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We developed a long-period grating based single-mode fiber to single-mode fiber coupler. By applying strain to the fibers, the power transfer at 1476 nm and 1552 nm increased 6 dB and 8 dB, respectively.

Here, we numerically propose and demonstrate a technique to couple light between two multi-core fibers (MCFs) using long-period gratings (LPGs). The light is coupled from one core of the input MCF to all cores of the output MCF. For that, an LPG is inscribed in the input core of the input MCF and identical LPGs are inscribed in all cores of the output MCF. First, the light is launched into the input core of the MCF and the optical power is transferred to the cladding due to the LPG inscribed in that core. The optical power in the cladding is then transferred to the other MCF cladding by evanescent field coupling. The optical power in the cladding of the output MCF is distributed by all its cores due to the identical LPGs inscribed in them. We optimized the LPGs period, their lengths and offset distance to increase the power transfer at 1480 nm. We achieved a power transfer of 92% of the input power, distributed by all MCF cores, in 10.6 cm of length. We also studied the power transfer sensitivity to the LPGs period.

In this work, we propose and demonstrate numerically a long-period grating (LPG) based technique to couple light from a single-mode fiber (SMF) to all cores of a multi-core fiber (MCF), i.e., an SMF to MCF coupler. The light launched into the SMF core is coupled to the SMF cladding due to the LPG inscribed in the core. Then, the optical power is transferred between fibers claddings, enhanced by the reduction of the SMF cladding radius. Finally, the MCF cladding optical power is distributed by all cores of the MCF due to identical LPGs inscribed in them. We use the coupled-mode theory to study and design the proposed device. We achieve a coupling efficiency of approximately 90% of the input power in a total length of 15.1 cm. We also study the coupler’s sensitivity to the SMF radius and LPGs period. Results show that the proposed device can improve the pumping efficiency of MCF amplifiers. published

In this paper, we demonstrate both numerically and experimentally the capability to control and enhance the hydrostatic pressure sensitivity of an adhesive based Fabry-Perot (FP) sensor. The fiber sensor consists of a polymerized resin in between two single-mode fiber terminals that act as low-reflectance mirrors. The theoretical evaluation of the proposed sensor showed that the strain in the region between the fiber end faces increases with increasing dimensions of the resin structure surrounding the inner FP cavity. Experimentally, the photopolymerizable resin was added in layers, increasing the structure dimensions, allowing to improve the hydrostatic pressure sensitivity from 102 to 475 pm/MPa for the cavity filled with resin just in between the fiber end faces and for the cavity covered with several layers of resin, respectively. The sensor fabrication is simple and cost effective, allowing an easy and affordable way to control and enhance the hydrostatic pressure sensitivity of resin based FP sensors.

In this work we report the fabrication of a dual fiber sensor composed of an adhesive based Fabry–Perot cavity combined with a polymer fiber Bragg grating (PFBG), for the simultaneous detection of humidity and temperature. The Fabry–Perot structure was fabricated through a modified version of the self-written waveguide technology, by employing a no-core fiber, while the PFBG was inscribed in a flat-sides microstructured polymer fiber (mPOF) using the phase mask technology through the 248 nm UV laser. The combination of these two polymer based technologies allow an easy fabrication and provide an efficient route for the simultaneous detection of humidity and temperature with high resolution.

In this work, we demonstrate for the first time the capability to inscribe long-period gratings (LPGs) with UV radiation using simple and low cost amplitude masks fabricated with a consumer grade 3D printer. The spectrum obtained for a grating with 690 µm period and 38 mm length presented good quality, showing sharp resonances (i.e., 3 dB bandwidth < 3 nm), low out-of-band loss (~0.2 dB), and dip losses up to 18 dB. Furthermore, the capability to select the resonance wavelength has been demonstrated using different amplitude mask periods. The customization of the masks makes it possible to fabricate gratings with complex structures. Additionally, the simplicity in 3D printing an amplitude mask solves the problem of the lack of amplitude masks on the market and avoids the use of high resolution motorized stages, as is the case of the point-by-point technique. Finally, the 3D printed masks were also used to induce LPGs using the mechanical pressing method. Due to the better resolution of these masks compared to ones described on the state of the art, we were able to induce gratings with higher quality, such as low out-of-band loss (0.6 dB), reduced spectral ripples, and narrow bandwidths (~3 nm).

