field Matching Down-Tapers on Single-Mode Optical Fibers for Edge Coupling Towards Generic Photonic Integrated Circuit Platforms

“…All previous considerations can be applied to these components as well. Moreover, it is possible to scale up the fabrication process and print taper structures on multi-fiber array glass blocks to increase the fiber count and density [29].…”

“…This fabrication technology allows the creation of 3D structures with full design freedom and submicrometer resolution [24]. The technique has already been used in the development of a microstructured antireflective coating [25], phase masks [26], lenses [27], [28] and mode-field expansion up-taper structures [29] on optical fiber tips. In the latter, we demonstrated the fabrication method for use in physical contact expanded beam fiber-to-fiber connections to relax the alignment tolerances.…”

Mode-field matching design, 3D fabrication and characterization of down-tapers on single-mode optical fiber tips for coupling to photonic integrated circuits

“…In recent years, 3D nanoprinting technology, based on two-photon polymerization, is driving advancements in photonic miniaturization and integration. Research in this topic has shown that optical fibers can be functionalized for many applications, where the 2PP additive manufacturing technique has already been used in the development of a microstructured antireflective coating 8 , phase masks 9 , lenses 10,11 and mode-field expansion up-taper structures 12 on optical fiber tips. In the latter, we demonstrated the fabrication method for use in alignment tolerant physical contact expanded beam fiber-to-fiber connections.…”