Shilie Zheng

Multiplexed Millimeter Wave Communication with Dual Orbital Angular Momentum (OAM) Mode Antennas

Communications using the orbital angular momentum (OAM) of radio waves have attracted much attention in recent years. In this paper, a novel millimeter-wave dual OAM mode antenna is cleverly designed, using which a 60 GHz wireless communication link with two separate OAM channels is experimentally demonstrated. The main body of the dual OAM antenna is a traveling-wave ring resonator using two feeding ports fed by a 90° hybrid coupler. A parabolic reflector is used to focus the beams. All the antenna components are fabricated by 3D printing technique and the electro-less copper plating surface treatment process. The performances of the antenna, such as S-parameters, near-fields, directivity, and isolation between the two OAM modes are measured. Experimental results show that this antenna can radiate two coaxially propagating OAM modes beams simultaneously. The multiplexing and de-multiplexing are easily realized in the antennas themselves. The two OAM mode channels have good isolation of more than 20 dB, thus ensuring the reliable transmission links at the same time.

Instantaneous Microwave Frequency Measurement Using an Optical Phase Modulator

A novel technique for instantaneous microwave frequency measurement using an optical phase modulator is proposed and demonstrated. In the proposed system, a microwave signal with its frequency to be measured is modulated on two optical wavelengths at the phase modulator, with the phase-modulated optical signals sent to a dispersive element, and detected at two photo-detectors. Due to the chromatic dispersion of the dispersive element, the two microwave signals will experience different power fading, leading to different power versus frequency functions. A fixed relationship between the microwave frequency and the microwave powers is established. By measuring the microwave powers, the microwave frequency is estimated. Compared with the techniques using an intensity modulator, the proposed approach is simpler with less loss. Since no bias is needed the system has a better stability, which is highly expected for defense applications. Experimental verification is presented.

Transmission Characteristics of a Twisted Radio Wave Based on Circular Traveling-Wave Antenna

A traveling-wave circular loop antenna with its phase distribution along the circle of lφ is demonstrated to generate the twisted radio wave. Theoretical formulations of its radiation fields are deduced in the cylindrical coordinate system and used to analyze its transmission characteristics, such as the radiation patterns, the evolution of the polarization states, and the angular momentum modes including the orbital angular momentum (OAM) modes and the spin angular momentum (SAM) modes. The prototype of a practical configuration for such antenna is proposed and conducted to validate the theoretical results. This theoretical analysis is applicable not only to radio waves but also to the whole electromagnetic spectrum.

Microwave spectral analysis based on photonic compressive sampling with random demodulation.

In this Letter, we present a photonic compressive sampling scheme based on optical sampling and random demodulation for microwave spectral analysis. A novel (to our knowledge) approach to realizing the multiplication of a pseudorandom binary sequence and the input microwave signal of interest in the optical domain is proposed, which largely simplifies the implementation of the compressive sampling. A spectrally sparse signal can be successfully captured by an electrical digitizer with a sampling rate much lower than the Nyquist rate with the help of random demodulation and the sparse reconstruction algorithm. Identification of the signals with multiple frequency components is successfully demonstrated.

Optically Tunable Frequency-Doubling Brillouin Optoelectronic Oscillator With Carrier Phase-Shifted Double Sideband Modulation

An optically tunable frequency-doubling optoelectronic oscillator (FD-OEO) based on stimulated Brillouin scattering (SBS) and carrier phase-shifted double sideband (CPS-DSB) modulation is proposed and demonstrated. SBS effect provides narrowband filtering for the OEO to generate an oscillation signal with frequency equal to the Brillouin frequency shift, while a CPS-DSB modulation by using a dual-parallel Mach-Zehnder modulator is implemented to double the oscillation frequency. Owing to the wavelength-dependent Brillouin frequency shift, frequency tunability is realized by tuning the wavelength of the laser source. In the experiments, frequency-doubling microwave signals from 18.38 to 18.74 GHz are generated when the wavelength of the laser source is tuned from 1565 to 1535 nm.

Microwave spectrum sensing based on photonic time stretch and compressive sampling.

An approach to realizing microwave spectrum sensing based on photonic time stretch and compressive sampling is proposed. The time stretch system is used to slow down the input high-speed signal and the compressive sampling based on random demodulation can further decrease the sampling rate. A spectrally sparse signal in a wide bandwidth can be captured with a sampling rate far lower than the Nyquist rate thanks to both time stretch and compressive sampling. It is demonstrated that a system with a time stretch factor 5 and a compression factor 8 can be used to capture a signal with multiple tones in a 50 GHz bandwidth, which means a sampling rate 40 times lower than the Nyquist rate. In addition, the time stretch of the microwave signal largely decreases the data rate of random data sequence and therefore the speed of the mixer in the random demodulator.

A Wideband Frequency-Tunable Optoelectronic Oscillator Based on a Narrowband Phase-Shifted FBG and Wavelength Tuning of Laser

A wideband frequency-tunable optoelectronic oscillator (OEO) based on a narrowband phase-shifted fiber Bragg grating (PSFBG) and wavelength tuning of the laser is proposed and demonstrated. With assistance of an optical single-sideband modulator, the PSFBG with a narrow transmission peak acts like an equivalent high-Q microwave filter to select the oscillation frequency. Frequency tunability of the OEO can be simply realized by tuning the wavelength of a laser source. An X-band optoelectronic oscillating signal with frequency tunable at wide range from 8.4 to 11.8 GHz is generated and its performance is investigated in the experiment.

High-Resolution Multiple Microwave Frequency Measurement Based on Stimulated Brillouin Scattering

A novel multiple microwave frequency measurement scheme is proposed based on the selective conversion of phase modulation to amplitude modulation, which is realized by stimulated Brillouin scattering. The principle of this scheme is theoretically elucidated with its advantages and disadvantages discussed. Experiments are established to verify its feasibility and the results show that this scheme is competent in determining the frequency information among multiple frequency signal with very high resolution and accuracy. The maximum measurement error is less than 30 MHz.

Ultralow Reflectivity Spiral Phase Plate for Generation of Millimeter-wave OAM Beam

An ultralow reflectivity spiral phase plate (SPP) is proposed to generate an orbital angular momentum (OAM) beam at millimeter-wave frequency. The SPP is composed of unit cells whose equivalent permittivity and thickness are designed to satisfy the impedance matching condition based on transmission line theory. The designed SPP is fabricated by a 3D printing technique. The near-field and far-field phase distributions clearly exhibit the azimuth phase shifting, and the far field directivity pattern shows that the direction, gain, and 3-dB beam-width of the main lobe are about 10.5°, 14.6 dB, and 14.5°, respectively. Compared with no impedance-matched SPP, the reflectivity of the SPP is improved by more than 20 dB.

Orbital angular momentum mode-demultiplexing scheme with partial angular receiving aperture.

For long distance orbital angular momentum (OAM) based transmission, the conventional whole beam receiving scheme encounters the difficulty of large aperture due to the divergence of OAM beams. We propose a novel partial receiving scheme, using a restricted angular aperture to receive and demultiplex multi-OAM-mode beams. The scheme is theoretically analyzed to show that a regularly spaced OAM mode set remain orthogonal and therefore can be de-multiplexed. Experiments have been carried out to verify the feasibility. This partial receiving scheme can serve as an effective method with both space and cost savings for the OAM communications. It is applicable to both free space OAM optical communications and radio frequency (RF) OAM communications.