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U-shaped tight curvatures in optical fibers lead to resonant couplings between the fundamental and higher order modes that are sensible to different parameters, such as strain or temperature, for example. The optical response of the sensor consists on the shift of the resonant wavelength of the coupling. In the case of singlemode fibers, the coupling involves a so-called “cladding mode” and, due to its evanescent field, the curved region will be sensible to changes in the external medium, as well. In this paper, we present the fabrication and characterization of a robust, easy-to-make, U-shaped fiber sensor based on singlemode telecom fiber and its application for biosensing. The resonant nature of the sensing mechanism presents the advantage of large dynamic ranges for RI variations without the ambiguity of other techniques such as interferometry. We studied the performance of the U-shaped fiber sensor for different bending radii, to optimize its sensitivity and detection limit at 1550 nm operation wavelength, as well as the effect of temperature on its response. The shift of the resonant wavelength was measured in detail as a function of the external RI within the range [1.33-1,37]; the detection limit was established in (3.71±0.03)×10-5 RIU. Furthermore, the device was successfully tested as a proof of concept biosensor, using a system model antigen-antibody (BSA-aBSA.)

[EN] The nanostructuration of biolayers has become a paradigm for exploiting nanoscopic light-matter phenomena for biosensing, among other biomedical purposes. In this work, we present a photopatterning method to create periodic structures of biomacromolecules based on a local and periodic mild denaturation of protein biolayers mediated by UV-laser irradiation. These nanostructures are constituted by a periodic modulation of the protein activity, so they are free of topographic and compositional changes along the pattern. Herein, we introduce the approach, explore the patterning parameters, characterize the resulting structures, and assess their overall homogeneity. This UV-based patterning principle has proven to be an easy, cost-effective, and fast way to fabricate large areas of homogeneous one-dimensional protein patterns (2 min, 15 x 1.2 mm, relative standard deviation ? 16%). This work also investigates the implementation of these protein patterns as transducers for diffractive biosensing. Using a model immunoassay, these patterns have demonstrated negligible signal contributions from non-specific bindings and comparable experimental limits of detection in buffer media and in human serum (53 and 36 ng & BULL;mL-1 of unlabeled IgG, respectively)., This work was financially supported by the Ministerio de Ciencia e Innovacion/Agencia Estatal de Investigacion (MCIN/AEI/10.13039/501100011033) , co-funded by the European Union "ERDF A way of making Europe", under grants PID2019-110713RB-I00 and PDI2019-104276RB-I00, and Generalitat Valenciana (PROMETEO/2020/094 and PROMETEO/2019/048) . A.J.-D. acknowledges the FPI-UPV 2017 grant program. The authors thank Angel Lopez Munoz for the construction of the scanning system.

Whispering Gallery Mode (WGM) hollow microcavities turn out to be the site of an extremely rich and complex phenomenological scenario when pumped with a continuous-wave laser source. The coexistence of numerous non-linear and optomechanical effects have been reviewed in this paper. In our previous works we have investigated and described non-linear emissions as the stimulated Brillouin and Raman scattering, the degenerated and non-degenerated Kerr effects, such as four wave mixing (FWM). These effects happened concomitantly to parametric optomechanical oscillations which are the consequence of the radiation pressure. We have confirmed the regenerative oscillation of acoustic eigenmodes of the cavity leading to parametric instabilities and the activation of optomechanical chaotic oscillations. Finally, we have demonstrated that the blue-side excitation of WGM resonances lead to the chaos transition with a spectral evolution depending on the cavity size.

We report the activation of optomechanical chaotic oscillations and chaos transfer from a strong pump to a very weak probe in microbubble resonators, both signals follow the same route to chaos.

The research on photonic biosensors is a scientific hot topic at the moment, with a significant potential impact on industry and medicine. Label-free, miniaturized, inexpensive and low-loss biosensors are developed based on optical fiber technology. Our approach is based on a Bio-Bragg-Grating (BBG) patterned on the surface of a microfiber. We present the design, fabrication and proof of concept of our device, as well as its multiplexing and tunability perspectives [1] .

We report on the experimental and theoretical analysis of parametrical optomechanical oscillations in hollow spherical phoxonic whispering gallery mode resonators due to radiation pressure. The optically excited acoustic eigenmodes of the phoxonic cavity oscillate regeneratively leading to parametric oscillation instabilities.

