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In this article, we report robust vector soliton bunches arising in a passively mode-locked fiber laser based on carbon nanotube (CNT). By introducing a polarization-route-assisted module (PRAM) and finely adjusting the cavity birefringence, the soliton bunches can be flexibly manipulated to operate with controllable soliton numbers and positions. Moreover, the potential bandwidth resource provided by the concept of soliton bunches for the ease of breaks a new path for the enhancement of data-carrying capacity. Our research is helpful to extend the theory of vector soliton dynamics in fiber lasers and promotes the promising application in optical communication systems.

Polarization-maintaining (PM) all-fiber cavity is always essential to realize stable ultrafast-pulse generation. With the help of five sections of PM fibers with independently specific splicing angles, we successfully obtain a femtosecond pulse output from a PM Ytterbium-doped fiber laser (YDFL) mode-locked by the nonlinear polarization evolution (NPE) technique. Using a hybrid component, the PM all-fiber cavity can be greatly simplified. Ultrafast-pulses with 24.5-MHz repetition rate, 20-nm spectral bandwidth, and 260-fs pulse duration after external compression can be steadily generated. In comparison with the non-PM fiber cavity, the proposed YDFL has excellent long-term environmental stability, making it ideal for various practical applications.

A near-infrared (NIR) supercontinuum and ultrashort pulses are generated via phase-mismatched cascaded frequency conversion in DSTMS (4-N, N-dimethylamino-4'-N'-methyl-stilbazolium 2, 4, 6-trimethylbenzenesulfonate) crystal. NIR pulses with a central wavelength of 1.5 μm and 63 fs pulse duration are incident into the crystal, and the spectrum is broadened to over 1200-2100 nm. Compensating the dispersion by fused silica, ultrashort NIR pulses with 16.6 fs pulse duration are obtained. Meanwhile, intense single-cycle terahertz pulses are generated via optical rectification in DSTMS crystal.

We demonstrate a scheme for correcting the angular dispersion of the 3.1- $\mu$m idler beam from a high repetition rate, KTiOAsO $_4$ (KTA) based noncollinear optical parametric amplifier pumped at 1.03 $\mu$m and seeded by broadband signal pulses at 1.55 $\mu$m. Following angular dispersion correction, successful temporal chirp compensation was possible, and a close to transform-limited pulse duration of 70 fs and a pulse energy of 30 $\mu$J at a repetition rate of 100 kHz were obtained. The angular chirp compensated KTA-based scheme is scalable to higher pulse energies and average powers and has various advantages compared to periodically poled and angle-tuned LiNbO$_3$ -based amplifiers, which exhibit low resistance to photorefractive damage.

In this paper, we investigated the imaging condition of asymmetric pulses on a temporal imaging (TI) system comprising two optical fibers and a phase modulator. We introduced a fitness function to evaluate the difference between target and output waveforms to quantitatively estimate TI characteristics. We successfully determined the optimal combination of phase modulation index and phase deviation to provide good TI by simulating the fitness function. We generated chirp-free pulses with symmetric and asymmetric waveforms using an in-line waveguide pulse synthesizer, i.e., an optical pulse synthesizer, based on pulse shaping and experimentally confirmed the TI condition in a time lens system. Moreover, TI was achieved not only at a theoretical value of the modulation index satisfying the TI condition but at a much smaller value than the theoretical value for a time-reversal mode as well. Measured waveforms of the experimental output agreed with simulation results. This may be important for practical applications because a TI system requires a much smaller modulation power.

Exploiting the characteristics of spatially chirped ultrafast pulses has been an increasingly active area of research. In this paper, we review the developments in the past year of the microscopy, materials processing, and micromachining fields, where the spatiotemporal structure of these beams is important. We also summarize progress in theoretical and experimental work to better control and characterize spatially chirped beams.

International audience; We analyze the performance of a reservoir computer based on time delayed feedback and optical injection, which is drawing benefits from the high-speed polarization dynamics of a Vertical Cavity Surface Emitting Laser (VCSEL). We demonstrate that such a system has high computation performance and yields deeper memory than existing single-mode laser-based reservoir computer. Performance is demonstrated on several benchmarking tasks. In particular, the error rate is an order of magnitude smaller when performing channel equalization.

We report on a Yb-pumped optical parametric oscillator (OPO) that delivers 30 fs pulses with spectral coverage from 680 to 910 nm and an average output power of up to 1.1 W. The resulting peak power is similar to 0.5 MW, which is, to the best of our knowledge, the highest ever demonstrated in a femtosecond OPO. The intensity noise remains at a level of 0.2% rms, and rapid wavelength tuning is obtained by simply scanning the resonator length. The performances of the OPO are promising for a variety of applications in nonlinear microscopy and ultrafast spectroscopy. (C) 2017 Optical Society of America

We recently developed the tomographic ultrafast retrieval of transverse light E-fields (TURTLE) as a self-referenced method for retrieving vector-shaped ultrashort laser pulses. TURTLE combines three or more linear polarization projections of the pulse, which are measured with existing single-polarization pulse characterization techniques, to determine the full polarization state. We present in detail the two approaches for retrieving the full vector-shaped field: an analytic inversion and a parameter-fitting technique. By examining the impact of measurement noise on retrieval fidelity, we find that the fitting approach, which makes use of the additional redundancy inherent in some single-polarization measurements, is greatly superior to the analytic.

