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COVER Photonic implementations of signal processing have attracted a great deal of attention thanks to their potential to overcome the bandwidth and speed bottlenecks in electronic devices. Many all-optical signal processing techniques, which offer processing bandwidths as large as several THz, have been proposed and successfully used in applications such as ultrafast telecommunications, optical computing, microwave photonics and bio-photonics. The cover shows a time stretch microscopy technique that uses a multi-wavelength laser as a light source. By tuning the speed of the modulation signal, the frame rate of the imaging system can be raised to hundreds of MHz. In addition, the concept of anamorphic temporal imaging and its application to real-time optical analog data compression are reported for the first time. This new system performs time-bandwidth engineering and is designed based on a newly introduced mathematical function called the stretched modulation distribution. The background of the cover shows one such distribution reported in this issue (see the Special Topic: All-Optical Signal Processing).
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Volume 59 Number 22 August 2014
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CONTENTS CONTENTS
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Volume 59 Number 22 August 2014
I Towards Excellence in Science Chinese Academy of Sciences
SPECIAL TOPIC: All-Optical Signal Processing
EDITORIAL
2647 Preface MingLi•JoséAzaña•JianpingYao
INVITED ARTICLE
2649 Warped time lens in temporal imaging for optical real-time data compression MohammadH.Asghari•BahramJalali
PROGRESS
2655 All-optical signal processing for linearity enhancement of Mach–Zehnder modulators Xiao-PingZheng•Guo-QiangZhang•ShangyuanLi•Han-YiZhang•Bing-KunZhou
2661 Nanoscale all-optical devices based on surface plasmon polaritons JianjunChen•ChengweiSun•XiaoyongHu
2666 Analog-to-digital converters using photonic technology ZhiyaoZhang•HepingLi•ShangjianZhang•YongLiu
REVIEW
2672 Photonic generation of microwave signals with tunabilities HengyunJiang•LianshanYan•JiaYe•WeiPan•BinLuo•XihuaZou
ARTICLES
2684 Ultra-highsuppressionmicrowavephotonicbandstopfilters DavidMarpaung•BlairMorrison•MattiaPagani•RaviPant•BenjaminJ.Eggleton
2693 Serialtime-encodedamplifiedmicroscopyforultrafastimagingbasedonmulti-wavelengthlaser YeDeng•MingLi•NingboHuang•JoséAzaña•NinghuaZhu
2702 Non-blocking 2 × 2 switching unit based on nested silicon microring resonators with high extinction ratios and low crosstalks
JiayangWu•XinhongJiang•TingPan•PanCao•LiangZhang•XiaofengHu•YikaiSu
2709 All-optical wavelength converter using a microdisk resonator integrated with p-n junctions LinjieZhou•JingyaXie•JianpingChen
PROGRESS
Cell Biology2717 Progress in measuring biophysical properties of membrane proteins with AFM single-molecule force
spectroscopy MiLi•LianqingLiu•NingXi•YuechaoWang
LETTER
Ecology2726 Evaluatingtheinfluencesofmeasurementtimeandfrequencyonsoilrespirationinasemiaridtemperate
grassland BingweiZhang•ZhiqiangYang•ShipingChen•LimingYan•TingtingRen
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ARTICLES
Atomic & Molecular Physics2731 Laser intensity induced transparency in atom-molecular transition process JieMa•YuqingLi•JizhouWu•LiantuanXiao•SuotangJia
High-Energy Physics2736 Super solar particle event around AD775 was found DazhuangZhou•ChiWang•BinquanZhang•ShenyiZhang•PingZhou•YueqiangSun•JinbaoLiang•GuangwuZhu• JiWu
Developmental Biology2743 Generationoftetraploidcomplementationmicefromembryonicstemcellsculturedwithchemicaldefined
medium ChunjingFeng•HaifengWan•Xiao-YangZhao•LiuWang•QiZhou
2749 Endoderm contributes to endocardial composition during cardiogenesis YanLi•XiaoyuWang•ZhenglaiMa•ManliChuai•AndreaMünsterberg•KennethKaHoLee•XuesongYang
Ecology2756 Sexual/aggressive behavior of wild yak (Bos mutusPrejevalsky1883)duringtherut:influenceoffemale
choice PaulJ.Buzzard•DonghuaXu•HuanLi
Geophysics2764 Identificationofthethick-layergreigiteinsedimentsoftheSouthYellowSeaanditsgeologicalsignificances JianxingLiu•XuefaShi•ShulanGe•QingsongLiu•ZhengquanYao•GangYang
Materials Science2776 FunctionalizationofPCLfibrousmembranewithRGDpeptidebyanaturallyoccurringcondensation
reaction WentingZheng•DiGuan•YuxinTeng•ZhihongWang•SuaiZhang•LianyongWang•DelingKong•JunZhang
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Artic le Optoelectronics & Laser
All-optical wavelength converter using a microdisk resonatorintegrated with p-n junctions
Linjie Zhou • Jingya Xie • Jianping Chen
Received: 1 December 2013 / Accepted: 28 February 2014 / Published online: 27 May 2014
� Science China Press and Springer-Verlag Berlin Heidelberg 2014
Abstract We explore all-optical wavelength conversion in
a microdisk resonator integrated with interleaved p-n junc-
tions. Numerical simulation based on temporal coupled
mode theory is performed to study the free-carrier dynamics
inside the cavity. It reveals that the detuning of pump and
probe frequencies and the carrier lifetime have a significant
effect on the device performance. Experimental result con-
firms that the conversion speed can be considerably
improved by applying a reverse bias on the p-n junctions.
