Abstract
In this work, we demonstrate the measurement of the Brillouin gain spectra of vector modes in a few-mode fiber for the first time using a simple heterodyne detection technique. A tunable long period fiber grating is used to selectively excite the vector modes supported by the few-mode fiber. Further, we demonstrate the non-destructive measurement of the absolute effective refractive indices (neff) of vector modes with ~10−4 accuracy based on the acquired Brillouin frequency shifts of the modes. The proposed technique represents a new tool for probing and controlling vector modes as well as modes carrying orbital angular momentum in optical fibers with potential applications in advanced optical communications and multi-parameter fiber-optic sensing.
Highlights
Space division multiplexing (SDM) has been proposed to overcome the looming capacity crunch in conventional single mode fibers (SMFs)
The excitation of all these guided modes is possible at 1550 nm if the long period fiber grating (LPFG) is set at the proper angle, the measured Brillouin gain spectrum (BGS) shown in Fig. 4 were obtained at wavelengths slightly offset from the target 1550 nm wavelength due to imperfect fiber alignment on top of the LPFG’s grating lines when the latter is set at a non-zero angle
Measurement of the Brillouin gain spectra of the vector modes in a few-mode fiber (FMF) has been demonstrated for the first time using a simple heterodyne detection technique
Summary
Space division multiplexing (SDM) has been proposed to overcome the looming capacity crunch in conventional single mode fibers (SMFs). The few-mode fiber used in the experiment is an inverse parabolic graded-index fiber designed to mitigate the modal crosstalk between different vector modes by ensuring large Δneff values between adjacent guided modes[19]. This FMF with 3 μm core radius supports the fundamental HE11 (even and odd) mode, the TE01, HE21 (even and odd), TM01, EH11 (even and odd), and HE31 (even and odd) vector modes in the C-band.
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