Simultaneous trapping of high and low refractive index particles using a single-fiber optical trap with coexisting LP01 and LP11 modes.

We propose and demonstrate a fiber optical trap based on the coexistence of LP01 and LP11 modes for the simultaneous trapping of both high refractive index particles and low refractive index particles. Since different mode beams have different propagation constants, they exhibit different focused light fields. We fabricated a tapered fiber probe using thermal fusion to converge the beam, which generates a strong gradient force field near the fiber tip, as well as a dark trap along the axial direction. High refractive index particles are attracted near the fiber tip by a strong gradient force, and low refractive index particles are trapped in the dark cage along the axial direction. The proposed optical trap, which can simultaneously trap particles with different refractive indices, makes it easier to manipulate cells or molecules with different properties and explore multi-molecule interactions, which can facilitate research related to biology and chemistry.

Vibration measurement technology based on the reverse point recognition algorithm for laser self-mixing interference.

The self-mixing interference (SMI) signal carries the information of the external moving object, which has great physical significance and application prospects for extracting and analyzing the information of the external object. In this paper, we propose a vibration measurement method based on a reverse point recognition algorithm on the SMI laser signal. By extracting and analyzing the hill and valley values of the SMI signal to determine the reverse point, combined with the semifringe counting method, the vibration information of external objects can be accurately extracted. The method we propose simplifies the displacement reconstruction process with high accuracy. The simulation and experimental results show that this method can achieve high-precision measurements of microvibration with an absolute error of less than 19 nm.

Rotation velocity measurement based on a self-mixing grating interferometer.

A novel rotational velocity measurement method based on the self-mixing grating interferometer (SMGI) is explored and presented in this paper. In this method, the target object rotational velocity is measured by the Doppler frequency shift, which can be extracted through the power spectrum without measuring incident angles. The experimental results show that the relative errors are below 0.5%.

Measurement of rotation speed based on double-beam self-mixing speckle interference.

A rotation speed measurement based on double-beam self-mixing speckle interference is presented. The self-mixing speckle signal is analyzed by a cross-correlation algorithm. The experimental results show that, compared with the Doppler frequency shift method, the proposed method can measure high speed at a low sampling rate.

Velocity measurement based on multiple self-mixing interference.

This study proposes a novel algorithm based on the multiple self-mixing interference (MSMI) theory to measure the velocity of a remote target without contact. The principle of MSMI is presented and the corresponding formulas for velocity measurement are derived. Fast Fourier transform is applied to detect signal frequency and calculate velocity values. A low-cost, compact, and easy-to-operate experimental setup is also constructed. Experiments are conducted to validate the correctness of our algorithm. This algorithm can improve resolution more easily than conventional self-mixing interference methods.