Optimization of the splice loss between photonic-bandgap fibers and conventional single-mode fibers

Abstract

To understand the loss limitations of a splice between a hollow-core fiber and a conventional fiber, we use a numerical model to calculate the expected coupling loss between the NKT Photonics' HC-1550-02 fiber and a single-mode fiber (SMF) of arbitrary step-index profile. When the SMF parameters are optimized, the splice loss is predicted to be as low as~0.6 dB. This minimum is believed to be largely due to mode-shape mismatch. These predictions are confirmed experimentally by optimizing the splice loss between this photonic-bandgap fiber and five SMFs with different mode-field diameters (MFDs) and V numbers. With the SMF-28 fiber, the measured loss is 1:3 dB, in excellent agreement with theory. Using a SMF with parameters close to the optimum values (MFD ¼ 7:2 μm and V ¼ 2:16), this loss was reduced to a new record value of 0:79 dB. . A lower splice loss of 1 dB has also been demonstrated by applying longitudinal pressure to these two fibers prior to applying the arc [4]. In contrast, a simple overlap calculation using a Gaussian mode approximation based on the mode-field diameter of the two fibers (∼7:5 and ∼10:4 μm, respectively) predicts that the buttcoupling loss should be 0:46 dB [3]. Although this 0.5 to 1 dB difference has been tentatively explained by differences in the mode shapes, there is still a need to conduct thorough simulations to explain this measured loss. It is also important to explore the possibility of achieving a lower splice loss by selecting a solid-core fiber with a mode-field diameter (MFD) better matched to that of the hollow-core fiber.In this Letter, we use a numerical model previously reported [5] to calculate the exact fields of the HC-1550-02 fiber's fundamental mode, and with them we compute the expected coupling loss between this fiber and an arbitrary step-index SMF. This analysis predicts that, when the SMF parameters are optimized (MFD ≈ 7:25 μm and V ¼ 2:405), the splice loss should be as low as ∼0:6 dB. We confirm these predictions by optimizing the splice loss between this PBF and five SMFs with different MFDs and V numbers. With the SMF-28 fiber, we measured a loss of 1:3 dB, in good agreement with theory. Using a SMF with parameters close to the optimum values (MFD ¼ 7:2 μm and V ¼ 2:16), we reduced the splice loss to 0:79 dB. This is the lowest value reported to date for a splice between a hollow-core and a solid-core fiber using an arc splicer.The field transmission (t) and reflection (r) coefficients at a butt-coupled junction between a SMF and a PBF can be described in terms of the normalized vector electric and magnetic fields E i and H i of the HE 11 mode of the SMF, and the corresponding fields E t and H t of the PBF's fundamental mode. These modes are normalized to carry 1 W power, orwhere A is the cross-sectional area of the fiber. A similar expression applies for the SMF mode. Neglecting coupling into higher-order modes of the PBF, the continuity of the transverse fields at the interface between the fibers imposeswhere the subscript T represents the transvers...

Large-core photonic microcells for coherent optics and laser metrology

“…These compare with the lowest-reported loss of 0.9 dB for a splice between SMF-28 and bandgap-guiding HC-PCF [10]. For completeness, it is worth noting here that a loss of 0.79 dB between SMF with a mode field diameter optimized to match 7-cell PBG HC-PCF is reported in [31].…”

Splice Loss Optimization of a Photonic Bandgap Fiber via a High V-Number Fiber

“…2 shows the superiority of the intermediate fiber method, which can reduce the coupling loss dramatically to 0.35 dB. It is generally believed the theoretical limit of the coupling loss is set by Fresnel reflection coefficient of 0.18 dB [10], [14]. Here we want to emphasize that the 0.18 dB (4%) Fresnel reflection mentioned frequently is measured at the normal incident angle.…”

“…The formula proposed in Ref. [10] are used to calculate the loss at the butt-coupled 1041-1135 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.…”

“…We systematically investigate the splice loss between the HC-1550-02 fiber and the intermediate fiber by including the effects of mode size, mode shape and Fresnel reflection. It has been pointed out in [10] that the theoretical loss limit between the HC-1550-02 and a conventional SMF is 0.6 dB. To break this limit, we extend our research to cover multimode step-index fibers.…”

“…The reported fusion splice loss between two most widely used commercial fibers, i.e. NKT Photonics' 7-cell HC-1550-02 fiber and Corning's SMF28 fiber, keeps in Manuscript [10]. By replacing the SMF28 fiber with a more mode-matched fiber (Nufern's GF3), Aghaie et al [10] pushed this number down to 0.79 dB, representing the lowest splice loss record for 7-cell HC-PBGF.…”