Wavelength conversion at 10 Gb/s data rate is achieved with
a pump power of 5.41 dBm and a bias voltage of -6 V.
Keywords Resonators � Wavelength conversion �Optical signal processing � Integrated photonics
1 Introduction
All-optical wavelength conversion is one of the powerful
signal processing techniques that can be used to solve the
wavelength contention issues in future transparent wave-
length division multiplexing (WDM) optical communica-
tion networks. It is foreseeable that low-level signal
processing has to be performed in the optical domain
whenever possible in order to allow Tb/s data signals to
transparently route through complex network architectures
[1, 2]. The all-optical conversion provides a solution to
overcome the bottlenecks encountered at current power-
hungry and low-speed optical-electrical-optical (O\E\O)
approaches. There are multiple ways to realize wavelength
conversion including using semiconductor optical amplifi-
ers (SOAs) [3, 4], optical fibers [5, 6], chalcogenide
waveguides or fibers [7, 8], periodically-poled lithium
niobate (PPLN) waveguides [9], and GaAs [10] etc. Silicon
photonics based approaches have attracted much attention
due to their compactness and compatibility with the com-
plementary metal-oxide-semiconductor (CMOS) fabrica-
tion process [11]. All-optical wavelength conversion based
on four-wave mixing (FWM) in high-confinement silicon
waveguides has been demonstrated [12–16]. To obtain high
conversion efficiency with FWM, the waveguide group
velocity dispersion (GDD) needs to be carefully engi-
neered. A long waveguide and large pump power are
always required. By making use of the resonant enhance-
ment effect in silicon micro-resonators, low-power wave-
length conversion is achieved in micron-scale device
footprint [17, 18]. The optical intensity needed to excite the
Kerr nonlinear effect is usually high enough that free-car-
riers are generated via two photon absorption (TPA), which
is detrimental to FWM. On the other hand, however, the
free-carrier plasma dispersion (FCD) effect can also be
utilized for wavelength conversion [19, 20]. The original
optical signal (pump) is translated to free-carrier modula-
tion, which as a result enables the intensity modulation of
another optical beam (probe) via resonance shift. This
process can be regarded as all-optical modulation in con-
trast to the electro-optic modulation as widely investigated
in recent years [21]. Because the conversion is facilitated
by free-carriers, it does not need to satisfy the crucial phase
matching condition, which greatly eases the device design.
In this paper, we first numerically study the wavelength
conversion process in a microdisk resonator based on
SPECIAL TOPIC: All-Optical Signal Processing
L. Zhou (&) � J. Xie � J. Chen
State Key Laboratory of Advanced Optical Communication
Systems and Networks, Department of Electronic Engineering,
Shanghai Jiao Tong University, Shanghai 200240, China
e-mail: [email protected]
123
Chin. Sci. Bull. (2014) 59(22):2709–2716 csb.scichina.com
DOI 10.1007/s11434-014-0405-4 www.springer.com/scp
temporal coupled mode equations. The effect of pump and
probe frequency detuning on the free-carrier dynamics and
the converted signal quality is analyzed. Simulation sug-
gests that reducing carrier lifetime can effectively improve
the conversion speed. We then present our experimental
results using a 6-lm-radius silicon microdisk resonator
integrated with interleaved p-n junctions. The small mode
volume and high Q-factor of the microdisk resonator are
critical for low power operation. Previous work used pas-
sive microring resonators and their operation speed is pri-
marily limited by the ns-long carrier lifetime [5, 6]. In our
device, we integrate interleaved p-n junctions in the reso-
nator so that the high electric field upon reverse bias can
considerably reduce the carrier lifetime, leading to an
increased conversion speed.
