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2 pages, 159 KiB

Open AccessEditorial

Editorial for the Special Issue on Femtosecond Laser Micromachining for Photonics Applications

by Andrea Crespi and Giacomo Corrielli

Micromachines 2020, 11(11), 994; https://doi.org/10.3390/mi11110994 - 06 Nov 2020

Cited by 1 | Viewed by 1299

Abstract

Femtosecond laser pulses have proven, in the recent years, their formidable potential as a micromachining tool applicable to a variety of materials [...] Full article

(This article belongs to the Special Issue Femtosecond Laser Micromachining for Photonics Applications)

Research

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16 pages, 4016 KiB

Open AccessArticle

A Miniature Fibre-Optic Raman Probe Fabricated by Ultrafast Laser-Assisted Etching

by Calum A. Ross, David G. MacLachlan, Brian J. E. Smith, Rainer J. Beck, Jonathan D. Shephard, Nick Weston and Robert R. Thomson

Micromachines 2020, 11(2), 185; https://doi.org/10.3390/mi11020185 - 11 Feb 2020

Cited by 11 | Viewed by 4480

Abstract

Optical biopsy describes a range of medical procedures in which light is used to investigate disease in the body, often in hard-to-reach regions via optical fibres. Optical biopsies can reveal a multitude of diagnostic information to aid therapeutic diagnosis and treatment with higher [...] Read more.

Optical biopsy describes a range of medical procedures in which light is used to investigate disease in the body, often in hard-to-reach regions via optical fibres. Optical biopsies can reveal a multitude of diagnostic information to aid therapeutic diagnosis and treatment with higher specificity and shorter delay than traditional surgical techniques. One specific type of optical biopsy relies on Raman spectroscopy to differentiate tissue types at the molecular level and has been used successfully to stage cancer. However, complex micro-optical systems are usually needed at the distal end to optimise the signal-to-noise properties of the Raman signal collected. Manufacturing these devices, particularly in a way suitable for large scale adoption, remains a critical challenge. In this paper, we describe a novel fibre-fed micro-optic system designed for efficient signal delivery and collection during a Raman spectroscopy-based optical biopsy. Crucially, we fabricate the device using a direct-laser-writing technique known as ultrafast laser-assisted etching which is scalable and allows components to be aligned passively. The Raman probe has a sub-millimetre diameter and offers confocal signal collection with 71.3% ± 1.5% collection efficiency over a 0.8 numerical aperture. Proof of concept spectral measurements were performed on mouse intestinal tissue and compared with results obtained using a commercial Raman microscope. Full article

(This article belongs to the Special Issue Femtosecond Laser Micromachining for Photonics Applications)

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11 pages, 1725 KiB

Open AccessArticle

A Comparison between Nanogratings-Based and Stress-Engineered Waveplates Written by Femtosecond Laser in Silica

by Jing Tian, Heng Yao, Maxime Cavillon, Enric Garcia-Caurel, Razvigor Ossikovski, Michel Stchakovsky, Celine Eypert, Bertrand Poumellec and Matthieu Lancry

Micromachines 2020, 11(2), 131; https://doi.org/10.3390/mi11020131 - 24 Jan 2020

Cited by 16 | Viewed by 2468

Abstract

This paper compares anisotropic linear optical properties (linear birefringence, linear dichroism, degree of polarization) and performances (absorption coefficient, thermal stability) of two types of birefringent waveplates fabricated in silica glass by femtosecond laser direct writing. The first type of waveplate is based on [...] Read more.

This paper compares anisotropic linear optical properties (linear birefringence, linear dichroism, degree of polarization) and performances (absorption coefficient, thermal stability) of two types of birefringent waveplates fabricated in silica glass by femtosecond laser direct writing. The first type of waveplate is based on birefringence induced by self-organized nanogratings imprinted in the glass. One the other hand, the second design is based on birefringence originating from the stress-field formed around the aforementioned nanogratings. In addition to the provided comparison, the manufacturing of stress-engineered half waveplates in the UV-Visible range, and with mm-size clear aperture and negligible excess losses, is reported. Such results contrast with waveplates made of nanogratings, as the later exhibit significantly higher scattering losses and depolarization effects in the UV-Visible range. Full article

(This article belongs to the Special Issue Femtosecond Laser Micromachining for Photonics Applications)

