Bias-Free Silicon-Based Optical Single-Sideband Modulator Without 2nd-Order Sideband

Abstract

In this paper, a bias-free silicon optical single-sideband (OSSB) modulator without 2nd-order sideband is proposed and theoretically investigated. The proposed modulator is based on a dual-drive Mach-Zehnder modulator (DDMZM) and silicon photonics platform. In the proposed structure, a piece of silicon waveguide is used in one of the arms of the unbalanced DDMZM which acts as a bias for the modulator. So, the operating point of the modulator can be tuned by adjusting the optical wavelength. Analytical models for all the components in the structure are derived and closed-form expressions are found for optical transmission, optical spectrum, etc. Modulator nonlinear behavior under small and large signal modulation is discussed. Conditions on the optical wavelength to have an OSSB modulated signal with/without 2nd-order sideband are found. It has also shown that optical carrier-to-sideband ratio (OCSR) can be tuned by adjusting the applied voltage. By proper adjusting the applied voltage, suppressed carrier or equal carrier to the first sideband can be obtained in OSSB modulator without 2nd-order sideband. Analytical results are verified by simulations and previously reported measurement data. The proposed analytical model is a general model that can be used for any nonlinear electro-optic modulators such as phase and absorption modulators.