Changjian Ke

All-Optical Highly Sensitive Chromatic Dispersion Monitoring Method Utilizing Phase-Matched Four-Wave Mixing

This letter represents a highly sensitive all-optical chromatic dispersion (CD) monitoring method utilizing phase-matched four-wave mixing (FWM) in highly nonlinear optical fibers (HNLFs). The monitoring ability arises from the exponential FWM gain which provides an exponential power transfer function (PTF) mapping the CD experienced by the signals onto the average power of the output idler wave. Our method is simple and much more sensitive compared to the other PTF-based monitoring methods proposed before. The sensitivity enhancement is important for highly accurate dispersion compensation and makes the method effective for signals with high duty cycles. Furthermore, by tailoring the phase-matched wavelength range our method can be used to monitor CD in a wavelength-division-multiplexing (WDM) network.

Photonic Generation of Frequency-Quadrupled Microwave Signal With Tunable Phase Shift

A photonic scheme for frequency-quadrupled microwave signal generation with full 360 ° arbitrarily tunable phase shift is proposed and experimentally demonstrated. Two coherent optical components are generated by biasing a Mach-Zehnder modulator at maximum transmission point to suppress odd-order sidebands. Then, two second order sidebands together with the optical carrier are sent to a programmable filter to reject the optical carrier and introduce a phase shift to one of the second order sidebands. A frequency-quadrupled microwave signal with tunable phase is finally obtained by beating the two sidebands at a photodetector. Tunable phase shift of full 360 ° with a microwave frequency from 30 to 42.4 GHz is experimentally demonstrated. The proposed approach has potential applications in the broadband array signal processing system.

Electro-optic chaotic system based on the reverse-time chaos theory and a nonlinear hybrid feedback loop

A novel electro-optic chaos source is proposed on the basis of the reverse-time chaos theory and an analog-digital hybrid feedback loop. The analog output of the system can be determined by the numeric states of shift registers, which makes the system robust and easy to control. The dynamical properties as well as the complexity dependence on the feedback parameters are investigated in detail. The correlation characteristics of the system are also studied. Two improving strategies which were established in digital field and analog field are proposed to conceal the time-delay signature. The proposed scheme has the potential to be used in radar and optical secure communication systems.

Enhanced Secure Strategy for OFDM-PON System by Using Hyperchaotic System and Fractional Fourier Transformation

We propose and experimentally demonstrate a scheme whereby hyperchaos and fractional Fourier transform (FrFT) techniques are integrated in an orthogonal frequency-division multiplexing (OFDM) passive optical network system. In our experiment, both security issues and transmission performance are investigated under an overall frame, and 7.64-Gb/s 16-quadrature-amplitude-modulation OFDM data with a four-level encryption scheme are successfully transmitted over a 25-km standard single-mode fiber. The results show that the system security and the transmission performance can be improved simultaneously. Moreover, the proposed scheme allows a flexible adjustment between the safety and the transmission performance according to the actual requirements.

An Optically Coupled Electro-Optic Chaos System With Suppressed Time-Delay Signature

We present an optically coupled chaotic system involving three-phase modulated electro-optic nonlinear loops and an optical coupler. The dynamical properties and the time delay signature (TDS) suppressing performance of the system is analyzed in detail. Numerical results show that the TDS can be suppressed not only under statistical analysis of a single output, but also under mutual statistical analysis of the multiple outputs. Compared with the intensity modulated electrically coupled scheme, the presented system has less interior noise due to the simpler construction.

Experimental Demonstration of Ultra-Dense WDM-PON With Seven-Core MCF-Enabled Self-Homodyne Coherent Detection

We demonstrate an ultra-dense wavelength-division-multiplexing (UDWDM) passive optical network (PON) in a spatial-division-multiplexing system utilizing our home-made seven-core multicore fiber (MCF) with a self-homodyne coherent detection (SHCD) scheme. In the SHCD system, we transmit 12 channels of 40-Gb/s UDWDM-PON signals using polarization-division-multiplexing quadrature phase-shift keying (PDM-QPSK) with a 12-GHz grid through the six outer cores of the seven-core MCF with the central core used to transmit the pilot tone. An optical frequency comb generator is employed to supply the multi-carriers for cost saving. After 37-km low-crosstalk seven-core MCF long-reach transmission with compact fan-in/fan-out multiplexers, a large transmission capacity of 2.88 Tb/s and a power budget of 26 dB are obtained. At the optical network unit side, a narrow linewidth local oscillator laser is no longer necessary since SHCD is adopted in our system. The complexity of the digital signal processing procedure at the coherent receiver is also greatly reduced as the carrier phase recovery and carrier frequency offset estimation are not needed.

High resolution and selectivity SBS-based filter utilizing a dual-stage scheme

A dual-stage SBS-based filter is demonstrated experimentally. By mitigating the gain saturation, a spectral resolution of ~22 MHz and a selectivity of ~50 dB together with a sensitivity of -65 dBm are achieved simultaneously.

Characterization of Fiber Bragg Grating Inscribed in Few-Mode Silica-Germanate Fiber

We present a temperature and strain fiber sensor utilizing fiber Bragg grating (FBG) inscribed in silica-germanate few-mode fiber. The temperature and strain sensitivities of resonant wavelength formed by mode LP01 self-coupling and mode LP01-LP11 cross-coupling are investigated theoretically and characterized experimentally. Two resonant wavelengths demonstrate different temperature sensitivities of 11.5 pm/°C 10.6 pm/°C, respectively, due to different mode profile, while the strain sensitivities are quite similar with a value of 0.9 pm/με. By using FBG character matrix, the proposed fiber sensor can measure those two parameters simultaneously within a compact and cost-effective setup.

Power transfer function–based dispersion monitoring method applicable to signals with different duty cycles and optical signal-to-noise ratio

This paper represents a power transfer function (PTF)-based chromatic dispersion (CD) monitoring method applicable to signals with different duty cycles and optical signal-to-noise ratio (OSNR). Our method relies on phase-mismatched four wave mixing to provide a steep PTF that maps the CD experienced by the signal onto the average power of the output signal. The steep PTF greatly enhances the monitoring sensitivity, thus solves the problem that former PTF-based methods cannot be applied to signals with high duty cycles and low OSNR because of low output contrast. Furthermore, because the optical power required is low, our method is optically efficient and easy-to-implement. Numerical simulations are then used to demonstrate the effectiveness and efficiency of this monitoring method.

Downhill simplex algorithm based approach to holey fiber design for tunable fiber parametric wavelength converters

We present a new approach to the design of the holey fibers that have ultra-high nonlinearity and dispersion properties optimized for tunable fiber parametric wavelength converters based on degenerated four wave mixing. This hybrid approach combines downhill simplex algorithms with four wave mixing modeling. Exploiting the relations between fiber properties and the converters characteristics, this method is not only much faster than other methods proposed before but also enables an inverse design of the holey fibers according to the pre-set device characteristics, like conversion gain, tuning range, fiber length and pump power. We then investigate the sensitivity of these characteristics to the small variations in the fiber structural parameters and find adjusting the pump power can to some extent mitigate the impact of the fabrication errors.