This PDF file contains the front matter associated with SPIE Proceedings Volume 11233 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

A novel concept of optical-fiber humidity sensor using cellulose nanocrystals (CNC) composite fiber using electrospinning is presented. The humidity sensor measures relative humidity based on the effective refractive index change due to water vapor absorption. A simple evanescent detection scheme is set up for the fiber sensor where evanescent absorbance can be measured directly proportional to the vapor concentration and the effective fraction of the total guided power in the sensing region of the fiber. Due to cellulose’s high affinity to water, the sensor should exhibit relatively high sensitivity compare to non-cellulose based sensor. In this report, both fabrication of the sensor and experiment will be presented.

We demonstrate a pyrometric contactless temperature sensor using a flexible fused silica fiber of 360 μm diameter for endoscopic/laparoscopic surgery equipment. The large bandwidth (up to several kilohertz), and the broad temperature range (from 35°C to 250°C) of the sensor can be instrumental for time-resolved analysis and control of laser ablation and electrothermal surgery procedures. Fused silica fibers, as opposed to dedicated MIR fibers, are non-degrading, low-cost and biocompatible. Through dual-band detection, we also demonstrate a ratiopyrometric measurement scheme, which improves the detection of hot-spots, providing a helpful tool for focused thermal processes observed, for example, in pulsed laser ablation.

In this paper, sensitivity analysis has been carried out of TiO₂ coated fiber Bragg grating (FBG) sensor for chemical detection. FBG has been fabricated by Cu-vapour laser based second harmonic generation technique. Then TiO₂ is coated in home on FBG sensing head by targeting the 99.99% pure TiO₂ material by electron beam gun evaporation system. The thickness of TiO₂ has been numerically optimized irrespective of FBG design parameters, before depositing the material on FBG sensing head. It has been found that the proposed sensor is quite able to sense a minute change of adulteration in chemical with an accuracy of more than 0.01 ppm. After developing and testing of the sensor, the fieldwork will be decided at Indian coal mines for their possible deployment in coal fields.

Cutaneous malignant melanoma is the deadliest and most aggressive form of skin cancer and is fatal if left untreated. Currently, the most commonly used technique to detect melanoma relies on a purely subjective test termed the asymmetry, border, core, diameter, and evolution (ABCDE) test, which is performed visually by dermatologists or other medical professionals. The ABCDE method is at best a qualitative guideline, the success of which depends strongly on the skill and experience of the practitioner. The dermascope is the primary instrument for identification of skin cancer; however, successful results using dermoscopy also require skilled practitioners for accurate diagnosis. Therefore, a significant need exists to identify the presence of melanoma using non-invasive methods that do not require specialized training or skill. To meet this need, we are investigating a biomimetic, non-spectroscopic infrared (IR) optical approach for detection of skin cancer. The biomimetic approach, inspired by human color vision, only requires three broadband optical filters in the mid-infrared (2 – 8 μm), to classify tissue as cancerous or non-cancerous. We present preliminary results demonstrating the ability of this approach to discriminate between cancerous and non-cancerous skin tissue. The biomimetic approach outlined in this paper has the potential to lead to the development of small, inexpensive, portable sensors for various medical applications such as skin cancer diagnosis. Such sensors would require minimal or no training, and could be widely deployed in areas with less access to specialized care.

Per- and polyfluoroalkyl substances (PFAS) are a group of man-made chemicals used in a variety of industries (i.e. anti-stain and water proof materials, food packaging, firefighting foams) and are known for their persistence in the environment and human body. With more scientific works pursuing studies of these compounds, recently the general public has become concerned about their occurrence and effect. Current monitoring of PFAS employs mass spectrometry, primarily coupled with liquid chromatography, for assessing concentrations ranging from low ng/L (in drinking water) to high µg/L levels (in contaminated sites). This methodology has been demonstrated to achieve the required sensitivity and provide accurate and reproducible results but has limited applicability for fast measurements in the field. Hence, we discuss the opportunity of new field-deployable techniques and scenarios in which novel spectroscopy-based technologies could contribute to the advancement in PFAS monitoring.

