We present a full-polymer respiratory monitoring device suited for application in environments with strong magnetic fields (e.g., during an MRI measurement). The sensor is based on the well-known evanescent field method and consists of a 1 mm plastic optical fiber with a bent region where the cladding is removed and the fiber is coated with poly-dimethylacrylamide (PDMAA). The combination of materials allows for a mass-production of the device by spray-coating and enables integration in disposable medical devices like oxygen masks, which we demonstrate here. We also present results of the application of an autocorrelation-based algorithm for respiratory frequency determination that is relevant for real applications of the device.

In the past years, several examples of waveguides or gratings manufactured by laser radiation in various glasses or transparent polymers have been demonstrated. As these devices rely on a modification of the refractive index in the vicinity of the focal point of a writing laser, phase retrieval methods are well suited to determine the induced phase change inside the material experimentally. Thus, phase retrieval can assist parameter-studies and reveal information about the internal structure of the modifications which can hardly be obtained using other methods. Here, we demonstrate the application of a modified phase retrieval technique especially suited to determine the optical properties of phase objects such as femtosecond written gratings or waveguide arrays inscribed in transparent materials. Using the presented algorithm, we quantify the correlation between pulse energy and phase deviation as well as the structure width for femtosecond laser induced refractive index modifications in poly(methyl methacrylate) which, in the future, can be used to create tailored micro-optical structures for sensing applications.