Sparse seismic instrumentation in the oceans limits our understanding of deep Earth dynamics and submarine earthquakes. Distributed acoustic sensing (DAS), an emerging technology that converts optical fiber to seismic sensors, allows us to leverage pre-existing submarine telecommunication cables for seismic monitoring. Here we report observations of microseism, local surface gravity waves, and a teleseismic earthquake along a 4192-sensor ocean-bottom DAS array offshore Belgium. We observe in-situ how opposing groups of ocean surface gravity waves generate double-frequency seismic Scholte waves, as described by the Longuet-Higgins theory of microseism generation. We also extract P- and S-wave phases from the 2018-08-19 Fiji deep earthquake in the 0.01-1 Hz frequency band, though waveform fidelity is low at high frequencies. These results suggest significant potential of DAS in next-generation submarine seismic networks.

We demonstrate a method to achieve an extremely wide and flexible external control of the group velocity of signals as they propagate along an optical fiber. This control is achieved by means of the gain and loss mechanisms of stimulated Brillouin scattering in the fiber itself. Our experiments show that group velocities below 71 000 km/ s on one hand, well exceeding the speed of light in vacuum on the other hand and even negative group velocities can readily be obtained with a simple benchtop experimental setup. We believe that the fact that slow and fast light can be achieved in a standard single-mode fiber, in normal environmental conditions and using off-the-shelf instrumentation, is very promising for a future use in real applications.

Supercontinuum generation can be achieved in the continuous-wave regime with a few watts of pump power launched into kilometer-long fibers. High power spectral density broadband light sources can be obtained in this way. Using a generalized nonlinear Schrödinger equation model and an ensemble averaging procedure that takes into account the partially-coherent nature of the pump laser, we fully explain for the first time the spectral broadening mechanisms underlying this process. Our simulations and experiments confirm that continuous-wave supercontinuum generation involve Raman soliton dynamics and dispersive waves in a way akin to pulsed supercontinua. The Raman solitons are however generated with a wide distribution of parameters because they originate from the random phase and intensity fluctuations associated with the pump incoherence. This soliton distribution is averaged out by experimental measurements, which explains the remarkable smoothness of experimental continuous-wave supercontinuum spectra.

Phase-sensitive optical time-domain reflectometry (ϕOTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. We show in this Letter that modulation instability (MI) can induce a position-dependent signal fading in long-range ϕOTDR over conventional optical fibers. This fading leads to a complete masking of the interference signal recorded at certain positions and therefore to a sensitivity loss at these positions. We illustrate this effect both theoretically and experimentally. While this effect is detrimental in the context of distributed vibration analysis using ϕOTDR, we also believe that the technique provides a clear and insightful way to evidence the Fermi-Pasta-Ulam recurrence associated with the MI process. © 2013 Optical Society of America OCIS codes: 290.5900, 190.2640, 060.2370 Phase-sensitive optical time-domain reflectometry (ϕOTDR) is a powerful technique that allows the fully distributed monitoring of vibrations along an optical fiber cable. This technique has attracted considerable attention due to its application in the monitoring of intrusions over large perimeters. Conventional systems described in the literature allow the distributed measurement of vibrations of up to 1 kHz with a resolution of 5 m and dynamic range of a few tens of kilometers (<50 km) [1,2]. A ϕOTDR works by injecting a pulse of highly coherent light into a conventional single-mode fiber. Unlike traditional OTDRs, which can only measure intensity variations along the fiber, in a ϕOTDR the light reflected from different scattering centers interferes coherently to produce the detected optical power trace. The detected value at a certain position is therefore sensitive to the relative phases among the reflected fields coming from the different scattering centers around that position. In the case of localized vibrations, the trace shows variations synchronized with the vibration frequency.To achieve reliable vibration measurements, it is indispensable to have a good signal-to-noise ratio (SNR) in the measured trace. In addition, it is generally desired to have the best possible range and resolution. The range, resolution, and SNR are tightly related parameters. For a given resolution (input pulse width), an increase of dynamic range and SNR of a ϕOTDR sensor can only be achieved by increasing the input pump peak power. However, the input pump peak power cannot be indefinitely increased due to the onset of nonlinear effects. Some of these nonlinear limitations have been briefly described in the general context of coherent OTDRs [3]. Among these nonlinear limitations, the first effect to arise in usual conditions for ϕOTDR is modulation instability (MI).MI in fibers results from the interplay of the Kerr effect and anomalous dispersion. In the spectral domain, MI manifests as the buildup of two sidebands at each side of the center beam wavelength. MI has been theoretically and experimentally described [4,5]. In the strong conversion regime, the MI process exhibits a reversib...

Slow & fast light with null amplification or loss of a light signal is experimentally demonstrated. This novel method for producing zero-gain slow & fast light takes advantage of the great flexibility of stimulated Brillouin scattering in optical fibers to generate synthesized gain spectra. Generation of optical delays and advancements with minor amplitude change is realized through the superposition of gain and loss profiles showing very different spectral widths, resulting in a synthesized spectral profile identical to an ideal electromagnetically-induced transparency.

Sub-meter resolution in long-distance Brillouin Optical Time Domain Analysis (BOTDA) cannot be trivially achieved due to several issues including: resolution-uncertainty trade-offs, self-phase modulation, fiber attenuation, depletion, etc. In this paper we show that combining Raman assistance, differential pulse-width pair (DPP) measurements and a novel numerical de-noising procedure, we could obtain sub-meter resolution Brillouin optical time-domain analysis over a range of 100 km. We successfully demonstrate the detection of a 0.5 meter hot-spot in the position of worst contrast along the fiber. Gonzalez-Herraez, "Raman assisted Brillouin distributed temperature sensor over 100 km featuring 2 m resolution and 1.2 °C uncertainty," J. Lightwave Technol. 30(8), ©2012 Optical Society of America

The structural, morphological, electrical and optical properties of In-rich AlxIn1−xN (0  <  x  <  0.39) layers grown by reactive radio-frequency (RF) sputtering on sapphire are investigated as a function of the deposition parameters. The RF power applied to the aluminum target (0 W–150 W) and substrate temperature (300 °C–550 °C) are varied. X-ray diffraction measurements reveal that all samples have a wurtzite crystallographic structure oriented with the c-axis along the growth direction. The aluminum composition is tuned by changing the power applied to the aluminum target while keeping the power applied to the indium target fixed at 40 W. When increasing the Al content from 0 to 0.39, the room-temperature optical band gap is observed to blue-shift from 1.76 eV to 2.0  eV, strongly influenced by the Burstein–Moss effect. Increasing the substrate temperature, results in an evolution of the morphology from closely-packed columnar to compact. For a substrate temperature of 500 °C and RF power for Al of 150 W, compact Al0.39In0.61N films with a smooth surface (root-mean-square surface roughness below 1 nm) are produced.

In this work, we investigate the effects of deposition conditions on the structural and morphological properties of AlInN thin films deposited on p-doped Si (111)