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9 pages, 3655 KiB

Open AccessArticle

Rapid Fabrication of Continuous Surface Fresnel Microlens Array by Femtosecond Laser Focal Field Engineering

by Linyu Yan, Dong Yang, Qihuang Gong and Yan Li

Micromachines 2020, 11(2), 112; https://doi.org/10.3390/mi11020112 - 21 Jan 2020

Cited by 23 | Viewed by 5052

Abstract

Femtosecond laser direct writing through two-photon polymerization has been widely used in precision fabrication of three-dimensional microstructures but is usually time consuming. In this article, we report the rapid fabrication of continuous surface Fresnel lens array through femtosecond laser three-dimensional focal field engineering. [...] Read more.

Femtosecond laser direct writing through two-photon polymerization has been widely used in precision fabrication of three-dimensional microstructures but is usually time consuming. In this article, we report the rapid fabrication of continuous surface Fresnel lens array through femtosecond laser three-dimensional focal field engineering. Each Fresnel lens is formed by continuous two-photon polymerization of the two-dimensional slices of the whole structure with one-dimensional scan of the corresponding two-dimensional engineered intensity distribution. Moreover, we anneal the lens array to improve its focusing and imaging performance. Full article

(This article belongs to the Special Issue Femtosecond Laser Micromachining for Photonics Applications)

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8 pages, 1258 KiB

Open AccessArticle

Fabrication of Tapered Circular Depressed-Cladding Waveguides in Nd:YAG Crystal by Femtosecond-Laser Direct Inscription

by Carolina Romero, Javier García Ajates, Feng Chen and Javier R. Vázquez de Aldana

Micromachines 2020, 11(1), 10; https://doi.org/10.3390/mi11010010 - 19 Dec 2019

Cited by 17 | Viewed by 2591

Abstract

Crystalline materials are excellent substrates for the integration of compact photonic devices benefiting from the unique optical properties of these materials. The technique of direct inscription with femtosecond lasers, as an advantage over other techniques, has opened the door to the fabrication of [...] Read more.

Crystalline materials are excellent substrates for the integration of compact photonic devices benefiting from the unique optical properties of these materials. The technique of direct inscription with femtosecond lasers, as an advantage over other techniques, has opened the door to the fabrication of true three-dimensional (3D) photonic devices in almost any transparent substrate. Depressed-cladding waveguides have been demonstrated to be an excellent and versatile platform for the integration of 3D photonic circuits in crystals. Here, we present the technique that we have developed to inscribe tapered depressed-cladding waveguides with a circular section for the control of the modal behavior. As a proof of concept, we have applied the technique to fabricate structures in Nd:YAG crystal that efficiently change the modal behavior from highly multimodal to monomodal, in the visible and near infrared, with reduction factors in the waveguide radius of up to 4:1. Our results are interesting for different devices such as waveguide lasers, frequency converters or connectors between external devices with different core sizes. Full article

(This article belongs to the Special Issue Femtosecond Laser Micromachining for Photonics Applications)

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12 pages, 6011 KiB

Open AccessFeature PaperArticle

Femtosecond Laser Written Depressed-Cladding Waveguide 2 × 2, 1 × 2 and 3 × 3 Directional Couplers in Tm³⁺:YAG Crystal

by Nikolay Skryabin, Alexander Kalinkin, Ivan Dyakonov and Sergei Kulik

Micromachines 2020, 11(1), 1; https://doi.org/10.3390/mi11010001 - 18 Dec 2019

Cited by 23 | Viewed by 3524

Abstract

Ion-doped crystal-based compact devices capable of beam splitting and coupling are enthralling for a broad range of classical and quantum integrated photonics applications. In this work, we report on the fabrication of depressed-cladding waveguide 2D 2 × 2, 1 × 2 and 3D [...] Read more.

