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ABSTRACT: We propose a configuration of signal multiplexing with four polarization states, and investigate its transmission performance over single-mode-fiber links. Assisted by coherent detection and digital signal processing (DSP), the demodulation of four-polarization multiplexed (4PM) on-off-keying (OOK) and phase-shift-keying (PSK) signals are achieved. We then discuss the impact of the crosstalk from polarization mode dispersion (PMD) on 4PM systems. The transmission distance is extended from ~50-km to ~80 km by employing feedback-decision-equalizers. We also compare the back-to-back characteristics of the 40-Gbit/s 4PM-OOK system and 40-Gbit/s PDM-QPSK system with the same spectral efficiency. The results show that the performance of 4PM systems is comparable to that of PDM-QPSK systems, which indicates that the proposed scheme is a potentially promising candidate for future optical networks.
Optics Express 05/2013; 21(9):11590-605. · 3.59 Impact Factor
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ABSTRACT: We report on the realization of a hybrid chaos-based communication scheme using three chaotic semiconductor ring lasers (SRLs). In this scheme, two slave SRLs (S-SRLs) are identically driven by a master SRL (M-SRL) subject to delayed optical feedback. Under proper conditions, the S-SRLs are completely synchronized with each other due to the symmetric operation, and they are also synchronized with the M-SRL through the injection-locking effect. The results also show that a message encrypted through chaos shift keying at the M-SRL end can be successfully decrypted by the two S-SRLs, while the two uncoupled S-SRLs allow for dual-channel chaos communication when both counterpropagating modes of one S-SRL are encoded with a message.
Applied Optics 03/2013; 52(7):1523-30. · 1.41 Impact Factor
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ABSTRACT: A tunable all-optical single-bandpass photonic microwave filter (PMF) based on spectrally sliced broadband optical source and phase modulation is proposed and experimentally demonstrated. A broadband optical source and a Mach-Zehnder interferometer (MZI) are used to generate continuous optical spectral samples, which are employed to form a finite impulse response filter with a single-bandpass response with the help of a single-mode fiber. A phase modulator is then adopted to eliminate the baseband components in the filtering response. The center frequency of the PMF can be tuned by changing the free spectral range of the MZI. An experiment is performed, and the results demonstrate that the proposed PMF has a single-bandpass without baseband components and a tuning range of 5-15 GHz.
Applied Optics 01/2013; 52(2):302-6. · 1.41 Impact Factor
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ABSTRACT: A metal-insulator-metal (MIM)-based four-port quasi-circulator consisting of four bus waveguides and eight narrow inside/outside slits is proposed without using nonreciprocity. Once the input port is defined, only a specific output port could be obtained by proper the design of parameters of the waveguides and slits. Simulation results based on finite-different time-domain (FDTD) method demonstrate that the transmittance at the center wavelength of the appropriate output port can reach 0.63 while those of the other two output ports are lower than 0.06. Through adjusting the slits spacing or optimizing the insulator material in the slits, the isolation of the circulator could be further improved with a slight sacrifice of the transmission. Such structure could also be used for wavelength demultiplexing with the center wavelength determined by the length of the bus waveguides and slits.
Optics Express 12/2012; 20(27):28025-32. · 3.59 Impact Factor
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ABSTRACT: We investigate a plasmonic waveguide system based on side-coupled complementary split-ring resonators (CSRR), which exhibits electromagnetically induced transparency (EIT)-like transmission. LC resonance model is utilized to explain the electromagnetic responses of CSRR, which is verified by simulation results of finite difference time domain method. The electromagnetic responses of CSRR can be flexible handled by changing the asymmetry degree of the structure and the width of the metallic baffles. Cascaded CSRRs also have been studied to obtain EIT-like transmission at visible and near-infrared region, simultaneously.
Optics Express 10/2012; 20(22):24348-55. · 3.59 Impact Factor
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ABSTRACT: Successful high-speed fiber-optic transmission using a four-chaotic-semiconductor-laser system is numerically demonstrated. The system performance is benefited from the properties of bandwidth enhancement and the implementation of a two-channel scheme. The bit-error rate of the recovered
message is evaluated for different fiber lengths and message bit rates, respectively. In particular, acceptable communication performance can be achieved for a bit rate up to 8 Gb/s when
the fiber length is approximately 60 km. Such a system could lead to high-speed chaos-based encryption/decryption if the fiber transmission module is considered.
