We investigate the noise due to the locking process in frequency stabilization of a laser onto an optical fiber delay line with the Pound-Drever-Hall method. Preliminary measurements revealed a white frequency noise floor that limited the locking performance. We conducted a combined experimental and theoretical analysis to identify the source of this limitation, focusing on the role of frequency discriminator nonlinearity. By increasing the locking bandwidth, we demonstrate a reduction in this white noise to a level where this nonlinearity is no longer a limiting factor.

Temporal pulse contrast [1], defined as ratio between the peak of a pulse and its pedestal on a hundred picoseconds time range, is a key parameter for laser-matter interaction on UHI (Ultrahigh Intensity) laser system. In this context, we aim to develop a high-energy (> 200 mJ) laser front-end which delivers more than 8-nm-spectral-bandwidth pulses with a central wavelength of 1053 nm and a 2-Hz-repetition-rate. In order to get high temporal contrast, this front-end is based on parametric amplification process. The first part of the front-end consists of a $\mu\mathrm{J}-\text{range}$ FOPCPA (Fiber-Optical Parametric Chirped-Pulse Amplification) [2], [3] source, followed by a free-space OPCPA (Optical Parametric Chirped-Pulse Amplification) [4] based power-amplifier.

We theoretically and experimentally analyze the benefit of hetero-structured cladding in Solid-Core Photonic BandGap fibers so as to increase the loss ratio between high order modes and fundamental mode. This property is applied to the realization of 19-cells core fibers practically single-mode around 1050 nm. When designed to operate in the 4th BandGap, a new design is proposed which permits to obtain mode field diameter of 44 μm whereas, for operation in the 3rd BandGap, a mode field diameter of 33 μm is obtained with 20 cm bending radius. The impact of the shape of hetero-structure on single-mode behavior is discussed.

Using photonic first-order differentiator applied on a partially coherent field, we generate two correlated temporal waveforms and experimentally study their correlation properties upon nonlinear propagation along the two orthogonal polarization axis of an optical fiber.

modulation (SPM), one of those very fascinating effects discovered in the early days of nonlinear optics, refers to the phenomenon by which an intense optical beam propagating in a Kerr medium (e.g., an optical fibre) induces through the nonlinearity of the medium a modulation of its phase that is proportional to its own intensity profile [1]. For an input pulsed beam, the induced time-dependent phase change is associated with a modification of the optical which depends on the initial frequency modulation (chirp) of the pulse electric field. If the pulse is initially Fourier-transform-limited or up-chirped, SPM leads to spectral broadening, whereas an initially down-chirped pulse is spectrally compressed by the effects of SPM [2]. For strong SPM, the optical spectrum can exhibit strong oscillations. In this work, firstly we present a simple theoretical approach to predict the main features of optical spectra affected by SPM, which is based on regarding the optical spectrum modification as an interference effect [3, 4]. The typical oscillatory character of the spectrum indeed originates from strong excursions of the instantaneous frequency, so that in general there are contributions from different times to the Fourier integral for a given frequency component. Depending on the exact frequency, these contributions may constructively add up or cancel each other. A two-wave interference model is found sufficient to describe the SPM-broadened spectra of initially transform-limited or up-chirped pulses, whereas a third wave should be included in the model for initially down-chirped pulses. but fully tractable analytical formulae are derived, which accurately predict the positions of the extreme values of the spectra. The latter provide a more plausible measure of the spectrum extent than the approximate or root-mean-square expressions for the spectral bandwidth that are commonly used. Secondly, we discuss a simple technique to suppress undesirable SPM of optical pulses in fibre-optic systems, which is based on using an electro-optic phase modulator to impart the opposite phase to the pulses and, thus, emulates the use of a material with a negative nonlinear index of refraction. We present a proof-of-principle experiment demonstrating that for input pulses with standard intensity profiles, such as Gaussian or hyperbolic secant pulses, the use of a simple sinusoidal drive signal for the phase modulator with appropriate amplitude and frequency is sufficient to reduce the nonlinear spectrum broadening to a large degree, and to significantly enhance the spectral quality of the pulses while their temporal duration remains unaffected [5]. Further, we present an in-depth characterisation of the SPM mitigation by a sinusoidally time varying phase based on analytic results and numerical simulation of the governing equation [6]. We assess the effects of the initial pulse shape and duration on the effectiveness of the technique, and we highlight the differences between pre- and post-propagation compensation schemes. [1] F. Shimizu, Frequency Broadening in Liquids by a Short Light Pulse, Phys. Rev. Lett 19, 1097-1100 (1967). [2] R. H. Stolen and C. Lin, Self-phase modulation in silica optical fibers, Phys. Rev. A 17, 1448-1453 (1978). [3] C. Finot, F. Chaussard, and S. Boscolo, Impact of a temporal sinusoidal phase modulation on the optical spectrum, Eur. J. Phys. 39, 055303 (2018). [4] C. Finot, F. Chaussard, and S. Boscolo, Simple guidelines to predict self-phase modulation patterns, J. Opt. Soc. Am. B in press(2019). [5] F. Audo, S. Boscolo, J. Fatome, B. Kibler, and C. Finot, Nonlinear spectrum broadening cancellation by sinusoidal phase modulation, Opt. Lett. 42, 2902-2905 (2017). [6] S. Boscolo, F. Audo, and C. Finot, Impact of initial pulse characteristics on the mitigation of self-phase modulation by sinusoidally time varying phase, Opt. Quant. Electron 50, 62 (2018).

