Shangyuan Li

Highly Linear Radio-Over-Fiber System Incorporating a Single-Drive Dual-Parallel Mach–Zehnder Modulator

We propose a highly linear radio-over-fiber system with low intermodulation distortion (IMD) using a single-drive dual-parallel Mach-Zehnder modulator (SD-DPMZM). The optical carrier is modulated in one of the two parallel modulators, while remaining unmodulated in the other one. There exists optimal working points for SD-DPMZM that makes its two kinds of origins of third-order IMD (IMD3) have opposite phase and equal intensity, and cancel each other; hence the output IMD3 is suppressed dramatically. Experimental results show that the proposed scheme can achieve a spurious-free dynamic range of up to 122.9 dB · Hz2/3, which is in agreement with the theoretical analysis. It is about 20 dB more than a conventional MZM. The error vector magnitude of the proposed scheme, for a 16-QAM 10-MSym/s signal centered at 4 GHz, is 1.94%.

Compensation of dispersion-induced power fading for highly linear radio-over-fiber link using carrier phase-shifted double sideband modulation.

A carrier phase-shifted (CPS) double sideband (DSB) modulation technique in radio-over-fiber (RoF) system is proposed and experimentally demonstrated. By tuning the biases in a single-drive dual parallel Mach-Zehnder modulator (SD-DPMZM), the optical carrier in the DSB spectrum acquires additional phase shift. The transmittance response of a dispersive RoF link is thus being controlled and shifted in the frequency domain. Experiments successfully turned the maximum transmission frequency to 10 GHz and 15 GHz for both 25 and 39 km fiber links. This is also a highly linear scheme, of which a spurious-free dynamic range (SFDR) of 111.3 dB·Hz2/3 is experimentally obtained.

Postcompensation for nonlinearity of Mach-Zehnder modulator in radio-over-fiber system based on second-order optical sideband processing.

A postcompensation technique for nonlinearity of a Mach-Zehnder modulator in a radio-over-fiber (ROF) system is proposed and experimentally demonstrated based on second-order optical sideband processing and optical carrier band attenuation. The phase of the second-order optical sideband is shifted to suppress the third-order intermodulation distortion (IMD3) in a direct detection ROF link. The optical carrier band is attenuated to make two kinds of origins of IMD3 have equal intensity and cancel each other out. A spurious-free dynamic range of 124.8 dB·Hz(2/3) is achieved, which is about 25 dB more than that without compensation.

Generating the orbital angular momentum of radio frequency signals using optical-true-time-delay unit based on optical spectrum processor

A system for generating radio frequency signals with orbital angular momentum (OAM) is proposed and certificated for the first time, which employs an array of multiple optical-true-time-delay elements and circular antennas array (CAAs). A constructive Fourier series theory about CAAs collectively forming an OAM radio beam is demonstrated. An optical spectrum processor offers the four lines high-resolution time delay by adding a series of linear optical phase shifts. The OAM radio beam with topological charge L=1 is produced and measured successfully.

Dynamic range improvement strategy for Mach-Zehnder modulators in microwave/millimeter-wave ROF links

Intermodulation distortions are generated by Mach-Zehnder modulators when they are driven by signals with certain bandwidth in microwave (MW) and millimeter-wave (MMW) radio-over-fiber (ROF) links. The optical spectral structure of the distorted optical signal is investigated. A strategy to improve the dynamic range of MW and MMW ROF links directly in the optical domain is proposed and experimentally demonstrated. Based on optical spectrum processing, the third-order intermodulation distortions (IMD3s) of the generated signals are suppressed. A 107.2dB∙Hz2/3 spurious-free dynamic range (SFDR) of the MW/MMW ROF link is obtained, which is improved more than 20dB. A 16QAM signal is transmitted in the system and the error vector magnitude (EVM) is measured with and without the proposed technique. The influence of the nonlinearity of modulators on EVM is almost completely eliminated.

True time-delay line with high resolution and wide range employing dispersion and optical spectrum processing

True time-delay line with a high resolution and wide range is proposed and demonstrated. Tunable lasers and dispersion fibers are employed to control the time delay coarsely. An optical spectrum processor is utilized to realize high-resolution time-delay control by adding a quadratic optical phase shift, which compensates the group velocity dispersion of the fiber simultaneously. A coarse tuning range of 1717 ps is realized by changing the wavelength of the optical carrier, and a high resolution of 0.67 ps is achieved by translating the symmetry axis of the quadratic phase shift.

Highly linear millimeter-wave over fiber transmitter with subcarrier upconversion

By linearized modulation of a heterodyne subcarrier source using a dual-parallel Mach-Zehnder modulator, a subcarrier up-converted millimeter-wave over fiber transmitter is proposed and experimentally demonstrated with an SFDR of 122.7dB·Hz2/3.

Idler-free microwave photonic mixer integrated with a widely tunable and highly selective microwave photonic filter

A novel structure consisting of an idler-free microwave photonic mixer integrated with a widely tunable and highly selective microwave photonic filter is presented, which is comprised of a spectrum-sliced broadband optical source, a dual-parallel Mach-Zehnder modulator (DPMZM), and a spatial light amplitude and phase processor (SLAPP). By adjusting the optical phase shift in the DPMZM, the dispersion-induced mixing power fading can be eliminated. By applying a phase processor with the SLAPP, the distortion of the mixing filter brought upon by third-order dispersion is also compensated. Experiments are performed and show that the up/down-conversion signal has a clean spectrum and the mixing filter can be tuned from 12 to 20 GHz without any change to the passband shape. The out-of-band suppression ratio of the mixing filter is more than 40 dB, and the 3 dB bandwidth is 140 MHz.

Multisideband Detection Radio-Over-Fiber Link With Phase Modulation and Fiber Demodulation for Vector Signal Transmission

We propose and demonstrate a multisideband detection (MSD) radio-over-fiber (RoF) link with optical phase modulation (PM) and fiber demodulation to transmit vector signals. In the scheme, the optical PM signal is demodulated by the fiber dispersion. The fading effect can be almost entirely overcome thanks to the MSD. In case of 50-Msymbols/s vector signal with frequencies of subcarrier ranging from 2 to 12 GHz over 25-, 50-, and 100-km single-mode fibers, respectively, the RoF-links error vector magnitude of better than 4.5% and spurious-free dynamic range of more than 97 dB·Hz2/3 are obtained experimentally.

Simultaneous multiwavelength optical SSB generation for WDM radio-over-fiber systems using a DGD element and a polarizer

The simultaneous generation of multi-wavelength optical single sideband (SSB) modulation for wavelength division multiplex (WDM) Radio-over-Fiber systems using a differential group delay (DGD) element and a polarizer is constructed in the paper. Simulation proved the principle shows the capacity of such filtering scheme works for at least 8 channels. Experiment results accorded with simulations. Experiment also shows the operating range of the system is more than 40nm, which covers the whole C-band. The sideband suppression ratio for all possible channels is greater than 20dB.