Abstract

The method used to manufacture a Young’s double pinhole interferometer is discussed. This interferometer is destined to be used in a surface profilometer using two wavelengths so that the zero order fringe can be determined. Hence stringent requirements are placed on the absolute length difference between the two output fibers of a single mode coupler. These requirements are discussed along with the manufacturing process. The interferometer is shown along with measurements showing a length difference on the order of 6µm.

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References

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  1. G. Indebetouw, "Profile measurement using projection of running fringes," Appl. Opt. 17, 2930- 2933 (1978).
    [CrossRef] [PubMed]
  2. M. Takeda and K. Mutoh, "Fourier transform profilometry for the automatic measurement of {3--D} object shapes," Appl. Opt. 22, 3977-3982 (1983).
    [CrossRef] [PubMed]
  3. T. L. Pennington, H. Xiao, R. May and A. Wang, "Miniaturized 3D surface profilometer using a fiber optic coupler," submitted to Optics and Laser Technology, Jan 2000.
  4. Optical Society of America, Handbook of Optics, W. G. Driscoll, ed. (McGraw-Hill, New York, 1978).
  5. Z. G. Wang, Wavelength compensation in fused fiber couplers, Ph.D. Disseration, (Virginia Polytechnic Institute and State University, Blacksburg, VA, 1996).
  6. T. Li, A. Wang, K. Murphy and R. Claus, "White-Light Scanning Fiber Michelson Interferometer for Absolute Position-Distance Measurement," Opt. Lett. 20, 785-787 (1995).
    [CrossRef] [PubMed]

Other (6)

G. Indebetouw, "Profile measurement using projection of running fringes," Appl. Opt. 17, 2930- 2933 (1978).
[CrossRef] [PubMed]

M. Takeda and K. Mutoh, "Fourier transform profilometry for the automatic measurement of {3--D} object shapes," Appl. Opt. 22, 3977-3982 (1983).
[CrossRef] [PubMed]

T. L. Pennington, H. Xiao, R. May and A. Wang, "Miniaturized 3D surface profilometer using a fiber optic coupler," submitted to Optics and Laser Technology, Jan 2000.

Optical Society of America, Handbook of Optics, W. G. Driscoll, ed. (McGraw-Hill, New York, 1978).

Z. G. Wang, Wavelength compensation in fused fiber couplers, Ph.D. Disseration, (Virginia Polytechnic Institute and State University, Blacksburg, VA, 1996).

T. Li, A. Wang, K. Murphy and R. Claus, "White-Light Scanning Fiber Michelson Interferometer for Absolute Position-Distance Measurement," Opt. Lett. 20, 785-787 (1995).
[CrossRef] [PubMed]

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Figures (8)

Fig. 1.
Fig. 1.

Schematic of the fiber alignment used to compute the optical path difference using Eq. (2). L 1 is the length of the long fiber, L 2 is the length of the short fiber, d is the normal distance between two lines parallel to the fiber endfaces, ϕ 1 is the phase of the light exiting the long fiber, ϕ′ 2 is the phase exiting the short fiber and ϕ 2 is the phase of the short fiber’s light when it is parallel to the long fiber endface.

Fig. 2.
Fig. 2.

The coupler manufacturing station used to make the coupler in this system.

Fig. 3.
Fig. 3.

The fiber length difference is measured using a white light interferometer.

Fig. 4.
Fig. 4.

The fibers are mounted onto the polishing machine so that the pressure of each fiber against the lap can be controlled. Polishing continues until the desired length difference is achieved.

Fig. 5.
Fig. 5.

Sample spectra obtained during the fringe generator manufacturing process. (a) The initial spectrum which shows a fiber length difference of approximately 1mm. (b) A spectrum mid-way through the process; the length difference has decreased to 230µm.

Fig. 6.
Fig. 6.

A comparison of the final spectrum (red) and initial spectrum (blue) taken at the same time as Figure 5(a). The fringes readily observed are noise arising from some other reflection in the system.

Fig. 7.
Fig. 7.

A low-pass filtered version of a spectra in Figure 6.

Fig. 8.
Fig. 8.

A cross section of the fringe pattern after the fibers were polished and aligned. The red trace is for the HeNe and the blue trace is for the 830nm laser diode. The zero order fringe is located pixel number 82.

Equations (4)

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I ( x , y ) = 2 I o [ 1 + cos ( 2 a d k x + Δ ϕ ) ] ,
Δ ϕ ( 1 , 2 ) = 2 π [ n f Δ L n o d ] ( 1 2 1 2 ) + 2 π 2 Δ n Δ L ,
Δ L max = 2 Δ ϕ max 2 π Δ n .
Δ L = 1 2 2 n 1 2 ,

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