We present a tilted fiber Bragg grating (TFBG)-based fiber optic sensor for the simultaneous measurement of liquid level and temperature. Due to different responses of cladding modes and core mode in TFBG spectrum to liquid level and temperature changes, both values can be measured independently. The examined 3.5° TFBG exhibits linear liquid level, as well as temperature, responses and sensitivities of -0.456 ± 0.009 dB/mm and 11.4 ± 0.2 pm/°C, respectively. In addition, greater sensor applicability is proposed for liquids having lower refractive indexes using TFBG with greater tilt angle. The presented system is capable of being applied in chemical, food, and automotive industries as well as, thanks to its all-fiber structure, in potentially hazardous environments where the immunity to electromagnetic fields or/and electric isolation is required.

Hollow-core optical fibers (HCFs) have unique properties like low latency, negligible optical nonlinearity, wide low-loss spectrum, up to 2100 nm, the ability to carry high power, and potentially lower loss then solid-core single-mode fibers (SMFs). These features make them very promising for communication networks and similar applications. However, this class of fibers is still in development. Current applications are almost exclusively limited to low-latency data links for High-Speed Trading (HST); other uses are in the trial stage now. In this paper, we comprehensively review the progress in the development of HCFs including fiber design, fabrication and parameters (with comparisons to conventional single-mode fibers) and support technologies like splicing and testing. A variety of HCF applications in future telecom networks and systems is analyzed, pointing out their strengths and limitations. Additionally, we review the influence of filler gas and entry of contaminants on HCF attenuation, and propose a new fusion splicing technique, avoiding the destruction of the fiber’s photonic cladding at high temperature.

A novel concept of a Fabry–Perot (F–P) cavity composed of two linearly chirped fiber Bragg gratings written in a thermally fused fiber taper is presented. Both chirped gratings are written in counter-directional chirp configuration, where chirps resulting from the optical fiber taper profile and linearly increasing grating periods cancel each other out, forming a high-quality F–P resonator. A new strain-sensing mechanism is proposed in the presented structure, which is based on strain-induced detuning of the F–P resonator. Due to the different strain and temperature responses of the cavity, the resonator can be used for the simultaneous measurement of these physical quantities, or it can be used as a temperature-independent strain sensor.

In this paper, spectrally tailored tapered chirped fiber Bragg gratings (TCFBGs) are considered for use as strain sensors. Both gratings were written in fused tapered optical fiber using linearly chirped fiber Bragg gratings in co-directional and counter-directional chirp configurations. Theoretical and numerical analysis as well as experimental verification of the influence of applied strain on spectral width of both TCFBG structures were carried out. The results show that TCFBGs exhibit monotonic strain response over the wide operating range of the applied force. Compared with standard tapered FBG written using uniform phase mask, in the case of co-directionally written TCFBG with substantially larger grating chirp the monotonic operating range can be easily broadened toward the higher strain values (even above the applied force at which the optical fiber breaks). In turn, the intrinsic chirp of the counter-directionally written TCFBG can be tailored in such a way as to ensure that the monotonicity of its strain response is always satisfied when tensile force is applied. This is due to the spectral broadening of the reflected spectrum when strain increases.

Efficient continuous-wave laser operation at 2.982 μm is achieved with a Dy3:fluoride fiber pumped using an inhouse-built 1.1 μm ytterbium (III) fiber laser. The laser output power reached is 554 mW, with a maximum slope efficiency of 18% with respect to the launched pump power. Additionally, the measured spontaneous luminescence within the visible wavelength range, under 1.1 μm pumping, is presented and attributed to excited state absorption (ESA). The influence of the ESA on the laser performance is discussed. The results confirm that high output powers from Dy: fluoride fiber laser pumped at 1.1 μm are possible.