Yongjun Li

A Radio-Over-Fiber System With Frequency 12-Tupling Optical Millimeter-Wave Generation to Overcome Chromatic Dispersion

A radio-over-fiber system with frequency 12-tupling optical millimeter-wave (mm-wave) generation using an integrated nested Mach-Zehnder modulator (MZM) is proposed and demonstrated by simulation. Through properly adjusting the direct current bias voltages of two sub-MZMs, the RF local oscillator (LO) voltages and phases, and the gain of base-band signal, the frequency 12-tupling optical mm-wave with data only carried by one sixth-order sideband is generated. As the signal is transmitted along the fiber, there is no periodical fading and bit walk-off effect caused by chromatic dispersion. The eye diagrams stay open even when the signal is transmitted over 60 km and the power penalty is 0.67 dB at a BER of 10-10. Furthermore, it is also proved to be valid that the BER is insensitive to the deviation of modulator extinction ratio and RF LO voltage.

A Linearized Optical Single-Sideband Modulation Analog Microwave Photonic Link Using Dual Parallel Interferometers

Dual parallel Mach-Zehnder interferometers (MZIs) are presented to linearize the optical single-sideband (OSSB) modulation analog microwave photonic link. By using a dual-drive Mach-Zehnder modulator at the transmit side of the link, an OSSB modulation can be obtained. By exploiting different RF responses of two MZIs at the receive end, the third-order intermodulation distortion (IMD3) is well suppressed and the spurious-free dynamic range (SFDR) is enhanced. More importantly, we demonstrate fundamental-to-IMD3 ratio of 49 dB for an RF input signal power value of 10 dBm, which is 24 dB more than a conventional OSSB modulation link, and SFDR of 132 dB for a bandwidth of 1 Hz at the received optical power of 8 dBm assuming shot noise is the dominant noise contribution, which is improved approximately 20 dB.

Optimization of intersatellite microwave photonic links by utilizing an optical preamplifier under dual-tone modulation

An optical preamplifier is utilized to improve the signal-to-noise and distortion ratio (SNDR) of intersatellite microwave photonic links employing a Mach-Zehnder modulator under dual-tone modulation. The resulting SNDR at an appropriate direct current (DC) bias phase shift is additionally investigated without small-signal approximation in order to optimize the performance of all the links. It is observed that the most limiting factor degrading the SNDR performance is changed, and the fundamental power is seen to increase more compared with the power of third-order intermodulation (IM3) plus noise due to the optical preamplifier. Thus, SNDR can be improved with respect to the case of a nonoptical preamplifier. For the preamplifier gain of 20 dB and noise figure of 3 dB, an increase of about 24 dB in optimum SNDR is accessible. In addition, the optimum DC bias phase shift is found to be insensitive to the preamplifier gain and noise figure, while the optimum SNDR is sensitive to the preamplifier gain and noise figure.

Impact of pointing errors on performance of an intersatellite microwave photonics link with an optical preamplifier under dual-tone modulation.

The intersatellite microwave photonics link with an optical preamplifier is affected by third-order intermodulation distortion under dual-tone modulation and pointing errors due to beam wander, which would greatly degrade the link performance. An exact analytical expression for signal-to-noise and distortion ratio (SNDR) is derived considering the signal fade caused by the pointing errors of transceiver. It is shown that, given the desired SNDR and the rms random pointing jitter, an optimum modulation index of Mach-Zehnder modulator exists that minimizes laser output power. Moreover, an optimized model for laser output power and modulation index is established. The effects of the optical preamplifier gain and noise figure on the optimum link performance are also examined. Numerical results show that the minimum laser output power required to achieve the desired SNDR is more sensitive to the preamplifier noise figure. For an SNDR of 20 dB, doubling the preamplifier noise figure results in an 8.95 dB increase in minimum laser output power at the rms pointing jitter of 0.5 μrad.

Effect of a simple double-confined structure on nanosecond pulse ablative laser propulsion

We succeeded in obtaining propulsion of an aluminum bullet by a gigawatt nanosecond pulse Nd:glass laser, in which we demonstrated the effectiveness of a simple double-confined structure that consists of a thin black-paint coat covered with a glass board as a transparent overlay. The black-paint coat not only serves as a substitute for the target to be ablated, but also improves the absorbency of the incident laser energy. Another main feature of this structure is that it can lead to the enhancement of the coupling coefficient due to plasma confinement and impedance mismatch. Adopting this simple double-confined structure, a coupling coefficient up to 160 dyne/W was achieved, which was enhanced by about 20 times with respect to direct ablation.

