Abstract

We describe a fiber optic confocal sensor (FOCOS) system that uses an optical fiber and a lens to accurately detect the position of an object at, or close to, the image plane of the fiber tip. The fiber characteristics (diameter and numerical aperture) and optics (lens F∕# and magnification) define the span and precision of the sensor and may be chosen to fit a desired application of position and displacement sensing. Multiple measurement points (i.e., fiber-tip images) may be achieved by use of multiple wavelengths in the fiber, so that each wavelength images the fiber at a different plane due to the chromatic dispersion of the optics. Further multiplexing may be achieved by adding fibers on the optical axis. A FOCOS with multiplexed fibers and wavelengths may also be used for velocity measurements.

© 2006 Optical Society of America

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  1. H.-J. Jordan, M. Wegner, and H. J. Tiziani, "Highly accurate non-contact characterization of engineering surfaces using confocal microscopy," Meas. Sci. Technol. 9, 1142-1151 (1998).
    [CrossRef]
  2. T. Dabbs and M. Glass, "Fiber-optic confocal microscope: FOCON," Appl. Opt. 31, 3030-3035 (1992).
    [CrossRef] [PubMed]
  3. L. Yang, G. Wang, J. Wang, and Z. Xu, "Surface profilometry with a fibre optical confocal scanning microscope," Meas. Sci. Technol. 11, 1786-1791 (2000).
    [CrossRef]
  4. J. Cohen-Sabban, J. Gaillard-Groleas, and P. J. Crepin, "Extended-field confocal imaging for 3D surface sensing," in Optical Fabrication, Testing, and Metrology, R. Geyl, D. Rimmer, and L. Wang, eds., Proc. SPIE 5252, 366-371 (2004).
    [CrossRef]
  5. B. E. Jones, R. S. Medlock, and R. C. Spooncer, "Intensity and wavelength-based sensors and optical actuators," in Optical Fiber Sensors, B. Culshaw and J. Dakin, eds. (Artech House, 1989), Vol. 2, pp. 431-473.
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    [CrossRef]
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    [CrossRef] [PubMed]
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    [CrossRef]
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    [CrossRef]
  11. E. Shafir and G. Berkovic, "Multi-wavelength fiber optic displacement sensing," in Optical Fibers:Applications, L. R. Jaroszewicz, B. Culshaw, and A. G. Migmani, eds., Proc. SPIE 5952, 247-251 (2005).
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    [CrossRef] [PubMed]

2005 (1)

E. Shafir and G. Berkovic, "Multi-wavelength fiber optic displacement sensing," in Optical Fibers:Applications, L. R. Jaroszewicz, B. Culshaw, and A. G. Migmani, eds., Proc. SPIE 5952, 247-251 (2005).

2004 (2)

R. J. Garzón, J. Menese, G. Tribillon, T. Gharbi, and A. Plata, "Chromatic confocal microscopy by means of continuum light generated through a standard single-mode fibre," J. Opt. A: Pure Appl. Opt. 6, 544-548 (2004).
[CrossRef]

J. Cohen-Sabban, J. Gaillard-Groleas, and P. J. Crepin, "Extended-field confocal imaging for 3D surface sensing," in Optical Fabrication, Testing, and Metrology, R. Geyl, D. Rimmer, and L. Wang, eds., Proc. SPIE 5252, 366-371 (2004).
[CrossRef]

2000 (1)

L. Yang, G. Wang, J. Wang, and Z. Xu, "Surface profilometry with a fibre optical confocal scanning microscope," Meas. Sci. Technol. 11, 1786-1791 (2000).
[CrossRef]

1998 (1)

H.-J. Jordan, M. Wegner, and H. J. Tiziani, "Highly accurate non-contact characterization of engineering surfaces using confocal microscopy," Meas. Sci. Technol. 9, 1142-1151 (1998).
[CrossRef]

1996 (1)

1992 (2)

T. Dabbs and M. Glass, "Fiber-optic confocal microscope: FOCON," Appl. Opt. 31, 3030-3035 (1992).
[CrossRef] [PubMed]

R. Juskaitis and T. Wilson, "Imaging in reciprocal fibre-optic based confocal scanning microscopes," Opt. Commun. 92, 315-325 (1992).
[CrossRef]

1991 (1)

1989 (1)

B. E. Jones, R. S. Medlock, and R. C. Spooncer, "Intensity and wavelength-based sensors and optical actuators," in Optical Fiber Sensors, B. Culshaw and J. Dakin, eds. (Artech House, 1989), Vol. 2, pp. 431-473.

