METHOD AND EQUIPMENT FOR DIMENSIONAL MEASUREMENT OF A MICRO PART BASED ON FIBER LASER WITH MULTI-CORE FBG PROBE

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.

Claims

1. A method for dimensional measurement of a micro part based on ring fiber laser with a multi-core fiber Bragg grating (FBG) probe, comprising: directing a pumping light generated by an optical pumping source (1) into a gain medium erbium-doped fiber through a wavelength division multiplexer (WDM) (2) and generates a stimulated emission light; dividing by a coupler (16) the stimulated emission light into two portions with one portion being directed to a ring cavity composed by the WDM (2), an erbium-doped fiber (3), a circulator 4, the coupler (16) and an isolator (15b) successively; the other portion is used as a laser output; the portion propagating in the ring cavity is directed into a port A of the circulator (4) and is directed out from port B and then passes through a saturable absorber (5) for eliminating multi-longitudinal mode oscillation and suppressing mode hopping to obtain a single longitudinal mode light with a narrow line width; directing the light enters a wavelength selection device which includes a multi-core FBG probe (12) and an external reference FBG (7); the light portion is reflected into the port B of the circulator and is directed out from port C, and continues to propagate along the ring cavity; with the increase of pumping power, the spontaneous emission being gradually suppressed and finally a stable output of the system with a single longitudinal mode and narrow line width; contacting the multi-core FBG probe with the part under test, to shift the center wavelength of reflected spectrum of FBG to changes the wavelength of the output laser; detecting by an optical spectrum analyzer (14) the wavelength of output laser which is wavelength selected by the multi-core FBG in the probe (12) and external reference FBG (7) by switching a multi-channel optical switches (6); and calculating a relative contact displacement of the probe from a zero-force position to achieve the dimensional measurement of the micro part.

2. The method of claim 1, wherein the multi-core FBG probe (12) is a twin FBG probe (33); during data processing, obtaining wavelength of the laser output from the fiber ring laser the two FBGs in the two FBG probes work as laser wavelength selection device respectively, 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 temperature drift; in the meantime, obtaining an average value of these two laser wavelength and differentiating the average value with an output laser wavelength with the external reference FBG (7) works as the laser wavelength selection device to obtain a result of the axial displacement without coupled radial displacement and temperature drift.

3. The method of claim 1, wherein the multi-core FBG probe (12) is a two-core FBG probe (35); in data processing, obtaining two wavelengths of the laser from the fiber ring laser respectively with the two FBGs in the two-core FBG probe work as the laser wavelength selection device; differentiating these two laser wavelength to decouple one-dimensional radial displacement along the axis determined by the two cores of the two-core FBG probe and temperature drift; in the meantime, obtaining an average value of these two laser wavelength and differentiating the average value with an output laser wavelength with the external reference FBG (7) works as the laser wavelength selection device to obtain a result of the axial displacement without coupled radial displacement and temperature drift.

4. The method of claim 1, wherein the multi-core FBG probe (12) is a three-core FBG probe (37); in data processing, obtaining wavelength of the laser with two eccentric FBGs in the three-core FBG probes work as the laser wavelength selection device respectively, and differentiating these two wavelengths to decouple one-dimensional radial displacement along the axis determined by the two eccentric cores of the three-core FBG probe and temperature drift; in the meantime, obtaining output laser wavelengths of the center FBG in the three-core FBG probe and the external reference FBG (7) with the center FBG in the three-core FBG probe and the external reference FBG (7) are selected as the laser wavelength selection device respectively, differentiating these two output laser wavelengths to obtain a result of the axial displacement without coupled radial displacement and temperature drift.

5. The method of claim 1, wherein the multi-core FBG probe (12) is a four-core FBG probe (39); in data processing, obtaining output laser wavelengths from two sets of orthogonal eccentric FBGs in the four-core FBG probe with the two sets of orthogonal eccentric FBGs chosen as the optical fiber ring laser wavelength selection devices respectively; 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 temperature drift; and obtaining an average of four output laser wavelength with the four FBGs in the four-core FBG probe selected as the laser wavelength selection respectively; differentiating the average value with an output laser wavelength with the external reference FBG (7) works as the laser wavelength selection device to obtain a result of the axial displacement without coupled radial displacement and temperature drift.

