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This service develops its activity in the areas of optical sources, optical communications, fiber optic sensors and micro-manufacturing, having facilities for the design and development of electronic systems.

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Browsing CAP by Author "6596"
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    Addressing the Fabrication Difficulties of Femtosecond Laser Written Surface Waveguides for Enhanced Evanescent Coupling
    ( 2019) Vítor Oliveira Amorim ; João Miguel Maia ; Viveiros,D ; Marques,PVS ; 6407 ; 6596
    In this work, the fabrication of optical waveguides embedded in fused silica (Suprasil1) and boro-aluminosilicate glass (Eagle2000) is demonstrated with femtosecond laser direct writing, as well as their suitability to be brought to the surface, through wet etching, for enhanced evanescent coupling with the external dielectric medium. Fused silica demonstrated to be inappropriate in this particular application, as the guiding region is at the bottom of the induced modification, creating a barrier between the guided mode and the substrate’s boundary. Furthermore, the existence of nanogratings meant that, upon contact of the top of the induced modification with the substrate’s boundary, the waveguide is quickly etched. Eagle2000 demonstrated to be superior to fused silica due to its characteristic modification cross-section and absence of nanogratings, which allowed the placement of the guiding region as close to the substrate’s surface as required. However, surface roughness arising from the creation of insoluble products in the HF solution was found. The addition of HCl to dissolve these products was implemented.
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    Advances in Fs-Laser Micromachining Towards the Development of Optofluidic Devices
    ( 2019) João Miguel Maia ; Vítor Oliveira Amorim ; Daniel Alexandre ; Paulo Vicente Marques ; 4287 ; 4382 ; 6407 ; 6596
    In this chapter the developments made in femtosecond laser micromachining for applications in the fields of optofluidics and lab-on-a-chip devices are reviewed. This technology can be applied to a wide range of materials (glasses, crystals, polymers) and relies on a non-linear absorption process that leads to a permanent alteration of the material structure. This modification can induce, for instance, a smooth variation of the refractive index or generate etching selectivity, which can be used to form integrated optical circuits and microfluidic systems, respectively. Unlike conventional techniques, fs-laser micromachining offers a way to produce high-resolution three-dimensional components and integrate them in a monolithic approach. Recent advances made in two-photon polymerization have also enabled combination of polymeric structures with microfluidic channels, which can provide additional functionalities, such as fluid transport control. In particular, here it is emphasised the integration of microfluidic systems with optical layers and polymeric structures for the fabrication of miniaturized hybrid devices for chemical synthesis and biosensing. © 2019, Springer Nature Switzerland AG.
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    Characterization of Femtosecond Laser Direct Written Mach-Zehnder Interferometers Based on Titanium Dioxide Coated Long Period Fiber Gratings
    ( 2020) Carlos Duarte Viveiros ; Vasconcelos,H ; De Almeida,JMMM ; Coelho,L ; Amorim,VA ; João Miguel Maia ; Jorge,PAS ; Marques,PVS ; 5872 ; 6596
    Optical fiber Mach-Zehnder interferometers were fabricated by combining two TiO2 coated LPFGs fabricated through femtosecond laser direct writing. Results of its refractometric characterization are presented and compared with the single LPFGs sensors. Wavelength sensitivity of 1175 nm/RIU at 1.38 and spectral resolution of 2.2×10-5 were achieved. © 2021 The Author(s).
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    Fabrication of Microfluidic Channels by Femtosecond Laser Micromachining and Application in Optofluidics
    ( 2017) João Miguel Maia ; Vítor Oliveira Amorim ; Daniel Alexandre ; Paulo Vicente Marques ; 4287 ; 4382 ; 6407 ; 6596
    Micromachining with femtosecond laser can be exploited to fabricate optical components and microfluidic channels in fused silica, due to internal modification of the glass properties that is induced by the laser beam. In this paper, we refer to the formation of microfluidic channels, where an optimization of the fabrication procedure was conducted by examining etch rate and surface roughness as a function of the irradiation conditions. Microfluidic channels with high and uniform aspect ratio and with smooth sidewalls were obtained, and such structures were successfully integrated with optical components. The obtained results set the foundations towards the development of new optofluidic devices.
