Low-coherence reflectometry method and device employing time-frequency detection

Patent metadata

Field	Value
Publication number	US-11226188-B2
Application number	US-201816495769-A
Country	US
Kind code	B2
Filing date	Mar 12, 2018
Priority date	Mar 21, 2017
Publication date	Jan 18, 2022
Grant date	Jan 18, 2022

Abstract

A low-coherence interferometer apparatus for determining information on interfaces of an object including: a polychromatic light source; an optical system generating a measurement optical beam and a reference optical beam; a delay line introducing a variable optical delay between the optical beams; detection optics combining the beams, and producing a spectral signal representative of an optical-power spectral density of the resulting interference signal; a control and processing module acquiring a plurality of spectral signals for a plurality of optical delays, determining, for each spectral signal, optical retardation information between interfering beams within a spectral measurement range, analyse the variation in the retardations, and assign the optical retardation determined on the basis of the different spectral signals to interface curves, corresponding to straight lines with positive, negative, zero or almost-zero gradient, depending on the respective optical delay of the acquisition of the spectral signals, and to deduce information of the object.

First claim

The invention claimed is:

1. A low-coherence interferometer device for determining information on the structure and/or the location of interfaces of an object, the device comprising:
a polychromatic light source;
an optical system for generating a measurement optical beam reflected by said object, and a reference optical beam;
a delay line for introducing a variable optical delay between the measurement optical beam and the reference optical beam;
an optical detector for combining the measurement optical beam and the reference optical beam and producing a spectral signal representative of an optical-power spectral density of the resulting interference signal;
a control and processing module arranged to:
acquire a plurality of spectral signals for a plurality of optical delays;
determine, for each spectral signal, optical retardation information between interfering beams within a measurement range called spectral measurement range;
analyze the evolution of said optical retardations depending on the optical delay and assign the optical retardation or retardations determined from the different spectral signals to one or more curves called interface curves defined entirely by straight lines having positive, or negative unitary, constant gradients, or zero gradients, depending on the respective optical delay of the acquisition of said spectral signals; and
deduce therefrom information on the structure and/or the location of interfaces of the object by using the interface curve or curves.

2. The device of claim 1 , which comprises a light source emitting a polychromatic light in the form of pulses and an optical detector of the spectral type.

3. The device of claim 1 , which comprises a light source with a tunable or scanning laser, and an intensity optical detector.

4. The device of claim 1 , which comprises a delay line making it possible to introduce optical delays in discrete steps.

5. The device of claim 4 , in which the delay line comprises an optical switch.

6. The device of claim 1 , which comprises a delay line making it possible to introduce a continuously variable optical delay.

7. The device of claim 1 , which comprises a common-path interferometer with a measurement arm in order to direct the measurement beam towards the object, and a semi-reflective element inserted in said measurement arm in order to generate the reference optical beam.

8. The device of claim 7 , which comprises a differential delay line with optical reflectivity at a fixed position, and the delay line.

9. A method for determining information on the structure and/or the location of interfaces of an object utilizing a low-coherence interferometer, the method comprising the steps of:
emitting a polychromatic light with a polychromatic light source;
generating a measurement optical beam reflected by said object to be measured, and a reference optical beam;
introducing a variable optical delay between the measurement optical beam and the reference optical beam with a delay line;
combining, by means of optical detection, the measurement optical beam and the reference optical beam and producing a spectral signal representative of an optical-power spectral density of the resulting interference signal;
acquiring a plurality of spectral signals for a plurality of optical delays;
determining, for each spectral signal, optical retardation information between interfering beams within a measurement range called spectral measurement range;
analyzing the evolution of said optical retardations depending on the optical delay and assignment of the optical retardation or retardations determined from the different spectral signals to one or more curves, called interface curves, defined entirely by straight lines having positive, or negative unitary, constant gradients, or zero gradients, depending on the respective optical delay of acquisition of said spectral signals; and
deducing information on the structure and/or the location of interfaces of the object by using the interface curve or curves.

10. The method of claim 9 , which comprises acquiring a plurality of spectral signals for a plurality of optical delays within a range of optical delays making it possible to generate optical route equalities between the reference optical beam and the measurement optical beam when the object is located within a measurement range called temporal measurement range.

11. The method of claim 9 , which comprises acquiring a plurality of spectral signals for a plurality of optical delays spaced apart by an increment corresponding at most to half of the spectral measurement range.

12. The method of claim 9 , in which determining optical retardation information between interfering beams comprises calculating a temporal interference signal, and determining positions of interference peaks.

13. The method of claim 9 , in which the structure and/or location of interfaces of the object is determined by determining the respective optical delay or delays for which the optical retardation along an interface curve is zero.

14. An appliance comprising a device according to claim 1 , implementing a method for determining information on the structure and/or the location of interfaces of an object utilizing a low-coherence interferometer, comprising the steps of:
emitting a polychromatic light with a polychromatic light source;
generating a measurement optical beam reflected by said object to be measured, and a reference optical beam;
introducing a variable optical delay between the measurement optical beam and the reference optical beam with a delay line;
combining, by means of optical detection, the measurement optical beam and the reference optical beam and producing a spectral signal representative of an optical-power spectral density of the resulting interference signal;
acquiring a plurality of spectral signals for a plurality of optical delays;
determining, for each spectral signal, optical retardation information between interfering beams within a measurement range called spectral measurement range;
analyzing the evolution of said optical retardations depending on the optical delay and assignment of the optical retardation or retardations determined from the different spectral signals to one or more curves, called interface curves, corresponding to straight lines having positive, or negative unitary gradients, or zero gradients, depending on the respective optical delay of acquisition of said spectral signals; and
deducing information on the structure and/or the location of interfaces of the object by using the interface curve or curves.

15. The appliance according to claim 14 , comprising measuring distances and/or thicknesses of layers on an object comprising components and/or elements of integrated electronics and/or integrated optics.

16. The appliance according to claim 14 , comprising measuring distances and/or thicknesses of layers or layer structures on a biological object.

Assignees

• Fogale Nanotech

Inventors

• Courteville Alain
• Neel Christian
• Godavarthi Charankumar

Classifications

• G01B9/02078

  Caused by ambiguity · CPC title

• G01B9/02057

  by using common path configuration, i.e. reference and object path almost entirely overlapping · CPC title

• G01N21/4795

  spatially resolved investigating of object in scattering medium (in vivo A61B) · CPC title

• A61B5/1075

  for measuring dimensions by non-invasive methods, e.g. for determining thickness of tissue layer (A61B8/0858 takes precedence) · CPC title

• G01B9/0209 Primary

  Low-coherence interferometers · CPC title