Microwave photonics: radio-over-fiber links, systems,
and applications [Invited]
Kun Xu,* Ruixin Wang, Yitang Dai, Feifei Yin, Jianqiang Li, Yuefeng Ji, and Jintong Lin
State Key Laboratory of Information Photonics & Optical Communications (Beijing University of Posts and
Telecommunications), P.O. Box 55 (BUPT), Beijing 100876, China
*Corresponding author: xukun@bupt.edu.cn
Received March 17, 2014; revised June 18, 2014; accepted June 19, 2014;
posted June 20, 2014 (Doc. ID 208382); published July 14, 2014
Microwave photonics (MWPs) uses the strength of photonic techniques to generate, process, control, and distrib-
ute microwave signals, combining the advantages of microwaves and photonics. As one of the main topics of
MWP, radio-over-fiber (RoF) links can provide features that are very difficult or even impossible to achieve with
traditional technologies. Meanwhile, a considerable number of signal-processing subsystems have been carried
out in the field of MWP as they are instrumental for the implementation of many functionalities. However, there
are still several challenges in strengthening the performance of the technology to support systems and applications
with more complex structures, multiple functionality, larger bandwidth, and larger processing capability. In this
paper, we identify some of the notable challenges in MWP and review our recent work. Applications and future
direction of research are also discussed. © 2014 Chinese Laser Press
OCIS codes: (060.5625) Radio frequency photonics; (060.0060) Fiber optics and optical communications;
(060.2360) Fiber optics links and subsystems; (060.4254) Networks, combinatorial network design; (120.3940)
Metrology.
http://dx.doi.org/10.1364/PRJ.2.000B54
1. INTRODUCTION
Microwave photonics (MWPs) is an interdisciplinary field
that studies the interaction between microwaves and light-
waves, combining in consequence the advantages brought
by both areas [
1–6]. In general, MWP uses the strength of
photonic techniques to generate, distribute, process, and an-
alyze microwave signals. Because of the inherent properties
of photonics, such as low loss transmission, there has been
an increasing effort to develop MWP techniques for different
applications, including broadband wireless access networks
[
7], satellite communications [8], optical signal processing
[
9], electronic warfare systems [10], and optical coherence
tomography techniques [
11]. Many of these application areas
demand ever-increasing values for speed, bandwidth, and dy-
namic range while at the same time requiring devices that
feature small size, lightweight and low-power performance,
large tenability, and strong immunity to electromagnetic
interference.
Radio-over-fiber (RoF) is one of the main topics of MWP,
providing features that are very difficult or even impossible
to achieve with traditional technology. In its simplest form, a
RoF link consists of a directly or externally modulated laser,
where one or more analog electrical signal placed at differ-
ent microwave frequencies is imposed on an optical carrier,
and a detector after the optical fiber link, where the micro-
wave signal is recovered from the optical carrier. The RoF
concept has numerous applications, such as phased-array an-
tennas and broadband wireless access networks. However,
the nonlinearity of the link generates mixing products of
the microwave carrier frequencies. The prominent problem
is the third-order intermodulation distortion (IMD3) since
it is in-band and cannot be filtered out. Therefore, the
nonlinearity of the system must be kept small to obtain a
high spurious-free dynamic range (SFDR). Besides, the envi-
ronment perturbations such as physical vibrations and tem-
perature fluctuations degrade the phase stability of the
microwave frequency. Therefore, the phase error must be
small to accomplish ultrastable microwave frequency deliv-
ery, which is useful in many modern metrology and funda-
mental physics applications, such as particle physics,
relativity tests, and radio astronomy.
On the other hand, a considerable number of signal
processing subsystems [
1,5,9] have been carried out in the
field of MWP as they are instrumental for the implementation
of many functionalities, including filtering, analog-to-digital
conversion, optical beam forming, broadband frequency
measurement, and photonic radio frequency (RF) signal
switching. However, there are still several challenges in
strengthening the performance of the technology to support
systems and applications with more complex structures,
multiple functions, larger bandwidths, and stronger process-
ing capabilities.
In this paper, we identify some of the notable challenges in
MWP and review our recent work in three main aspects:
(1) high linearity conversion and control between lightwaves
and microwaves in RoF links; (2) precise processing and han-
dling of broadband microwave signals; and (3) efficient utiliza-
tion and dynamic management of the resources in distributed
antenna systems (DASs).
The remainder of this paper is organized as follows. The
challenges are addressed and our corresponding work is
reviewed in Section
2. In Section 3, applications and future
directions are discussed. Finally, this paper is summarized
in Section 4.
B54 Photon. Res. / Vol. 2, No. 4 / August 2014 Xu et al.
2327-9125/14/040B54-10 © 2014 Chinese Laser Press
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