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In radar technology, the term pulse compression refers to a set of techniques that allows achieving the resolution of short and high peak-power pulses by transmitting long signals with relatively low peak powers [1] . This result is possible thanks to the use of modulated or coded waveforms with an enlarged time-bandwidth product, which can be easily amplified without the onset of nonlinearities. After these waveforms are sent to a remote target, the cross-correlation (CC) of the detected back-reflections with a reference signal (in a process called matched filtering) produces narrow pulses, enabling a range resolution set by the bandwidth of the transmitted signal. So far, the concept of pulse compression, when extended to the the optical counterpart of radar (lidar), has been mostly limited to incoherent optical waveforms coded in intensity. In this paper, we present a scheme for laser ranging by all-optical coherent pulse compression. It consists in a bidirectional frequency shifting loop (FSL), composed of a couple of acousto-optic frequency shifters (AOFS1 and AOFS2), an optical amplifier (EDFA) and a tunable bandpass filter (TBPF), see Fig. 1a [2] . The system is configured so that the recirculation of the light inside the loop produces two optical frequency combs (OFCs) with quadratic spectral phases, and whose frequency spacings differ by a small quantity δf. By a precise adjustment, the FSL generates two trains of optical chirps with similar chirp rate but slightly different period. The interference of these quasi-continuous waveforms on a photodetector (PDcc), followed by a low-pass filter, produces the matched filtering in a purely analog manner. Simultaneously, the dual-comb interference enables to reduce by orders of magnitude the detection electronics bandwidth.

We propose and demonstrate a novel approach of mode locked laser to generate pulse trains at high repetition rate, with low phase noise and broadband tunability. The architecture takes advantage of regenerative mode locking to enhance the frequency selectivity by more than 25 dB and the noise performances of rational mode locking. The output pulse train phase noise combines ideal frequency multiplication of the RF synthesizer at low offset frequency (up to 10 kHz) and low residual phase noise of regenerative lasers at higher offset frequencies.

We report on recent works on photonics based architectures for the generation of high purity RF signals. Different configurations of 10 GHz fixed frequency optoelectronic oscillators are studied (dual-loop, all-photonic gain, and coupled). All these configurations provide phase noise below -90 dBc/Hz at 100 Hz frequency offset, and below -140 dBc/Hz above 10 kHz frequency offset. Every configuration exhibits state-of-the-art phase noise performances. Integration perspectives are also given, with preliminary acceleration sensibility measurements.

Recently, methods based on all-optical pulse rate multiplication have emerged to overcome the limitation of standard RF synthesiser for the generation of high frequencies. Among them, Frequency Shifting Loops (FSLs) injected by a CW laser, so called Talbot lasers, can generate pulse trains with a repetition rate tunable over several order of magnitudes (up to tens of GHz) from a low frequency synthesiser [1]. Until now, Talbot lasers have been theoretically described in the frame of a passive cavity in the steady state. Here, we present a simple model based on rate equations dedicated to the dynamics of Talbot lasers. This model allows to successfully explain experimental results with both solid-state and semi-conductor gain media, without parameter adjustment.

Actively and harmonically mode locked lasers (AHMLL) have been extensively studied as an optical clock source for photonic-assisted analog-to-digital conversion of broadband RF signals. Such lasers can generate high repetition rate pulse train with ultralow timing jitter [1]. The optical injection of AHMLL has been shown to be an interesting way to reduce the supermode noise, which is an important source of residual phase noise at high offset frequency [2]. Although efforts have been put to stabilize the external seed laser on a longitudinal mode of the AHMLL [3], no study on the impact of seed laser parameters have been reported. We present here our first results on the parametric study of a CW-injected AHMLL to understand better the evolution of the laser performance under different power and optical gain conditions.

Rapidly tunable RF signals at high frequency (>10 GHz) with high purity is a challenge that is more and more faced with optical solutions. Optical mixing of two laser fields has extensively been studied for that purpose. However, when the two fields come from independent laser sources, their phase locking remains a tour de force. Direct generation of two optical fields with close frequency difference in a single laser, so-called dual frequency laser (DFL), greatly reduces the drifts, as the cavity is shared [1]. We here report our last achievements in the generation of Ka-band RF signal generation with DFL technology.

We report on the generation of GHz pulse trains with a regenerative frequency shifting cavity at 780 nm using a semiconductor optical amplifier. This configuration improves the sidemode rejection, and delivers pulse train with mW power.

International audience; We present a direct measurement of the intracavity dispersion of a coupled optoelectronic oscillator (COEO). The measurement can be performed while the COEO is oscillating, taking into account the dispersion of the modulator and the saturated active medium, without any other component than the ones composing the oscillator. It eases the dispersion management before the detection stage for minimal amplitude-to-phase noise coupling.

