Broadband spatial mode conversion by chirped fiber bending.

Area of Science:

• Photonics and Waveguide Devices
• Optical Coupler Design
• Chirped Grating Structures

Background:

• Codirectional mode couplers are essential components in photonic integrated circuits.
• Achieving broadband operation in these devices is a key challenge for many applications.
• Existing uniform couplers have limited operational bandwidth.

Purpose of the Study:

• To develop design rules for broadband codirectional mode couplers using linear chirp.
• To theoretically and experimentally demonstrate the bandwidth enhancement capabilities of chirped couplers.
• To provide a comparative analysis between chirped and uniform couplers.

Main Methods:

• Solving the coupled-mode equations for linearly chirped codirectional mode couplers.
• Developing analytical design rules based on the derived solutions.
• Fabricating and experimentally characterizing a chirped coupler and comparing its performance to a uniform coupler.

Main Results:

• High coupling efficiency is achievable over a substantially wider bandwidth in chirped couplers compared to uniform ones.
• A designed chirped coupler exhibited a 99% bandwidth of 47 nm at 1090 nm, 5.8 times larger than a comparable uniform coupler.
• Experimental results validated the theoretical predictions, showing a bandwidth improvement factor of 5.4.

Conclusions:

• Linear chirp is an effective strategy for designing broadband codirectional mode couplers.
• The developed design rules enable the creation of photonic devices with significantly enhanced spectral performance.
• Chirped couplers offer a viable solution for applications requiring wide operational bandwidths in integrated photonics.