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6 pages, 1805 KiB

Open AccessCommunication

Epoxy-Coated Side-Polished Fiber-Optic Temperature Sensor for Cryogenic Conditions

by Umesh Sampath and Minho Song

Sensors 2023, 23(5), 2850; https://doi.org/10.3390/s23052850 - 6 Mar 2023

Cited by 4 | Viewed by 2177

We propose coating side-polished optical fiber (SPF) with epoxy polymer to form a fiber-optic sensor for cryogenic temperature measuring applications. The thermo-optic effect of the epoxy polymer coating layer enhances the interaction between the SPF evanescent field and surrounding medium, considerably improving the temperature sensitivity and robustness of the sensor head in a very low-temperature environment. In tests, due to the evanescent field–polymer coating interlinkage, transmitted optical intensity variation of 5 dB and an average sensitivity of

- 0.024

dB/K were obtained in the 90–298 K range. Full article

(This article belongs to the Special Issue Applications of Optical Fiber Sensors and Measurement Systems)

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10 pages, 2602 KiB

Open AccessArticle

Ultrafast Yb-Doped Fiber Laser Using Few Layers of PdS₂ Saturable Absorber

by Ping Kwong Cheng, Shunxiang Liu, Safayet Ahmed, Junle Qu, Junpeng Qiao, Qiao Wen and Yuen Hong Tsang

Nanomaterials 2020, 10(12), 2441; https://doi.org/10.3390/nano10122441 - 6 Dec 2020

Cited by 34 | Viewed by 4211

Abstract

Two-dimensional (2D) transition metal dichalcogenide (TMD) materials have exceptional optoelectronic and structural properties, which allow them to be utilized in several significant applications in energy, catalyst, and high-performance optoelectronic devices. Among other properties, the nonlinear optical properties are gaining much attention in the research field. In this work, a unique pentagonal TMD material, palladium disulfide (PdS₂), is employed as a saturable absorber (SA) in an ytterbium-doped fiber (YDF) laser cavity and mode-locked laser pulse is generated. At first, liquid phase exfoliation is performed to prepare PdS₂ nanoflakes. Afterward, the PdS₂-nanoflakes solution was incorporated in the side-polished fiber (SPF) to form SPF-based PdS₂-SA. By utilizing this SA, a highly stable mode-locked laser pulse is realized at pump power of 160 mW, which has a center wavelength of 1033 nm and a 3-dB spectral bandwidth of 3.7 nm. Moreover, the pulse duration, maximum power output and corresponding single-pulse energy were determined as 375 ps, 15.7 mW and 0.64 nJ, respectively. During the experiment, the mode-locked pulse remained stable till the pump power reached a value of 400 mW and, for the regulation of power, the slope efficiency is calculated at about 4.99%. These results indicate that PdS₂ material is a promising nonlinear optical material for ultrafast optical applications in the near-infrared (NIR) region. Full article

(This article belongs to the Special Issue Photonic Nanomaterials)

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10 pages, 2896 KiB

Open AccessArticle

Sensing Characteristics of Side-Polished Fiber Based on the Alterations in Helical Structure of Thermo-Sensitive Cholesteric Liquid Crystals

by Yuqi Han, Yan Jiang and Wei Guo

Crystals 2019, 9(9), 465; https://doi.org/10.3390/cryst9090465 - 5 Sep 2019

Cited by 10 | Viewed by 3231

Abstract

Cholesteric liquid crystals (CLCs) are sensitive to environmental temperature changes, and have been employed as a specific intermediary for biosensors. Considering the temperature-dependent structural changes of CLCs, this study aimed to determine the sensing properties of side-polished fibers (SPFs) after coating with CLCs. The experimental results demonstrated that, with regard to the transmitted spectrum, the loss peak of CLC-coated SPFs exhibited a positive linear relationship with temperature changes over a range of 20 to 50 °C. The linear correlation coefficient achieved 97.8% when the temperature increased by 10 °C, and the loss peak drifted by 12.72 nm. The reflectance spectrum of CLCs coated on the polished surface were obtained using optical fiber sensors. The feasibility of measuring the helical structure of CLCs was further verified using SPF transmission spectroscopy. The findings indicated that the transmitted spectrum of SPFs could be adopted to characterize the helical structure of CLCs, which lays a solid foundation for further study on SPF-based biosensors. Full article

