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A high temperature real-time accurate monitoring system based on photoelectric oscillation had been proposed and demonstrated. We use the narrow bandwidth characteristics of phase-shifting fiber Bragg grating (PS-FBG) to generate stable photoelectric oscillation signals. After the PS-FBG is ceramic packaged to adapt to and apply to 500 °C high temperature, the wavelength shift caused by temperature change is precisely responded by narrow linewidth PS-FBG, so the change of photoelectric oscillation signal can be monitored in real time with high precision. The experimental results show that the sensitivity is −1.24 GHz/°C and the linearity is −0.99953. The system has a resolution of 0.0083 °C. The test system has excellent potential application value in precise control of high temperature environment such as metal smelting, crystal growth, chemistry and pharmaceutical engineering.

A Fabry-Perot cavity with chirped fiber gratings(CFGs) has been proposed and experimental demonstrated We use an ordinary single-mode fiber manufacturing two CFGs with reflection center wavelength 1549.74 nm by ultraviolet irradiation methods of phase mask method, two chirp fiber gratings with the same parameters: the length of the grating region is 10 mm, reflectivity is 95%, and bandwidth is 2.72 nm, chirp rate of 2 nm/cm, 1, 3 and 5 cm of two CFGs spacing. The Fabry-Perot (FP) cavity is composed of two CFGs as reflection faces. When an optical signal is input into the resonant cavity, the wavelength within the bandwidth of the CFGs satisfies the resonance condition, so the resonance is formed within the bandwidth. The structure is analyzed theoretically and the relationship between resonance spectrum and parameters is discussed. Wavelength changes are monitored by a spectral analyzer in real time. The experimental results show that the tunable laser output can be realized in optical communication system by changing the structure and parameters of the resonator.

The ability to achieve low phase noise single-mode oscillation within an optoelectronic oscillator (OEO) is of fundamental importance. In the frequency-tunable OEO, the wide microwave photonic filter (MPF) bandwidth is detrimental to select single-mode among the large number of cavity modes, thus leading to low signal quality and spectral purity. Stable single–mode oscillation can be achieved in a large time delay OEO system by harnessing the mechanism from parity-time (PT) symmetry. Here, a PT-symmetric tunable OEO based on dual-wavelength and cascaded phase-shifted fiber gratings (PS-FBGs) in a single-loop is proposed and experimentally demonstrated. Combining the merits of wide frequency tuning of PS-FBG-based MPF and single mode selection completed by the PT-symmetric architecture of the OEO, where the gain and loss modes carried by dual-wavelengths to form two mutually coupled resonators in a single-loop, signals range from 1 GHz to 22 GHz with the low phase noise distributed in −122∼ −130 dBc/Hz at 10 kHz offset frequency are obtained in the experiment.

A cantilever deflection fiber-optic sensor based on chirped fiber grating (CFG) Fabry–Perot (FP) cavity had been proposed and experimental demonstrated. Two CFBGs with the same chirped coefficient direction and grating parameters are written in one single-mode fiber by UV mask exposure to form the CFG-FP cavity. The central wavelength of two CFGs is 1549.6072 nm, the 3 dB bandwidth is 2.9897 nm, and the physical cavity length of two CFGs is 1 cm. The grating region of two CFGs are straightness fixed on a cantilever beam, forming a sensor. Then the optical properties of this sensor are tested with different stresses at different positions of the cantilever beam. The experimental results show that this sensor can obtain linear displacement of a cantilever beam, overcoming the abilities of the FBG sensor, which only performed point measurement defect. The wavelength drift sensitivity of the sensor is 2.31 pm/g, and linearity is 0.99916. This sensor has great application value in the precise measurement of cantilever beam type and two-dimensional scale strain.

A humidity fiber sensor based on both end-sides of a fiber Bragg grating (FBG) coated with polyimide has been proposed and demonstrated. Polyimide is coated on both end-sides of FBG, and a thermal curing treatment is performed to form a dense film of a certain shape. The reflection centre wavelength of the FBG is shifted 0.5 nm by bring prestress to bear on the FBG, and then the two ends of this FBG are fixed on a base with ultraviolet (UV) glue. This structure will not damage the grating part of FBG and ensure the bandwidth and reflectivity of the FBG keeping stable. In addition, this sensor avoided the curing shrinkage of the moisture sensitive film, chirp effect caused by uneven coating or the warpage of the film caused by thermal curing. The experimental results showed that the sensor has a linearity of 99%, a sensitivity of 3–4 pm/%RH and an accuracy of 5% over a wide RH range from 20 to 95%. Furthermore, this sensor has a small hysteresis, better long-term stability and simple structure and can realize multi-point quasi-distributed sensing, which has broad application prospects.

An intensity-modulated and large bandwidth magnetic field fiber sensor with tapered fiber Bragg grating (TFBG) had been proposed and demonstrated by experiments. Fiber Bragg grating (FBG) was created into a tapered fiber to form TFBG, which not only had powerful evanescent field but also possessed large bandwidth for the fiber refractive index decreased along the tapered region. The TFBG inserted into a 0.3 mm diameter glass tube which was filled with the magnetic-fluid (MF), and then this structure was packaged to form an integration magnetic-field fiber sensor. The refractive index of the MF will changed under varied magnetic-field, so the reflection spectral of the sensor should have a corresponding changed with the magnetic-field changed due to the tunable refractive index of MF. We designed the experiments and tested the sensor. The experimental results show that a nonlinear curve is between light intensity variation and changed MF intensity variation, the uniformity fitting degrees are 0.999 and 0.996 among the magnetic field increased and declined and the maximum sensitivity is −0.1933 dB/Oe and −0.1533 dB/Oe, respectively. Moreover, we find magnetic hysteresis has no obvious affection on the magnetic vectors (0 and 180 deg). This proposed magnetic-field sensor has the benefits of no direction disturbance, large bandwidth, high sensitivity, and integration.

A polyimide-coated fibre Bragg grating (FBG) relative humidity sensor with bandwidth response is proposed and demonstrated. A 12-μm-diameter micro-nano fibre is fabricated and the FBG was written by a 244-nm-UV laser, followed by the coating of polyimide on the FBG to form the sensor. The principle of the bandwidth response sensing based on the relationship between the humidity and the reflection spectra bandwidth is described. The sensor is examined under different relative humidity conditions. The results show that, with an increase in the relative humidity, the bandwidth changes at a rate of 0.00297 nm/%RH, and the linearity value is 99.3%. However, when the relative humidity is decrease, the linearity values are 97% and 98%, and the sensitivity values are 0.0035 nm/%RH and 0.0008 nm/%RH at ranges of 90–65 %RH and 65–30 %RH, respectively. In addition, the sensor has been tested the bandwidth change with temperature change under different humidity, the bandwidth-temperature sensitivity is about 0.35 pm/°C.