Exploring the fundamental limits of integrated beam splitters with arbitrary phase via topology optimization

Area of Science:

• Integrated optics
• Quantum photonics
• Electromagnetics

Background:

• Optical beam splitters are fundamental components in photonic integrated circuits.
• Traditional lossless beam splitters have fixed output phase shifts (π), limiting applications.
• Achieving arbitrary beam splitter phase (BSP) in integrated devices is challenging.

Purpose of the Study:

• To investigate the theoretical limits of symmetrical integrated beam splitters.
• To explore the design of beam splitters with arbitrary BSP using inverse design.
• To optimize 2D beam splitter designs considering fabrication constraints.

Main Methods:

• Adjoint-based topology optimization was employed.
• Exploration of theoretical design space for various loss and phase combinations.
• Analysis of algorithm convergence for objectives within and outside theoretical limits.

Main Results:

• Optimized 2D designs for integrated beam splitters with arbitrary BSP were obtained.
• The optimization algorithm successfully converged for designs within theoretical limits.
• Algorithm failed to converge for objectives outside the established theoretical boundaries.

Conclusions:

• Theoretical limits for integrated beam splitters with arbitrary BSP were successfully explored.
• The developed methods provide a pathway for designing novel beam splitters.
• These arbitrary phase beam splitters hold potential for advancing quantum information processing.