Vector fiber Bragg gratings accelerometer based on silicone compliant cylinder for low frequency vibration monitoring

Vector accelerometer has attracted much attention for its great application potential in underground seismic signal measurement. We propose and demonstrate a novel vector accelerometer based on the three fiber Bragg gratings(FBGs)embedded in a silicone rubber compliant cylinder at 120° distributed uniformly. The accelerometer is capable of detecting the orientation of vibration with a range of 0°–360° and the acceleration through monitoring the central wavelength shifts of three FBGs simultaneously. The experimental results show that the natural frequency of the accelerometer is about 85 Hz, and the sensitivity is 84.21 pm/g in the flat range of 20 Hz–60 Hz. Through experimental calibration, the designed accelerometer can accurately obtain vibration vector information, including vibration orientation and acceleration. In addition, the range of resonant frequency and sensitivity can be expanded by adjusting the hardness of the silicone rubber materials. Due to the characteristics of small size and orientation recognition, the accelerometer can be applied to low-frequency vibration acceleration vector measurement in narrow spaces.

Self-synchronized multi-color Q-switched fiber laser using a parallel-integrated fiber Bragg grating

We demonstrate an intracavity self-synchronized multi-color Q-switched fiber laser using a parallel-integrated fiber Bragg grating(PI-FBG), fabricated by a femtosecond laser with a point-by-point parallel inscription method. The multi-color Q-switched pulses can be always self-synchronized when the group delay differences between neighboring spectra range from-3.4 to 3.4 ps.The starting and evolution dynamics indicate that the saturable absorption effect of the carbon nanotube plays a dual role: synchronously triggering the startup of the pulse at successive colors by active Q-switching and spontaneously compensating to some extent the temporal walk-off of the multi-color pulses through the cross saturable absorption modulation. This work unveils the intracavity self-synchronization mechanism of the multi-color Q-switched pulses and also demonstrates the potential of PI-FBGs for the customizable generation of the synchronized multi-color pulse in a single cavity.

Ultra-low loss Rayleigh scattering enhancement via light recycling in fiber cladding

Rayleigh backscattering enhancement(RSE)of optical fibers is an effective means to improve the performance of distributed optical fiber sensing.Femtosecond laser direct-writing techniques have been used to modulate the fiber core for RSE.However,in-core modulation loses more transmission light,thus limiting the sensing distance.In this work,a cladding-type RSE(cl-RSE)structure is proposed,where the femtosecond laser is focused in the fiber cladding and an array of scatterers is written parallel to the core.The refractive-index modulation structure redistributes the light in the cladding,and the backward scattered light is recovered,which enhances the Rayleigh backscattered signal with almost no effect on the core light.

Robust integration of nitrogen-vacancy centers in nanodiamonds to optical fiber and its application in all-optical thermometry

In this Letter,we developed a robust method for integrating nanodiamonds(NDs)to optical fiber.The NDs,containing nitrogen-vacancy(NV)centers,were uniformly mixed with UV adhesive before coating the end surface of a multimode fiber as a hemispherical film.The excitation and collection efficiency of NV fluorescence can be enhanced by increasing the thickness of UV adhesive film and additional aluminum film deposition.The fiber-based quantum sensor was also experimentally demonstrated for all-optical thermometry application.The variation of the refractive index of UV adhesive under different temperatures will also affect the NV collection efficiency by changing the light confinement.The demonstrated facile integration approach paves the way for developing fiber-based quantum thermometry and magnetometry.