Kunpeng Feng

FBG Interrogation Method with High Resolution and Response Speed Based on a Reflective-Matched FBG Scheme

In this paper, a high resolution and response speed interrogation method based on a reflective-matched Fiber Bragg Grating (FBG) scheme is investigated in detail. The nonlinear problem of the reflective-matched FBG sensing interrogation scheme is solved by establishing and optimizing the mathematical model. A mechanical adjustment to optimize the interrogation method by tuning the central wavelength of the reference FBG to improve the stability and anti-temperature perturbation performance is investigated. To satisfy the measurement requirements of optical and electric signal processing, a well- designed acquisition circuit board is prepared, and experiments on the performance of the interrogation method are carried out. The experimental results indicate that the optical power resolution of the acquisition circuit border is better than 8 pW, and the stability of the interrogation method with the mechanical adjustment can reach 0.06%. Moreover, the nonlinearity of the interrogation method is 3.3% in the measurable range of 60 pm; the influence of temperature is significantly reduced to 9.5%; the wavelength resolution and response speed can achieve values of 0.3 pm and 500 kHz, respectively.

A Twin Fiber Bragg Grating Probe for the Dimensional Measurement of Microholes

A fiber probe with a novel structure of twin fiber Bragg grating sensitive to both contacts along x-axis and z-axis is proposed for measurement of microholes with high aspect ratio. The main conundrums during the dimensional measurement of microholes with high aspect ratio, such as shadowing effect, limited probing space, and requirement of multidimensional tactile sense are well solved using the proposed probe. Sensing principle and decoupling algorithm has been verified through experiments. Experimental results indicate that the influence of manufacture defects and the misalignment between probe and measurement coordinates can be reduced through rotation and tilt calibration. The contact displacement sensitivity is 12.91 pm/μm and 49.75 pm/μm along x-axis and z-axis, respectively. A microhole with an aspect ratio of 10:1 can be measured using the proposed twin fiber Bragg grating probe.

A Twin FBG Probe and Integration With a Microhole-Measuring Machine for the Measurement of Microholes of High Aspect Ratios

To enhance the precision manufacture of the microholes of high aspect ratios, a fiber Bragg grating (FBG) probe with a twin fiber structure based on capillary-driven self-assembly fabrication method is developed for a micro-hole-measuring machine to do the high-precision measurement. The sensing principle of the twin FBG probe is investigated through analyzing the strain distribution within the probe under an axial or radial contact displacement. Then, the design and fabrication method of the twin FBG probe is demonstrated. To improve the accuracy of the measurement, both data processing method and measuring method are proposed. A data processing method for acquiring the triggering position with the transformation of the signal domain and multiple fitting is implemented to raise the accuracy of the triggering position. And a method for measuring the diameter of a microhole with perpendicular bisector of the chords and dichotomization scanning is utilized to enhance the determination accuracy of the diameter. Experimental and simulation results indicate that the data processing method and measuring method are robust, and the accuracy of the measurement can be improved.

Double fiber probe with a single fiber Bragg grating based on the capillary-driven self-assembly fabrication method for dimensional measurement of micro parts

Focusing on the ultra-precision dimensional measurement of parts with micro-scale dimensions and high aspect ratios, a two-dimensional double fiber probe with a single fiber Bragg grating (DS-FBG probe) is investigated in detail in this paper. The theoretical analysis of the sensing principle is verified by spectrum simulations of the DS-FBG probe with a modified transfer matrix method using the strain distribution within the DS-FBG probe. The fabrication process and physical principle of the capillary-driven self-assembly of double fibers in the UV adhesive with a low viscosity are demonstrated. Experimental results indicate that resolutions of 30 nm in radial direction and 15 nm in axial direction can be achieved, and the short-term displacement drifts within 90 seconds are 28.0 nm in radial direction and 7.9 nm in axial direction, and the long-term displacement drifts within 1 hour are 61.3 nm in radial direction and 17.3 nm in axial direction. The repeatability of the probing system can reach 60 nm and the measurement result of a standard nozzle is 300.49 μm with a standard deviation of 20 nm.

Three-dimensional fiber probe based on orthogonal micro focal-length collimation for the measurement of micro parts.

A 3-dimensional fiber probe based on orthogonal micro focal-length collimation (MFL-collimation) is proposed for the measurement of micro parts with high aspect ratios. The probe consists of a fiber stylus which acts as a micro focal-length cylindrical lens (MFLC-lens) of the two orthogonal MFL-collimation optical paths and a probe tip fixed on the free end of the fiber stylus for touching the workpiece. The fiber stylus will deflect (deflection mode) or buckle (buckling mode) under contacts, and the deflection or buckling of the fiber stylus will cause corresponding shifts of the fringe images of the two orthogonal MFL-collimation optical paths. Therefore, the 3-dimensional displacements of the probe tip are transformed into the centroid position shifts of the zero-order fringe images. Experimental results indicate that the fiber probe has a measuring capability in 3-dimensional tactility, and a radial and axial resolution of 5 nm and 3 nm can be obtained respectively. The probe is easily applied in the measurement of micro parts because of its high resolution, low cost, high measurable aspect ratio, low probing forces and capability in three-dimensional tactility.

