Compact in-line optical notch filter based on an asymmetric microfiber coupler

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Development of compact, high-performance optical filters is crucial for advanced photonic systems.
• Existing filters often face limitations in bandwidth, footprint, or integration.

Purpose of the Study:

• To propose and experimentally demonstrate novel compact in-line optical filters.
• To achieve narrow rejection bandwidths and high transmission extinction ratios.

Main Methods:

• Fabrication of asymmetric microfiber (MF) couplers using silica and bismuth-oxide-glass.
• Experimental characterization of filter performance, including transmission dips, extinction ratio, and bandwidth.
• Theoretical modeling to validate experimental findings.

Main Results:

• Demonstrated filters with lengths under 500 μm.
• Achieved single transmission dips over a 300 nm wavelength range.
• Obtained transmission extinction ratios exceeding 30 dB.
• Realized a -20 dB bandwidth as narrow as 0.88 nm, attributed to a large refractive index difference between MFs.

Conclusions:

• The proposed microfiber optical filters offer a simple, fiberized, and compact solution.
• The demonstrated performance makes these filters attractive for micro/nanophotonics, optical sensing, signal processing, and optical fiber communications.