[EN] Discovering nanoscale phenomena to sense biorecognition events introduces new perspectives to exploit nano science and nanotechnology for bioanalytical purposes. Here we present Bio Bragg Gratings (BBGs), a novel biosensing approach that consists of diffractive structures of protein bioreceptors patterned on the surface of optical waveguides, and tailored to transduce the magnitude of biorecognition assays into the intensity of single peaks in the reflection spectrum. This work addresses the design, fabrication, and optimization of this system by both theoretical and experimental studies to explore the fundamental physicochemical parameters involved. Functional biomolecular gratings are fabricated by microcontact printing on the surface of tapered optical microfibers, and their structural features were characterized. The transduction principle is experimentally demonstrated, and its quantitative bioanalytical prospects are assessed in a representative immunoassay, based on patterned protein probes and selective IgG targets, in label-free conditions. This biosensing system involves appealing perspectives to avoid unwanted signal contributions from non-specific binding, herein investigated in human serum samples. The work also proves how the optical response of the system can be easily tuned, and it provides insights into the relevance of this feature to conceive multiplexed BBG systems capable to perform multiple label-free biorecognition assays in a single device., Spanish Ministry of Science and Innovation (CTQ2016-75749-R and TEC2016-80385-P), Agencia Estatal de Investigacion and Fondo Europeo de Desarrollo Regional (PID2019-110877 GB-I00 and PDI2019-104276RB-I00) and Generalitat Valenciana (PROMETEO/2019/048 and PROMETEO/2017/103). A.J.-D. acknowledges the FPI-UPV 2017 grant program, M.A.-O acknowledges the APSOSTD/2019 program of the GVA.

We report on the experimental analysis of parametrical optomechanical oscillations and photo-acoustical applications such as flow cytometers in hollow phoxonic whispering gallery mode resonators. Both phenomena can be enchanced or suppressed and showed chaotic behavior.

We report on the experimental analysis of parametrical optomechanical oscillations and nonlinear frequency generation in hollow phoxonic whispering gallery mode resonators. Both phenomena can be enchanced or suppressed and showed chaotic behavior.

The strategy to incorporate graphene oxide (GO) in a composite material offers significant opportunities to realize compact photonic devices, such as saturable absorbers and polarization selective devices. However, the processing of GO-based composites by direct laser writing, which would afford vast patterning and material flexibility in a single step process, has been little addressed. In this work, we investigated the mechanisms underlying a mode cleaning effect in polymeric whispering gallery mode microresonators containing GO, aiming at the development of on-chip integrable photonic devices. We fabricated the microresonators (cavity loaded Q-factor of 20 000 at 1550 nm) in a single step of femtosecond laser writing via two-photon polymerization. By calculating the resonance response to damping mechanisms in the microresonators, we showed that additional losses introduced by GO play a major role in reducing the visibility of a number of resonances up to the point of effectively filtering a set of modes out. Interestingly, although the presence of GO leads to extra losses in the microresonator, it does not change the order of magnitude of the Q-factor of the highest extinction ratio resonances. Overall, this work offers interesting physical insights that can be useful for the design and fabrication of GO-based photonic micro/nanodevices. PIRSES-GA-2013- 612267 FAPESP 2018/ 11283-7 FAPESP 2015/22392-3 CAPES 88882.328716/2018-01

The strain-optic coefficients of PMMA are measured in a broad wavelength range from 800 to 2000 nm. The sensitivity of the azimuthal whispering gallery mode resonances to the strain is exploited to measure the strain-optic coefficients of PMMA micro-rods. The technique is based on measuring the wavelength shift of the resonances of both polarizations states, the TE and TM, when an axial strain is applied to the polymer rods. This method enables the determination of the strain-optic coefficients of the material in a broad wavelength range. In particular, in the near-infrared range, the PMMA exhibits negligible dispersion and anisotropy, and the strain-optic coefficients show constant values within the experimental error: p11 = 0.298 ± 0.010 and p12 = 0.294 ± 0.010.

Fiber whispering gallery modes (WGMs) are surface waves that propagate azimuthally along the outer surface of the fiber cladding. Those waves that are in phase every turn give rise to narrow resonances defined by the resonant wavelength and a high Q factor. The actual values of the resonant wavelengths depend on the radius and the refractive index of the fiber cladding, enabling the development of several fiber characterization techniques. In addition, the typical high Q factor of these resonances (Q > 106) provides the characterization techniques with a low detection limit. Here, we report the development of a technique for measuring temperature profiles along the optical fiber, which enables the characterization of UV-induced absorption loss in photosensitive fibers, and a technique for the measurement of the elasto-optic coefficients and the anisotropy generated by the axial strain in standard fibers.