6. The method of claim 1, wherein the multi-core FBG probe (12) is a five-core FBG probe (41); in data processing, obtaining output laser wavelengths from two sets of orthogonal eccentric FBGs in the five-core FBG probe with the two sets of orthogonal eccentric FBGs chosen as the optical fiber ring laser wavelength selection devices respectively; 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 five-core FBG probe and temperature drift; in the meantime, obtaining output laser wavelengths 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 a result of the axial displacement without coupled radial displacement and temperature drift.

7. A equipment for dimensional measurement of a micro part based on ring fiber laser with a multi-core FBG probe, comprising: a pumping source (1) connected with a ring cavity (17) through a wavelength division multiplexer (2), a fiber ring laser cavity (17) consisting of a wavelength division multiplexer (2), an erbium-doped fiber (3), a circulator (4), a coupler (16) and an isolator (15b), a multi-core FBG probe (12) for sensing contact displacement, a saturable absorber (5) used to eliminate the multi-longitudinal mode oscillation and suppress the mode hopping, a multi-channel optical switch (6) controlled by a measurement computer (13) for switching optical paths of multi-core FBG probe (12) and the external reference FBG (7) in a time-division-multiplexing manner, a multi-core fiber fan-out (9) for making single mode fibers (8) access to every core of the multi-core fiber probe (12), a multi-core fiber (10) for connecting the multi-core fiber fan-out (9) with the multi-core fiber probe (12), a reference FBG (7) for compensating temperature drift, an optical spectrum analyzer (14) for detecting output laser wavelength, a measurement computer (13) utilized to calculate the contact displacement of the multi-core FBG probe and control the switch of the multi-channel optical switch (6); the coupler (16) is connected to the optical spectrum analyzer (14) and the measurement computer (13) through the isolator (15a); the multi-channel optical switch (6) is linked with the circulator (4) through the saturable absorber (5), and is also linked with a multi-core fiber through single mode fibers (8) and the multi-core fiber fan-out (9); the multi-channel optical switch (6) is connected to the measurement computer (13) and is also connected to the reference FBG (7); the multi-core FBG probe (12) is fixed by a probe holder on the bottom of the multi-core fiber (10); the multi-core FBG probe (12) and the reference FBG (7) are chosen as a wavelength selection device in turn by switching the multi-channel optical switch.

8. The equipment of claim 7, wherein the multi-core FBG probe is a twin FBG 33.

9. The equipment of claim 7, wherein the multi-core FBG probe is a two-core FBG (35).

10. The equipment of claim 7, wherein the multi-core FBG probe is a three-core FBG (37).

11. The equipment of claim 7, wherein the multi-core FBG probe is a four-core FBG (39).

12. The equipment of claim 7, wherein the multi-core FBG probe is a five-core FBG (41).

13. A method for dimensional measurement of a micro part based on linear fiber laser with a multi-core FBG probe, comprising: generating a pumping light by a pumping source (19), directing the pumping light to passes through a port of a wavelength division multiplexer (WDM) 20 and enters into a linear cavity composed of a single core FBG (21), an erbium-doped fiber (22), an external reference FBG (24) or a single core FBG (21), an erbium-doped fiber (22), a multi-core FBG probe (29) successively; and a stimulated emission light is produced when the light passes through the gain medium erbium-doped fiber; the stimulated emission light is reflected for many times in the linear cavity and its intensity is enhanced; when the gain is greater than the loss in one period of oscillation in the cavity, it will output laser with narrow linewidth; directing the stimulated emission light out of another port of WDM (20) and is detected by an optical spectrum analyzer (31); contacting the multi-core FBG probe (29) with the part under test, the center wavelength of reflected spectrum of FBG will shift, which changes the wavelength of the output laser; detected by an optical spectrum analyzer (31) the wavelength of output laser which is wavelength selected by the multi-core FBG in the probe (29) and external reference FBG (24) by switching multi-channel optical switches (23) controlled by the measurement computer (32); calculating the relative contact displacement of the probe from a zero-force position.

14. The method of claim 13, wherein the multi-core FBG probe 29 is a twin FBG probe 33; in data processing, obtaining laser output wavelengths from the fiber ring laser with the two FBGs in the two FBG probe work as laser wavelength selection device respectively and differentiating the wavelengths to decouple one-dimensional radial displacement along the axis the axis determined by the two fibers of the twin FBG probe and temperature drift; at the same time, obtaining an average value of these two wavelengths; and differentiating the average value with the output laser wavelength with the external reference FBG (24) works as the laser wavelength selection device to obtain a result of the axial displacement without coupled radial displacement and temperature drift.

