132409543
Optical Fiber Refractive Index Sensor With Low Detection Limit and Large Dynamic Range Using a Hybrid Fiber Interferometer
A refractive index (RI) fiber sensor with low detection limit but large dynamic range is proposed and demonstrated using an exposed core microstructured optical fiber. The exposed-core fiber is highly birefringent due to its asymmetry and also supports multimode propagation; thus, can be used simultaneously as a Mach-Zehnder and Sagnac interferometer. The Mach-Zehnder interference is significantly more phase sensitive to RI due to a longer effective path length difference. This leads to a lower detection limit compared to that for the Sagnac interferometer, which has a larger free spectral range that allows the dynamic range of the RI measurement to be extended. By combining these two interferometers, the proposed sensor achieves a detection limit of as low as 6.02 × 10−6 refractive index units (RIU) while maintaining a large dynamic range from 1.3320 to 1.3465 RIU. The proposed sensor also has the advantages of biocompatibility, low cost, high stability, small size, ability to operate remotely and to be fabricated.
3225442
High-Sensitive Hydrogen Sensor Based on Photonic Crystal Fiber Model Interferometer
A new in-line mode coupling interferometer based on photonic crystal fiber (PCF) was designed for hydrogen sensing. The external surface of the PCF was coated with Pd-WO3 hydrogen-sensitive film using the sol–gel scheme. Pd-WO3 film refractive index and volume changing influenced the model of the PCF interferometer while the hydrogen concentration was changing, which caused the output spectrum to shift. Therefore, the relationship between the wavelength shift and the hydrogen concentration was established. In the experiment, the wavelength shift showed good linearity as the hydrogen concentration changed from 0% to 1%, while the sensitivity was 1.09 nm/% and the detection resolution was 0.3 perthousand. The sensor showed good repeatability and the wavelength error was less than 40 pm in 30 min. In addition, the sensor was not affected by external temperature fluctuations, which indicates good practical development prospects.
1218853
Modified POF Sensor for Gaseous Hydrogen Fluoride Monitoring in the Presence of Ionizing Radiations
This paper describes the development of a sensor designed to detect low concentrations of hydrogen fluoride (HF) in gas mixtures. The sensor employs a plastic optical fiber (POF) covered with a thin layer of glass- like material. HF attacks the glass and alters the fiber transmission capability so that the detection simply requires a LED and a photodiode. The coated POF is obtained by means of low-pressure plasma-enhanced chemical vapor deposition that allows the glass-like film to be deposited at low temperature without damaging the fiber core. The developed sensor will be installed in the recirculation gas system of the resistive plate chamber muon detector of the Compact Muon Solenoid experiment at the Large Hadron Collider accelerator of the European Organization for Nuclear Research (CERN).
100018333
A fully distributed fibre optic sensor for relative humidity measurements
Abstract In this paper we describe the characteristics of a 64-m-long distributed relative humidity sensor with cm spatial resolution. The sensing element is an optical fibre with a hygroscopic coating that undergoes a reversible expansion on water uptake, thereby transferring a strain on the fibre. The resulting distributed strain profile was interrogated using Rayleigh backscatter based optical frequency domain reflectometry. Investigations of the distributed sensor under controlled relative humidity and temperature were carried out. The distributed sensor is strongly humidity sensitive when polyimide coated fibre is used, and only weakly sensitive when acrylate coating is used. When using polyimide coated fibre the distributed sensor shows a near linear response across the entire range of relative humidity tested covering 15–92%, with a sensitivity ∼1.3 μe/%RH and showing low hysteresis. The system is able to resolve relative humidity changes ∼0.1%. The response time of the sensor was found to be strongly dependent on temperature in the range tested, covering 30–50 °C. Using reference temperature and humidity measurements, it was demonstrated that the distributed sensor accurately reported the combined effects of temperature and humidity variations over a cm spatial scale.