2 Device structure and theoretical model
Figure 1a shows the schematic of the microdisk resonator
integrated with interleaved p-n junctions along the disk rim
[22]. The microdisk resonator has high-Q whispering gallery
modes (WGMs). The optical power is greatly enhanced inside
the resonator on resonance. The enhancement factor is given by
(jF/p)2, where j is the waveguide-resonator coupling coeffi-
cient and F is the resonator finesse defined as the ratio between
the free spectral range (FSR) and the full-width half-maximum
(FWHM) width of the resonance [23]. If the resonator is criti-
cally coupled (all input power is coupled into the resonator on
resonance), then the enhancement factor becomes F/p. There-
fore, resonators with high Q-factors and small volumes favor
the resonant enhancement effect. When strong pump light is
coupled into the microdisk resonator, free-carriers are gener-
ated due to the TPA effect, which in turn detunes the resonance
frequency because of the FCD effect. The resonance Q-factor is
also varied by the accompanied free-carrier absorption (FCA).
Therefore, the resonance frequency can be modulated by the
pump light. If a continuous probe light is also coupled into the
resonator, then the resonance modulation can be translated into
intensity modulation of the probe light. This is the working
principle of all-optical wavelength conversion using the pump-
probe method. As the conversion is enabled via the intermediate
FCD effect, the operation speed is limited by the free-carrier
dynamics. To ensure a fast response, the free-carriers should
have a short lifetime. Besides the carrier lifetime, the cavity
photon lifetime is also a possible limiting factor to the response
speed, because the optical field needs time to build up and decay
in the cavity.
According to the temporal coupled mode theory, the
dynamic behavior of the pump (control) and probe energy
inside the resonator can be described by the following two
rate equations [23]:
d
dtac
r tð Þ ¼ �j xc � x0 � DxL0 tð Þ � DxNL
0 tð Þ� �
acr tð Þ
� 1
2r0 þ DrL
0 tð Þ þ DrNL0 tð Þ
� �ac
r tð Þ
� re
2ac
r tð Þ � jffiffiffiffire
pAc
i tð Þ; ð1Þ
d
dtap
r tð Þ ¼ �j xp � x0 � DxL0 tð Þ � DxNL
0 tð Þ� �
apr tð Þ
� 1
2r0 þ DrL
0 tð Þ þ DrNL0 tð Þ
� �ap
r tð Þ � re
2ap
r tð Þ
� jffiffiffiffire
pA
pi tð Þ; ð2Þ
where ar(t) is the energy-normalized amplitude in the
resonator, xc and xp are the pump and probe signal
frequencies respectively, x0 is the resonance frequency,
DxL0 tð Þ is the linear resonance frequency shift caused by
FCD, DxNL0 tð Þ is the nonlinear resonance frequency shift
caused by the Kerr effect, r0 is the resonator intrinsic delay
rate, DrL0 tð Þ is the linear delay rate due to FCA, DrNL
0 tð Þ is
the nonlinear delay rate due to TPA, re is the external delay
rate due to waveguide coupling, and Ai tð Þ is the power-
normalized input field amplitude. The output of the
transmitted probe amplitude is given by
Apo tð Þ ¼ A
pi tð Þ � j
ffiffiffiffire
pap
r tð Þ: ð3Þ
Based on the above theoretical model, we can study the
behavior of optical field and free-carriers in the resonator
with the presence of a pump signal. It should be noted that
the above theoretical model does not incorporate the
thermo-optic effect. In practice, the wavelength conversion
process is always accompanied by the thermo-optic effect
since the pump power is relatively high in the cavity.
However, the thermo-optic effect has a slow response in
the time scale of ls, several orders smaller than the ns free-
carrier response time. With the use of p-n junctions, the
carrier lifetime can be even shorter. Therefore, the slow
thermo-optic effect does not interfere significantly with the
fast wavelength conversion process if the optical signal
date rate is high. The effect of the thermal heating is only
to red-shift the resonance wavelengths. Hence, the pump
and probe wavelengths need to be tuned accordingly to
match the resonances.
