A 4-mode EDFA was constructed to compare the two cladding pumping schemes, and the results show that helix side pumping is more conducive to increased gain and reduced DMG.

In this paper, an integrated few-mode erbium-doped fiber amplifier (FM-EDFA), with high gain, low differential modal gain (DMG), and low gain flatness for multi-wavelength amplification, is constructed using homemade weakly-coupled ring-core few-mode erbium-doped fiber (FM-EDF) and low insertion-loss passive components. The gain characteristics of the FM-EDFA for multi-wavelength amplification are analyzed in detail and compared with single-wavelength amplification. The experimental results demonstrate that, although multi-wavelength amplification in different modes has an impact on the gain characteristics, through simple LP 01 core pumping only, all guided modes can achieve a gain higher than 22.4 dB when simultaneously amplifying 8 wavelength channels. The DMG is less than 1.179 dB, the minimum DMG across the C-band is as low as 0.168 dB, and the wavelength gain flatness is less than 3.232 dB. Furthermore, when the three-signal mode is multiplexed for amplification, the DMG can be stabilised at less than 2 dB. The constructed FM-EDFA can achieve gain equalization in multi-wavelength amplification across the C-band, which has essential practical applications in long-haul WDM-MDM transmission systems.

We report an S-band amplifier that can provide at least 28 dB gain across 1460~1530 nm. This demonstration shows the potential of S-band amplifiers to extend communication windows.

A double-cladding weakly-coupled FM-EDF was fabricated, and the cladding-pumped FM-EDFA was constructed. In C-band, the average gain after simultaneous amplification of the 4-LP mode is 21.62 dB, and the DMG is less than 2.37 dB.

In this paper, we report an all-fiber 4-mode fiber multiplexer and its measurement, which uses a fused tapering method to fabricate different mode-selective coupler. The insertion loss of a single mode-selective is less than 0.7dB, the insertion loss of LP 01 , LP 11 , LP 21 and LP 02 is less than 3 dB after cascading, while the modal crosstalk is lower than −15dB. This device can be applied in mode-division multiplexing transmission systems.

We report the coupling and measurement of fan-in/fan-out for 8-core multi-core fiber applicable using three-dimensional waveguide. The average coupling loss of multi-core fiber or single-mode fiber array with three-dimensional wave-guide is less than 0.31dB and the crosstalk of the cores are less than -35dB.