A new gas detection technique through cross-correlation with a complex aperiodic FBG

Optical cross-correlation is a technique that can achieve both high specificity and high sensitivity when deployed as the basis for a sensing technology. Offering significant gains in cost, size and complexity, it can also deliver significantly higher signal-to-noise ratios than traditional approaches such as absorption methodologies. In this paper, we present an optical cross-correlation technology constructed around a bespoke customised Fiber Bragg Grating (FBG). Exploiting the remarkable flexibility in design enabled by multiple aperiodic Bragg gratings, optical filters are devised that exactly mimic the absorption features of a target gas species (for this paper, acetyleneC 2 H 2 ) over some waveband of interest. This grating forms the heart of the sensor architecture described here that employs modulated optical cross-correlation for gas detection. An experimental demonstration of this approach is presented, and shown to be capable of differentiating between different concentrations of theC 2 H 2 target gas. Furthermore these measurements are shown to be robust against interloper species, with minimal impact on the detection signal-to-noise arising from the introduction of contaminant gases. This represents is a significant step toward the use of customised FBGs as low-cost, compact, and highly customisable photonic devices for deployment in gas detection.

Design and navigation method of a soft robot for single-port transvesical radical prostatectomy

PURPOSE

Currently, the rigid instruments used for laparoscopic radical resection of prostate cancer not only have the risk of damage to tissues, blood vessels, and nerves, but their limited freedom will also cause surgical blind areas. Soft robots are expected to solve these issues due to inherent flexibility, compliance, and safe interaction with tissues and organs. In addition, to achieve high surgical accuracy and provide precise guidance for surgeons, the navigation method should be studied for the soft robot.

METHODS

A soft robot system for single-port transvesical radical prostatectomy (STRP) is developed, and a navigation method combining fiber Bragg gratings and electromagnetic tracking is proposed for the soft robot. To validate the soft robot design and the effectiveness of the navigation method, different groups of experiments are conducted.

RESULTS

The proposed navigation method can achieve accurate location and shape sensing of the soft manipulator. The experiments show that the maximum tip sensing error is 2.691 mm, which is 5.38 % of the robot length for static configurations, and that the average tip sensing error is 1.966 mm, which corresponds to 3.93 % of the robot length for dynamic scenarios. Additionally, phantom tests demonstrate that the designed soft robot can enter the prostate through navigation guidance in a master-slave control mode and cover the entire prostate space.

CONCLUSIONS

The designed soft robot system, due to its soft structure, good flexibility, and accurate navigation, is expected to improve surgical safety and precision, thereby exhibiting significant potential for STRP.

On thermal characterization method of integrated magnetic components

The operating temperature of integrated magnetic components can be critical. Excessively high temperature can significantly modify the properties of components, especially those of magnetic material, such as saturation magnetization and magnetic permeability. This article introduces an experimental characterization method using two different sensors. We compare the results obtained from these sensors. Initially, the method is validated using a "meander component, and subsequently, it is applied to planar spiral inductors, both with and without magnetic material.

Physics-based Models for photonic thermometers

Resistance thermometry, meticulously developed over the last century, provides a time-tested method for taking temperature measurements. However, fundamental limits to resistance-based approaches along with a desire to reduce the cost of sensor ownership, increase sensor stability and meet the growing needs of emerging economy has produced considerable interest in developing photonic temperature sensors. In this study we utilize Della-Corte-Varshni treatment for thermo-optic coefficient to derive models for temperature-wavelength relationships in silicon ring resonators and Fiber Bragg gratings. Model evaluation is carried out using a Bayesian criteria that selects models for superior out-of-sample predictive accuracy whilst minimizing model complexity. Our work presents physics-based framework for photonic thermometry reference functions, putting constraints on model complexity and parameter bounds, pointing the way towards a reference function that can be utilized for future standardization and inter-comparison of photonic thermometers.

Hysteresis Compensation in Temperature Response of Fiber Bragg Grating Thermometers Using Dynamic Regression

In recent years there has been considerable interest in using photonic thermometers such as Fiber Bragg grating (FBG) and silicon ring resonators as an alternative technology to resistance-based legacy thermometers. Although FBG thermometers have been commercially available for decades their metrological performance remains poorly understood, hindered in part by complex behavior at elevated temperatures. In this study we systematically examine the temporal evolution of the temperature response of 14 sensors that were repeatedly cycled between 233 K and 393 K. Data exploration and modelling indicate the need to account for serial-correlation in model selection. Utilizing the coupled-mode theory treatment of FBG to guide feature selection we evaluate various calibration models. Our results indicates that a dynamic regression model can effectively reduce measurement uncertainty due to hysteresis by up to ≈ 70% .

