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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JLT.2017.2776276, Journal of
Lightwave Technology
JLT-21305-2017-final
Two Microwave Vector Signal Transmission on a
Single Optical Carrier Based on PM-IM Conversion
Using an On-chip Optical Hilbert Transformer
Yishi Han, Weifeng Zhang, Student Member, IEEE, Jiejun Zhang, Student Member, IEEE and Jianping Yao,
Fellow, IEEE, Fellow, OSA
Abstract— A new microwave photonic link (MPL) to
simultaneously transmit and detect two microwave vector signals
modulated on a single optical carrier based on orthogonal
modulation and optical Hilbert transformation is proposed and
demonstrated, for the first time to the best of our knowledge. In
the proposed system, two microwave vector signals are phase and
intensity modulated on a single optical carrier at a dual-parallel
Mach-Zehnder modulator (DP-MZM) and transmitted over a
single-mode fiber (SMF). At the receiver, the optical signal is
applied directly to a photodetector (PD) to recover the microwave
vector signal that is intensity modulated and the second microwave
vector signal is recovered by using an on-chip optical Hilbert
transformer (OHT) to perform phase-modulation to
intensity-modulation conversion followed by photodetection at a
second PD. An experiment is performed. The transmission of a
16QAM and a QPSK signal with a total data rate of 2.4 Gb/s over
a 10-km SMF is implemented. The performance of the
transmission in terms of error vector magnitude, bit error rate and
energy efficiency is evaluated.
Index Terms—Vector signal generation, phase modulation to
intensity modulation conversion, optical Hilbert transformer,
silicon microdisk resonator.
I. INTRODUCTION
hanks to the low propagation loss, ultra-broad bandwidth
and immunity to electromagnetic interference, microwave
photonic links (MPLs) have been considered a good solution for
wideband and low-loss microwave signal transmission and have
found numerous applications such as in radio over fiber
communications and antenna remoting [1, 2]. To meet the
ever-increasing demand of higher-data-rate transmission, future
wireless access networks are required to have a high spectrum
efficiency to maximize the use of the limited spectrum
resources. To reach this goal, advanced modulation formats can
be used. These advanced modulated signals are vector signals,
such as phase-shift keying (PSK) and quadrature-amplitude
modulation (QAM). The combination of the MPL transmission
technology and advanced signal modulation schemes can
further enhance the data transmission capacity, which has
become an active research topic recently [3-13].
To transmit a microwave vector signal over an optical fiber, a
microwave vector signal is usually generated in the electrical
domain and encoded on an optical carrier at an electro-optic
modulator for transmission over an optical fiber [3-5]. Since the
microwave vector signal generated in the electrical domain has
a low microwave carrier frequency, to have a high carrier
-frequency microwave vector signal, photonic techniques have
been proposed [6-11]. For example, an optical heterodyning
technique can be used to up-convert a low carrier-frequency
microwave signal to a high carrier-frequency. However, the
main problem associated with this technique is that only one
microwave vector signal is carried by an optical carrier, which
limits the spectrum efficiency. To have a high spectrum
efficiency, it is highly preferred that multiple microwave vector
signals could be carried by a single optical carrier and
transmitted over a single optical fiber. Recently, we proposed
two approaches to generate and transmit multiple vector
microwave signals that are carried by a single optical carrier
[12-13]. In [12], two microwave vector signals are modulated
on a single optical carrier and transmitted over a fiber at the
transmitter. At the receiver, coherent detection using a local
oscillator (LO) light source assisted with digital signal
processing (DSP) is performed to recover the two microwave
vector signals. To further enhance the spectrum efficiency [13],
four microwave vector signals are modulated on a single optical
carrier, and the detection of the four microwave vector signals is
performed based on coherent detection and DSP using an
advanced algorithm. Although coherent detection-based MPL
could offer an increased spectral efficiency and improved
receiver sensitivity, an expensive coherent receiver, an LO light
source and a high-speed DSP unit are needed, which would
make the system implementation complicated and costly.
To have a high spectrum efficiency while maintaining a
s
imple configuration, in this paper we propose and demonstrate
an MPL to simultaneously transmit two microwave vector
signals modulated on a single optical carrier based on intensity
Manuscript received September 29, 2017. This work was supported by the
Natural Sciences and Engineering Research Council of Canada. The work of
Y. Han was supported in part by the National Science Foundation of China
(Grant No.61471130),
Science and Technology Planning Project of
Guangdong Province, China (Grand No.2016B090918061) and Science and
Technology Planning Project of Guangzhou City, China (Grand No.
201604016079).
Y. Han is with the Microwave Photonics Research Laboratory, School of
Electrical Engineering and Computer Science, University of Ottawa, Ottawa
ON K1N 6N5, Canada, and also with School of Information Engineering,
Guangdong University of Technology, Guangzhou 510006, China.
W. Zhang, J. Zhang and J. Yao are with the Microwave Photonics Research
Laboratory, School of Electrical Engineering and Computer Science,
University of Ottawa, Ottawa ON K1N 6N5, Canada (e-mail: