Stimulated Brillouin scattering (SBS) is a highly efficient nonlinear optical interaction between acoustic waves and light. It enables the mediation of spectrally fine radio-frequency signals, with potential applications in quantum signal processing. Here, we investigate the storage of the state of polarization of light in a silica optical nanofiber (ONF) that guides both optic and acoustic waves. It adds an extra degree of information to Brillouin optoacoustic memories. The ONF possesses multiple acoustic modes. We show promising results with read/write operation for a longitudinal acoustic mode and investigate the TR21 acoustic mode polarization sensitivity.
Extending the range of distributed fiber sensors is one of the major challenges in the development of offshore wind turbines in order to monitor the transmitted electrical power inside the cables. Here we report a novel technique allowing to monitor the fiber up to 140 km, with a spatial resolution of 20 m in single-ended. Our method relies on the Brillouin anti-Stokes backscattering measurements that directly depend on the temperature along the optical fiber. The actual commercial devices have a range of 75 km. As a consequence, long infrastructures can’t be monitored in single-ended. Here the proposed method allows us to monitor the temperature without the need for an amplification module.
KEYWORDS: Temperature metrology, Single mode fibers, Optical fibers, Temperature distribution, Spatial resolution, Temperature sensors, Fiber optics sensors, Multimode fibers
We demonstrate the potential of Brillouin distributed fiber sensor for the measurement of groundwater flow in an experimental site of Port Douvot close to the city of Besan¸con. The flow measurement is obtained by using active heating method based on heat pulse instrument. An industrial sensor cable with single mode fiber and multimode fiber was immersed on ground. We compare distributed Brillouin sensor reflectometry (BOTDR) and Analysis (BOTDA) on single mode fiber (SMF) and multimode optical fiber (MMF) with a spatial resolution of 1 m, a temperature resolution of 0.2 °C and an acquisition time of 1 min. These parameters are compatible with hydrology application. Active heating of borehole water in conjunction with fiber optic distributed temperature sensor measurements are realized. Contrary to Raman based distributed temperature sensor, Brillouin instrument allows measuring absolute temperature measurement and simplify the implementation on the setup. We demonstrate in this paper that Brillouin scattering based temperature sensor can be used for hydrogeology application.
KEYWORDS: Fiber Bragg gratings, Photon counting, Single photon detectors, Reflectometry, Temperature metrology, Sensors, Spatial resolution, Single mode fibers, Signal attenuation
We present a long-range Brillouin optical time domain reflectometer (BOTDR) based on photon counting technology using single-mode fibres. We use the slope of a fiber Bragg grating (FBG) as a frequency discriminator, in order to convert count rate variation into a frequency shift. We demonstrate experimentally the ability to perform a distributed temperature measurement, by detecting a hot spot in a thermal bath and the possibility to achieve measurement above 100 km with a spatial resolution of 10 m. A performance study of our distributed sensor as a function of the photon counter efficiency is also presented.
Optical nanofibers have recently emerged as attractive nanophotonic platforms for several applications ranging from quantum technologies to nonlinear optics due to both the tight optical confinement and their wide evanescent field. In this work, we report on a theoretical and experimental investigation of the optical Kerr effect in the evanescent field of silica nanofibers immersed in several highly nonlinear liquids such as ethanol, acetone and water and we further compare them with air cladding. We provide formula of the effective nonlinear coefficients including the contribution of the nanofiber silica core and of the evanescent field for varying nanofiber diameter and for different surrounding media. Our results show that the contribution of the silica core inversely scales with the effective mode area, while the cladding contribution via the evanescent field depends both on the taper diameter and the nonlinear properties of the liquid. More specifically, it is shown in a silica nanofiber immersed in acetone that the evanescent field contribution to the total Kerr effect is greater than that of the silica core for a taper diameter smaller than 560 nm. We further report the observation of a strong evanescent Kerr effect through measurements of the stimulated Raman-Kerr scattering in a silica nanofiber immersed in acetone. The evanescent Kerr effect is shown to give rise to a strong asymmetric spectral broadening of the first Raman order generated in the nonlinear liquid. Finally, the evanescent Kerr and Raman effects demonstrated in this work may find potential applications to ultra-sensitive liquid sensing and Raman spectroscopy, as the optical mode propagating in the nanofiber essentially interacts with the outer environment without any major contribution from the nanofiber itself.
We demonstrate, build and optimize evanescent Raman converters at the sub-nanosecond regime based on a silica nanofiber immersed in ethanol. Two different standard silica fibers (SMF28, 460HP) are tested and compared. The converters are pumped at 532 nm and deliver pulses at 630 nm, which is the first Stokes order wavelength of ethanol. They present highly reproductible performances. A maximum output Stokes energy of 0.29 μJ is usually reached with an external conversion efficiency of 60%. Lowering the Raman threshold and pushing up the nanofiber breakdown allow a higher conversion operating range, that is the conception key of these converters.
