Optical single sideband polarization modulation
for radio-over-fiber system and microwave
photonic signal processing
Yamei Zhang, Fangzheng Zhang, and Shilong Pan*
Key Laboratory of Radar Imaging and Microwave Photonics, Ministry of Education,
Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
*Corresponding author: pans@ieee.org
Received March 17, 2014; revised June 27, 2014; accepted June 28, 2014;
posted July 1, 2014 (Doc. ID 208376); published August 1, 2014
An approach to implementing optical single sideband (OSSB) polarization modulation, which is a combination of
two orthogonally polarized OSSB modulations with complementary phase differences between the optical carrier
and the sideband, is demonstrated based on two cascaded polarization modulators (PolMs). The two PolMs are
driven by two RF signals that are 90° out of phase. By properly adjusting the polarization state between the two
PolMs, OSSB polarization modulation with large operation bandwidth can be realized. An experiment is
performed. OSSB polarization modulation with an operation bandwidth from 2 to 35 GHz is successfully dem-
onstrated. The spectral profile of the OSSB polarization-modulated signal is observed through an optical spectrum
analyzer, and its complementary phase properties are analyzed by sending the signal to a photodetector (PD) for
square-law detection. Due to the complementary phase differences between the optical carrier and the sideband
along the two polarization directions, no microwave frequency component is generated after the PD. The gener-
ated OSSB polarization-modulated signal is transmitted through 25 and 50 km single-mode fiber with 50 Mbaud
16 quadrature amplitude modulation baseband data to investigate the transmission performance of the proposed
system in radio-over-fiber applications, and very small error vector magnitude degradation is observed. OSSB
polarization modulation is also employed to realize a microwave photonic phase shifter. A full-range tunable
phase shift is obtained for 2 and 35 GHz microwave signals. © 2014 Chinese Laser Press
OCIS codes: (060.5625) Radio frequency photonics; (130.4110) Modulators; (070.1170) Analog optical sig-
nal processing.
http://dx.doi.org/10.1364/PRJ.2.000B80
1. INTRODUCTION
Radio-over-fiber (ROF) technology has attracted a lot of
attentions thanks to its capability for low-loss transmission
of microwave/millimeter-wave signals over broadband optical
fibers [
1–3]. Optical single sideband (OSSB) modulation is
regarded as one of the most promising techniques to deal with
chromatic dispersion-induced power fading and improve the
spectral efficiency in ROF systems [
4]. Many methods have
been proposed to implement OSSB modulation over the past
few decades [
5–17]. For instance, OSSB modulation can be
realized by using a single sideband modulator, which can
be a dual-drive Mach–Zehnder modulator (MZM) [
5,6], four
parallel phase modulators [
7,8], a hybrid modulator consisting
of an amplitude modulator and a phase modulator [
9], two
parallel electro-absorption modulators (EAMs) [
10], or a bidi-
rectional intensity modulator placed inside a Sagnac interfer-
ometer (SI) [
11]. By carefully controlling the phase difference
between the input RF signals (usually π∕2), one of the first-
order sidebands can be suppressed. OSSB modulation can
also be achieved by passing a double sideband (DSB) signal
through an optical filter [
13–17]. In this approach, a DSB signal
is first generated by intensity or phase modulating an optical
carrier with an electrical RF signal. An optical filter, which can
be a fiber Bragg grating (FBG) [
13–15], a stimulated Brillouin
scattering (SBS) based filter [
16], or a ring resonator [17], is
followed to remove one of the first-order sidebands.
However, the above methods can only achieve OSSB
modulation along a single polarization direction. Recently,
a concept called OSSB polarization modulation is proposed
[
18], which is actually a combination of two complementary
OSSB modulations along the two orthogonal polarization
axes; i.e., the subtraction of the phase differences between
the optical carrier and the remaining sideband along the two
orthogonal polarization axes is 180°. OSSB polarization modu-
lation has been demonstrated with more flexibilities over the
conventional single-polarization OSSB modulation [
18–24].
For example, in [
18], the OSSB polarization-modulated signal
is sent into a length of polarization maintaining fiber (PMF) to
introduce different time delays along the two principal axes,
based on which an ultrawideband (UWB) microwave pho-
tonic filter (MPF) is constructed and used in a UWB signal
generator. In [
19], by introducing a 90° phase shift to one prin-
cipal axis of the OSSB polarization-modulated signals and
then combining the two orthogonally polarized OSSB signals
with a tunable polarizer, a microwave photonic phase shifter
is obtained, which features full-range tunability, flat magni-
tude response, large operation bandwidth, and the potential
for high-speed tuning. Based on the microwave photonic
phase shifter in [
19], a high-speed photonic microwave phase
B80 Photon. Res. / Vol. 2, No. 4 / August 2014 Zhang et al.
2327-9125/14/040B80-06 © 2014 Chinese Laser Press