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In this paper, the proof-of-concept of an optical fiber sensing technique based on a frequency shifting loop (FSL) is proposed. The system combines both a refreshing rate of the sensing measurement in the MHz range and a centimetric spatial resolution. The FSL is used as a versatile source of broadband optical chirped waveforms, with controllable chirp rate. Digital pulse compression is applied to optimize the system's signal-to-noise-ratio. The sensor system is used to monitor the phase perturbation applied to a localized transducer (an electro-optic phase modulator) placed in an optical fiber. A preliminary and promising sensitivity

We report on a detailed analysis of the effect of CW injection in an actively mode-locked laser at 780 nm, on the noise performances of the laser. The optical properties of the emitted pulse train, and the phase and amplitude noise of the RF pulse train generated after photodetection have been characterized with respect to the laser pumping rate, and to the injected power. We show that when injected, the laser exhibits a dramatic improvement of both RF phase noise and power spectrum, but at the expense of a degraded optical relative intensity noise.

High repetition rate optical pulse trains are essential for a wide range of applications, including photonic-assisted sampling. Among the different solutions proposed so far, Talbot lasers, based on the generation of an optical frequency comb in a frequency shifting loop, are a simple yet efficient source of short transform-limited pulses. By controlling the comb spectral phase, the repetition rate is reconfigurable. It can be set to a (possibly large) multiple of the comb spacing and reach the GHz range, while only requiring a low bandwidth synthesizer (typ. 100 MHz). The noise characteristics of this pulse trains is a key factor for its application. Therefore, we investigate the phase noise properties of Talbot lasers. In particular, we prove theoretically and demonstrate experimentally that the phase noise at high offset frequency from the carrier, does not depend on the multiplication factor $q$ . We also demonstrate that the phase noise at low offset frequencies, which increases as $20 \log q$ , can be strongly reduced by a simple locking technique. Finally, we show that in addition to their reconfigurability, Talbot lasers can provide timing jitters at 8.2 GHz as low as 350 fs (integrated from $10^{5}$ Hz to the Nyquist frequency), making them suitable candidates for time metrology applications.

International audience; We demonstrate a new and simple dynamic laser ranging platform based on analog all-optical coherent pulse compression of modulated optical waveforms. The technique employs a bidirectional acousto-optic frequency shifting loop, which provides a dual-comb photonic signal with an optical bandwidth in the microwave range. This architecture simply involves a CW laser, standard telecom components and low frequency electronics, both for the dual-comb generation and for the detection. As a laser ranging system, it offers a range resolution of a few millimeters, set by a dual-comb spectral bandwidth of 24 GHz, and a precision of 20 µm for an integration time of 20 ms. The system is also shown to provide dynamic measurements at scanning rates in the acoustic range, including phase-sensitive measurements and Doppler shift velocimetry. In addition, we show that the application of perfect correlation phase sequences to the transmitted waveforms allows the ambiguity range to be extended by a factor of 10 up to ∼20 m. The system generates quasi-continuous waveforms with low peak power, which makes it possible to envision long-range telemetry or reflectometry requiring highly amplified signals.

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.

An optical fiber sensing system with a frequency shifting loop monitor phase perturbations applied to a transducer in an optical fiber. A sensitivity below 4 µrad/Hz^(1/2) in a 20 kHz – 2 MHz bandwidth is obtained.

We perform laser ranging using a dual-comb system that generates trains of optical chirps with slightly different periods. It allows analog pulse compression with low-frequency electronics and the possibility of expanding the ambiguity range.

A complete model describing both single- and dual-loop optoelectronic oscillators (OEO) is introduced. It is compared to several experimental configurations, with excellent agreement in all cases. The physical insight into noise coupling mechanisms brought by the model further allows us for the design of ultralow noise OEO. Phase noise performances at 10 GHz with a single 1 km delay line and with a dual 1 km/100 m delay lines are reported. An optimized dual loop configuration exhibits low phase noise floor at high offset frequency (–160 dBc/Hz at 100 kHz) and low spur levels (–145 dBc/Hz), here again in close agreement with our model.

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.

