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Publications

Publications by João Miguel Maia

2017

Optimization of Broadband Y-Junction Splitters in Fused Silica by Femtosecond Laser Writing

Authors
Amorim, VA; Maia, JM; Alexandre, D; Marques, PVS;

Publication
IEEE PHOTONICS TECHNOLOGY LETTERS

Abstract
Optical Y-junction power splitters owe their inherent broadband spectral behavior to their design. However, depending on the fabrication technique employed, asymmetries in the junction might arise, perturbing its performance; this is the case in femtosecond laser written Y-junctions where one arm is typically written over the top of the other. In this letter, the spectral behavior of Y-junctions fabricated in fused silica by the femtosecond laser direct writing technique was analyzed and optimized for the first time, to the best of our knowledge. The junction arms output power balance as well as the corresponding spectral flatness between 1300 and 1600 nm is substantially increased by the implementation of an initial separation between the arms at the junction diverging point, enabling the manufacturing of balanced broadband Y-junctions.

2017

Real-Time Optical Monitoring of Etching Reaction of Microfluidic Channel Fabricated by Femtosecond Laser Direct Writing

Authors
Maia, JM; Amorim, VA; Alexandre, D; Marques, PVS;

Publication
JOURNAL OF LIGHTWAVE TECHNOLOGY

Abstract
Femtosecond laser direct writing is a three dimensional fabrication technique that can be applied to produce integrated optical components with high spatial resolution or microfluidic channels when combined with HF etching. The same fabrication technique can thus be employed to produce monolithic optofluidic devices for sensing applications. One of the most common sensing schemes involves evanescent optical interaction; therefore, the channel must meet some requirements regarding surface roughness, which will depend on the laser writing conditions, as described in this paper. However, of more significance is the distance between waveguiding medium and microfluidic channel that must be accurately defined. This control can be achieved by monitoring the etching reaction of a waveguide grating written a few microns from the channel, as introduced in this paper. In addition to its function as an etching monitor, the grating can also be used as a coarse refractive index sensor device.

2015

Automatized and desktop AC-susceptometer for the in situ and real time monitoring of magnetic nanoparticles' synthesis by coprecipitation

Authors
Fernandez Garcia, MP; Teixeira, JM; Machado, P; Oliveira, MRFF; Maia, JM; Pereira, C; Pereira, AM; Freire, C; Araujo, JP;

Publication
REVIEW OF SCIENTIFIC INSTRUMENTS

Abstract
The main purpose of this work was to design, develop, and construct a simple desktop AC susceptometer to monitor in situ and in real time the coprecipitation synthesis of magnetic nanoparticles. The design incorporates one pair of identical pick-up sensing coils and one pair of Helmholtz coils. The picked up signal is detected by a lock-in SR850 amplifier that measures the in-and out-of-phase signals. The apparatus also includes a stirrer with 45 degrees-angle blades to promote the fast homogenization of the reaction mixture. Our susceptometer has been successfully used to monitor the coprecipitation reaction for the synthesis of iron oxide nanoparticles. (C) 2015 AIP Publishing LLC.

2017

Fabrication of Microfluidic Channels by Femtosecond Laser Micromachining and Application in Optofluidics

Authors
Maia, JM; Amorim, VA; Alexandre, D; Marques, PVS;

Publication
PROCEEDINGS OF THE 5TH INTERNATIONAL CONFERENCE ON PHOTONICS, OPTICS AND LASER TECHNOLOGY (PHOTOPTICS)

Abstract
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.

2017

Integrated Optical Devices Fabrication of Multimode Interference Devices in Fused Silica by Femtosecond Laser Direct Writing

Authors
Amorim, VA; Maia, JM; Alexandre, D; Marques, PVS;

Publication
PROCEEDINGS OF THE 5TH INTERNATIONAL CONFERENCE ON PHOTONICS, OPTICS AND LASER TECHNOLOGY (PHOTOPTICS)

Abstract
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.

2017

Monolithic Add–Drop Multiplexers in Fused Silica Fabricated by Femtosecond Laser Direct Writing

Authors
Amorim, VA; Maia, JM; Alexandre, D; Marques, PVS;

Publication
Journal of Lightwave Technology

Abstract

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