We demonstrate ultralow phase noise 10-GHz microwave signal generation from a free-running mode-locked Er-fiber laser with -142 and -157 dBc/Hz single-sideband absolute phase noise at 10- and 100-kHz offset frequencies, respectively. The absolute RMS timing jitter is 1.5 fs when integrated from 1-kHz to 5-GHz (Nyquist frequency) offset frequency. In the 10-kHz to 10-MHz integration bandwidth typically used for microwave generators, the RMS integrated jitter is 0.49 fs. The Er-fiber laser is operated in the stretched-pulse regime at close-to-zero dispersion to minimize the phase noise of extracted microwaves. In order to suppress the excess phase noise in the optical-to-electronic conversion process, we synchronize a low-noise voltage-controlled oscillator to the fiber laser using a fiber Sagnac-loop-based optical-microwave phase detector., 7 pages, 3 figures

We experimentally demonstrate a compact and efficient arrangement for fiber delivery of sub-30 fs energetic light pulses at 800 nm. Pulses coming from a broadband Ti:Sapphire oscillator are negatively pre-chirped by a grism-pair stretcher that allows for the control of second and third orders of dispersion. At the direct exit of a 2.7-m long large mode area (LMA) photonic crystal fiber 1-nJ pulses are temporally compressed to 29 fs producing close to 30 kW of peak power. The tunability of the device is studied. Comparison between LMA fibers and standard SMF fibers is also discussed. This work is supported by the French “Agence Nationale de la Recherche” (ANR) project Invivo-ONL and by the CNRS-SCS Armenia-France funding.

We describe a simple terahertz (THz) time domain spectrometer with a bandwidth extending up to 7.5 THz. We show that by keeping the generation and detection crystals close to each other a high signal-to-noise ratio (SNR) can be achieved without using lock-in detection and dry nitrogen flushing. The observed spectra show very good agreement with the spectra calculated based on a simple model which includes phase matching and absorption in the generation and detection crystals. Using this set-up we have measured the absorption lines in D-tartaric acid from 0.5 THz up to 7 THz. We show that the high frequency region > 3 THz is the better choice to measure small changes in the water content of a hygroscopic sample compared to the low frequency region.

We present 2D measurements of the full THz electric field behind a sample consisting of multiple slits in a metal foil. Our measurements, which have a sub-wavelength spatial, and a sub-period temporal resolution, reveal electric field lines, electric field vortices and saddle points. From our measurements we are able to reconstruct the magnetic field and, finally, the position and time-dependent Poynting vector which shows the flow of energy behind the sample. Our results show that it is possible to study the flow of light near sub-wavelength plasmonic structures such as slit-arrays and, by implication, other metamaterial samples.

We present measurements and calculations of the terahertz (THz) electric field measured in the near field of a metal tip used in THz apertureless near-field optical microscopy (THz-ANSOM). An analytical model in which we treat the metal tip as a linear wire antenna allows us to predict almost all of the features observed in the measurements, such as the relatively slow decay of the near-field amplitude when the tip-crystal separation increases. When the tip-crystal separation is modulated, in conjunction with lock-in detection at the modulation frequency, a smaller THz spot size is observed underneath the tip. A comparison with analytical expressions shows that in this case the electric field originates predominantly from the tip apex, with negligible contributions from the tip shaft. In the unmodulated case, the observed signal is the spatial integral of the electrooptic (EO) effect over the interaction length between the THz near field and the probe laser pulse. In the modulated case, to a good approximation, we find that the signal is proportional to the value of the THz near field at the surface of the EO crystal only.

Intense mid-infrared pulses tunable between 5 and 14 µm with pulse energies of several microjoules were generated by difference-frequency mixing (DFM) in a GaSe crystal. Longer wavelengths (up to 18 µm) were achieved by DFM in a CdSe crystal. The infrared pulses were then characterized using various techniques: The spectrum was measured using a Fourier-transform spectrometer, which was then modified to determine the interferometric second-order autocorrelation. The electric field spectral phase was measured using the same setup, thus leading to a full characterization of the mid-infrared pulses. The spectral phase was measured using the time-domain homodyne optical technique for spectral phase interferometry for direct electric field reconstruction, where spectral interferometry was replaced with time-domain interferometry. The measured pulse duration was 100 fs, nearly transform limited.

A novel method developed to increase the temporal resolution of x-ray streak cameras is described. The method is analogous to the time-correlated single-photon-counting technique, which is commonly used in atomic physics. By use of short-pulse x-ray radiation from a laser-produced plasma, generated by an ultrafast laser, it is shown that a standard x-ray streak camera with a nominal temporal resolution of \>5ps can yield a temporal response of 1.6 ps. The readout technique also removes temporal jitter with respect to the triggering laser. Capabilities and limitations of the technology are discussed.