Abstract

The forward scattering of light by an optical fiber produces an interference fringe pattern, and the fringe period is inversely proportional to the fiber diameter. An electrooptic system has been developed to produce and detect this scattering pattern to provide an instrument which will measure fiber diameter during the drawing operation. The system measures the fiber diameter at a 1-kHz rate with a precision of 0.25 μm and an accuracy of ±0.25 μm over a range of 50–150-μm diams. The instrument allows the fiber to move laterally in a 1-cm diam window maintaining the above accuracy. The system can be calibrated optically and does not need a standard fiber for this procedure. The instrument has been used for months without the need for recalibration. In addition to the digital diameter output, the system employs a microprocessor to compute mean and standard deviation values for various sample lengths and provides suitable signals for feedback control of fiber diameter.

© 1977 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. L. S. Watkins, J. Opt. Soc. Am. 64, 767 (1974).
    [Crossref]
  2. P. H. Krawarik, in Digest of Topical Meeting on Optical Fiber Transmission (Optical Society of America, Washington, D.C., 1975), paper PD1.
  3. D. H. Smithgall, R. E. Frazee, IEEE Trans. Ind. Electron. Control Instrum. 23, Number 3, 258 (August1976).
    [Crossref]

1976 (1)

D. H. Smithgall, R. E. Frazee, IEEE Trans. Ind. Electron. Control Instrum. 23, Number 3, 258 (August1976).
[Crossref]

1974 (1)

Frazee, R. E.

D. H. Smithgall, R. E. Frazee, IEEE Trans. Ind. Electron. Control Instrum. 23, Number 3, 258 (August1976).
[Crossref]

Krawarik, P. H.

P. H. Krawarik, in Digest of Topical Meeting on Optical Fiber Transmission (Optical Society of America, Washington, D.C., 1975), paper PD1.

Smithgall, D. H.

D. H. Smithgall, R. E. Frazee, IEEE Trans. Ind. Electron. Control Instrum. 23, Number 3, 258 (August1976).
[Crossref]

Watkins, L. S.

IEEE Trans. Ind. Electron. Control Instrum. (1)

D. H. Smithgall, R. E. Frazee, IEEE Trans. Ind. Electron. Control Instrum. 23, Number 3, 258 (August1976).
[Crossref]

J. Opt. Soc. Am. (1)

Other (1)

P. H. Krawarik, in Digest of Topical Meeting on Optical Fiber Transmission (Optical Society of America, Washington, D.C., 1975), paper PD1.

Cited By

OSA participates in Crossref's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (13)

Fig. 1
Fig. 1

Composite graphs of experimental and theoretical forwardscattering patterns: (a) comparison of wave theory to the experimentally measured patterns (heavy line shows experimental results); (b) fringe position calculated from path difference between refracted and reflected rays using geometric ray tracing; (c) fringe modulation found by geometrically calculating the interference between the refracted ray that traverses the core and the one that goes through the cladding only.

Fig. 2
Fig. 2

Plot of critical angle θc and its relation to core to outer diameter ratio in a step-index fiber.

Fig. 3
Fig. 3

Schematic of the arrangement for illuminating the fiber. Cube rotates to center beam onto fiber maintaining the same beam incidence angle.

Fig. 4
Fig. 4

First order design of optics to collect the scattering pattern and display it on the diode array. Movement of fiber does not influence the angle displayed on the diode array. Filter compensates for the variation in flux of the scattering pattern.

Fig. 5
Fig. 5

Effect of lateral fiber movement on detector optics. Limit of movement governed by aperture of image relay lens.

Fig. 6
Fig. 6

Three designs for the scattering image and field lens. Upper design has the least distortion; however, the lower design gives the largest window. Middle design is the best compromise.

Fig. 7
Fig. 7

Window distortion in terms of the percentage diameter indication error against fiber radial position for above designs. Vertical lines represent the maximum window available.

Fig. 8
Fig. 8

Circuit schematic for processing the diode detector signal. Counts peaks and valley of the fringe pattern each diode scan (1 msec). Microprocessor computes mean and standard deviation and also detects and compensates for defects in the fiber as indicated by distortions of the scattering pattern.

Fig. 9
Fig. 9

Fiber window with diameter indication variations plotted to show ±0.25-μm accuracy limits.

Fig. 10
Fig. 10

Video output from diode array detector and the resulting signal from the fringe counter. Demonstrates the boxcar output from the diode array which causes phase shifts in the detected fringe signal. Shows that the fringe period is larger at the smaller angles and then reduces for larger angles.

Fig. 11
Fig. 11

Fringe pattern and diode array for the situation of two diodes per fringe. Effect of θ phase difference between diodes and fringes causes θ phase shift in fringe pattern on video signal.

Fig. 12
Fig. 12

Theoretical output from the fringe counter for increasing fiber diameter showing the way it increases by two and then reduces by one etc.

Fig. 13
Fig. 13

Actual output from the instrument for a fiber with sinusoidal diameter variation indicating the reading stays within ±1 count of the actual diameter.

Equations (19)

Equations on this page are rendered with MathJax. Learn more.

d f 2 = ( v p d p 2 ) / ( v f ) ,
Δ ( θ ) = 2 b [ sin θ 2 + ( m 1 2 + 1 - 2 m 1 cos θ 2 ) 1 / 2 ] + λ 4 ,
A = 1 + cos k Δ ,
N = { k [ Δ ( θ 2 ) - Δ ( θ 1 ) ] } / ( 2 π ) ,
N = 2 b λ { [ sin θ 2 2 + ( m 1 2 + 1 - 2 m 1 cos θ 2 2 ) 1 / 2 ] - [ sin θ 1 2 + ( m 1 2 + 1 - 2 m 1 cos θ 1 2 ) 1 / 2 ] } .
N = [ ( 2 b ) / λ ] · 1.28
δ = 2 ( m 2 - m 1 ) a .
d = 2 f 1 tan [ ( θ 2 - θ 1 ) / 2 ] ,
M = r / d ,
m e = ± f 1 M 2 N 3 ( M + 1 ) ,
m e = ± [ f 1 M 2 ( M + 1 ) N 3 ( 1 - N 3 b 3 f 3 ) ] ,
m z = ± m e tan [ ( θ 2 - θ 1 ) / 2 ] .
f ( t ) = sin ( w t - θ ) ,
g ( t ) = ± ( 2 / π ) cos θ ,
h ( t ) = ( 2 / π ) cos θ sin w t .
E d = ± [ π / ( n d ) ] .
E p = ± [ π / ( n p ) ] .
E p = ± [ ( 3 π ) / ( 2 n p ) ] .
E max = E p + E d = 0.95 π = 0.24 μ m .

Metrics