Ultra-high extinction dual-output thin-film lithium niobate intensity modulator

TL;DR

This paper presents a high-performance, dual-output thin-film lithium niobate electro-optic modulator with ultra-high extinction ratio, low voltage operation, and wide bandwidth, suitable for advanced photonic communication systems.

Contribution

It introduces a novel dual-output folded Mach Zehnder modulator with record extinction ratio and low voltage, advancing integrated photonic modulation technology.

Findings

Extinction ratio over 45 dB at each output port

Vπ less than 3.0 V with 3.3 V·cm efficiency

Bandwidth of approximately 30 GHz

Abstract

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 (V$\pi$) of less than 3.0 V, or a modulation efficiency (V$\pi\cdot$L) of 3.3 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.