Xiaozhong Ge

Triangular pulse generation using a dual-parallel Mach–Zehnder modulator driven by a single-frequency radio frequency signal

A simple scheme for the generation of full-duty-cycle triangular pulses is proposed and experimentally demonstrated using a dual-parallel Mach-Zehnder modulator driven by a single-frequency RF signal. By properly setting the bias voltages and the RF power, even-order harmonics in the optical intensity are suppressed, and the amplitude of the first-order harmonic is 9 times of that of the third-order harmonic. A periodical triangular pulse train is obtained in the time domain. 2.5, 5, and 10 GHz triangular pulse trains are experimentally generated, which verifies the feasibility of the proposed scheme.

Phase-coded microwave signal generation based on a single electro-optical modulator and its application in accurate distance measurement

A novel scheme for photonic generation of a phase-coded microwave signal is proposed and its application in one-dimension distance measurement is demonstrated. The proposed signal generator has a simple and compact structure based on a single dual-polarization modulator. Besides, the generated phase-coded signal is stable and free from the DC and low-frequency backgrounds. An experiment is carried out. A 2 Gb/s phase-coded signal at 20 GHz is successfully generated, and the recovered phase information agrees well with the input 13-bit Barker code. To further investigate the performance of the proposed signal generator, its application in one-dimension distance measurement is demonstrated. The measurement accuracy is less than 1.7 centimeters within a measurement range of ~2 meters. The experimental results can verify the feasibility of the proposed phase-coded microwave signal generator and also provide strong evidence to support its practical applications.

Photonic generation of pulsed microwave signals with tunable frequency and phase based on spectral-shaping and frequency-to-time mapping

A scheme for photonic generation of pulsed microwave signals with tunable frequency and phase based on optical spectral-shaping and frequency-to-time mapping is proposed and experimentally demonstrated. The spectral shaping is realized by a tunable optical comb filter consisting of a differential group delay (DGD) element, a polarization modulator (PolM), and a polarizer. By passing a short optical pulse through the tunable comb filter and a dispersive element (DE), a pulsed microwave signal is generated after optical-to-electrical conversion. The phase of the generated microwave signal can be continuously tuned by tuning the voltage applied to the PolM. The frequency of the microwave signal can be tuned by changing the DGD and/or the dispersion of the DE. An experiment is performed. The generation of a pulsed microwave signal with tunable frequency and phase is demonstrated.

Simplified 2-bit photonic digital-to-analog conversion unit based on polarization multiplexing

Abstract. A 2-bit photonic digital-to-analog conversion unit is proposed and demonstrated based on polarization multiplexing. The proposed 2-bit digital-to-analog converter (DAC) unit is realized by optical intensity weighting and summing, and its complexity is greatly reduced compared with the traditional 2-bit photonic DACs. Performance of the proposed 2-bit DAC unit is experimentally investigated. The established 2-bit DAC unit achieves a good linear transfer function, and the effective number of bits is calculated to be 1.3. Based on the proposed 2-bit DAC unit, two DAC structures with higher (>2) bit resolutions are proposed and discussed, and the system complexity is expected to be reduced by half by using the proposed technique.

Stimulated Brillouin scattering based optical frequency comb generation using a stocks wave recycling loop

A novel approach to generating an optical frequency comb (OFC) based on stimulated Brillouin scattering (SBS) in optical fiber is proposed using a stocks wave recycling loop. Thanh to the stocks wave recycling loop, the SBS threshold is reduced and the SBS conversion efficiency is greatly improved, leading to increased number and enhanced flatness of the generated comb lines. An experiment is carried out. An OFC with a frequency spacing of 9.5 GHz is generated. The comb line number is increased from 6 to 9 by using the stocks wave recycling loop, and the flatness is also significantly improved. In addition, the self-lasing cavity modes are well suppressed.

Flat optical frequency comb generation using a single polarization modulator and a Mach-Zehnder interferometer

A flat optical frequency comb generation scheme using a polarization modulator and a Mach-Zehnder interferometer is proposed and experimentally demonstrated. OFCs with up to 11 comb-lines are generated with good flatness and tunable frequency spacing.

Phase stable radio distribution over optic cable by phase conjugation using an optical frequency comb

A phase stable radio frequency (RF) distribution technique is proposed and experimentally demonstrated. The system transmits optical frequency comb lines through an optic cable with multiple fibers. At the receiver, RF phase variation is removed by frequency mixing based on phase conjugation. In the proposed system, round-trip transmission is implemented through different fibers, thus the signal degradation due to bidirectional fiber transmission is eliminated. Besides, electrical frequency manipulations are not required because different frequency components can be generated by beating the comb lines at a photodetector, which leads to a simplified structure and alleviated signal distortion. Another advantage of the proposed scheme is that a series of phase stabilized frequencies at In times (n is a positive integer) of the comb spacing can be obtained simply by tuning the electrical filters. In the experiment, phase stable distribution of a 5 GHz signal and a 10 GHz signal over a 1.5 km optic cable is successfully demonstrated in a temperature varying environment. The residual delay variation of the 5 GHz signal is confined within ±1.1 ps, and the phase noise of the signal is well preserved after fiber distribution.

Photonic generation of binary differential phase-coded microwave signals

A scheme for photonic generation of binary differential phase-coded microwave signals is proposed and demonstrated. In the proposed system, two optical sidebands are generated and phase modulated by an electrical signal. Then, the two optical sidebands are separated by a Mach-Zehnder interferometer (MZI) and properly delayed between each other before combined at an optical coupler. By balanced photodetection after the optical coupler, a binary differential phase-coded microwave signal is generated. The carrier frequency of the generated signal is doubled compared with the signal source in the system, thus the requirement for high frequency electrical devices is relaxed. The proposed system is the first microwave photonic signal generator with differential phase coding, which can find applications in radar and communication systems.