This paper presents a brief overview of the technologies used to implement surface plasmon resonance (SPR) effects into fiber-optic sensors for chemical and biochemical applications and a survey of results reported over the last ten years. The performance indicators that are relevant for such systems, such as refractometric sensitivity, operating wavelength, and figure of merit (FOM), are discussed and listed in table form. A list of experimental results with reported limits of detection (LOD) for proteins, toxins, viruses, DNA, bacteria, glucose, and various chemicals is also provided for the same time period. Configurations discussed include fiber-optic analogues of the Kretschmann–Raether prism SPR platforms, made from geometry-modified multimode and single-mode optical fibers (unclad, side-polished, tapered, and U-shaped), long period fiber gratings (LPFG), tilted fiber Bragg gratings (TFBG), and specialty fibers (plastic or polymer, microstructured, and photonic crystal fibers). Configurations involving the excitation of surface plasmon polaritons (SPP) on continuous thin metal layers as well as those involving localized SPR (LSPR) phenomena in nanoparticle metal coatings of gold, silver, and other metals at visible and near-infrared wavelengths are described and compared quantitatively.

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Review of plasmonic fiber optic biochemical sensors: improving the limit of detection.

The development of highly-sensitive miniaturized sensors that allow real-time quantification of analytes is highly desirable in medical diagnostics, veterinary testing, food safety, and environmental monitoring. Photonic Crystal Fiber Surface Plasmon Resonance (PCF SPR) has emerged as a highly-sensitive portable sensing technology for testing chemical and biological analytes. PCF SPR sensing combines the advantages of PCF technology and plasmonics to accurately control the evanescent field and light propagation properties in single or multimode configurations. This review discusses fundamentals and fabrication of fiber optic technologies incorporating plasmonic coatings to rationally design, optimize and construct PCF SPR sensors as compared to conventional SPR sensing. PCF SPR sensors with selective metal coatings of fibers, silver nanowires, slotted patterns, and D-shaped structures for internal and external microfluidic flows are reviewed. This review also includes potential applications of PCF SPR sensors, identifies perceived limitations, challenges to scaling up, and provides future directions for their commercial realization.

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Photonic crystal fiber based plasmonic sensors

We propose a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) with selectively filled analyte channels. Silver is used as the plasmonic material to accurately detect the analytes and is coated with a thin graphene layer to prevent oxidation. The liquid-filled cores are placed near to the metallic channel for easy excitation of free electrons to produce surface plasmon waves (SPWs). Surface plasmons along the metal surface are excited with a leaky Gaussian-like core guided mode. Numerical investigations of the fiber’s properties and sensing performance are performed using the finite element method (FEM). The proposed sensor shows maximum amplitude sensitivity of 418 Refractive Index Units (RIU−1) with resolution as high as 2.4 × 10−5 RIU. Using the wavelength interrogation method, a maximum refractive index (RI) sensitivity of 3000 nm/RIU in the sensing range of 1.46–1.49 is achieved. The proposed sensor is suitable for detecting various high RI chemicals, biochemical and organic chemical analytes. Additionally, the effects of fiber structural parameters on the properties of plasmonic excitation are investigated and optimized for sensing performance as well as reducing the sensor’s footprint.

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Photonic Crystal Fiber-Based Surface Plasmon Resonance Sensor with Selective Analyte Channels and Graphene-Silver Deposited Core

A surface plasmon resonance (SPR) sensor with two open-ring channels based on a photonic crystal fiber (PCF) is described. The sensor is designed to detect low refractive indexes between 1.23 and 1.29 with the operation wavelength in mid-infrared region between 2550 nm and 2900 nm. The coupling characteristics and sensing properties are numerically analyzed by the finite element method. The average spectral sensitivity is 5500 nm/RIU and a maximum resolution of 7.69 × 10-6 RIU can be obtained. Our analysis shows that the PCF-SPR sensor is suitable for mid-infrared detection.