We consider a microdisk resonator with a radius of 6
lm. The quality factor of the resonator is assumed to be
Q = 39104 (consistent with our experiment). The funda-
mental WGM has a confinement factor of about 0.9. The
TPA coefficient of silicon at 1.55 lm wavelength is
0.6 cm/GW and the Kerr coefficient is 6.3910-18 m2/W
[24]. The carrier lifetime is assumed to be 200 ps, which in
practice can be tuned by applying a reverse bias on the p-n
junctions. Figure 1b shows the transmission spectrum of
the waveguide coupled microdisk resonator. The coupling
2710 Chin. Sci. Bull. (2014) 59(22):2709–2716
123
coefficient is chosen such that the resonance is critically
coupled.
Figure 2a shows the pump and probe signals input to the
access waveguide. The pump is a square-like pulse with 8
mW optical power and 1 ns pulse width, and the probe is a
continuous wave (CW) with 0.8 mW optical power. The
pump and probe wavelengths are both set at the resonance
frequency. Due to the resonant enhancement effect, the 8
mW power is high enough to induce sufficient resonance
shift. The probe power is 10 times less leading to negligible
nonlinear effect in the cavity. Once the pump signal is
turned on, the optical energy trapped in the cavity gradually
Fig. 1 (Color online) Wavelength conversion process in a microdisk resonator. a Schematic graph illustrating the microdisk resonator integrated
with interleaved p-n junctions; b Transmission spectra before (solid line) and after (dashed line) optical pumping
Fig. 2 (Color online) Simulated wavelength conversion process in the microdisk resonator. a Waveforms of the pump and probe input signals;
b Variation of optical energy stored in the cavity; c Variation of the free-carrier concentration in the cavity and detuning of the resonance
frequency; d Waveform of the output probe signal
Chin. Sci. Bull. (2014) 59(22):2709–2716 2711
123
increases. As a result of TPA, free-carriers are generated.
Figure 2b shows the pump and probe optical energy accu-
mulated in the cavity. It is noticeable that there is a sharp
peak at the leading edge of the pump energy curve, resulted
from the interplay between external coupling and resonance
shift by free-carriers. After the peak, the pump energy is
stabilized to 0.1 pJ. On one side, the pump power is con-
tinuously fed into the cavity via waveguide coupling, and
the stored energy in the cavity could reach the maximum if
the resonance were not shifted. However, on the other hand,
the increasing energy generates free-carriers which inevita-
bly blue-shift the resonance frequency. The blue-shifted
wavelength reduces the stored energy until the system is
stabilized. For the probe light, the initially stored energy in
the cavity begins to decay following the pump pulse. It
recovers to the original level when the pump is turned off.
The free-carrier concentration overall follows the
stored energy in the cavity as shown in Fig. 2c. Because
the carrier lifetime is not short enough, it cannot resolve
the narrow dip in the pump energy profile. The resonance
frequency detuning is determined by both FCD and Kerr
effects. The FCD effect is much stronger than the Kerr
effect, and therefore, resonance shift almost follows the
free-carrier concentration curve. Figure 2d shows the
output probe signal. It is worth mentioning that the peak
optical power (1 mW) at the leading edge exceeds the
input power (0.8 mW) due to the resonance dynamic
tuning. At the steady state, the probe output power is 0.55
mW, a little lower than the input power because of the
Lorentzian spectral profile of the resonance.
From the above discussion, one sees that the pump
signal may not necessarily be set at the original resonance
frequency in order to obtain the maximum resonance
shift. Blue-shift of the pump signal helps to form positive
feedback so that more power can be coupled and stored in
the cavity. Figure 3a and b show the variation of free-
carrier concentration and the resultant output probe
waveforms, respectively, when the pump is slightly blue-
shifted from the original resonance frequency. The blue-
detuning of the pump first increases the steady-state car-
rier concentration until it reaches the maximum around
dxc = 0.003 FSR. Although the leading peak is always
present in the carrier concentration curves, it is gradually
diminished in the output probe signals. This is because
the probe transmission is less sensitive to the resonance
shift when it is at the on-state. The rising edge of the
output signal becomes slower with the increasing pump
detuning as it needs more time to build up the pump
energy in the cavity. With further detuning after the
maximum point, the coupled power decreases consider-
ably, resulting in low free-carrier concentration and weak
distorted output signal.
In the proceeding simulation, the resultant probe signal
has the same polarity with the pump signal. If we set the
Fig. 3 (Color online) Effect of the pump frequency detuning on the device performance. a Variation of free-carrier concentration; b Output
waveforms of the probe signal
2712 Chin. Sci. Bull. (2014) 59(22):2709–2716
123
probe to the blue-shifted resonance frequency, then the
output probe signal becomes inverted as shown in Fig. 4.
