Optical fiber test instrument calibrator

• US 4,497,575 A
• Filed: 11/01/1982
• Issued: 02/05/1985
• Est. Priority Date: 11/01/1982
• Status: Expired due to Fees

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Philipp, Harald
• Primary Examiner(s): McGraw, Vincent P.
• Application Number:
  US06/438,102
• Time in Patent Office: 827 Days
• Field of Search: 356/73.1, 356/243, 356/434, 356/435, 350/96.15, 324/74
• 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: G01M 11/39 in which light is projected from both sides of the fiber or waveguide end-face

Abstract

An optical time domain reflectometer including a light source and a light detector is calibrated using an optical directional coupler having a first port connected to the reflectometer and second and third ports connected to two opposite ends of an optical transmission member. Light pulses from the light source are introduced into the transmission member by way of one end thereof, and reflected and backscattered light from the transmission member is detected by the light detector. The reflectometer provides a display of the time relation between light pulses generated by the light source and electrical signals generated by the light detector, and the display is utilized in conjunction with a known propagation characteristic of the optical transmission member, to calibrate the reflectometer.

Claims

1. A calibration device, for calibrating an optical time domain reflectometer of the type comprising a light source for generating pulses of light, a light detector for generating electrical signals in response to light received thereby, an optical coupler for coupling the light source and the light detector to one end of an optical fiber whereby light pulses from the light source are introduced into the optical fiber by way of said one end and electrical signals are generated by the light detector in response to light leaving the optical fiber by way of said one end, and display means for providing a display of the time relation between light pulses generated by the light source and electrical signals generated by the light detector, the calibration device comprising:

a first optical transmission member having two opposite ends, one of which is connected, in use, to the coupler of the reflectometer to be tested;

optical directional coupling means having at least first, second and third ports and being connected by way of its first port to the other of said two opposite ends of the first optical transmission member, the coupling means directing light received by way of the first port to the second port but not substantially to the third port, dividing light received by way of the second port and directing it to the third port and to the first port, and directing light received by way of the third port to the second port; and

a second optical transmission member having a known propagation characteristic and having two opposite ends connected respectively to the second and third ports of the coupling means.

whereby the nature of the display provided by the display means of the reflectometer when the reflectometer is operative and is connected to the calibration device can be utilized, in conjunction with the known propagation characteristic of the second optical transmission member, to calibrate the reflectometer.

2. A device according to claim 1, wherein the known propagation characteristic is the propagation time.

3. A device according to claim 1, wherein the known propagation characteristic is the propagation loss.

4. In combination:

an optical time domain reflectometer of the type comprising a light source for generating pulses of light, a light detector for generating electrical signals in response to light received thereby, an optical coupler for coupling the light source and the light detector to one end of an optical fiber, whereby light pulses from the light source are introduced into the optical fiber by way of said one end and electrical signals are generated by the light detector in response to light leaving the optical fiber by way of said one end, and display means for providing a display of the time relation between light pulses generated by the light source and electrical signals generated by the light detector; and

a calibration device comprising an optical directional coupling means having at least first, second and third ports and connected by way of its first port to the coupler of the reflectometer, the coupling means directing light received by way of the third port to the second port, and an optical transmission member of having a known propagation characteristic and having two opposite ends connected respectively to the second and third ports of the coupling means, whereby the nature of the display provided by the display means of the reflectometer when the combination is in use can be utilized, in conjunction with the known propagation characteristic of the optical transmission member, to calibrate the reflectometer.

5. A combination according to claim 4, wherein the known propagation characteristic is the propagation time.

6. A combination according to claim 4, wherein the known propagation characteristic is the propagation loss.

7. A method of calibrating an optical time domain reflectometer of the type comprising a light source for generating pulses of light, a light detector for generating electrical signals in response to light received thereby, an optical coupler for coupling the light source and the light detector to one end of an optical fiber, whereby light pulses from the light source are introduced into the optical fiber by way of said one end and electrical signals are generated by the light detector in response to light leaving the optical fiber by way of said one end, and display means for providing a display of the time relation between light pulses generated by the light source and electrical signals generated by the light detector, said method comprising:

connecting optical directional coupling means having a least first, second, and third ports to the coupler of the reflectometer by way of said first port, the coupling means directing light received by way of the first port to the second port but not substantially to the third port, dividing light received by way of the second port and directing it to the third port and to the first port, and directing light received by way of the third port to the second port;

connecting two opposite ends of an optical transmission member having a known propagation characteristic to the second and third ports respectively of the coupling means; and

utilizing the display provided by the display means of the reflectometer, in conjunction with the known propagation characteristic of the optical transmission member, to calibrate the reflectometer.

8. A method according to claim 7, wherein the known propagation characteristic is the propagation time.

9. A method according to claim 7, wherein the known propagation characteristic is the propagation loss.