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    Fabrication of Monolithic Add-Drop Filters in Pure Silica by Femtosecond Laser Writing
    ( 2018) Paulo Vicente Marques ; Vítor Oliveira Amorim ; João Miguel Maia ; Daniel Alexandre ; Carlos Duarte Viveiros ; 5872 ; 4287 ; 4382 ; 6596 ; 6407
    This paper will review the fabrication of monolithic integrated optical devices by laser direct writing with femtosecond pulsed laser sources, starting with the description of experimental procedures and optimal conditions to fabricate low loss optical waveguides, directional couplers, Y-junctions and first order Bragg gratings by point-by-point writing methods. Finally, the characterization results of a fully operational Add-Drop filter in pure fused silica substrate are described. © 2018 IEEE.
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    Fabrication of periodic structures in optical fibers by femtosecond laser micromachining for sensing applications
    ( 2019) Carlos Duarte Viveiros ; João Miguel Maia ; Vítor Oliveira Amorim ; Pedro Jorge ; Paulo Vicente Marques ; 3565 ; 4287 ; 5872 ; 6407 ; 6596
    A femtosecond laser direct writing system was developed to explore the fabrication of periodic structures in optical fibers. The possibility to write type I first- A nd second-order Bragg gratings in the same single-mode fiber (SMF-28e), with reflectivities of 99.6 % and 59.3 %, respectively, is presented. The fabrication of structures (waveguides and grating) in a coreless and in a SMF-28e fiber was first demonstrated, and the gratings were then exposed to a thermal annealing up to 1000°C. The FBG inscribed in the SMF-28e fiber presents thermal stability at temperatures of 800 °C and a temperature sensitivity of 14.34 pm/°C was determined. © 2019 SPIE.
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    Femtosecond Laser Direct Writing of Turn Around Point Long Period Fiber Gratings Coated with Titanium Dioxide for Improved Sensitivity
    ( 2020) Carlos Duarte Viveiros ; De Almeida,JMMM ; Luís Carlos Coelho ; Vasconcelos,H ; João Miguel Maia ; Amorim,VA ; Pedro Jorge ; Paulo Vicente Marques ; 3565 ; 4287 ; 5256 ; 5872 ; 6596
    The fabrication of Turn Around Point Long Period Fiber Grating in standard SMF-28e fibers through femtosecond laser direct writing is demonstrated and its sensing sensitivity is improved by coating the fiber with titanium dioxide through physical vapor deposition. © 2021 The Author(s).
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    Femtosecond laser direct written off-axis fiber Bragg gratings for sensing applications
    ( 2020) Carlos Duarte Viveiros ; Vítor Oliveira Amorim ; João Miguel Maia ; Susana Oliveira Silva ; Orlando Frazão ; Pedro Jorge ; Fernandes,LA ; Paulo Vicente Marques ; 3565 ; 4061 ; 4287 ; 4678 ; 5872 ; 6407 ; 6596
    First order off-axis fiber Bragg gratings (FBGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond laser direct writing. A minimum offset distance between the grating and core center of 2.5 µm was found to create a multimode section, which supports two separate fiber modes (LP0,1 and LP1,1), each split into two degenerate polarization modes. The resulting structure breaks the cylindrical symmetry of the fiber, introducing birefringence (˜10-4) resulting in a polarization dependent Bragg wavelength for each mode. Based on the modal and birefringence behavior, three off-axis FBGs were fabricated with 3.0, 4.5 and 6.0 µm offsets from the core center, and then characterized in strain, temperature, and curvature. The tested off-axis FBGs exhibited a similar strain sensitivity of ~1.14 pm/µ? and a temperature sensitivity of ~12 pm/C. The curvature and orientation angle were simultaneously monitored by analyzing the intensity fluctuation and the wavelength shift of the LP1,1 Bragg resonance. A maximum curvature sensitivity of 0.53 dB/m-1 was obtained for the off-axis FBG with a 3.0 µm offset. © 2020 Elsevier Ltd
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    Femtosecond laser direct written off-axis fiber Bragg gratings for sensing applications
    ( 2020) Carlos Duarte Viveiros ; Vítor Oliveira Amorim ; João Miguel Maia ; Susana Oliveira Silva ; Orlando Frazão ; Pedro Jorge ; Fernandes,LA ; Paulo Vicente Marques ; 3565 ; 4061 ; 4287 ; 4678 ; 5872 ; 6407 ; 6596