IEEE Photonics Technology Letters 06/2012; 24(12):1072-1074. · 2.19 Impact Factor
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ABSTRACT: A novel optoelectronic oscillator (OEO) using cascaded recirculating delay lines (RDLs) is proposed and experimentally demonstrated. In the proposed OEO, instead of the use of an electronic microwave ðlter, two infinite impulse response (IIR) photonic microwave ðlters (PMFs) formed by two RDLs are employed to select oscillation frequencies. Specifically, an amplified spontaneous emission (ASE) source is adopted to avoid self-interference of each RDL, and two approximately equal gain RDLs are employed to reduce the influence of mutual interference between the two RDLs. Therefore, a stable microwave signal can be generated from the OEO loop. In the experiment, by tuning the lengths of RDLs, microwave signals at different frequencies, such as 194.1MHz, 648.5MHz and 2.99GHz, have been generated. The phase noise performance of the generated microwave signal is also investigated. The proposed approach has the potential for the generation of microwave signals up to tens of GHz with the use of integrated micro-ring devices.
Optics Express 06/2012; 20(12):13296-301. · 3.59 Impact Factor
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ABSTRACT: We have discussed numerically the characterization of time delay (TD) signature in a chaotic verticalcavity
surface-emitting laser (VCSEL) subject to optical feedback, where the results for polarizationpreserved
optical feedback (PPOF) and polarization-rotated optical feedback (PROF) are presented
comparatively. It is found that, when the feedback strength is moderate, TD signature can be retrieved
successfully by analyzing the total intensity, intensities of x-linearly polarized (x-LP) mode, and y-LP
mode in a VCSEL with PPOF; while for PROF case, the intensity amplitude peaks in autocorrelation
function (ACF)/delayed mutual information (DMI) of the two orthogonal LP modes are located at
multiple values of TD. Furthermore, the influence of the feedback strength and time delay has been
investigated. The results show that, a further increase of the feedback strength (roughly440 ns�1)
leads to the successful identification of the TD signature in the two LP mode intensities of VCSELs with
PROF. It is also observed that the estimation of TD depends significantly on the value of the spin–flip
relaxation rate (gs). For low relaxation rates the TD signature could be much easier to be revealed by the
two LP modes than that for large values of relaxation rate in VCSELs with PROF. Finally the influence of
injection current and the device linear anisotropies is investigated, and the results of TD estimation are
confirmed by calculating permutation entropy (PE).
Optics Communications 06/2012; 285:3837–3848. · 1.49 Impact Factor
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ABSTRACT: Pump encoding is an effective approach to enhance the weak signal detection in distributed Brillouin fiber sensors. In this
paper, a new encoding matrix that can improve the detection performance is proposed. Furthermore, a distributed fiber sensor
for both single and encoding pump operations is numerically analyzed by using Brillouin-scattering coupled amplitudes equations.
The results demonstrate that the matrix can reduce the transmission times for pumping light and simplify the coding process.
The power of the scattering signal and the coding gain can be improved with the increasing code length. The detected scattering
optical power is almost three orders of magnitude higher than that of the single pulse pump, as the coding length is 31, corresponding
to 14.4 % improvement for the coding gain compared with the S matrix encoding method. At the same time, the temperature uncertainty can also be decreased.
Optoelectronics Letters 04/2012; 6(3):232-236.
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ABSTRACT: We perform a theoretical study on the polarization-resolved compound lasing mode (CLM) of two mutually coupled vertical-cavity
surface-emitting lasers (VCSELs). Different solutions of CLMs are derived though stability analysis of the spin-flip model.
The dynamical evolvements of CLMs with the existence of polarization degrees of freedom are also charactered. The most stable
CLM with the smallest carrier density tend to be excited, since the gain needed for this mode to emit is the lowest. In the
given system, varying values of injection rate or birefringence, etc., will change the generation of the preferred CLMs in
the two polarization directions, and thus influence the polarization switching (PS) characteristics. Thus, hoppings between
CLMs are also companied by PSs. Through mapping of average power in the parameter space, the influences of coupling rate and
anisotropy parameters (linear dichroism and linear birefringence) on PS and hopping between CLMs are discussed.
