Optimizing the internal phase reference to shape the output of a multimode optical fiber.

Area of Science:

• Optics
• Biomedical Engineering
• Waveguide Optics

Background:

• Multimode fibers (MMF) enable advanced imaging by pre-shaping light for distal facet applications.
• Transmission matrix measurement is crucial for imaging through optically turbid MMFs.
• Internal reference beams offer interferometric stability but have controversial merits and drawbacks, including potential 'blind spots'.

Purpose of the Study:

• To investigate the impact of internal reference beam selection on transmission matrix measurement accuracy in MMFs.
• To enhance the focusing efficiency of calibration procedures utilizing internal reference beams.
• To address the controversial aspects and limitations associated with internal reference beam configurations.

Main Methods:

• Characterization of light scrambling in optically turbid MMFs.
• Interferometric measurement of the transmission matrix using output speckle and a reference beam.
• Optimization of the internal reference beam's properties within the MMF.
• Quantitative analysis of focusing efficiency based on reference beam choice.

Main Results:

• The choice of internal reference beam critically influences transmission matrix measurement.
• Observed 'blind spots' in calibration due to phase singularities of the reference beam.
• Optimizing the internal reference beam increased calibration focusing efficiency by several percent.

Conclusions:

• Careful selection of the internal reference beam is essential for accurate and efficient MMF calibration.
• The study demonstrates a practical method to improve focusing efficiency in MMF-based imaging systems.
• Addressing reference beam properties overcomes limitations and enhances the utility of MMFs for advanced optical applications.