Zihang Zhu

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.

Routing and wavelength assignment in a satellite optical network based on ant colony optimization with the small window strategy

Ant colony optimization (ACO) with the small window strategy is put forward to solve the routing and wavelength assignment problem in satellite optical networks. The intersatellite distance, link duration, and wavelength idle ratio are introduced as the heuristic functions, and the small window strategy is used to promote the convergence speed. By calculating the intersection of idle wavelengths on adjacent links, the algorithm can accomplish routing selection and wavelength assignment on a single ant. The results show that, compared with the Dijkstra+FF algorithm, the blocking probability of ACO can decrease by 50% at most, and improvement of the resource utilization ratio can reach 45%.

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.

Dynamic Range Improvement for an Analog Photonic Link Using an Integrated Electro-Optic Dual-Polarization Modulator

A novel analog photonic link with enhanced spurious-free dynamic range (SFDR) based on an integrated electro-optic dual-polarization modulator is presented and demonstrated. The dual-polarization modulator, which consists of a polarization beam splitter, a polarization beam combiner, and two z-cut LiNbO3 MZMs, can achieve complementary intensity modulation along the orthogonal polarization directions with different modulation indexes. By properly adjusting the power relationship of the orthogonal polarization directions, two third-order intermodulation distortions (IMD3) have equal intensity and opposite phase and cancel each other out. Combined with a low-biasing technique to reduce the noise power, the SFDR of the link can be further improved. A theoretical analysis is presented and validated by a simulation. The IMD3 can be suppressed by 30.6 dB, giving an improvement in SFDR of about 22 dB compared with a conventional optical double-sideband modulation link.

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.

Photonically Assisted Microwave Signal Generation Based on Two Cascaded Polarization Modulators With a Tunable Multiplication Factor

Filterless photonic generation of microwave signals with various frequency multiplication factors via series connected polarization modulators is proposed and demonstrated experimentally. Frequency octupling, sextupling, or quadrupling microwave signal can be obtained when the polarization state of the light wave, the modulation indices of the modulators, and the phase of the radio frequency (RF) driving signal are suitably set. The optical sideband suppression ratios and RF spurious suppression ratios of the generated frequency multiplication signals are measured. Besides, the frequency-tunable ability and phase noise are analyzed.

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.

Photonic Generation of Frequency and Bandwidth Multiplying Dual-Chirp Microwave Waveform

A photonic approach to generate a frequency and bandwidth multiplying dual-chirp microwave waveform using a single dual-polarization quadrature phase shift keying (DP-QPSK) modulator is proposed and demonstrated. In the proposed scheme, an RF carrier is applied to one QPSK modulator and a baseband single-chirp waveform is applied to another. By setting the driving signals applied to the modulator and adjusting the dc bias phases in the modulator, high-order optical sidebands can be obtained with the optical carrier suppressed. After optical to electrical conversion, a frequency-doubling and bandwidth-quadrupling, or frequency-quadrupling and bandwidth-octupling dual-chirp microwave can be generated. The approach is verified by simulation. Dual-chirp microwave waveforms with 16-GHz central frequency, 2048-MHz bandwidth and 32-GHz central frequency, 4096-MHz bandwidth are generated through an 8-GHz RF carrier and 512-MHz bandwidth baseband signal. The generated dual-chirp microwave waveform can be used in a radar system to improve its range-Doppler resolution.