We present and discuss a non-expensive mechanical experiment which is very suitable for a classroom demonstration of the fold catastrophe behaviour. The apparatus consists of a bar attached to a pulley, to which a hanging body is connected by means of a thread wrapped around its rim. The system may perform stable oscillations or, else, the body may continuously fall down, while the pulley executes a sequence of 360° rotations. This behaviour is analysed in connection with the shape of the potential, which is a good example of a fold catastrophe potential. For the system to perform stable oscillations, that shape reminds a clothes washboard, with local maxima and minima, a potential well known in superconducting quantum computing. We provide some hints for the instructor to explore the device in lab classes. MF and RN are grateful to the Portuguese Physical Society and to the Royal Spanish Physical Society for the invitations to deliver talks during their national meetings on 'Catastrophic potentials'. These talks were motivational to write the paper.

We present the current state-of-the-art in photonic beamforming for communications satellite payloads, reflect on the now finished project BEACON, and trace the path for further innovations in the field.

We theoretically demonstrate a long-period grating (LPG) based single-mode fiber to multi-core fiber coupler. The coupling efficiency achieved was 24% of the input power, evenly distributed by all cores, using LPGs of length 4 cm.

This study presents the use of a sensing device composed of an all ZEONEX-480R polymer fiber Bragg grating, in series with a silica fiber, for the control/enhancement of the strain sensitivity. The results show that the amount of strain imposed in the total gauge length is unequally distributed in each fiber section. The low Young's modulus and diameter of the polymer fiber employed, compared to the silica one, leads to a higher strain density in the former. Additionally, the control of the length of each fiber section plays also an important role on the distribution of strain in each fiber. Theoretical results show that higher strain sensitivities are easier to achieve for short and long polymer and silica fiber lengths, respectively. Experimental characterization of a sensing head composed by a 2.6 cm polymer optical fiber and different lengths of silica fiber, led us to control and improve the strain sensitivity of the sensing device.

In this paper, we report, to our knowledge, the first extended study of the inscription of Bragg gratings in surface-core fibers and their application in refractive index and directional curvature sensing. The research ranges from fiber fabrication and grating inscription in untapered and tapered fibers to the performance of simulations and sensing measurements. Maximum sensitivities of 40 nm/RIU and 202.7 pm/m−1 were attained in refractive index and curvature measurements respectively. The obtained results compares well to other fiber Bragg grating based devices. Ease of fabrication, robustness and versatility makes surface-core fibers an interesting platform when exploring fiber sensing devices.

An in-line and real time chromatic sensor for liquids based on plastic optical fiber was developed. It uses an air gap, fiber to fiber, transmission principle. Its dependency to turbidity and refractive index is studied and characterized. This information will provide the necessary knowledge for future implementation of more complex auto-compensations routines. Due to the predictable behavior of the sensor to variations of turbidity and refractive index, it is shown that a posterior compensation could be applied for the discrimination of color. The real-time color sensor can be used in different turbid liquids and contain different refractive indices.

This chapter presents a broad view of some of the published and most used techniques and schemes for sensing with polymer optical fibers (POF), and presents a small part of the sensing devices using POF since the same techniques can be used to measure several different parameters with slight modifications. In quest for low-cost ways of parameter measurement using POF, different approaches can be found in academia. The most common method of detecting is based on intensity variation which requires simple operation principles and instrumentation. One of the extrinsic sensing techniques employed and commonly used is the light transmission configuration. In the intrinsic sensing techniques, light does not physically leave the fiber but tries to promote the interaction of its evanescent field with the external medium. Intrinsic sensors can be produced not only by changing the structure of the fiber but also by altering the refractive index of the fiber waveguide in the sensing area by ultraviolet or infrared-light exposure.

This manuscript presents low-cost sensing systems for the monitoring of liquids, namely water and beverages quality assessment, with remote and in-site monitoring capabilities. The collaboration with several research groups allowed the development of smart optical platforms and low-cost sensors based on plastic optical fibers for the measurement of turbidity, color, refractive index and water contaminants.