When the pump is at the original resonance frequency (dxc
= 0), the steady-state free-carrier concentration is 291016
cm-3 and the resonance blue-shift is 0.0025 FSR (Fig. 2c).
Therefore, we can set the probe detuning to be
dxp = 0.0025 FSR. The corresponding output signal is
shown in the top panel of Fig. 4. The leading peak in the
free-carrier concentration is translated into a small peak at
the off-state of the output signal. When the pump is set at
dxc = 0.003 FSR, the probe needs to be detuned to dxp =
0.005 FSR as shown in the middle panel of Fig. 4. To
reduce the impact of the leading peak, we can set dxp =
0.0055 FSR at the expense of more ripples at the off-state
as shown in the bottom panel of Fig. 4.
As the wavelength conversion is enabled by the free-
carrier dynamics in the cavity, the conversion speed is
ultimately limited by the carrier lifetime as well as the
photon lifetime. Figure 5 shows the variation of free-car-
rier concentration in the cavity and the corresponding
output waveforms for three different carrier lifetimes.
There is no frequency detuning for both the pump and
probe signals. Two consequences are resulted for shorter
carrier lifetime. First, the trailing edge of the output signal
becomes sharper as is expected. Second, the on-state output
power is reduced as the free-carrier concentration becomes
lower for shorter carrier lifetime.
3 Experimental results
Figure 6a shows the optical microscope image of the fab-
ricated device. The access waveguide is 300 nm wide and
its separation from the microdisk is 0.25 lm. The period of
the interleaved p-n junctions is about 1 lm with a half duty
cycle. The junction width along the radial direction is 2.3
lm. Compared to a single circular p-n junction, the inter-
leaved p-n junctions have larger fabrication tolerance [25].
Moreover, the electric field of the p-n junctions has larger
overlap with the WGMs, so that the free-carriers generated
by TPA can be fast swept out. The doping concentration of
the p and n regions is about 1017 cm-3 to minimize the
absorption loss. The doping concentration of the inner n?
and outer p? regions is about 1020 cm-3 to form good
ohmic contact. The inner doping radius is 4.2 lm so that it
does not deteriorate the first radial-order WGM [26]. The
device was first patterned using 248-nm deep ultra-violet
(DUV) photolithography followed by plasma dry etch.
Then a 1.5 lm thick silicon dioxide layer was deposited
Fig. 4 (Color online) Inverted output waveform when the probe
frequency is blue-detuned from the resonance frequency
Fig. 5 (Color online) Effect of the free-carrier lifetime on the device performance. a Variation of free-carrier concentration in the cavity;
b Output waveforms of the probe signal
Chin. Sci. Bull. (2014) 59(22):2709–2716 2713
123
using plasma-enhanced chemical vapor deposition (PEC-
VD). Finally, aluminum (Al) layer was sputtered and pat-
terned. The entire process is CMOS compatible.
Figure 6b shows the measured transmission spectrum of
the microdisk for transverse electric (TE) polarization. The
device fiber-to-fiber insertion loss is about 20 dB. Three
pronounced WGMs are observed in the spectrum. We
selected the resonances at k1 = 1,530.6 nm and k2 = 1,548.8
nm (first radial-order mode) for our wavelength conversion
experiment. The Q-factor of these resonances is 39104 and
the extinction ratio is about 8 dB. There is also another
resonance mode (second radial-order mode) with a higher
extinction ratio but a lower Q-factor of 4,600 that can also
be utilized for wavelength conversion. The third radial-
order mode has significant overlap with the central high-
doping region, and therefore it has the lowest Q-factor of
only 700. The insets show the magnified resonance spectral
profiles around k1 and k2. The photon lifetime of this mode
is s = Q1k1/2pc = 25.2 ps, determined by the microdisk
resonator internal loss and external coupling strength.
Figure 7 shows the experimental setup for wavelength
conversion. The pump and probe light waves are coupled
into the microdisk from the two ends of the access
waveguide. Their wavelengths are tuned to the left
shoulder of the resonances as indicated in the insets of
Fig. 6. We note that the resonance is red-shifted due to
the thermo-optic effect after pump power is coupled into
the resonator. The pump and probe wavelengths are
adjusted accordingly following the resonance red-shift.
