Ultra-High Extinction Dual-Output Thin-Film Lithium Niobate Intensity Modulator

A low voltage, wide bandwidth compact electro-optic modulator is a key building block in the realization of tomorrow’s communication and networking needs. Recent advances in the fabrication and application of thin-film lithium niobate, and its integration with photonic integrated circuits based in silicon make it an ideal platform for such a device. In this work, a high-extinction dual-output folded electro-optic Mach Zehnder modulator in the silicon nitride and thin-film lithium niobate material system is presented. This modulator has an interaction region length of 11 mm and a physical length of 7.8 mm. The device demonstrates a fiber-to-fiber loss of roughly 12 dB using on-chip fiber couplers and DC half wave voltage (
$\text{V}\pi $
) of less than 3.0 V, or a modulation efficiency (
$\text{V}\pi \cdot \text{L}$
) of 3.3
$\text{V}\cdot $
cm. The device shows a 3 dB bandwidth of roughly 30 GHz. Notably, the device demonstrates a power extinction ratio over 45 dB at each output port without the use of cascaded directional couplers or additional control circuitry; roughly 31 times better than previously reported devices. Paired with a balanced photo-diode receiver, this modulator can be used in various photonic communication systems. Such a detecting scheme is compatible with complex modulation formats such as differential phase shift keying and differential quadrature phase shift keying, where a dual-output, ultra-high extinction device is fundamentally paramount to low-noise operation of the system.