Laser Self-mixing Interference Research Articles

Multiple self-mixing interference with the Faraday effect for detecting magnetic fields.

Detection of magnetic fields is widely used in magnetic materials, electronic devices, medical imaging, and navigation systems. We conducted the experiments using a TGG crystal in different magnetic fields to observe multiple laser self-mixing interference in the frequency domain for experimentation. Every spectral line of the multiple laser self-mixing interference contained the peaks exhibiting a decay trend due to the rotation of the light's polarized orientation according to the Faraday effect. The decay rate of the spectral line depended on the magnetic field density. To quantify the decay rate, the decay coefficient was obtained via fitting of the spectral line. The equation between the decay coefficient and the magnetic field density was established from the experimental results, and the magnetic field density was detected using the equation. This work exhibited a potential detection capability for magnetic fields.

Research on measuring method of self-mixing interference magnetic field based on Faraday effect

In this paper, the magnetic field measurement method of laser self-mixing interference based on the Faraday effect is proposed. The polarization plane of the linearly polarized light is changed by the terbium gallium garnet crystal with the influence of the magnetic field. The light modulated by the magnetic field reentered into the laser cavity through the Brewster window and formed the self-mixing effect. The theoretical analysis of the self-mixing interference model based on the Faraday effect is conducted, which explains essential features of the experimental results. The magnetic field is measured by the peak-to-peak value of self-mixing interference signal. The experimental results show that the relative error of the magnetic field measurement is within ±1.6%. The measurement method has the advantage of simple and compact structure with strong anti-interference ability.

Laser self-mixing interference displacement signal filtering method based on empirical mode decomposition and wavelet threshold

In laser self-mixing interferometry displacement measurement, noise interference has a significant impact on the measurement results. To improve measurement accuracy, this paper proposes a filtering method that combines empirical mode decomposition (EMD) with wavelet thresholding. First, the signal is decomposed into several intrinsic mode functions (IMFs) using EMD. Then, wavelet thresholding is applied to each IMF. Subsequently, the processed IMFs are reconstructed to achieve signal filtering. Finally, by integrating the principles of interpolation and fringe counting, the reconstructed displacement signal is recovered, realizing accurate displacement measurement. This paper presents comprehensive simulation analyses and experimental validations for the proposed method. The accuracy of the displacement recovery is quantitatively evaluated using the absolute error and standard error, comparing the recovered displacement signal with the actual displacement. The experimental results demonstrate that the laser self-mixing interferometry displacement signal filtering method based on EMD and wavelet thresholding has high accuracy.

Laser Self-Mixing Interference: Optical Fiber Coil Sensors for Acoustic Emission Detection

Laser Self-Mixing Interference: Optical Fiber Coil Sensors for Acoustic Emission Detection

Denoising of Laser Self-Mixing Interference by Improved Wavelet Threshold for High Performance of Displacement Reconstruction

This article proposes an improved wavelet threshold denoising for laser self-mixing interference signals. The improved wavelet threshold function exhibits smoothness and continuity near the threshold. By replacing hard or soft wavelet threshold with the improved wavelet threshold, it can eliminate the generation of fake self-mixing interference peaks due to local oscillation induced by hard wavelet threshold, as well as the loss of self-mixing interference peaks due to over-smoothness induced by the soft wavelet threshold. Compared with hard and soft wavelet threshold denoising, theoretical simulations and experimental results demonstrate that the displacement of vibrations are well reconstructed based on the improved wavelet threshold denoising.

Combined Feature Extraction and Random Forest for Laser Self-Mixing Vibration Measurement without Determining Feedback Intensity.

To measure the vibration of a target by laser self-mixing interference (SMI), we propose a method that combines feature extraction and random forest (RF) without determining the feedback strength (C). First, the temporal, spectral, and statistical features of the SMI signal are extracted to characterize the original SMI signal. Secondly, these interpretable features are fed into the pretrained RF model to directly predict the amplitude and frequency (A and f) of the vibrating target, recovering the periodic vibration of the target. The results show that the combination of RF and feature extraction yields a fit of more than 0.94 for simple and quick measurement of A and f of unsmooth planar vibrations, regardless of the feedback intensity and the misalignment of the retromirror. Without a complex optical stage, this method can quickly recover arbitrary periodic vibrations from SMI signals without C, which provides a novel method for quickly implementing vibration measurements.