We investigate both theoretically and experimentally the polarization properties of Brillouin light scattering in silica optical nanofibers. Our results show that while all hybrid acoustic waves scatter light without altering the state of polarization, one of the surface acoustic wave generates a depolarized Stokes light. Because of the slight ellipticity of the nanofiber, the surface wave is actually split into two torso-radial modes which give rise to polarization scrambling of the backward Brillouin Stokes signal. Our model also predicts that the polarization of the scattered light can be restored for one specific pump polarization.
We demonstrate a simple and efficient technique that allows for a complete characterization of silica-based tapered optical fibers with sub-wavelength diameters ranging from 0.5 μm to 1.2 μm. The technique is based on Brillouin reflectometry using a single-ended heterodyne detection. It has a high precision sensitivity down to 1% owing to the strong dependence of the Brillouin spectrum on the taper diameter. We further investigate the tensile strain dependence of the Brillouin spectrum for an optical microfiber up to 5% of elongation. The results show strong dependences of several Brillouin resonances with different strain coefficients ranging from 290 MHz/% to 410 MHz/% with a specific nonlinear deviation at high strain. Those results therefore show that optical micro and nanofibers could find potential application for sensitive strain optical sensing.
Fabrication and characterization of submicron optical waveguides is one of the major challenges in modern photonics, as they find many applications from optical sensors to plasmonic devices. Here we report on a novel technique that allows for a complete and precise characterization of silica optical nanofibers. Our method relies on the Brillouin backscattering spectrum analysis that directly depends on the waveguide geometry. Our method was applied to several fiber tapers with diameter ranging from 500 nm to 3 μm. Results were compared to scanning electron microscopy (SEM) images and numerical simulations with very good agreement and similar sensitivity.
Light propagation in small-core photonic crystal fibers enables tight optical confinement over long propagation lengths to enhance light-matter interactions. Not only can photonic crystal fibers compress light spatially, they also provide a tunable means to control light-hypersound interactions. By exploring Brillouin light scattering in a small-core and high air-filling fraction microstructured fiber, we report the observation of Brillouin scattering from surface acoustic waves at lower frequencies than standard Brillouin scattering from bulk acoustic waves. This effect could find potential applications for optical sensing technologies that exploit surface acoustic waves.
We report on the study of two-photon interference in the frequency domain. Bell and Hong-Ou-Mandel experiments
are investigated. These experiments involve the manipulation of photons in the frequency domain, using
off-the-shelf telecommunication components such as electro-optic phase modulators and narrow-band frequency
filters. In the first experiment, photon pairs entangled in frequency are created and separated. Each photon
is then directed through an independent electro-optic phase modulator. Variation of the radio-frequency parameters
of the modulation gives rise to a well-controlled Bessel-shape two-photon interference pattern in the
frequency domain. This is efficiently measured with narrow-band frequency filters and superconducting single
photon detectors. Experimental measurements exhibit high visibilities (over 99 percent both for net and raw
visibilities) and allow the (theoretically proven) optimal violation of a Bell inequality for our setup (by more than
18 standard deviations). The second experiment is a Hong-Ou-Mandel experiment in the frequency domain. We
show that a grating (spatial domain) or a phase modulator (temporal domain) can be seen as a frequency beam
splitter. A broadband spectrum of photon pairs is divided into two interleaved frequency combs, each one used
as an independent input to this acting beam splitter. A theoretical calculation shows clear photon anti-bunching
behavior.
The aim of this work is to compare advantages and disadvantages of different techniques for coupling a mini-discoptical-
resonator to determine quality factor of its resonance. Optical fiber coupled to a resonator consists in a mini disc
with whispering gallery modes at its circumference. We choose to work with three materials and design compact
miniresonators. Fused silica is found to be suitable for these applications thanks to its hardness in the range 6-7 and the
behavior to mechanical shocks, despite its sensitivity to water pollution. With its tetragonal crystal and a good behavior
with risk of water pollution, Calcium fluoride is a good candidate despite sensitivity to mechanical shocks. Magnesium
fluoride is the third material used. As a critical step, taper coupling is set with a 20nm resolution positioning system.
Miniresonator is excited from a system equipped with a tunable laser diode with a tunability from 1490 to 1640 nm and a
linewidth narrower than 300kHz. Light is coupled into the microsphere either from glass or fiber prism or with fiber
taper via evanescent field. We have also used a single frequency 660nm laser diode with a linewidth narrower than
100kHz which can be tuned about 10pm to test a single resonant peak. Both sources are used with either a tapered fiber
or a filed fiber. Resonance is observed and quality factor of the resonators is found to be in the range of 108.
