A simple all-fiber comb filter based on the combined effect of multimode interference and Mach-Zehnder interferometer

Area of Science:

• Photonics
• Optical Engineering
• Fiber Optics

Background:

• Fiber optic filters are crucial components in optical communication systems.
• Existing filter technologies face challenges in terms of integration and tunability.

Purpose of the Study:

• To propose and demonstrate a novel polarization-dependent all-fiber comb filter.
• To investigate the influence of fiber types and lengths on filter performance.
• To explore the potential applications in dense wavelength division multiplexing (DWDM) systems.

Main Methods:

• Fabrication of an all-fiber comb filter by fusion splicing a multimode fiber (MMF) with single-mode fibers (SMF).
• Utilizing a combination of multimode interference (MMI) and Mach-Zehnder interferometer (MZI) principles.
• Investigating the effect of different fiber types, lengths, and input light polarization states.

Main Results:

• Successfully demonstrated polarization-dependent all-fiber comb filters.
• Achieved free spectral range (FSR) values from 0.236 to 1.524 nm.
• Demonstrated adjustable extinction ratios from 6 to 11.1 dB by controlling polarization, without altering FSR.

Conclusions:

• The proposed MMI-MZI based all-fiber comb filter offers a novel approach for optical filtering.
• The device exhibits polarization-dependent characteristics, enabling tunable performance.
• This technology holds promise for advanced optical communication systems, particularly DWDM.