1984 (1)

G. Molesini, G. Pederini, P. Poggi, and F. Quercioli, "Focus-wavelength encoded optical profilometer," Opt. Commun. 49, 229-233 (1984).
[CrossRef]

1982 (1)

Achi, R.

Berkovic, G.

E. Shafir and G. Berkovic, "Multi-wavelength fiber optic displacement sensing," in Optical Fibers:Applications, L. R. Jaroszewicz, B. Culshaw, and A. G. Migmani, eds., Proc. SPIE 5952, 247-251 (2005).

Cohen-Sabban, J.

J. Cohen-Sabban, J. Gaillard-Groleas, and P. J. Crepin, "Extended-field confocal imaging for 3D surface sensing," in Optical Fabrication, Testing, and Metrology, R. Geyl, D. Rimmer, and L. Wang, eds., Proc. SPIE 5252, 366-371 (2004).
[CrossRef]

Crepin, P. J.

J. Cohen-Sabban, J. Gaillard-Groleas, and P. J. Crepin, "Extended-field confocal imaging for 3D surface sensing," in Optical Fabrication, Testing, and Metrology, R. Geyl, D. Rimmer, and L. Wang, eds., Proc. SPIE 5252, 366-371 (2004).
[CrossRef]

Dabbs, T.

Gaillard-Groleas, J.

J. Cohen-Sabban, J. Gaillard-Groleas, and P. J. Crepin, "Extended-field confocal imaging for 3D surface sensing," in Optical Fabrication, Testing, and Metrology, R. Geyl, D. Rimmer, and L. Wang, eds., Proc. SPIE 5252, 366-371 (2004).
[CrossRef]

Gan, X.

Garzón, R. J.

R. J. Garzón, J. Menese, G. Tribillon, T. Gharbi, and A. Plata, "Chromatic confocal microscopy by means of continuum light generated through a standard single-mode fibre," J. Opt. A: Pure Appl. Opt. 6, 544-548 (2004).
[CrossRef]

Gharbi, T.

R. J. Garzón, J. Menese, G. Tribillon, T. Gharbi, and A. Plata, "Chromatic confocal microscopy by means of continuum light generated through a standard single-mode fibre," J. Opt. A: Pure Appl. Opt. 6, 544-548 (2004).
[CrossRef]

Glass, M.

Gu, M.

Hayashi, A.

Jones, B. E.

B. E. Jones, R. S. Medlock, and R. C. Spooncer, "Intensity and wavelength-based sensors and optical actuators," in Optical Fiber Sensors, B. Culshaw and J. Dakin, eds. (Artech House, 1989), Vol. 2, pp. 431-473.

Jordan, H.-J.

H.-J. Jordan, M. Wegner, and H. J. Tiziani, "Highly accurate non-contact characterization of engineering surfaces using confocal microscopy," Meas. Sci. Technol. 9, 1142-1151 (1998).
[CrossRef]

Juskaitis, R.

R. Juskaitis and T. Wilson, "Imaging in reciprocal fibre-optic based confocal scanning microscopes," Opt. Commun. 92, 315-325 (1992).
[CrossRef]

Kitagawa, Y.

Krämer, R. N.

Medlock, R. S.

B. E. Jones, R. S. Medlock, and R. C. Spooncer, "Intensity and wavelength-based sensors and optical actuators," in Optical Fiber Sensors, B. Culshaw and J. Dakin, eds. (Artech House, 1989), Vol. 2, pp. 431-473.

Menese, J.

R. J. Garzón, J. Menese, G. Tribillon, T. Gharbi, and A. Plata, "Chromatic confocal microscopy by means of continuum light generated through a standard single-mode fibre," J. Opt. A: Pure Appl. Opt. 6, 544-548 (2004).
[CrossRef]

Molesini, G.

G. Molesini, G. Pederini, P. Poggi, and F. Quercioli, "Focus-wavelength encoded optical profilometer," Opt. Commun. 49, 229-233 (1984).
[CrossRef]

Pederini, G.

G. Molesini, G. Pederini, P. Poggi, and F. Quercioli, "Focus-wavelength encoded optical profilometer," Opt. Commun. 49, 229-233 (1984).
[CrossRef]

Plata, A.

