Parallel six-mode-selective converter based on photonic crystal fiber without holes in the cladding

Area of Science:

• Photonics and Optical Engineering
• Fiber Optics Communications

Background:

• Cascaded waveguide-based mode-selective converters (MSCs) in mode division multiplexing (MDM) systems suffer from large size, high insertion loss, and mode crosstalk.
• Existing MSCs limit the integration and performance of high-capacity optical communication systems.

Purpose of the Study:

• To propose and demonstrate a compact, parallel six-mode-selective converter (6-MSC) for enhanced integration in MDM systems.
• To achieve efficient parallel conversion between fundamental modes and six orthogonal fiber modes using a novel photonic crystal fiber (PCF) structure.

Main Methods:

• A novel PCF structure without cladding holes was designed, allowing arbitrary adjustment of the distance between PCF and step-index fiber (SIF) cores.
• A parallel 6-MSC was fabricated by integrating the PCF with six SIFs.
• Numerical simulations were performed to evaluate the performance of the proposed 6-MSC at a wavelength of 1.55 µm.

Main Results:

• The proposed 6-MSC achieved parallel conversion from fundamental modes in SIFs to six corresponding LP modes in the PCF with a device length of 800 µm.
• Maximum coupling efficiency reached 96.22% with crosstalk below 3.45%.
• Coupling efficiencies exceeded 80% across the 1.538–1.560 µm wavelength range, with a 3-dB bandwidth covering the entire C-band.

Conclusions:

• The proposed PCF-based 6-MSC offers superior integration and performance compared to conventional waveguide-based MSCs.
• This work represents the first demonstration of parallel conversion between six orthogonal fiber modes and fundamental modes using PCF.
• The developed 6-MSC shows significant potential for future high-capacity integrated MDM systems.