Generalized Tensor Analysis Model for Multi-Subcarrier Analog Optical Systems

We propose and develop a general tensor analysis framework for a subcarrier multiplex analog optical fiber link for applications in microwave photonics. The goal of this work is to construct an uniform method to address nonlinear distortions of a discrete frequency transmission system. We employ tensorial representation, i.e., multidimensional arrays, to unify the multi-subcarrier intermodulation effect. Based on the tensorial expression of the optical field in a subcarrier vector space, various kinds of modulation methods, dispersive transmission as well as detection schemes are specified. In addition, it is demonstrated that each corresponding tensor is formally determined by device structures, which allows for a synthesized study of device combinations more systematically. For implementing numerical methods, the practical significance of the tensor model is it simplifies the derivation details compared with series-based approaches by hiding the underlying multi-fold summation and index operation. The integrity of the proposed methodology is validated by investigating the classical intensity modulated system. Furthermore, to give an application model of the tensor formalism, we make a study of two multi-subcarrier systems with detailed performance discussions. We believe the tensor model provides us not only a consolidated notation, but also an alternative numerical approach to effectively analyze multi-subcarrier analog optical systems.

I. Introduction

Microwave photonics (MWP), which combines microwave engineering and optoelectronics, is a fast emerging technology and has been developed and investigated intensively for various applications, such as wireless communications, sensor networks and radar [1]–[3]. Taking advantage of the ultrawide bandwidth and the extremely low loss of optical fiber, the convergence of microwave signals and optical fiber has prospects for applications of analog fiber links. In recent years, with the emergence of high-speed wireless access and ultra-fast waveform generation, analog fiber systems operating in a spectral range of multi-gigahertz are highly desirable. Therefore, high-speed photonic devices such as external modulators have become key components in analog fiber systems, as well as the use of diverse modulation formats [4], [5]. Meanwhile, subcarrier multiplexing technology is also widely employed in order to carry multi-service signals or form a customizable waveform using harmonic generation technologies [6]–[8]. The various applications of subcarrier multiplexing and the use of state-of-the-art photonic components provide a strong motivation to develop a generalized model to analyze multi-subcarrier analog optical fiber systems.