A tunable FP Perot coupling interferometer on thin-film lithium niobate

This paper presents the development of a tunable Fabry-Perot (FP) interferometer on a thin-film lithium niobate (TFLN) platform. The device utilizes electro-optic (EO) and thermo-optic (TO) tuning methods to modulate the reflectivity of the FP cavity mirrors, enabling efficient and fast tuning. This system is demonstrated to operate with a modulation voltage as low as 3.5 V and a short modulation length of 3.5 mm.

Key points include:

1. Device Design: The FP cavity is designed using cascaded Mach-Zehnder interferometers (MZIs) with loop mirrors. The reflectivity of the mirrors is modulated by tuning the phase difference between the arms of the MZIs using either electro-optic or thermo-optic methods.

2. Fabrication Process: The device is fabricated on a TFLN wafer with waveguides and directional couplers (DCs) created using photolithography and dry etching. Thermal tuners are implemented using NiCr heaters, and electro-optic tuning is done using co-planar waveguide (CPW) electrodes.

3. Measurement Results: The performance of the FP cavity is measured under both thermal and electro-optic tuning conditions. The reflectivity of the cavity mirrors is modulated by adjusting the heater voltages, and the quality factor (Q) of the cavity is tuned from 40,000 to 200,000. The transmission of the FP cavity is also modulated using electro-optic tuning, achieving a full modulation with just 3.5 V.

4. Applications: This tunable FP cavity is applicable to high-speed electro-optic modulation, on-chip lasers, wavelength division multiplexing, nonlinear frequency conversion, and quantum light generation.

In conclusion, this work demonstrates a compact and efficient tunable FP interferometer on the TFLN platform, with potential applications in photonic technologies requiring precise modulation, such as high-speed communication and quantum optics.