In fiber acousto-optics has been demonstrated to be a versatile, highly sensitive technique that allows characterizing different parameters of singlemode or few-mode fibers, such as dispersion curves, radius or core refractive index, in a broadband wavelength range. The working principle of the technique relies in the fact that a variation in a parameter of the fiber leads to a shift in the optical wavelength that fulfills the acousto-optic phase matching condition. Thus, by measuring this wavelength shift it is possible to evaluate the change in the parameter under study. The technique shows a low detection limit: for example, it is as low as 10-8 for the core refractive index, in singlemode fibers. In addition, short sections of fiber (~20 cm) are required to perform the measurements.To fabricate gratings in photosensitive fibers, the core refractive index is increased, typically, in 10-5 – 10-4. In this work we characterize the refractive index change induced by UV radiation in hydrogenated, telecom-fiber (SMF28 from Corning), by means of the acousto-optic tool. Broadband characterization is performed in one go, using only one section of irradiated fiber. We characterized the refractive index variation as a function of the UV energy delivered to the fiber, in the range 1 – 2 μm.

Whispering gallery mode resonators (WGMR) have attracted a great interest in the last decade. WGMR have been fabricated in different geometries, solid and hollow, spherical, toroidal, and bottled shaped. Hollow spherical WGMR or microbubble resonators (MBR) are the last arrived in the family of resonators. The approach used for their fabrication is based on surface tension driven plastic deformation on a pressurized capillary, similar to glassblowing. Using such technique we are able to fabricate large surface area and thin spherical shells with high quality factor (Q). MBR are efficient phoxonic cavities that can sustain both optical photons and acoustic phonons. It has been demonstrated that MBR can be used to study Turing comb patterns (Kerr modulation) and Stimulated Brillouin Scattering (SBS). Radiation pressure is another mechanism that also leads to excitation of acoustic phonons with lower frequencies, in the range of hundreds of kHz to tens of MHz in the case of silica MBR. The frequency of such oscillations occurs very close to the mechanical eigenfrequencies of the cavity. We have studied the temporal behavior of the cavity, the coexistence and the suppression of the oscillation while generating Turing comb patterns. The observed phenomenology can be explained by the geometrical characteristics of a MBR. MBRs are spheroidal WGM resonators with quite dense spectral characteristics. The total dispersion of MBR is anomalous and large, as expected for very large MBR. Thus, Kerr comb formation is allowed for all MBR used in this work.

We report on the experimental and theoretical analysis of parametrical optomechanical oscillations in hollow spherical PhoXonic whispering gallery mode resonators due to radiation pressure. The optically excited acoustic eigenmodes of the PhoXonic cavity oscillate regeneratively leading to parametric oscillation instabilities.

We propose the implementation of fiber Bragg gratings in tapered few-mode and multimode fibers to accomplish single-mode operation by reducing the core diameter, while preserving the core-cladding structure. The gratings present a single reflection band, and the device shows low insertion losses after the taper fabrication and the fiber Bragg gratings inscription. The excitation of high-order odd modes in the core of the fiber has been identified as the main loss mechanism; it can be prevented by means of symmetric illumination of the fibers. We also demonstrate the excitation of high-order cladding modes (cladding-air modes) along the taper transitions; these modes can be removed without a significant increment of the insertion loss.

In-fiber acoustic gratings exhibit a turning point in which the sensitivity of the coupling resonances to environment changes is extremely high. The frequency of the acoustic wave enables easy matching of the turning point.

UV-assisted fabrication of gratings using photosensitive fibers is a well-established technique, based on the UV-induced permanent modification of the refractive index of the fiber material. As a result, the absorption coefficient is also changed. Here, we exploit the thermal sensitivity of whispering gallery mode resonances of the fiber itself to measure the profile of the heating along an irradiated fiber versus the input power and for different UV radiation intensities. Our technique allows discriminating between the absorption and scattering contributions to the overall losses, by comparing the results obtained with our technique with direct transmission measurements. Different photosensitive fibers are characterized by means of this technique. Nonuniform UV irradiation of photosensitive fibers can be characterized with this technique.

When a photosensitive (PS) fiber is exposed to UV-irradiation, a permanent refractive index change is induced in the core. As a result, according to Kramers-Kronig relations, the absorption coefficient (α) is also increased. This increment of the absorption can lead to a significant heating of the fiber when it is illuminated by a moderate optical power. Thermal effects may produce spectral changes in some fiber devices, as for example Long Period Gratings (LPGs) or Fiber Bragg Gratings (FBGs) [1].

