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US3879128A
Expired / Lapsed
US
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Method and apparatus for measuring the refractive index and diameter of optical fibers
Assignee: AT&T Inc
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Filing: 1973-08-15
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Granted: 1975-04-22
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Expires: 1993-08-15
Abstract
Abstract A method is disclosed for monitoring and controlling the refractive index profile and the diameter of optical fibers. The technique is based upon an analysis of the backscattered radiation produced when an optical beam impinges upon the fiber. It can be shown, by a geometrical optical analysis, that the position of a sharp cutoff in the radiation pattern is a function of the refractive index profile while the distance between two successive minima (or maxima) is a function of the fiber diameter. For certain simple fiber configurations, this data can be translated directly into a number for the fiber core index and a number for the fiber core diameter. For more complicated fiber configurations, such as fibers having graded-index cores, the resulting radiation pattern can be compared to that of a reference fiber, and any unusual deviations noted. The method is advantageously used in conjunction with a feedback system for monitoring fibers as they are drawn, and for controlling the drawing machinery so as to maintain the fiber parameters within specified tolerances.
Inventors
- 👤 Herman Melvin Presby
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 15:52
CPC Classifications
G; G01; G01N; G01N21/00; G01N21/17; G01N21/41; G01N21/412; G01B; G01B11/00; G01B11/08; G01B11/10; G01B11/105
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
76 words
The method of controlling the diameter of an optical fiber comprising the steps of: illuminating said fiber with the beam from a CW laser; converting the backscattered radiation pattern produced by said illuminated fiber into a time-varying electrical signal; generating a pulse train whose pulse width equals the time interval between selected adjacent minima or maxima along said electrical signal; and using said pulse train to control the rate at which said fiber is being pulled.
Claim 2
Independent Claim
76 words
The method of controlling the diameter of an optical fiber comprising the steps of: illuminating said fiber with the beam from a CW laser; converting the backscattered radiation pattern produced by said illuminated fiber into a time-varying electrical signal; generating a pulse train whose pulse width equals the time interval between selected adjacent minima or maxima along said electrical signal; and using said pulse train to control the rate at which said fiber is being pulled.
Claim 3
Independent Claim
76 words
The method of controlling the diameter of an optical fiber comprising the steps of: illuminating said fiber with the beam from a CW laser; converting the backscattered radiation pattern produced by said illuminated fiber into a time-varying electrical signal; generating a pulse train whose pulse width equals the time interval between selected adjacent minima or maxima along said electrical signal; and using said pulse train to control the rate at which said fiber is being pulled.
Claim 4
Independent Claim
76 words
The method of controlling the diameter of an optical fiber comprising the steps of: illuminating said fiber with the beam from a CW laser; converting the backscattered radiation pattern produced by said illuminated fiber into a time-varying electrical signal; generating a pulse train whose pulse width equals the time interval between selected adjacent minima or maxima along said electrical signal; and using said pulse train to control the rate at which said fiber is being pulled.
Claim 5
Independent Claim
70 words
A method of measuring the refractive index of a transparent rod comprising the steps of: illuminating said rod with a beam of radiant energy; converting the backscattered radiation pattern produced by said illuminated rod into an electrical signal whose intensity variations, as a function of time, correspond to the spatial variations of said radiation pattern; and measuring the time interval between the two end intensity peaks of said electrical signal.
Claim 6
Independent Claim
70 words
A method of measuring the refractive index of a transparent rod comprising the steps of: illuminating said rod with a beam of radiant energy; converting the backscattered radiation pattern produced by said illuminated rod into an electrical signal whose intensity variations, as a function of time, correspond to the spatial variations of said radiation pattern; and measuring the time interval between the two end intensity peaks of said electrical signal.
Claim 7
Independent Claim
119 words
A method of measuring the cross-sectional dimension of a transparent rod comprising the steps of: illuminating said transparent rod by means of a beam from a narrow band signal source; generating a time varying electrical signal by means including a radiation detector located so as to respond to the spatial variations of the backscattered radiation pattern produced by said illuminated rod; measuring a time interval between selected points along said electrical signal; and converting said measured time interval into an indication of the rod cross-sectional dimension, where said indication is proportional to h2(1-n/2), where h is the axial distance traversed by said radiation between said rod and said detector, and n is the refractive index of the rod material.
Claim 8
Independent Claim
119 words
A method of measuring the cross-sectional dimension of a transparent rod comprising the steps of: illuminating said transparent rod by means of a beam from a narrow band signal source; generating a time varying electrical signal by means including a radiation detector located so as to respond to the spatial variations of the backscattered radiation pattern produced by said illuminated rod; measuring a time interval between selected points along said electrical signal; and converting said measured time interval into an indication of the rod cross-sectional dimension, where said indication is proportional to h2(1-n/2), where h is the axial distance traversed by said radiation between said rod and said detector, and n is the refractive index of the rod material.
Claim 9
Dependent Claim
14 words
The method according to claim 3 wherein said signal source is a CW laser.
Claim 10
Dependent Claim
17 words
The method according to claim 3 wherein the time interval measured is that between adjacent intensity minima.
Claim 11
Dependent Claim
17 words
The method according to claim 3 wherein the time interval measured is that between adjacent intensity maxima.
Claim 12
Independent Claim
144 words
A method of measuring the cross-sectional dimension of a transparent rod comprising the steps of: illuminating said transparent rod by means of a beam from a narrow band signal source; generating a time varying electrical signal by means including a radiation detector located so as to respond to the spatial variations of the backscattered radiation pattern produced by said illuminated rod; measuring the time intervAl corresponding to the distance between the two end intensity peaks of said pattern; and converting said measured time interval into an indication of the rod cross-sectional dimension, where said dimension a and said measured time interval Delta T are related by Delta T about tan (2.1 X 105 (H/48) ( lambda / a) ), where lambda is the wavelength of the illuminating beam, H (9(4-n2) 1/2 /4(n2-1) 2/3 ), and n is the refractive index of the rod material.
Claim 13
Independent Claim
144 words
A method of measuring the cross-sectional dimension of a transparent rod comprising the steps of: illuminating said transparent rod by means of a beam from a narrow band signal source; generating a time varying electrical signal by means including a radiation detector located so as to respond to the spatial variations of the backscattered radiation pattern produced by said illuminated rod; measuring the time intervAl corresponding to the distance between the two end intensity peaks of said pattern; and converting said measured time interval into an indication of the rod cross-sectional dimension, where said dimension a and said measured time interval Delta T are related by Delta T about tan (2.1 X 105 (H/48) ( lambda / a) ), where lambda is the wavelength of the illuminating beam, H (9(4-n2) 1/2 /4(n2-1) 2/3 ), and n is the refractive index of the rod material.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-04-21 | 1978-10-21 | 1979-04-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-04-21 | 1982-10-21 | 1983-04-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-04-21 | 1986-10-21 | 1987-04-22 | $7700.00 | Window Closed / Lapsed |