Performance study of optical triangular-shaped pulse
generation with full duty cycle
Ze Hao (郝 泽), Jing Li (李 晶)*, Chuangye Wang (王创业), and Jin Yuan (袁 瑾)
Key Lab of All Optical Network & Advanced Telecommunication Network of EMC, Beijing Jiaotong University,
Beijing 100044, China
*Corresponding author: lijing@bjtu.edu.cn
Received June 16, 2017; accepted August 15, 2017; posted online September 4, 2017
A scheme of triangular-shaped pulses with full duty cycle generation is proposed and analyzed. Benefiting from
the feature of orthogonal polarization, two approximate sinusoidal signals on different polarization states can be
combined without inducing coherent interference. By tuning the time mismatching between the two signals, an
approximately triangular-shaped profile can be obtained in the optical intensity. It is found that the modulation
index β is no longer a fixed one, but it can be aligned within a proper range of 0.92 to 1.57. To evaluate the
proposal, impacts of radio frequency voltage fluctuation, bias voltage drift, and time mismatching are discussed.
Within the defined fitting error (η ≤ 3%), the tolerable range of the modulation index, time mismatching, and
voltage have been found, which insures a simple operation in practice.
OCIS codes: 060.1155, 060.5625, 060.4080.
doi: 10.3788/COL201715.110601.
Photonic generation of an optical or radio frequency (RF)
triangular-shaped waveform has been a topic of interest
recently, which can find many applications in the all-
optical converter, pulse compression, microwave photonic
systems, and high-speed all-optical signal processing and
manipulation
[1–4]
. Various approaches have been reported
to generate an optical triangular-shaped waveform. One
method based on optical spectrum shaping combined
with frequency-to-time mapping is reported
[5,6]
. The draw-
back of the approach is the fact that they only generate
triangular-shaped pulses with a small duty cycle (<1).
For many applications, signals with a full duty cycle
are desirable. Another alternative approach based on ex-
ternal modulation of a continuous-wave (CW) laser is re-
ported to achieve high quality triangular-shaped profile.
The key point is to manipulate the harmonics of optical
intensity approximately equal to the first two-term
Fourier components of an ideal triangular-shaped wave-
form. In Ref. [
7], a Mach–Zehnd er modulator (MZM )
followed by a dispersion element is used to generate the
triangular-shaped pulse. Its principle depends on the rela-
tionship between fiber dispersion and driving frequency,
which leads to poor frequency tunability. In Ref. [
8],
spectrum manipulation of four modulation side-bands
is used to generate a triangular signal with a tunable rep-
etition rate. Thi s scheme requires an ultra-short pulse
source, which always leads to high cost and complex ar-
chitecture. Then, in Ref. [
9], Dai et al. reports a solution
for versatile waveform generation (including the triangu-
lar shape) based on the optical spectral comb, which re-
quires large signal modulation. In Ref. [
10], Li et al.
proposed a frequency-doubled triangular pulse (full duty
cycle) signal generator, which requires a dual-parallel
MZM driven by a sinusoidal signal. Except for the above
approaches
[5–10]
, a triangular-shaped signal can also be
generated by using optical polarization manipulation
[11]
,
time domain processing
[12]
, nonlinear polarization rota-
tion
[13]
, stimulated Brillouin scattering
[14]
, and an optoelec-
tronic oscillator
[15]
. In Ref. [12], a scheme of multiple
waveform (including the triangular shape) generation is
proposed based on time domain processing. By combini ng
two rectangular-shaped waveforms with a specific time
mismatching, triangular-shaped pulses can be generated.
But this scheme is based on optical-to-electrical insensitiv-
ity of narrow-bandwidth photo-detection, which means
the triangular-shaped signal can only generated in electri-
cal domain.
In this Letter, we proposed a photonic approach to
generate a triangular-shaped pulse through a single drive
MZM (SD-MZM), which is driven by the RF signal. The
signal from the SD-MZM is split into two paths. Benefit-
ing from the feature of orthogonal polarization, two ap-
proximately sinusoidal signals on different polarization
states can be combined without inducing coherent infer-
ence. By tuning the time mismatching between the two
signals, an approximately triangular-shaped profile can
be obtained in the optical intensity. Different from the
approach in Ref. [
12], this proposal can generate a triangu-
lar pulse in the optical domain, which will enhance its
application in all-optical processing.
The schematic diagram of the proposed scheme is shown
in Fig.
1. Here, the SD-MZM is biased at the quadrature
point (QT). An expression of the driving sinusoidal signal
is V
RF
cosðΩtÞ, where V
RF
and Ω represent the magnitude
and angular frequency of the driving RF signal; the optical
field at the output of the SD-MZM can be expressed as
E
A
ðtÞ¼E
0
ðtÞcos
π
2
p
V
π
V
RF
cosðΩtÞþ
π
4
exp
j
π
4
;
(1)
COL 15(11), 110601(2017) CHINESE OPTICS LETTERS November 10, 2017
1671-7694/2017/110601(5) 110601-1 © 2017 Chinese Optics Letters
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