This paper reports on the fabrication of long period fiber gratings having subnanometric bandwidth in the 1500 nm spectral region. Large gratings have been photo-inscribed in a high NA fiber, the grating pitch and the order of the HE cladding mode are optimized to produce gratings with a large number of periods and preventing the coupling to TE, TM or EH modes. Resonances with a FWHM of 0.83 nm and 0.68 nm have been achieved for gratings 15 and 20 cm long respectively, the free spectral range between transmission notches is 125 nm. The polarization effects and the sensitivity of the gratings to temperature and to strain variations are presented as well. © 2015 Optical Society of America This paper reports on the fabrication of long period fiber gratings having subnanometric bandwidth in the 1500 nm spectral region. Large gratings have been photo-inscribed in a high NA fiber, the grating pitch and the order of the HE cladding mode are optimized to produce gratings with a large number of periods and preventing the coupling to TE, TM or EH modes. Resonances with a FWHM of 0.83 nm and 0.68 nm have been achieved for gratings 15 and 20 cm long respectively, the free spectral range between transmission notches is 125 nm. The polarization effects and the sensitivity of the gratings to temperature and to strain variations are presented as well. © 2015 Optical Society of America

Nanometric narrowband Long Period Gratings (LPG) are investigated for the implementation of improved fiber optic biosensors. The reduction of more than one order of magnitude in the linewidth of the LPG with respect standard LPG at 1500 nm, leads to the improvement of the resolution of the sensor. By selecting the proper fabrication parameters (high numerical aperture, relatively high order mode and large length), LPGs with a 3-dB bandwidth of 1.5 nm were fabricated. The sensitivity of the LPG as a refractometer was calculated, and experimentally characterized in detail. In particular, the LP0,17 and LP0,18 resonances were investigated, in order to select the most suitable one for the bioexperiments. The surface of the LPG was functionalized and the detection of the hybridization of DNA is demonstrated. When the biosensor was immersed in a 2 μM solution of the complementary DNA strand, the resonances of the LPG shifted in wavelength. When measuring the response of the sensor in terms of variation of its transmittance as the resonance shifted in wavelength, the sensitivity was ~10%/μM for both resonances. The detection limit was estimated in 10 nM

We present a perturbative approximation to calculate the relative shift of the WGM resonances in a conventional optical fibers when an axial strain is applied. We consider the anisotropic character of the elasto-optic effect.

An acoustically Q-switched distributed feedback fiber laser with enhanced performance is presented. It is based on an FBG written in an erbium doped fiber, in which a dynamic defect is introduced by means of a short acoustic pulse. The performance of the laser depends on the reflectivity of the grating. In this work, we present two different Q-switched distributed feedback fiber lasers realized with active gratings of different reflectivities. Both lasers are characterized at different pump powers and repetition rates. It is shown that the performance of the laser based on the weaker grating was significantly improved with respect to the laser based on the stronger grating. In terms of peak power, the improvement was a factor of two. The average power was also improved. For example, at 50 kHz, it was increased from 280 μW up to 500 μW. In addition, we studied the performance of the laser when an electric square signal was used to drive the transducer, obtaining similar results to the case when a harmonic electric pulse was used.

Q-switching of fiber lasers using bulk elements has important drawbacks as reduced mechanical stability and high insertion losses. The development of efficient all-fiber modulation techniques is the key to obtain robust, compact and efficient Q-switched all-fiber lasers. Certainly, the development of fiber Bragg gratings (FBG) has been crucial to make progress on fiber lasers. FBGs permit a simple way to assemble all-fiber laser cavities and can be written in the active fiber itself. The Q-factor of this type of cavities is determined by the reflectivity of the FBGs and the losses of the fiber. Here, we focus on the use of magnetostrictive materials and the acousto-optic interaction to develop efficient Q-factor modulators. Most of these modulators include an FBG and take advantage of the specific interaction of the magnetostrictive materials or the acoustic wave with the FBG itself. Fiber optic technologies permit the development of a rather unique type of fiber lasers, i.e., actively Q-switched distributed feedback (DFB) fiber lasers. In this case, both the use of magnetostrictive materials and the acousto-optic interaction permit the generation of dynamic defects in an FBG that has been previously written in a highly Er-doped fiber.

We report an actively Q-switched all-fibre laser using a fibre-optic resonant acousto-optic modulator as Q-switching element. The modulator consists of a short-length fibre Bragg grating modulated by a standing longitudinal elastic wave, being the grating length much shorter than the acoustic wavelength. Q-switch pulses were successfully obtained from an Er3+-doped fibre laser at repetition rates of 18 and 37 kHz.

