Refractive index sensing in a monolithic micro-optofluidic lithium niobate chip

Area of Science:

• Materials Science
• Optoelectronics
• Microfluidics

Background:

• Lithium niobate (LiNbO3) possesses excellent electro-optic, acousto-optic, and nonlinear properties.
• These properties make it suitable for integrated photonic devices and lab-on-a-chip applications.

Purpose of the Study:

• To fabricate and demonstrate a monolithic optofluidic refractive index sensor on a lithium niobate platform.
• To evaluate the sensor's sensitivity, accuracy, and repeatability for potential lab-on-a-chip applications.

Main Methods:

• Fabrication of a microfluidic channel in lithium niobate using femtosecond laser inscription and selective etching.
• Smoothing of the microchannel surfaces via annealing.
• Characterization of the sensor's performance using sucrose solutions and an air-filled channel.

Main Results:

• A high-contrast (24 dB) Fabry-Pérot interference spectrum was achieved, indicating good optical quality.
• The sensor demonstrated a sensitivity of 1215 nm RIU⁻¹ at 1554 nm.
• Refractive index changes of 10⁻³ were measured with high accuracy (8.5 × 10⁻⁵) and low repeatability error.

Conclusions:

• The fabricated lithium niobate optofluidic sensor shows promise for integrated lab-on-a-chip devices.
• The device exhibits excellent performance metrics for refractive index sensing.
• Femtosecond laser-based fabrication offers a viable route for creating complex optofluidic devices in lithium niobate.