R. J. Garzón, J. Menese, G. Tribillon, T. Gharbi, and A. Plata, "Chromatic confocal microscopy by means of continuum light generated through a standard single-mode fibre," J. Opt. A: Pure Appl. Opt. 6, 544-548 (2004).
[CrossRef]

Poggi, P.

G. Molesini, G. Pederini, P. Poggi, and F. Quercioli, "Focus-wavelength encoded optical profilometer," Opt. Commun. 49, 229-233 (1984).
[CrossRef]

Quercioli, F.

G. Molesini, G. Pederini, P. Poggi, and F. Quercioli, "Focus-wavelength encoded optical profilometer," Opt. Commun. 49, 229-233 (1984).
[CrossRef]

Shafir, E.

E. Shafir and G. Berkovic, "Multi-wavelength fiber optic displacement sensing," in Optical Fibers:Applications, L. R. Jaroszewicz, B. Culshaw, and A. G. Migmani, eds., Proc. SPIE 5952, 247-251 (2005).

Sheppard, J. R.

Spooncer, R. C.

B. E. Jones, R. S. Medlock, and R. C. Spooncer, "Intensity and wavelength-based sensors and optical actuators," in Optical Fiber Sensors, B. Culshaw and J. Dakin, eds. (Artech House, 1989), Vol. 2, pp. 431-473.

Tiziani, H. J.

H.-J. Jordan, M. Wegner, and H. J. Tiziani, "Highly accurate non-contact characterization of engineering surfaces using confocal microscopy," Meas. Sci. Technol. 9, 1142-1151 (1998).
[CrossRef]

H. J. Tiziani, R. Achi, R. N. Krämer, and L. Wiegers, "Theoretical analysis of confocal microscopy with microlenses," Appl. Opt. 35, 120-125 (1996).
[CrossRef] [PubMed]

Tribillon, G.

R. J. Garzón, J. Menese, G. Tribillon, T. Gharbi, and A. Plata, "Chromatic confocal microscopy by means of continuum light generated through a standard single-mode fibre," J. Opt. A: Pure Appl. Opt. 6, 544-548 (2004).
[CrossRef]

Wang, G.

L. Yang, G. Wang, J. Wang, and Z. Xu, "Surface profilometry with a fibre optical confocal scanning microscope," Meas. Sci. Technol. 11, 1786-1791 (2000).
[CrossRef]

Wang, J.

L. Yang, G. Wang, J. Wang, and Z. Xu, "Surface profilometry with a fibre optical confocal scanning microscope," Meas. Sci. Technol. 11, 1786-1791 (2000).
[CrossRef]

Wegner, M.

H.-J. Jordan, M. Wegner, and H. J. Tiziani, "Highly accurate non-contact characterization of engineering surfaces using confocal microscopy," Meas. Sci. Technol. 9, 1142-1151 (1998).
[CrossRef]

Wiegers, L.

Wilson, T.

R. Juskaitis and T. Wilson, "Imaging in reciprocal fibre-optic based confocal scanning microscopes," Opt. Commun. 92, 315-325 (1992).
[CrossRef]

Xu, Z.

L. Yang, G. Wang, J. Wang, and Z. Xu, "Surface profilometry with a fibre optical confocal scanning microscope," Meas. Sci. Technol. 11, 1786-1791 (2000).
[CrossRef]

Yang, L.

L. Yang, G. Wang, J. Wang, and Z. Xu, "Surface profilometry with a fibre optical confocal scanning microscope," Meas. Sci. Technol. 11, 1786-1791 (2000).
[CrossRef]

Appl. Opt. (3)

J. Opt. A: Pure Appl. Opt. (1)

R. J. Garzón, J. Menese, G. Tribillon, T. Gharbi, and A. Plata, "Chromatic confocal microscopy by means of continuum light generated through a standard single-mode fibre," J. Opt. A: Pure Appl. Opt. 6, 544-548 (2004).
[CrossRef]

J. Opt. Soc. Am. A (1)

Meas. Sci. Technol. (2)

L. Yang, G. Wang, J. Wang, and Z. Xu, "Surface profilometry with a fibre optical confocal scanning microscope," Meas. Sci. Technol. 11, 1786-1791 (2000).
[CrossRef]

H.-J. Jordan, M. Wegner, and H. J. Tiziani, "Highly accurate non-contact characterization of engineering surfaces using confocal microscopy," Meas. Sci. Technol. 9, 1142-1151 (1998).
[CrossRef]

Opt. Commun. (2)