40135394
A Humidity Sensor Based on a Singlemode-Side Polished Multimode–Singlemode Optical Fibre Structure Coated with Gelatin
A novel relative humidity sensor based on a singlemode-side polished multimode-singlemode fibre structure coated with gelatin material is reported. The sensing principle and fabrication method of the proposed sensor are presented. The experimental method is demonstrated to provide the optimum thickness of coating layers in order to achieve the highest sensitivity of 0.14 dB/%RH and a fast response time of 1000 ms for a given relative humidity sensing range. The developed humidity fibre optic sensor based on a gelatin coating shows great potential for many applications such as industrial production, food processing, and environmental monitoring.
93940168
Fiber optic SPR sensor for liquid concentration measurement
Abstract A novel chemical method based on silver mirror reaction is proposed to fabricate the optic fiber surface plasmon resonance sensing probe for liquid concentration measurement. Compared to traditional physical methods, this chemical method is more convenient, resources conservation and inexpensive. And it does not need any complicated equipment. A liquid concentration measurement system with end-reflection optic fiber SPR sensor was set up. Then the comparison experiment between darkroom environment and natural light environment was conducted. As a result, the effect from natural light was eliminated. Glycerol solutions with different volume concentrations (from 0% to 50%) were measured, and the shifts in resonance wavelength were obtained. The sensitivity of the sensor is found to range from 346.7 nm/% to 890.7 nm/%.
3635878
Fiber-Optic SPR Sensor for Temperature Measurement
A fiber-optic surface plasmon resonance (SPR) sensor for temperature detection has been proposed by utilizing a thermosensitive liquid as the intermediate and combining with the fiber SPR structure. The sensing element of the sensor has been fabricated by packaging the fiber probe coated with a silver layer into a capillary filled with thermosensitive anhydrous ethanol. This packaging can protect the metal layer from oxidation and damage. Moreover, this proposed sensor achieves a sensitivity of 1.5745 nm/°C, which is much higher than that of the traditional fiber SPR sensor according to the comparative experiments.
5169980
All fiber magnetic field sensor with Ferrofluid-filled tapered microstructured optical fiber interferometer.
An ultra-compact optical fiber magnetic field sensor based on a microstructured optical fiber (MOF) modal interference and ferrofluid (FF) has been proposed and experimentally demonstrated. The magnetic field sensor was fabricated by splicing a tapered germanium-doped index guided MOF with six big holes injected with FF to two conventional single-mode fibers. The transmission spectra of the proposed sensor under different magnetic field intensities have been measured and theoretically analyzed. Due to an efficient interaction between the magnetic nanoparticles in FF and the excited cladding mode, the magnetic field sensitivity reaches up to117.9pm/mT with a linear range from 0mT to 30mT. Moreover, the fabrication process of the proposed sensor is simple, easy and cost-effective. Therefore, it will be a promising candidate for military, aviation industry, and biomedical applications, especially, for the applications where the space is limited.
3648223
Fiber Optic Fabry-Perot Magnetic Field Sensor With Temperature Compensation Using a Fiber Bragg Grating
Based on the characteristic of magnetic-controlled refractive index, magnetic fluid was used as a sensitive medium in fiber optic Fabry-Perot (F-P) cavity. Combined with the temperature sensing property of fiber Bragg grating (FBG), a novel fiber optic F-P magnetic field sensor with temperature compensation was proposed. The sensor probe has the advantages of simple structure, low cost, and high magnetic field measurement accuracy. Magnetic field and temperature can be simultaneously measured by the proposed sensor. Sensing mechanism and experimental results indicated that the temperature cross effect on magnetic field measurement can be effectively compensated using a FBG. The maximal magnetic field intensity is up to 600 Gs with a sensitivity of 0.04 nm/Gs and measurement resolution is 0.5 Gs.
30647386
Photonic crystal fiber interferometric pH sensor based on polyvinyl alcohol/polyacrylic acid hydrogel coating.