15. The method of claim 13, wherein the multi-core FBG probe 29 is a two-core FBG probe (35); in data processing, obtaining wavelengths of the laser from the fiber ring laser with the two FBGs in the two-core FBG probe work as the laser wavelength selection device respectively; and differentiating these two wavelengths to decouple one-dimensional radial displacement along the axis determined by the two cores of the two-core FBG probe and temperature drift; at the same time, obtaining an average value of these two laser wavelengths and differentiating the average value with an output laser wavelength when the external reference FBG (24) works as the laser wavelength selection device to obtain a result of the axial displacement without coupled radial displacement and temperature drift.

16. The method of claim 13, wherein the multi-core FBG probe (29) is a three-core FBG probe (37); in data processing, obtaining a wavelength of the laser with two eccentric FBGs in the three-core FBG probe work as the laser wavelength selection device respectively; and differentiating these two wavelengths to decouple one-dimensional radial displacement along the axis determined by the two eccentric cores of the three-core FBG probe and temperature drift; in the meantime, obtaining output laser wavelengths of the center FBG in the three-core FBG probe with the external reference FBG (24) as works the laser wavelength selection device respectively and differentiating the two output laser wavelengths to obtain a result of the axial displacement without coupled radial displacement and temperature drift.

17. The method of claim 13, wherein the multi-core FBG probe 29 is a four-core FBG probe 39; in data processing, obtaining laser output wavelengths with the two sets of orthogonal eccentric FBGs in the four-core FBG probe chosen as the optical fiber ring laser wavelength selection devices respectively; differentiating the wavelengths to decouple two-dimensional radial displacement along the axes determined by the two orthogonal eccentric cores of the four-core FBG probe and temperature drift; and obtaining an average of four output laser wavelength when the four FBGs in the four-core FBG probe are chosen as the laser wavelength selection respectively; at the same time, and differentiating the average value with an output laser wavelength recorded when the external reference FBG 24 works as the laser wavelength selection device to obtain a result of the axial displacement without coupled radial displacement and temperature drift.

18. The method of claim 13, wherein the multi-core FBG probe 29 is a five-core FBG probe 41; in data processing, the two sets of orthogonal eccentric FBGs in the five-core FBG probe are chosen as the optical fiber ring laser wavelength selection devices respectively; according to the differential data of two in each set respectively, two-dimensional radial displacement along the axes determined by the two orthogonal eccentric cores of the five-core FBG probe and temperature drift be decoupled; at the same time, obtaining output laser wavelengths 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 output laser wavelengths to obtain a result of the axial displacement without coupled radial displacement and temperature drift.

19. A equipment for dimensional measurement of a micro part based on linear fiber laser with a multi-core FBG probe for, comprising: a single core FBG (21), an erbium-doped fiber (22), an external reference FBG (24) or a single core FBG (21), an erbium-doped fiber (22), a multi-core FBG probe (29) successively, a pumping source (19), connected to a linear cavity through a first port of the wavelength division multiplexer (20); a second port of WDM (20) is connected to an optical spectrum analyzer (31) and a measurement computer (32) through an isolator (30), a multi-core FBG probe (29) for sensing contact displacement, a multi-channel optical switch (23) controlled by the measurement computer (32) for switching optical paths of multi-core FBG probe (29) and the external reference FBG (24) in a time-division-multiplexing manner, a multi-core fiber fan-out (26) for making single mode fibers (25) access to each core of the multi-core fiber probe (29), a multi-core fiber (27) for connecting the multi-core fiber fan-out (26) with the multi-core fiber probe (29), a reference FBG (24) for compensating temperature drift, an optical spectrum analyzer (31) for detecting output laser wavelength, a measurement computer (32) utilized to calculate a contact displacement of the multi-core FBG probe (29) and control the switch of the multi-channel optical switch (23), the multi-core FBG probe (29) is fixed by the probe holder (28) on the bottom of the multi-core fiber (27); the multi-core FBG probe (29) and the reference FBG (24) can be switched by the multi-channel optical switch (23) to be a wavelength selection device respectively; the working condition of linear output response of the method and device for dimensional measurement of a micro part is defined by: $0.8.Math.\sqrt{\frac{{\mathrm{\Delta \lambda }}_1^2+{\mathrm{\Delta \lambda }}_3^2}{8.Math..Math.\ln .Math..Math.2}}\le .Math.{\lambda }_1-{\lambda }_3.Math.\le 1.2.Math.\sqrt{\frac{{\mathrm{\Delta \lambda }}_1^2+{\mathrm{\Delta \lambda }}_3^2}{8.Math..Math.\ln .Math..Math.2}},.Math.0.8.Math.\sqrt{\frac{{\mathrm{\Delta \lambda }}_2^2+{\mathrm{\Delta \lambda }}_3^2}{8.Math..Math.\ln .Math..Math.2}}\le .Math.{\lambda }_2-{\lambda }_3.Math.\le 1.2.Math.\sqrt{\frac{{\mathrm{\Delta \lambda }}_2^2+{\mathrm{\Delta \lambda }}_3^2}{8.Math..Math.\ln .Math..Math.2}}$ respectively wherein λ.sub.1 is the initial center wavelength of the reference FBG (24), λ.sub.2 is the initial center wavelength of multi-core FBG in the multi-core FBG probe (29) and λ.sub.3 is the initial center wavelength of single core FBG (21).