The pump signal is generated by modulating a CW light
using a LiNiO3 amplitude modulator (AM) driven by a
pulse pattern generator (PPG) followed by a microwave
Fig. 6 (Color online) Fabricated device and its transmission spectrum. a Optical microscope image of the fabricated device; b Transmission
spectrum of the microdisk resonator. The insets show the zoom-in of the resonance dips. The pump and signal wavelengths (kc and kp) are
marked
Fig. 7 (Color online) Experimental setup for wavelength conversion. EDFA Erbium-doped fiber amplifier; BPF Band pass filter; PC
Polarization controller; AM Amplitude modulator; MA Microwave amplifier; PPG Pulse pattern generator; PD Photodetector
2714 Chin. Sci. Bull. (2014) 59(22):2709–2716
123
amplifier (MA). Tunable erbium-doped fiber amplifiers
(EDFA) are used to adjust the pump and probe light
power. Polarization controllers are used to set light waves
to TE polarization. The pump and probe signals are
separated by two circulators.
We first investigate the effect of junction bias on the
wavelength-converted signal. Figure 8a shows the resultant
output probe waveforms in response to a 100 MHz square
wave pump signal. The waveguide-coupled optical power of
the pump is 5 dBm. The open circuit configuration has the
slowest response, as there is no closed loop for the free-
carriers to recombine. The signal transition edge becomes
much sharper once the short circuit loop is formed. Reverse
bias of the p-n junctions can form strong electric field across
the depletion region, and therefore the TPA generated free-
carriers can be fast swept out of the cavity, leading to reduced
carrier lifetime and hence faster transition. At 28 V bias, the
transition time is as short as 100 ps, which is almost two
orders smaller than the open circuit case. Hence, it demon-
strates that using high electric field to deplete free-carriers is
an effective way to speed up the all-optical modulation. We
also perform wavelength conversion at 10 Gb/s using a
custom non-return-to-zero (NRZ) waveform pattern as
shown in Fig. 8b. The average optical powers of the pump
and probe light waves in the waveguide are 5.41 and 25.89
dBm, respectively. The bias voltage is set at 26 V. As we set
the pump and probe wavelengths to the left shoulder of the
resonances, the converted bit sequence is complementary to
the original one in consistence with the simulation shown in
Fig. 4 (bottom panel). As the waveforms were recorded by
an 8 GHz oscilloscope (Tektronix Digital Serial Analyzer),
the conversion speed is partially limited by the oscilloscope
bandwidth.
In our experiment, wavelengths of the pump and probe
signals are carefully tuned to follow the red-shift of reso-
nances after thermal heating by the pump light. As silicon
has a relatively large thermo-optic coefficient, it is hard to
circumvent self-heating in our current device. However, it
is possible to implement temperature-independent silicon
photonic devices by upper-cladding materials with a neg-
ative thermo-optic coefficient such as polymethyl meth-
acrylate (PMMA) and titanium dioxide (TiO2) [27, 28]. In
this way, the resonances can be stabilized, and hence the
operation wavelengths are independent of the pump power
level.
4 Conclusion
In summary, we theoretically studied and experimentally
demonstrated wavelength conversion in a silicon micro-
disk resonator integrated with interleaved p-n junctions.
The wavelength conversion is enabled by the free-carrier
plasma dispersion effect in the cavity. The interplay
between external optical feeding and intra-cavity free-
carrier dynamics is critical to the quality of wavelength
conversion. In particular, we analyzed the influence of
pump and probe frequency detuning and the carrier
lifetime on the converted signal. The experiment using a
6 lm-radius microdisk resonator with a Q-factor of
39104 also confirms that reverse bias can significantly
shorten free-carrier lifetime and improve conversion
speed. We successfully realized wavelength conversion of
a 10 Gb/s bit sequence with 5.41 dBm pump power and
-6 V bias.
Fig. 8 (Color online) Experimental results. a Wavelength-converted square waveforms at 100 MHz speed for various biases. i: open circuit; ii:
short circuit; iii: -4 V bias; iv: -8 V bias; b Optical waveform conversion using a 10 Gb/s bit sequence. i: input pump signal; ii: wavelength-
converted output probe signal. The bias is set at -6 V
Chin. Sci. Bull. (2014) 59(22):2709–2716 2715
123
Acknowledgments This work was supported in part by the National
Basic Research Program of China (ID2011CB301700), the National
High Technology Research and Development Program of China
(2013AA014402), the National Natural Science Foundation of China
(61007039, 61001074, 61127016, 61107041), the Science and
Technology Commission of Shanghai Municipality (STCSM) Project
(12XD1406400). We also acknowledge IME Singapore for device
fabrication.
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