We present a simple photonic crystal fiber interferometer (PCFI) that operates in reflection mode for pH measurement. The sensor is made by coating polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel onto the surface of the PCFI, constructed by splicing a stub of PCF at the distal end of a single-mode fiber with its free end airhole collapsed. The experimental results demonstrate a high average sensitivity of 0.9 nm/pH unit for the 11 wt.% PVA/PAA coated sensor in the pH range from 2.5 to 6.5. The sensor also displays high repeatability and stability and low cross-sensitivity to temperature. Fast, reversible rise and fall times of 12 s and 18 s, respectively, are achieved for the sensor time response.
67823724
Interferometric-type optical biosensor based on exposed core microstructured optical fiber
Abstract This work presents a novel biosensor using the multimode interference effect in an exposed core microstructured optical fiber (ECF). In this work biotin molecules are immobilized onto the ECF core surface to serve as the capturing probe for streptavidin, the target molecules. Since each distinct guided mode in the ECF interacts with the surrounding medium differently, the interference between any two specific modes will experience a fringe shift (or phase change) upon a change in the refractive index (RI) of the surrounding medium, or a localized RI change on the surface of the ECF core as a result of a biological binding event. In our experiment, the interferometric sensing platform was realized by splicing a section of ECF with lead-in and lead-out single mode fibers (SMFs). An interference pattern is obtained in the transmission spectrum as the result of multiple excited modes (excited and re-collected at the lead-in and lead-out splicing points) propagating in the ECF with different propagation constants. The interference pattern is non-uniform, indicating that there are more than two modes involved. Fast Fourier transform (FFT) is used to separate individual interference patterns that contribute to this complex spectrum and monitor their phase changes upon RI variation of the surrounding medium. In this way multiple RI sensitivities can be realized because each spatial frequency possesses a distinct sensitivity with respect to the surrounding RI. The operation of this device was validated by measuring the phase changes that occur when the sensing platform was subjected to solutions of different RIs or functionalized with different molecules. A biosensor was demonstrated based on this novel platform using biotin as the capturing probe to specifically detect streptavidin with low non-specific adsorption. The proposed platform is reliable, cost-effective, and offers a potential label-free biosensing alternative to the widely used surface plasmon resonance (SPR) technique.
46867781
High-sensitivity DNA biosensor based on microfiber Sagnac interferometer.
Nucleic acid detection with label-free biosensors circumvents the need for costly fluorophore functionalization steps associated with conventional assays by utilizing optical fiber transducers. In spite of their technological prowess, however, these biosensors' sensitivity is limited by the design/configuration of their transducers. Therefore, it is imperative to integrate novel optical fiber transducers with existing label-free approaches to overcome those limitations. Herein, we present a high sensitivity label-free fiber optic biosensor that employs polarimetric interference of a high-birefringence (Hi-Bi) microfiber to specifically detect DNA molecules. A slight target DNA concentration change is converted into an optical wavelength shift of polarimetric interference generated by the microfiber Sagnac interferometer. The sensor provides a log-linear response to target ssDNA concentrations range from 100 pM to 1 μM and a minimum detectable concentration of 75 pM.
