Ultra-Compact, High-Efficiency Vertical Meta-Grating Couplers for Meta-Photonic Integrated Circuits.

Area of Science:

• Photonics
• Metamaterials
• Integrated Optics

Background:

• Vertical meta-grating couplers (VMGCs) are crucial for meta-photonic integrated circuits (MPICs).
• Existing VMGCs exhibit low coupling efficiency, limiting their practical applications.
• Advanced optimization techniques are needed to improve VMGC performance.

Purpose of the Study:

• To introduce an improved adjoint optimization method for VMGCs.
• To enhance computational efficiency and optimization effectiveness.
• To demonstrate high-performance VMGCs for MPICs.

Main Methods:

• Adjoint optimization method
• Computational modeling and simulation
• Design of ultra-compact single-polarization and dual-polarization couplers.

Main Results:

• Achieved 81.57% coupling efficiency for a single-polarization VMGC with a 92 nm 3 dB bandwidth.
• Demonstrated a dual-polarization beam-splitting coupler with >52% efficiency for both polarizations.
• Exceeded 60 nm 3 dB bandwidth and achieved >26.4 dB extinction ratio with negligible polarization dependent loss at 1550 nm.

Conclusions:

• The improved adjoint optimization method significantly enhances VMGC performance.
• The demonstrated VMGCs represent a record simulation achievement for perfect vertical couplers without bottom reflectors.
• This work paves the way for broader applications of VMGCs in MPICs.