We report on the development of infrared sensor for monitoring of nitrogen as nitrate, nitrite and ammonia in municipal wastewater. To overcome the challenge of strong absorption of the infrared radiation in water, the radiation is transmitted through a waveguide in contact with water rather than through water itself, implementing an attenuated total reflection (ATR) mechanism. Infrared spectroscopy is a powerful tool for identification and quantification of functional molecular groups. Introduction of QCLs reduces the reliance on bulky Fourier Transform Infrared (FT-IR) spectrometers that are sensitive to vibrations and enables development of versatile, portable instrumentation. Efficient nitrogen removal is one of the key objectives of any municipal wastewater treatment operation, yet today, nitrogen is monitored through grab-sampling and sending samples to laboratories for analysis. The sensor will enable reliable, real-time, unsupervised sensing in harsh environment.

We developed AgClBr fibers that are flexible, non-hygroscopic, non-toxic and highly transparent in the mid-IR. A U-shaped AgClBr fiber was connected to an FTIR spectrometer, or a QCL, and its center was immersed in polluted water. In this setup fiber-optic evanescent wave spectroscopy (FEWS) made it possible to find out in a single measurement the chemical composition and concentration of a pollutant or a mixture of pollutants. This allowed us to monitor the water quality in real time and in a remote location (i.e. in field measurements) and determine whether it presents a health hazard. Using FEWS we monitored pollutants such as volatile organic compounds (VOC), in water, in concentrations of few ppb, as needed for environmental protection. We also monitored toxic pollutants, such as pesticides, in concentrations of few ppm, as needed for homeland security.

We report on a new class of turnkey liquid analyzers powered by tunable mid-IR quantum cascade lasers. These analyzers offer excellent chemical selectivity, speed and sensitivity in a variety of applications from water quality assessment to biopharmaceutical process monitoring. We will discuss the theory of operation of these new instruments and provide relevant application examples.

Interferometric phase microscopy (IPM) is an optical technique for quantitative three-dimensional imaging, which is completely label free. Till recently, however, IPM could not be implemented outside of the optical lab due to the setup bulkiness, non-portability and the requirement for specific optical skills to align and use it. I will present our latest technological advances in developing compact IPM systems for wave-front sensing in field conditions, making this technique affordable and acceptable for inspection of small particles and bacteria in water.

Optical detection of aromatic water-contaminants from petroleum or industrial spills is challenging due to background signals from natural and/or man-made components. Further, while target contaminants are regulated at microgram per liter (μg/L) levels, conventional Raman, FTIR and UV-VIS spectroscopy are generally limited to milligram per liter (mg/L) detection ranges. This study reports on patented A-TEEM spectroscopy which primarily uses fluorescence excitation emission matrix data that are corrected for inner-filter effects (IFE) to eliminate spectral distortion. IFE correction improves resolution of low concentration contaminants from higher concentration backgrounds. The multidimensional ATEEM dataset contains spectral information in the UV-VIS range for all chromophoric and fluorescent compounds in the sample matrix. Nevertheless, because the spectra of many compounds overlap or vary in intensity extracting qualitative and quantitative information generally requires multivariate analyses. Importantly, the UV-VIS and EEM data can be analyzed in a ‘multi-block’ format to leverage the resolution capacity of these simultaneously acquired independent data sets. We evaluated Benzene, Toluene, Ethylbenzene and Xylene (BTEX) as well as naphthalene in filtered (0.45 μm) raw surface water before drinking water treatment. We show that typical methods including Partial Least Squares (PLS) and Parallel Factor Analysis (PARAFAC) exhibit a variety of pitfalls that can confound accurate contaminant detection and quantification. We report that classification and regression using methods including Support Vector Machine (SVM) and especially XGradient Boost (XGB) algorithms can be more effectively validated to rapidly yield lower μg/L detection limits with potential to automate early-warning reporting.

