Optical low-coherence reflectometry using optical amplification

• US 5,291,267 A
• Filed: 01/22/1992
• Issued: 03/01/1994
• Est. Priority Date: 01/22/1992
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Sorin, Wayne V., Baney, Douglas M.
• Primary Examiner(s): Turner, Samuel A.
• Assistant Examiner(s): KIM, ROBERT H
• Application Number:
  US07/823,936
• Time in Patent Office: 769 Days
• Field of Search: 250/227.19, 250/227.27, 372/6, 372/1, 372/39, 372/69, 385/12, 356/350, 356/345, 356/349, 356/359, 356/73.1
• US Class Current: 356/479
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02003 using beat frequencies
• CPC Class Codes: G01B 9/0209 Low-coherence interferometers
• CPC Class Codes: G01D 5/266 by interferometric means G01D5/353 takes precedence
• CPC Class Codes: G01M 11/3172 Reflectometers detecting the back-scattered light in the frequency-domain, e.g. OFDR, FMCW, heterodyne detection
• CPC Class Codes: G01M 11/319 Reflectometers using stimulated back-scatter, e.g. Raman or fibre amplifiers

Abstract

An improved low-coherence reflectometer is disclosed for use in measuring Rayleigh backscattering. The invention utilizes an optical amplifier to amplify the backscattered light thereby reducing the measurement times. The preferred optical amplifier is a diode-pumped superfluorescent fiber which acts both as the amplifier and the low-coherence light source. Reductions in signal averaging times of a factor of 100 are achieved by the use of the amplifier.

Claims

1. An optical interferometer for measuring the optical properties of a device, said interferometer comprising:

source means for providing a low-coherence light signal;

splitting means for dividing said low-coherence light signal into first and second light signals;

means for applying a portion said first light signal to said device;

adding means for combining light signals on first and second ports thereof to generate a combined light signal;

detection means for measuring the amplitude of said combined light signal;

means for collecting a portion of the backscattered light generated by the application of said first light signal to said device and for inputting a portion of said collected backscattered light to said first port of said adding means;

means for inputting a portion of said second light signal to said second port of said adding means;

means for varying the difference in the optical path lengths traveled by said backscattered light and said second light signal before entering said adding means; and

optical amplification means for amplifying said portion of said collected backscattered light prior to said portion of said backscattered light entering said adding means such that the intensity of said backscattered light entering said adding means is increased relative to said second light signal.

2. The interferometer of claim 1 wherein said amplification means further comprises a light source which acts as said light source means.

3. The interferometer of claim 2 wherein said amplification means comprises a diode-pumped superfluorescent fiber.

4. The interferometer of claim 2 wherein said amplification means comprises a semiconductor-based optical amplifier.

5. The interferometer of claim 1 wherein said means for varying the difference in the optical path lengths traveled by said backscattered light and said second light signal before entering said adding means comprises a moveable mirror comprising a portion of the optical path between said adding means and said collecting means.

6. The interferometer of claim 5 wherein said collecting means includes said splitting means and wherein said amplification means is located between said splitting means and said moveable mirror.