The understanding of frequency-shifting loops’ (FSLs) transient response is fundamental for their implementation in microwave photonic systems. We developed a numerical model, enabling us to describe the specific dynamics of the frequency comb generated in a FSL seeded by a CW laser. The model, based on laser rate equations, predicts the temporal evolution of the power of the individual comb lines during on/off cycles of the injection power, for FSLs operating below the lasing threshold. To prove the validity of the model, we performed experimental measurements of the power of the individual comb lines with time. Numerical simulations based on the model, for different gain media and pumping rates, are in excellent agreement with the experimental results. This paper provides guidance for the concrete implementation of FSLs for microwave photonic applications.

We propose and demonstrate an improved Talbot laser including a regenerative RF feedback loop. This architecture greatly enhances both amplitude and noise performances of the pulsed laser, while preserving the broadband tunability of its repetition rate. The phase noise power spectral density of the associated RF signal is found to be independent of the repetition rate. For a 4.9 GHz repetition rate, the timing jitter is as low as 54 fs (integrated between 10 kHz and 100 MHz offset frequency). This architecture paves the way towards tunable high performances coupled opto-electronic microwave oscillators.

International audience; We present a 10 GHz optoelectronic oscillator (OEO) based on optical amplification. The setup uses a 1-km of standard optical fiber at 1.5 μm and a semiconductor optical amplifier (SOA). The phase noise is -90 dBc/Hz at 100 Hz and 132 dBc/Hz at 10 kHz, currently limited by the oscillator noise floor.

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 experimentally investigate the impact of relevant parameters such as dispersion regime, and coupling ratio between the two loops on the phase noise performances of a 10 GHz coupled optoelectronic oscillator (COEO). The setup is based on a mode-locked semi-conductor laser at 1.55μm combined to a classical OEO. Optimization of these parameters leads to ultra-low phase noise at close-to-carrier frequencies (-100 dBc/Hz at 100 Hz and -125 dBc/Hz at 1 kHz).

We present a detailed analysis of a setup capable of arbitrary amplitude, phase, and polarization shaping of broadband visible femtosecond pulses at 1 kHz via a pair of actively phase stabilized acousto-optic programmable dispersive filters arranged in a Mach-Zehnder interferometer geometry. The setup features phase stability values around λ/225 at 580 nm as well as degrees of polarization of at least 0.9 for any polarization state. Both numbers are important metrics to evaluate a setup's potential for applications based on polarization-shaped femtosecond pulses, such as fully coherent multi-dimensional electronic spectroscopy.

International audience; We present an experimental study on two key elements to design a low phase noise coupled optoelectronic oscillator (COEO). Fiber lengths and dispersions are investigated to highlight the differences between the optical and optoelectronic loops. After optimization, a 10 GHz COEO at 1.5 μm with a total of 590 m of fiber exhibits phase noise levels of -125 dBc/Hz at 1 kHz and -140 dBc/Hz at 10 kHz.

International audience; We present our recent results on a 10 GHz coupled optoelectronic oscillator (COEO). With a total of 550 m of fiber, the COEO exhibits phase noise level of -140 dBc/Hz at 10 kHz and -137 dBc/Hz for the first spur.

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.

International audience; We present two dual loop optoelectronic oscillators using short fibers (1 km range). Fiber lengths are optimized using a simple model which predicts both configurations ultra-low phase noise results, improving either the close-to-carrier phase noise, or the spur level.

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.

International audience; We report on an optoelectronic oscillator (OEO) at 10 GHz based on a single 1 km long fiber delay, and exhibiting simultaneously an ultra-low close-in phase noise (-94 dBc/Hz @100 Hz) and a low spurious level (below -110 dBc/Hz). These results are well predicted by a model taking into account the frequency and intensity noise from the laser source that are converted into phase noise.

We characterized 11.7 fs nearly perfect Fourier Transform pulses with self-referenced spectral interferometry (SRSI), a new recently demonstrated technique. These pulses were first precisely optimized with three feedback loops between the SRSI setup and an AOPDF. An inherent control criterion to confirm that the measurement quality is theoretically derived and experimentally demonstrated. Each experimental result was cross-checked with SPIDER.

