Optical Frequency Comb and Active Demultiplexer-enabled 60 GHz mmW ARoF Transmission using Directly Modulated 64-QAM UF-OFDM signals

Abstract

Over the past decade, the global demand for communication capacity has seen a continous growth, fuelled mainly by the proliferation of smart devices, ultra-high-definition multimedia and cloud-based services. To fulfil this incessant growth a high network capacity and high data rate is required. This can only be met by the 5 th generation (5G) of mobile systems with millimetre-wave (mmW) frequencies (>28 GHz), where large bands of un-allocated spectrum are available [1] . A promising cost reduction approach for the implementation of 5G is to use the centralized or cloud radio access network (C-RAN) scenario. CRAN consists of a pool of baseband processing units (BBU) connected with remote radio units (RRU) by an optical fiber or mmW wireless link [2] . Further savings can be achieved by employing an analog radio over fiber (ARoF), a transmission method, where the mmW signal is generated at RRU by means of optical heterodyning (OH) [3] . OH is the promising technique used to generate low phase noise mmW signals. Amongst many approaches to OH, the use of optical frequency combs (OFCs) [4] enables a cost-efficient generation of multiple high quality RF signals simultaneously. This stems from the fact that an OFC consists of a number of tones with precise channel spacing and excellent phase correlation between them. However, the division of power of the laser across the multiple tones of the OFC, results in low output power per the individual tone. This issue is worsened by the insertion losses of passive demultiplexers and external modulators. We have recently demonstrated that this challenge can be overcome by employing an active demultiplexer [5] . Such a device can simultaneously filter, amplify and modulate the demultiplexed OFC tone. In this paper, we generate 60 GHz ARoF signals, using an OFC and two active demultiplexers, and transmit it over 40 km of standard single-mode fiber (SSMF), achiving BER below the hard decision (HD-) FEC limit of 3.8e-3.