97254518
Label-Free Biosensor Based on an All-Polymer DFB Laser
emission threshold. [ 15 ] Here, we introduce an all-polymer labelfree biosensor combining a semiconducting polymer DFB laser with a stable 3D hydrogel recognition layer. In this active optical resonator biosensor, the optical design is improved by integration of an analyte recognition layer. The fabrication of this biosensor is inexpensive, it is compatible with the mass production of microfl uidic chips, and it can serve as a high-throughput biosensor due to its contactless excitation and detection system. We demonstrate the capability of the biosensor to perform label-free, selective, and real-time detection by using the biotin‐ avidin interaction as a model. The biosensor is a stack of three functional layers comprising a holographic surface relief grating (SRG) as an optical resonator prepared from a low refractive-index polymer, a blend of two semiconducting polymers with high refractive index as a gain medium, and a biotinylated hydrogel layer as the recognition element ( Figure 1 ). The gain supports the propagation of the TE 0 mode. The TE mode exhibits low emission threshold which it benefi cial for long term measurements. [ 16 ] The excited mode propagates and diffracts throughout the gain medium, providing the required gain for laser action. The master SRG was inscribed by a holographic technique based on an azobenzene material. This alloptical technique is fast (10‐15 min under 50 mW/cm 2 laser exposure), fl exible, and overcomes the time consuming preand post-processing steps required in the case of electron-beam lithography. The SRG pattern was transferred by nanoreplica molding to a UV-curable polymer with a low refractive index. Above this layer, a blend of two semiconducting polymers with
97678357
Fiber-optic conical microsensors for surface plasmon resonance using chemically etched single-mode fiber
A new type of the fiber-optic microsensor for surface plasmon resonance (SPR) was created on the basis of the fabrication technology of optical fiber probes in near-field scanning optical microscopy (NSOM). The newly developed SPR microsensors were prepared by coating a gold-metallic film on the chemically etched single-mode fiber containing a conical core. They were applied to the real-time monitoring of the refractive index (RI) of transparent liquids flowing in the microfluidic device. When SPR microsensors were chemically modified with a self-assembled monolayer presenting a hydroxyl group, they successfully responded to the refractive index from 1.33 to 1.40 RI with a sensitivity of 0.008 RI units that covers the interesting regions for SPR biosensor operated in a water solution.
10346035
Sensitive optical biosensors for unlabeled targets: a review.
This article reviews the recent progress in optical biosensors that use the label-free detection protocol, in which biomolecules are unlabeled or unmodified, and are detected in their natural forms. In particular, it will focus on the optical biosensors that utilize the refractive index change as the sensing transduction signal. Various optical label-free biosensing platforms will be introduced, including, but not limited to, surface plasmon resonance, interferometers, waveguides, fiber gratings, ring resonators, and photonic crystals. Emphasis will be given to the description of optical structures and their respective sensing mechanisms. Examples of detecting various types of biomolecules will be presented. Wherever possible, the sensing performance of each optical structure will be evaluated and compared in terms of sensitivity and detection limit.
92874760
Refractive index sensing based on photonic crystal fiber interferometer structure with up-tapered joints
Abstract A simple, ultra compact and highly sensitive photonic crystal fiber interferometer (PCFI) for external refractive index (ERI) sensing was proposed and demonstrated in this paper. The PCFI was formed by splicing photonic crystal fiber (PCF) between two single mode fibers (SMFs) with a slight core-offset. The both joints were up-tapered joints which acted as mode splitter/combiner and were made by fusion tapering technique. The Mach–Zehnder interferometer (MZI) incorporated intermodal interference between core mode and cladding modes of the PCF. When the ERI changed, a RI variation of cladding modes would occur and the output interference spectrum would shift. By measuring the wavelength shift of the interference pattern, temperature-insensitive RI measurement could be achieved. In addition, the refractive index sensing properties with the different PCF diameters were also investigated experimentally. Experimental results showed that RI sensitivity could be up to 252 nm/RIU in the refractive index range of 1.333–1.379. And it could be anticipated that RI sensitivity could be improved if the PCF diameter continues to decrease. Meanwhile, the sensor had the advantages of simple structure, small size, high sensitivity, low cost and low temperature sensitivity.
3546988
Label-free detection of bovine serum albumin based on an in-fiber Mach-Zehnder interferometric biosensor.
