Device for interferometric distance measurement

Patent metadata

Field	Value
Publication number	US-10746532-B2
Application number	US-201816047691-A
Country	US
Kind code	B2
Filing date	Jul 27, 2018
Priority date	Aug 1, 2017
Publication date	Aug 18, 2020
Grant date	Aug 18, 2020

Abstract

An interferometric distance measurement device includes a multiple wavelength light source, supplying a light beam having at least three different wavelengths. An interferometer unit is provided, which splits the light beam into a measuring light beam and a reference light beam. The measuring and reference light beams reflected back by measuring and reference reflectors are superimposed in an interfering manner to form an interference light beam. The interference light beam is split via a detection unit such that, in each instance, a plurality of phase-shifted, partial interference signals result per wavelength. With the aid of a signal processing unit, an absolute position information item regarding the measuring reflector is determined from the partial interference signals of different wavelengths.

First claim

What is claimed is:

1. A device for interferometric distance measurement, comprising:
a multiple wavelength light source adapted to emit a light beam having at least three different wavelengths and arranged as a fiber laser including at least three different Bragg gratings having grating constants matched to the wavelengths;
an interferometer unit adapted to split up the light beam into a measuring light beam that propagates in a measuring arm in a direction of a measuring reflector and that is reflected back by the measuring reflector and into a reference light beam that propagates in a reference arm in a direction of a stationary reference reflector and that is reflected back by the reference reflector, the measuring and reference light beams reflected back by the measuring and reference reflectors being superimposed in an interfering manner to form an interference light beam;
a detection unit adapted to split the interference light beam to generate a plurality of phase-shifted partial interference signals for each wavelength; and
a signal processing device adapted to determine an absolute position of the measuring reflector from the partial interference signals of the different wavelengths;
wherein the multiple wavelength light source includes:
a pump light source;
at least three Bragg gratings integrated into at least one laser-active fiber, each Bragg grating having a phase shift of magnitude π; and
coupling optics adapted to couple pump radiation emitted by the pump light source into the laser-active fiber.

2. The device according to claim 1 , wherein the Bragg gratings are positioned in the laser-active fiber to completely overlap along a fiber extension direction, the phase shifts of all of the Bragg gratings being arranged at the same location.

3. The device according to claim 1 , wherein the Bragg gratings are displaced with respect to each other along the fiber extension direction by particular offset distances, the phase shifts of all of the Bragg gratings being displaced with respect to each other along a fiber extension direction, by the offset distances.

4. The device according to claim 3 , wherein the multiple wavelength light source includes three Bragg gratings, and
a) at offset distances between 0% and 50% of an effective grating length of a Bragg grating, the laser-active fiber includes first grating sections having Bragg gratings with one grating constant, second grating sections having two overlapping Bragg gratings with different grating constants, and third grating sections having three overlapping Bragg gratings of different grating constants;
b) at offset distances between 50% and 100% of the effective grating length of a Bragg grating, the laser-active fiber includes first grating sections having Bragg gratings of one grating constant and second grating sections having two overlapping Bragg gratings of different grating constants; or
c) at offset distances of 100% of the effective grating length of a Bragg grating, the laser-active fiber includes only grating sections having Bragg gratings of one grating constant.

5. The device according to claim 1 , wherein the laser-active fiber includes an erbium-doped, single-mode glass fiber adapted to emit laser radiation having a specific polarization direction.

6. The device according to claim 1 , wherein the laser-active fiber is mounted in tension in a fiber holding device, between two fixing points, and the Bragg gratings are arranged between the two fixing points of the fiber holding device.

7. The device according to claim 1 , further comprising a control unit adapted to control the multiple wavelength light source via at least one control element, in order to generate laser radiation having specific wavelengths, wherein an electrical signal derived from an optical signal of only one of the different wavelengths acts as an input signal of the control unit.

8. The device according to claim 7 , wherein the control elements include:
a) a piezoelectric actuator unit adapted to exert a specific mechanical tension on the laser-active fiber; and/or
b) a tempering unit adapted to set a specific temperature of the laser-active fiber; and/or
c) a current source adapted to set a specific pump current of a pumping light source for the laser-active fiber.

9. The device according to claim 7 , wherein the control elements include a piezoelectric actuator unit adapted to exert a specific mechanical tension on the laser-active fiber.

10. The device according to claim 7 , wherein the control elements include a tempering unit adapted to set a specific temperature of the laser-active fiber.

11. The device according to claim 7 , wherein the control elements include a current source adapted to set a specific pump current of a pumping light source for the laser-active fiber.

12. The device according to claim 1 , wherein the multiple wavelength light source is adapted to emit radiation having a first wavelength and two further wavelengths, satisfying the following conditions:

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Assignees

• Heidenhain Gmbh Dr Johannes

Inventors

• Meissner Markus
• Holzapfel Wolfgang

Classifications

• G01B9/02007 Primary

  Two or more frequencies or sources used for interferometric measurement (using only beat G01B9/02003) · CPC title

• G01S17/36

  with phase comparison between the received signal and the contemporaneously transmitted signal · CPC title

• G01B11/026

  by measuring distance between sensor and object (G01B11/0608 takes precedence) · CPC title

• G01S17/10

  using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32) · CPC title

• H01S3/1067

  using pressure or deformation · CPC title