R. Juskaitis and T. Wilson, "Imaging in reciprocal fibre-optic based confocal scanning microscopes," Opt. Commun. 92, 315-325 (1992).
[CrossRef]

G. Molesini, G. Pederini, P. Poggi, and F. Quercioli, "Focus-wavelength encoded optical profilometer," Opt. Commun. 49, 229-233 (1984).
[CrossRef]

Proc. SPIE (2)

J. Cohen-Sabban, J. Gaillard-Groleas, and P. J. Crepin, "Extended-field confocal imaging for 3D surface sensing," in Optical Fabrication, Testing, and Metrology, R. Geyl, D. Rimmer, and L. Wang, eds., Proc. SPIE 5252, 366-371 (2004).
[CrossRef]

E. Shafir and G. Berkovic, "Multi-wavelength fiber optic displacement sensing," in Optical Fibers:Applications, L. R. Jaroszewicz, B. Culshaw, and A. G. Migmani, eds., Proc. SPIE 5952, 247-251 (2005).

Other (1)

B. E. Jones, R. S. Medlock, and R. C. Spooncer, "Intensity and wavelength-based sensors and optical actuators," in Optical Fiber Sensors, B. Culshaw and J. Dakin, eds. (Artech House, 1989), Vol. 2, pp. 431-473.

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Figures (10)

Fig. 1
Fig. 1

Principle of fiber optic confocal sensor (FOCOS) for object: (i) at the image plane and (ii) displaced from the image plane.

Fig. 2
Fig. 2

Setup to test and demonstrate the FOCOS technique. The unused output port of the coupler is coated with index-matching gel to eliminate backreflection to the detector. Concentricity and parallelism of the active output fiber (terminated in a standard FC-type connector) and lens axis is ensured by mounting both components in a cylindrical lens tube.

Fig. 3
Fig. 3

FOCOS signal at 1∕3 magnification using 2   mm diameter F∕1 aspheric lens C150TM-C and (dashed curve) SMF-28 fibers and (solid curve) 50   μm MM (multimode) fiber. The fiber is positioned approximately 8   mm from the lens, and the object mirror is optimally imaged at a distance approximately 2.7   mm from the principal plane of the lens. Thus the effective NA for the MM fiber is 0.12, essentially the same as for the SM (single-mode) fiber.

Fig. 4
Fig. 4

Dependence of FOCOS signal FWHM (squares) on magnification for 8   mm diameter F∕1 aspheric lens C240TM-C and 50   μm MM fiber. The peak FOCOS signals approach that of 100 % efficiency of collection of reflected light by the fiber. The dashed curve is the prediction of the simplified geometric model.

Fig. 5
Fig. 5

FOCOS signal using 1 in. diameter F∕1 optics (pair of doublets LAC-382C). The 50   mm fiber is placed 90   mm from the closest lens, and in order to be imaged, the mirror must be positioned approximately 35   mm from the lens. The inset shows the arrangement of the two doublet lenses.

Fig. 6
Fig. 6

Schematic of setups with (a) two and (b) four fibers for distributed sensing of the object position.

Fig. 7
Fig. 7

Two-fiber FOCOS sensor, using 50   μm core fibers, and two LAC-382C doublet lenses giving 25   mm focal length F∕1 optics (top). The bottom curve is the response signal for a mirror, initially 35   mm away, translated toward the sensor.

Fig. 8
Fig. 8

FOCOS signals using different wavelength sources. The 50   μm MM fiber tip is 25   mm from the 8   mm diameter F / 1 aspheric lens aspheric lens C240TM-C. Each curve represents a discrete experiment using a single wavelength. (a) FOCOS signals as a function of mirror position. The zero reference position is the mirror position giving the FOCOS peak with the 1531   nm source, at a nominal distance of 12   mm from the lens. (b) Plot of observed shifts of the FOCOS peak with wavelength versus calculated shifts.

Fig. 9
Fig. 9

Setup for a FOCOS sensor using two fibers and two wavelengths. The lenses are a pair of LAC-382C doublets giving F / 1 optics of 25   mm focal length. The results show four peaks as the mirror is translated toward the sensor; the peaks at 0   mm and 3.38   mm come from the 1531   nm light (with the longer effective focal length), while the other two peaks come from the 980   nm light.

Fig. 10
Fig. 10

Dynamic FOCOS signal as recorded on an oscilloscope (horizontal scale 500   μs ∕ division) using the two-fiber (single wavelength) FOCOS sensor shown in Fig. 7. The dynamic experiment is described in the text.

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