20. The equipment of claim 19, wherein the multi-core FBG probe is a twin FBG (33).

21. The equipment of claim 19, wherein the multi-core FBG probe is a two-core FBG (35).

22. The equipment of claim 19, wherein the multi-core FBG probe is a three-core FBG (37).

23. The equipment of claim 19, wherein the multi-core FBG probe is a four-core FBG (39).

24. The equipment of claim 19, wherein the multi-core FBG probe is a five-core FBG (41).

Description

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

[0012] FIG. 1: construction of equipment based on ring fiber laser with a multi-core FBG probe for dimensional measurement of a micro part;

[0013] FIG. 2: construction of equipment based on linear fiber laser with a multi-core FBG probe for dimensional measurement of a micro part;

[0014] FIG. 3 (a): a cross-sectional view of multi-core FBG probe embodied as a twin FBG;

[0015] FIG. 3 (b): a section A.sub.1-A.sub.1 view of multi-core FBG probe embodied as a twin FBG;

[0016] FIG. 3 (c): a cross-sectional view of multi-core FBG probe embodied as a two-core FBG;

[0017] FIG. 3 (d): a section A.sub.2-A.sub.2 view of multi-core FBG probe embodied as a two-core FBG;

[0018] FIG. 3 (e): a cross-sectional view of multi-core FBG probe embodied as a three-core FBG;

[0019] FIG. 5 (f): a section A.sub.3-A.sub.3 view of multi-core FBG probe embodied as a three-core FBG;

[0020] FIG. 3 (g): a cross-sectional view of multi-core FBG probe embodied as a four-core FBG;

[0021] FIG. 3 (h): a section A.sub.4-A.sub.4 view of multi-core FBG probe embodied as a four-core FBG;

[0022] FIG. 3 (i): a cross-sectional view of multi-core FBG probe embodied as a five-core FBG;

[0023] FIG. 3 (j): a section A.sub.5-A.sub.5 view of multi-core FBG probe embodied as a five-core FBG;

DETAILED DESCRIPTION OF EMBODIMENTS

[0024] A multi-core FBG probe with FBGs 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 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.

[0025] Referring to FIG. 1, the invention can be embodied in way 1:

[0026] The equipment comprises:

a pumping source 1 connected with a ring cavity 17 through a wavelength division multiplexer 2,
a fiber ring laser cavity 17 consisting of wavelength division multiplexer 2, erbium-doped fiber 3, circulator 4, coupler 16 and isolator 15b,
a multi-core FBG probe 12 for sensing contact displacement,
a saturable absorber 5 used to eliminate the multi-longitudinal mode oscillation and suppress the mode hopping,
a multi-channel optical switch 6 controlled by a measurement computer 13 for switching optical paths of multi-core FBG probe 12 and reference FBG 7 in a time-division-multiplexing way,
a multi-core fiber fan-out 9 for making single mode fibers 8 access to every core of the multi-core fiber probe 12,
a multi-core fiber 10 for connecting the multi-core fiber fan-out 9 with the multi-core fiber probe 12,
a reference FBG 7 for compensating temperature drift,
an optical spectrum analyzer 14 for detecting output laser wavelength,
a measurement computer 13 utilized to calculate the contact displacement of the multi-core FBG probe and control the switch of the multi-channel optical switch 6;

