Fiberoptic in-line filter and technique for measuring the transmission quality of an optical fiber through the use of a fiberoptic in-line filter

• US 5,453,827 A
• Filed: 02/24/1993
• Issued: 09/26/1995
• Est. Priority Date: 02/24/1993
• Status: Expired due to Fees

• Current Assignee: DiCon Fiber Optics Incorporated
• Original Assignee: DiCon Fiber Optics Incorporated
• Inventors: Lee, Ho-Shang
• Primary Examiner(s): Limanek, Robert P.
• Assistant Examiner(s): Ostrowski, David
• Application Number:
  US08/021,790
• Time in Patent Office: 944 Days
• Field of Search: 356/73.1, 250/227.11, 250/227.15, 250/227.16, 250/227.18
• US Class Current: 356/73.1
• CPC Class Codes: G01M 11/3109 Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
• CPC Class Codes: G02B 6/2937 In line lens-filtering-lens devices, i.e. elements arranged along a line and mountable in a cylindrical package for compactness, e.g. 3- port device with GRIN lenses sandwiching a single filter operating at normal incidence in a tubular package
• CPC Class Codes: G02B 6/32 having lens focusing means positioned between opposed fibre ends with lens being an integral part of the single fibre end G02B6/262
• CPC Class Codes: H04B 10/07 Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
• CPC Class Codes: H04B 10/071 using a reflected signal, e.g. using optical time domain reflectometers [OTDR]

Abstract

A technique for determining the existence and location of faults within an optical fiber is disclosed. The technique is accomplished through the use of fault detecting means such as an optical time domain reflectometer used in conjunction with an in-line optical filtering device which filters out selected wavelengths of optical radiation within an optical fiber. Specifically, the filtering device comprises two GRIN lenses placed along the optical path of the fiber such that light within the fiber is collimated by the first GRIN lens, and returned to the fiber by the second GRIN lens. The means of wavelength selection is achieved by an optical filter coating on the surface of at least of the GRIN lenses. The optical filter can be an edge pass filter, a band-pass filter, or an absorption filter. The invention provides for a broadband wavelength selection, which is not achieved by fused biconic type wavelength division multiplexers.

Claims

1. An optical device for filtering out specified wavelengths of optical radiation being passed from a first optical fiber having a first end to a second optical fiber having a second end, wherein said device is located between said first and second optical fibers, and wherein said device comprises:

a first collimating means for collimating optical radiation;

a second collimating means for collimating optical radiation being spaced apart from said first collimating means by a gap, wherein at least one of said first and second collimating means comprises first filter means for filtering out a first set of predetermined and unchanging wavelengths of optical radiation passing through said at least one collimating means; and

means for supporting said first and said second collimating means, said first and second optical fibers being respectively positioned adjacent to said first and second collimating means such that light being passed from said first optical fiber to said second optical fiber is forced to pass through said first collimating means, through said first filter means, and through said second collimating means.

2. The device of claim 1 wherein said filter means comprises at least one layer of a thin film device which selectively rejects or transmits optical radiation depending on its wavelength.

3. The device of claim 1 wherein said first and said second collimating means are GRIN lenses.

4. The device of claim 1 wherein

the central axis of said first optical fiber forms a first angle with respect to a first plane created by the surface of said first end;

the central axis of said second optical fiber forms a second angle with respect to a second plane created by the surface of said second end; and

wherein said first and second angles are other than 90 degrees.

5. The device of claim 4 wherein:

the surface of said first collimating means positioned adjacent to said first optical fiber forms a plane which is substantially parallel to said first plane; and

wherein

the surface of said second collimating means positioned adjacent to said second optical fiber forms a plane which is substantially parallel to said second plane.

6. The device of claim 1 wherein said first collimating means comprises said first filter means, and second collimating means comprises a second filter means for filtering out a second set of predetermined and unchanging wavelengths of optical radiation passing through said second collimating means, and wherein the light being passed from said first optical fiber to said second optical fiber is further forced to pass through said second filter means.

7. The device of claim 6 wherein said first set of predetermined wavelengths and said second set of predetermined wavelengths are identical.

8. The device of claim 6 wherein said first set of predetermined wavelengths and said second set of predetermined wavelengths are not identical.

9. The device in accordance with claim 6 wherein said first and said second collimating means function together to form either a short pass optical filter, a long pass optical filter, or a band pass optical filter depending upon the predetermined wavelengths of optical radiation for which the first and second filter means have been designed to selectively filter out.

10. An optical transmission loss locating apparatus for determining the existence and location of optical transmission loss areas within a first optical fiber connected between an optical coupling device and an optical system comprising an optical transmitter, wherein said apparatus is optically coupled to said first optical fiber via said optical coupling device, said apparatus comprising:

a second optical fiber connected to said optical coupling device;

optical fiber transmission loss locating means connected to said second optical fiber for determining the existence and location of optical transmission loss areas within said first optical fiber;

first filter means connected to said first optical fiber for filtering out a first set of specific wavelengths of optical radiation from said first optical fiber, wherein said first filter means is located between said optical transmitter and said coupling device; and

second filter means connected to said second optical fiber for filtering out a second set of specific wavelengths of optical radiation from said second optical fiber, wherein said second filter means is located between said transmission loss locating means and said coupling device.

11. The apparatus of claim 10 wherein each of said first and second filter means comprises collimating means for collimating optical radiation.

