Sub-second mode measurement of fibers using C2 imaging

Area of Science:

• Optical Engineering
• Photonics
• Fiber Optics

Background:

• Multi-mode optical fibers support complex light propagation patterns (modes).
• Characterizing these modes is crucial for optimizing fiber performance and applications.
• Existing methods for modal analysis can be time-consuming and complex.

Purpose of the Study:

• To implement and validate a novel frequency-domain cross-correlated imaging (fC(2)) technique.
• To enable rapid and accurate reconstruction of individual modes and their relative powers in multi-mode fibers.
• To demonstrate the utility of fC(2) imaging for real-time modal analysis and system optimization.

Main Methods:

• Implementation of cross-correlated imaging in the frequency domain (fC(2)).
• Utilizing a tunable light source and specific apodization functions for modal discrimination.
• Performing measurements on a double-clad test fiber to reconstruct guided modes.

Main Results:

• Simultaneous reconstruction of six guided modes in a double-clad fiber.
• Measurement completion time under one second (950 ms) with a signal-to-noise ratio up to 25 dB.
• Achieved group-delay temporal resolution as high as 720 fs.
• Demonstrated optimization of fiber alignment, achieving >95% mono-mode purity.

Conclusions:

• Frequency-domain cross-correlated imaging (fC(2)) is a powerful tool for near-real-time modal content analysis in multi-mode optical fibers.
• The developed system offers high speed, excellent signal-to-noise ratio, and tunable temporal resolution.
• fC(2) imaging facilitates efficient fiber characterization, alignment optimization, and modal power measurement.