[0027] The coupler 16 is connected to the optical spectrum analyzer 14 and the measurement computer 13 through the isolator 15a. The multi-channel optical switch 6, is linked with the circulator 4 through the saturable absorber 5, and is also linked with a multi-core fiber through single mode fibers 8 and the multi-core fiber fan-out 9. The multi-channel optical switch 6 is connected to the measurement computer 13 and it is also connected to the reference FBG 7. The multi-core FBG probe 12 is fixed by a probe holder on the bottom of the multi-core fiber 10. The multi-core FBG probe 12 and the reference FBG 7 can be chosen as a wavelength selection device in turn by switching the multi-channel optical switch.

[0028] The measurement method is described as follows:

[0029] The pumping light generated by an optical pumping source 1 goes into the gain medium erbium-doped fiber through a wavelength division multiplexer (WDM) 2 and generates stimulated emission light. The stimulated emission light is divided by a coupler 16. One part of the light goes into the ring cavity composed by the WDM 2, erbium-doped fiber 3, circulator 4, coupler 16 and isolator 15b successively. Another part becomes the laser output. The light propagating in the ring cavity goes into the port A of the circulator 4 and gets out from port B. Then the light passes through a saturable absorber 5 for eliminating the multi-longitudinal mode oscillation and suppressing the mode hopping, so the single longitudinal mode light with a narrow linewidth can be obtained. After that, the light enters the wavelength selection device which includes a multi-core FBG probe 12 and an external reference FBG 7. Afterwards, the reflected light goes into the port B of the circulator and gets out from port C, and continues to propagate along the ring cavity. With the increase of pumping power, the spontaneous emission will be gradually suppressed and finally the system will have a stable output with a single longitudinal mode and narrow line width. When a micro part is measured, the multi-core FBG probe contacts with the part under test, the center wavelength of reflected spectrum of FBG will shift, which will change the wavelength of the output laser. By switching multi-channel optical switches 6, the wavelength of output laser which is wavelength selected by the multi-core FBG in the probe 12 and external reference FBG 7, can be detected by an optical spectrum analyzer 14. Finally, a measurement computer 13 is used to calculate the relative contact displacement of the probe from the zero-force position, and the dimensional measurement of a micro part is realized thereby.

[0030] The multi-core FBG probe 12 can be a twin FBG probe 33 shown in the FIG. 3(a). In data processing, the two FBGs in the two FBG probes work as laser wavelength selection device respectively, and we get wavelength of the laser output from the fiber ring laser respectively. According to the differential data of these two, one-dimensional radial displacement along the axis determined by the two fibers of the twin FBG probe and temperature drift can be decoupled. At the same time, we can get the average value of these two. The output laser wavelength when the external reference FBG 7 works as the laser wavelength selection device has also been recorded. According to the differential data of these two values above, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and two-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0031] The multi-core FBG probe 12 can be a two-core FBG probe 35 shown in the FIG. 3(c). In data processing, the two FBGs in the two-core FBG probe work as the laser wavelength selection device respectively, and we get wavelength of the laser from the fiber ring laser respectively. According to the differential data of these two, one-dimensional radial displacement along the axis determined by the two cores of the two-core FBG probe and temperature drift can be decoupled. At the same time, we can get the average value of these two. The output laser wavelength when the external reference FBG 7 works as the laser wavelength selection device has also been recorded. According to the differential data of these two values above, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and two-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0032] The multi-core FBG probe 12 can be a three-core FBG probe 37 shown in the FIG. 3(e). In data processing, two eccentric FBGs in the three-core FBG probes work as the laser wavelength selection device respectively, and the wavelength of the laser is recorded respectively. According to the differential data of these two, one-dimensional radial displacement along the axis determined by the two eccentric cores of the three-core FBG probe and temperature drift can be decoupled. Meantime, we choose the center FBG in the three-core FBG probe and the external reference FBG 7 as the laser wavelength selection device respectively, and get their output wavelength respectively. According to the differential data of these two, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and two-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0033] The multi-core FBG probe 12 can be a four-core FBG probe 39 shown in the FIG. 3(g). In data processing, the two sets of orthogonal eccentric FBGs in the four-core FBG probe are chosen as the optical fiber ring laser wavelength selection devices respectively. According to the differential data of two in each set respectively, two-dimensional radial displacement along the axes determined by the two orthogonal eccentric cores of the four-core FBG probe and temperature drift can be decoupled. And we also get the average of four output laser wavelength when the four FBGs in the four-core FBG probe are chosen as the laser wavelength selection respectively. At the same time, the output laser wavelength when the external reference FBG 7 works as the laser wavelength selection device has also been recorded. According to the differential data of these two values above, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and three-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0034] The multi-core FBG probe 12 can be a five-core FBG probe 41 shown in the FIG. 3(i). In data processing, the two sets of orthogonal eccentric FBGs in the five-core FBG probe are chosen as the optical fiber ring laser wavelength selection devices respectively. According to the differential data of two in each set respectively, two-dimensional radial displacement along the axes determined by the two orthogonal eccentric cores of the five-core FBG probe and temperature drift can be decoupled. At the same time, we record the output laser wavelength when the center FBG in the five-core FBG probe and the external reference FBG work as the laser wavelength selection device respectively. According to the differential data of these two, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and three-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0035] FIG. 2 illustrates the second embodiment of the invention. The embodiment of FIG. 2 is similar to the embodiment of FIG. 1 on the principle. The difference between these two is that in the first embodiment the fiber laser has a ring cavity but the second has a linear cavity.

