Electro-Absorption Modulator in Lithium Niobate

Abstract

LLithium niobate presents a good choice for integrated optics in optical communications and networks applications. Titanium diffused waveguides in lithium niobate are low loss and have a high coupling efficiency with single mode optical fibers at 1.55μm wavelength.

Lithium niobate has also been extensively used to fabricate modulators owing to its high electro-optic coefficients. The modulators fabricated in lithium niobate suffer primarily from large device footprint which makes it difficult to integrate variety of devices on a single chip.

To help overcome this limitation, two device design configurations for electro-absorption modulation is studied. The first architecture consists of a stack of Indium Tin Oxide (ITO)/SiO2/Au films on the lithium niobate waveguide. The second device configuration also consists of ITO/SiO2/Au stack but includes an additional extended TiO2 film over the waveguide. TiO2 film having a refractive index higher than lithium niobate shifts the optical field towards the surface of the waveguide. This helps to enhance light matter interaction with ITO which serves as the active material.

Simulation of the device architecture predicts 5.24dB extinction ratio for the first configuration on a 100μm device length, and 3.75dB extinction ratio for the second architecture with a 20μm modulator length. These are highest reported extinction ratio in lithium niobate based modulators for such a small device footprint.