Mid-infrared surface plasmon resonance sensor based on photonic crystal fibers

A simple multi-core flat fiber (MCFF) based surface plasmon resonance (SPR) sensor operating in telecommunication wavelengths is proposed for refractive index sensing. Chemically stable gold (Au) and titanium dioxide (TiO2) layers are used outside the fiber structure to realize a simple detection mechanism. The modeled sensor shows average wavelength interrogation sensitivity of 9,600 nm/RIU (Refractive Index Unit) and maximum sensitivity of 23,000 nm/RIU in the sensing range of 1.46-1.485 and 1.47-1.475, respectively. Moreover, the refractive index resolution of 4.35 × 10−6 is demonstrated. Additionally, proposed sensor had shown the maximum amplitude interrogation sensitivity of 820 RIU−1, with the sensor resolution of 1.22 × 10−5 RIU. To the best of our knowledge, the proposed sensor achieved the highest wavelength interrogation sensitivity among the reported fiber based SPR sensors. Finally we anticipate that, this novel and highly sensitive MCFF SPR sensor will find the potential applications in real time remote sensing and monitoring, ultimately enabling inexpensive and accurate chemical and biochemical analytes detection.

Highly sensitive multi-core flat fiber surface plasmon resonance refractive index sensor.

Multi-hole fiber based surface plasmon resonance sensor operated at near-infrared wavelengths

Micro-nano fiber downloading filter based on rainbow local effect

A special optical fiber is investigated, which has a helical core in the cylindrical cladding. The beam propagation method (BPM) is used for analyzing the impacts of the geometric and physical parameters on the properties of mode losses of the helical-core fiber. The propagation loss is 0.32 dB/m for the fundamental mode and the propagation loss is 20.95 dB/m for the LP11 mode in the wavelength range of 1050–1065 nm when the core diameter is 19 μm, the pitch of the core’s helix is 2.66 μmm, and the offset of the helix core from the center of the fiber axis is 31 μm. The core diameter of the single-mode helical-core fiber well exceeds that of the conventional large-mode-area fiber. The helical-core fiber can provide the effective large-mode-area single-mode operation without coiling fiber or selecting excitation mode.

Loss characteristics of helical-core fiber

We propose a novel embedded-core hollow optical fiber composed of a central circular air hole and a semi-elliptical core embedded in an annular cladding. Both the phase birefringence and group birefringence are investigated based on the finite element method (FEM). The embedded-core hollow optical fiber has polarization-preserving properties. The birefringence magnitude of the proposed fibers is the same order as that of the side-hole optical fiber. The theoretical results reveal that the birefringence of embedded-core hollow optical fibers can reach the order of 10-4. The group birefringence of the fiber is obtained by using the wavelength scanning technique and can reach 4.7×10-5. The measurement results are basically consistent with the theoretical simulations. © (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Theoretical and experimental analysis of the birefringence in embedded-core hollow optical fibers

A novel surface plasmon resonance (SPR) sensor based on the multihole optical fiber with TiO 2 layer is proposed and numerically characterized. The finite element method(FEM) is used to analyze the characteristics of the SPR sensor. The effects of the pitch between air holes, the thicknesses of the gold film and titanium dioxide layer on the sensor characteristics are investigated, and the sensitivity of proposed sensor is also given. The results indicate that when the thickness of gold film increases, the resonance wavelength shif ts to longer wavelength, and the resonance peak broadens. The spectral tuning of the plasmon resonance can be more efficiently realized by changing the TiO 2 layer thickness. The maximal refractive-index resolution of the proposed sensor for aqueous analytes is 5×10 -5 . 1. INTRODUCTION Optical fiber surface plasmon resonance (S PR) sensors are the unique combination of optical fiber technology and SPR technology. In the past few decades, the optical fiber SPR sensor has been widely applied in biochemical detection, environmental and food testing, structural health monitoring

Di Gao

Papers

Multi-hole fiber based surface plasmon resonance sensor operated at near-infrared wavelengths

Micro-nano fiber downloading filter based on rainbow local effect

Loss characteristics of helical-core fiber

Theoretical and experimental analysis of the birefringence in embedded-core hollow optical fibers

Surface plasmon resonance sensor based on multihole optical fiber with TiO2 layer