[0036] The equipment comprises:

a single core FBG 21, an erbium-doped fiber 22, an external reference FBG 24 or a single core FBG 21, an erbium-doped fiber 22, a multi-core FBG probe 29 successively,
a pumping source 19, connected with the linear cavity through a port of the wavelength division multiplexer 20. The other port of WDM 20 is connected with an optical spectrum analyzer 31 and a measurement computer 32 through an isolator 30,
a multi-core FBG probe 29 for sensing contact displacement,
a multi-channel optical switch 23 controlled by the measurement computer 32 for switching optical paths of multi-core FBG probe 29 and reference FBG 24 in a time-division-multiplexing way,
a multi-core fiber fan-out 26 for making single mode fibers 25 access to every core of the multi-core fiber probe 29,
a multi-core fiber 27 for connecting the multi-core fiber fan-out 26 with the multi-core fiber probe 29,
a reference FBG 24 for compensating temperature drift,
an optical spectrum analyzer 31 for detecting output laser wavelength,
a measurement computer 32 utilized to calculate the contact displacement of the multi-core FBG probe 29 and control the switch of the multi-channel optical switch 23,
a multi-core fiber 513 for connecting the multi-core fiber fan-out 512 with the multi-core fiber stylus 514;

[0037] The multi-core FBG probe 29 is fixed by the probe holder 28 on the bottom of the multi-core fiber 27. The multi-core FBG probe 29 and the reference FBG 24 can be switched by the multi-channel optical switch 23 to be a wavelength selection device respectively.

[0038] λ.sub.1 the initial center wavelength of the reference FBG 24, λ.sub.2 is the initial center wavelength of multi-core FBG in the multi-core FBG probe 29 and λ.sub.3 is the initial center wavelength of single core FBG 21. The working condition of linear output response of the method and device for dimensional measurement of a micro part is

[00001]$0.8.Math.\sqrt{\frac{{\mathrm{\Delta \lambda }}_1^2+{\mathrm{\Delta \lambda }}_3^2}{8.Math..Math.\ln .Math..Math.2}}\le .Math.{\lambda }_1-{\lambda }_3.Math.\le 1.2.Math.\sqrt{\frac{{\mathrm{\Delta \lambda }}_1^2+{\mathrm{\Delta \lambda }}_3^2}{8.Math..Math.\ln .Math..Math.2}},.Math.0.8.Math.\sqrt{\frac{{\mathrm{\Delta \lambda }}_2^2+{\mathrm{\Delta \lambda }}_3^2}{8.Math..Math.\ln .Math..Math.2}}\le .Math.{\lambda }_2-{\lambda }_3.Math.\le 1.2.Math.\sqrt{\frac{{\mathrm{\Delta \lambda }}_2^2+{\mathrm{\Delta \lambda }}_3^2}{8.Math..Math.\ln .Math..Math.2}}$

respectively. And the measurement method is described as follows:

