Compact mode dimension sorter enabled by an on-chip graded-index metamaterial lens

Area of Science:

• Photonics and Nanotechnology
• Integrated Optics
• Metamaterials

Background:

• Precise control of on-chip optical modes is essential for miniaturizing devices and enabling high-speed optical interconnects, particularly in Mode Division Multiplexing (MDM) systems.
• Subwavelength structures offer versatile control over on-chip optical fields, driven by advances in nanofabrication.
• Existing mode sorters often face limitations in size and robustness.

Purpose of the Study:

• To propose and analyze a compact mode sorter based on a subwavelength waveguide grating for efficient on-chip optical mode separation.
• To demonstrate the device's performance in separating TE0, TE1, and TE3 modes on a silicon-on-insulator (SOI) platform.
• To present a generalizable design framework for metamaterial-based on-chip lenses using eigenmode analysis.

Main Methods:

• Design of a compact mode sorter utilizing a subwavelength waveguide grating.
• Application of the eigenmode expansion method for device design and analysis.
• Optical field distribution analysis at the focal plane of an on-chip lens for various incident modes.

Main Results:

• Achieved efficient separation of TE0, TE1, and TE3 modes within an 8.3 µm footprint on an SOI platform.
• Demonstrated low insertion losses (0.79 dB, 0.97 dB, 0.91 dB for TE0, TE1, TE3) and a wide bandwidth (114 nm) for a complete (de)multiplexer.
• Simulations indicated superior robustness to fabrication tolerances compared to traditional devices, with crosstalk below 15 dB.

Conclusions:

• The proposed subwavelength waveguide grating offers a compact and robust solution for on-chip optical mode sorting.
• The device enables efficient mode separation and reconstruction, paving the way for advanced integrated photonic applications.
• The presented design framework is generalizable for metamaterial-based on-chip lenses and mode manipulation.