    First order off-axis fiber Bragg gratings (FBGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond laser direct writing. A minimum offset distance between the grating and core center of 2.5 µm was found to create a multimode section, which supports two separate fiber modes (LP0,1 and LP1,1), each split into two degenerate polarization modes. The resulting structure breaks the cylindrical symmetry of the fiber, introducing birefringence (˜10-4) resulting in a polarization dependent Bragg wavelength for each mode. Based on the modal and birefringence behavior, three off-axis FBGs were fabricated with 3.0, 4.5 and 6.0 µm offsets from the core center, and then characterized in strain, temperature, and curvature. The tested off-axis FBGs exhibited a similar strain sensitivity of ~1.14 pm/µ? and a temperature sensitivity of ~12 pm/C. The curvature and orientation angle were simultaneously monitored by analyzing the intensity fluctuation and the wavelength shift of the LP1,1 Bragg resonance. A maximum curvature sensitivity of 0.53 dB/m-1 was obtained for the off-axis FBG with a 3.0 µm offset. © 2020 Elsevier Ltd
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    Femtosecond laser micromachining of an optofluidics-based monolithic whispering-gallery mode resonator coupled to a suspended waveguide
    ( 2021) João Miguel Maia ; Amorim,VA ; Carlos Duarte Viveiros ; Paulo Vicente Marques ; 4287 ; 5872 ; 6596
    A monolithic lab-on-a-chip fabricated by femtosecond laser micromachining capable of label-free biosensing is reported. The device is entirely made of fused silica, and consists of a microdisk resonator integrated inside a microfluidic channel. Whispering gallery modes are excited by the evanescent field of a circular suspended waveguide, also incorporated within the channel. Thermal annealing is performed to decrease the surface roughness of the microstructures to a nanometric scale, thereby reducing intrinsic losses and maximizing the Q-factor. Further, thermally-induced morphing is used to position, with submicrometric precision, the suspended waveguide tangent to the microresonator to enhance the spatial overlap between the evanescent field of both optical modes. With this fabrication method and geometry, the alignment between the waveguide and the resonator is robust and guaranteed at all instances. A maximum sensitivity of 121.5 nm/RIU was obtained at a refractive index of 1.363, whereas near the refractive index range of water-based solutions the sensitivity is 40 nm/RIU. A high Q-factor of 10(5) is kept throughout the entire measurement range.
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    Femtosecond laser micromachining of Fabry-Perot interferometers in SMF-28 fiber for pressure sensing (Conference Presentation)
    ( 2020) Carlos Duarte Viveiros ; José Almeida ; Luís Carlos Coelho ; João Miguel Maia ; Amorim,VA ; Vasconcelos,H ; Pedro Jorge ; Paulo Vicente Marques ; 5256 ; 5799 ; 5872 ; 6596 ; 3565 ; 4287
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    Femtosecond Laser Micromachining of Fabry-Pérot Interferometers for Magnetic Field Sensing
    ( 2019) João Miguel Maia ; Vítor Oliveira Amorim ; Viveiros,D ; Marques,PVS ; 6407 ; 6596
    Fs-laser micromachining is a high precision fabrication technique that can be used to write novel three-dimensional structures, depending on the nature of light-matter interaction. In fused silica, the material modification can lead to (i) an increase of the refractive index around the focal volume, resulting in the formation of optical circuits, or (ii) an enhancement of the etch rate of the laser-affected zones relative to the pristine material, leading to a selective and anisotropic etching reaction that enables fabrication of microfluidic systems. Here, both effects are combined to fabricate a Fabry-Pérot interferometer, where optical waveguides and microfluidic channels are integrated monolithically in a fused silica chip. By filling the channel with a magnetic fluid whose refractive index changes with an external magnetic field, the device can be used as a magnetic field sensor. A linear sensitivity of -0.12 nm/mT is obtained in the 5.0±0.5 to 33.0±0.5 mT range, with the field being applied parallel to the light propagation direction.
