Optical fiber communication systems form the backbone of our information-driven society and economy. Since 2000, the traffic in optical communications networks has presented an exponential growing, near 50% to 60% per year [1], which is associated to the ever-growing number of users and devices connected to the Internet around the world. In order to satisfy the great demand of information and increase the transmission rates, it was required to develop several technological breakthroughs such as the development of low-loss Single Mode Fibers (SMFs), Erbium-Doped Fiber Amplifiers (EDFAs), Wavelength Division Multiplexing (WDM), Polarization Division Multiplexing (PDM) and Digital Signal Processor (DSP) that enables coherent transmission [2]. Currently, WDM coherent optical communication systems have already depleted all degrees of freedom, namely, frequency, quadrature, and polarization in SMFs. Then, the space is the only extra dimension that can be employed in the future of optical fiber communication systems. The so-called spatial division multiplexing (SDM), which includes mode division multiplexing (MDM) using few-mode fibers (FMFs) [3-7] and/or multiplexing using multicore fibers (MCF) [8,9], has attracted much attention in recent years for the next growth of optical communication capacity. To enable SDM transmission, Spatial SMUX and DEMUX are critical components to transform signals from parallel SMFs to SDM signals that contain the superposition of the different modes. Each MUX-DEMUX has two components: a mode-converter and a combiner. Therefore, to make a correct implementation of this technique, it is mandatory the design of new devices that allow the conversion and control of the propagated modes in an optical fiber. On the other side, in the last decades, optical fibers have been widely used not only in the telecommunication industry, but also in sensing applications, due to their multiple advantages compared to conventional electric sensors [10,11]. Currently, fiber-optic sensors are implemented in the measurement and monitoring of various physicochemical variables such as pressure, displacement, pH, temperature, refractive index, strain, etc. [12–15], becoming increasingly important for applications in industrial process and quality control, biomedical analysis, and environmental monitoring. The development of fiber-optic sensors is being continuously addressed, leading to the search for new alternatives through the simplification of some processes, such as the construction of the sensor itself and the way in which measurement and/or exploration of new strategies and techniques is performed. The current interest is the development of all-fiber optic devices since these types of photonic components have compact size, high efficiency, fast response and versatility compared to electronic devices [16,17]. To carry out this task, it is mandatory the use of a new generation of optical fibers known as Photonic Crystal Fibers (PCFs) [16,18,19]. This research project is aimed to develop photonic devices based on PCFs for active mode conversion in telecommunications and sensing applications. For this end, the project will focus on two types of structures: the PCF with integrated electrodes and the asymmetric double-core PCF. In the first phase of this work, we will explore the optical properties associated to both fibers and as they can be perturbed through external effects such as temperature, electric current, pressure or refractive index. Based on this step, we will select one of these fibers to demonstrate its application as a novel mode-converter for telecommunications. In this case, we will employ experimental schemes to validate the capability of the device to couple the propagating modes. Based on the previous works, we also want to explore the design and experimental validation of one or two sensing configurations to measure some physical parameters such as temperature, strain or refractive index change.