R EIEW A R TCLE Abstract As an emerging topic, photonic-assisted microwave measurements with distinct features such as wide frequency coverage, large instantaneous bandwidth, low frequencydependent loss, and immunity to electromagnetic interference, have been extensively studied recently. In this article, we provide a comprehensive overview of the latest advances in photonic microwave measurements, including microwave spectrum analysis, instantaneous frequency measurement, microwave channelization, Doppler frequency-shift measurement, angle-of-arrival detection, time–frequency analysis, compressive sensing, and phase-noise measurement. A photonic microwave radar, as a functional measurement system, is also reviewed. The performance of the photonic measurement solutions is evaluated and compared with the electronic solutions. Future prospects using photonic integrated circuits and software-defined architectures to further improve the measurement performance are also discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.201600019

Photonics for microwave measurements

We describe the stabilization of the beatnote of an Er,Yb:glass dual-frequency laser at 1.5 mum with and without an external microwave reference. In the first case, a classical optical phase-locked loop (OPLL) is used, and absolute phase noise levels as low as -117 dBrad2/Hz at 10 kHz from the carrier are reported. In the second case one or two fiber-optic delay lines are used to lock the frequency of the beatnote. Absolute phase noise levels as low as -107 dBrad2/Hz at 10 kHz from the carrier are measured, fairly independant of the beatnote frequency varying from 2 to 6 GHz. An analysis of the phase noise level limitation is presented in the linear servo-loop theory framework. The expected phase noise level calculated from the measurement of the different noise sources fits well with the predictions.

Dual-Frequency Laser at 1.5 $\mu$ m for Optical Distribution and Generation of High-Purity Microwave Signals

Tunable dual-frequency oscillation is demonstrated in a vertical external-cavity surface-emitting laser. Simultaneous and robust oscillation of the two orthogonally polarized eigenstates is achieved by reducing their overlap in the optical active medium. The class-A dynamics of this laser, free of relaxation oscillations, enables one to suppress the electrical phase noise in excess that is usually observed in the vicinity of the beat note.

Experimental demonstration of a tunable dual-frequency semiconductor laser free of relaxation oscillations

Opto-electronic components and their performances are well suited to be integrated in radar systems. In this paper, two optical architectures illustrate functions that are specific to optical processing of microwave signals, i.e., time-delay-based processing and arbitrary waveform generation of large frequency bandwidth signals.

Optical signal processing in Radar systems

We propose and demonstrate tunable microwave phase shifters based on electrically tunable silicon-on-insulator microring resonators. The phase-shifting range and the RF-power variation are analyzed. A maximum phase-shifting range of 0-600 degrees is achieved by utilizing a dual-microring resonator. A quasi-linear phase shift of 360 degrees with RF-power variation lower than 2dB and a continuous 270 degrees phase shift without RF-power variation at a microwave frequency of 40GHz are also demonstrated.

https://orbit.dtu.dk/files/12270659/9FBBDd01.pdf

Widely tunable microwave phase shifter based on silicon-on-insulator dual-microring resonator.

A fibred optoelectronic arbitrary waveform generator for radar calibration purposes is proposed. The ability to generate radar arbitrary waveforms composed of 700 Doppler frequency components from 12 up to 14 GHz with 20 dB spurious free dynamic range is demonstrated.

Optically generated arbitrary waveforms for radar applications

An optoelectronic arbitrary-waveform generator has been proposed and experimentally developed for radar applications. It permits generating predefined waveforms by driving the amplitudes and phases of optically carried microwave signals. The optical architecture combines a high- resolution frequency shifter (for the heterodyne generation of the microwave signal) with spatial light modulators (for the parallel control of amplitudes and phases). Such a waveform generator can be attractive for target recognition or for target simulation.

Optoelectronic arbitrary-waveform generator for radar applications

The invention concerns a generator of a multiple frequency component electric signal (fk) applicable in particular to simulation of targets or recognition by correlation of radar waveform. It comprises: a generator (L) of a first dual-frequency optical beam (F0) whereof the two components have a frequency offset equal to the central frequency (f0) of the signal s(t) to be generated, a device for generating (GEN) from the first beam (F0) N dual-frequency beams (Fk), N > 1, having each a frequency offset (fk) equal to a frequency component of the signal to be generated, an optoelectronic phase and amplitude multichannel modulator (MOD) for receiving on each channel a dual-frequency optical beam (Fk) and enabling control of the amplitude and relative phase shift between the components (F1,k, F2,k) of each of the beams based on phase and amplitude laws of the signal (s(t)) to be generated, a photodetector (PD) receiving the set of beams derived from the multichannel modulator device (MOD).

Generator of a multiple frequency component electric signal

We propose an optoelectronic arbitrary radar waveform generator. It permits to generate predefined electrical waveforms according to radar specifications by driving phase and amplitude distributions of optically carried microwave signals. The control of amplitudes and phases of each radar spectrum frequency component is optically achieved by spatial light modulators (SLM). We present and experimentally demonstrate two ways to achieve the kilohertz high resolution between the frequency components of a radar signal at 7.1 GHz central frequency.

Aymeric Monsterleet

Papers

Optical signal processing in Radar systems

Optically generated arbitrary waveforms for radar applications

Optoelectronic arbitrary-waveform generator for radar applications

Generator of a multiple frequency component electric signal

Optical arbitrary waveform generator for radar applications