Search

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.

Here we present a self-started passively mode-locked thulium-doped fiber laser with in-band pumping at 1561 nm that fully retains polarization and emits beyond 2 μm. We obtained a sequence of light pulses at 13.084 MHz, where the pulse and spectral widths were 94 ps and 70 pm, respectively, at 2069.5 nm. The measured instantaneous angular frequency shows that these light pulses are chirp-free.

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.

In this paper, we present a brief review of the noise operation mode of fiber lasers. These lasers were studied recently by collaborative group that includes researchers, professors, and Ph.D. students from the Centro de Investigaciones en Optica, A.C. (Leon, Guanajuato, Mexico) and from the Universidad de Valencia (Valencia, Spain). Meanwhile, the pioneer works in this topic important for understanding the physics behind fiber lasers’ operation and for practical applications were done with the active participation of Dr. Evgeny Kuzin from the Instituto Nacional de Astrofisica, Optica y Electronica (Puebla, Mexico) and Dr. Georgina Beltrán-Pérez from the Benemérita Universidad Autónoma de Puebla (Puebla, Mexico), whose Ph.D. study was supervised by him. The fiber lasers under study were based on commercial erbium- and ytterbium-doped fibers as gain media and operated in continuous-wave and actively Q-switched regimes. All these fiber lasers were arranged in Fabry-Perot cavity configuration with fiber Bragg gratings as narrow-band reflectors. In the case of actively Q-switched lasers a standard fiberized acousto-optic modulator was placed close to the rear (100%) reflector. The most important conclusion of all the works grounding the present review is that, independently on laser operation regime, continuous wave or actively Q-switched, these fiber lasers operate in the extremely noise regime with the photon statistics described by Bose-Einstein distribution inherent to narrow-band thermal light sources.

In this article, a symmetrical nonlinear optical loop mirror (NOLM) exhibiting a polarization-dependent transmission is evaluated to generate optical pulse emission in a figure-eight fiber laser in the soliton and noise-like pulse (NLP) regimes. The NOLM structure relies on a 50:50 fiber coupler, a loop with highly twisted single-mode optical fiber and a quarter-wave retarder (QWR) to break the polarization asymmetry. The pulse operation regime is determined by properly adjusting the NOLM low-power transmission, which is easily realized by the rotation of the QWR angle. Soliton pulses of 1.48 ps pulse duration and peak power of 18 W were observed with a peak to peak separation of 1.25 µs, corresponding to a fundamental cavity repetition rate of 0.8 MHz. Moreover, by incrementing the NOLM low-power transmission, NLP emission is generated exhibiting a wide and smooth spectrum of 8.5 nm bandwidth.

Electromagnetic whispering gallery modes (WGM) are surface waves guided by the curvature of an interface. Microspheres, microdisks and microcylinders –as for example standard optical fibers– are high quality microresonators for the WGM. In fact, they can be regarded as compact and small ring resonators. Here, we present a comparison between wave propagation and energy balance models, stablishing the equivalence and discussing the basic characteristics of these two complementary approaches.

We report the basic spectroscopic properties of a home-made holmium-aluminum-germanium co-doped silica fiber, designed for laser applications. We present the ground-state and excited-state absorpti...

Transverse acoustic mode resonances enable a high accuracy determination of Poisson’s ratio and elastic properties of optical fibers. An all-optical pump and probe technique is used for efficient excitation and accurate characterization of both, radial and torsional-radial acoustic resonances of optical fibers. Simple and precise algebraic expressions for the frequencies of high order acoustic resonances are derived, enabling a rigorous analysis of the experimental data using standard least squares fitting. Following this approach, the determination of Poisson’s ratio does not require the measurement of any physical length, but only frequency measurements are required. An accuracy better than 1 ‰ is achieved. The dependence of the fiber Poisson’s ratio with temperature is also determined experimentally.

We discuss a method to determine both the group delay and the phase of a given pulse in the Fourier optics domain. The proposal is based on the measurement of two intensity spectra, before and after a known quadratic phase modulation. A simple analytical equation is then used to determine the group delay in one step. If necessary, the spectral phase can be determined by simple spectral integration of the determined group delay. The proposal is supported by various numerical results and an experimental measurement to prove the concept.

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.

Accurate knowledge of the nonlinear coefficient is extremely important to make reliable predictions about optical pulses propagating along waveguides. Nevertheless, determining this parameter when dispersion and loss are as important as nonlinear effects brings both theoretical and experimental challenges that have not yet been solved. A general method for measuring the nonlinear coefficient of waveguides under these demanding conditions is here derived and demonstrated experimentally in a kilometer-long standard silica fiber pumped close to 2 µm.

