Photonic-assisted wideband microwave frequency measurement based on optical heterodyne detection.

A photonic-assisted microwave frequency measurement (MFM) method based on optical heterodyne detection is proposed and experimentally demonstrated. In the proposed MFM system, a linearly chirped optical waveform (LCOW) from a three-electrode distributed Bragg reflector laser diode (DBR-LD) and a multi-wavelength signal from a Mach-Zehnder modulator (MZM), where the signal under test (SUT) is modulated on an optical carrier from a distributed feedback laser diode (DFB-LD), are heterodyne detected by the photodetector (PD). A bandpass filter then filters the detected signal, and the envelope is detected by an oscilloscope. Then, frequency-to-time mapping is realized, and the signal frequency is measured. Thanks to the fast tuning rate and large tuning range of the DBR-LD, the proposed MFM system has a high measurement speed and a broad instantaneous measurement bandwidth. In the experimental demonstration, a measurement error below 39.1 MHz is achieved at an instantaneous bandwidth of 20 GHz and a measurement speed of 1.12 GHz/µs. The MFM of a frequency-hopping signal is also experimentally demonstrated. The successful demonstration of the MFM system with a simple structure provides a new optical solution for realizing broadband and fast microwave frequency measurements.

Phase locking and homodyne detection of repetitive laser pulses.

A method to realize pulse laser phase locking and homodyne detection is proposed, which can be used in lidar and continuous variable quantum key distribution (CVQKD) systems. Theoretical analysis shows that homodyne detection of pulse laser has a sensitivity advantage of more than 4 dB over heterodyne detection. An experimental verification setup was constructed to realize phase-locking and homodyne detection of pulse lasers at repetition rates from 50 kHz to 2.4 MHz. For 320 ns signal laser pulses at 300 kHz with peak power of -65 dBm, the phase error is 8.9° (mainly limited by the chirp effect in the modulation of signal laser), and the detection signal-to-noise ratio reaches 20.2 dB. When the peak power is reduced to -75 dBm, phase locking and homodyne detection can still be achieved. Homodyne detection based on phase locking could serve as a novel weak-laser-pulse receiving method with high sensitivity and anti-interference performance.

Integrated waveguide true time delay beamforming system based on an SOI platform for 28 GHz millimeter-wave communication.

In this paper, we propose an on-chip waveguide beamforming system for a 28 GHz millimeter-wave signal based on silicon-on-insulator (SOI) technology. The system consists of four true time delay (TTD) lines, each of which consists of nine Bragg gratings with different periods. The minimum period of the grating is 312 nm, and the maximum period is 344 nm. By optimizing the position of the Bragg grating in the adjacent TTD lines, a time delay difference can be generated between the adjacent channels. By adjusting the operation wavelength of the optical carrier, the TTD lines can provide 9 different beamforming direction angles from -60∘ to 60° when the direction angular resolution is 15°. This proposed system has a useful application prospect in the phased array antennas of millimeter-wave communication.