High-Quality Fiber Bragg Gratings Inscribed by Femtosecond Laser Point-by-Point Technology

We experimentally studied the inscription of fiber Bragg gratings by using femtosecond (fs) laser point-by-point (PbP) technology. The effects of the focusing geometry, grating order, laser energy and grating length on the spectral characteristics of the PbP FBG were investigated. After optimizing these parameters, a high-quality first-order PbP FBG with a reflectivity > 99.9% (i.e., Bragg resonance attenuation of 37.7 dB) and insertion loss (IL) of 0.03 dB was successfully created. Moreover, taking advantage of the excellent flexibility of the fs laser PbP technology, high-quality FBGs with various Bragg wavelengths ranging from 856 to 1902.6 nm were inscribed. Furthermore, wavelength-division-multiplexed (WDM) FBG arrays consisting of 10 FBGs were rapidly constructed. Additionally, a Fabry-Perot cavity was realized by using two high-quality FBGs, and its birefringence could be reduced from 3.04 × 10−5 to 1.77 × 10−6 by using a slit beam shaping-assisted femtosecond laser PbP technology. Therefore, such high-quality FBGs are promising to improve the performance of optical fiber sensors, lasers and communication devices.

Miniature Fabry-Perot Cavity Based on Fiber Bragg Gratings Fabricated by Fs Laser Micromachining Technique

Fabry-Perot cavity (FPC) based on Fiber Bragg gratings (FBGs) is an excellent candidate for fiber sensing and high-precision measurement. The advancement of the femtosecond laser micromachining technique provides more choices for the fabrication of FBGs-based FPCs. In this paper, we fabricate miniature FBGs-based FPCs, using the femtosecond laser line-by-line scanning writing technique for the first time. By this method, the FBGs can be limited to a specific area in the fiber core region. The grating length, position, and the distance between two successive FBGs can be conveniently controlled to achieve the desired transmission spectrum. For future applications in sensing, the temperature and strain responses of the fabricated FBGs-based FPCs were studied experimentally. This work provides a meaningful guidance for the fabrication and application of miniature FPCs based on FBGs.

Three-dimensional guidance including shape sensing of a stentgraft system for endovascular aneurysm repair

PURPOSE

During endovascular aneurysm repair (EVAR) procedures, medical instruments are guided with two-dimensional (2D) fluoroscopy and conventional digital subtraction angiography. However, this requires X-ray exposure and contrast agent is used, and the depth information is missing. To overcome these drawbacks, a three-dimensional (3D) guidance approach based on tracking systems is introduced and evaluated.

METHODS

A multicore fiber with fiber Bragg gratings for shape sensing and three electromagnetic (EM) sensors for locating the shape were integrated into a stentgraft system. A model for obtaining the located shape of the first 38 cm of the stentgraft system with two EM sensors is introduced and compared with a method based on three EM sensors. Both methods were evaluated with a vessel phantom containing a 3D-printed vessel made of silicone and agar-agar simulating the surrounding tissue.

RESULTS

The evaluation of the guidance methods resulted in average errors from 1.35 to 2.43 mm and maximum errors from 3.04 to 6.30 mm using three EM sensors, and average errors from 1.57 to 2.64 mm and maximum errors from 2.79 to 6.27 mm using two EM sensors. Moreover, the videos made from the continuous measurements showed that a real-time guidance is possible with both approaches.

CONCLUSION

The results showed that an accurate real-time guidance with two and three EM sensors is possible and that two EM sensors are already sufficient. Thus, the introduced 3D guidance method is promising to use it as navigation tool in EVAR procedures. Future work will focus on developing a method with less EM sensors and a detailed latency evaluation of the guidance method.

Strain Monitoring of a Composite Drag Strut in Aircraft Landing Gear by Fiber Bragg Grating Sensors

This work reports on the use of Fiber Bragg Grating (FBG) sensors integrated with innovative composite items of aircraft landing gear for strain/stress monitoring. Recently, the introduction of innovative structures in aeronautical applications is appealing with two main goals: (i) to decrease the weight and cost of current items; and (ii) to increase the mechanical resistance, if possible. However, the introduction of novel structures in the aeronautical field demands experimentation and certification regarding their mechanical resistance. In this work, we successfully investigate the possibility to use Fiber Bragg Grating sensors for the structural health monitoring of innovative composite items for the landing gear. Several FBG strain sensors have been integrated in different locations of the composite item including region with high bending radius. To optimize the localization of the FBG sensors, load condition was studied by Finite Element Method (FEM) numerical analysis. Several experimental tests have been done in range 0-70 kN by means of a hydraulic press. Obtained results are in very good agreement with the numerical ones and demonstrate the great potentialities of FBG sensor technology to be employed for remote and real-time load measurements on aircraft landing gears and to act as early warning systems.

