LNOI Three-Channel Mode Multiplexer Covers 800 Nanometers

Photonic integrated circuits need a way to carry more data without crowding everything onto one path. Mode-division multiplexing offers one answer. It lets several optical mode signals share a single channel, including a multimode waveguide. That can raise the capacity of a communication system.

A mode (de)multiplexer is central to this process. It changes separate single-mode signals into matching multimode signals. It then joins them inside the same physical channel. The device can also reverse the process.

A new design uses subwavelength grating structures to redistribute the optical field. It is made on lithium niobate on insulator, or LNOI. This approach is intended to support mode conversion across a much wider wavelength range.

For a proof of concept, a three-channel mode (de)multiplexer was designed and fabricated. Simulations predict an operating bandwidth of 800 nanometers, from 1.2 to 2.0 micrometers, with insertion loss below 1 decibel. Tests from 1500 to 1600 nanometers found insertion loss under 1.0 decibel and crosstalk below -15.9 decibels for every device. The measured results broadly matched the simulations, supporting the potential of high-performance photonic integrated circuits on the LNOI platform.