Umesh Tiwari

Immobilization of enzyme on long period grating fibers for sensitive glucose detection.

Glucose oxidase (GOD) immobilized long period grating (LPG) fibers have been proposed for the specific and sensitive detection of glucose. The treatment of LPG fibers with aminopropyl triethoxysilane has induced biding sites for the subsequent GOD immobilization. Field emission scanning electron microscopy, confocal laser scanning microscopy, infrared spectroscopy and Raman spectroscopy have provided detailed evidences about the effectiveness of the adopted biofunctionalization methodology. The enzyme activity is conserved during the immobilization step. Fabricated LPG sensor was tested on different glucose solutions to record the transmission spectra on an optical spectrum analyzer. The wavelength shifts in the transmission spectra are linearly correlated with the glucose concentration in the range of 10-300 mg dL(-1). The fabricated sensor gives fast response and is demonstrated to be of practical utility by determining glucose contents in blood samples. Proposed technique can further be extended to develop LPG fiber based novel, sensitive and label free nanosensors for disease diagnosis and clinical analysis.

EDF-Based Edge-Filter Interrogation Scheme for FBG Sensors

A fiber Bragg grating (FBG) sensor employing an interrogation scheme based on erbium-doped fiber (EDF) edge detection filter, with enhanced detection bandwidth and intrinsic temperature insensitivity, is proposed and experimentally demonstrated. The edge filter is based on the spectral dependence of absorption in EDF with the possibility of tailoring the absorption profile using appropriate lengths of EDF. A wide filter bandwidth of about 10 nm and a slope detection sensitivity of 1.0 dB/nm in the C-band is demonstrated and validated by simulation results. The proposed scheme is versatile and allows for simultaneous interrogation of multiple FBGs.

Method for Enhancing and Controlling Temperature Sensitivity of Fiber Bragg Grating Sensor Based on Two Bimetallic Strips

This paper presents a novel structure based on bimetallic strips for enhancing temperature sensitivity of fiber Bragg grating (FBG) sensors. Two different types of sensor heads have been designed for this implementation. The first sensor head consists of an FBG that is fixed between ceramic block on one side and a bimetallic strip made up of aluminum and copper on the other. The second sensor head consists of an FBG that is fixed between two bimetallic strips. Theoretical and experimental studies carried out on these proposed sensor heads resulted in an increase in temperature sensitivity of about six times greater than that of bare FBG sensor. Further, the proposed sensors have shown good linearity and stability.

Fiber Bragg grating sensor for monitoring bone decalcification

INTRODUCTION Estimation of decalcification is a vital tool to discern bone health. Different techniques are used for its quantitative measurement, e.g. DEXA, QCT & QUS. All these techniques, although noninvasive, suffer from limitations such as radiation exposure and inaccurate values. Recently, fiber optic techniques are fast emerging for medical applications owing to their various attractive features like immunity to EMI/RFI, geometric versatility, chemical inertness, etc. MATERIAL AND METHODS The effect of decalcification on strain response of a goat tibia was investigated in vitro using fiber Bragg grating (FBG) sensing technique. The bone was strained by using three-point bending technique and corresponding Bragg wavelength shifts were recorded. Two similar bone samples from the same animal were taken and one was partially decalcified. Strain response of decalcified and untreated bone was taken concurrently to monitor the effects of calcium loss and that of degradation with time. RESULTS AND CONCLUSION The strain generated for same stress increased with greater degree of decalcification and a steep increase occurred after 2g calcium loss, indicating the onset of damage. The strain response, therefore gives a direct indication of the degree of calcium present in the bone. LEVEL OF EVIDENCE Level III.

Tunable wavelength division multiplexing channel isolation filter based on dual chirped long-period fiber gratings

We propose and demonstrate a wavelength tunable wavelength division multiplexing channel isolation filter based on two concatenated chirped long-period fiber gratings (LPGs). An intergrating space (IGS), deliberately introduced between the two gratings, provides an extra phase difference between the core and cladding modes. Changing this phase by heating the IGS without affecting the gratings tunes the channels. A theoretical account of the filter action is also presented and the results are found to be in excellent agreement with the experiments. Unlike the filters based on normal concatenated chirped LPGs without an IGS, the current filter shows a linear tuning over an increased spectral range.

Etched multimode microfiber knot-type loop interferometer refractive index sensor

We propose a novel refractive index sensor based on multimode microfiber knot-type loop (NL) interferometer. The middle portion (~5 cm) of a 15 cm long multimode fiber is etched in 48% hydrofluoric acid to reduce its diameter to ~12 μm. A NL of diameter <1 mm is made from the etched fiber. The ends of etched fiber are spliced with single-mode fibers for launching and detecting light from the NL interferometer. The NL introduces path differences to produce interferometric spectra with free spectral range ~16 nm. The spectrum shifts as the surrounding refractive index of the loop is changed by adding chemicals. We observe the highest sensitivity of the NL interferometer ~172 nm/RIU (refractive index unit) at a refractive index value 1.370 as obtained experimentally using commonly available chemicals. The design could be used as simple, low cost, and highly sensitive biological and chemical sensor.

