Direct in-fiber mode excitation enabled by on-chip spatial field engineering

Area of Science:

• Photonics
• Integrated Optics
• Optical Communications

Background:

• Efficiently coupling light between integrated photonic circuits and optical fibers is essential for advanced communication systems.
• Exciting specific higher-order modes in fibers directly from chip-based sources simplifies device architectures.

Purpose of the Study:

• To introduce and validate an interface-level field-mapping mechanism for direct excitation of higher-order fiber modes.
• To enable selective mode generation without requiring separate on-chip mode-conversion stages.

Main Methods:

• Engineering the spatial distribution of optical fields at the chip-fiber interface.
• Establishing a correspondence between on-chip phase-polarization and target fiber eigenmodes.
• Utilizing a silicon-on-insulator platform with a grating-emitter array for programmable control.

Main Results:

• Theoretical analysis predicted an idealized modal-overlap upper bound of 97.8%.
• Experimental near-field measurements confirmed selective excitation of LP12 and LP21 modes at 1550 nm.
• The results qualitatively agreed with theoretical mode-selection behavior.

Conclusions:

• The proposed field-mapping mechanism enables compact, direct chip-to-fiber spatial-mode manipulation.
• This approach offers a simplified route for integrated mode-division multiplexing interfaces.
• Further optimization is needed to reach theoretical overlap limits, but the concept is validated.