Manufacturing and Characterization of Femtosecond Laser-Inscribed Bragg Grating in Polymer Waveguide Operation in an IR-A Wavelength Range

Abstract

Optical sensors, such as fiber Bragg gratings, offer advantages compared to other sensors in many technological fields due to their outstanding characteristics. This sensor technology is currently transferred to polymer waveguides that provide the potential for cost-effective, easy, and flexible manufacturing of planar structures. While sensor production itself, in the majority of cases, is performed by means of phase mask technique, which is limited in terms of its degrees of freedom, other inscription techniques enable the manufacture of more adaptable sensor elements for a wider range of applications. In this article, we demonstrate the point-by-point femtosecond laser direct inscription method for the processing of polymer Bragg gratings into waveguides of the epoxy-based negative photoresist material EpoCore for a wavelength range around 850 nm. By characterizing the obtained grating back-reflection of the produced sensing element, we determined the sensitivity for the state variables temperature, humidity, and strain to be 45 pm/K, 19 pm/%, and 0.26 pm/µε, respectively. Individual and more complex grating structures can be developed from this information, thus opening new fields of utilization.

Optical evanescent field sensor based on point-by-point laser inscribed Bragg grating in planar polymer ridge waveguide

“…The temperature sensitivity of the sensor is similar to the waveguide Bragg grating sensor presented by Meyer et al, who used the same photo resist for the fabrication of their non-evanescent sensors and achieved -44 pm/K temperature sensitivity. 5 The validation of the liquid-phase evanescent field of the RWBG sensor was carried out by applying different aqueous isopropyl (IPA)-water mixture ranging from 0-99.9% IPA concentration. During the measurements, According to the measurement results, the sensitivity of the RWBG sensor in the range of 1.33 to 1.38 refractive index unit (RIU) increases from 2.7 nm/RIU for pure water to 6.5 nm/RIU for 99.9% pure IPA.…”

“…3,4 Therefore, optical waveguides, manufactured without claddings, are better suited for evanescent sensing applications. Polymer planar waveguide optical sensors with Bragg grating structures were presents by Meyer et al 5 The presented sensor has shown an increased sensitivity compared to FBGs in temperature and strain. However, their presented sensor was coated with an additional cladding layer, shielding the environment from interaction with the evanescent field.…”

3D optical measurement techniques

“…The advent of fiber-based spectrometers with fiber Bragg gratings (FBG) are an enormously powerful approach to build more compact, more robust, and cost-effective sensors since the whole spectrometer consist only of the fiber with the dispersive and focusing FBG and a line sensor affixed to the FBG portion of the fiber [22,23]. The improved compactness is preferential also for robust applications in harsh and industrial environments.…”

Recent Advances in Femtosecond Laser Fabrication: From Structures to Applications

“…A fiber Bragg grating structure could be processed in the core of the fiber and were able to embed Fourier optics and non-diffractive beam devices on the end face of the fiber [38]. In addition, the Bragg grating was inscribed with a near-infrared femtosecond laser through point irradiation to modulate the refractive index of the material [39].…”