Combination of FTIR spectroscopy with fiber optics provides a powerful diagnostic tool for diagnosing of human diseases, including osteoarthritis. To detect cartilage degradation, an arthroscopic probe based on polycrystalline fibers was developed and evaluated on equine cartilage specimen. The hook shape allows reaching a significant portion of the articular surface; the flat tip ensures avoidance of tissue destruction. Efficient QCL-coupling and stable transmission of PIR fibers under bending allows the assembling of effective thin arthroscopy probes and customized multispectral systems for medical diagnostic applications. The presented work was performed within the MIRACLE project (Grant Agreement No 780598, Horizon 2020).

A multimodal catheter for characterizing airway collapse in obstructive sleep apnea (OSA) was introduced at Photonics West in 2019. This newly developed device showed the potential for improved diagnosis of OSA with the aim to distinguish which patients would benefit from one of the variety of treatments currently available. We build upon these findings and present preliminary results for in-vivo studies that highlight the ability of fiber Bragg grating (FBG) based pressure and temperature measurements to characterize upper airway obstruction during OSA. Significantly, our recent data is derived from a sleep study in a human subject with diagnosed OSA during natural sleep as it is considered that upper airway collapse occurs differently when awake or in a drug induced state. We demonstrate how pressure measurements from 10mm spaced FBGs can determine the location of the site(s) of collapse. Using video recordings from the catheter integrated micro-camera, we also identify the mechanism of collapse and associated anatomical features. Combining the video capture with the simultaneous and temperature independent optical measurements we present evidence of upper airway collapse during natural sleep. It is considered that improved diagnostic data of this kind would advance the ability of clinicians to better guide subsequent therapeutic interventions.

In this study, Cylindrical Diffusing Optical Fiber Probe (CDOFP) is used for tumor treatment using Photolon-based photodynamic therapy induced apoptosis and necrosis in thyroid papillary carcinoma (BCPAP) cells. In conclusion, owing to multiple advantageous properties of Photolon as a PDT agent, including preferential accumulation in tumor, biodegradability and unprecedented photosensitizer packing, we evaluate Photolon mediated PDT as a minimally invasive, tumor specific treatment for thyroid cancer. the Photolon-PDT inhibited the growth of human papilloma thyroid cancer cells and effectively decreased xenograft tumor progression in both 10mm and 15mm diffusing length probe. Therefore, this study preliminarily suggests the use of CDOFP and Photolon-PDT for more effective treatment of human thyroid cancer.

Most biosensors rely on immobilized antibodies or aptamers. In contrast, receptor proteins exist naturally in lipid bilayers and are highly specific to small molecules. We use a frequency-locked optical whispering evanescent resonator (FLOWER) system for real-time quantification of rhodopsin incorporation into an artificial lipid membrane and observe photo-induced molecular transformations upon light activation. Our study of proteolipid membrane coated microtoroids for probing the local activity of G-protein coupled receptors was further expanded to kappa-opioid receptors and their endogenous ligand Dynorphin-A. G-protein coupled receptor signaling probed by a microtoroid-proteolipid system will facilitate drug discovery and therapeutic interventions.

Stability of orthopedic implant such as pedicle screw and acetabular cup is essential to prevent bone union failure. The subsequent complication is cause further surgery because of its aberration and looseness. A quantitative diagnosis approach which can be adaptable in surgery was developed resonance frequency analysis scheme based on laser induced vibration. As a principle of the diagnosis, a laser pulse irradiated onto the orthopedic implants to induce vibration, then the induced vibration was measured by acceleration sensor or laser Doppler vibrometer. The measured signal was analysed by fast Fourier transform method. In the case of the evaluation for acetabular cup which was set by press-fit, one of the peak frequencies of the induced vibration were increased with increasing an index of the stability defined by pull-down force as mechanical evaluation. The diagnosis scheme was considered for adaptation to surgery situation including usage for another implants and flexible handling. Optical multimode fiber and pedicle screw were used for validation. The stability diagnosis system was proposed as quantitative evaluation scheme adaptable in the surgery situation.

This paper proposes a glucose optical biosensor based on a Bragg diffraction grating fabricated in Poly(dimethylsiloxane) (or PDMS), suitable for integration in an ophthalmologic contact lens. One of the periodic layers of the grating is functionalized with Glucose Oxidase (GOx) to change its refractive index proportionally with glucose concentration and, therefore, modify the response of the resulting filter. Different layers are fabricated and characterized by spectroscopic ellipsometry considering different glucose concentrations. The proposed structure can detect changes in glucose levels from 80 mg/dl to 180 mg/dl, reducing its optical response to 65% at 521 nm, being capable of real-time, continuous and non-invasive sensing.

Raman spectroscopy is used in many areas including pharmaceuticals, geology, chemical engineering, semiconductors, and the life sciences. More recently, Raman fiber sensors have been developed for minimally invasive applications in clinical histopathology. This paper describes the modeling, fabrication, and testing of filters directly deposited onto the excitation and collection fiber tips of a Raman probe. The narrow spectral width of laser rejection filters on the collection fibers should allow for the detection of low wavenumber Raman scattering within the “fingerprint” region. Deep blocking of the laser radiation is enabled by coating both ends of the collection fibers.

Distributed temperature sensing, achieved by Optical Backscattering Reflectometry (OBR), has potential in applications that require high sensitivity and resolution, such as thermal ablation. The working principle of OBR is based on monitoring the spectral signature of the light backscattered by the infinitesimal non-homogeneities inside the fiber, which changes as a result of strain or temperature variation. All the standard single-mode telecom optical fibers have almost the same scattering level, therefore, when multiple fibers are connected in parallel to the OBR, the instrument is unable to differentiate the pattern of each fiber. To overcome this issue, we proposed the use of fibers with different scattering level. Higher scattering can be achieved by creating a doping of MgO nanoparticles (size is 20-100 nm) in the fiber core, which results in roughly 50 dB increase of the scattering power. Several nanoparticles doped fibers (NPDF) have been spliced to standard single-mode fibers with variable lengths, in order to achieve spatial separation. The obtained fibers have been connected to the OBR by a 1x8 splitter. The backscattered spatial pattern consisted of several high-power regions separated by low-scattering zones given by fibers parallel. The proposed setup, applied in thermal ablation experiments, has shown that each sensing fiber is able to detect temperature variations distributed over the sensor length, and the scattering-level enabled multiplexing setup allows a detailed 2-dimensional temperature map. The resolution achieved in the pixel of the thermal map is in the order of millimeter. Moreover, the technique can be extended to obtain a 3D temperature map.

A reflector-less refractive index fiber sensor, exploiting the high-scattering of a MgO nanoparticle (NP) fiber, is proposed. The sensor is obtained by etching the fiber to expose the core to the surrounding analyte, and the backscattering signal is read by an Optical Backscatter Reflectometer (OBR). This approach permits distributed sensing, offered by OBR detection, and permits spatial-multiplexing of parallel sensors, thanks to the scattering-level multiplexing (SLMux) of the NP-doped fiber. Simultaneous physical properties detection is also possible. Experiments, performed to detect refractive index and temperature, showed a sensitivity of roughly 0.6 nm/RIU, with a simultaneous measurement of 100°C of temperature.

Antibiotic resistance is a burgeoning global public health threats of our time. Antibiotic resistance is a multifactorial and complex problem which cannot be solved by only developing stronger and better antibiotic compounds. Rapid detection and characterization of pathogenic bacteria are critical for effectively treating bacterial infections without exacerbating the resistance problem. Here, we present a novel highly-sensitive and label-free platform, Rapid-Ultra-Sensitive-Detector (RUSD), that utilizes the high reflectance coefficient of light at the interface between low-refractive-index and high-refractive-index media. The sensitivity of RUSD is three to four orders of magnitude higher than conventional optical density-based methods. Utilizing RUSD, we can detect as low as ~20 bacterial cells or a single fungal cell. This technique does not require any sophisticated signal processing steps and it enables growth rate measurements in less than an hour. Finally, we can now measure antibiotics resistance of several gram-negative and gram-positive bacteria, including Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, within two hours.

In this work, we demonstrate an optical fiber biosensor based on Fabry-Perot (F-P) interferometers using polydimethylsiloxane (PDMS) as a support for bioactive lipids. The sensors are fabricated by dip-coating producing PDMS end-capped devices. For biosensing, the PDMS cap was functionalized with a previously characterized bioactive lipid antigen cocktail from Mycobacterium fortuitum, used as a surrogate source of antigens for tuberculosis diagnosis. The performance of the biosensor was evaluated upon monitoring the changes in the interference pattern associated to the interactions between the active lipids and the antibody-containing sera. Our results show that the proposed biosensor offers new and attractive possibilities for developing novel lipidomic analytical tools.

Head and neck squamous cell carcinoma (HNSCC) is a fatal disease with 650,000 newly diagnosed cases worldwide. Early detection of this cancer improves survival significantly. Salivary biomarker analysis demonstrates that screening of HNSCC is possible and potentially improves survival. Interleukin-8 (IL-8), a cytokine produced in abundance by the HNSCC stem cells, induces epithelial-mesenchymal transformation (EMT), enhances metastasis, and can be used as a salivary biomarker for HNSCC screening. A healthy individual has 300 – 500 picogram/ml (pg/ml) in saliva, while HNSCC patients have 1700 – 2500 pg/ml. We have developed a novel tapered optical fiber biosensing system for label-free detection of antigens by attaching a molecular recognition agent to a tapered fiber surface for augmenting sensitivity and specificity of the analyte. In a tapered fiber, the evanescent electromagnetic field, which extends outside the fiber, is able to detect minute changes of the refractive index caused by the environment. The evanescent field intensity exponentially decreases with distance away from the surface of the fiber on a length scale in the order of the wavelength of light. Light from a tunable fiber laser is introduced into the tapered fiber from one end and the transmitted intensity is detected by a photodetector. Received data is then analyzed using Fourier transformation to find phase changes related to the biomolecular coating of the fiber, which is directly related to the antigen concentration. Real-time measurement of antigen concentrations at the level of 10 pg/ml is shown to be possible by successful integration of hardware and software systems. This approach has the potential to develop a pointof-care device to be used in the clinics.

Review of the latest progress in specialty fiber optics of broad 0.4-16µm range. The advanced fiber solutions for minimal invasive laser medicine and biomedical diagnostics will be presented: minimal invasive laser angioplasty at 355nm, inter-corporal InfraRed-imaging of esophagus during RF-ablation, multi-spectral tissue diagnostics to detect tumor margins ex-vivo, etc. Fiber optics enables more effective and less invasive medical operations when used for operation monitoring in so called "theranostics" – the synergy fusion of diagnostics with therapy. Mid IR-fiber endoscopy, for example, helps to eliminate risk of RF-Ablation in the common treatment used against atrial fibrillation – by providing the IR-imaging inside esophagus.

A fiber-coupled transmission spectroscopy setup using a pulsed external-cavity quantum cascade laser (EC-QCL, 1200-900 cm⁻¹ ) has been developed and demonstrated for measurements of aqueous solutions. The system has been characterised with regard to the laser noise and optimal optical pathlength. Solutions with glucose were used to further test the setup, and glucose concentrations down to physiologically relevant levels (0-600 mg/dl) were investigated. Albumin, lactate, urea, and fructose in various concentrations were added as interfering substances as their absorption bands overlap with those of glucose, and because they may be of interest in a clinical setting. Analyte concentrations were predicted using partial least-squares (PLS) regression, and the root-mean-square error of cross-validation for glucose was 10.7 mg/dl. The advantages of using a convolutional neural network (CNN) for regression analysis in comparison to the PLS regression were also shown. The application of a CNN gave an improved prediction error (8.3 mg/dl), and was used to identify important spectral regions. These results are comparable to state-of-the-art enzymatic glucose sensors, and are encouraging for further research on optics-based glucose sensors.

The mid-infrared spectral region is a great technical and scientific interest in numerous research field and applications. Among these studies, the generation of mid-infrared supercontinuum in fibers has attracted strong interest in the last decade, because of unique properties such as broad wavelength-coverage and brightness. In this work, a cascaded supercontinuum generated in a fluoride and a chalcogenide fiber spanning from 2 to 10 µm has been used for the detection of infrared signatures of organic compounds. Those results open a new way for remote sensing and spectroscopy in the mid-IR.

