IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 27, NO. 12, JUNE 15, 2015 1313
Tunable Optoelectronic Oscillator Using FWM
Dynamics of an Optical-Injected DFB Laser
Tingting Zhang, Jintian Xiong, Peng Wang, Jilin Zheng, Fangzheng Zhang, Tao Pu, Member, IEEE,
and Xiangfei Chen, Senior Member, IEEE
Abstract—A wideband frequency-tunable optoelectronic
oscillator using four-wave mixing nonlinear dynamics of an
optical-injected distributed feedback (DFB) semiconductor
laser is proposed and experimentally demonstrated. Utilizing
the wavelength-selective optical gain of the DFB laser under
optical injection, a frequency-tunable microwave photonic filter
is realized, which is used as the desired oscillation frequency
selector. Therefore, the electrical bandpass filter is not required
in the proposed scheme. An optoelectronic oscillating signal
with a frequency tuned from 9.63 to 19.11 GHz is obtained by
changing the injection parameters. The single sideband phase
noise of the generated 13.74-GHz microwave signal is measured
to be −103.19 dBc/Hz at 10-kHz offset.
Index Terms—Distributed feedback lasers, microwave
generation, optoelectronic oscillators.
I. INTRODUCTION
O
PTOELECTRONIC oscillators (OEOs) have attracted
considerable attention in research community over
the past decades, featuring extremely low phase noise, high
stability, and high spectral purity of the generated high-
frequency microwave signals [1]. They have many potential
applications, such as optical and wireless communications,
radar systems, and optical signal processing [2], [3]. In a
conventional OEO system, a high-Q electrical bandpass
filter (EBPF) is required to ensure a stable single frequency
operation [4]. However, the EBPF usually has a fixed central
frequency, which limits the tunability of the OEO. To obtain
a wideband frequency-tunable microwave signal, a high-Q
EBPF with wideband tunability is needed, which is expensive
and is difficult to implement. Microwave photonic bandpass
Manuscript received January 4, 2015; revised March 8, 2015; accepted
April 5, 2015. Date of publication April 8, 2015; date of current version
June 1, 2015. This work was supported in part by the Jiangsu Province Natural
Science Foundation under Grant BK2012058, in part by the Technology
Support Program of Jiangsu Province under Grant BE2012157, and in part
by the National Natural Science Foundation of China under Grant 61032005,
Grant 61177065, and Grant 61475193.
T. Zhang, P. Wang, and X. Chen are with the Nanjing National
Laboratory of Microstructures, College of Engineering and Applied Sciences,
Nanjing University, Nanjing 210093, China (e-mail: zhtt0823@163.com;
09wangp@gmail.com).
J. Xiong is with the 63rd Research Institution, PLA University of Science
and Technology, Nanjing 210007, China (e-mail: ydpanda@163.com).
J. Zheng and T. Pu are with the PLA University of Science and Technology,
Nanjing 210007, China (e-mail: zhengjilinjs@126.com; nj_putao@163.com).
F. Zhang is with the Key Laboratory of Radar Imaging and Microwave
Photonics, Ministry of Education, Nanjing University of Aeronautics and
Astronautics, Nanjing 210016, China (e-mail: zhangfangzheng@nuaa.edu.cn;
chenxf@nju.edu.cn).
Color versions of one or more of the figures in this letter are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LPT.2015.2421291
filter (MPBF) is regarded as the reasonable candidate to
replace the electrical filter with great advantages in terms
of good electromagnetic immunity, wideband tunability, and
high reconfigurability [5]. Several approaches using MPBF
to obtain wideband frequency-tunable OEOs have been
proposed [6]–[11]. As mentioned in [6], a high-Q MPBF
based on phase-modulation to intensity-modulation (PM-IM)
conversion is realized by the joint operation of a phase
modulator (PM) and a narrow-band phase-shifted fiber Bragg
grating (PS-FBG). An OEO with a tuning range of 25 GHz
is achieved by changing the wavelength of the optical carrier.
However, the PS-FBG is sensitive to the environmental
perturbations, such as temperature and vibration, which
deteriorate the stability of the proposed system. A novel
microresonator-based OEO with the frequency tuned from
2 GHz to 15 GHz is obtained in [7]. In this scheme, a LiTaO
3
whispering gallery mode resonator is used as the tunable
optical filter to realize PM-IM conversion. In [8], an OEO
with larger frequency tuning range is demonstrated. The key
device of this approach is the optical bandpass filter, whose
central frequency is set to have a small detuning compared
to the frequency of the laser. The tunability is implemented
by changing the bandwidth of the optical bandpass filter. The
major limitation of this approach is that the optical bandpass
filter must have a sharp roll-off factor and the frequency detun-
ing should be carefully set to obtain an ultra-narrow bandwidth
to ensure a single frequency operation. Another scheme using
the relaxation oscillation frequency of a directly modulated
distributed feedback (DFB) semiconductor laser as a bandpass
selector is proposed in [9]. Although neither an external
modulator nor an electrical filter is required, the tuning range
is very limited due to the packaging of the DFB laser.
In this letter, a novel optoelectronic oscillator is proposed
by using four-wave mixing (FWM) nonlinear dynamics of an
optical-injected DFB laser. Utilizing the wavelength-selective
optical gain of the DFB laser under optical injection [12],
PM-IM conversion is obtained and a wideband tunable MPBF
is realized by changing the injection parameters. Our previous
work [13] has demonstrated an MPF with a frequency tuning
range of 30 GHz. However, the performance of the MPF is
limited in terms of the varied response shape, the large 3-dB
bandwidth of around 1.2 GHz and the out-of-band suppression
ratio of only 20 dB. In this letter, a phase modulator and
a DFB laser with narrower linewidth are employed, which
has greatly improved the performance of the MPF with the
maximal 3-dB bandwidth of 172.7 MHz and the out-of-band
suppression ratio of over 28 dB. In addition, the bias drifting
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