Sources of photon pairs based on spontaneous four-wave mixing in silica fibers are generally considered limited by the spectrally broad spontaneous Raman scattering noise. I experimentally show that fluorescence from native or residual doping defects in silica fibers can become preponderant in situations where Raman scattering is normally eliminated, revealing a new, to the best of my knowledge, source of noise in silica-fiber-based sources of pairs of photons. I show that this noise depends on the fiber used, and that a new parameter must be carefully surveyed for the optimization of a fibered source of entangled pairs of photons.

We will present a rapid and non-destructive technique for the measurement of the mean diameter of a silica nanofiber using the wavelength position of the signal peak in a spontaneous four wave mixing experiment. The nanofiber diameter can be characterized in a range going at least from 650 to 1250nm. Several nanofibers were characterized, and the measured diameter show a good accordance with the one obtained using a Scanning Electron Microscope. The technique is simple to use and has even the potential to be implemented in situ in order to realize a diameter measurement during the pulling of the nanofiber for a better control of the final diameter of the nanofiber.

We present measurements of the temperature of optical microfibers self-heated by a cw laser emitting at 1.48 μm. The experimental method we have implemented is simple and enables to perform for the first time to our knowledge spatially distributed measurements along the tapers and the microfiber part. Temperature rise of more than 20 °C is measured for moderate powers (200 mW) and relatively large radii (1.45 μm). The results are confronted to a numerical model we have developed and enable to determine range of values for the couple thermal transfer coefficient/surface absorption coefficient.

Recent advances towards the loss reduction in silicon nitride (SiN) has increased its interest as a material platform compatible with complementary metal-oxide-semiconductor (CMOS) processing [1]. SiN offers a large transparency range reducing multiphoton absorption processes, yet its nonlinear Kerr coefficient remains about 10 times lower than that of Silicon. Now, the new coming challenges in the development of optical integrated devices rise the need for highly nonlinear CMOS-compatible optical platforms based on hybrid waveguide structures. Hereafter we report on the properties of nonlinear hybrid SiN waveguides with a Ge 23 Sb 7 S 70 (GSS) chalcogenide glass cladding of layer thickness comprised between 100 and 200 nm. Using a bi-directional spectral broadening based method, we demonstrate that hybrid SiN waveguides with a 200 nm thick GSS cladding reach an effective nonlinear refractive index $n_{2} = 0.8\pm 0.2 \cdot 10^{-18} \mathrm{m}^{2}/\mathrm{W}$ close to that of Silicon ( $n^{2} = 2 \cdot 10^{-18} \mathrm{m}^{2}/\mathrm{W}$ ), but without noticeable TPA.

After presenting a theoretical modelling based on the heat equation, we show two different experiments to measure the laser induced temperature variation in silica nanofibers in air, a direct one and an indirect one based on Brillouin scattering, leading to an estimated value of the convective parameter h.

The emerging interest in integrated optical technologies raises the need for precise characterisation techniques for waveguides presenting nonlinearities. Here we propose a non-interferometric measurement to accurately characterise the Kerr contribution in hybrid waveguides and illustrate its performances using SiN waveguides with a GSS chalcogenide top-layer. The sensitivity of our technique in terms of nonlinear phase reaches 10 mrad and its accuracy makes possible to extract the nonlinear contributions from the top-layer.

We present experimental results demonstrating the possibility to tune the wavelength of the photon pair emitted through four wave mixing in a nanofiber, using the pressure of a gas surrounding the nanofiber. Using Argon, a shift of idler wavelength of -1.1nm/bar is measured demonstrating fine adjustment possibility of emission wavelength, allowing to choose between different WDM channels.

We present the operating range of Raman wavelength converters based on silica nanofibers immersed in liquids for the design of all fibered wavelength converters that can be inserted in optical networks with very low losses.

We present the operating range of Raman wavelength converters based on silica nanofibers immersed in liquids for the design of all fibered wavelength converters. This range is bounded on the lower limit by the pump energy necessary to reach the Raman threshold and on the upper limit by the laser induced breakdown of the nanofiber. These breakdown energies are measured in the ns regime for different liquids (water, ethanol, isopropanol) and for air. We finally define guidelines that open the way to a new family of low-cost compact and efficient all-fibered Raman converters that can be directly inserted in optical fibered networks with very low losses.

In this paper, we describe experimental observation and characterization of emission of photon pairs through four-wave mixing (FWM) in a silica nanofiber, with high coincidence to accidental ratio (CAR, at best greater than 20 000 in the cw regime at pump power 24 mW and 40 000 in the pulsed regime at pump power approximate to 150 mu W) and high pair emission rate (above 1 MHz in the pulsed regime with CAR around 100 at pump power approximate to 7 mW), despite residual presence of Raman spontaneous scattering (in the vicinity of the 12th silica Raman band) on the idler side. Moreover, these pairs of photons are observed with either a single-longitudinal-mode source or a multimode source (as well as a pulsed source) showing a factor of 2 increase of emission rate with the multimode source thanks to its random temporal fluctuation coupled to the quadratic response of FWM.