In this paper we present the main research activities of the Laboratorio de Fibras Opticas del Instituto de Ciencia de los Materiales de la Universidad de Valencia. We show some of the main results obtained for devices based on tapered fibers, fiber Bragg gratings, acousto-optic effects and photonic crystal fibers.

The temperature sensitivity of whispering-gallery mode resonances of an optical fiber is exploited to measure thermal effects induced by an optical signal of moderate power along a fiber Bragg gating (FBG). The UV inscription technique used for the fabrication of FBG introduces a permanent change in the absorption coefficient of the fiber; thus, thermal effects are expected. The resonance wavelength shift of whispering-gallery modes provides information about the temperature change in the fiber, point to point. We present the experimental characterization of the thermal effects in FBG as a function of the wavelength and the power of the launched optical signal through the grating.

We present the measurement of the temperature variation along a fiber Bragg grating (FBG) written in a photosensitive fiber, using azimuthal whispering gallery modes (WGM) resonances of the fiber itself. The FBG is regarded as a cylindrical microresonator, in which the azimuthal WGM resonances are excited with an auxiliary 2 μm taper. The wavelengths of the WGM resonances shift as the temperature of the grating increases at a given point. The temperature profile along the FBG is obtained by monitoring the WGM resonances at different points, as a function of the power and wavelength of the optical signal. Our experiments give useful information to study the small absorption changes produces by the standard UV photo-inscription technique and the thermally induced chirping effects generated when FBGs are used with moderate power levels.

Experimental characterization of the refractive index anisotropy generated by the elasto optic effect in a conventional optical fiber under axial strain by using WGMs resonances and their tunability with strain.

We present the fabrication of a polarizing, endlessly single-mode microstructured fiber with high polarization-dependent loss. The fiber was fabricated by the stack-and-draw method. The resulting structure consists of a pure silica core surrounded by a regular lattice of air holes, in which four air holes in the inner ring have been enlarged. An extinction ratio of 16 dB/m with a transmission loss of 0.9 dB/m was achieved at a wavelength of 1550 nm

We report a wavelength-switchable fiber ring laser that includes a Bragg grating-based acoustooptic superlattice modulator. Wavelength switching of the laser emission is achieved by controlling the peak reflectivity of the different reflection bands that appear on both sides of the Bragg wavelength when a longitudinal acoustic wave propagates along the grating.

In this letter, we present the fabrication of a microstructured fiber with high birefringence suitable for nonlinear applications. The fiber has been fabricated adapting the stack and draw method for microstructured fibers. The birefringence of the fiber is achieved inducing ellipticity to the air-hole array by controlling the lateral tension between preform and jacketing tube. Values of the group index birefringence higher than 7/spl times/10/sup -3/ are demonstrated.

The elasto-optic effect in optical fibers under axial strain can be characterized by means of the whispering gallery mode (WGM) resonances of the fiber itself. This technique enables a direct measurement of the anisotropy, the determination of the individual Pockels' coefficients, and the study of the wavelength dependence. The method is based on a rigorous theoretical study of WGM resonances in cylindrical microresonators. The shift of the WGM resonances as a function of strain was measured for the TE and TM modes, showing a strong modal anisotropy. In particular, the shift rate for TE modes was 1.84 times the one for TM modes. From these measurements, experimental values for the Pockels' coefficients were obtained: psub11/sub=0.116 and psub12/sub=0.255 at 1531 nm, and psub11/sub=0.131 and psub12/sub=0.267 at 1064 nm. The dispersion of psub44/subwith wavelength was shown to be 5% μmsup-1/sup.

We report a novel dynamic fiber-optic add-drop multiplexer that combines the properties of Bragg gratings and the acousto-optic effect in optical fibers. It is a noninterferometric, nonfrequency shifting device that allows adding/dropping a certain optical channel when it is required. The prototype presented here exhibits a time response of /spl sim/95/spl mu/s.

We present simulation results along with measured spectral and dispersion data for a highly birefringent PCF designed to produce naturally narrowband photons, at telecoms wavelengths, from a 1064 nm pump through cross-polarised four-wave mixing.

We report the generation of supercontinuum confined to the visible in submicron fiber structures pumped by femtosecond pulses centered at 540 nm.

Third harmonic generation in fibre nanotapers by intermodal coupling is experimentally characterized. UV radiation is generated from a pulsed 1064 nm laser in a 3 cm taper of 492 nm diameter.