Design and Simulation of a Broadband Plasmonic Optical Isolator

Review Article

Ann Materials Sci Eng. 2021; 5(2): 1042.

# Design and Simulation of a Broadband Plasmonic Optical Isolator

Olyanasab A1 and Rostami A1,2*

¹Photonics and Nanocrystals Research Lab (PNRL), University of Tabriz, Tabriz, Iran

²SP-EPT Lab, ASEPE Company, Industrial Park of Advanced Technologies, Tabriz, Iran

*Corresponding author: Ali Rostami, Photonics and Nanocrystals Research Lab (PNRL), University of Tabriz, Tabriz, Iran; SP-EPT Lab, ASEPE Company, Industrial Park of Advanced Technologies, Tabriz, 5364196795, Iran

Received: August 25, 2021; Accepted: September 29, 2021; Published: October 06, 2021

## Abstract

In this paper, a new approach for optical isolator based on the Plasmonic effect is proposed. Metallic nanoparticles of different sizes are used to realize the proposed idea. Metallic nanoparticles spin-coated on alumina thin layer that is coated on Silicon waveguide. We demonstrated that the proposed idea operates in a broadband spectral range (more than 800nm) as well as back-propagating wave attenuated more than 120dB. The proposed idea can enhance the isolation ratio and also can provide wider bandwidth for isolation. The proposed idea is based on solution process nanotechnology that is simple, low cost, and available.

Keywords: Optical isolator; Broadband isolation; Nanoparticles; Fe Nanoparticles; Isolation ratio

## Introduction

An optical isolator or optical diode is a device that restricts light to travel in one direction and allows it to go in another direction. An optical isolator is an essential device in optical communication systems and lasers. It prevents back reflections of light, which could damage other devices. A variety of optical isolators have been proposed over the past years. Rayleigh proposed the first optical isolator which was designed utilizing a Faraday rotator and two polarizers. The origin of non-reciprocity was the Faraday rotator. Because of its magnetically induced anisotropy, the light traveling in two directions along the device rotates differently. By using the polarizers, the light gets blocked in one direction. Rayleigh’s isolator had some major problems. It could not function as a broadband isolator because the rotator depends on wavelength. The second problem is the strong magnetic field, which was used to induce anisotropy to the rotator. Also, it is challenging to make magnets in smaller sizes, which means this device is bulky and could not be integrated with other devices. Additionally, the magnetic field and Verdet constant are temperature-dependent which makes designing this isolator difficult. Strong dependency on the length of the rotator is another difficulty of this isolator. Some of these issues are remained as a problem for fabrication and developing optical isolators. The primary parameters of an optical isolator are isolation ratio, insertion loss, and bandwidth. To gain a high isolation ratio, low insertion loss, and broad bandwidth several works have been done. In most of the structures, iron or garnet was used as the main material and the anisotropy was induced to the iron or garnet by a magnetic field. Table 1 shows the main parameters of the proposed structures. Broad bandwidth and high isolation have not been reached in the presented works and a broadband isolator with high isolation is strongly needed.