Contents lists available at ScienceDirect Optical Fiber Technology journal homepage: www.elsevier.com/locate/yofte Regular Articles Simultaneous transmission of wired and wireless signals based on double sideband carrier suppression Mekuanint Agegnehu Bitew, Run-Kai Shiu, Peng-Chun Peng ⁎ , Cheng-Hao Wang, Yan-Ming Chen Department of Electro-Optical Engineering, National Taipei University of Technology, Taipei, Taiwan ARTICLE INFO Keywords: Hybrid transmission Dual-output mach-zehnder modulator Double sideband carrier suppression Optical fiber communication ABSTRACT In this paper, we proposed and experimentally demonstrated simultaneous transmission of wired and wireless signals based on double sideband optical carrier suppression. By properly adjusting the bias point of the dual- output mach-zehnder modulator (MZM), a central carrier in one output port and a pair of first-order sidebands in another output port are generated. The pair of first-order sidebands are fed into a second MZM to generate second-order order sidebands. A wired signal is embedded on the central carrier while a wireless signal is embedded on the second-order sidebands. Unlike other schemes, we did not use optical filter to separate the carrier from the optical sidebands. The measured bit error rate (BER) and eye-diagrams after a 25 km single- mode-fiber (SMF) transmission proved that the proposed scheme is successful for both wired and wireless signals transmission. Moreover, the power penalty at the BER of 10 -9 is 0.3 and 0.7 dB for wired and wireless signals, respectively. 1. Introduction The increase number of high capacity smart devices as well as broadband multi-media services available to the consumer demand high-speed wireless communications. As the frequency spectrum below 10 GHz is saturated, it is difficult to maintain an adequate bandwidth provision for the growing customer demand. Optical fiber commu- nication systems transmit information at higher bandwidth and longer distances than wire cables [1–3]. Radio-over-fiber (RoF) techniques have become attractive solutions in realizing future broadband wireless networks [4–7]. RoF systems have been proposed for many applications such as wireless access networks, sensors networks, and radars. The transmission rate of a data can be increased significantly using higher frequency carriers such as microwave and millimeter wave signals. Generation of millimeter and microwave signals in the optical domain is cost effective and not complex as in the electrical domain. Moreover, distribution of microwave or mm-wave signal in the electrical domain is not practical due to the high attenuated signal loss transmitted through electrical distribution lines, such as coaxial cable. Hence, generation and distribution of microwave or millimeter wave signals in an optical domain greatly simplifies the equipment requirement and distribute a signal through an optical fiber from a central station to a remote base station with a low signal loss. Microwave or millimeter-wave signal generation techniques in the optical domain can be categorized into three main groups: optical phase locking between two laser diodes, direct beating of a dual-wavelength laser at a photodetector, and external modulation [8–12]. Among these three signal generation techniques, high-spectrum-purity and low phase-noise microwave or mm-wave can be achieved using the external modulation technique. External modulation schemes proposed in [13–15] simultaneously generate and transmit wired and wireless sig- nals based on RoF systems. These schemes require optical filters in order to separate the optical carrier from the second-order sidebands. However, optical filters are affected by temperature and may not be accurate enough to select the center frequency of the laser source. A bidirectional RoF scheme proposed in [16] uses MZM to simultaneously generate baseband, microwave and millimeter wave signals. Besides the optical filter requirement, the modulated data in millimeter wave, mi- crowave and baseband are identical. Millimeter wave generation schemes proposed in [17–20] use cascaded single-electrode Mach- Zehnder modulators (SEMZM) without optical filter based on double- sideband suppressed-carrier modulation. These schemes are cost ef- fective and advantageous to maximize receiver sensitivity and spectral efficiency with low power penalty. However, the schemes designed for only wireless access services; i.e., these schemes don’t provide wired and wireless access services simultaneously. This paper proposes and experimentally demonstrates simultaneous transmission of wired and wireless signals using dual-output MZM without implementing optical filter. Properly biasing the dual-output MZM to a null point generates a carrier and two first-order sidebands http://dx.doi.org/10.1016/j.yofte.2017.09.006 Received 6 July 2017; Received in revised form 1 September 2017; Accepted 5 September 2017 ⁎ Corresponding author. E-mail address: pcpeng@ntut.edu.tw (P.-C. Peng). Optical Fiber Technology 38 (2017) 108–112 1068-5200/ © 2017 Elsevier Inc. All rights reserved. MARK