Broadband MIMO all-optical unitary converter based on compact multimode interference on LNOI.

Area of Science:

• Photonics
• Integrated Optics
• Optical Signal Processing

Background:

• Multi-input multi-output (MIMO) optical signal processing is crucial for advanced communication systems.
• All-optical unitary converters (OUCs) are key components for performing complex optical transformations.
• Existing OUCs often face limitations in bandwidth, size, or insertion loss.

Purpose of the Study:

• To propose and demonstrate a reconfigurable 4x4 MIMO OUC.
• To enhance operational bandwidth and reduce device footprint compared to previous designs.
• To leverage the lithium-niobate-on-insulator (LNOI) platform for high-performance integrated photonics.

Main Methods:

• Utilized non-uniform multimode interference (nMMI) couplers to replace traditional uniform MMI couplers.
• Designed and fabricated a 4x4 OUC on an LNOI platform.
• Characterized the device performance, including loss, crosstalk, and operational bandwidth.

Main Results:

• Achieved a reconfigurable four-mode demultiplexing functionality.
• Demonstrated broadband operation over a 100 nm wavelength range (1520 nm to 1620 nm).
• Exhibited low wavelength-dependent loss (< 3 dB) and low crosstalk (< -17.3 dB).
• Achieved low insertion loss of ~0.21 dB/coupler at 1550 nm.

Conclusions:

• The proposed nMMI-OUC offers significant advantages in terms of bandwidth, compactness, and low loss.
• The LNOI platform is suitable for fabricating high-performance integrated optical devices.
• This nMMI-OUC is a promising building block for future reconfigurable optical signal processing systems.