A new femtosecond pulse characterization, named self-referenced spectral interferometry, is introduced. Based on linear spectral interferometry, the reference pulse is self created from the pulse being characterized. This self reference results from pulse shaping optimization and non-linear temporal filtering.

We report on the demonstration of the chirp transform algorithm for the instantaneous optical frequency analysis of wide band radiofrequency signals. The process exploits photon echoes in an Er 3 + : YSO crystal at 1536 nm. The analysis covers a 1.6 GHz instantaneous bandwidth together with more than 24,000 independent channels. These performances require a frequency agile laser source that is phase-locked in order to take advantage of the tens of μ s of coherence time offered by the crystal optical transition.

We demonstrate a 10 GHz spectrum analyzer with MHz resolution and a 30 dB dynamic range using the spectral hole burning (SHB) Tm 3 + : 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 also investigate theoretically and experimentally the requirements for the frequency chirped laser sources spectral purity and their influences on the precision of our experiment.

We report on experimental observations of spectral diffusion mechanisms occurring in an optically pumped erbium-doped Y 2 SiO 5 crystal. The diffusion is characterized using photon echo spectroscopy on the I 15 / 2 4 → I 13 / 2 4 transition. Optical pumping creates population inversion on the transition before the echo sequence. Spectral diffusion is then studied under different population inversion conditions. These observations raise new questions on the spectral diffusion mechanisms.

Quantum storage, which aims at transferring photon quantum states into matter, can be obtained by using an ensemble of atoms whose levels form a three level A system. In these systems, two optical transitions couple two levels to a third one. This quantum storage scheme could be obtained with rare-earth ions in single crystals, since their optical and ground-state hyperfine transitions can exhibit long coherence lifetimes and their hyperfine structures could be used to build a three level A system. Tm 3+ ions in Y 3 Al 5 O 12 are especially interesting since the 3 H 6 - 3 H 4 transition can be driven by ultra-stable laser diodes. However, the selection rules on the nuclear spin projection can forbid the simultaneous coupling of two levels to a third one. In this paper, the hyperfine structure of Tm 3+ is investigated by hole burning spectroscopy under a magnetic field and compared to theoretical calculations based on crystal field calculations. The experimental results are found to be in good agreement with theory and show that some magnetic field orientations are able to relax the selection rules on the nuclear spin projection.

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.

Quantum storage of photons in an atomic ensemble can be obtained by using three-level Λ systems. In these schemes, two levels are coupled by optical transitions to a third one. Ideally, the two transitions should have similar intensities and long coherence lifetimes. Rare earth ion doped crystals are attractive materials for quantum storage because their hyperfine levels can have coherence lifetimes longer than 100 μs and thus can be used to build Λ systems. Tm 3+ ions are especially interesting since they can be excited by ultra-stable laser diodes. In this paper, the hyperfine structures of the 3 H 6 (0) and 3 H 4 (0) crystal field levels of Tm 3+ in Y 3 Al 5 O 12 are investigated by hole burning spectroscopy under a magnetic field. The results are compared to theoretical calculations and found to be in reasonable agreement. Moreover, it is shown that an appropriate magnetic field is able to relax the selection rule on the nuclear spin projection, an absolutely necessary condition to obtain an efficient three-level Λ system with Tm 3+ in this host. Finally, a magnetic field orientation optimized with respect to the Λ system transition intensity ratio is predicted for a convenient experimental set-up.

We investigate the coherent driving of atomic systems by Complex Hyperbolic Secant (CHS) pulses in optical domain. First, with the help of a Rapid Adiabatic Passage approach we get physical insight into the process. We discuss the limiting factors on spectral selectivity and transfer efficiency, such as finite coherence lifetime and excitation finite duration. Then, with a highly-stabilized cw laser and fast electronic equipment, we experimentally explore the CHS process at μs-timescale in a Tm3+:YAG crystal. We demonstrate efficient adiabatic transfer over a few hundreds of kHz-wide spectral interval within the inhomogeneous linewidth. We calculate and detect the Free Induction Decay signal as the signature of the atomic coherences during the process.