Broadband linearized analog intersatellite microwave photonic link using a polarization modulator in a Sagnac loop

A novel orthogonal polarization optical carrier suppression with carrier (OCS+C) modulation and a coherent balanced detection intersatellite microwave photonic link with improved signal-to-noise and distortion ratio (SNDR) is proposed. By bidirectional use of a polarization modulator in a Sagnac loop in conjunction with a polarization beam splitter and two polarization controllers, only the light wave along the clockwise direction is effectively modulated while the counterclockwise light wave is not modulated due to the velocity mismatch, which generates the orthogonal polarization OCS+C modulation signal to mitigate the third-order intermodulation distortion (IMD3) and the signal-amplifier spontaneous emission beating noise. By demultiplexing and adjusting the polarization of the orthogonal polarization OCS+C modulation signal, coherent balanced detection can be realized without a local oscillator signal in the receiver, which suppresses the second-order distortions. Thus, a broadband linearized intersatellite microwave photonic link with high SNDR is achieved. Simulation results show that the maximum SNDR of 36.2 dB can be obtained when the optimum modulation index is 0.26, which is 8 dB higher than our previously proposed intersatellite microwave photonic link with an optical preamplifier.

Optical millimeter-wave generation with modified frequency quadrupling scheme

Abstract. A dispersion-tolerant full-duplex radio-over-fiber (RoF) system based on modified quadrupling-frequency optical millimeter (mm)-wave generation using an integrated nested Mach–Zehnder modulator (MZM), an electrical phase modulator, and an electrical gain is proposed. Not only does the scheme reduce the cost and complexity of base station by reusing the downlink optical carrier, but also the generated optical mm-wave signal with base-band data carried only by 1-s order sideband can overcome both the fading effect and bit walk-off effect caused by the fiber dispersion. Simulation results show that the eye diagram keeps open and clear even when the quadrupling-frequency optical mm-wave is transmitted over 120-km single-mode fiber, and the bidirectional 2.5  Gbit/s data are successfully transmitted over 40 km for both upstream and downstream channels with <1-dB power penalty.

Weighted Algebraic Connectivity Maximization for Optical Satellite Networks

In this paper, the topology configuration methods for heterogeneous optical satellite networks are investigated. Our objectives are to maximize weighted algebraic connectivity with respect to both network initialization and reconfiguration scenarios subject to onboard hardware constraints. The problems are not strictly convex and have been proven as NP-hard. In order to solve the problems in polynomial time, the original problems are relaxed to a convex optimization problem. Specifically, the relaxed problem is transformed to a positive semidefinite programming form, which can be solved exactly and more efficiently. Furthermore, based on the perturbation theory of matrices, we propose two greedy heuristic methods to deal with the initialization and reconfiguration case from the relaxed solutions, respectively. Simulation results show that the proposed algorithms are able to accomplish network initialization and reconfiguration correctly in the overwhelming majority of situations. The final sub-optimal solutions can also be obtained under low computational complexity.

A novel two-layered optical satellite network of LEO/MEO with zero phase factor

Optical satellite communication has advantages over the RF satellite communication in capacity, speed, secrecy and anti-interference. Space information superhighway composed of GEO/MEO/LEO satellites which are linked by optical inter-satellite links (OISL) would play important roles in communication, navigation, martial recon, remote sensing and deep space exploration. A novel LEO/MEO two-layered optical satellite network with global coverage is designed with the street-of-coverage technique. The layer of LEO satellites is the walker-delta constellation with zero phase factor and has the quasi-stable logical structure of Mesh. Equatorial and polar orbit satellites constitute the layer of MEO satellite, which can cover LEO layer effectively. Rising satellites of the system can provide 99.9% of coverage for the whole globe and 100% for China averagely. The network can provide a minimum elevation angle at 21° with single-satellite visibility for China, and at 16° with the dual-satellite visibility. Simulation results of the inter-satellite links show LEO constellation of zero phase factor outperforms non-zero phase factor constellations in azimuth angle, elevation angle and distance, which is very fit for the OISL. Simulation results of the communication performance indicate a little difference between short wave band and long wave band at low communication speed (several Gbit/s); however, the wave band at 1550 nm is a better choice at high communication speed (100 Gbit/s).

A Space-Circle Architecture Design and Performance Analysis of Spatial Backbone Network Based on Geostationary Satellite Collocation

With the development of satellite technology, and continuous improvement of relay, communication, navigation, remote sensing and meteorological satellite systems in China, massive heterogeneous spatial information needs for convergence, integration, storage, transmission, processing, forwarding and so on had put forward higher requirements to the construction of spatial backbone network. Proceeding from the architecture design of spatial backbone network, using the method of geostationary satellite collocation to build the backbone node was proposed. And then several typical geostationary satellite collocation styles were analyzed and compared. Using Orbital dynamics and spherical geometry theory, a fly around model with space-circle configuration was designed, and its AER performance was analyzed through simulation software and optimization algorithm. The simulation results showed that the configuration completely meet design requirements of spatial backbone network.