Long period fiber grating based sensor for the detection of triacylglycerides

In this paper, stable, label free enzyme based sensor using long period fiber grating (LPG) is described for the detection of triacylglycerides. A stable covalent binding technique for lipase enzyme immobilization on an optical fiber is reported. An active and stable attachment of the functional group of the enzyme on the fiber surface is achieved using this method. Enzyme immobilization is confirmed by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. The stability is confirmed by lipase p-nitrophenyl palmitate (PNP) assay. In contrast to widely used amperometric based biosensor, where a number of enzymes are required, only one enzyme, namely, lipase is required in our sensor. The sensor shows optimum response within one minute at a temperature of 37°C and pH of 7.4. The sensor is based on the shift in resonance wavelength of the LPG transmission spectrum due to the interaction of triacylglycerides with the enzyme. The biosensor is highly specific towards triacylglycerides and is unaffected by the presence of many other interfering substances in serum. Interaction between the bio-molecules and the long period grating surface is also modeled theoretically using a four layer model for the LPG fiber with the bio-recognition layer and the results obtained are consistent with experimentally obtained results. The sensor shows a high sensitivity of 0.5 nm/mM and a low detection limit of 17.71 mg/dl for the physiological range of triacylglycerides in human blood.

Fiber Bragg Grating Sensor for Temperature Measurement in Micro Turning of Optical Surfaces with High Surface Integrity

This article presents the use of Fiber Bragg Grating (FBG) sensor to measure the temperature induced at the tip of the tool, while micro-face turning of optical surfaces. FBG sensor of 120 μm diameter was mounted near the tip of the tool and the shift in Bragg wavelength due to induced temperature was acquired with the help of an interrogator. The experiments were conducted on a Taylor Hobson DT-250 SPDT machine, over three different optical grade alloys namely Aluminum 6061, OFHC (Oxygen free highly conducting) copper and stainless steel. It was observed that while machining stainless steel, temperature at tool tip was highest and in case of OFHC copper it was lowest. The roughness and waviness of machined optical surfaces were measured using PGI 400 Profilometer. The results confirm that temperature induced in micro cutting and the rate of heat dissipation of work material contributes significantly to optical surface integrity.

Single fiber Bragg grating sensor with two sections of different diameters for longitudinal strain and temperature discrimination with enhanced strain sensitivity

A single fiber Bragg grating (FBG) sensor with two sections of different diameters is proposed and experimentally demonstrated for discrimination and measurement of strain and temperature. A section of single FBG is etched in hydrofluoric acid solution to reduce diameter of the fiber by factor of <1/2 to increase its strain sensitivity. Different shifts of the Bragg wavelengths of chemically etched and nonetched gratings caused by different strain sensitivities are used to discriminate and measure strain and temperature. Maximum errors of +/-13 microepsilon (microstrain) and +/-1 degrees C are reported over 1700 microepsilon and 60 degrees C measurement ranges, respectively. Depending upon the diameter of the etched fiber grating, the design can also discriminate nanostrain from temperature.

Shock absorption ability of laminate mouth guards in two different malocclusions using fiber Bragg grating (FBG) sensor

PURPOSE The majority of orofacial injuries affect the upper jaw, with the maxillary incisors being most prone to injury, often accounting for as many as 80% of all cases. Children with malocclusion in the anterior segment of the maxilla are more prone to traumatic injuries than those exhibiting normal occlusion, because most often the damaging force impacts directly against the maxillary anterior teeth. Hence, because of the difference of dissipation of the impact force because of the presence or absence of malocclusion, the mouthguards shock absorption capacity would be influenced by certain factors. In the present study, a unique in vitro experiment utilizing fiber Bragg Grating (FBG) as distributed strain sensors was carried out to evaluate the shock absorption ability of laminate customized mouthguards in two different malocclusions compared with normal occlusion. MATERIAL AND METHODS The impact was produced using a customized pendulum device with three interchangeable impact objects on typhodont models with two different malocclusions and normal occlusion from different heights. Response of gratings was monitored using an optical spectrum analyzer. Strain induced because each impact was determined from the Braggs wavelength shifts for each grating. For every model, 12 impact strikes were measured using three different impact objects on the two specified sites by releasing the object from two different heights. RESULTS AND CONCLUSIONS The laminated mouthguards showed significant variation in shock absorption ability when different malocclusions were compared. Hence, modifications in the original design of the laminated mouthguards should be considered for athletic competitors with malocclusion to provide adequate protection against impact. FBG sensor has shown the unique advantage of high sensitivity to strain measurement and can be used in further studies. The height of the impact is an important variable in determining the shock absorption ability of mouthguards.