Science in China Series F Information Sciences 04/2012; 51(5):592-598. · 0.66 Impact Factor
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ABSTRACT: We propose and experimentally demonstrate a photonic approach to the measurement of the time-difference-of-arrival (TDOA) and the angle-of-arrival (AOA) of a microwave signal. In the proposed system, the TDOA and the AOA are equivalently converted into a phase shift between two replicas of a microwave signal received at two cascaded modulators. The light wave from a CW laser is externally modulated by the microwave signal at the first modulator, which is biased to suppress the optical carrier, leading to the generation of two first-order sidebands, which are further modulated by the phase-delayed microwave signal at the second modulator. Two optical components at the carrier wavelength are generated. The total power at the carrier wavelength is a function of the phase shift due to the coherent interference between the two components. Thus, by measuring the optical power, the phase shift is estimated. The AOA is calculated from the measured phase shifts. In our experiment, the phase shift of a microwave signal at 18 GHz from -160° to 40° is measured with measurement errors of less than ±2.5°.
Optics Letters 02/2012; 37(4):755-7. · 3.40 Impact Factor
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ABSTRACT: The time-convolutionless (TCL) non-Markovian master equation was generally
thought to break down at finite time due to its singularity and fail to produce
the asymptotic behavior in strong coupling regime. However, in this paper, we
show that the singularity is not an obstacle for validity of the TCL master
equation. Further, we propose a multiscale perturbative method valid for
solving the TCL master equation in strong coupling regime, though the ordinary
perturbative method invalidates therein.
02/2012;
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ABSTRACT: In strain measurement applications, the matched fiber Bragg gratings (FBG) method is generally used to reduce temperature dependence effects. The FBG parameters have to be designed to meet the requirements by the particular application. The bandwidth and slope of the FBG has to be balanced well, according to the measurement range, accuracy and sensitivity. A sensitivity enhanced strain demodulation method without sacrificing the measurement range for FBG sensing systems is proposed and demonstrated utilizing a pair of reference FBGs. One of the reference FBGs and the sensing FBG have almost the same Bragg wavelength, while the other reference FBGs has a Bragg wavelength offset relative to the sensing FBG. Reflected optical signals from the sensing FBG pass through two reference FBGs, and subtract from each other after the detection. Doubled strain measurement sensitivity is obtained by static rail load experiments compared to the general matched grating approach, and further verified in dynamic load experiments. Experimental results indicate that such a method could be used for real-time rail strain monitoring applications.
Sensors 01/2012; 12(4):3891-900. · 1.74 Impact Factor
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ABSTRACT: In this paper, a secure optical chaos-based communication scheme is proposed. A semiconductor laser (SL) subjected to polarization-rotated optical feedback serves as the drive laser (DL), and two identical or near-identical SLs act as the transmitter laser (TL) and receiver laser (RL). The TL and the RL receive identical polarization rotated optical injection from the DL. Two channels are used, and the TM mode of the DL, after being rotated by 90°, serves as the perturbation quantity. The communication performance is numerically studied. More importantly, the high fidelity and high degree of privacy of the proposed scheme are verified in detail, and the failure of two potential attacker scenarios is demonstrated, even if the attacker can get access to both channels simultaneously.
Journal of the Optical Society of America B 01/2012; 29(1):101-108. · 2.18 Impact Factor
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ABSTRACT: To quantify the unpredictability of chaotic signals generated by vertical-cavity surface-emitting lasers (VCSELs) subject to polarized optical feedback, we numerically investigate the properties of recently introduced quantifier based on information theory, i.e., permutation entropy (PE) H . VCSEL1 subject to polarization-preserved optical feedback and VCSEL2 subject to polarization-rotated optical feedback are considered. The H for X-polarization (XP) mode, Y-polarization (YP) mode, and total output for both VCSELs are discussed and compared in detail. The influences of feedback strengths, feedback delays, and injection currents are focused on. For lower injection current, the 2-D maps illustrate that the trends of H for the XP mode, YP mode, and total output are different for both VCSELs. While for higher injection current, the values of H for both VCSELs increase with the feedback strengths, are not sensitive to feedback delays, and are higher than the counterparts for lower injection current. Moreover, the H increases with injection current for both VCSELs with a decreasing slope. These results show that the PE is an effective tool for quantifying the degree of unpredictability of chaotic signals of VCSELs, and provides valuable information for choosing the proper chaotic carrier.