The different types of errors affecting the spectral purity of a rapidly chirped continuous wave laser are experimentally studied using an unbalanced interferometer. The response of the interferometer to the deterministic (periodic and aperiodic) and stochastic quantum and technical laser frequency noises is theoretically analysed and experimentally investigated with an external cavity diode laser operating at 793 nm and providing chirps in excess of 10 GHz on the ms timescale. The system is shown to be able to measure the laser frequency to better than 1 MHz during the chirp. It provides an error signal that can be used to servo-control the laser frequency in real time while it is chirped.

We report on the frequency stabilisation of an extended cavity diode laser for the coherent driving of thulium ions. This stabilisation loop uses a single locking point on an intra-cavity electro-optic crystal. It uses neither the diode current, nor any piezoelectric actuator, making its conception simple, versatile, and independent of the diode itself. Thanks to this, the laser linewidth with respect to the reference cavity is reduced well below 1 kHz. The laser coherence time is then much longer than the atomic coherence lifetime of the thulium ions. The performances of this stabilised source are used in basic coherent driving experiments in a Tm 3+ :YAG crystal. Efficient inversion of population by single adiabatic transfer and creation of narrow absorption lines by repetitive excitations are achieved.

We demonstrate implementation of the chirp transform algorithm with photon echoes in an Er/sup 3+/:YSO crystal at 1536 nm for application to spectral analysis of RF signals. The principle and features of the technique are presented using a simple picture in the time-frequency plane. Experimental results with low-bandwidth RF signals demonstrate 40-kHz spectral resolution and a time-bandwidth product of 500. Extension to broad-band RF signals is discussed.

The demand for ever shorter light pulses presents a challenge to the detection and stabilization of the carrier-envelope phase (CEP) in amplifier systems. Here we present a combination of single-shot detection and a fast actuator that is capable of measuring and correcting the CEP in every single shot emitted by a millijoule-scale, multi-kHz femtosecond laser amplifier. The residual CEP noise within 50 s amounts to 98 mrad rms in-loop (fast detection, 5·105 shots) and 140 mrad out-of-loop (slow detection, 6250 shots), approaching the noise floor of the f-to-2f measurement. Both values represent a twofold improvement of the CEP stability over previously published results in comparable systems.

A frequency agile extended cavity diode laser using an integrated Bragg reflector in a Ti : Fe : LiNbO/sub 3/ waveguide is developed and characterized. The laser emits up to 7 mW in the 1.5-/spl mu/m telecommunication window. The emission spectrum exhibits a 18-kHz linewidth, >40-dB sidemode suppression ratio, and a wavelength stability of /spl plusmn/1 pm over hours. Very fast mode hop-free frequency tuning is achieved through the electrooptic effect, with a tuning slope of 55.5 MHz/V.

The carrier-envelope phase of every single shot emitted by a 10 kHz, mJ-class amplifier is measured with a fast spectrometer. A novel high-speed actuator allows arbitrary phase control, with closed-loop integrated phase noise on seed oscillator level (98 mrad, 500000 shots, 50 s).

We demonstrate the first 10-GHz instantaneous bandwidth radio-frequency spectrum analyzer based on spectral hole burning in Tm/sup 3+/:YAG. It exhibits 10 000 frequency channels and a resolution better than 1 MHz. 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 millisecond range. Its linear dynamic range of 16 dB is presently essentially limited by the modest amount of optical power available and can be further improved.

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.

We demonstrate a dual pulse-shaper setup capable of independent polarization, phase, and amplitude control over each pulse. By using active phase stabilization, we achieve a phase stability of ~λ/314 between the two pulse shapers, making the dual-shaper setup suitable for both two-quantum and one-quantum measurements. The setup is compact and easily switchable between pump-probe and collinear geometries. We further illustrate the functionality of the dual-shaper setup by performing two-color 2D visible spectroscopy on colloidal CdSe quantum dots in pump-probe geometry.

We demonstrate a fastscan-delay with a precision of 20 as and scan rates exceeding 30 kHz. The fiber-compatible device is based on an acousto-optic programmable dispersive filter and is ideally suited for pump-probe experiments.