Xinlu Gao

Measurement of the rotational Doppler frequency shift of a spinning object using a radio frequency orbital angular momentum beam

An indirect approach based on phase measurement is proposed to measure the rotational Doppler frequency shift, which takes full advantage of the phase structure of orbital angular momentum (OAM) beams in radio domain, using a vector network analyzer (VNA) as a phase discriminator. A proof-of-concept experiment is established by an optical-controlled system with the OAM state of 1. By analyzing the experiments results, the rotational Doppler frequency shift is measured as 24.83 Hz (max error rate 0.67%) at 50π rad/s rotational velocity, deducing the rotational velocity as 50.18π (average error rate 0.36%).

Wideband RF photonic phase shifter with a full 360° phase tunable range

A novel photonic approach to the implementation of RF photonic phase shifter is proposed. It is based on a polarization dependent optical phase modulator and a dual-parallel Mach-Zehnder modulator. The phase shift of RF signal has a predefined linear relationship with the dc bias voltage of the optical phase modulator. This enables users to easily determine the control voltage needed to realize the desired phase shift of RF signal. It can realize multiple photonic RF phase shifters simultaneously applied in optical controlled Phased Array Antennas. Results show the RF phase shifter can achieve a continuous −180 ∼ phase shift with little phase and amplitude variations over a wide frequency range.

Anti-dispersion phase-tunable microwave mixer based on a dual-drive dual-parallel Mach-Zehnder modulator

An optically-controlled phase-tunable microwave mixer based on a dual-drive dual-parallel Mach-Zehnder modulator (DDDP-MZM) is proposed, which supports wideband phase shift and immunity to power fading caused by chromatic dispersion. By using carrier-suppressed single side-band (CS-SSB) modulation for the local oscillator (LO) signal and carrier-suppressed double side-band (CS-DSB) modulation for the input signal, no vector superposition for the same output microwave frequency occurs, making the system immune from power fading caused by chromatic dispersion. Phase tuning is achieved by shifting the phase of the LO signal, and direct electrical tuning of the wideband microwave input signal is avoided, thus supporting large working bandwidth. A phase-shifted down-conversion experiment is carried out, where a phase shift with 0 ~390° and down-conversion are achieved with a phase variation of less than 5° and power variation less than 3.5 dBm when the input signal sweeps between 12 ~16 GHz. The mixer is simple and power-efficient since it uses a single compact modulator, and does not require any optical filters. No power notches are observed in the output microwave spectrum, proving that the dispersion-related frequency-selective fading is mitigated.

Bidirectional radio over fiber system with wavelength reuse based on optical carrier polarization-suppressed DSB modulation

To overcome the limitation of wavelength-dependent optical filter, we have experimentally demonstrated a bidirectional RoF system based on carrier polarization-suppressed DSB modulation. After transmitted over 10.5-km SMF, 0.3-dB power penalty is achieved for bidirectional links.

Optical-controlled pencil-beam steering phased-array based on FD-OP

A pencil-beam steering phased-array based on optical-controlling scheme is proposed. FD-OP is used to gain flexibility and high tunablility. Experiments are conducted at 17 GHz to validate the 2D beams-steering ability of the system.

High spectral purity millimeter wave generation and wavelength reuse radio over fiber system based on modified double sideband

A modified double sideband modulation(DSB) scheme to realize frequency doubling and wavelength reuse in the uplink is proposed. In the modified DSB scheme, by adjusting the phase difference between two arms of the intensity modulator, the optical carrier and the two first-order sidebands are generated, after beaten by the photodiode, a high spectrum purity and low phase noise millimeter-wave (mm-wave) signal with double times of the RF frequency without any optical filter or dc bias is generated. Theoretical analysis and numerical simulation are performed, showing that the power penalties for bidirectional signals are less than 2 dB after transmitted over 40 km single mode fiber. Additionally, the proposed scheme has simple configuration and good quality.

Tunable RF photonic phase shifter based on optical DSB modulation and FBG filtering

A broadband RF photonic phase shifter that can achieve the tunable phase shift with little RF amplitude variation is presented. It is based on homodyne mixing technique. The beating between phase-modulated optical carrier and the sidebands can generate RF signal with desired phase shift. Results show the RF phase shifter can achieve a continuous phase shift with low amplitude variation.

The First Experiment to Transmit RF Data in OAM Mode with Optical-assisted Circular Antenna Arra

We conducted the first experiment to transmit an RF IQ signal in OAM mode by OCAA, to prove that OAM modes coexists with IQ modulation and could be measured. Directionality and transmission quality is assessed.

Tunable and integrated RF photonic phase shifter based on phase modulation and FBG filtering

An integrated RF photonic phase shifter that can achieve a tunable phase shift with little RF amplitude variation is presented. The beating between phase-modulated optical carrier and the first-order sideband can generate RF signal with desired phase shift. Results show the RF phase shifter can achieve a continuous 0° − 360° phase shift with low amplitude variation.

Full-Duplex ROF Link with Seamless Convergence and High-Speed Broadband Wireless Access

Full-duplex ROF link with seamless convergence and high-speed broadband wireless access is proposed. The simulation of V-band (62.4GHz) and conventional 802.11n (2.4GHz) with 16QAM signal transmission shows that our novel schedule maintains quite good performance.