[0039] The pumping light generated by a pumping source 19 passes through a port of the wavelength division multiplexer (WDM) 20 and enters into the linear cavity composed of a single core FBG 21, an erbium-doped fiber 22, an external reference FBG 24 or a single core FBG 21, an erbium-doped fiber 22, a multi-core FBG probe 29 successively. And the stimulated emission light will be produced when the light passes through the gain medium erbium-doped fiber. The light is reflected for many times in the linear cavity and its intensity is enhanced. When the gain is greater than the loss in one period of oscillation in the cavity, it will output laser with narrow linewidth. The light gets out of another port of WDM 20 and is detected by an optical spectrum analyzer 31. When a micro part is measured, the multi-core FBG probe 29 contacts with the part under test, the center wavelength of reflected spectrum of FBG will shift, which will change the wavelength of the output laser. By switching multi-channel optical switches 23 controlled by the measurement computer 32, the wavelength of output laser which is wavelength selected by the multi-core FBG in the probe 29 and external reference FBG 24, can be detected by an optical spectrum analyzer 31. Finally, a measurement computer 32 is used to calculate the relative contact displacement of the probe from the zero-force position, and the dimensional measurement of a micro part is realized thereby.

[0040] The multi-core FBG probe 29 can be a twin FBG probe 33 shown in the FIG. 3(a). In data processing, the two FBGs in the two FBG probe work as laser wavelength selection device respectively, and we get wavelength of the laser output from the fiber ring laser respectively. According to the differential data of these two, one-dimensional radial displacement along the axis determined by the two fibers of the twin FBG probe and temperature drift can be decoupled. At the same time, we can get the average value of these two. The output laser wavelength when the external reference FBG 24 works as the laser wavelength selection device has also been recorded. According to the differential data of these two values above, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and two-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0041] The multi-core FBG probe 29 can be a two-core FBG probe 35 shown in the FIG. 3(c). In data processing, the two FBGs in the two-core FBG probe work as the laser wavelength selection device respectively, and we get wavelength of the laser from the fiber ring laser respectively. According to the differential data of these two, one-dimensional radial displacement along the axis determined by the two cores of the two-core FBG probe and temperature drift can be decoupled. At the same time, we can get the average value of these two. The output laser wavelength when the external reference FBG 24 works as the laser wavelength selection device has also been recorded. According to the differential data of these two values above, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and two-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0042] The multi-core FBG probe 29 can be a three-core FBG probe 37 shown in the FIG. 3(e). In data processing, two eccentric FBGs in the three-core FBG probe work as the laser wavelength selection device respectively, and the wavelength of the laser is recorded respectively. According to the differential data of these two, one-dimensional radial displacement along the axis determined by the two eccentric cores of the three-core FBG probe and temperature drift can be decoupled. Meantime, we choose the center FBG in the three-core FBG probe and the external reference FBG 24 as the laser wavelength selection device respectively, and get their output wavelength respectively. According to the differential data of these two, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and two-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0043] The multi-core FBG probe 29 can be a four-core FBG probe 39 shown in the FIG. 3(g). In data processing, the two sets of orthogonal eccentric FBGs in the four-core FBG probe are chosen as the optical fiber ring laser wavelength selection devices respectively. According to the differential data of two in each set respectively, two-dimensional radial displacement along the axes determined by the two orthogonal eccentric cores of the four-core FBG probe and temperature drift can be decoupled. And we also get the average of four output laser wavelength when the four FBGs in the four-core FBG probe are chosen as the laser wavelength selection respectively. At the same time, the output laser wavelength when the external reference FBG 24 works as the laser wavelength selection device has also been recorded. According to the differential data of these two values above, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and three-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0044] The multi-core FBG probe 29 can be a five-core FBG probe 41 shown in the FIG. 3(i). In data processing, the two sets of orthogonal eccentric FBGs in the five-core FBG probe are chosen as the optical fiber ring laser wavelength selection devices respectively. According to the differential data of two in each set respectively, two-dimensional radial displacement along the axes determined by the two orthogonal eccentric cores of the five-core FBG probe and temperature drift can be decoupled. At the same time, we record the output laser wavelength when the center FBG in the five-core FBG probe and the external reference FBG work as the laser wavelength selection device respectively. According to the differential data of these two, we can get the result of the axial displacement without coupled radial displacement and temperature drift, and three-dimensional measurement of a micro part with no temperature interference is realized thereby.

[0045] There have been described and illustrated herein several embodiments of methods based on fiber laser with a multi-core FBG probe for dimensional measurement of a micro part. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as so claimed.