We report on the experimental demonstration of a multi-gigahertz bandwidth RF spectrum analyzer based on spectral hole burning in a 3 K-cooled rare-earth ion-doped crystal. We implemented the so-called “rainbow” architecture in which the optically carried spectral components of the incoming signal are angularly separated by the crystal, and are then acquired with a pixelated photo-detector. With this setup, we have been able to monitor and record the spectrum of complex microwave signals over an instantaneous bandwidth above 20 GHz, with a time resolution below 100 μs, 400 resolvable frequency components and a 100% probability of intercept. RF pulsed signals in the µs range are perfectly analyzed with this high time-resolved set-up. The best achievable sensitivity for pulsed signals is computed and compared with another spectral hole burning technique.

RF Spectrum Analyzer for Pulsed Signals: Ultra-Wide Instantaneous Bandwidth, High Sensitivity, and High Time-Resolution

We present several laser sources dedicated to advanced microwave photonic applications. A quantum-dash mode-locked laser delivering a high-power, ultra-stable pulse train is first described. We measure a linewidth below 300 kHz at a 4.3 GHz repetition rate for an output power above 300 mW and a pulse duration of 1.1 ps after compression, making this source ideal for microwave signal sampling applications. A widely tunable (5–110 GHz), monolithic millimeter-wave transceiver based on the integration of two semiconductor distributed feedback lasers, four amplifiers, and two high-speed uni-traveling carrier photodiodes is then presented, together with its application to the wireless transmission of data at 200  Mb/s. A frequency-agile laser source dedicated to microwave signal processing is then described. It delivers arbitrary frequency sweeps over 20 GHz with high precision and high speed (above 400  GHz/ms). Finally, we report on a low-noise (below 1 kHz linewidth), solid-state, dual-frequency laser source. It allows independent tuning of the two frequencies in the perspective of the implementation of a tunable optoelectronic oscillator based on a high-Q optical resonator.

Laser sources for microwave to millimeter-wave applications [Invited]

An approach to performing photonic-assisted temporal convolution of two microwave signals is proposed and experimentally demonstrated. Temporal convolution involves three operations: time reversal of one microwave signal, the multiplication of the time-reversed signal with a second microwave signal, and the integration of the multiplied microwave signal, which can be implemented optically by a linearly chirped fiber Bragg grating (LCFBG), a Mach-Zehnder modulator, and a second LCFBG in conjunction with a low-speed photodetector, respectively. The proposed temporal convolution is experimentally evaluated, in which the calculation of three temporal convolutions between two rectangular waveforms, between an inverse sawtooth waveform and a rectangular waveform, and between an arbitrary waveform and a short pulse is experimentally demonstrated.

Photonic-Assisted Microwave Temporal Convolution

We propose and experimentally demonstrate a novel technique to achieve broadband and precise microwave time reversal using a single linearly chirped fiber Bragg grating (LCFBG). In the proposed approach, the time reversal is realized by the LCFBG that is operating in conjunction with a polarization beam splitter (PBS) to enable a triple use of the LCFBG with the microwave waveform entering the LCFBG from either the long or the short wavelength end. Since the LCFBG has a wide bandwidth and is used three times with exactly complementary and identical dispersion, broadband and precise microwave time reversal is ensured. A theoretical analysis is performed which is validated by simulations and an experiment. The time reversal of three different microwave waveforms with a bandwidth over 4 $~$ GHz and a time duration of approximately 10 ns is demonstrated.

Broadband and Precise Microwave Time Reversal Using a Single Linearly Chirped Fiber Bragg Grating

Interlaced spin grating is a scheme for the preparation of spectrospatial periodic absorption gratings in an inhomogeneously broadened absorption profile. It relies on the optical pumping of atoms in a nearby long-lived ground state sublevel. The scheme takes advantage of the sublevel proximity to build large contrast gratings with unlimited bandwidth and preserved average optical depth. It is particularly suited to Tm-doped crystals in the context of classical and quantum signal processing. In this paper, we study the optical pumping dynamics at play in an interlaced spin grating and describe the corresponding absorption profile shape in an optically thick atomic ensemble. We show that, in Tm:YAG, the diffraction efficiency of such a grating can reach $18.3%$ in the small-angle and $11.6%$ in the large-angle configuration when the excitation is made of simple pulse pairs, considerably outperforming conventional gratings.

Interlaced spin grating for optical wave filtering

The time-reversal (TR) protocol we implement in an erbium-doped YSO crystal is based on photon echoes but avoids the storage of the signal to be processed. Unlike other approaches implying digitizing or highly dispersive optical fibers, the proposed scheme reaches the μs range and potentially offers high bandwidth, both required for RADAR applications. In this Letter, we demonstrate faithful reversal of arbitrary pulse sequences with 6 μs duration and 10 MHz bandwidth. To the best of our knowledge, this is the first demonstration of TR via linear filtering in a programmable material.

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H. Linget

Papers

Time reversal of optically carried radiofrequency signals in the microsecond range.