Distance measuring device with magneto-optical effect and measuring chain incorporating same

• US 6,521,884 B1
• Filed: 04/09/2001
• Issued: 02/18/2003
• Est. Priority Date: 10/09/1998
• Status: Expired due to Fees

• Current Assignee: Thomson-Csf Sextant
• Original Assignee: Thomson-Csf Sextant
• Inventors: Breda, Jean-Marc
• Primary Examiner(s): Pyo, Kevin
• Assistant Examiner(s): Sohn, Seung C.
• Application Number:
  US09/806,471
• Time in Patent Office: 680 Days
• Field of Search: 250/225, 250/227.17, 250/227.21, 250/231.1, 324/96, 324/174-175, 324/244.1, 324/260, 324/262
• US Class Current: 250/225
• CPC Class Codes: G01B 11/14 for measuring distance or clearance between spaced objects or spaced apertures G01B11/26 takes precedence; rangefinders G01C3/00
• CPC Class Codes: G01D 5/344 using polarisation G01D5/35303 takes precedence

Abstract

A magneto-optical effect distance measuring device and measuring rig incorporating the device. The device can measure the distance separating two members which can be displaced one with respect to the other by the magneto-optical effect. A permanent magnet is fixed on one of the members and an electro-optical device is fixed on the other member. The electro-optical device includes a diode emitting an optical beam. Further, a Faraday-effect magneto-optical film is disposed, on the one hand, between a polarizer and an analyser and, on the other hand, in the magnetic field of the magnet when the two members are in proximity to one another, the optical beam passing through the assembly. A diode receives the optical beam retransmitted by the analyzer so as to transform the luminous intensity of the beam into an electrical signal whose amplitude depends on the distance separating the two members when they are in proximity to one another. Such a device may find particular application to monitoring the closure of aircraft doors.

Claims

1. Device for measuring the distance separating two members which can be displaced one with respect to the other comprising a permanent magnet fixed on a first surface of one of the members and a first electro-optical device fixed on a second surface of the other member, the first electro-optical device comprising:

a beam source configured to emit an optical beam along a first path extending along the second surface and leading to an optical assembly,

a Faraday-effect magneto-optical film disposed with optical components configured to act as a polarizer and an analyser along a second path inside the optical assembly, the Faraday-effect magneto-optical film also being disposed in a magnetic field of the permanent magnet when the first and second surfaces of the two members are in proximity to one another, the optical beam entering the optical assembly and traveling along the second path to interact with the Faraday-effect magneto-optical film and the optical components and then exiting from the optical assembly, and

a photodetector disposed to receive the optical beam exiting from the optical assembly and configured to transform the optical beam luminous intensity into an electric signal whose amplitude depends on the distance separating the first and second surfaces of the two members when they are proximate to one another.

2. The device according to claim 1, further comprising a second electro-optical device identical to the first electro-optical device and also fixed on the second surface, wherein the identical electro-optical devices provide two optical beams that illuminate the two photodetectors of the two electro-optical devices after passing through the two optical assemblies including the two Faraday-effect magneto-optical films and the optical components of each identical electro-optical device.

3. The device according to claim 1, wherein the Faraday-effect magneto-optical film is disposed between the optical component configured to act as the polarizer and a return mirror configured to reflect the optical beam back along the second optical path to again interact with the optical component configured to act as polarizer so that the return mirror and the optical component configured to act as the polarizer together form the optical component configured to act as the analyzer.

4. The device according to claim 1, wherein one of the members is an aircraft door.

5. Rig for measuring distance between two members which can be displaced one with respect to the other, comprising:

a source configured to emit an optical beam;

a single optical fiber coupled at a first end to said source to receive and transmit the optical beam along the single optical fiber;

a photodetector coupled to said first end of the single optical fiber and configured to transform the luminous intensity of the optical beam received from a return of the optical beam transmitted along the single optical fiber into an electrical signal whose amplitude depends on the distance separating the two members when they are in proximity to one another

a specified number N of magneto-optical effect sensors coupled to a second end of the single optical fiber, each sensor comprising a permanent magnet fixed on a first one of the members and an electro-optical device fixed on a second one of the members, each electro-optical device comprising,

a Faraday-effect magneto-optical film disposed along an optical path in the electro-optical device between a polarizer and a reflector, the Faraday-effect magneto-optical film also being disposed in the magnetic field of the permanent magnet when the two members are in proximity to one another, the optical beam being transmitted from the single optical fiber along the optical path through the polarizer and the Faraday-effect magneto-optical film to the reflector to be reflected and returned through the polarizer acting as an analyser and back to the single optical fiber, and

a sensor optical fiber of specified length which is different for each sensor optical fiber of each electro-optical device so as to provide a different temporal shift for each sensor optical fiber, with each sensor optical fiber being coupled at a first sensor optical fiber end to the polarizer and coupled at a second sensor optical fiber end to the second end of the single optical fiber.

6. The rig according to claim 5, wherein the lengths of each of the sensor optical fibers of the sensors are all different from one another so as to temporally separate the signals provided by each electro-optical device in response to a single excitation signal applied to the source configured to emit an optical beam pulse as the optical beam.

7. The rig according to claim 6, wherein the lengths of the optical fibers are chosen to be proportional by an integer number to the length L of the shortest sensor optical fiber.

8. The rig according to claim 7, wherein the single excitation signal is only a few nanoseconds induration.

9. The rig according to claim 5, wherein one of the sensors is configured to provide a constant proximity distance value as a reference value.

10. The rig according to claim 5, wherein polarizer in each sensor is provided by a polarization-maintaining single-mode optical fibers and the source configured to emit an optical beam is further configured as a source emitting polarized light and an analyser is disposed at the first end of the single optical fiber in front of the photodetector.

11. The rig according to claim 5, wherein a lens is interposed between the polarizer and each sensor optical fiber.

12. The rig according to claim 5, wherein one of the members is an aircraft door.