Method and equipment for dimensional measurement of a micro part based on fiber laser with multi-core FBG probe

Patent metadata

Field	Value
Publication number	US-10082383-B2
Application number	US-201615555028-A
Country	US
Kind code	B2
Filing date	Mar 4, 2016
Priority date	Mar 5, 2015
Publication date	Sep 25, 2018
Grant date	Sep 25, 2018

Abstract

A method and equipment for dimensional measurement of a micro part based on fiber laser with multi-core fiber Bragg grating probe are provided, wherein a multi-core FBG probe with FBGs ( 12,29 ) inscribed in the core or cores out of the center of the multi-core fiber is used to transform the two-dimensional or three-dimensional contact displacement into the spectrum shifts with a high sensitivity. At the meantime, the FBGs in the multi-core FBG probe ( 12,29 ) work as the wavelength selection device of the fiber laser, the wavelength of the fiber laser will change thereby. So the contact displacement is finally converted into the wavelength change of the fiber laser. The method and equipment have the advantage of high sensitivity, low probing force, compact structure, high inspecting aspect ratio and immunity to environment interference.

First claim

What is claimed is:

1. A method for dimensional measurement of a micro part based on a multi-core Fiber Bragg Grating (FBG) probe, comprising:
directing a pumping light generated by an optical pumping source into a gain medium erbium-doped fiber through a wavelength division multiplexer (WDM) to generate a stimulated emission light;
dividing the stimulated emission light into two portions with one portion being directed to a ring cavity composed by the WDM, an erbium-doped fiber, a circulator, the coupler and an isolator connected successively, and with the other portion being used as an output laser; wherein the portion of the stimulated emission light propagating in the ring cavity is directed into a first port of the circulator and is directed out from a second port of the circulator and then passes through a saturable absorber for eliminating multi-longitudinal mode oscillation and suppressing mode hopping to obtain a single longitudinal mode light with a narrow line width;
directing the single longitudinal mode light into a wavelength selection device which includes a multi-core FBG probe and an external reference FBG; the single longitudinal mode light is reflected into the second port of the circulator and is directed out from a third port, and continues to propagate along the ring cavity; wherein as pumping power increases, spontaneous emission is gradually suppressed and a stable output of the system with a single longitudinal mode and narrow line width is obtained;
contacting the multi-core FBG probe with the micro part to shift the center wavelength of a reflected spectrum of the multi-core FBG to changes the wavelength of the output laser;
detecting respective center wavelengths of the output laser with the multi-core FBG in the probe and the external reference FBG as the wavelength selection device; and
calculating, by a measurement computer a relative contact displacement of the probe from a zero-force position based on the detected center wavelengths of the output laser through a data processing process to achieve the dimensional measurement of the micro part.

2. The method of claim 1 , wherein the multi-core FBG probe is a twin FBG probe; and
wherein the data processing process comprising:
obtaining two wavelength values of the laser output from the fiber ring laser with each of the two FBG in the twin FBG probe works as the laser wavelength selection device of the fiber ring laser;
differentiating the two laser wavelengths value to decouple one-dimensional radial displacement along the axis determined by the two fibers of the twin FBG probe and a temperature drift;
and in the meantime,
obtaining an average value of the two laser wavelength values; and
differentiating the average value with the output laser wavelength value with the external reference FBG works as the laser wavelength selection device to obtain a result of the axial displacement without coupled radial displacement and a temperature drift.

3. The method of claim 1 , wherein the multi-core FBG probe is a two-core FBG probe; and
wherein the data processing process comprising:
obtaining two wavelength values of the laser from the fiber ring laser respectively with each of the two FBGs in the two-core FBG probe works as the laser wavelength selection device;
differentiating the two laser wavelength values to decouple one-dimensional radial displacement along the axis determined by the two cores of the two-core FBG probe and a temperature drift;
and in the meantime,
obtaining an average value of the two laser wavelength values; and
differentiating the average value with an output laser wavelength value with the external reference FBG works as the laser wavelength selection device to obtain a result of the axial displacement without coupled radial displacement and a temperature drift.

