Cantilever deflection optical fiber sensor based on a chirped fiber grating Fabry-Perot cavity.

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.

Fractal analysis of self-mixing speckle signal in velocity sensing.

A new method based on fractal theory is proposed to analyze velocity sensing. The waveform of a self-mixing speckle signal is processed as a pattern of a fractal. Fractal boxes are defined as a set of grids used to divide the fractal pattern, and box-counting (BC) is introduced to characterize the statistical property of a speckle signal. A group of simulated speckle signals are analyzed by calculating the BCs corresponding to different velocities of the object. A linear dependence between the BCs of speckle signals and velocities is obtained, the result of which is validated by the analysis of a group of signals obtained from experiments. The performance of the fractal analysis is compared with those of the previous analysis methods. Better linearity and higher measurement sensitivity of the fractal analysis are indicated. The experimental result shows that the fractal method can be used as a valid analysis tool for the self-mixing speckle signal in velocity sensing.

Optical feedback effect in DFB lasers for remote reflectivity detecting.

A new approach for remote reflectivity detecting based on optical feedback effect in distributed feedback (DFB) lasers is presented. A linear dependent relationship between the reflectivity of external target and the signal modulation depth is obtained. The experimental results show a good agreement with the theoretical analysis and the simulation, and indicate that the active sensing based on optical feedback effect in DFB laser is an effective approach for reflectivity detecting. With the advantage of simple and compact structure, this application can easily enhance the development of a new generation of active sensor.

Self-mixing speckle interference in DFB lasers.

Theoretical analysis and experimental results of self-mixing speckle interference in a distributed feedback (DFB) laser are presented in this paper. Self-mixing speckle interference occurs when external optical feedback comes from a moving rough surface. Dynamic output variations in the DFB laser as well as their probability density functions (PDFs) are analyzed on the basis of speckle theory and self-mixing interference in the DFB laser. Numeric simulations and experiments are in agreement with each other. The both results show that self-mixing speckle interference in DFB laser can be used to measure velocity of target.

Experiment observation of self-mixing interference in distributed feedback laser.

The experiment observation of self-mixing interference in distributed feedback (DFB) laser has been illuminated in this paper. The influences on self-mixing interference have been discussed in both simulation and experiment through changing the conditions of external cavity. The experiment results show a good agreement with the simulation results, and validate the feasibility of DFB lasers for self-mixing interference application. Combining the self-mixing interference technique and DFB laser, we can obtain the compact structure and high-accuracy self-mixing interference sensors.