12. The apparatus of claim 11 wherein said collimating means is a GRIN lens.

13. The apparatus of claim 10 wherein said transmission loss locating means comprises means for introducing a test pulse light into said first optical fiber, and wherein the wavelength of said test pulse light differs from that of a communication light used for transmitting data within said first fiber.

14. The apparatus of claim 13 wherein said first set of specific wavelengths includes the wavelength of said test pulse light and does not include the wavelength of said communication light.

15. The apparatus of claim 13 wherein said second set of specific wavelengths includes the wavelength of said communication light and does not include the wavelength of said test pulse light.

16. The apparatus of claim 13 wherein said introducing means introduces said test pulse light towards said optical transmitter.

17. The apparatus of claim 10 wherein said transmission loss locating means is an optical time domain reflectometer.

18. An optical transmission loss locating apparatus for determining the existence and location of optical transmission loss areas within a plurality of optical fibers, each of said plurality of fibers being connected between a corresponding optical coupling device and a corresponding optical transmitter, wherein said apparatus is optically coupled to a selected optical fiber of said plurality of optical fibers via a multi-channel optical switch connected to said corresponding coupling device, said apparatus comprising:

a second optical fiber connected to said multi-channel optical switch;

optical fiber transmission loss locating means connected to said second optical fiber for determining the existence and location of optical transmission loss areas within said selected fiber;

a plurality of first filter means connected to each of said plurality of optical fibers for filtering out a first set of specific wavelengths of optical radiation from each of said plurality of optical fibers, wherein at least one of said plurality of first filter means is located between said corresponding coupling device and said corresponding optical transmitter; and

second filter means connected to said second optical fiber for filtering out a second set of specific wavelengths of optical radiation from said second optical fiber, wherein said second filter means is located between said transmission loss locating means and said optical switch.

19. The apparatus of claim 18 wherein said second filter means and each of said plurality of first filter means comprises collimating means for collimating optical radiation.

20. The apparatus of claim 19 wherein said collimating means is a GRIN lens.

21. The apparatus of claim 18 wherein said transmission loss locating means comprises means for introducing a test pulse light into each of said plurality of optical fibers, and wherein the wavelength of said test pulse light differs from that of a communication light used for transmitting data within said plurality of fibers.

22. The apparatus of claim 21 wherein said first set of specific wavelengths includes the wavelength of said test pulse light and does not include the wavelength of said communication light.

23. The apparatus of claim 21 wherein said second set of specific wavelengths includes the wavelength of said communication light and does not include the wavelength of said test pulse light.

24. The apparatus of claim 21 wherein said introducing means introduces said test pulse light towards said corresponding optical transmitter.

25. A method for determining the existence and location of optical transmission loss areas within a first optical fiber connected between an optical coupling device and an optical system comprising an optical transmitter, wherein an optical fiber transmission loss locating device is optically coupled to said first optical fiber via a second optical fiber connected to said optical coupling device, said method comprising the steps of:

(a) introducing a test pulse light by said transmission loss locating device into said first optical fiber, wherein the wavelength of said test pulse light differs from that of a communication light used for transmitting data within said first fiber;

(b) filtering out said test pulse light from said first optical fiber using a first optical filter before said test pulse light reaches said optical transmitter;

(c) filtering out said communication light from said second optical fiber using a second optical filter before said communication light reaches said transmission loss locating device;

(d) receiving a plurality of backscattered signals into said transmission loss locating device;

(e) measuring the detected intensity and time of arrival of each of said plurality of backscattered signals; and

(f) determining a loss of signal per unit length of fiber for every desired point along said first optical fiber based upon the relative intensity and time of arrival of each of said backscattered signals.

26. The method of claim 25 wherein the filtering steps of both (b) and (c) respectively include passing said test pulse light and said communication light through at least one GRIN lens.

27. The method of claim 25 wherein said introducing step introduces said test pulse light towards said optical transmitter.

29. The method of claim 25 wherein said determining step (f) includes the step of determining the existence and location of faults within said first optical fiber.

28. A method for determining the existence and location of optical transmission loss areas within a selected fiber of a plurality of optical fibers, each of said plurality of fibers being connected between a corresponding optical coupling device and a corresponding optical transmitter, wherein an optical fiber transmission loss locating device is optically coupled to said plurality of fibers via a second optical fiber connected to a multi-channel optical switch, said method comprising the steps of:

(a) optically connecting to said second fiber a selected fiber from said plurality of fibers through the corresponding coupling device of said selected fiber and said switch;

(b) introducing a test pulse light by said transmission loss locating device into said selected fiber, wherein the wavelength of said test pulse light differs from that of a communication light used for transmitting data within said selected fiber;

(c) filtering out said test pulse light from said selected fiber using one of a plurality first optical filters before said test pulse light reaches said corresponding optical transmitter;

(d) filtering out said communication light from said second optical fiber using a second optical filter before said communication light reaches said transmission loss locating device;

(e) receiving a plurality of backscattered signals into said transmission loss locating device;

(f) measuring the detected intensity and time of arrival of each of said plurality of backscattered signals; and

(g) determining a loss of signal per unit length of fiber for every desired point along said selected fiber based upon the relative intensity and time of arrival of each of said backscattered signals.

30. The method of claim 28 wherein said determining step (g) includes the step of determining the existence and location of faults within said first optical fiber.