Low-power-penalty wavelength multicasting
for 36 Gbit/s 16-QAM coherent
optical signals in a silicon waveguide
Xiaoyan Wang, Lingchen Huang, and Shiming Gao*
Center for Optical and Electromagnetic Research, State Key Laboratory of Modern Optical Instrumentation,
Zhejiang University, Hangzhou 310058, China
*Corresponding author: gaosm@zju.edu.cn
Received October 13, 2014; revised November 6, 2014; accepted November 14, 2014;
posted November 14, 2014 (Doc. ID 224787); published December 10, 2014
All-optical wavelength multicasting has been experimentally demonstrated for 36 Gbit/s 16-quadrature amplitude
modulation signals based on four-wave mixing processes in a silicon waveguide with multiple pumps. In our experi-
ment, dual pumps are injected together with the signal into the waveguide and nine idlers are generated, involving
five wavelength multicasting channels. Coherent detection and advanced digital signal processing are employed,
and the recovered constellation diagrams of the multicasting idlers show a root-mean-square error vector magnitude
degradation as small as 2.74%. The bit error rate (BER) results are measured for these multicasting idlers, and the
power penalties are all lower than 0.96 dB at the BER of 3.8 × 10
−3
(corresponding to the forward error correction
threshold). © 2014 Optical Society of America
OCIS codes: (130.3120) Integrated optics devices; (190.4390) Nonlinear optics, integrated optics; (190.4380) Nonlin-
ear optics, four-wave mixing.
http://dx.doi.org/10.1364/OL.39.006907
All-optical signal processing is considered as a promising
technique in next-generation optical communication net-
works, which can avoid the complexity of electrical-
optical-electrical conversion to reduce the probability of
wavelength blocking and satisfy the rapidly increasing
capacity demand. As a key technique of all-optical signal
processing, wavelength multicasting can simultaneously
transmit original data to multiple destinations via different
optical carrier wavelengths in wavelength-routing net-
works, and significantly reduce the amount of network
resources compared to unicast networks [
1]. Many wave-
length multicasting schemes have been demonstrated
by use of various nonlinear effects such as self-phase
modulation (SPM) [
2], cross-phase modulation (XPM)
[
3], cross-absorption modulation (XAM) [4], and single-
pump cascaded four-wave mixing (FWM) [
5] in nonlinear
media such as highly nonlinear fibers (HNLFs), semicon-
ductor optcial amplifiers (SOAs), and electro absorption
modulators. According to the physical properties used
to convey digital information, the optical modulation for-
mats can be divided into amplitude-shift keying (ASK),
polarization-shift keying (PolSK), and phase-shift keying
(PSK), etc. Because of the operation principles, the above
schemes are only available for ASK signals. In compari-
son, FWM processes with multiple pumps in nonlinear
media show strict transparency for modulation formats
since both the amplitude and phase can be preserved in
this kind of nonlinear parametric process [
6]. In particular,
advanced modulation formats such as quadrature phase-
shift keying (QPSK) and quadrature amplitude modulation
(QAM) that combine amplitude and phase information
have been introduced to improve the spectrum efficiency
and system capacity [
7,8]. For these advanced modulation
formats, wavelength multicasting based on multiple-pump
FWMs shows more competitions in speed, capacity, and
transparency.
FWM is conventionally supported by some kinds of non-
linear media and devices, including SOAs [
9], HNLFs [10],
and silicon waveguides [
11]. Moreover, silicon waveguides
have attracted a lot of interest because of their excellent
performance in dense integration. Ultra-highly integrated
optical signal processing devices are expected to be real-
ized in nonlinear silicon waveguides. Using FWM, several
kinds of silicon-based optical signal processing functions
such as signal regeneration [
12], parametric amplification
[
13], and wavelength conversion [14–16]havebeenreal-
ized. Wavelength multicasting has also been demonstrated
based on FWM in silicon waveguides for non-return-zero
(NRZ) ASK [
17], polarization-division-multiplexing ASK
[
18], differential phase-shift keying (DPSK) [19], and QPSK
signals [
20]. Recently, wavelength conversion and multi-
casting of 16-QAM signals were demonstrated in a
dispersion engineered silicon nanowire [
21], and a power
penalty of 7.8 dB was measured at the forward error
correction (FEC) threshold (corresponding to BER
3.8 × 10
−3
). In this Letter, we propose and demonstrate
an error-free wavelength multicasting scheme with low
power penalty for 16-QAM signals based on FWM proc-
esses in a silicon waveguide with multiple pumps. By using
dual pumps, five multicasting idlers carrying a 36 Gbit/s
16-QAM sequence of data are experimentally generated.
The constellation diagrams of these generated idlers are
recovered by coherent detection and advanced digital sig-
nal processing (DSP) technology. The bit error rate (BER)
results are also measured, and a maximum power penalty
as low as 0.96 dB is achieved at the BER of 3.8 × 10
−3
.
Multiple FWM processes will occur in a silicon wave-
guide when a signal and several pumps are injected into it
simultaneously. The more input from the pumps, the
more idlers are generated and the more multicasting
channels are involved. Figure
1 shows an example with
dual pumps P
1
and P
2
. In this case, nine idlers will
be created via the interactions among signal S and
pumps P
1
and P
2
. These nine idlers can be divided
into four types according to their originations: (i) from
non-degenerate FWMs among the signal and dual pumps
December 15, 2014 / Vol. 39, No. 24 / OPTICS LETTERS 6907
0146-9592/14/246907-04$15.00/0 © 2014 Optical Society of America