We propose and experimentally validate an all-fiber based approach to characterize the phase and intensity profiles of optical pulses. Based on three optical spectra affected by different levels of self-phase modulation, we were able to reconstruct the temporal details of pulses typical of optical telecommunications.

Simple photonic fiber-based workbenches have been able to emulate well-known nonlinear wave dynamics occurring in deep or shallow water conditions. Here, by investigating the nonlinear reshaping of a flat-top pulse upon propagation in an anomalous dispersive optical fiber, we observe that typical signatures of focusing dam break flows and Peregrine-like breather events can locally coexist in spontaneous pattern formations. The experimental measurements are in good agreement with our numerical predictions.

The propagation of intense ultra-short optical pulses in a Kerr medium such as an optical fibre still remains a critical issue for the performance of many optical systems such as beam delivery, optical communication or pulse amplification systems. This is because the self-phase modulation (SPM) of the propagating pulse usually causes a broadening of the pulse spectrum that is typically accompanied by an oscillatory structure covering the entire frequency range. Several strategies have been proposed and successfully deployed to counteract the deleterious effects of SPM in fibre-optic systems. These include spatial or temporal scaling to reduce the impact of nonlinearity via the use of very large mode area fibres or chirped pulse amplification. A different class of approaches relies on the exploitation of the peculiar properties of parabolic shaped pulses and self-similar evolution, the use of other types of pre-shaped input pulses, and the compensation of nonlinear phase shifts with third-order dispersion. However, none of these last techniques preserves the pulse temporal duration. A simple technique to compensate the nonlinear phase due to SPM and related spectrum broadening of nanosecond or picosecond optical pulses consists in using an electro-optic phase modulator to impart the opposite phase to the pulses. This method, which emulates the use of a material with a negative nonlinear index of refraction, has proved successful in fibre-optic and free-space optical telecommunication applications using phase-shift keying systems and in the generation of high-peak-power nanosecond pulses. We have recently experimentally demonstrated that for Gaussian shaped input pulses, the use of a simple sinusoidal drive signal for the phase modulator with appropriate amplitude and frequency is sufficient to reduce the nonlinear spectrum broadening to a large degree, and to significantly enhance the spectral quality of the pulses while their temporal duration remains unaffected. In this paper, we present a comprehensive analysis of the SPM-mitigation method involving the use of a sinusoidal phase modulation. Most of the previous works are primarily experimental in nature and have not discussed the sensitivity of the technique to the initial pulse characteristics. First, we recall the concept of our method and overview our proof-of-principle experiment. Next, we derive an exact closed formula for the rms spectral width of an initially Gaussian pulse after undergoing SPM and with the corrective phase applied, which confirms the substantial reduction of the SPM-induced spectrum broadening attainable with the phase compensation. Then, we describe the impact of the initial pulse shape and duration on the effectiveness of the technique through numerical simulation of the governing equation. We show that for hyperbolic secant pulses, optimisation of the parameters of the modulating sinusoid through a scan of the amplitude-frequency space outperforms the parameter choice based on simple analytic guidelines. By varying the initial pulse duration across an order of magnitude, we highlight the significant differences in performance between pre- and post-propagation compensation schemes, and show that remarkable SPM mitigation is attainable even in the presence of non-negligible fibre dispersion.

