Apparatus, method and computer program for determining a distance to an object using a determined peak width of a self-mixing interference (SMI) signal

Patent metadata

Field	Value
Publication number	US-9677873-B2
Application number	US-201113811397-A
Country	US
Kind code	B2
Filing date	Jul 19, 2011
Priority date	Jul 26, 2010
Publication date	Jun 13, 2017
Grant date	Jun 13, 2017

Abstract

An apparatus, method and computer program for measuring a distance using a self-mixing interference (SMI) unit that generates an SMI signal. The SMI unit comprises a laser emitting a first laser beam directed to an object and wherein the SMI signal depends on an interference of the first laser beam and a second laser beam reflected by the object. A peak width determination unit determines a peak width of the SMI signal, and a distance determination unit determines a distance between the object and the SMI unit depending on the determined peak width of the SMI signal. Since the distance is determined depending on the peak width of the SMI signal, without requiring a laser driving current modulation, advanced electronics for modulating the driving current of the laser are not needed. This reduces the technical efforts needed for determining the distance.

First claim

The invention claimed is:

1. An apparatus for measuring a distance, the apparatus comprising:
a self-mixing interference (SMI) unit comprising a laser configured to emit a first laser beam directed to an object, a cavity SMI positioned to receive a portion of the first laser beam and a second laser beam as a reflection of the first laser beam from the object, and a detector configured to generate an SMI signal based on an interference of the portion of the first laser beam by the second laser beam;
a distance measuring processor circuit coupled to the detector to receive the generated SMI signal, and coupled to a storage medium having instructions stored thereon, the distance measuring processor circuit configured by the instructions stored on the storage medium to:
determine a peak width of a frequency peak in a frequency spectrum of the received SMI signal,
determine a distance between the object and the SMI unit based on the determined peak width of the SMI signal and an assignment between peak widths of the SMI signal and distances between the object and the SMI unit within a predefined distance range in which the peak widths of the SMI signal varies substantially linearly with distances between the object and the SMI unit, and
produce an output indicating the determined distance between the object and the SMI unit.

2. The apparatus of claim 1 , wherein the distance measuring processor circuit is further configured by the instructions stored on the storage medium to calculate a normalized SMI signal from the received SMI signal and determine the peak width of the normalized SMI signal.

3. The apparatus of claim 1 , wherein the distance measuring processor circuit is further configured by the instructions stored on the storage medium to calculate the distance within a plurality of predefined distance ranges in which the distance depends linearly on the peak width.

4. The apparatus of claim 1 , further comprising a focusing unit positioned between the emitted first laser beam and the object to focus the first laser beam, wherein the focusing unit comprises modifiable focusing settings, wherein the distance measuring processor circuit comprises different assignments between a) peak widths of the SMI signal and b) distances between the object and the SMI unit in different predefined distance ranges, wherein the different assignments correspond to different focusing settings of the focusing unit and wherein the distance measuring processor circuit is coupled to receive the focus setting of the focusing unit and is configured by the instructions stored on the storage medium to determine the distance between the object and the SMI unit depending on the determined peak width of the SMI signal and the assignment which corresponds to the received focusing setting of the focusing unit.

5. The apparatus of claim 1 , wherein the distance measuring processor circuit is configured by the instructions stored on the storage medium to detect whether the apparatus is in a feedback independent regime in which the peak width is independent of the intensity of the second laser beam.

6. The apparatus of claim 5 , wherein the distance measuring processor circuit is configured by the instructions stored on the storage medium to only determine the distance when the feedback independent regime detection unit detects that the apparatus is in the feedback independent regime.

7. The apparatus of claim 5 , wherein the distance measuring processor circuit is configured by the instructions stored on the storage medium to determine whether the apparatus is in the feedback independent regime based on an amplitude of the SMI signal being smaller than a predefined threshold.

8. The apparatus of claim 5 , wherein the apparatus comprises an attenuator positioned to attenuate the second laser beam and wherein the distance measuring processor circuit is configured by the instructions stored on the storage medium to determine whether the apparatus is in the feedback independent regime based on a peak width measured while the attenuation of the second laser beam is modified by the attenuator.

9. The apparatus of claim 5 , wherein the apparatus comprises an attenuator positioned to attenuate the second laser beam and wherein the attenuator is controlled to actively modify the attenuation of the second laser beam based on whether the apparatus is in the feedback independent regime.

10. The apparatus of claim 1 , wherein the apparatus further comprises: a focusing unit positioned to focus the first laser beam, wherein the distance measuring processor circuit is coupled to the focusing unit and configured by the instructions stored on the storage medium to control the focusing unit depending on the determined distance.

11. A focusing apparatus comprising:
a self-mixing interference (SMI) unit comprising a laser configured to emit a first laser beam directed to an object, a cavity positioned to receive a portion of the first laser beam and a second laser beam as a reflection of the first laser beam from the object, and a detector configured to generate an SMI signal based on an interference of the portion of the first laser beam by the second laser beam;
a focusing unit positioned between the emitted first laser beam and the object to change a focus of the first laser beam;
a distance measuring processor circuit coupled to the detector to receive the generated SMI signal, coupled to the focusing unit to control the focus of the focusing unit and coupled to a storage medium having instructions stored thereon, the distance measuring processor circuit configured by the instructions stored on the storage medium to:
determine a peak width of a frequency peak in a frequency spectrum of the received SMI signal within a predefined distance range in which the peak widths of the SMI signal varies substantially linearly with distances between the object and the SMI unit,
control the focus of the focusing unit based on the determined peak width.

12. The focusing apparatus of claim 11 , wherein the distance measuring processor circuit is configured by the instructions stored on the storage medium to control the focusing unit such that the peak width of the SMI signal remains constant.

13. A method for measuring a distance, the method performed by a distance measuring processor circuit coupled to a storage medium having instructions stored thereon, the distance measuring processor circuit configured by the instructions stored on the storage medium to:
control emission of a first laser beam from a self-mixing interference (SMI) unit directed to an object;
receive a portion of the first laser beam and a second laser beam as a reflection of the first laser beam from the object;
generate an SMI signal based on an interference of the portion of the first laser beam by the second laser beam; determining a peak width of a frequency peak in a frequency spectrum of the SMI signal,
determine a distance between the object and the SMI unit based on the determined peak width of the SMI signal and an assignment between peak widths of the SMI signal and distances between the object and the SMI unit within a predefined distance range in which the peak widths of the SMI signal varies substantially linearly with distances between the object and the SMI unit, and
produce an output indicating the determined distance between the object and the SMI unit.

Assignees

• Van Der Lee Alexander Marc
• Carpaij Mark
• Koninl Philips Electronics Nv

Inventors

• Van Der Lee Alexander Marc
• Carpaij Mark

Classifications

• G01S7/4916

  using self-mixing in the laser cavity · CPC title

• G01B11/14 Primary

  for measuring distance or clearance between spaced objects or spaced apertures (G01B11/26 takes precedence; rangefinders G01C3/00) · CPC title

• G01S17/46

  Indirect determination of position data · CPC title

• G01S7/497 Primary

  Means for monitoring or calibrating · CPC title

• G01S17/32

  using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated · CPC title