The large interest in utilising fibre Bragg grating (FBG) strain sensors for minimally invasive surgery (MIS) applications to replace conventional electrical tactile sensors has grown in the past few years. FBG strain sensors offer the advantages of optical fibre sensors, such as high sensitivity, immunity to electromagnetic noise, electrical passivity and chemical inertness, but are not limited by phase discontinuity or intensity fluctuations. FBG sensors feature a wavelength-encoding sensing signal that enables distributed sensing that utilises fewer connections. In addition, their flexibility and lightness allow easy insertion into needles and catheters, thus enabling localised measurements inside tissues and blood. Two types of FBG tactile sensors have been emphasised in the literature: single-point and array FBG tactile sensors. This paper describes the current design, development and research of the optical fibre tactile techniques that are based on FBGs to enhance the performance of MIS procedures in general. Providing MIS or microsurgery surgeons with accurate and precise measurements and control of the contact forces during tissues manipulation will benefit both surgeons and patients.

This paper experimentally demonstrates the feasibility of improving the sensing performance of fiber Bragg grating (FBG) based point sensors by deploying two pulse coding techniques, simplex coding (SSC) and Golay complementary codes (GCC). The two techniques are separately combined with the conventional time domain multiplexed FBG (TDM-FBG) interrogation sensor, and their results are compared with respect to the conventional single pulse interrogation techique. Consistently with the theory, for both coding techniques, we have confirmed that the signal-to-noise ratio improved proportionally to the code length. In details, for both techniques, the signal-to-noise improvement ratio (SNIR) of two FBGs located after around 16.35 km of fiber has significantly increased up to about 6 dB. Furthermore, the decoded signals from both techniques conserve their original spatial properties, confirming the successfulness of Hadamard transform and Golay auto-correlation calculations. Our experimental analysis confirms the simplex codes with their significant noise reduction ability which is translated into well-formed and accurate mean amplitude calculations. Moreover, the analysis of TDM-FBG based GCCs have confirmed the unique properties of the auto-correlation process to increase the FBG signals up to around 128 times compared to the single pulse case.

In this paper, a combination of two simulation tools provided by Optiwave Systems Inc. is used to perform a remote fiber Bragg grating (FBG) based strain-temperature sensor setup. Two Gaussian apodized FBG sensors were designed and characterized by OptiGrating. The customized FBGs were incorporated into OptiSystem tool to perform the analysis. Full ability to utilize the combination to perform remote strain-independent temperature FBG setup was demonstrated. 1.2 pm/μstrain and 14.4 pm/°C sensitivities obtained for strain and temperature respectively.

This work investigates a new interrogation method of a fiber Bragg grating (FBG) sensor based on longer and shorter wavelengths to distinguish between transversal forces and temperature variations. Calibration experiments were carried out to examine the sensor’s repeatability in response to the transversal forces and temperature changes. An automated calibration system was developed for the sensor’s characterization, calibration, and repeatability testing. Experimental results showed that the FBG sensor can provide sensor repeatability of 13.21 pm and 17.015 pm for longer and shorter wavelengths, respectively. The obtained calibration coefficients expressed in the linear model using the matrix enabled the sensor to provide accurate predictions for both measurements. Analysis of the calibration and experiment results implied improvements for future work. Overall, the new interrogation method demonstrated the potential to employ the FBG sensing technique where discrimination between two/three measurands is needed.

For almost a half-decade, the unique autocorrelation properties of Golay complementary pairs (GCP) have added a significant value to the key performance of conventional time-domain multiplexed fiber Bragg grating sensors (TDM-FBGs). However, the employment of the unipolar form of Golay coded TDM-FBG has suffered from several performance flaws, such as limited improvement of the signal-to-noise ratio (SNIR), noisy backgrounds, and distorted signals. Therefore, we propose and experimentally implement several digital filtering techniques to mitigate such limitations. Moving averages (MA), Savitzky–Golay (SG), and moving median (MM) filters were deployed to process the signals from two low reflectance FBG sensors located after around 16 km of fiber. The first part of the experiment discussed the sole deployment of Golay codes from 4 bits to 256 bits in the TDM-FBG sensor. As a result, the total SNIR of around 8.8 dB was experimentally confirmed for the longest 256-bit code. Furthermore, the individual deployment of MA, MM, and SG filters within the mentioned decoded sequences secured a further significant increase in SNIR of around 4, 3.5, and 3 dB, respectively. Thus, the deployment of the filtering technique alone resulted in at least four times faster measurement time (equivalent to 3 dB SNIR). Overall, the experimental analysis confirmed that MM outperformed the other two techniques in better signal shape, fastest signal transition time, comparable SNIR, and capability to maintain high spatial resolution.