Ion-doped crystal-based compact devices capable of beam splitting and coupling are enthralling for a broad range of classical and quantum integrated photonics applications. In this work, we report on the fabrication of depressed-cladding waveguide 2D 2 × 2, 1 × 2 and 3D 3 × 3 directional couplers in Tm

^{3 +}

:YAG crystal by femtosecond laser writing. The performances of the couplers are characterized at 810 nm, showing single-mode guidance, polarization independence, finely matched splitting ratios. These results open up new opportunities in the beneficial fabrication of 3D circuits and devices in crystals. Full article

(This article belongs to the Special Issue Femtosecond Laser Micromachining for Photonics Applications)

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9 pages, 2909 KiB

Open AccessArticle

STED Direct Laser Writing of 45 nm Width Nanowire

by Xiaolong He, Tianlong Li, Jia Zhang and Zhenlong Wang

Micromachines 2019, 10(11), 726; https://doi.org/10.3390/mi10110726 - 28 Oct 2019

Cited by 19 | Viewed by 4190

Abstract

Controlled fabrication of 45 nm width nanowire using simulated emission depletion (STED) direct laser writing with a rod-shape effective focus spot is presented. In conventional STED direct laser writing, normally a donut-shaped depletion focus is used, and the minimum linewidth is restricted to [...] Read more.

Controlled fabrication of 45 nm width nanowire using simulated emission depletion (STED) direct laser writing with a rod-shape effective focus spot is presented. In conventional STED direct laser writing, normally a donut-shaped depletion focus is used, and the minimum linewidth is restricted to 55 nm. In this work, we push this limit to sub-50 nm dimension with a rod-shape effective focus spot, which is the combination of a Gaussian excitation focus and twin-oval depletion focus. Effects of photoinitiator type, excitation laser power, and depletion laser power on the width of the nanowire are explored, respectively. Single nanowire with 45 nm width is obtained, which is λ/18 of excitation wavelength and the minimum linewidth in pentaerythritol triacrylate (PETA) photoresist. Our result accelerates the progress of achievable linewidth reduction in STED direct laser writing. Full article

(This article belongs to the Special Issue Femtosecond Laser Micromachining for Photonics Applications)

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8 pages, 1638 KiB

Open AccessArticle

High-Precision Propagation-Loss Measurement of Single-Mode Optical Waveguides on Lithium Niobate on Insulator

by Jintian Lin, Junxia Zhou, Rongbo Wu, Min Wang, Zhiwei Fang, Wei Chu, Jianhao Zhang, Lingling Qiao and Ya Cheng

Micromachines 2019, 10(9), 612; https://doi.org/10.3390/mi10090612 - 15 Sep 2019

Cited by 23 | Viewed by 5868

Abstract

We demonstrate the fabrication of single-mode optical waveguides on lithium niobate on an insulator (LNOI) by optical patterning combined with chemomechanical polishing. The fabricated LNOI waveguides had a nearly symmetric mode profile of ~2.5 µm mode field size (full-width at half-maximum). We developed [...] Read more.

We demonstrate the fabrication of single-mode optical waveguides on lithium niobate on an insulator (LNOI) by optical patterning combined with chemomechanical polishing. The fabricated LNOI waveguides had a nearly symmetric mode profile of ~2.5 µm mode field size (full-width at half-maximum). We developed a high-precision measurement approach by which single-mode waveguides were characterized to have propagation loss of ~0.042 dB/cm. Full article

(This article belongs to the Special Issue Femtosecond Laser Micromachining for Photonics Applications)

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17 pages, 4891 KiB

Open AccessArticle

A Monolithic Gimbal Micro-Mirror Fabricated and Remotely Tuned with a Femtosecond Laser

by Saood Ibni Nazir and Yves Bellouard

Micromachines 2019, 10(9), 611; https://doi.org/10.3390/mi10090611 - 14 Sep 2019

Cited by 7 | Viewed by 4139

Abstract

With the advent of ultrafast lasers, new manufacturing techniques have come into existence. In micromachining, the use of femtosecond lasers not only offers the possibility for three-dimensional monolithic fabrication inside a single optically transparent material, but also a means for remotely, and arbitrarily, [...] Read more.

With the advent of ultrafast lasers, new manufacturing techniques have come into existence. In micromachining, the use of femtosecond lasers not only offers the possibility for three-dimensional monolithic fabrication inside a single optically transparent material, but also a means for remotely, and arbitrarily, deforming substrates with nanometer resolution. Exploiting this principle and combining it with flexure design, we demonstrate a monolithic micro-mirror entirely made with a femtosecond laser and whose orientation is tuned in a non-contact manner by exposing some part of the device to low energy femtosecond pulses. Given the non-contact nature of the process, the alignment can be very precisely controlled with a resolution that is many orders of magnitude better than conventional techniques based on mechanical positioners. Full article

(This article belongs to the Special Issue Femtosecond Laser Micromachining for Photonics Applications)

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