Cut-off wavelength measurements for single-mode optical fibers

Area of Science:

• Optical Fiber Technology
• Photonics
• Waveguide Optics

Background:

• Accurate characterization of optical fiber modes is essential for designing advanced photonic devices.
• The disappearance of higher-order modes at the cut-off wavelength is a critical parameter.
• Existing methods for cut-off wavelength measurement can be complex or lack precision.

Purpose of the Study:

• To introduce a new, direct technique for measuring the cut-off wavelength of optical fibers.
• To assess the accuracy and optimal conditions for this novel measurement method.
• To investigate the attenuation mechanisms of higher-order modes near the cut-off wavelength.

Main Methods:

• Excitation of an optical fiber with a variable wavelength source.
• Monitoring changes in the fiber's near-field pattern as wavelength is varied.
• Direct measurement of the wavelength at which the first higher-order mode vanishes.

Main Results:

• The proposed technique directly measures the cut-off wavelength with an accuracy of +/-5 nm.
• Optimal fiber length for precise measurement was determined to be between 10-20 mm.
• Rapid attenuation of the first higher-order mode near cut-off is attributed to waveguide imperfections, primarily core-cladding boundary distortions.

Conclusions:

• The developed near-field pattern analysis offers a precise and direct method for cut-off wavelength determination.
• Waveguide imperfections significantly impact higher-order mode propagation near cut-off, with boundary distortions being the dominant loss factor.
• This technique provides valuable insights for optical fiber fabrication and performance optimization.