Ultra-compact all-in-fiber-core Mach-Zehnder interferometer

Area of Science:

• Optics and Photonics
• Fiber Optic Devices
• Interferometry

Background:

• Mach-Zehnder interferometers (MZIs) are crucial for optical modulation, signal processing, and sensing.
• Existing MZI fabrication methods can be complex and costly.
• There is a need for simpler, more robust MZI designs.

Purpose of the Study:

• To introduce a novel, assembly-free, all-in-fiber-core Mach-Zehnder interferometer (MZI).
• To demonstrate a new fabrication technique using a femtosecond laser.
• To highlight the advantages of this new MZI design for various optical applications.

Main Methods:

• Directly writing an MZI into the fiber core using a femtosecond laser.
• Creating a positive refractive index-modified zone in half of the fiber core.
• Converting a single-mode fiber section into a few-mode fiber section to induce mode coupling.

Main Results:

• Achieved a well-defined interference spectrum in transmission due to strong coupling between the two lowest-order guided modes.
• Demonstrated ease of fabrication, stability, low insertion loss, and robustness.
• Exhibited an extremely broad operating bandwidth and precise, controllable cavity lengths.

Conclusions:

• The developed all-in-fiber-core MZI offers significant advantages over conventional MZIs.
• This novel device is highly attractive for widespread adoption in fiber communications, signal processing, sensors, and laser wavelength control.
• The femtosecond laser fabrication method provides a scalable and efficient approach for MZI production.