Measurement microscale vibration information with living biological probes

We report on the first demonstration of a living biological probe that is utilized to measure microscale vibration information. The microsphere-based living biological probes were precisely manipulated through optical fiber tweezers technology, enabling to transmission and focus of the emitted light on the surface of the vibrating microstructure and then combining it with laser self-mixing interference to obtain the microscale vibration information. Experiments show that the living probes can successfully detect the microscale vibration information of microstructure, and the relationship between the interference fringe number of the self-mixing signal and the peak-to-peak amplitude of the vibration of the microstructure was analyzed. The presented living probes may expand the application of optical fiber probes for detecting microscale vibration information in the biological field.

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.

All-fiber hybrid displacement-sensing system based on self-mixing interference and intracavity spectroscopy

Micro-displacement is a classic application of laser self-mixing interference (SMI) measurement system, but most of the current researches are focused on single-channel measurement. In this paper, a dual-channel displacement-sensing system is proposed and demonstrated based on the SMI effect and intracavity spectroscopy. The 90.14-pm/μm sensitivity for the displacement sensing can be achieved when the intracavity spectroscopy is employed to monitoring the output spectra. For the SMI operation mode, the variational mode decomposition (VMD) is used to decompose and reduce the noise of the SMI signal, and the interference fringe counting method is used to reconstruct the displacement of the noise-reduced SMI signal to realize the displacement measurement of the target object. It is demonstrated that the displacement-reconstruction error is 110 nm when the frequency is 30 Hz and the peak-to-peak amplitude is 4 μm.

Simultaneous displacement measurement method of multiple targets based on laser self-mixing interference

Simultaneous displacement measurement method of multiple targets based on laser self-mixing interference

Angle measurement method based on speckle affected laser self-mixing interference signal

Due to the speckle effect in the laser self-mixing interference (SMI), the signal amplitude will fluctuate greatly, which will affect the measurement accuracy and range. The angle measurement method based on speckle affected SMI signal is presented. The high frequency and low frequency noises in SMI signal can be filtered out simultaneously by variable mode decomposition. The envelope of SMI signal is calculated by Hilbert transform and the envelope signal is used to normalize the speckle affected SMI signal. The angle is calculated indirectly according to displacement measurement results obtained by fringe counting method. The experimental results show that the relative error of angle is ±2% with the angle measurement range of 1°.

A new fiber self-mixing temperature sensor with phase compensation for harmonic vibrations

Abstract A new fiber temperature sensor is proposed based on dual-longitudinal mode laser self-mixing interference effect in a distributed Bragg reflector fiber laser. The temperature analytical model is established by use of the three-mirror cavity model and the interference superposition theory of the multi-longitudinal mode laser. It is indicated that this preferable model is sufficient to real-time track the change of the self-mixing signal waveform resulting from the ambient temperature variation by means of the phase compensation method and the waveform separation phenomena. Furthermore, the experimental measurements show that the relative error can be lower to 1.43% corresponding to 4.95 × 10-4 m/°C of the temperature sensitivity ranging from 20.14 to 46.02 °C. It has demonstrated that the measured results are in good consistent with the reference values, thereby which this sensor proves capable of measuring ambient temperature with high sensitivity and accuracy.

A Method of Human Eye Parameter Measurement Based on Laser Self-Mixing Interference

The eye is the most important sensory organ of the human body, and the cornea and anterior chamber are very important components In surgeries like vision correction, it is necessary to know the accurate corneal thickness and anterior chamber depth of human eyes. Their accurate measurement cannot only provide a reference for doctors, but also provide a strong guarantee of surgical results. In order to achieve high-precision measurements of human corneal thickness and anterior chamber depth, we develop an equivalent human-eye optical system and a measurement method for the thickness. This method designs an equivalent double-membrane system to simplify the physiological structure of the cornea and anterior chamber of the human eye and irradiate the double-membrane system through laser. The reflected light returns to the laser cavity and the original light self-mixing interference, and a photodetector collects and processes the interference signals to obtain the corneal thickness and anterior chamber depth. The correctness of the theoretical calculations is verified by the experimental system, and the measurement accuracy can reach the micrometer level.

Displacement measurement method based on laser self-mixing interference in the presence of speckle

In order to achieve the accurate measurement of displacement, this Letter presents a self-mixing interference displacement measurement method suitable for the speckle effect. Because of the speckle effect, the amplitude of the self-mixing interference signal fluctuates greatly, which will affect the measurement accuracy of displacement. The ensemble empirical mode decomposition is used to process the interference signal, which can filter out high-frequency noise and low-frequency noise at the same time. The envelope of the self-mixing interference signal is extracted by Hilbert transform, and it is used to realize the normalization of the signal. Through a series of signal processing, the influence of speckle can be effectively reduced, and the self-mixing interference signal can be transformed into standard form. The displacement can be reconstructed by fringe counting and the interpolation method. The experimental results show that the method is successfully applied to the displacement measurement in the presence of speckle, which verifies the effectiveness and feasibility of the method.

