This PDF file contains the front matter associated with SPIE Proceedings Volume 10517, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

We demonstrate two novel and complementary techniques that allow the single-shot recordings of amplitude and phase of irregular waves with a high temporal resolution (~200 fs ) over a long time window (~40 ps) [1]. The key point is a completely new combination of the so-called time lens strategy [2,3] and of heterodyne detection [4,5]. We superimpose the input signal to a CW reference so that fringes of interference are produced in a c(2) crystal. As in the time microscope geometry published in [2], the temporal information is first encoded onto the spectrum of field by using sum frequency generation (SFG) between the signal and a chirped pump pulse. Then we design an original imaging time-lens system, which finally encodes the temporal evolution of the fringe line onto the horizontal axis and the fringes themselves onto the vertical axis of an sCMOS camera. We first demonstrate the use of this technique by recording partially coherent waves emitted by an amplified spontaneous source having a spectral width of 1THz. We secondly demonstrate the formal analog of digital holography used here as an ultrafast measurement technique (that we call SEAHORSE). As an important application, our results open the way to novel fundamental investigations of nonlinear propagation of random waves in optical fibers. In particular, our system unveiled the special evolution of the phase (and amplitude) of rogue waves in integrable turbulence, and the compatibility with the expected Peregrine solitons [2]. REFERENCES [1] A. Tikan et al, arxiv/1707.07567, (2017) [2] B.H. Kolner and M. Nazarathy, Opt. Lett. 14, 12, (1989) [3] P. Suret et al., Nat. Commun., 7, 13136 (2016) [4] D.H. Broaddus et al., CLEO/QELS Laser Science to Photonic Applications, San Jose, CA, (2010) [5] C. Dorrer, Opt. Lett., 31, 4, pp 540-542, (2006)

We investigated ultrafast rogue waves in fiber lasers and found three different patterns of rogue waves: single- peaks, twin-peaks, and triple-peaks. The statistics of the different patterns as a function of the pump power of the laser reveals that the probability for all rogue waves patterns increase close to the laser threshold. We developed a numerical model which prove that the ultrafast rogue waves patterns result from both the polarization mode dispersion in the fiber and the non-instantaneous nature of the saturable absorber. This discovery reveals that there are three different types of rogue waves in fiber lasers: slow, fast, and ultrafast, which relate to three different time-scales and are governed by three different sets of equations: the laser rate equations, the nonlinear Schrodinger equation, and the saturable absorber equations, accordingly. This discovery is highly important for analyzing rogue waves and other extreme events in fiber lasers and can lead to realizing types of rogue waves which were not possible so far such as triangular rogue waves.

Mode‐locked lasers exhibit a rich landscape of unstable dissipative soliton dynamics as stable mode‐locking builds up from noise due to the interplay of nonlinearity and dispersion with cavity gain and loss. Here, we combine, for the first time, real‐time spectral dispersive Fourier transform and time lens measurements with sub-nm and sub-picosecond resolution, respectively, to characterize the spectral and temporal profiles of dissipative solitons emerging during the turn‐on phase of a passively mode‐locked fiber laser. The fact that both measurements of the spectral and temporal intensities are performed in real-time and simultaneously allows for the use of standard phase retrieval algorithm to reconstruct the full field (intensity and phase). Our measurements then allows us to follow how the pulses evolve from round trip to round trip, revealing a range of complex dynamics typical of dissipative solitons including molecules, collisions, and collapse. These results are significant in providing a unique picture of the internal evolution of fiber laser dissipative solitons, and we anticipate their application in the optimization and design of lasers with improved stability characteristics. More generally, we believe that our results will stimulate the widespread use of simultaneous temporal and spectral characterization as a standard technique for the study of ultrafast complex optical systems including e.g. rogue wave and modulation instability that also display complex transient dynamics.

