Optics

30 pages, 3998 KiB

Open AccessReview

Optical Fibre Micro/Nano Tips as Fluorescence-Based Sensors and Interrogation Probes

by Simone Berneschi, Andrea Barucci, Francesco Baldini, Franco Cosi, Franco Quercioli, Stefano Pelli, Giancarlo C. Righini, Bruno Tiribilli, Sara Tombelli, Cosimo Trono and Ambra Giannetti

Optics 2020, 1(2), 213-242; https://doi.org/10.3390/opt1020017 - 27 Aug 2020

Cited by 10 | Viewed by 4585

Abstract

Optical fibre micro/nano tips (OFTs), defined here as tapered fibres with a waist diameter ranging from a few microns to tens of nanometres and different tip angles (i.e., from tens of degrees to fractions of degrees), represent extremely versatile tools that have attracted growing interest during these last decades in many areas of photonics. The field of applications can range from physical and chemical/biochemical sensing—also at the intracellular levels—to the development of near-field probes for microscope imaging (i.e., scanning near-field optical microscopy (SNOM)) and optical interrogation systems, up to optical devices for trapping and manipulating microparticles (i.e., optical tweezers). All these applications rely on the ability to fabricate OFTs, tailoring some of their features according to the requirements determined by the specific application. In this review, starting from a short overview of the main fabrication methods used for the realisation of these optical micro/nano structures, the focus will be concentrated on some of their intriguing applications such as the development of label-based chemical/biochemical sensors and the implementation of SNOM probes for interrogating optical devices, including whispering gallery mode microcavities. Full article

(This article belongs to the Special Issue Recent Development of Resonance-Based Optical Sensors and Biosensors)

► Show Figures

Figure 1

11 pages, 3181 KiB

Open AccessArticle

A Miniature pH Probe Using Functional Microfiber Bragg Grating

by Yang Ran, Peng Xiao, Yongkang Zhang, Deming Hu, Zhiyuan Xu, Lili Liang and Bai-Ou Guan

Optics 2020, 1(2), 202-212; https://doi.org/10.3390/opt1020016 - 11 Aug 2020

Cited by 11 | Viewed by 2894

Abstract

Operando and precisely probing aqueous pH is fundamentally demanded, both in chemical and biological areas. Conventional pH probes, subjected to the larger size, are probably unfit for application in some extreme scenarios, such as a trace amount of samples. In this paper, we have further developed the pH sensor that leverages the microfiber Bragg grating with an ultra-compact size down to an order of magnitude of 10⁻¹⁴ m³. Using the electrostatic self-assembly layer-by-layer technique, the functional film consisting of sodium alginate, which harnesses a pH-dependent hygroscopicity, is immobilized on the fiber surface. Consequently, the alteration of aqueous pH could be quantitatively indicated by the wavelength shift of the grating resonance via the refractive index variation of the sensing film due to the water absorption or expulsion. The grating reflections involving fundamental mode and higher order mode exhibit the sensitivities of −72 pm/pH and −265 pm/pH, respectively. In addition, temperature compensation can be facilitated by the recording of the two reflections simultaneously. Furthermore, the modeling and simulation results predict the pivotal parameters of the configuration in sensitivity enhancement. The proposed proof-of-concept enriches the toolbox of pH sensor for catering to the need of detection in some extremely small spaces—for example, the living cells or the bio-tissues. Full article

(This article belongs to the Special Issue Recent Development of Resonance-Based Optical Sensors and Biosensors)

► Show Figures

Graphical abstract

11 pages, 3942 KiB

Open AccessArticle

Dispersion Management in 10-PW Laser Front End

by Xingyan Liu, Cheng Wang, Xinliang Wang, Xiaoming Lu, Peile Bai, Yanqi Liu, Yanyan Li, Keyang Liu, Lianghong Yu, Yuxin Leng and Ruxin Li

Optics 2020, 1(2), 191-201; https://doi.org/10.3390/opt1020015 - 15 Jul 2020

Cited by 6 | Viewed by 3281

Abstract

To improve pulse contrast in chirped pulse amplification petawatt laser systems, the regenerative amplifier is substituted with a multipass amplifier at the Shanghai Superintense Ultrafast Laser Facility (SULF). To reduce the consequent angular dispersion of the broadband spectrum, a double-grating stretcher is established in the SULF front end. A grating compressor is set up for the 10-PW front end to obtain 20-TW output. An accurate adjustment method of grating attitude (angular position) is presented, which references the direction of gravity, improving dispersion management and focusing ability of the beam. After a pulse passes the front end compressor, its duration and phase in the frequency domain are measured, and the duration can be continuously compressed to <24 fs. Full article

► Show Figures

Figure 1

16 pages, 9035 KiB

Open AccessArticle

A First Step towards Determining the Ionic Content in Water with an Integrated Optofluidic Chip Based on Near-Infrared Absorption Spectroscopy

by Gerwin W. Steen, Adam D. Wexler, Elmar C. Fuchs and Herman L. Offerhaus

Optics 2020, 1(2), 175-190; https://doi.org/10.3390/opt1020014 - 11 Jul 2020

Viewed by 3047

Abstract

In this work, we present a feasibility study of integrated optofluidic chips to measure the ionic content in water using differential absorption spectroscopy. The second overtone of the OH-stretch vibration of water is used as indicator for both the type and concentration of the dissolved ions. The optofluidic chips are based on silicon nitride (TripleX) containing Mach–Zehnder interferometers (MZI) with two 5 cm sensing paths for the sample and reference arms, respectively. Simulations show that, theoretically, the determination of both the type and concentration of a mixture of four electrolytes is possible with the techniques presented. However, the performance of the chips deviated from the expected results due to the insufficient reproducibility and precision in the fabrication process. Therefore, at this early stage, the chips presented here could only determine the ion concentration, but not differentiate between the different ion types. Still, this work represents the first steps towards the realization of an online and real-time sensor of ionic content in water. Full article

(This article belongs to the Special Issue Fabrication and Applications of Photonic Micro-Devices)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Optics, Volume 1, Issue 2 (September 2020) – 4 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI