We study the Bessel-like beam generator (BBG) exploiting a large-diameter fiber optic platform. The Bessel-like beam is the laser with a specific intensity profile similar to the square of zeroth-order Bessel function, [J₀(x)]² , and has a nondiffractive property. This device is based on the φ=200 microns coreless silica fiber (CSF), which has a larger dimension than generally used optical fiber with 125 microns cladding diameter. As a Gaussian beam from single-mode fiber (SMF) propagates along with this large-diameter CSF, it was successfully converted into a Bessel-like beam serving more lobes than the other all-fiber BBG previously reported. A large number of the lobes can provide a longer nondiffractive length of the Bessel-like beam but, more optical power is required as the beam area gets larger, generating undesirable laser-induced heating in H₂O. To solve this problem, we used an 852nm laser which is the wavelength with a small absorption coefficient of water. This enables to reduce of the photothermal effect in the aqueous application of this all-fiber BBG. In this paper, the fabrication of the all-fiber large-diameter BBG and its principle are presented. The photothermal generation in water by the BBG is numerically analyzed for two different wavelengths, 852nm, and 976nm. Furthermore, this photonic device is utilized as an optical tweezer in H₂O, discovering its feasibility for an aqueous environment.

This PDF file contains the front matter associated with SPIE Proceedings Volume 11953 including the Title Page, Copyright information, and Table of Contents.

Cellulose materials offer new biodegradable alternatives for fabricating optical fibers for sensing applications. Unlike glass and polymer optical fibers, these environmentally friendly materials have intrinsic properties making them attractive candidates for functional optical fibers. Cellulose fibers are hygroscopic and thus can rapidly take water vapors from the surroundings and dry quickly. Cellulose-based optical fibers can be manufactured from regenerated cellulose or cellulose derivatives which offer a large property space. They can be resistant or soluble in water, and the refracting index of the material can be tuned as needed. In this work, feasibility for sensor applications of three different cellulose optical fibers have been tested: regenerated cellulose for water and humidity sensing, carboxymethyl cellulose for respiratory rate monitoring, and methylcellulose for short-range 150 Mbit/s signal transmission at 1310 nm. Therefore, fast signal transmission can be achieved with short cellulose-based sensor fibers. The work shows the scientific and technical potential of a novel optical material for photonics.

Ni-Ti tube is used as a supporting tube for the infrared hollow fiber to obtain flexibility and strong mechanical strength. The loss of hollow optical fiber is inversely proportional to the cube of the inner diameter. Considering this, it is expected that the large-diameter hollow optical fiber has a low loss. Even with a large inner diameter of 700 μm, the Ni-Ti tube with a wall thickness of 75 μm can be bent easily to a bending radius as small as 15 mm. Therefore, 700-μm-bore hollow optical fiber based on Ni-Ti tube was fabricated. 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 were demonstrated.

Exosomes are important mediators of intercellular communications and carry parent cell-specific cargos of proteins, lipids, and genetic materials. Every cell releases exosomes as part of its cellular process. Different cell types, including normal cells and cancer cells, produce a heterogeneous mixture of exosomes in body fluids. Exosomes derived from cells with abnormal conditions can be exploited as a potential biomarker for the respective disease condition. While these exosomes carry various biomarkers, they share a common biomarker called CD63. Therefore, CD63 can be used as an analyte to track exosomes. Toward this endeavor, this work reports a fiber-optic sensor functionalized with anti-CD63 to measure the exosomes by quantifying exosomal CD63 in real-time. For this purpose, an anti-CD63 antibody functionalized surface plasmon resonance (SPR)-based fiber-optic sensor was developed that measured variations in localized SPR due to the changes in local refractive index in response to CD63 binding onto the fiber. Gold-thiol chemistry was used to covalently functionalize the fiber-optic probe with anti-CD63, wherein the antigen-binding sites of anti-CD63 were uniquely exposed to target CD63 molecules. In our preliminary experiment, the fiber-optic sensor exhibited a sensitivity of 2.83 % light reflection variations per Log(ng ml^-1 ) concentration of CD63 per cm2 sensing area and a detection limit of 2.64 ng ml^-1 . Protein concentrations in culture media were used to calibrate the sensor for precision measurements. Considering excellent dynamic detection range and sensitive thiol chemistry, the developed sensor could hold promises in future in-vivo probe development, significantly impacting real-time monitoring and therapeutic planning.

In this paper, a D-optical fiber plasmonic sensor has been demonstrated for highly sensitive detection of refractive index variations. The formation of curvature in the optical fiber is attained by wet etching technique. The D-shape curvature greatly facilitates the excitation of surface plasmons which in turn results in improved sensitivity due to the enhanced coupling of surface plasmon polaritons (SPP) modes at the point of discontinuity. In the process, a 400 micron multimode D-shaped fiber has been coated with a gold film of approximately 50 nm thickness. The sensor has been investigated for the detection of bovine serum albumin (BSA) after immobilizing it with the anti-BSA antibodies. BSA is an important biomarker to predict certain diseases, particularly in cattle. The anti-BSA antibody is conjugated to the mercaptopropionic acid (MPA) modified D-fiber via carbodiimide mediated amide bond formation between the MPA layer and the antibody. The shift in the resonance wavelength of the absorption spectra is studied for measuring the RI variations. The sensitivity of the D-fiber sensor is 1200 nm/RIU. The suitability of this sensor for the protein detection is also explored.

In this work, we design and numerically analyze a D-shaped photonic crystal fiber (PCF) plasmonic sensor based on metallic grating. The influence of the geometrical and optical parameters of the metallic grating on the performance of the proposed plasmonic refractive index sensor are thoroughly investigated considering several metals and grating configurations. The metallic grating is placed over the polished surface and gold and silver are used for this purpose. The sensitivity of the sensor and the resonant wavelength can be tuned by judiciously adjusting the grating parameters: shape, thickness, width and period. The proposed sensor exhibits excellent sensing characteristics and can be applied for several real time and fast response applications such as biological, biochemical and environmental sensing..

We developed a fully automated abdominal tissue classification algorithm for swept-source OCT imaging using a hybrid multilayer perceptron (MLP) and convolutional neural network (CNN) classifier. For MLP, we incorporated an extensive set of features and a subset was chosen to improve network efficiency. For CNN, we designed a threechannel model combining the intensity information with depth-dependent optical properties of tissues. A rule-based decision fusion approach was applied to find more convincing predictions between these two portions. Our model was trained using ex vivo porcine samples, (~200 B-mode images, ~200,000 A-line signals), evaluated by a hold-out dataset. Compared to other algorithms, our classifiers achieve the highest accuracy of 0.9114 and precision of 0.9106. The promising results showed its feasibility for real-time abdominal tissue sensing during robotic-assisted laparoscopic OCT surgery.

Deep anterior lamellar keratoplasty (DALK) is a partial-thickness cornea transplant procedure in which only the recipient’s stroma is replaced, leaving the host’s Descemet’s membrane (DM) and endothelium intact. This highly challenging “Big Bubble” procedure requires micron accuracy to insert a hydro-dissection needle as close as possible to the DM. Here, we report the design and evaluation of a downward viewing common-path optical coherence tomography (OCT) guided hydro-dissection needle for DALK. This design offers the flexibility of using different insertion angles and needle sizes. With the fiber situated outside the needle and eye, the needle can use its’ full lumen for a smoother air/fluid injection and image quality is improved. The common-path OCT probe uses a bare optical fiber with its tip cleaved at the right angle for both reference and sample arm which is encapsulated in a 25-gauge stainless still tube. The fiber was set up vertically with a half-ball epoxy lens at the end to provide an A-scan with an 11-degree downward field of view. The hydro dissection needle was set up at 70 degrees from vertical and the relative position between the fiber end and the needle tip remained constant during the insertion. The fiber and needle were aligned by a customized needle driver to allow the needle tip and tissue underneath to both be imaged within the same A-scan. Fresh porcine eyes (N = 5) were used for the studies. The needle tip position, the stroma, and DM were successfully identified from the A-scan during the whole insertion process. The results showed the downward viewing OCT distal sensor can accurately guide the needle insertion for DALK and improved the average insertion depth compared to freehand insertion.

We present a new modified graded-index (GRIN) fiber lens for extending the depth of field (DOF) of a miniature optical fiber probe for optical coherence tomography (OCT). The index profile of the GRIN fiber is designed to extend the DOF by 2X using a single piece of the GRIN fiber lens while maintaining an outside diameter of 125 μm. The output beam profiles of the optical fiber probe made with such GRIN fiber lens are measured and found to be in good agreement with the theoretical simulation.

There is a growing demand for hand-held and/or field-grade sensors for biochemical analysis of fluids. These systems have applications in monitoring of nitrogen-based compounds (such as nitrate and ammonia) in the wastewater treatment industry; bacterial detection in drinking water; analysis of biofluids, such as urine or blood; and in many other areas. Mid-infrared (midIR) spectroscopy is a powerful tool for identification and quantification of a wide range of common organic and inorganic compounds. Although IR radiation is strongly absorbed in water, this technology can be adapted for analysis of fluids by utilizing the principles of attenuated total reflection (ATR). In this contribution we highlight the application of IR spectroscopy in wastewater analysis as well as for metabolomic analysis in bioreactors. We discuss the requirements for IR signal stability that are necessary for biochemical analysis of fluids and provide examples of challenges encountered during transition from FTIR to a QCL-based platform. Overall, our stepwise efforts target eventual integration of a QCL light source, waveguide sensor, and IR detector onto a single photonic integrated circuit (PIC) for applications in the defense sector as well as for a broad consumer market.

Recent developments in infrared (IR) microfluidics for sensitive monitoring of molecular adsorption at solid–liquid interfaces are briefly reviewed. A microfluidic platform is presented that uses a metallic island film for surface enhanced IR absorption (SEIRA) coupled to IR spectroscopies for bio-sensing and vibrational investigations of molecular monolayers and their adsorption kinetics. Exemplarily, IR spectral monitoring of the monolayer formation of 4-mercaptobenzonitrile (4-MBN) in liquid environment is discussed as a Langmuir isotherm. Adsorption isotherms of specific molecular vibrations are analyzed from the time-dependent evolution of band amplitudes and peak areas during adsorption. Given the detection limit of 0.03 nmol/cm2 , the isotherms of 4-MBN, gluthathione (GSH) monolayer formation, and the sensing of 4-nitrobenzylmercaptan (4-NBM) by the MP/graphene surface are compared. Potential applications are bio- and bio-medical sensing as well as the study of processes, e. g., enzymatic reactions, chemical or catalytic reactions, receptor–ligand interactions, and structural changes of molecules due to environmental stimuli.

A new approach of fiber enhanced Raman spectroscopy for different metal cations detection and quantification is presented. The creation of a functional sodium-alginate hydrogel within the core of a self-fabricated microstructured polymer optical fiber, allows light guidance of the incident and scattered light due to the modified total internal reflection. This fact enhances the Raman spectra of the molecules placed in the core. Moreover, the functional hydrogel created in the core is capable of differentiating among high and low affinity target molecules. Experimental results demonstrate the feasibility of this sensing platform due to the aforementioned selectivity and Raman enhancement.

Optical coherence tomography (OCT) with a robust depth-resolved attenuation compensation method for a wide range of imaging applications is proposed and demonstrated. We derive a model for deducing the attenuation coefficients and the signal compensation value using the depth-dependent backscattering profiles, to mitigate under and overestimation in tissue imaging. We validated the method using numerical simulation and phantoms, where we achieved stable and robust compensation results over the entire depth of samples. The comparison between other attenuation characterization models and our proposed model is also performed.

Detecting single molecules without labels or capture probes is of great interest for both medical applications and scientific research. Frequency-locked microtoroid optical resonators are capable of label-free single molecule detection, however, this approach requires a priori knowledge of the molecule to be detected as well as surface functionalization of the cavity. Optical frequency microcombs can be a precise source of spectral information on molecules, however, microcombs have not been generated in an aqueous biological sensing environments due to altered dispersion, coupling instability, and reduced quality factor of the resonator. Here we suggest a way toward single-molecule spectroscopy by demonstrating frequency comb generation in water and air at visible wavelengths using a microtoroid optical resonator. Local anomalous dispersion is achieved because of the interaction between different transverse mode families in an overall normal dispersion region. With this approach, the advantageous structure and material of the microtoroid resonator for biosensing is preserved. We believe that in the future this will enable single molecule detection and identification simultaneously in both air and liquid at any wavelength with no labels or capture probes.

In this paper we present a method to transfer ultra-thin polymer-encapsulated metallic metasurfaces onto optical fibers to enable ultra-thin imaging devices. The metasurface is first produced by conventional e-beam lithography on a silicon substrate and encapsulated by a resist layer. After patterning the resist layer to the target shape, the encapsulated metasurfaces are peeled off from the substrate and then glued onto the tip of a single- or multi-mode optical fiber. As a proof-of-concept we demonstrate a nanowire grating polarizer on the tip of an optical fibre. This method will allow the design and fabrication of multi-layered metasurface endoscopic devices for imaging and sensing.

Raman spectroscopy can be used extensively, from handheld substance identification systems to in-vivo cancer detection. The ability to quickly and non-invasively identify compounds based on intrinsic vibrational signatures has seen Raman applications skyrocket in recent years - many using fiber optic probes. This paper describes the modeling, deposition, lithographic patterning, and testing of filters directly deposited onto the distal tip of a fiber bundle. These spectrally sharp bandpass and long pass filters allow for the detection of Raman scattering down to about 200 cm^-1 . Blocking of laser radiation above OD6 is enabled by coating both the distal and proximal tips.

Chemical pesticides drone spraying is becoming increasingly available due to its advantages such as autonomy and fast operation. A major consideration that currently limits widespan application of the technique is the undesirable drift of the spraying cloud in neighboring areas. Herein we propose the use of optical fiber long period gratings (LPGs) of extended length (~9cm) as line sensors for tracing spraying droplet distribution. Preliminary results indicate a linear trend between particle density and LPG wavelength shift and extinction ratio change. Indicatively, for a coverage of 3.9 droplets/mm2 the corresponding LPG strength and wavelength changes are 1.3dB and 65pm, respectively.

Recent studies have shown that root system architecture determines crop resilience and productivity. However, roots grow invisibly underground and are notoriously difficult to track. Root visualization requires digging, which is time-consuming and destructive. The lack of real-time non-invasive underground imaging methods has made it challenging to study this vital organ. Here, we report a method for imaging underground root system using the distributed fiber optic sensor. device named “Fiber-RADGET”. By formulating an optical fiber into spiral polytetrafluoroethylene film, the sensor device named Fiber-RADGET detects and monitors geophysical strain generated by root development. Agricultural technology is increasingly becoming automated with seamless feedback through Internet-of-Things remote sensors. The device highlighted here represents a significant addition to the repertoire of tools that next-generation agriculturalists can use for data-driven automation.

Photonic systems are gaining an important role in the field of medical diagnosis due to the achievable high sensitivity and selectivity and low cost, enabling the fabrication of disposable point of care diagnosis systems for multiple pathologies. In this work we present the detector subsystem developed for a multi-channel surface plasmon resonance (SPR) based sensor. The core of the system is a multimode interferometer splitter, fabricated in amorphous silicon, followed by multiple sensitive SPR structures with a functionalized gold layer that modulate the transmitted light waves, in the presence of the biomarker, which are then detected by infrared detectors. For this purpose a highly adaptable detection system based on a InGaAs line CCD device was developed. The IR sensor used in the prototype has 128 (50 x 250 μm) pixels but other formats are supported. To adapt to different light guiding structures, the CCD pixels can be combined forming multiple detection channels. Optical sensor configuration and readout operations are performed trough a USB connection using the SCPI standard. The system includes an analog front end with a programmable gain amplifier and offset adjustment followed by a fast analog to digital converter feeding the data to a STM32 family processor. A computer application was also developed for system configuration and signal readout and storage. The testing results from the complete system are presented. Documentation of the developed system is provided for third party use, all the material generated within this work is available online in a repository.

The present study reports on the numerical investigation carried out on a newly designed photonic crystal fiber (PCF) based plasmonic sensor for sensitivity enhancement and wide range refractive index (RI) detection. Gold (Au) is used as active plasmonic material and an additional overlayer of tantalum pentoxide (Ta₂O₅) is used. This study presents the detail sensor performance without and with the Ta₂O₅ overlayer by using finite element method (FEM) and the sensor performance is analyzed using surface plasmon resonance (SPR) phenomena. Maximum sensitivity of 9500 nm/RIU is reported in this study. Because of the tunable nature of the proposed sensor it is possible to detect a wide range of analyte RI from 1.32 to 1.40. Besides, coating of Ta₂O₅ overlayer results an enhancement of sensitivity. This study proposed a new designing technology to tune its operation range followed by sensitivity enhancement as per authors best knowledge. Moreover, as the wide detection range falls into the analyte of biological interest, so, after proper functionalization the proposed sensor can be treated with biorecognition elements and finally biofunctionalized sensing probe can be applicable as potential biosensor.

Diffuse Reflectance Spectroscopy (DRS) uses light in the visible-near-infrared (NIR) spectrum for sub-surface sensing within optically turbid media such as biological tissues. Commonly, DRS based tissue sensing uses fiber-optic probes in direct contact with tissue, creating illumination and detection spots on the tissue sample at a fixed source-detector separation (SDS). Such a geometry eliminates Fresnel reflections from being collected by the detector and only samples multiply back-scattered light from the medium. Although fibers provide a straightforward means to implement DRS, physical contact of the fiber with tissue may perturb optical properties and, in several cases, may not be feasible. Here, we develop a non-contact, broadband optical system to acquire DRS measurements from a flat medium at a working distance of 2-3 cm. We characterize the beam profiles and geometry of our system and investigate the impact of varying working distance. Preliminary results show that the non-contact DRS system detects signatures of oxygenated hemoglobin in DRS measurements from human tissue and was sensitive to changes in spectral absorption in phantoms.