Experimental Analysis of Bragg Reflection Peak Splitting in Gratings Fabricated Using a Multiple Order Phase Mask

We performed an experimental analysis of the effect of phase mask alignment on the Bragg grating reflection spectra around the wavelength of λ_B = 1560 nm fabricated in polymer optical fiber by using a multiple order phase mask. We monitored the evolution of the reflection spectra for different values of the angle ϕ by describing the tilt between the phase mask and the fiber. We observed that the peak at λ_B is split into five separate peaks for the nonzero tilt and that separation of the peaks increases linearly with ϕ. Through comparison with theoretical data we were able to identify the five peaks as products of different grating periodicities, which are associated with the interference of different pairs of diffraction orders on the phase mask.

Investigating the Strain, Temperature and Humidity Sensitivity of a Multimode Graded-Index Perfluorinated Polymer Optical Fiber with Bragg Grating

In this work we investigate the strain, temperature and humidity sensitivity of a Fiber Bragg Grating (FBG) inscribed in a near infrared low-loss multimode perfluorinated polymer optical fiber based on cyclic transparent optical polymer (CYTOP). For this purpose, FBGs were inscribed into the multimode CYTOP fiber with a core diameter of 50 µm by using a krypton fluoride (KrF) excimer laser and the phase mask method. The evolution of the reflection spectrum of the FBG detected with a multimode interrogation technique revealed a single reflection peak with a full width at half maximum (FHWM) bandwidth of about 9 nm. Furthermore, the spectral envelope of the single FBG reflection peak can be optimized depending on the KrF excimer laser irradiation time. A linear shift of the Bragg wavelength due to applied strain, temperature and humidity was measured. Furthermore, depending on irradiation time of the KrF excimer laser, both the failure strain and strain sensitivity of the multimode fiber with FBG can be controlled. The inherent low light attenuation in the near infrared wavelength range (telecommunication window) of the multimode CYTOP fiber and the single FBG reflection peak when applying the multimode interrogation set-up will allow for new applications in the area of telecommunication and optical sensing.

Femtosecond FBG Written through the Coating for Sensing Applications

Type I fiber Bragg gratings (FBG) written through the coating of various off-the-shelf silica fibers with a femtosecond laser and the phase-mask technique are reported. Inscription through most of the common coating compositions (acrylate, silicone and polyimide) is reported as well as writing through the polyimide coating of various fiber cladding diameters, down to 50 µm. The long term annealing behavior of type I gratings written in a pure silica core fiber is also reported as well as a comparison of the mechanical resistance of type I and II FBG. The high mechanical resistance of the resulting type I FBG is shown to be useful for the fabrication of various distributed FBG arrays written using a single period phase-mask. The strain sensing response of such distributed arrays is also presented.

Sensitive detection of C-reactive protein using optical fiber Bragg gratings

An accurate and highly sensitive sensor platform has been demonstrated for the detection of C-reactive protein (CRP) using optical fiber Bragg gratings (FBGs). The CRP detection has been carried out by monitoring the shift in Bragg wavelength (ΔλB) of an etched FBG (eFBG) coated with an anti-CRP antibody (aCRP)-graphene oxide (GO) complex. The complex is characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. A limit of detection of 0.01mg/L has been achieved with a linear range of detection from 0.01mg/L to 100mg/L which includes clinical range of CRP. The eFBG sensor coated with only aCRP (without GO) show much less sensitivity than that of aCRP-GO complex coated eFBG. The eFBG sensors show high specificity to CRP even in the presence of other interfering factors such as urea, creatinine and glucose. The affinity constant of ∼1.1×10(10)M(-1) has been extracted from the data of normalized shift (ΔλB/λB) as a function of CRP concentration.

Optical fiber sensing based on reflection laser spectroscopy

An overview on high-resolution and fast interrogation of optical-fiber sensors relying on laser reflection spectroscopy is given. Fiber Bragg-gratings (FBGs) and FBG resonators built in fibers of different types are used for strain, temperature and acceleration measurements using heterodyne-detection and optical frequency-locking techniques. Silica fiber-ring cavities are used for chemical sensing based on evanescent-wave spectroscopy. Various arrangements for signal recovery and noise reduction, as an extension of most typical spectroscopic techniques, are illustrated and results on detection performances are presented.