We report a widely tunable optically-carried radio-frequency source relying on two hybrid distributed Bragg reflector lasers. Our source is based on the butt-coupling between two monolithic InGaAsP/InP reflective semiconductor optical amplifiers and a silicon nitride circuit on silicon chip that integrates two Bragg gratings and a 3 dB coupler. We measure a minimum optical linewidth of 10 kHz for the DBR lasers, in good agreement with the theoretical predictions obtained from a dedicated model based on hybrid-cavity analysis. Our optically-carried RF source demonstrates, for the wavelength separation Δλ, a thermal tuning range of Δλ  =  1.2 nm. Combined with bias-current tuning, it leads to a continuous RF beatnote tunability over 150 GHz.

We unambiguously determine the long-term frequency drift of a Brillouin-assisted self-linewidth-narrowing photonic oscillator, an original architecture that yields high spectral purity without any active stabilization, as we recently reported [ Opt. Express 33 , 1021 –1033 ( 2025 ) OPEXFF 1094-4087 10.1364/OE.534463 ]. A Pound–Drever–Hall locking scheme is used to compare the frequency of the free-running laser to a resonance frequency of a high-finesse Fabry–Perot cavity. The spectral purity of the optical wave, exhibiting a Flicker linewidth of 400 Hz for 0.1 s integration time, is shown to be preserved owing to a locking bandwidth of 5 Hz only. A smooth frequency drift bounded to 1 MHz over 7 h is revealed for the free-running laser. It demonstrates a stability of less than 10 −9 for 1000 s of integration time, outperforming the stabilities reported for free-running lasers.

We report the implementation of a single-pass tilt-locking stabilization scheme in an opto-electronic oscillator using a high-finesse Fabry-Perot as photonic filter. A table-top setup leads to a phase noise level of -80 dBc/Hz at 1 kHz offset from a 6 GHz carrier and a Allan deviation measurement of 3 x 10(-10)s integration time. Future improvements leading to a compact fiber-free OEO are discussed.

We detail here the general principle of a self-adaptive oscillator in which the intertwined operation of a 100-m-long active optical resonator and a standard semiconductor laser mutually coupled by stimulated Brillouin scattering offers an ultimate high spectral purity. Single frequency operation of this self-adaptive photonic oscillator is achieved without any servo locking or stabilization electronics. In free running operation, this principle leads to a Lorentzian linewidth of 40 mHz and a Flicker noise linewidth of 200 Hz for 0.01 s integration time. The long-term drift of the optical frequency without absolute frequency locking is in the range of 10 MHz over hours. This principle applies to any wavelength attainable by laser diodes which opens tremendous opportunities, in particular in applications where atomic or molecular transitions require precise wavelengths.

We report the generation of an optical pulse train with a 10 GHz repetition rate in a dual loop direct-modulation optoelectronic oscillator (OEO). Pulse generation is achieved using nonlinear compression in the OEO 5-km-long optical delay line. 3 ps pulses with a timing jitter of 13 fs are reported, while the OEO maintains a phase noise of -133 dBc/Hz at 10 kHz from the carrier. Two architectures are compared experimentally and theoretically. A frequency comb with a 1.2 THz linewidth at -30 dB is generated. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

We propose a theoretical description and experimental validation of a frequency self-stabilized photonic oscillator. This photonic oscillator which relies on a solid-state laser and a nonreciprocal Brillouin fiber resonator (BFR) arranged in an optical phase-locked loop (OPLL) was recently shown to provide very narrow linewidth in the Hz range. Special attention is given to end up with analytical expressions relying on coupled-mode formalism, of the BFR dynamics in which the non-resonant configuration for the pump has to be addressed. Furthermore, the transfer function of the full system is derived from the response of each component within the OPLL leading to two interleaved loops, relative to the phase and to the amplitude fluctuations of the optical field. An experimental setup including a solid-state Er:Yb laser is detailed and used to test the model predictions, both for phase noise level and response time. This model opens the way to the optimization of this new type of photonic oscillator which can be adapted to any kind of pump laser.

We have demonstrated a widely tunable Radio Frequency (RF) source based on hybrid cavity dual wavelength narrow linewidth Distributed Bragg Reflector (DBR) lasers. The source is formed by joining a double InP reflective semiconductor optical amplifier (R-SOA) and a Silicon Nitride (Si 3 N 4 ) circuit on silicon chip integrating two Bragg grating reflectors and a directional coupler integrated in. The hybrid circuit demonstrated a tuning range of the wavelength separation of 152 GHz. Due to limitations of the measurement setup the RF beat-note tuning range was measured only up to 67 GHz.

A phase-modulated frequency-shifting loop is injected by a single-frequency laser at 1.5 μm. In so-called Talbot conditions, i.e., when the modulation frequency is an integer multiple of the inverse of the cavity round-trip time, the loop generates a frequency comb whose temporal trace consists in a train of pulse doublets whose positions in time depend on the frequency of the injection laser. When the modulation frequency is slightly detuned from the Talbot condition, nonlinear frequency chirps are predicted and observed in the output pulse train. We demonstrate that these nonlinear chirps are not restricted to sinusoidal shapes, and also that the loop can be stabilized by exploiting the intracavity phase modulation.

