Full-duplex WDM-RoF system based on OFC with dual frequency microwave signal generation and wavelength reuse

Highlights

• We have proposed a novel full duplex WDM-RoF system based on OFC with dual frequency microwave signal generation and wavelength reuse.

• In TOFC generator, we employ two EAMs and a FM to generate optical carriers.

• The optical carriers can be flexibly adjusted according to the needs of the WDM-RoF system, which greatly reduces the cost of the optical source.

• Some of optical carriers are reused in the BS to provide optical source for [1], [2], [3], [4], [11] uplink transmission, which avoids the use of lasers in the BS to reduce the cost of the WDM-RoF system.

• In the BS, dual frequency microwave signals are generated in the downlink.

• The downlink and uplink of this WDM-RoF system demonstrate superior transmission performance with the high receiver sensitivity and the smallest power penalty over long distance delivery.

• In the results, the average power penalties of 6 WDM channels each carrying 6 × 2.5 Gb/s data for the downlink and the uplink are less than 1 dB after 20 km SMF transmission.

• The receiver sensitivity of 6 WDM channels for uplink and downlink after 20 km SMF transmission is less than −25.2dBm and −15.6dBm, respectively.

• Moreover, the eye diagrams remain open for both the uplink and downlink after 40 km SMF transmission.

• Therefore, the proposed WDM-RoF scheme with good transmission performance and cost-efficient configuration provides a potential way in the next-generation broadband optical-wireless access networks.

Abstract

A novel full-duplex wavelength division multiplexing radio-over-fiber (WDM-RoF) system based on optical frequency comb (OFC), which can generate dual frequency microwave signal simultaneously and realize wavelength reuse for uplink transmission, is proposed. In this proposal, OFC, which serves as the optical carriers of the WDM-RoF network, is performed by cascading two electro-absorption modulators (EAMs) and a frequency modulator (FM). The optical carriers are modulated by the radio frequency (RF) signal in LiNbO₃ Mach-Zehnder modulator (LN-MZM) to produce multiple optical single sidebands (OSSB). The multiple OSSB signals are divided into multiple individual channels by AWG, and each channel contains two optical carriers and two corresponding +1 order sidebands. The first optical carrier of each channel is reflected by fiber bragg grating (FBG) and reused to provide the optical source for the uplink transmission in the base station (BS), which simplify the configuration of base station. Dual-frequency microwave signals are generated in the downlink by beating the remaining second optical carrier and two +1 order sidebands. In the simulation, 6 WDM channels each carrying 2.5 Gb/s downlink data have been up-converted to 15 GHz and 25 GHz microwave signals simultaneously, and 6 WDM channels each carrying 2.5 Gb/s uplink baseband data are sent to the central station. Both downlink and uplink transmission with less than 1 dB power penalty on average after 20 km SMF transmission. This full-duplex WDM-RoF system shows high spectral-efficiency, large communication capacity, simple cost-efficient configuration and good performance over long distance transmission.

Introduction

With the rapid increase of the mobile communication services, the spectrum resources of low frequency bands are becoming more and more crowded [1], [2], [3]. In order to solve this problem, attention is focused on the higher frequency microwave band due to its greater communication capacity and higher data transmission rate [4]. However, the propagation distance of high frequency microwave signals is greatly limited for wireless communication due to the fact that the high frequency microwave is subjected to high atmospheric attenuation and the poor diffraction [5], [6].

Radio over fiber (RoF) system combines the advantages of optical fiber communication and wireless communication to effectively solve limited coverage of high frequency microwaves signals [7], which has the advantages of low loss, wide bandwidth, long-distance transmission, strong anti-interference ability, low cost and easy maintenance. In order to further improve the communication capacity of the RoF system and reduce the construction cost, the WDM-RoF system is formed by combining the RoF system with the wavelength division multiplexing (WDM) technology. The WDM-RoF system can achieve seamless connection between wired and wireless networks, and meet the needs of high-speed, large-capacity in future mobile communication systems [8], [9].

In recent years, many WDM-RoF schemes have been investigated. Most of them only studied downlink communication and lacked the research on uplink communication [10], [11], [12], [13]. In some full-duplex WDM-ROF systems, multiple independent lasers serve as the optical carriers [14], [15], [16], which increases the cost and complexity of the system. A few schemes only generate single-frequency microwave signal in the base station [17], [18], which hardly meet the demands of base station in different occasions. A full-duplex broadcast RoF-WDM-PON with self-coherent detection and photonic frequency up/down-conversion was presented [19], in which base station cost is significantly increased and stability is reduced due to the complexity of the base station structure. A full-duplex WDM-RoF system based on tunable optical frequency comb generator was proposed [20], in which only 5 optical carriers are used among the numerous optical carriers in each base station, resulting in low spectral-efficiency of the whole system.

In this work, we propose a novel full-duplex WDM-RoF system based on optical frequency comb. For the convenience of research, we study the downlink of this scheme using broadcast communication instead of multi-channel modulation. The flat optical frequency combs generated by cascaded EAMs and FM are used as the optical carriers of the WDM-RoF system, so the complexity and cost of the system are greatly reduced. In addition, this WDM-RoF system with optical carrier reuse can realize the uplink transmission without any local optical sources in the base station. Meanwhile, dual frequency microwave signals are generated in the base station for wireless communication. The feasibility and transmission performance of our scheme are successfully verified by Optisystem software. This paper is organized as follows. Section 2 describes the principle and theoretical analysis of the proposed full-duplex WDM-RoF system. In section 3, the simulation results and performances of the full-duplex WDM-RoF system are discussed. Finally, the conclusions are presented in section 4.