First demonstration of a 2μm few-mode TDFA for mode division multiplexing

Area of Science:

• Optical Communications
• Fiber Optics
• Photonics

Background:

• Mode division multiplexing (MDM) is a promising technique to increase optical fiber capacity.
• Few-mode fiber amplifiers are crucial for enabling MDM systems by amplifying signals across multiple spatial modes.
• Thulium-doped fiber amplifiers (TDFAs) offer potential for operation in the 2μm window, relevant for specific communication bands.

Purpose of the Study:

• To demonstrate the first inline few-mode thulium-doped fiber amplifier (TDFA) for mode division multiplexed (MDM) transmission.
• To evaluate the gain and noise figure performance for different spatial modes (LP(01) and LP(11)) within the TDFA.
• To characterize the amplifier's operational bandwidth and noise performance at 2μm.

Main Methods:

• Development and implementation of a cladding-pumped, 2-mode group TDFA.
• Inline amplification of optical signals in a few-mode fiber setup.
• Measurement of gain and noise figure for LP(01) and LP(11) modes across relevant wavelengths.

Main Results:

• Achieved comparable gain and noise figure performance for both LP(01) and LP(11) modes.
• Maximum measured gain of 18.3dB at 1970nm.
• Observed a 3dB gain bandwidth of 75nm and an average noise figure between 7-8dB for wavelengths >1970nm.

Conclusions:

• The demonstrated inline few-mode TDFA is suitable for MDM transmission at 2μm.
• The amplifier exhibits mode-independent performance, a key requirement for practical MDM systems.
• This work represents a significant step towards higher capacity optical communication systems using spatial multiplexing.