A soliton explosion refers to a phenomena in passive mode locked lasers where spectral structure of the laser pulse disappear suddenly but returns back its original shape after a few roundtrips. This phenomena timescale is from nanoseconds to microseconds, and therefore this particular event of single-shot pulse spectrum cannot be detected by using a conventional spectrometer which consists on a grating and a linear array detector. Progress on photonic time-stretch is enabling the single-shot spectral measurement in real-time. Previous observations of soliton explosion in fiber lasers was limited to dissipative soliton in an operation state between mode locking and noise-like pulses. Here we report the first observation of soliton explosion in an unstable mode locking region in the stretched pulse configuration via nonlinear polarization evolution with time stretch spectroscopy. Developing with an Yb doped fiber laser and capturing 8000 consecutive single-shot spectra, we observed that the features of soliton explosion dynamics between narrow and broadband mode locking regimes. We anticipate that the explosion dynamics are related to a pulse energy decreasing process during the stabilizing toward the steady state mode locking operation. We believe that these results provide us novel insights into understanding the broadband spectral formation and evolution in unstable mode locking regime of lasers.

Stimulated Raman scattering spectroscopy is a powerful nonlinear optical technique for label-free identification of molecules, based on their characteristic vibrational fingerprint. Current implementations of SRS, while achieving extremely high acquisition speeds up to the video rate, mostly work at a single frequency, thus providing limited chemical information. Broadband implementation of SRS is technically challenging, as for imaging dilute species in biological microscopy applications one must detect very small (approx. 10^-5) signals sitting on a large background via modulation transfer technique. We introduce and experimentally demonstrate a novel approach to broadband SRS spectroscopy based on photonic time stretch (PTS). The broadband femtosecond Stokes pulse, after interacting with the sample, is stretched by a telecom fiber to 15ns duration, mapping its spectrum in time. The signal is sampled through a fast analog-to-digital converter, providing single-shot spectra at 80-kHz rate. We demonstrate 10^-5 sensitivity, over 500 cm-1 bandwidth in the C-H region with high resolution. These performances are already suitable for a number of applications, such as monitoring microfluidic flows, the onset of chemical reactions or solid-state samples such as pharmaceutical products. As the acquisition speed of PTS does not depend upon the covered spectral region, we are planning to extend the spectral coverage of SRS to the fingerprint region. Furthermore, using commercially available lasers with higher rep-rates, we could shorten the acquisition time considerably. This will pave the way to high-speed broadband vibrational imaging for materials science and biophotonics.

The time stretch dispersive Fourier Transform (TS-DFT) technique based on a fiber chromatic dispersion is a powerful tool for pulse-by-pulse single-shot spectrum measurement for highrepetition rate optical pulses. The distributed feedback laser diode (DFB-LD) with the gain switch operation can flexibly change the pulse repetition frequency (PRF). In this paper, we newly introduce a semiconductor gain-switched DFB-LD operating from 1 MHz up to 1 GHz PRF into the TS-DFT based spectrum measurement system to improve the flexibility and the operability. The pulse width can be below 2 ps with a pulse compression technique. We successfully measure the spectrum of each optical pulse at 1 GHz, 100 MHz, and 10 MHz PRF, and demonstrate the flexibility of the measurement system.

The speed of data acquisition is a major hurdle for hyperspectral spontaneous Raman imaging to be widely adopted in the clinical setting. To address this problem, we proposed a new approach to achieve fast spectroscopic imaging while keeping high spectral resolution, in which narrow-band or wide-band imaging quickly captures all required data and then full spectra at all pixels are reconstructed efficiently. We started by developing a method to enable the reconstruction of diffuse reflectance spectra from color images with high accuracy. This method was further developed for hyperspectral Raman imaging from narrow-band measurements. Then a series of Wiener estimation based methods were developed to improve the accuracy of spectral reconstruction and reduce the need of acquiring a training dataset. A four-channel Raman imaging system has been built to acquire all narrow-band images in one single frame and an eight-channel imaging system is currently under evaluation. This technique could speed up the acquisition of hyperspectral data cube by two to three orders of magnitude, which opens the possibility of rapid Raman imaging for the monitoring of dynamically changing events in biological samples. Moreover, other hyperspectral imaging modalities including diffuse reflectance and fluorescence imaging can also benefit from this fast spectroscopic imaging technique, which have been demonstrated in flap assessment during plastic surgery on an animal model.

Broadband laser ranging uses spectral interferometry and a dispersive Fourier transform to perform high repetition rate position measurements of explosively-driven surfaces typically moving at several km/s. A broadband fiber laser and fiber interferometer record distance as a relative delay between short pulses, and the beat spectrum of the pulses is mapped into the time domain via long propagation in dispersive fiber. Optical amplification and a fast oscilloscope allow the dispersed spectrum to be recorded in real-time, often at measurement rates of 20-40 MHz. The third-order phase of the dispersive fiber causes distortions in mapping the spectrum into time that must be compensated for when analyzing the measured data.

