Breaking dense integration limits: inverse-designed lithium niobate multimode photonic circuits.

Area of Science:

• Photonics
• Materials Science
• Integrated Optics

Background:

• Thin film lithium niobate (TFLN) is a promising material for photonic integrated circuits (PICs).
• Challenges include moderate refractive index, CMOS-incompatibility, and material anisotropy, hindering dense integration.
• Achieving dense integration comparable to silicon photonics while retaining TFLN's superior properties is a key goal.

Purpose of the Study:

• To develop a photonic inverse design method for miniaturizing TFLN PIC components.
• To demonstrate the feasibility of dense integration for TFLN-based photonic circuits.
• To enable high-capacity data communications using miniaturized TFLN devices.

Main Methods:

• Photonic inverse design methodology applied to TFLN.
• Experimental fabrication of ultra-compact components: mode-division (de)multiplexers, multimode waveguide crossings, and waveguide bends.
• Construction of multimode photonic circuits and integration with electro-optic modulators.

Main Results:

• Demonstrated ultra-compact components: mode-division (de)multiplexer (19×25 μm²), waveguide crossing (15×15 μm²), and 30 μm bending radius.
• Achieved dense integration of over 10 waveguide elements within a 0.06 mm² chip area.
• Demonstrated high-speed data modulation at 120 Gbps per channel with multimode signal transmission.

Conclusions:

• Photonic inverse design significantly enhances the integration density of TFLN PICs.
• This advancement facilitates the development of compact, high-capacity optical communication systems.
• The method is expected to increase TFLN passive component area density by tenfold.