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    Femtosecond laser micromachining of Fabry-Pérot interferometers in fused silica for refractive index sensing
    ( 2019) João Miguel Maia ; Vítor Oliveira Amorim ; Carlos Duarte Viveiros ; Paulo Vicente Marques ; 4287 ; 5872 ; 6407 ; 6596
    A Fabry-Pérot interferometer was fabricated inside a fused silica substrate through femtosecond laser micromachining. The influence of the waveguide's writing parameters on the measured signal's quality was studied for an interferometer with a 27-µm wide cavity. Optimal signal-to-noise ratio and fringe visibility were obtained for waveguides written at 75 nJ and 50 µm/s. The same device was characterized with different refractive index liquids, and a maximum sensitivity of 1181.4±23.6 nm/RIU was obtained in the index range of 1.2962 to 1.3828 (at 1550 nm) for the spectral order o?'š = 46. © 2019 SPIE.
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    Femtosecond laser micromachining of suspended silica-core liquid-cladding waveguides inside a microfluidic channel
    ( 2022) João Miguel Maia ; Carlos Duarte Viveiros ; Amorim,VA ; Paulo Vicente Marques ; 4287 ; 5872 ; 6596
    This work addresses the fabrication of straight silica-core liquid-cladding suspended waveguides inside a microfluidic channel through fs-laser micromachining. These structures enable the reconfiguration of the waveguide's mode profile and enhance the evanescent interaction between light and analyte. Further, their geometry resembles a tapered optical fiber with the added advantage of being monolithically integrated within a microfluidic platform. The fabrication process includes an additional post-processing thermal treatment responsible for smoothening the waveguide surface and reshaping it into a circular cross-section. Suspended waveguides with a minimum core diameter of 3.8 µm were fabricated. Their insertion losses can be tuned and are mainly affected by mode mismatch between the coupling and suspended waveguides. The transmission spectrum was studied and it was numerically confirmed that it consists of interference between the guided LP01 mode and uncoupled light and of modal interference between the LP01 and LP02 modes. © 2022 Elsevier Ltd
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    Femtosecond laser-written long period fibre gratings coated with titanium dioxide for improved sensitivity
    ( 2020) Carlos Duarte Viveiros ; José Almeida ; Luís Carlos Coelho ; Vasconcelos,H ; Vítor Oliveira Amorim ; João Miguel Maia ; Pedro Jorge ; Paulo Vicente Marques ; 3565 ; 4287 ; 5256 ; 5799 ; 5872 ; 6407 ; 6596
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    Inscription of surface waveguides in glass by femtosecond laser writing for enhanced evanescent wave overlap
    ( 2020) Vítor Oliveira Amorim ; João Miguel Maia ; Carlos Duarte Viveiros ; Paulo Vicente Marques ; 4287 ; 6596 ; 5872 ; 6407
    Near-surface optical waveguides were fabricated in alkaline earth boro-aluminosilicate glass (Eagle2000), by femtosecond laser direct writing, using two distinct approaches. First, the capability of directly inscribing optical waveguides close to the surface was tested, and then, compared to the adoption of post writing wet etching to bring to the surface waveguides inscribed at greater depths. Laser ablation was found to limit the minimum surface to core center distance to 6.5 mu m in the first method, with anisotropic wet etching limiting the latter to 3 mu m without any surface deformation; smaller separations can be achieved at the cost of the planar surface topography. Furthermore, the waveguide's cross-section was seen to vary for laser inscription nearing the surface, observations that were also corroborated by its distinct guiding characteristics when compared to the adoption of post writing wet etching. The spectral analysis (in the 500-1700 nm range) also evidenced an increase in insertion loss for longer wavelengths and smaller surface to core center separations, caused, most likely, by coupling loss due to the interaction between the propagating mode and the surface. Different lengths of waveguide exposed to the surface were also tested, revealing that scattering loss due to surface roughness is not an issue at the centimeter scale.