The detection of perfluorobutanesulfonic acid (PFBS) in water is presented for the first time exploiting a low-cost optical chemical sensing strategy, based on plastic optical fibers and molecularly imprinted polymers (MIPs), able to detect pollutants in water. The sensor’s response measured in this work for the detection of PFBS is similar to the one obtained with Perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA), already investigated. The detection limit of PFBS is considered of interest when compared to those obtained by using different expensive traditional approaches, e.g. high performance liquid chromatography-mass spectrometry (HPLC-MS). Moreover, the use of this sensing approach is a very attractive perspective for fast, in situ, and remote low-cost detection of pollutants in water for smart cities applications.

In this study the influence of the surface roughness on the transmission capacities of D-shaped plastic optical fibers (POFs) and sensors performance was investigated. Five D-shaped POF sensors were produced and characterized for refractive index sensing between 1.33 and 1.41. The sensors were characterized using a low-cost optical sensing system based on the variation of the transmitted light though the POF with refractive index changes (RI). Higher surface roughness increases the scattering losses through the POF and influences the sensors&rsquo, performance, therefore, a balance must be attained. Generally, the best performance was achieved when the sensing region was polished with P600 sandpaper as a final polishing step. Polishing with sandpapers of lower grit size resulted in lower scattering, higher linearity of the sensor response and generally lower performance for RI sensing. A sensor resolution of 10&minus, 3&ndash, 10&minus, 4 RIU, dependent on the value of the external refractive index, was obtained through simple and low-cost manufacturing procedures. The obtained results show the importance of surface roughness in the development of POF sensors which can be used in several applications, such as for water quality assessment.

The purpose of this study was to compare the linear polymerization shrinkage of different restorative resin-based composites (RBCs) using fiber Bragg grating (FBG) sensors. Five RBCs were evaluated: Zirconfill&reg, (ZFL), Aura Bulk-Fill (ABF), Tetric&reg, N-Ceram Bulk-Fill (TBF), FiltekTM Bulk-Fill (FBF), and Admira Fusion-Ormocer&reg, (ADF). Ten samples per resin were produced in standardized custom-made half-gutter silicone molds. Two optical FBG sensors were used to assess temperature and polymerization shrinkage. Light curing was performed for 40 s and polymerization shrinkage was evaluated at 5, 10, 40, 60, 150, and 300 s. Statistical analysis was accomplished for normal distribution (Shapiro-Wilk, p &gt, 0.05). Two-way repeated measures ANOVA with Greenhouse-Geisser correction followed by Bonferroni&prime, s post-hoc test was used to analyze the linear shrinkage data (p &lt, 0.05). ZFL showed the highest linear shrinkage and ADF the lowest. Shrinkage increased for all RBCs until 300 s, where significant differences were found between ADF and all other resins (p &lt, 0.05). Among bulk-fill RBCs, TBF showed the lowest shrinkage value, but not statistically different from FBF. The ADF presented lower linear shrinkage than all other RBCs, and restorative bulk-fill composites exhibited an intermediate behavior.

Ubiquitous satellite communications are in a leading position for bridging the digital divide. Fulfilling such a mission will require satellite services on par with fibre services, both in bandwidth and cost. Achieving such a performance requires a new generation of communications payloads powered by large-scale processors, enabling a dynamic allocation of hundreds of beams with a total capacity beyond 1 Tbit s−1. The fact that the scale of the processor is proportional to the wavelength of its signals has made photonics a key technology for its implementation. However, one last challenge hinders the introduction of photonics: while large-scale processors demand a modular implementation, coherency among signals must be preserved using simple methods. Here, we demonstrate a coherent photonic-aided receiver meeting such demands. This work shows that a modular and coherent photonic-aided payload is feasible, making way to an extensive introduction of photonics in next generation communications satellites., Satellite communications shall only thrive if being able to compete with fibre in both bandwidth and cost. Here, the authors demonstrate that a coherent and yet modular photonic-aided payload is feasible, paving the way for a new generation of communications satellites with photonics at their core.

Plastic Optical Fibers (POFs) are becoming popular for the development of sensors with multiple applications. In this work, we report a preliminary study related with the coating of modified POFs with proteins. Samples of POF were immersed in buffer and in proteins’ solutions under different experimental conditions: modification of the POF sample, immersion time, temperature, buffer solution and concentration of protein. A simple and easy methodology using protein staining solution was performed to confirm the coating of the POFs with proteins and to evaluate the dependency with the experimental conditions. Further developments will be focused on the coating of POFs with modified proteins for the selective detection of contaminants in water contributing to the development of low-cost POF chemical sensors and biosensors.