We characterize the accuracy and precision of BLR systems by performing a scan of static positions and comparing our single-shot measurements against position measurements from a commercial Michelson interferometer. We demonstrate a combination of hardware and data analysis that measures position to within 30 microns over a 27 cm range with very high precision.

Photonic time stretch has been a successful imaging and spectroscopy technique that provides single-shot and real-time performance by employing highly dispersive optical elements to slow down the modulated optical signals and overcome the speed bottleneck present at analog-to-digital conversion. Photonic time stretch has also been generalized to warped stretch with tailored chromatic dispersion profiles, enabling non-uniform (foveated) sampling. However, such tailored profiles are currently only available with fixed elements which cannot be reconfigured, lowering the robustness of such systems and limiting their applicability to static samples and environments that have relatively constant sample statistics. To address this limitation, we demonstrate an arbitrarily programmable source of chromatic dispersion which has a 1-ns wide delay range, and inherently devoid of ghost artifacts common in spectral phase-based optical devices. Extending the concept of chromo-modal dispersion (CMD), we use an acousto-optic deflector to create a digitally synthesized and modulated angular spread of optical wavelengths, which are then coupled into the chosen waveguide mode of a multimode fiber to create the desired modal dispersion. The range and tunability enables us to on-the-fly reconfigure and correct optical dispersion. As proof-of-concept, we demonstrate real-time channel noise correction via optical feedback for warped stretch spectroscopy at 36.6 MHz.

We study the existence and propagation of multidimensional dark non-diffractive and non-dispersive spatiotemporal optical wave-packets in nonlinear Kerr media. We report analytically and confirm numerically the properties of spatiotemporal dark lines, X solitary waves and lump solutions of the (2 + 1)D nonlinear Schrodinger equation (NLSE). Dark lines, X waves and lumps represent holes of light on a continuous wave background. These solitary waves are derived by exploiting the connection between the (2 + 1)D NLSE and a well-known equation of hydrodynamics, namely the (2+1)D Kadomtsev-Petviashvili (KP) equation. This finding opens a novel path for the excitation and control of spatiotemporal optical solitary and rogue waves, of hydrodynamic nature.

We report a novel experimental setup to perform distributed characterization in intensity and phase of the nonlinear stage of modulation instability by means of a non-invasive experimental setup : a heterodyne time domain reflectometer.

Even more than 15 years after their first experimental demonstration, supercontinua have remained an extremely active field of research. In particular, photonic crystal fibers enable the broadening a laser source with a few nanometer initial spectral coverage to a supercontinuum that may encompass several octaves. Unfortunately, this extreme broadening does not come without a caveat: the initially coherent laser light loses most of this favorable property, which makes it impossible to compress the white-light pulse train to the bandwidth-limited single-cycle duration that two octaves could theoretically support. More precisely, this problem arises because of a loss of interpulse coherence, i.e., subsequent white-light pulses exhibit dramatically varying amplitude and phase structures. In fact, these variations are so extreme that they do not even follow a Gaussian distribution anymore, which gives rise to the phenomenon of optical rogue waves. Optical rogue waves are often explained by soliton dynamics. In the light of the above considerations, however, this seems quite paradoxical as solitons are coherent waveforms that evolve in a highly deterministic fashion. Moreover, frequency metrology applications of supercontinua exist which do not seem to be corrupted by a loss of interpulse coherence. In order to resolve this apparent conflict, we propose a new intrapulse coherence definition, which is experimentally verified by fringe contrast measurements in an f-to-2f interferometer. Numerical simulations indicate that intrapulse coherence is typically quite robust in the case of Kerr-dominated spectral broadening whereas it also quickly vanishes in plasma-dominated broadening scenarios, e.g., during filamentation. Interpulse coherence, in contrast, becomes more fragile at the low photon numbers of oscillator sources. As these two types of coherence appear rather independent of each other, situations can arise where interpulse coherence is conserved but intrapulse coherence vanishes and vice versa. Moreover, compressibility into a train of short pulses must not be used to conclude on the robustness of intrapulse coherence. We believe that this new coherence criterion has important implications, both for frequency metrology as well as for carrier-envelope phase stabilization of lasers. Specifically, in frequency metrology, limitations may arise for the obtainable maximum precision of optical frequency measurements. These limitations may impact the redefinition of the fundamental time and length units replacing the current microwave cesium standard by an optical one.