(This article belongs to the Special Issue Advances in Cholesteric Liquid Crystals)

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10 pages, 3953 KiB

Open AccessArticle

Investigation of Surface Plasmon Resonance (SPR) in MoS₂- and WS₂-Protected Titanium Side-Polished Optical Fiber as a Humidity Sensor

by Rozalina Zakaria, Nur Aina’a Mardhiah Zainuddin, Tan Chee Leong, Rosnadiya Rosli, Muhammad Farid Rusdi, Sulaiman Wadi Harun and Iraj Sadegh Amiri

Micromachines 2019, 10(7), 465; https://doi.org/10.3390/mi10070465 - 11 Jul 2019

Cited by 27 | Viewed by 4721

Abstract

In this paper, we report the effects of a side-polished fiber (SPF) coated with titanium (Ti) films in different thicknesses, namely 5 nm, 13 nm, and 36 nm, protected by a thin layer of transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂), which provide ultra-sensitive sensor-based surface plasmon resonance (SPR) covering from the visible to mid-infrared region. The SPF deposited with Ti exhibits strong evanescent field interaction with the MoS₂ and WS₂, and good optical absorption, hence resulting in high-sensitivity performance. Incremental increases in the thickness of the Ti layer contribute to the enhancement of the intensity of transmission with redshift and broad spectra. The findings show that the optimum thickness of Ti with 36 nm combined with MoS₂ causes weak redshifts of the longitudinal localized surface plasmon resonance (LSPR) mode, while the same thickness of Ti with WS₂ causes large blueshifts. The redshifts are possibly due to a reduced plasmon-coupling effect with the excitonic region of MoS₂. The observed blueshifts of the LSPR peak position are possibly due to surface modification between WS₂ and Ti. Changing the relative humidity from 58% to 88% only elicited a response in Ti/MoS₂. Thus, MoS₂ shows more sensitivity on 36-nm thickness of Ti compared with WS₂. Therefore, the proposed fiber-optic sensor with integration of 2D materials is capable of measuring humidity in any environment. Full article

(This article belongs to the Special Issue MEMS/NEMS Sensors: Fabrication and Application, Volume II)

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9 pages, 2106 KiB

Open AccessArticle

Side-Polished Fiber-Optic Line Sensor for High-Frequency Broadband Ultrasound Detection

by Jeongmin Heo, Kyu-Tae Lee, Ryun Kyung Kim and Hyoung Won Baac

Sensors 2019, 19(2), 398; https://doi.org/10.3390/s19020398 - 18 Jan 2019

Cited by 6 | Viewed by 5152

Abstract

We demonstrate a side-polished fiber-optic ultrasound sensor (SPFS) with a broad frequency bandwidth (dc–46 MHz at 6-dB reduction) and a wide amplitude detection range from several kPa to 4.8 MPa. It also exhibits a high acoustic sensitivity of 426 mV/MPa with a signal-to-noise ratio of 35 dB and a noise-equivalent pressure of 6.6 kPa (over 1–50 MHz bandwidth) measured at 7-MHz frequency. The SPFS does not require multi-layer-coated structures that are used in other high-sensitivity optical detectors. Without any coating, this uses a microscale-roughened structure for evanescent-field interaction with an external medium acoustically modulated. Such unique structure allows significantly high sensitivity despite having a small detection area of only 0.016 mm² as a narrow line sensor with a width of 8 μm. The SPFS performance is characterized in terms of acoustic frequency, amplitude responses, and sensitivities that are compared with those of a 1-mm diameter piezoelectric hydrophone used as a reference. Full article

(This article belongs to the Section Physical Sensors)

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