Low-loss commercial optical fibers are known as perfect candidates to explore the richness of the dynamics of nonlinear physics. Indeed, the excellent knowledge of linear and nonlinear properties of these optical waveguides is a key ingredient to carry out experimental demonstration of the theoretical solutions of the nonlinear Schrödinger equation (NLSE). As soon as the early 80s, solitons were demonstrated in single-mode optical fibers with anomalous dispersion. More recently, taking advantage of the components of the telecommunication industry, more complex breather solutions have been experimentally generated. Such structures can also be detected in deep water and other nonlinear medium governed by the NLSE. Normally dispersive fibers have also stimulated recent experimental research, mainly driven by the interest in the study of dispersive shock waves. Most of the time, nonlinear dynamics observed in both anomalous and normal dispersion regimes of propagation are regarded as two completely different cases: one dominated by bright soliton-like structures and modulation-instability that provides an analogue to deep-water conditions; the other one ruled by dispersive shock waves (DSW) that satisfies the so-called nonlinear shallow water equations. However, recent theoretical works have stressed that a shock wave may appear in the regime of focusing nonlinearity with weak dispersion, thus leading to the emergence of dispersive dam break flows in the NLSE box problem. A DSW-like nonlinear wave train regularizes an initial sharp transition between the uniform plane wave and the zero-intensity background. In particular, theoretical solutions essentially describe a modulated soliton train. This provides a new semi-classical interpretation of what has been previously described in the spatial domain as a nonlinear Fresnel diffraction. The box problem (i.e., an initial square profile) then gives rise to two counter-propagating modulation dynamics of opposite velocities, whose interaction may turn into a cluster of breathers. In the present contribution, we confirm some of the above theoretical predictions by providing a detailed experimental observation of the regularization of sharp transitions from a super-Gaussian pulse in the presence of focusing nonlinearity and weak anomalous dispersion. Our results recorded in the temporal domain and based on an all-fibered test-based platform confirm the former qualitative behavior observed in the spatial domain as well as the strength of the space/time duality. After an initial shock induced by the overlap of the highly chirped and sharp wings of the pulse with the top region, strong temporal oscillations appear and nonlinearly reshape into a Peregrine-like structure at each maximum compression. This transient evolution is then marked by the breathing of the wave structures, both in the temporal and spectral domains. This transition may be followed by an asymptotic stage dominated by solitons. Finally, we also characterize the interaction event of the two counter-propagating dispersive dam break flows. Dispersive shock waves and Peregrine breathers have been shown to locally coexist, thus providing new insights into spontaneous pattern formations and novel possible interactions.

