## 1 Introduction  
Fiber sensors have been replacing conventional electronic sensors at a rapid rate because of their high sensitivity, compactness, robustness, immunity to electromagnetic interferences [1], etc. Typical ways to make a fiber sensor are by writing grating or micro-structures within the fiber-core, splicing, etc. Different configurations of fiber sensors including Fiber Bragg Grating (FBG) [2], Long Period Grating (LPG) [3, 4], Mach-Zehnder Interferometer (MZI) [5, 6], Michelson Interferometer (MI) [7, 8], Fabry-Perot Interferometer (FPI), etc. have been studied and developed for various applications from medical to military, oil and gas, structural health monitoring, chemical, etc. [9, 10]. An FPI structure can either be of an intrinsic or extrinsic type, depending on whether the cavity is internal or external to the optical fiber [11]. An external FPI provides the flexibility of using an air cavity or polymer type cavity. In contrast, a section of fiber is used as the cavity in an intrinsic FPI, and can be realized by thin-film coating [12, 13], mismatching of refractive index (RI) between two fibers [14], laser-irradiated points [15, 16], etc. An FPI has also been developed by sandwiching a piece of hollow-core fiber [17] and/or photonic crystal fiber [18] in-between two optical fibers, and tested for high-temperature applications [19; 20]. These methods have drawbacks of involving expensive equipment, special fiber type, use of toxic chemicals, etc. Compact MZI and MI using core-cladding mode interferometer without needing an extra optical fiber have also been reported. An inline FPI can simply be formed by using Bragg gratings instead of reflecting mirrors [21] which also enables the ease of packaging, array manufacturing, etc. Some applications making use of these configurations have been reported, such as cavity sensor for strain and temperature measurement [22]; strain measurement independent of temperature [23] (using KrF\({}_{2}\) excimer laser with phase mask); humidity and temperature measurement [24], for reducing cross-sensitivity between strain and temperature using polarization maintaining fiber [25; 26]; etc. Microfiber or small-diameter fiber-based sensors [27], resonators [28], and gratings [29] have been reported recently because these fibers offer unique properties, such as tight confinement, low-transmission loss, higher evanescent fields, etc. [30; 31; 32]. A tip-FPI fabricated by splicing a microfiber with standard single-mode fiber (SMF), has been tested up to 1000 \({}^{\circ}\)C [33]. Microfiber-based FP interferometer, for measuring temperature and RI simultaneously, is presented by [PERSON] et. al. [28] while the authors of [34; 35; 36] reported the strain characteristic of an FBG and FP structure written in a microfiber, by using ultraviolet (UV) laser and phase mask technique. A standard way of sensor fabrication is by writing a sensing structure in an optical fiber using UV laser, which requires the optical fiber to be photosensitive. In the case of a coated fiber (e.g., polyimide), the coating has to be stripped off before writing the sensor and then recoated after inscribing the structure [37]. The fs-laser has become a flexible and efficient tool to directly write (without phase mask) a waveguide or sensing structure in glass materials and to make other lab-on-chip devices [38; 39]. Recently, researchers have also used fs-laser to inscribe microstructures within the fiber cladding [40; 41]. This article investigates the feasibility of point-by-point writing of the FP structure in a fiber taper using fs-laser micromachining because scalability is one of the foremost requirements in sensor fabrication and deployment for many industrial applications. In addition, this article also investigates the strain and temperature characteristics of the sensor experimentally and will compare the response with a standard FBG sensor, which is the most commonly used fiber sensor for various structural health monitoring applications.