Laser self-mixing interference displacement measurement based on VMD and phase unwrapping

In order to measure displacement accurately and conveniently, the laser self-mixing interference measurement method based on variational mode decomposition (VMD) and phase unwrapping is proposed. The laser self-mixing interference technology has many advantages such as high sensitivity, ease of use and compactness. The VMD method can non-recursively decompose a self-mixing interference signal into a number of intrinsic mode functions and remove noise effectively. The linewidth enhancement factor and the optical feedback level factor are measured by the hysteresis phenomenon in the self-mixing interference. The reconstruction of displacement is implemented by phase unwrapping. The displacement measurement is carried out by the self-mixing interference experimental system. The experimental results show that the displacement measurement error is less than 80 nm, which verifies the correctness of the method.

Low-cost planar vibration sensor using a modified computer mouse

PurposeThe purpose of this study aims to modify a self-mixing laser mouse as an extremely cost-effective displacement sensor to measure the mechanical oscillation of a commercial shaker and a nano-positioning stage.Design/methodology/approachThis kind of laser mouse, mostly consisting of a pair of vertical cavity surface emitting lasers, two photodiodes and an integrated signal processing unit, is capable of directly giving the x-axis and y-axis components of the measured vibrating displacement. Based on the laser self-mixing interference, the velocity of the object is coded into the Doppler frequency shift of the feedback light, which allows accurate determination of the vibration of the object.FindingsA commercial shaker has been used to provide standard harmonic oscillation to test the displacement sensor. Within a vibrating frequency range of 110 Hz, the experimental results show that the micrometer scale resolution has been achieved at the velocity of up to 2 m/s, which is much improved compared with the image-based optical mouse. Furthermore, the measurements of the two dimensional displacement of a nano-positioning stage are performed as well. The minimum measurable velocity limit for this sensor has been discussed in detail, and the relative measurement error can be greatly reduced by appropriate selection of the modulation frequency of the triangular injection current.Originality/valueThese results demonstrate the feasibility of this device for the industrial vibration sensing applications.

Rotation velocity measurement based on self-mixing interference with a dual-external-cavity single-laser diode.

A novel Doppler velocity measurement method based on laser self-mixing interference with two parallel optical external cavities is investigated. In this method, the target object rotation velocity can be measured by the sum of two Doppler frequency shifts, which can be extracted by fast Fourier transform without setting and measuring incident angles. This study highlights the validity of the proposed method through a theoretical model analysis. Experiments realized velocity measurement with a relative error of less than 0.6%.

Large range stress measurement system based on large frequency difference laser self-mixing interference

Stress-birefringence measurement is critical in optical glass materials. A laser self-mixing interference (SMI) stress measurement system with a measuring range of 1 deg to 179 deg is presented. The light source of the system is a He-Ne laser with a variable frequency difference. Birefringent external cavity SMI experiments are conducted with the laser with different frequency differences. Experimental results show that a large frequency difference decreases the cross-saturation effect between the two laser eigenstates, and alternate oscillations are more likely to occur, which directly improves the sensitivity and expands the measuring range of the system. A piece of neodymium glass is tested with the system and the results are given, proving that the large frequency difference laser SMI system provides a simple, low-cost, and high-sensitivity stress measurement method.

ℓ1Time- and frequency-domain verification of laser self-mixing interference with two-external-cavity feedbackℓ1

ℓ1Time- and frequency-domain verification of laser self-mixing interference with two-external-cavity feedbackℓ1

Improvement on vibration measurement performance of laser self-mixing interference by using a pre-feedback mirror

In the laser self-mixing interference vibration measurement system, the self mixing interference signal is usually weak so that it can be hardly distinguished from the environmental noise. In order to solve this problem, we present a self-mixing interference optical path with a pre-feedback mirror, a pre-feedback mirror is added between the object and the collimator lens, corresponding feedback light enters into the inner cavity of the laser and the interference by the pre-feedback mirror occurs. The pre-feedback system is established after that. The self-mixing interference theoretical model with a pre-feedback based on the F–P model is derived. The theoretical analysis shows that the amplitude of the intensity of the interference signal can be improved by 2–4 times. The influence factors of system are also discussed. The experiment results show that the amplitude of the signal is greatly improved, which agrees with the theoretical analysis.