US 2014/0176959 A1Published application

Swing-style and high signal-to-noise ratio demodulation devices and corresponding demodulation method for the measurement of low coherence interference displacement

AssigneeTianjin University

InventorsTiegen Liu, Junfeng Jiang, Jinde Yin, Kun Liu, Shaohua Wang

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Abstract

This invention provides a swing-style and high signal-to-noise ratio low coherence interference demodulation devices and the corresponding demodulation method for the measurement of displacement. In the displacement sensing method, the optical path difference, which is built by the light reflections from the reference surface and the test object, varies with the displacement of the test object. When the reflected signal lights is sent to a low coherence polarization interference system, the birefringent wedge formulates a spatial distribution of optical path difference, from which the optical path difference of the reflection signals thus can be demodulated. In the displacement scanning method, the reflected signal lights are collimated and transferred to a time scanner consisting of a rotating mirror and a f-θ lens, to perform thin light beam scanning along the longitudinal direction of a birefringent wedge. This innovation provides two demodulation devices that are both applicable for the measurement methods. One uses a linear camera array and the other uses a linear micropore array and single PIN photoelectric detector, to receive interference fringes. Since the energy of the scanning beam is highly concentrated, the signal-to-noise ratio for low coherence interference signal is significantly higher than that of the traditional devices. In addition, the accuracy of these demodulation devices is significantly improved, because the linear camera array and the linear micropore array maintain a consistent spatial position of the received light spot.

Claims6

Dependent claims

A swing-style and high signal-to-noise ratio low coherence interference demodulation device for the measurement of displacement, comprising:

a light source which is a broadband light source with wide spectrum, such as LED, SLD and halogen lamps;
an optical circulator for sending the light from the light source to an object to be test and collecting the reflected signal light;
a GRIN lens for collimating and outputting the light beam from the optical circulator, and partially reflecting the light by the coated end surface;
a fixed mirror fixed on the test object, for reflecting optical signals from the GRIN lens;
a collimating device which collimates the signal light from the optical circulator into a thin beam, and sends the light beam to a rotating mirror;
a rotating mirror which reflects the collimated thin beam to a polarization interference system;
the scanning of the thin beam along the thickness variation direction of the optical wedge is conducted by swinging the rotating mirror;
and the scanning covers all the pixels of the linear array CCD;
a f-θ lens which conducts a parallel scan using the thin beam, along the longitudinal direction of the narrow strip shaped birefringent wedge, in which the reflection point of the rotating mirror coincides with the focus of the f-θ lens;
a polarizer for polarizing the signal light from the f-θ lens, where the angle between the polarizing direction and the optical axis of birefringent wedge is 45°;
a narrow strip shaped birefringent wedge which turns the linearly polarized light beam into two orthogonal beams, and the two linearly polarized light beams have a linearly distributed spatial optical path difference along the thickness variation direction of the optical wedge;
a polarization analyzer for projecting the two orthogonal linearly polarized light beams to generate interference, in which the polarization direction is parallel or perpendicular to that of the polarizer;
a linear camera array, a linear array CCD or CMOS, to collect the interference fringes produced by the polarization analyzer;
a data processing unit:
a computer or an embedded computing system, to process the collected interference fringes data and obtain the displacement information of the test object.

12 more elements

A swing-style and high signal-to-noise ratio low coherence interference demodulation device for the measurement of displacement, comprising

a light source which is a broadband light source with wide spectrum, such as LED, SLD and halogen lamps;
an optical circulator which sends the light from the light source to the test object and collects the reflected signal light;
a GRIN lens which is used to collimate and output the light beam from the optical circulator, and to partially reflect the light by the electroplated end surface;
a fixed mirror which is fixed on the test object for reflecting optical signals from the GRIN lens;
a collimating device which collimates the signal light reflected from the optical circulator into a thin beam, and sends the light beam to a rotating mirror;
a rotating mirror which reflects the collimated thin beam to a polarization interference system;
the scanning of the thin beam along the thickness variation direction of the optical wedge is performed by swinging the rotating mirror;
and the scanning covers all the pixels of the Linear array CCD.
a f-θ lens which conducts a parallel scan using the thin beam, along the longitudinal direction of the narrow strip shaped birefringent wedge, in which the reflection point of the rotating mirror coincides with the f-θ lens focus.
a polarizer which is used to polarize the signal light from the f-θ lens, where the angle between the polarizing direction and the optical axis of birefringent wedge is 45°;
a narrow strip shaped birefringent wedge which turns the linearly polarized light beam into two orthogonal beams, and the two linearly polarized light beams have a linearly distributed spatial optical path difference along the thickness variation direction of optical wedge;
a polarization analyzer which projects the two orthogonal linearly polarized light beams to generate interference, in which the polarization direction is parallel or perpendicular to the polarizer;
a micropore linear array for controlling the sampling position when the light beam scans;
A focusing lens which focuses the light beams, passing through the micropore linear array, into one point;
a PIN detector which receives the focused optical signals, and converting the light signals into electric signals;
and
a data processing unit which is a computer or an embedded computing system, to process the collected interference fringes data and obtain the displacement information of the test object.

14 more elements

Dependencies are inferred from the claim text.

Facts

Application: 13/880,730Filed 28 May 2012
Priority: CN 2011102269639 Aug 2011
Published: 26 Jun 2014
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

G01B 9/0209
Interferometers: low-coherence interferometers
G01B 9/02057
Passive reduction of errors: by using common path configuration, i.e. reference and object path almost entirely overlapping
G01B 9/02065
By particular adjustment of coherence gate, i.e. adjusting position of zero path difference in low coherence interferometry: using a second…
G02B 6/29302
With wavelength selective means: based on birefringence or polarisation, e.g. wavelength dependent birefringence, polarisation interferometers