Optical up-conversion for WDM-RoF transmission using multiple
optical carrier suppression in OFCG
Chan Zhang
a,b
, TiGang Ning
a,b
, Jing Li
a,b,
n
, Hongyao Chen
a,b
, Chao Li
a,b
, Zhiming Liu
c
a
Key Lab of All Optical Network & Advanced Telecommunication Network of EMC, Beijing Jiaotong University, Beijing 100044, China
b
Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China
c
The 41st Institute of China Electronics Technology Group Corporation, Qingdao 266555, China
article info
Article history:
Received 27 April 2015
Received in revised form
30 July 2015
Accepted 18 August 2015
Keywords:
WDM-RoF
Optical comb
Up-conversion
abstract
A tunable optical frequency comb generator (OFCG) by cascading an Electro-absorption modulator (EAM)
followed by a phase modulator (PM) and an intensity modulator (IM) is proposed for wavelength division
multiplexing radio-over-fiber (WDM-RoF) transmission. The generated OFCG serves as the carriers of
WDM-RoF system to realize all-optical up-conversion afterwards. In the proposal, each comb line is
modulated by the radio-frequency (RF) signal via multiple optical carrier suppression (OCS) after optical
comb generation. We have systematically compared the performances of the optical up-conversion based
on different modulation schemes. Among three schemes, the OCS modulation scheme shows the highest
receiver sensitivity and smallest power penalty over long-distance transmission. What's more, the OCS
modulation scheme can be easily implemented with a large number of WDM channels simultaneously
without any power saturation or other nonlinear impact. In the numerical simulation, 15 WDM channels
each carrying 15 Gb/s 5 Gb/s baseband signal have been up-converted to 10 GHz simultaneously. This
method still provides high performance after 20 km transmission, which shows simple cost-efficient
configuration and good performance over long distance delivery.
& 2015 Published by Elsevier Ltd.
1. Introduction
Recently, RoF technology has become an attractive solution to
increase capacity and speed as well as to reduce overall costs in
wireless communication [1,2]. In RoF systems, microwave signals
are delivered over an optical network from a central station (CS) to
a number of base stations (BSs). It is necessary to minimize the
cost of the BS and the complexity of the system. In addition, all-
optical up-conversion is one of the key techniques in RoF systems.
A few schemes for optical millimeter-wave generation and up-
conversion have been reported using external modulators based
on different modulation schemes including double-sideband
(DSB), single-sideband (SSB), and OCS [3–5]. Therefore, chromatic
dispersion should be considered for successful data transmission
in RoF system. Although SSB modulation is superior to DSB due to
its reduced effects in suffering dispersion in optical fiber, the re-
ceiver sensitivity of SSB is quite low. Compared with aforemen-
tioned schemes, OCS modulation shows the highest receiver sen-
sitivity, highest spectral efficiency, smallest power penalty over
long-distance delivery as well as lowest bandwidth requirement
for both electrical and optical components. Furthermore, the OCS
modulation can be easily implemented with a large number of
WDM channels simultaneously [10,11]. In order to further increase
the bandwidth and the capacity of wireless system, the WDM
technique has been employed in RoF systems [6–9], which means
WDM-RoF. For WDM-ROF system, one key issue is to develop a
compact and cost-effective optical source to reduce the cost and
consumption of the system. In most cases, mode-locked laser, a
DFB array or a super-continuum light source are employed as the
WDM optical source to provide multiple WDM channels [12–14].
However, the mode-locked laser is very expensive compared with
a CW laser. And, the overall cost increases a lot as the required
sources increase. Moreover, when a large number of independent
lasers are utilized, the number of WDM channels is limited due to
the difficulty of managing many independent lasers which is too
complicated and inevitably reduces the scalability and re-config-
urability of the WDM system. The lower spectral efficiency may
considerably decrease the transmission capacity and performance
of the link.
One key issue with WDM-RoF networks is to develop a com-
pact and cost-effective optical transmitter for the system. OFCG
has attracted great interest due to its widespread applications in
arbitrary waveform generation [15,16], signal processing [17], and
Contents lists available at ScienceDirect
journal homepage: www.elsevier.c om/locate/optlastec
Optics & Laser Technology
http://dx.doi.org/10.1016/j.optlastec.2015.08.014
0030-3992/& 2015 Published by Elsevier Ltd.
n
Corresponding author at: Key Lab of All Optical Network & Advanced Tele-
communication Network of EMC, Beijing Jiaotong University, Beijing 100044, China.
E-mail address: lijing@bjtu.edu.cn (J. Li).
Optics & Laser Technology 77 (2016) 91–97