4. The method of claim 1 , wherein the multi-core FBG probe is a three-core FBG probe; and wherein the data processing process comprising
obtaining wavelength values of the laser with each of the two eccentric FBGs in the three-core FBG probes works as the laser wavelength selection device respectively, and
differentiating the two wavelength values to decouple one-dimensional radial displacement along the axis determined by the two eccentric cores of the three-core FBG probe and a temperature drift;
in the meantime,
obtaining the output laser wavelength values of the center FBG in the three-core FBG probe and the external reference FBG with the center FBG in the three-core FBG probe and the external reference FBG ( 7 ) works as the laser wavelength selection device respectively; and
differentiating the two output laser wavelength values to obtain a result of the axial displacement without coupled radial displacement and a temperature drift.

5. The method of claim 1 , wherein the multi-core FBG probe is a four-core FBG probe; and wherein the data processing comprising:
obtaining output laser wavelength values from two sets of orthogonal eccentric FBGs in the four-core FBG probe with each of the two sets of orthogonal eccentric FBGs being chosen as wavelength selection devices of the optical fiber ring laser;
differentiating two output laser wavelengths in each set respectively to decouple two-dimensional radial displacement along the axes determined by the two orthogonal eccentric cores of the four-core FBG probe and a temperature drift; and
obtaining an average value of four output laser wavelength values with each of the four FBGs in the four-core FBG probe selected as the laser wavelength selection;
differentiating the average value with an output laser wavelength value with the external reference FBG works as the laser wavelength selection device to obtain a result of the axial displacement without coupled radial displacement and a temperature drift.

6. The method of claim 1 , wherein the multi-core FBG probe is a five-core FBG probe; and wherein the data processing comprising:
obtaining two output laser wavelength values from two sets of orthogonal eccentric FBGs in the five-core FBG probe with each of the two sets of orthogonal eccentric FBGs being chosen as the optical fiber ring laser wavelength selection devices;
differentiating the two output laser wavelengths in each set respectively to decouple two-dimensional radial displacement along the axes determined by the two orthogonal eccentric cores of the five-core FBG probe and a temperature drift;
in the meantime,
obtaining two output laser wavelength values of the center FBG in the five-core FBG probe and the external reference FBG with the center FBG in the five-core FBG probe and the external reference FBG work as the laser wavelength selection device respectively; and
differentiating the two wavelengths to obtain an axial displacement without coupled radial displacement and a temperature drift.

7. A method for dimensional measurement of a micro part based on linear cavity fiber laser and a multi-core Fiber Bragg Grating (FBG) probe, comprising:
generating a pumping light by a pumping source,
directing the pumping light to passes through a first port of a wavelength division multiplexer (WDM) to enter into a linear cavity composed by a single core FBG, an erbium-doped fiber, an external reference FBG or a single core FBG, an erbium-doped fiber, and the multi-core FBG probe connected successively to produce a stimulated emission light when the pumping light passes through the erbium-doped fiber; wherein the stimulated emission light is reflected a plurality of times in the linear cavity to enhance its intensity; when the gain is greater than the loss in one period of oscillation in the cavity, it will output laser with narrow line width;
directing the stimulated emission light out of a second port of the WDM directing the s

Assignees

• Harbin Inst Technology

Inventors

• Cui Jiwen
• Zhao Shiyuan
• Feng Kunpeng
• Dang Hong
• Li Junying
• Tan Jiubin

Classifications

• G02B6/02042

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• G01B11/007 Primary

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• H01S3/1608

  erbium · CPC title

• H01S3/06791

  Fibre ring lasers (fibre laser gyrometers G01C19/72) · CPC title

• G01B5/012

  Contact-making feeler heads therefor · CPC title