IEEE Journal of Selected Topics in Quantum Electronics 11/2011; · 3.78 Impact Factor
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ABSTRACT: The generation and synchronization of unpredictability-enhanced chaos in vertical-cavity surface-emitting lasers (VCSELs) are investigated numerically. The master VCSEL is subject to variable-polarization optical feedback. Two injection schemes, the polarization-preserved optical injection (PPOI) and variable-polarization optical injection (VPOI) are considered for the slave VCSELs. The influences of unpredictability degree on the synchronization quality and the synchronization properties of unpredictability-enhanced chaos are focused on. For the PPOI scheme, the synchronization quality is hardly affected by the unpredictability degree; high-quality synchronization can be achieved between unpredictability-enhanced chaos due to injection locking. However, for the VPOI scheme, the unpredictability degree affects the synchronization quality significantly. High degree of unpredictability leads to low synchronization quality. Only the low-unpredictability chaos can be well synchronized, while the unpredictability-enhanced chaos cannot be synchronized even with large injection strength. The achievement of unpredictability-enhanced chaos synchronization by the PPOI scheme is extremely useful for the security-enhanced VCSELs-based chaos communication systems.
IEEE Journal of Quantum Electronics 11/2011; · 1.88 Impact Factor
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ABSTRACT: A photonic approach to measuring microwave frequency with digital results is proposed and experimentally demonstrated. In the proposed approach, N photonic phase-shifted filters with a phase shift increment of π/N in the transmission responses are designed. The filters are then employed to process the single optical sideband generated by applying a microwave signal to a single sideband suppressed-carrier (SSB-SC) modulation module, to perform frequency-to-amplitude conversion and analog-to-digital conversion simultaneously. After the implementation of power detection and decision operation to the filtered optical sideband, an N-bit result in the form of the circular code is obtained, which indicates the frequency of the microwave signal. A proof-of-concept experiment is performed to verify the proposed approach and a 5-bit circular code is generated to indicate microwave frequency up to 40 GHz.
Optics Express 10/2011; 19(21):20580-5. · 3.59 Impact Factor
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ABSTRACT: Based on the protocol-low-energy adaptive clustering hierarchy (LEACH), we investigate an improved energy-efficient communication protocol for wireless sensor networks (WSNs) in the presence of distributed optical fiber sensor (DFS) links located at the center of WSN fields. Network performances in terms of lifetime of nodes are simulated for the cases that two WSNs can or cannot communicate with each other. The lifetime of the such sensor network with rectangular topology is further investigated.
IEEE Sensors Journal 10/2011; · 1.52 Impact Factor
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ABSTRACT: The effects of unpredictability degree on the chaos synchronization properties of vertical-cavity surface-emitting lasers with variable-polarization optical feedback are investigated numerically. For variable-polarization optical injection, only low-unpredictability chaos can be well synchronized, while high-unpredictability chaos cannot be synchronized even with large injection strength. On the other hand, for the polarization-preserved optical injection, the synchronization quality is hardly affected by the unpredictability degree, and high-quality synchronization can be achieved for both low- and high-unpredictability chaos due to injection locking.
Optics Letters 09/2011; 36(17):3497-9. · 3.40 Impact Factor
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ABSTRACT: We numerically analyze the effect of an injection current on the synchronization and communication features of two chaotic external cavity semiconductor lasers in a closed-loop configuration. The simulation results demonstrate that, by moderately increasing the injection current, the efficient bandwidth of the chaotic carrier would be broadened, high quality chaos synchronization can be preserved, and the communication performance can be enhanced.
Optics Letters 08/2011; 36(16):3197-9. · 3.40 Impact Factor
