In this work, an evanescent Bragg grating sensor inscribed in a few-mode planar polymer waveguide was integrated into microchannel structures and characterized by various chemical applications. The planar waveguide and the microchannels consisted of epoxide-based polymers. The Bragg grating structure was postprocessed by using point-by-point direct inscription technology. By monitoring the central wavelength shift of the reflected Bragg signal, the sensor showed a temperature sensitivity of −47.75 pm/K. Moreover, the functionality of the evanescent field-based measurements is demonstrated with two application examples: the refractive index sensing of different aqueous solutions and gas-phase hydrogen concentration detection. For the latter application, the sensor was additionally coated with a functional layer based on palladium nanoparticles. During the refractive index sensing measurement, the sensor achieved a sensitivity of 6.5 nm/RIU from air to 99.9% pure isopropyl alcohol. For the gas-phase hydrogen detection, the coated sensor achieved a reproducible concentration detection up to 4 vol% hydrogen. According to the reported experimental results, the integrated Bragg-grating-based waveguide sensor demonstrates high potential for applications based on the lab-on-a-chip concept.

A sensor for trinitrotoluene (TNT) detection was developed by using a combination of optical micro-ring technology and a receptor coating based on molecularly imprinted sol-gel layers. Two techniques for deposition of receptor layers were compared: Airbrush technology and electrospray ionization. A concentration of less than 5 ppb for TNT in the gas-phase, using electrospray deposition of the receptor layer, was detected. The cross-sensitivities to organic substances and further nitro-based explosives were compared. As a result, the sensitivity to TNT is about one order of magnitude higher in comparison to the explosives 2,4-dinitrotoluene (DNT) or 1,3-dinitrobenzene (DNB) and about four orders of magnitude higher than the organic substances phenol, ethanol, and acetone. The signal response of the sensor is fast, and the compact sensor design enables the deposition of different receptor layers on multiple optical micro-rings on one chip, which allows a more precise analysis and reduction of side effects and false alarms.

Minimally Invasive Surgery is often limited by the lack of tactile feedback. Indeed, surgeons have traditionally relied heavily on tactile feedback to estimate tissue stiffness - a critical factor in both diagnostics and treatment. With this in mind we present in this paper a flexible sensor foil, based on polymer optical waveguide. This sensor has been applied for real-time contact force measurement, material stiffness differentiation and surface texture reconstruction. Interrogated by a commercially available optoelectronic device, the sensor foil offers precise and reproducible feedback of contact forces up to 5 N, with a minimal detectable limit of 0.1 N. It also demonstrates distinct optical attenuation responses when indenting silicone samples of varying stiffnesses under controlled displacement. When integrated onto a 3D-printed module resembling an endoscopic camera and manipulated by a robotic arm, the sensor successfully generated spatial stiffness mapsof a phantom. Moreover, by sliding over structures with varying surface textures, the sensor foil was able to reconstruct surface profiles based on the light attenuation responses. The results demonstrate that the presented sensor foil possesses great potential for surgical applications by providing additional haptic information to surgeons.

In this work, an evanescent Bragg grating sensor inscribed in a few-mode planar polymer waveguide was integrated in microchannel structures and characterized with various chemical applications. The planar waveguide and the microchannels consisted of epoxide-based polymers. The Bragg grating structure was post-processed using point-by-point direct inscription technology. By monitoring the central wavelength shift of the reflected Bragg signal, the sensor showed a temperature sensitivity of -47.75 pm/K. Moreover, the functionality of the evanescent field-based measurements is demonstrated with two application examples: refractive index sensing of different aqueous solutions and gas-phase hydrogen concentration detection. For the latter application, the sensor was additionally coated with a functional layer based on palladium nanoparticles. During the refractive index sensing measurement, the sensor achieved a sensitivity of 6.5 nm/RIU from air to 99.9% pure isopropyl alcohol. For the gas-phase hydrogen detection, the coated sensor achieved a reproducible concentration detection up to 4 vol% hydrogen. According to the reported experimental results, the integrated Bragg grating-based waveguide sensor demonstrates high potential for applications based on lab-on-a-chip concept.

Three‐dimensional shape sensing using a single optical fiber is an attractive solution for applications requiring compact and flexible sensing elements, provided that sufficient measurement accuracy can be achieved. In this work, an optimized calibration method for fiber‐optic 3D shape sensors based on multicore fiber Bragg gratings (MCF‐FBGs) is presented. The approach specifically addresses systematic errors arising in conventional sine‐based calibration procedures, which assume homogeneous fiber rotation and neglect torsional and friction‐induced distortions. These non-ideal rotational effects introduce phase distortions in the measured sinusoidal wavelength responses and lead to systematic bias in the estimation of the effective distance to the neutral bending axis and curvature. The proposed calibration method is demonstrated using a four‐core single‐mode fiber incorporating 200 femtosecond‐laser‐inscribed FBGs, equally distributed along a 20 cm fiber length. Four FBGs located in a common fiber cross‐section form one sensor plane, resulting in 50 discrete measurement planes with a spacing of 4 mm. An algorithm‐based optimization is applied to each sensor plane individually, compensating for phase distortions and non‐ideal rotational effects during calibration. Experimental results show that the optimized calibration significantly improves curvature estimation and three‐dimensional shape reconstruction accuracy. For a 20 cm long sensor, the positioning error at the fiber tip is reduced by a factor of 4, from 8 mm to 2 mm, compared to the state‐of‐the‐art calibration method. The presented approach enhances measurement precision without increasing system complexity and provides a robust and reproducible calibration framework for high‐accuracy fiber‐optic 3D shape sensing.

Fiber-optic shape sensors require accurate calibration of the spatial orientation and effective core distances of their sensing planes. We present a rotation-angle correction procedure for sinusoidal calibration of multicore fiber Bragg grating (MCF-FBG) shape sensors. The method is demonstrated using a constant-radius groove template and a single rotation stage. Within the groove fixture, groove–fiber friction, finite torsional stiffness, and non-ideal boundary conditions may contribute to deviations between the local sensor-plane rotation and the motor-imposed angle, resulting in distorted sinusoidal wavelength responses and biased curvature estimation. The proposed method addresses deviations from the assumed sinusoidal response by jointly correcting the effective rotation angle assigned to the four FBG responses in each sensor plane while leaving the measured wavelength shifts unchanged. The method was demonstrated using a 20 cm four-core single-mode fiber containing 200 femtosecond-laser-inscribed FBGs arranged in 50 sensor planes at 4 mm spacing. Quantitative validation with planar constant-curvature templates showed tip-position errors of approximately 2–5 mm, compared with approximately 6–13 mm for conventional sine calibration. An additional endpoint-position test of the 50-plane sensor yielded a mean error of 11.28 mm and an RMSE of 13.73 mm, compared with 19.03 mm and 21.55 mm, respectively, for conventional sine calibration. Additional non-planar bending tests qualitatively illustrated the sensor’s three-dimensional reconstruction capability. The results show that rotation-angle correction can improve calibration accuracy while retaining a single-rotation-stage groove fixture.