Information on the wavelength is essential for most laser applications and a wide range of devices are available for measuring it. Commercially available wavemeters can provide femtometer resolution in a wide wavelength range but their refresh rate rarely goes into the kHz range. Streak cameras, on the other hand, provide extremely fast measurements with a wide spectrum. However, the spectral resolution is severely limited due to the use of a grating as the wavelength separating element. Here we present a wavemeter that combines a megahertz measurement rate and sub-picometer wavelength resolution. The technique uses the steep wavelength acceptance curve of a thick non-linear crystal to calculate the wavelength from just two power measurements. The bandwidth is limited only by the speed of a photodiode while the resolution and wavelength range can be engineered by choosing a suitable crystal type and geometry. We use the wavemeter to examine how the longitudinal mode evolves during a single pulse from a tapered diode laser. High resolution, high speed measurements of the wavelength can give new information about laser diodes, which is valuable for applications requiring short but wavelength stable pulses, such as pulsing of the second harmonic light.

Abstract: Optical Dynamic range compression (ODRC) is a new nonlinear signal processing concept that reshapes the dynamic range and signal-to-noise ratio. ODRC improves the detection sensitivity by boosting weak signals over the noise floor, while keeping the full-scale the same. Without requiring an optical receiver that has post-amplification or higher resolution, the detectable range is extended. For signals whose amplitude distribution is centered at a low value, ODRC effectively reduces the quantization error by assigning more quantization levels to weak signals, reducing the total number of bits to digitize. In amplifiers cascade, a low-noise ODRC serving as the pre-amplifier would relax the noise figure and linear range requirements of the second amplifier.

A complete ultrashort pulse diagnostic requires a linear spectrum associated with a nonlinear autocorrelation or interferometric measurement. A new method is presented requiring only a grating spectrometer and two second harmonic crystals. Spectra of fundamental, second harmonic, and two cascaded spectra are used to reconstruct the spectral phase. A few proof-of-concept examples with simple phases are demonstrated using Nelder-Mead algorithm. A differential evolution genetic algorithm is introduced when the pulse has a more complicated shape or phase.

We report the development of a platform, based-on a Field-Programmable Gate Arrays (FPGAs) and suitable for Time-Division-Multiplexed DFB lasers. The designed platform is subsequently combined with a spectroscopy setup, for detection and quantification of species in a gas mixture. The experimental results show a detection limit of 460 ppm, an uncertainty of 0.1% and a computation time of less than 1000 clock cycles. The proposed system offers a high level of flexibility and is applicable to arbitrary types of gas-mixtures.

Random fibre lasers constitute the class of random lasers, where the feedback is provided by amplified Rayleigh scattering on sub-micron refractive index inhomogenities randomly distributed over the fibre length. It is known than the nature of Rayleigh scattering is elastic. However, as the laser generates a smooth spectra, the feedback mechanism in random fibre lasers has been assumed to be incoherent. In the present talk we will use a real-time spectral measurement technique based on a scanning Fabry-Perot interferometer to reveal fast dynamics of the random fibre laser spectrum. We observe long-living narrowband components in the generation spectrum, and make a statistical analysis of a large number single-scan spectra to reveal a preferential interspacing between narrow-components. Further, we will discuss the results of advanced real-time spectral measurements via heterodyne-based measurements. We will show that ultra-narrow spectral components (with spectral width down to 1 kHz) are generated. The existence of such narrowband spectral components, together with their observed correlations, establishes a long-missing parallel between the fields of random fibre lasers and conventional random lasers.

It became necessary for proposing a remote non–contact method to measure angular positions and movement of an objects using Laser Dynamic Goniometer (LDG) as compared with the usual Photo-electrical autocollimators with narrow range of about 1deg. This article present analysis, errors as well as experimental results of using Laser Dynamic Goniometer to measure wide range with accuracy of approximately 0.1 arcs and a possibility of measuring constant angles with accuracy of 0.005 …0.1 arcs in the range of possible angles of 15…30degrees.