We propose and experimentally verify an innovative label-free optical fiber biosensor based on a Mach-Zehnder interferometer for bovine serum albumin (BSA) concentration detection. The proposed fiber biosensor utilized a micro-cavity within a single-mode fiber to induce Mach-Zehnder interference. A remarkable feature of this biosensor is that external media can directly interact with the fiber core signal through microfluidic channels connected to the micro-cavity and sensor surface. The device was fabricated by means of femtosecond laser micromachining and chemical etching. A fiber interferometer of this type exhibits an ultrahigh refractive index sensitivity of -10,055 nm/RIU and a detection limit of 3.5 × 10-5 RIU. Different concentrations of BSA with an infinitesimally small refractive index difference can be clearly differentiated in situ by the interferential spectra of the structure. Experiments demonstrated the biosensor exhibited a BSA solution concentration sensitivity of -38.9 nm/(mg/mL) and a detection limit of 2.57 × 10-4 mg/mL, respectively. Moreover, this biosensor is a sub-microliter dose and ultrasensitive at the low concentrations detected in BSA, which make it a promising for biochemical applications such as DNA hybridization, cancer screenings, medicine examination and environmental engineering, etc.
121229508
Fiber Fabry–Perot tip sensor based on multimode photonic crystal fiber
Abstract We propose a novel Fabry–Perot interferometer (FPI) sensor for simultaneous measurement of refractive index (RI) and temperature based on Fresnel reflection and the thermo-optic effect of silica. The sensor head consists of a short section of multimode photonic crystal fiber (MPCF) and a conventional single mode fiber (SMF), where two thin films are formed by collapsing the air holes of MPCF with a commercialized fusion splicer. Experimental results show that such a device has a linear RI sensitivity of ~21.52 dB/RIU (RI unit) and a linear optical path difference (OPD) temperature sensitivity of ~25 nm/°C. In addition, a high RI resolution of about ~1.7×10 −5 is obtained by using the Fourier transformation to decompose the spectral response in different spatial frequencies. Low-cost, easy fabrication and high resolution make it appropriate for practical applications.
20507957
Ultra-high sensitivity Fabry-Perot interferometer gas refractive index fiber sensor based on photonic crystal fiber and Vernier effect.
An ultra-high sensitivity open-cavity Fabry-Perot interferometer (FPI) gas refractive index (RI) sensor based on the photonic crystal fiber (PCF) and Vernier effect is proposed and demonstrated. The sensor is prepared by splicing a section of PCF to a section of fiber tube fused with a section of single mode fiber. The air holes running along the cladding of the PCF enable the gas to enter or leave the cavity freely. The reflection beam from the last end face of the PCF is used to generate the Vernier effect, which significantly improves the sensitivity of the sensor. Experimental results show that the proposed sensor can provide an ultra-high RI sensitivity of 30899 nm/RIU. This sensor has potential applications in fields such as gas concentration analyzing and humidity monitoring.
53543081
Reflection-based fibre-optic refractive index sensor using surface plasmon resonance
A reflection-based fibre-optic refractive index sensor using surface plasmon resonance (SPR) in a thin metal film sputtered on a bare core of a multimode optical fibre is presented. The sensing element of the SPR fibre-optic sensor is the core of a step-index optical fibre made of fused silica with a gold film double-sided sputtered on the whole core surface, including the core end face. Consequently, a terminated reflection-based sensing scheme to measure the refractive indices of liquids is realized. The sensing scheme uses a wavelength interrogation method and the refractive index of a liquid is sensed by measuring the position of the dip in the reflected spectral intensity distribution. As an example, the aqueous solutions of ethanol with refractive indices in a range from 1.333 to 1.363 are measured. In addition, the increase in the sensitivity of the SPR fibre-optic refractive index sensor with the decrease of the fibre sensing length is demonstrated.
10160889
Twin-core fiber SPR sensor.