Development of FBG probes for dimensional metrology with micro parts of high aspect ratio

The development is described of fiber Bragg grating (FBG) probes with single or four cores using spheres fixed onto optical fibers comprising Bragg gratings in their cores. Simulations and preliminary experiments were conducted to evaluate the performance of these FBG probes for dimensional metrology with micro parts of high aspect ratio. Simulation and experimental results indicate that a one-dimensional FBG probe with single core can be used to achieve an axial resolution of 100 nm at an aspect ratio of 15:1. A three-dimensional FBG probe with four cores can be used to achieve a theoretical axial resolution as high as that of a FBG probe with single core, with a capability of decoupling two-dimensional radial displacements with a resolution of 13 nm.

A 3D fiber probe based on orthogonal micro focal-length collimation and fiber Bragg grating

A 3D fiber probe is proposed for the precision measurement of micro parts with high aspect ratios. The probing system consists of two measuring systems: two mutually orthogonal micro focal-length collimation optical paths for the radial tactile probing measurement, and a matched fiber Bragg grating (FBG) pair interrogation system for the axial tactile probing measurement. The fiber probe consists of a fiber stylus and a probe tip, the fiber stylus works as a micro focal-length cylindrical lens, and the FBG inscribed in the fiber stylus works as a measuring FBG. The radial displacement of the probe tip is transformed into the centroid position shift of the two mutually orthogonal micro focal-length collimation optical paths; the axial displacement of the probe tip is transformed into the power ratio change of the matched FBG pair interrogation system. Experimental results indicate that the probe has a radial sensitivity of 71 pixel μm−1 in both X and Y directions, and an axial sensitivity of 4.9% μm−1 in Z direction; the probe can reach a radial resolution of 5 nm, and an axial resolution of 8 nm. The probe has a capability of decoupling the 3D tactility and it can be applied in the measurement of micro parts.

Four-Cores FBG Probe Based on Capillary Self-Assembly Fabrication Technique for 3D Measurement

A three-dimensional (3D) four-cores fiber Bragg grating (FBG) probe is developed by doubling the twin FBG structure to extend the 2D radial tactile capacity of an FBG probe. The measuring principle of the four-cores FBG is thoroughly investigated and the four-cores structure is also found to have a benefit of orthogonal radial decoupling capacity. To avoid the inscription of four-cores FBG and usage of fan-out device, and make the four-cores fiber customizable, a new approach, capillary self-assembly technique of optical fibers, is researched and an external constraint is introduced into a self-assembly system to fabricate square four-cores FBG using four single-core FBGs. The spectrum characteristic and performance of the four-cores FBG probe are thus much improved. Advantages of the probe and fabrication technique are low cost, customizable design, high precision, and high aspect ratio.

An example image super-resolution algorithm based on modified k-means with hybrid particle swarm optimization

This paper presents a novel example-based super-resolution (SR) algorithm with improved k-means cluster. In this algorithm, genetic k-means (GKM) with hybrid particle swarm optimization (HPSO) is employed to improve the reconstruction of high-resolution (HR) images, and a pre-processing of classification in frequency is used to accelerate the procedure. Self-redundancy across different scales of a natural image is also utilized to build attached training set to expand example-based information. Meanwhile, a reconstruction algorithm based on hybrid supervise locally linear embedding (HSLLE) is proposed which uses training sets, high-resolution images and self-redundancy across different scales of a natural image. Experimental results show that patches are classified rapidly in training set processing session and the runtime of reconstruction is half of traditional algorithm at least in super-resolution session. And clustering and attached training set lead to a better recovery of low-resolution (LR) image.

Investigation and development of a high spectral resolution coherent optical spectrum analysis system.

Focusing on high resolution optical spectroscopy, a coherent optical spectrum analysis (COSA) system is investigated in this paper. Principle is built to demonstrate the operation of COSA and its signal processing in both time and frequency domain. According to COSA principle, resolution bandwidth (RBW) filters are found to have significant influence on power accuracy and spectral resolution of the optical spectrum analysis (OSA). Much effort is paid to design RBW filters, including center frequency, bandwidth and type of filters. Two RBW filters are optimized to reduce the power uncertainty of different spectral resolution and satisfy different signal under test. Then, simulations and experiments are conducted to verify COSA principle and results show that the power uncertainty is less than 0.5% and 1.2% for high and medium spectral resolution application, respectively. Finally, experiments on the OSA of actual spectra indicate that COSA system can achieve a 6 MHz spectral resolution and has an excellent capacity in analysis of fine spectrum structures.