Recently, integrated optic applications on SOI substrate like add-and-drop structures or wavelength filters based on microdisk resonators have been investigated by many research groups. Microdisks exhibiting high quality-factor thanks to the high refractive index contrast between silica and silicon materials have been already reported. However efficient components usually show few micrometers diameter which is huge compared to photonic crystals ones. In this paper, realization and characterization of efficient and compact components are reported. The dropped-wavelength function, composed of a 1.5 μm radius disk and 0.3 μm x 0.3 μm square section waveguides is demonstrated. 22 dB extinction ratio is measured from spectral measurement while keeping a quality factor of 1000. In this structure, the distance between the microdisk and the waveguide is discussed from experimental point of view. Indeed, the efficiency of the add-and-drop strongly depends on this parameter. Moreover, a wavelength filter based on a 4 μm radius microdisk is also shown. Quality-factors of 92,900 ± 5500 were measured showing that these filters are more efficient than equivalent microring filters. A 10 dB extinction ratio of the wavelength rejected signal is reported. For some resonance wavelengths, spectral response degeneracy of the filter appears. An explanation of this effect is given in this paper.
In the past few years, many studies have been carried out to use the ability of light to transport information into silicon-based integrated photonic circuits. The realization of an efficient silicon-based light source is therefore necessary but however challenging. Lasing cannot be easily achieved from silicon emission because of its indirect bandgap. Therefore, one solution proposed is to use other efficient emitters, like rare earth, into silicon or Silicon On Insulator based microcavities. Silica microdisk has been demonstrated to support high-Q whispering-gallery modes, and can be upgraded to ultra-high-Q toroidal microcavities by a CO2 laser melting process. Microdisk high Q-factor balances the low gain generally obtained from the active medium. Thus, those microcavities may be good candidates
for silicon-based laser. In this paper, the fabrication and room
temperature operation of silica microdisk associated with Er-doped silicon rich oxide is presented. Er atoms are excited at the 351 nm wavelength via the silicon clusters, giving to the material a high photonic capture section, and therefore a good photoluminescence efficiency. We demonstrate efficient coupling of erbium atoms to high-Q whispering-gallery modes. The photoluminescence spectrum is then theoretically treated. The WGM resonances are thus identified. We also discuss the contribution of the spot excitation and the weak coupling to the higher radial order modes. Finally, the polarization dependence of the observed modes is investigated, and the experimental results are compared to our analytical model of disk-shape cavities. Those results give us to think that an integrated laser should be soon achieved.
The microgear cavity is a microdisk surrounded by a circular Bragg
grating. It is well known for its high Q Whispering Gallery Mode
(WGM) and its modal selectivity. Microgears are often simulated
thanks to two-dimensional (2-D) Finite-Difference Time-Domain
(FDTD) computations which are limited by their cartesian grid and
experience a high numerical complexity. In this paper, a fast and
accurate 2-D method describing the WGM in a microgear dielectric
resonators is presented. The model is based on the Floquet Bloch
formalism. The field is described analytically within the disk
and outside the grating. The field within the grating is
calculated with a finite difference formalism in polar
coordinates. The resonant wavelength and quality factor can be
deduced from the eigenvalue problem. Our method has been compared
to the Coupled Mode Theory and to 2-D FDTD computations, it proves
to be more accurate and much faster than both methods (few seconds
versus few hours for FDTD). Moreover, we have demonstrated a
polarization effect of the microgear. Finally, our model can be
applied to different structures. Micro-flowers and microgear
surrounded by multi-layer Bragg reflector are investigated.
We present a two dimensional analytical method for studying the
effect of gratings on microdisk dielectric resonators. Our model
based on a Coupled Mode Theory (CMT) needs the normalization of
the Whispering Gallery Mode (WGM). In the past, few normalizations
have been proposed, all of them assume the mode to be bound which
is not true as WGMs are leaky modes. In this paper, we propose a
new normalization with no approximation. Then we apply the CMT in
order to compute the resonance wavelength of the perturbated
structure. This theory has been checked against 2D FDTD and shows
accurate results with very little computation time.
The microdisk based devices principle of operation is presented. The advantages of analytical approach to design with accuracy this kind of structure are discussed. Problems caused by a random roughness on the microdisk periphery are also introduced. It is also shown that a periodic roughness such as a microgear structure can significantly increase the quality factor for some specifically chosen modes. Different design to extract the light from the resonator are presented. The case of a microdisk and waveguide output coupler is better developed. Through new analytical modeling based on perturbation theory, the effect of the interaction between a channel waveguide and a microdisk is indeed presented showing a fast and efficient approach to design such couplers.
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