We propose and demonstrate a novel surface plasmon resonance (SPR)-sensing approach by using the fundamental mode beam based on a twin-core fiber (TCF). Although normally in a fiber SPR sensor, a multimode fiber (MMF) has often been used to improve the coupling efficiency; for improving fiber SPR sensor sensitivity, single-mode beam is optimal. We provide a novel method to employ the single (fundamental)-mode beam to SPR sense based on the TCF. We grind the TCF tip to be a frustum wedge shape, and plate a 50-nm sensing gold film on the end face, and two 500-nm reflected gold films on the side faces of the wedge tip. By using this new configuration, we reduce the mode noise effectively and get a high testing sensitivity (the testing highest sensitivity reaches to 6463 nm/RIU). This SPR probe can be applied in a microfluidic chip and monitors the refractive index (RI) charges of the flow liquid in the microfluidic channel in real-time. The probe successfully monitors the refractive index of liquid ranged from 1.3333 to 1.3706, and the average sensitivity reaches to 5213 nm/RIU in the solution, which is much higher than most multimode SPR systems.
38785289
Femtosecond laser fabricated fiber Bragg grating in microfiber for refractive index sensing.
Fiber Bragg grating (FBG) is fabricated in the microfiber by the use of femtosecond laser pulse irradiation. Such a grating can be directly exposed to the surrounding medium without etching or thinning treatment of the fiber, thus possessing high refractive index (RI) sensitivity while maintaining superior reliability. The grating in the microfiber may have a number of propagation modes in its transmission spectrum, depending on the fiber diameter, and the higher order of mode has larger RI sensitivity. The RI sensitivity also depends on the fiber diameter and a smaller diameter corresponds to a large sensitivity. The maximum sensitivity obtained is approximately 231.4 nm per refractive index unit at the refractive index value of approximately 1.44 when the fiber diameter is approximately 2 microm. The FBG fabricated in the microfiber has high potential in various types of optical fiber sensor applications.
42526905
Fabrication, splicing, Bragg grating writing, and polyelectrolyte functionalization of exposed-core microstructured optical fibers.
Femtosecond laser written Bragg gratings have been written in exposed-core microstructured optical fibers with core diameters ranging from 2.7 µm to 12.5 µm and can be spliced to conventional single mode fiber. Writing a Bragg grating on an open core fiber allows for real-time refractive index based sensing, with a view to multiplexed biosensing. Smaller core fibers are shown both experimentally and theoretically to provide a higher sensitivity. A 7.5 µm core diameter fiber is shown to provide a good compromise between sensitivity and practicality and was used for monitoring the deposition of polyelectrolyte layers, an important first step in developing a biosensor.
34131318
Long period grating cascaded to photonic crystal fiber modal interferometer for simultaneous measurement of temperature and refractive index.
We propose and demonstrate a novel and simple dual-parameter measurement scheme based on a cascaded optical fiber device of long-period grating (LPG) and photonic crystal fiber (PCF) modal interferometer. The temperature and refractive index (RI) can be measured simultaneously by monitoring the spectral characteristics of the device. The implemented sensor shows distinctive spectral sensitivities of -30.82  nm/RIU (refractive index unit) and 47.4  pm/°C by the LPG, and 171.96  nm/RIU and 10.4  pm/°C by the PCF modal interferometer. The simultaneous measurement of the temperature and external RI is experimentally demonstrated by the sensor. The temperature shift and RI shift calculated by the sensor matrix agree well with the actual temperature and RI change in the experiment.
13789145
Simultaneous detection of liquid level and refractive index with a long-period fiber grating based sensor device
In this study, a long-period fiber grating (LPFG)-based optical fiber sensor device is proposed for simultaneous detection of liquid level and refractive index (RI). When part of the grating was submerged in an unknown liquid, the resonant wavelength of each cladding mode of the LPFG sensor varied linearly with the submerged length and nonlinearly with the RI of the liquid. By retaining the first-order (sensitivity) and second-order (cross sensitivity) terms of a Taylor expansion of the nonlinear relation, the changes in submerged length (or liquid level) and RI can be simultaneously evaluated from the changes in resonant wavelength of two cladding modes. The sensitivity coefficients to liquid level, RI, their cross effect and environmental effects were studied both analytically and experimentally. The maximum prediction error by the proposed evaluation algorithm was found to be 1 mm for liquid level and 0.005 for RI.