Fe/Cr/Fe trilayers and multilayers are prepared as model systems designed to furnish simple data comparable with calculation results for diffusion properties in nuclear materials. Their structure (epitaxy, residual strains and dislocations) is characterized in detail. The film structure (strain and stress) is shown to be different on MgO20nm/ SrTiO3 and MgO substrates due to the residual strain in the MgO buffer layer on SrTiO3. Superlattices with high crystalline quality are prepared, with Fe and Cr in coherent epitaxy. In-plane residual strain in Fe is +0.45(13)% on MgO substrates and decreases from 1.70(9)% to 0.47(2)% when increasing the thickness of the trilayers on MgO/SrTiO3 substrates. These strains enhance the contrast between Fe and Cr, opening the way to future kinetics studies using x-ray diffraction in this system, which is far more efficient (non-destructive and rapid) than high resolution transmission electron microscopy with electron energy loss spectroscopy or atom probe tomography.

We show that the polarized pumping can be used to control the relative powers of two linear, orthogonally polarized, eigenstates in a Yb:YAG laser. The experimental observations are in full agreement with a two-mode rate-equation model, highlighting the roles of both the gain anisotropy and the cross-saturation parameters, whose values are found to be ε=0.08 and β = 0.64, respectively, in a longitudinally pumped continuous-wave microchip laser. The application to dual-polarization frequency combs is discussed.

Opto-electronic oscillators (OEOs) are able to produce low phase noise radio-frequency signals thanks to their high-quality-factor resonator that includes a km-long optical delay line [1]. While the main use of OEOs is the synthesis of ultra-pure electrical signals and optical clock distribution, it is also possible to generate short optical pulses with low timing jitter, using for instance nonlinear compression in the OEO fiber [2], for applications such as optical sampling, remote sensing (RADAR, LiDAR), frequency comb generation and so forth. We have recently demonstrated a 10 GHz direct-modulation OEO (DM-OEO) with a phase noise of -135 dBc/Hz at 10 kHz. In this work, we propose to take advantage of the optical output of the DM-OEO in order to broaden the optical spectrum and possibly generate ultra-low jitter optical pulses by nonlinear compression in the long SMF fiber. To this end, we have designed an optoelectronic loop including a phase modulator to positively chirp the laser field, and an Erbium Doped Fiber Amplifier (EDFA) to increase the nonlinear effects in the fiber (see Fig. 1a).

Mode-locked lasers polarization states are typically fixed by gain dichroism in crystalline media. However, dual-polarization oscillation and pulse-to-pulse polarization control in bulk isotropic active media have attracted attention recently [1], [2]. Apart from using extra-cavity polarization devices, one can wonder whether an oscillator can generate directly adjustable polarization sequences. Here, we demonstrate how phase locking of two orthogonal polarization eigenstates can occur in a passively mode-locked Yb:YAG laser using two quarter-wave plates.

Ytterbium lasers are widely used for femtosecond pulse generation, in particular for dual-comb spectroscopy. Indeed, in the case of quasi-isotropic active media such as Yb:YAG or Yb:CaF2, two eigenstates with orthogonal polarizations can oscillate simultaneously, corresponding to two frequency combs with adjustable repetition rates [1]. In order to balance the powers of the two modes, one may wonder if the use of a polarized pump could create a gain dichroism, as it has already been demonstrated in neodymium lasers. To this aim, we have performed experimental studies on Yb-doped solid-state lasers, that were supported by a two-mode rate-equation model taking into account the pump-induced gain anisotropy.

A real-time spectral analysis is demonstrated experimentally with a frequency-shifting loop that includes an electro-optic phase modulator. When a single-frequency laser seeds the loop, pulse doublets are emitted if the integer Talbot condition is satisfied. With a polychromatic seed, frequency-to-time mapping is demonstrated, namely the temporal output of the loop maps the spectral power of the seed, with a resolution of 400 kHz. Due to the phase modulation function, the mapping is shown to be nonlinear. The results are in agreement with the theoretical predictions of [H. Yang et al., J. Opt. Soc. Am. B 37, 3162 (2020)JOBPDE0740-322410.1364/JOSAB.389801]. The extension to integrated systems for applications is discussed.

Talbot lasers are based on acousto-optic frequency-shifter (AOFS) loops seeded by a cw laser. When a single-frequency laser injects a frequency-shifting loop (FSL) system, constructive interferences occur periodically with time generating pulses at a repetition rate equal to (integer Talbot effect) or with a multiple of (fractional Talbot effect) the mode spacing of the comb. Talbot lasers have been shown to provide high-repetition rate pulse trains and have been applied to RF-optical signal processing, spectroscopy, and ranging. Here we investigate an all-fibered frequency-shifting loop (FSL) that includes an electro-optic intensity modulator (EOM) instead of the AOFS. Experimental results show that the intensity-modulating FSL generates short pulses with a repetition rate multiplication. It is based on the temporal fractional Talbot effect by adjusting the modulation frequency f_m and the fundamental frequency of the loop f_c as the ratio of two integers: f_m⁄f_c =p⁄q, leading to a repetition rate equal to qf_m= pf_c. In the experimental demonstration, the fundamental frequency of the loop f_c is constant while the modulating frequency f_m is adjusted thanks to the EOM. We observe pulses at a repetition rates tunable between 6 MHz and 600 MHz. The system is modeled by a simple linear interference model that takes the amplitude modulation function and loop delay into account. The model predicts the fractional Talbot property as in AOFS-based systems, but with an additional amplitude modulation of the pulse train, in good agreement with the experimental results. This experiment shows an alternative approach to AOFS loops, taking advantage of the inherent bandwidth and tunability of the EOM. This fractional Talbot laser may find applications in optical sampling, THz generation and ultrafast data processing systems.