We investigated a deep learning strategy to analyze optical coherence tomography image for accurate tissue characterization based on a single fiber OCT probe. We obtained OCT data from human breast tissue specimens. Using OCT data obtained from adipose breast tissue (normal tissue) and diseased tissue as confirmed in histology, we trained and validated a convolutional neural network (CNN) for accurate breast tissue classification. We demonstrated tumor margin identification based CNN classification of tissue at different spatial locations. We further demonstrated CNN tissue classification in OCT imaging based on a manually scanned single fiber probe. Our results demonstrated that OCT imaging capability integrated into a low-cost, disposable single fiber probe, along with sophisticated deep learning algorithms for tissue classification, allows minimally invasive tissue characterization, and can be used for cancer diagnosis or surgical margin assessment.

Chalcogenide glasses exhibit excellent transparency in the mid infrared wavelength range which make them unique candidates for the fabrication of complex optical elements for bio-sensing. However, one of the main shortcomings of chalcogenide glasses compared to their oxide counterpart is their relatively poor mechanical strength. Nevertheless, the rapid development of infrared technology has raised the need for robust infrared fibers suitable for use in demanding environments. Here we report the development of triple index hybrid fibers composed of a chalcogenide core-clad structure embedded in an oxide external cladding.

Ni-Ti tube is used as a supporting tube for the infrared hollow fiber to obtain flexibility and strong mechanical strength. In order to reduce roughness of inner surface of Ni-Ti tube which causes the additional transmission loss, an acrylic-silicon resin material is used as a buffer layer to the inner wall of Ni-Ti tube for a low-loss characteristic. For the dielectric inner-coating layer, cyclic olefin polymer (COP) is used to lower the transmission loss. The COP layer is formed by using liquid-phase coating method. The hollow fibers with optimized COP inner film thickness for CO₂ laser light were fabricated and reasonable transmission losses was demonstrated.

Shape sensing has become an area of great interest for many medical applications, such as epidural administration, colonoscopy, biopsies, and cardiac procedures, where real-time data of a dynamic object is required and visual contact is absent. Fiber Optic Shape Sensors (FOSS) consist of optical multi-fiber cables or Multicore Fibers (MCF) with embedded strain sensors, which can reconstruct the sensor shape from its multidimensional bending. Regrettably, the accuracy of three-dimensional shape sensing is remarkably restricted because of twisting, which makes impossible to correctly detect the bending direction. This paper reports an experimental study aimed at investigating the accuracy of optical shape sensors based on spun multicore fibers in sensing twisting, employing one of the most used multicore fiber geometry for sensing applications, the seven-core fiber. Firstly, a theoretical approach to model the mechanical behavior of multicore fiber was developed. Secondly, a pre-twisted fiber optic shape sensor was fabricated in the Institute for Telecommunications and Multimedia Applications (iTEAM), by inscribing four Fiber Bragg Gratings (FBG) in a Spun Multicore Fiber (diameter of 125.1 μm) with a pre-twisting of 64.9 rotation/meter, manufactured and provided by FIBERCORE. To conclude, a series of experiments were performed to corroborate the theoretical approach and evaluate the sensor performance. The proposed Spun-MCF-based Shape Sensor was able to sense twisting with a sensitivity of 0.23 pm/° and accuracy of 4.81° within a wide dynamic range of ± 270°, maintaining a perfectly elastic behavior at high level of twisting deformation

We propose an ultra-wide detection range refractive index sensor based on surface plasmon resonance (SPR) with photonic crystal fiber (PCF). The analyte is injected into the central air hole of fiber core. The properties of refractive index sensing are investigated. Simulation results show that the proposed sensor has an ultra-wide detection range from 1.29 to 1.49. The refractive index wavelength sensitivities of x-polarized and y-polarized core mode are -4156.82 nm/RIU and -3703.64 nm/RIU respectively, and the linear fitting degrees are 0.99598 and 0.99236, respectively. The maximum x-pol amplitude sensitivity is -456.589RIU^-1 . The maximum y-pol amplitude sensitivity is -1056.33RIU^-1 . The designed refractive index sensor has a great potential in the fields of biology, chemistry, environment and medicine.