122307715
Temperature insensitive refractive index sensor based on single-mode micro-fiber Sagnac loop interferometer
A single-mode micro-fiber Sagnac loop interferometer (SMSLI) based on single-mode micro-fiber with a diameter of wavelength scale is demonstrated theoretically and experimentally. The influence of structure parameters in SMSLI on its transmission spectra has been investigated by both experimental and theoretical analysis. The sensor responses to the ambient refractive index (RI) and temperature are also investigated experimentally. Experimental results show that the proposed sensor exhibits quite high sensitivity to the ambient RI, which is found to be ∼12 500 nm/RIU. In addition, the sensitivity of SMSLI to ambient temperature is also demonstrated to be only ∼3 pm/ °C by experiments.
120656521
Optical biosensor based on whispering gallery mode excitations in clusters of microparticles
A new concept for an optical biosensor based on whispering gallery mode (WGM) excitations in clusters of spherical microresonators is presented. Clusters of microresonators offer the advantage to exhibit specific WGM spectra that can be considered as their fingerprint. Therefore, individual clusters can be traced throughout an experiment even without knowledge of their precise positions. Polyelectrolyte adsorption onto clusters of 10μm polystyrene spheres is monitored in situ. It is shown that the WGMs shift to the same amount as those of a single microresonator and thus sensitivity does not depend on the number of microresonators present in the cluster.
46864161
High-sensitivity and large-dynamic-range refractive index sensors employing weak composite Fabry-Perot cavities.
Most sensors face a common trade-off between high sensitivity and a large dynamic range. We demonstrate here an all-fiber refractometer based on a dual-cavity Fabry-Perot interferometer (FPI) that possesses the advantage of both high sensitivity and a large dynamic range. Since the two composite cavities have a large cavity length difference, one can observe both fine and coarse fringes, which correspond to the long cavity and the short cavity, respectively. The short-cavity FPI and the use of an intensity demodulation method mean that the individual fine fringe dips correspond to a series of quasi-continuous highly sensitive zones for refractive index measurement. By calculating the parameters of the composite FPI, we find that the range of the ultra-sensitive zones can be considerably adjusted to suit the end requirements. The experimental trends are in good agreement with the theoretical predictions. The co-existence of high sensitivity and a large dynamic range in a composite FPI is of great significance to practical RI measurements.
103995329
High-sensitivity Sagnac-interferometer biosensor based on exposed core microstructured optical fiber
Abstract A novel, high sensitivity Sagnac-interferometer biosensor based on exposed core microstructured optical fiber (ECF) has been designed and implemented in this paper. The exposed core fiber has noncircular symmetry and thus exhibits birefringence and can form a sensing element within a Sagnac loop interferometer. The exposed-core fiber design provides direct access to the evanescent field, allowing the measurement of bulk refractive index (RI) with a sensitivity of up to −3137 nm/RIU while maintaining the fiber’s robustness. The sensor can also detect the localized refractive index changes at the fiber core’s surface as the result of a biological binding event. We demonstrate the use of this sensor for label-free sensing of biological molecules by immobilizing biotin onto the fiber core as the probe to capture the target molecule streptavidin.
11820591
Wavelength and Phase Detection Based SMS Fiber Sensors Optimized With Etching and Nanodeposition
The development of an optical fiber refractometer by hydrogen fluoride etching and sputtering deposition of a thin-film of indium tin oxide on a single-mode-multimode-single-mode fiber structure has been analyzed with the aim of improving the sensitivity to the changes of the refractive index (RI) of the external medium. The device is sensitive to the RI changes of the surrounding medium, which can be monitored by tracking the spectral changes of an attenuation band or with a fast Fourier transform (FFT) analysis. By using an optical spectrum analyzer combined with a simple FFT measurement technique, the simultaneous real-time monitoring is achieved. The results show that the sensitivity depends on the thin-film thickness. A maximum of 1442 nm/RIU (refractive index unit) in the 1.32–1.35 RIU range has been attained. In addition, a theoretical analysis has been performed, where simulations matched with the experimental results. As a practical application of the developed optical fiber structure, a °Brix (°Bx) sensor has been implemented with a sensitivity of 2.13 nm/°Bx and 0.25 rad/°Bx respectively for wavelength and phase shift detection.
