Nonlinear Mach-Zehnder interferometer isolator

Abstract

Isolators are important devices in optics, especially for low noise systems, as even a small amount of back reflection can be detrimental to the quality of the signal generated by the source impacting downstream applications. Traditionally, magneto-optical materials have been used in isolators for bulk and fiber based optical systems. However, they tend to have high insertion loss, and are complicated to integrate on a photonics chip. Another class of isolators is based on optical nonlinearity that do not require external magnetic bias. However, the devices demonstrated so far suffer from either limited bandwidth, high insertion loss or fabrication complexity. In this work, we demonstrate a monolithic, fully complementary metal-oxide-semiconductor compatible, nonlinear Mach-Zehnder interferometer isolator based on third order optical nonlinearity, that overcomes such issues. In this proof of principle study, we show up to 15 dB isolation with 0.4 dB insertion loss and a device footprint of 0.4 mm2 which can easily be improved on further. The device is broadband and is independent of wavelength, material, and the platform. Not only can such a device be used for integrated optical systems but also for the fibre based optical systems.