Here a novel paradigm of fiber optics 3D shape sensing is presented. Fiber optics technology offers a great potential for minimal invasive medical applications. The approach is supported by two basic cornerstones: the first is the Optical Backscattering Reflectometry (OBR), which gives the possibility of distributed strain sensing along the length of fiber sensor installed on the needle; the second is the principle of simultaneous scattering-level multiplexing (SLMux), which permits to interrogate a parallel of optical sensor in the same OBR scan. SLMux, which overtakes the OBR limitation to the interrogation of a single optical sensor, is possible by using a custommade MgO nanoparticles doped fiber (NPDF), which presents a core doped with a randomly distributed pattern of particles. NP-fiber shows a backscattering power of more than 40 dB higher than a standard single-mode fibers (SMF). By splicing NP-fiber cuts with different SMF pigtail it is possible to achieve a parallel where the higher NP-fiber backscattering can be effectively discriminated. With this approach it is possible to pack several sensors along the needle length to detect all the strain components. Experimentally, a parallel of four sensors has been fixed along the length of an epidural needle at 90 degrees from each other. 3D shape sensing is achieved by strain measurement from each fibers and distributed strain sensing along the needle. As a result of strain elaboration, shape deformation and bending of the needle during its insertion into a custom-made phantom, which mimics human spine anatomy, have been obtained.

Special featured Fibre Bragg grating has a great potential to meet the demand of development of highly sensitive optical fibre technology based chemical sensors working in harsh environment. Fibre Bragg grating assisted in between directional coupler could be significantly tuned the power coupling efficiency between two high refractive index layers. In this paper standard si-based FBG has been fabricated with square shape of apodization profile based on Cu-vapour laser and second harmonics generation based technique. Then FBG has been incorporated in between two high refractive index material followed by substrate in either side with low refractive index sensing layer. Finite difference method (FDM) based MATLAB program has been developed to extract the TE/TM modes supported by this proposed composite planar waveguide structure. Sensitivity has been calculated by b − λ graph technique for both angular/wavelength interrogation cases.

Cladding resonances generated in a Tilted Fiber Bragg Grating (TFBG) structure are readily employed for sensing purposes. They interact readily with surrounding media and allow for employing accurate refractometric applications. The grating parameters like angle of tilt, length and pitch of grating, have considerable impact on the nature of cladding resonances generated, and it turn, highly govern the specifics of sensing, like dynamic range, sensitivity, controllability, etc. In this paper, an organised and ellaborate study and analysis has been presented, to elucidate the correlation between cladding modes excited and various grating parameters in a TFBG structure. This is intended to facilitate the design of optimized TFBG sensor structures complying with pre-defined measures of sensitivity and dynamic range of operation. It is safe to imply that this study will enable fabrication of optimised sensors, according to pre-defined requirements. All analysis is based on simulations carried out on OptiGrating software and MATLAB.

In this work, a negative axicon is fabricated at the tip of an optical fiber probe by chemical etching in hydrofluoric acid which produces superior quality Bessel beam. It has large depth of focus, ~700μm along with a small central spot size, ~2μm. This negative axicon probe is utilized in a common-path optical coherence tomography (CP-OCT) setup which overcome the polarization mismatch and group velocity dispersion as both sample and reference beam travels from the similar physical path. This probe eliminates the trade-off between lateral resolution and penetration depth of the optical coherence tomography for high resolution imaging with large imaging depth. The performance of the optical fiber negative axicon probe is compared with the cleaved fiber tip. It is observed that the quality of OCT image for negative axicon probe is better than the cleaved tip. The working distance between the sample and probe for axicon probe is in larger than the cleaved tip. This axicon tip probe has great potential in endoscopic OCT in future for probing the deep tissue.