207321583
Ultimate resolution for refractometric sensing with whispering gallery mode microcavities.
Many proposed microfluidic biosensor designs are based on the measurement of the resonances of an optical microcavity. Fluorescence-based resonators tend to be simpler and more robust than setups that use evanescent coupling from tuneable laser to probe the cavity. In all sensor designs the detection limits depend on the wavelength resolution of the detection system, which is a limitation of fluorescence-based devices. In this work, we explore the ultimate resolution and detection limits of refractometric microcavity sensor structures. Because many periodic modes are collected simultaneously from fluorescent resonators, standard Fourier methods can be best suited for rapid and precise analysis of the resonance shifts. Simple numerical expressions to calculate the ultimate sensor resolution and detection limits were found, and the results compared to experiments in which the resonances of fluorescent-core microcapillaries responded to various sucrose concentrations in water.
25503047
Measurement of Magnetic Field and Temperature Based on Fiber-Optic Composite Interferometer
A novel, highly sensitive dual-parameter sensor based on a composite interference structure has been designed and implemented in this paper. The sensor was composed of a Fabry–Pérot interferometer, where the microcavity was filled by magnetic fluid (MF) and a Mach–Zehnder interferometer, where the photonic crystal fiber was filled with ethanol. The refractive index of the MF and ethanol would be changed with the increase of magnetic field and temperature. Hence, simultaneous measurement of temperature and refractive index can be achieved by monitoring the reflected spectrum and transmitted spectrum. The sensitivities of MF and ethanol can reach up to 0.033 nm/Gs and 0.236 nm/°C, respectively.
53494779
Silica exposed-core microstructured optical fibers
We report the fabrication of silica microstructured optical fibers with the core exposed along the whole length, and characterize the stability of these new fibers when exposed to some typical sensing and storage environments. We show the fiber loss to be the best achieved to date for exposed-core fibers, while the deterioration in the transmission properties is up to ∼2 orders of magnitude better than for the previously reported exposed-core fibers produced in soft glass. This opens up new opportunities for optical fiber sensors requiring long term and/or harsh environmental applications while providing real time analysis anywhere along the fibers length.
10346035
Sensitive optical biosensors for unlabeled targets: a review.
This article reviews the recent progress in optical biosensors that use the label-free detection protocol, in which biomolecules are unlabeled or unmodified, and are detected in their natural forms. In particular, it will focus on the optical biosensors that utilize the refractive index change as the sensing transduction signal. Various optical label-free biosensing platforms will be introduced, including, but not limited to, surface plasmon resonance, interferometers, waveguides, fiber gratings, ring resonators, and photonic crystals. Emphasis will be given to the description of optical structures and their respective sensing mechanisms. Examples of detecting various types of biomolecules will be presented. Wherever possible, the sensing performance of each optical structure will be evaluated and compared in terms of sensitivity and detection limit.
43759986
Comparison of various international guidelines for analytical method validation.
Analytical method validation is the systematic process of establishing that an analytical method is acceptable for its intended purpose. In general the developer or user of the method generates evidence on specificity, linearity range, accuracy, precision, detection limit, quantitation limit, ruggedness and robustness of the method for regulatory submissions or in-house application. The iterative process of method development and validation has a direct impact on the quality of the above data. Such validated analytical methods for qualitative or quantitative testing of drug molecules assume greater importance when they are employed to generate quality and safety compliance data during development and post-approval of drug products. The present paper aims to discuss salient points of the analytical method development and validation cycle. It also attempts to compare and summarize guidelines issued by different agencies for validation of analytical methods used for analysis of drug substances in the pure form and in pharmaceutical formulations.