Mode switch based on electro-optic long-period waveguide grating in lithium niobate.

Area of Science:

• Photonics
• Optical Engineering
• Materials Science

Background:

• Mode-division multiplexing (MDM) is a promising technique for increasing optical communication capacity.
• Efficient and reconfigurable mode converters are crucial components for MDM systems.
• Lithium niobate (LN) is a well-established material for electro-optic devices due to its excellent optical and electro-optic properties.

Purpose of the Study:

• To propose and demonstrate a novel electro-optic mode switch.
• To investigate the performance of a long-period grating in a lithium-niobate two-mode waveguide for mode switching.
• To assess the device's suitability for reconfigurable mode-division-multiplexing systems.

Main Methods:

• Fabrication of an 8 mm long grating in a proton-exchanged z-cut LN waveguide.
• Characterization of the mode switching performance under an applied driving voltage.
• Measurement of mode extinction ratio, 3-dB bandwidth, and temperature insensitivity at a wavelength of 1544 nm.

Main Results:

• Successful demonstration of mode switching between fundamental and higher-order modes at 35 V.
• Achieved a mode extinction ratio of -18 dB and a 3-dB bandwidth of approximately 25 nm.
• Observed that the device performance is insensitive to temperature variations, with experimental results aligning well with simulations.

Conclusions:

• The fabricated electro-optic long-period grating in LN waveguide functions effectively as a mode switch.
• The device exhibits high performance metrics (extinction ratio, bandwidth) and robustness against temperature changes.
• This mode switch is a viable candidate for future reconfigurable mode-division-multiplexing systems.