Escherichia coli bacteria are a source of food related illness. If irrigation water is contaminated by fecal matter runoff, crops may become infected prior to harvesting, processing, or packaging. Existing test methods require 16-48 hours for confirmation of bacterial infection in the irrigation water. Therefore, providing a means for a rapid detection of water borne coliform and E. coli within a typical workday of 8-10 hours would allow a preventative response. We have developed a method to determine bacteria presence by a measure of metabolic activity with a spectral analysis system. Metabolic activity of live bacteria will appear as a drop in solution pH in a relatively short time frame during the growth phase of the cultured bacteria. A blue LED is used to excite fluorescein fluorescence in the bacterial growth media. The fluorescence exhibits pH sensitive spectral properties within a range of pH 4-7. Unmixing of the fluorescence spectral profile yields the pH and confirms a growing bacteria culture. Results can be provided in hours instead of days, depending on the initial concentration of living bacteria.

We report a prototype reflection-mode fiber optic probe based on quantum dots filled micro-cavity. The probe was fabricated by sealing quantum dots liquid or coating inside a glass capillary pigtailed with a multimode optical fiber. And the probe was tested for in situ measurement of temperature change. By analyzing the back-reflected fluorescence signals generated from the quantum dots, the localized temperature of the microcavity structure could be correlated. The sensitivities based on fluorescence peak wavelength and full-width at half-maximum (FWHM) were calculated for both sensors in the biologically meaningful temperature range of 33.0-42.0C. This proposed reflection-mode trumpet-shape micro-cavity probe is attractive for chemical and biological sensing because it is cost-effective, simple to fabricate, mechanically robust and miniaturized in size.

The main purpose of this study is to evaluate the performance of different optical fibers after coupling an Er:YAG laser through them. This allows us to evaluate the feasibility of using them in future for minimally invasive ablation of bone, where a fiber has to be guided inside an endoscopic device. We coupled a high-power Er:YAG laser (λ = 2.94 μm) in different fibers separately. We analyzed the features and benefits of each fiber during the coupling process. The laser was operated at repetition rates of 1, 5, and 10 Hz in the energy range of 10-830 mJ. We used hollow-core, fluoride, sapphire and germanium oxide fibers with core sizes of 500, 450, 425 and 450 μm, respectively. The coupling efficiencies were determined by comparing the measured input and output energies for all the fibers. The resistance of each fiber to the input energy was evaluated by monitoring the stability of the measured output energy over time. From our observations, the coupling efficiencies for all the fibers were in the range 70 to 81 %. Due to the high coupling efficiency, all fibers have the potential to be used in endoscopic applications. However, their use will mostly depend on the individual need of a specific application.

In this work we report sliver mirror coated Deep Seated Negative Axicon (DSNA) optical fiber tip which significantly reduces the output power loss and increases the percentage Bessel-Gauss beam power output as compared to non-coated DSNA. The silver mirror has been deposited on the cladding of a highly Ge doped single mode double clad optical fiber using Tollen’s reagent and Glucose solution. DSNA is fabricated after deposition of the silver mirror. This coated DSNA is compared with a non-coated DSNA for measured output power by coupling with a He-Ne Laser. The measurement shows that after coating 88% of the total output power is contributing to the formation of Bessel-Gauss beam whereas it is just 30% in case of non-coated DSNA. The power in central spot of the Bessel-Gauss beam has also been increased from ~7% to ~12% of the power contributing in Bessel-Gauss beam generation. This silver mirror coated DSNA fiber tip could significantly improve the image contrast, Signal to noise ratio and sensitivity of the DSNA based Common-path optical coherence tomography system.

While fluorescence-based fiber optic sensors for measuring both pH and oxygen concentration (O₂) are well known, current sensors are often limited by their response time and drift, which limits the use of existing fiber optic sensors of this type in wider applications, for example in physiology and other fields. Several new fiber optical sensors have been developed and optimized, with respect to key features such as tip shape and coating layer thickness. In this work, preliminary results on the performance of a suite of pH sensors with fast response times, < 3 second and oxygen sensors (O₂) with response times < 0.2 second. The sensors have been calibrated and their performance analyzed using the Henderson–Hasselbalch equation (pH) and classic Lehrer-model (O₂).