Electro-optically tunable super-broadband filter based on long period grating in Ti:LiNbO₃ waveguide

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Integrated Optics

Background:

• Optical filters are crucial components in various photonic systems.
• Electro-optic tunability offers dynamic control over optical signal processing.
• Lithium niobate (LiNbO3) is a key material for integrated optics due to its electro-optic properties.

Purpose of the Study:

• To demonstrate an electro-optically tunable optical filter.
• To investigate the performance of a parallel structure with two long period gratings (LPGs).
• To explore the use of the photorefractive (PR) effect for tuning filter characteristics.

Main Methods:

• Fabrication of a Ti:LiNbO3 strip waveguide device with two parallel LPGs (675-μm and 880-μm pitch).
• Application of voltage to modulate the filter's stop-band contrast.
• Utilizing the PR effect for simultaneous resonant wavelength tuning.

Main Results:

• Achieved a linear increase in filter contrast up to ~30 dB with applied voltage (~300 V).
• Observed simultaneous linear tuning of the resonant wavelength, with ranges of 160 nm (675 μm pitch) and 200 nm (880 μm pitch).
• Demonstrated super-broadband filtering capability exceeding 360 nm using the dual-grating structure.

Conclusions:

• The proposed electro-optic tunable filter based on dual LPGs in Ti:LiNbO3 is effective for dynamic optical signal control.
• The PR effect enables simultaneous contrast modulation and wavelength tuning, crucial for advanced photonic applications.
• This device offers a pathway to realizing super-broadband tunable filtering in integrated photonic platforms.