In this paper, we present a design of an all-fiber source of correlated photon pairs based on standard telecommunications tapered fibers. We examine the generation of correlated photon pairs using parametric process χ ( 2 ) in silica tapered optical fibers. This nonlinear process is ensured thanks to surface dipole and bulk multipole nonlinearities. The process of photon creation is modeled by taking into account the vector aspect of the propagation of the optical field in a silica nanofiber. The phase matching is provided by propagating the pump field in one spatial mode while generating a photon pair in another spatial mode. The generation efficiency of photon pairs depends on diameter uniformity of the nanofiber after the manufacturing process. We size this nanofiber for a good optimization of photon pair generation efficiency, and we report that the tolerance in diameter uniformity is Δ d = 2 n m for a generation rate of photon pairs estimated to N ph ≈ 22 000 p a i r s / s , for 1 W power pump and a nanofiber length of 1.1 mm. Deposits on the nanofiber can be used in order to relax the manufacturing constraints on diameter to maximize the generation rate of photon pairs. As an example, the use of polytetrafluoroethylene on the nanofiber applied as a cladding whose thickness is infinite makes it possible to relax the constraints on the nanofiber diameter. For the same Δ d = 2 n m , a generation rate of photon pairs estimated to N ph ≈ 78 000 p a i r s / s for 1 W power pump and a nanofiber length of 2.4 mm is predicted.

Raman-scattering noise in silica has been the key obstacle toward the realisation of high quality fiber-based photon-pair sources. Here, we experimentally demonstrate how to get past this limitation by dispersion tailoring a xenon-filled hollow-core photonic crystal fiber. The source operates at room temperature, and is designed to generate Raman-free photon-pairs at useful wavelength ranges, with idler in the telecom, and signal in the visible range. We achieve a coincidence-to-accidentals ratio as high as 2740 combined with an ultra low heralded second order coherence g_H^(2)(0)=0.002 , indicating a very high signal to noise ratio and a negligible multi-photon emission probability. Moreover, by gas-pressure tuning, we demonstrate the control of photon frequencies over a range as large as 13 THz, covering S-C and L telecom band for the idler photon. This work demonstrates that hollow-core photonic crystal fiber is an excellent platform to design high quality photon-pair sources, and could play a driving role in the emerging quantum technology.

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 perform long-time measurements of the optical silica transmittance during several months in different environments and with different nanofiber lengths. These measurements are repeatable and give guidelines to control and to improve the lifetime and the performances of the nanofiber. The dust particles on the nanofiber surface is the fundamental reason behind its degradation. Enhancing the cleanness conditions of the nanofiber environment makes its lifetime increases significantly (from some hours to some months) and enables to avoid the dramatic decrease of its transmittance even after months. The nanofiber length does not contribute to the nanofiber transmittance degradation. Stabilizing the nanofiber transmittance after its decrease is possible by putting in in a dust free box.

We describe a technique that allows the improvement of the resolution of optical microscopes for nanofiber measurements beyond the diffraction limit. It can be readily implemented on any microscope. We demonstrated it by measuring tapered fibers radii from 0.4 to 4 µm with a resolution below the diffraction limit, from a few nanometers up to 50 nm in the worst case, depending on the radii. This technique is a non-contact measurement with the microscope objective placed a few centimeters from the nanofiber. We acquire the experimental diffraction pattern by scanning the object plane of the microscope system, upstream and downstream the nanofiber. We compare this experimental diffraction pattern to a bank of all the simulated patterns for all the radii. The radius of the simulated diffraction pattern that best matches to the experimental one is the sought radius.

We describe a technique that allows increasing the resolution of optical microscopes for nanofiber measurements. We demonstrated it by measuring the diameter of tapered fibers for radii ranging from 0.2 to $1.5\ \mu \mathrm{m}$.

We present highly efficient and reproducible Raman converters built with a silica nanofiber immersed in ethanol. The converters are pumped at 532 nm in the sub-nanosecond regime and the first Stokes order photons are generated in the evanescent field probing the liquid at 630 nm. Two standard fibers (SMF28 and 460HP) are tested and compared. The Raman conversion operating range limited by the damage threshold is optimized, leading to an external Raman conversion efficiency up to 60% with a nanofiber radius of 300 nm and a length of 8 cm. The extracted Stokes energy is 0.29 μJ, which is three times higher than the previous result. We give guidelines for the design of other efficient evanescent Raman converters, opening the way for a new family of all-fibered compact Raman sources.

We present a Raman converter emitting at 583 nm on the second Stokes order of propan-2-ol pumped by a microlaser at 532 nm in the sub-nanosecond regime with an internal conversion efficiency of 67%.

A simple and accurate determination of the diameters of tapered optical fibers is essential for the development of new optical components. For this purpose, we propose a technique to increase by more than 10 the resolution of optical microscopes. This technique can be readily implemented on any microscope. We demonstrated it by measuring the diameter of a tapered optical fiber with a resolution better than 100 nm with a x10 optical microscope whose aperture is 0.28.