A simple and inexpensive method to measure vibrations in mechanical structures is presented by means of Fabry-Perot interferometry and Doppler effect. The sensor consists of a transparent hydrogel sphere attached to an single-mode optical fiber from a 50:50 fiber coupler, laser light with a wavelength of 658 nm, and a photodetector which is connected to an oscilloscope. The vibrometric sensor works in the time domain by detecting the number of interference fringes. The tip of the prototype is composed of mechanical couplings that join the fiber with the hydrogel sphere. The sensor allows knowing the vibration frequency at which a mechanical part is oscillating. The analysis presented in this work shows several advantages over conventional methods, such as low cost, real-time measurement, and simplification in experimental setup. The sensor system is capable of capturing vibrations of up to 5000 Hz.

We report on a novel device to measure relative humidity. Materials used in the measurement of relative humidity are of different kinds. The sensor is based on surface diffraction gratings made of gelatin. This material swells and shrinks according to the content of water vapor in air. By sending a light beam to the grating, diffracted orders appear. Due to the gelatin swelling or shrinking, first order intensity changes according to the relative humidity. Calibration curves relating intensity versus relative humidity have been found. The fabrication process of diffraction gratings and the testing of the prototype sensing devices are described.

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] .

The interaction between light and sound in optical fibers is a phenomenon that researchers have been investigated for many decades. Among all the opto-acoustic effects that occurs in optical fibers, forward-stimulated Brillouin scattering (FSBS) has become of great interest as sensing mechanism due to the dependence of the excited acoustic resonances on both internal parameters [1] , [2] and surroundings [3] of the optical fiber. The vibrational modes behind FSBS are transverse acoustic resonances, in particular, the radial modes R 0m and the torsional-radial modes TR 2m . Most of the experiments reported based on FSBS exploit the properties of either the radial or the torsional-radial modes. In this work, we show that combining the characteristics of both types of resonances the possibilities of FSBS for fiber sensing can be extended further. In particular, we report the measurement of the Poisson ratio of the optical fiber with high accuracy, as well as its temperature dependence.

Measuring the nonlinear coefficient γ of any guiding medium, regardless of the sign and magnitude of its group-velocity dispersion parameter β 2 , is challenging because of the lack of general solutions of the nonlinear Schrodinger equation (NLSE). Indeed, existing approaches typically need to disregard chromatic-dispersion effects to determine γ [1] . Here we propose an all-encompassing approach to measure the ratio β 2 /γ and prove our method in polarization-maintaining (PM) and single-mode (SM) fibers with positive and negative β 2 .

Polarization modulation instability (PMI) is a nonlinear effect in which two pump photons with identical polarization propagating in a nonlinear medium give rise to two new photons of different frequency and orthogonal polarization with respect to the pump photons [1] . In this work, we report the experimental demonstration of broad spectral tuning of PMI generated in solid-core microstructured optical fibers (MOF) that were previously infiltrated with heavy water (D 2 O). MOFs were designed and fabricated with the appropriate dispersion characteristics to produce widely spaced PMI spectral bands when they were filled with D 2 O and pumped at 1064 nm. Heavy water was chosen due to suitable refractive index, large thermo-optic coefficient (~6.6×10 –5 K −1 ) and relatively low absorption in the near-IR. Tuning effect was achieved by exploiting the strong dependence of the PMI frequency shift on the fiber dispersion and birefringence [2] .

We report the experimental observation of the polarization modulation instability (PMI) effect in all-normal dispersion (ANDi) microstructured optical fibers (MOFs) with quasi-continuous pumping. The small unintentional birefringence (~10-5), that any realistic non-polarization maintaining MOF exhibits, contributes to this nonlinear effect. PMI can produce two sidebands whose polarization state is orthogonal to the polarization of the pump. In this work, only one type of PMI process is observed, i.e., when the pump is polarized along the slow axis of the fiber and sidebands are generated in the fast axis mode. This PMI process was studied experimentally in two ANDi fibers with different dispersion features and pumped with long (700 ps) pump pulses at 1064 nm. Experimental results are compared with theoretical calculations, with reasonably good agreement.

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.

Generation of widely spaced polarization modulation instability (PMI) sidebands in a wide collection of photonic crystal fibers (PCF), including liquid-filled PCFs, is reported. The contribution of chromatic dispersion and birefringence to the net linear phase mismatch of PMI is investigated in all-normal dispersion PCFs and in PCFs with one (or two) zero dispersion wavelengths. Large frequency shift sidebands are demonstrated experimentally. Suitable fabrication parameters for air-filled and liquid-filled PCFs are proposed as guidelines for the development of dual-wavelength light sources based on PMI.

[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.