In-line flat-top comb filter based on a cascaded all-solid photonic bandgap fiber intermodal interferometer

Area of Science:

• Photonics
• Optical Fiber Communications
• Interferometry

Background:

• All-solid photonic bandgap fibers offer unique light propagation properties.
• Modal interferometers are sensitive to changes in optical path length.
• Flat-top spectral responses are desirable for various optical filtering applications.

Purpose of the Study:

• To propose and construct an in-line fiber optic comb filter with a flat-top spectral response.
• To investigate the fabrication method and spectral characteristics of the proposed filter.
• To demonstrate the tunability of the filter's channel position.

Main Methods:

• Cascading two all-solid photonic bandgap fiber modal interferometers.
• Utilizing core-offset splices between all-solid photonic bandgap fibers and standard single-mode fibers.
• Employing a cut and resplice process on the central position of the all-solid photonic bandgap fiber.
• Applying longitudinal torsion to tune the channel position.

Main Results:

• Successfully fabricated an in-line comb filter with a flat-top spectral response.
• Demonstrated that controllable offset amounts during resplicing tailor interference spectra.
• Achieved a tunable channel position with up to 4 nm tuning range using longitudinal torsion.
• The filter exhibits an easy-to-fabricate nature with designable passband width and flat-top profile.

Conclusions:

• The proposed cascaded all-solid photonic bandgap fiber modal interferometer is an effective method for creating flat-top fiber comb filters.
• The fabrication process allows for precise control over spectral profiles and channel positioning.
• The filter's tunability and designability make it suitable for advanced optical communication systems.