A simple and efficient approach to suppress undesirable self-phase modulation (SPM) of optical pulses propagating in fiber-optic systems is based on imposing a sinusoidal temporal phase modulation on the pulses to offset the chirp generated by SPM (Audo et al. Opt Lett 42(15):2902–2905, 2017). Here, we present a detailed analysis of this method. We derive an exact formula for the reduction of the SPM-induced rms spectrum broadening of an initially Gaussian pulse enabled by the sinusoidal compensation, and we assess the effects of the initial pulse shape and duration on the effectiveness of the technique by means of numerical simulation. The differences between pre- and post-propagation compensation schemes are also discussed.

We report on our recent experimental and theoretical results on the use of a sinusoidally time-varying phase to suppress undesirable self-phase modulation of optical pulses propagating in fibre-optic systems.

We propose two new applications of the spectral focusing by self-phase modulation that occurs in a nonlinear optical fiber. We numerically show the possibility of using nonlinear spectral compression to improve the optical signal to noise ratio and mitigate the amplitude jitter of the signal pulses. We also demonstrate experimentally that use of spectral focusing in a combination with an external sinusoidal phase modulation achieves efficient suppression of coherent spectral background.

Summary form only given. Large arm length imbalance fibre-based interferometers have shown great potential for laser frequency stabilization and control, with frequency noise power spectral density close to the 10 -1 Hz/Hz 1/2 level [1]. In order to understand the performance of such frequency stabilization systems, it is important to distinguish the intrinsic noise of the frequency reference, which is ultimately limited by fibre thermal noise, and the locking noise, which is limited by the detection noise but can also be affected by residual amplitude modulation fluctuations in phase modulator or other less well known causes. It is often difficult to measure the out-of-loop locking noise when one laser is locked to a frequency reference. However, the fibre length noise practically cancels when two lasers are locked onto the same interferometer with a small frequency difference, which allows to measure the out-of-loop locking noise to a very low level [2].To prove this hypothesis, we have performed numerical simulations to calculate the effect of the nonlinearity of the optical frequency discriminator on the error signal. The results show indeed a white frequency noise with a level in excellent agreement with the experimental measurement. Thanks to the simulation we have been able to derive relations between the residual laser frequency noise and this white noise level. Those relations can be very useful to optimize the choice of the fibre spool length as a function of the frequency noise of the laser to be locked, in order to minimize this noise.

We propose and experimentally demonstrate a new approach to dramatically reduce the spectral broadening induced by self-phase modulation occurring in a Kerr medium. By using a temporal sinusoidal phase modulation, we efficiently cancel to a large extent the chirp induced by the nonlinear effect. Experimental validation carried out in a passive or amplifying fiber confirms the interest of the technique for the mitigation of the spectral expansion of long pulses.

This paper describes two methods for characterizing underwater optical elements under both hyper-baric pressure and high optical power. Commercial optical feedthroughs to be tested were inserted in a hyper-baric vessel and a 600 bar pressure was applied as an optical power of several Watts was sent over the optical fibers. An unexpected decrease of the optical losses was evidenced.

ABSTRACTA 10‐km long extension using power‐over‐fiber technology and dedicated to sea floor observatories is presented with a particular focus on the electrical both ends units. We propose a solution using a serial peripheral interface 3 wires protocol for large range of low‐power sensors like hydrophones. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2562–2568, 2013

Submarine cabled networks are designed to collect valuable data in geophysics, geochemistry, biology, or oceanography. Unfortunately, the development of such a network is expensive and needs complex subsea infrastructures. Once in place, a cabled network cannot be easily relocated. The current cost of cables and their installation are one of the major obstacles to these networks deployment. On the one hand, these cables are necessary to provide power supply and communication data, and on the other hand they drastically reduce the possibilities to extend the cabled observatory network in order to reach a closed area of significant interest. This is why, to address this issue, we propose a quasi-all-optical architecture to easily extend multidisciplinary cabled networks or to create a dedicated submarine hydrophone or seismometer network. This solution consists of using only a single fiber optic to transmit both the energy, required to supply the instrument, and the data, exchanged between the shore station or equivalent. In this paper, we present our proposed architecture, and we discuss its feasibility thanks to experimental results.