A highly sensitive optical fiber curvature sensor based on cascaded fiber interferometers (CFIs) is demonstrated theoretically and experimentally. Theoretical results show that the scheme of cascaded fiber interferometers can be regarded as an equivalent fiber interferometer with longer interference length and narrower FSR. It serves as a curvature sensor with sensitivity up to 4.362 nm/m-1 within the measurement range of 0 to 1.134 m-1. Compared to the single fiber modal interferometer, the curvature sensitivity of the CFI is almost doubled. In addition, simultaneous curvature and temperature measurement is achieved using coefficient matrix method, eliminating the issue of temperature cross sensitivity.

An all-fiber sensor scheme for simultaneous strain and temperature measurement is presented. The sensing head is formed by serially connecting a polarization maintaining photonic-crystal-fiber-based inter-modal interferometer (IMI) with a fiber Bragg grating (FBG). The IMI, exhibiting an opposite strain response as compared to that of the FBG, is highly sensitive to strain, while it is insensitive to temperature. This has potential for improving the strain and temperature measurement resolutions. A sensor resolution of $\pm 8.3\mathrm{\mu \epsilon }$ in strain and $\pm 2°\mathrm{C}$ in temperature are experimentally achieved within a strain range of $0–957.6\mathrm{\mu \epsilon }$ and a temperature range of $24°\mathrm{C}–64°\mathrm{C}$, respectively.

A novel lateral force sensor based on a core-offset multi-mode fiber (MMF) interferometer is reported. High extinction ratio can be obtained by misaligning a fused cross section between the single-mode fiber (SMF) and MMF. With the variation of the lateral force applied to a short section of the MMF, the extinction ratio changes while the interference phase remains almost constant. The change of the extinction ratio is independent of temperature variations. The proposed force sensor has the advantages of temperature- and phase-independency, high extinction ratio sensitivity, good repeatability, low cost, and simple structure. Moreover, the core-offset MMF interferometer is expected to have applications in fiber filters and tunable phase-independent attenuators.

A novel liquid-level sensor with a high-birefringence-fiber loop mirror (HBFLM) based on a uniform-strength cantilever beam (UCB) is proposed and demonstrated. Part of the high-birefringence fiber is pasted onto the central surface of the UCB. A hollow suspending pole is utilized to apply force at the end of the beam. The applied force varies with the change of the liquid level, leading to a change of transmission intensity. Thus the variation of liquid level can be determined via the laser wavelength within the quasi-linear transmission range of the HBFLM filter. Its sensitivity, resolution, and linear measurement range reach $0.047/\text{cm}$, $10\text{\hspace{0.17em} mm}$, and $140\text{\hspace{0.17em} mm}$, respectively. The advantages of the sensor include simple structure, high sensitivity, low cost, and good repeatability, etc. The sensing signal can be directly detected by a photodetector and does not require complicated demodulation devices.

We propose and demonstrate a temperature-insensitive and intensity-modulated embedded photonic-crystal-fiber (PCF) modal-interferometer-based microdisplacement sensor. The embedded PCF sensor has the structure of single-mode-fiber (SMF)–PCF–SMF, with a core offset at one splice joint. With the structure embedded in a cured carbon-fiber-composite-laminate-based simple-supported beam, the applied microdisplacement can be measured by monitoring its extinction ratio variation, while the extinction ratio variation is independent of the temperature variation and bending-induced strain. The sensitivity reaches $0.0024\mathrm{dB}/\mathrm{\mu m}$, the measurement resolution reaches $42\mathrm{\mu m}$, and the dynamic measurement range is within the range of $0–200\mathrm{Hz}$.

An all-fiber passively wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser is presented. With a low insertion loss carbon nanotube based saturable absorber, C- and L-band tunable Q-switched lasers are achieved by tuning the transmission wavelength of one C-band tunable filter and the other L-band one, respectively. The threshold of the Q-switched operation is only $12.8\mathrm{mW}$. The self-mode-locking effect on the Q-switching can be effectively reduced by introducing a spatial hole burning effect with two optical circulators. The tunable wavelength range of the Q-switching laser can be changed by inserting a variable optical attenuator in the laser cavity to tune the gain spectrum.