In this paper we present three applications of microwave photonics: a wideband spectrum analyzer based on spectral hole burning, an ultra-low noise optoelectronic oscillator, and a semiconductor-based mode-locked laser for high-speed sampling.

International audience; We present a 10 GHz dual loop optoelectronic oscillator (OEO), with very low phase noise (-144.7 dBc/Hz at 10 kHz) and low spur level (-145 dBc/Hz), despite using short fibers (1 km/100 m). The OEO is designed thanks to a simple model, which shows good agreement both with single and dual loop configurations.

Here we introduce a novel concept of an ultimate fastscan delay with sub-20 as precision and scan rates of tens of kHz. It is based on an acousto-optic programmable dispersive filter and exploits the propagation of the acoustic wave between successive optical pulses.

Carrier-envelope phase (CEP) stabilization in ultrafast laser systems is absolutely mandatory for physical experiments using attosecond pulses. Although oscillator CEP stabilization has now reached limits in terms of precision and bandwidth [1], extension to amplifiers is still subject to improvements. The development of multi-kHz laser chain pushes up the potential CEP “slow drift” correction bandwidth, which is not exploited by current technology. Acousto-Optic Programmable Dispersive Filters (AOPDF) have already been used for this slow drift correction up to 15 Hz [2]. We introduce here a novel feedback scheme using a new AOPDF electronic design with a potential 30 kHz input bandwidth. As an AOPDF can control the absolute spectral phase, it enables a fortiori CEP control. Proof of principle is achieved by stabilizing the phase of a Michelson interferometer below 25 mrad, at 7.5 kHz.

Self-referenced spectral interferometry (SRSI) is a recently demonstrated single-shot characterization technique [1]. This technique relies on the spectral interference between the pulse to characterize and a reference pulse generated from the pulse itself by cross-polarized wave generation (XPW)[2]. Under the right experimental conditions, the XPW pulse is shorter than the input pulse and exhibits a broader and smoother spectrum with a flat, or at least computable, spectral phase. Such properties are highly favorable for high-dynamic range spectral interferometry and high-contrast SRSI measurements have recently been demonstrated [3]. In this paper, we show the ability to optimize pulses down to 11.7 fs at their Fourier limit using feedback loops between a pulse shaper and the SRSI device.

In this paper, the first wide band and high resolution demonstration of the chirp transform algorithm is presented. Because it is performed with a frequency agile laser source, this demonstration opens the way to the wealth of wide band spectral coherent processes that rare-earth ion doped crystals can handle. Using this source, the chirp transform process is demonstrated with a bandwidth in excess of 1 GHz together with more than 20,000 independent frequency channels.

We demonstrate a 10 GHz spectrum analyzer with MHz resolution and > 30 dB dynamic range using the spectral-hole-burning (SHB) Tm3+: YAG crystal working at 793 nm. Thanks to the fast and linear chirping capabilities of the laser used, it has a potential 100% probability of interception and a response time in the ms range. The system is compared to a previously demonstrated SHB spectral analyzer.

We report on the demonstration of the chirp transform algorithm for the optical processing of wide band RF signals. The process uses photon echoes in an Er3+:YSO crystal at 1536 nm. The analysis covers a 1.5 GHz instantaneous bandwidth together with more than 20,000 independent channels. These performances require a frequency agile laser source that is phase-locked in order to take advantage of the high coherence of the system.

Our experiment permits to isolate different kinds of noises affecting the chirp. First, deterministic errors, such as, e.g., chirp non-linearity or extra frequency modulation have been isolated. Second, stochastic errors, such as the spontaneous-emission induced phase random walk or the technical 1/f frequency noise, have been characterised.

We report on the phase locking of a rapidly frequency chirped laser to a local oscillator. Deterministic and stochastic noises affecting the chirp purity are suppressed, and phase locking occurs in less than 1 mus.

We introduce a novel holographic configuration for spectral analysis of optically carried RF signals using spectral hole burning materials . We reach a 10 GHz-bandwidth, a MHz resolution, and a 34 dB linear dynamic range.

We introduce a frequency agile extended cavity diode laser using an integrated Bragg reflector in a Ti:Fe:LiNbO 3 waveguide, emitting in the 1.5-μm telecommunication window. Improved stability and efficient electro-optic frequency control are achieved.

In this contribution, we report on what is believed to be the first experimental demonstration of photon echoes in an amplifying rare-earth ion-doped crystal and highlighted the advantages of the process. It considerably improves the diffraction efficiency and the echo power in single shot, up to a factor 3 in our relatively low optical density sample.

We review recent demonstrations of wide band radio frequency (RF) spectral analyzers based on spectral hole burning technology. The optically-carried RF signal can be analyzed with sub-MHz resolution over tens of GHz instantaneous bandwidth.