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    Integrated Optical Devices Fabrication of Multimode Interference Devices in Fused Silica by Femtosecond Laser Direct Writing
    ( 2017) Vítor Oliveira Amorim ; João Miguel Maia ; Daniel Alexandre ; Paulo Vicente Marques ; 4287 ; 4382 ; 6407 ; 6596
    1xN (N=2, 3, 4) MMI power splitters were fabricated in a fused silica substrate by laser direct writing, using a focused 515 nm amplified femtosecond laser beam, and characterized at 1550 nm. To accomplish this, several low loss waveguides were fabricated side by side to form a multimode waveguide with the output in a polished facet of the substrate, while a single low loss waveguide was fabricated to inject light in the centre of the multimode waveguide. The performance of the fabricated devices was optimized by testing three different designs.
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    Intensity-modulated refractometer based on mode-mismatch in surface waveguides inscribed by femtosecond laser direct writing
    ( 2021) Vítor Oliveira Amorim ; Carlos Duarte Viveiros ; João Miguel Maia ; Paulo Vicente Marques ; 6407 ; 6596 ; 4287 ; 5872
    Optical waveguides were fabricated at the surface of Eagle2000 glass substrates, using femtosecond laser direct writing and wet etching, and their potential as intensity-modulated refractometers was assessed. Through the analysis of their broadband spectral response to different refractive index oils, we observed that mode mismatch is present when the guided mode reaches the surface of the substrate and interacts with the external medium, thus enabling the use of such optical waveguides in refractive index sensing. Refractive indices equal to or greater than that of the substrate also induced a coupling mechanism that was shown not to be suitable in these devices. The device's wavelength of operation was found to be tunable by controlling the distance between the surface and the center of the optical waveguide. However, the sensitivity was seen to diminish by increasing the latter, being nonexistent for distances greater than 5.5 mu m. In this study, the maximum sensitivity values were found for a surface to core center distance between 1 and 2 mu m, in the biological range, and 2.5 to 3 mu m, for a refractive index nearing that of the substrate. Accordingly, maximum sensitivities of approximate to 25 dB/RIU and approximate to 1200 dB/RIU were found between 1.300 < n(D)(25)degrees(C) < 1.400 and 1.490 < n(D)(25)degrees(C) < 1.500, respectively.
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    Loss mechanisms in femtosecond laser written optical waveguides
    ( 2021) Paulo Vicente Marques ; Amorim,VA ; João Miguel Maia ; Carlos Duarte Viveiros ; 4287 ; 5872 ; 6596
    Low loss optical waveguides are the key component for the fabrication of more complex integrated optics devices. In most works related to femtosecond laser written waveguides, the values presented give results at a single wavelength or in a narrow wavelength band; but some applications in optical sensing, for example, would benefit from waveguides having good propagation properties in a larger wavelength range. This paper presents results that allow one to gain insight into the major loss mechanisms present in laser written waveguides in two different types of glasses (fused silica and Eagle 2000 glass) and the dependence of those on the fabrication parameters. Finally, an example of application of broadband operating waveguides is given.
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    Loss Mechanisms of Optical Waveguides Inscribed in Fused Silica by Femtosecond Laser Direct Writing
    ( 2019) Vítor Oliveira Amorim ; João Miguel Maia ; Carlos Duarte Viveiros ; Paulo Vicente Marques ; 4287 ; 5872 ; 6407 ; 6596