CN101666685B - Device and method for extracting low coherence interference center fringe based on two-dimensional image - Google Patents

Abstract

The invention discloses a device and method for extracting low-coherence interference center fringes based on a two-dimensional image. The device consists of a low-coherence light source, a 3dB fiber coupler, a first single-mode fiber, a second single-mode fiber, a CMOS camera and a computer Composition: The light emitted from the low-coherence light source is divided into two beams after passing through the 3dB fiber coupler. One beam of light is irradiated on the lens of the CMOS camera after passing through the first single-mode fiber, and the other beam of light is passed through the second single-mode fiber. Irradiated on the lens of the CMOS camera, the two beams of light interfere in the CMOS camera to form a low-coherence interference fringe image and output it to the low-coherence interference center fringe extraction module in the computer. The invention adopts a CMOS camera to obtain optical information, and changes the traditional form of converting optical signals by using a photodetector.

Description

A device and method for extracting low-coherence interference center fringes based on two-dimensional images

technical field

The present invention relates to a device and method for extracting low-coherence interference center fringe information, more particularly, a device for extracting low-coherence interference center fringes by using a CMOS camera for image acquisition and then comparing fringe contour areas.

Background technique

The essence of light interference measurement is to measure with the wavelength of light wave as the unit. Traditional interferometry mainly detects interference fringes. By detecting changes in the position, shape, and spacing of fringes, the tiny values of some physical quantities are accurately measured. Among these measurement systems, the most commonly used are measurement systems that use various single-mode or narrow-band coherent laser devices as light sources; among them, lasers require extremely high accuracy of optical components, which often makes the system more complicated; therefore, This type of system has strict requirements on the external environment such as temperature, humidity, and pressure. When the above conditions cannot be met, it will make it difficult to guarantee the accuracy, repeatability, and long-term stability of the measurement.

Nowadays, in low-coherence measurement systems, photodetectors are mainly used to collect interference signals, that is, the collected interference signals are one-dimensional information. Therefore, in the low-coherence measurement system based on photodetectors, the processing of interference signals is mainly the processing of one-dimensional information.

Contents of the invention

One of the purposes of the present invention is to provide a simple structure, easy to implement low-coherence interference center fringe extraction device, the device consists of low-coherence light source, 3dB fiber coupler, the first single-mode fiber, the second single-mode fiber, CMOS Camera and computer system composition. The computer system is formed by a computer and a low-coherence interference center fringe extraction module stored in the computer.

The second object of the present invention is to propose a method for extracting low-coherence interference center fringes based on a two-dimensional image. The method first adopts an approximation method to obtain the fringe profile information of the two-dimensional image, then compares the area of the fringe profile information, and applies The contour coordinate relation finally obtains the low-coherence interference center fringe information.

In the present invention, the low-coherence interference center fringe extraction module includes a binarized image unit, an outline extraction unit, an outline area comparison unit and a reference point coordinate analysis unit.

The advantage of device of the present invention is:

(A) Using a CMOS camera to acquire optical information has changed the traditional way of converting optical signals using photodetectors.

(B) Using the mature computing power of the existing computer and the low-coherence interference central fringe extraction module embedded in the computer hard disk, the central fringe in the fringe image can be effectively extracted and tracked, and the coordinates of the reference point can be obtained and displayed.

(C) Combining a CMOS camera with a computer (the computer stores a low-coherence interference center fringe extraction module), it has strong anti-electromagnetic interference ability. Since the interference fringe collection and processing parts do not contain signal amplification, filtering and other circuits, it is anti-electromagnetic Interference ability is relatively strong.

The advantages of the method for extracting low-coherence interference center fringes of the present invention are:

(1) It is simpler and more economical to obtain optical information than the traditional method of using photodetectors.

(2) The combination of computer and low-coherence interference central fringe extraction module is used to extract the low-coherence interference central fringe. Its measurement accuracy is high, and the light intensity information is converted into the brightness information of the image. It is easy to distinguish between the central fringe and the ±1-level fringe. , so that it is easier to extract the central fringe; at the same time, the interference signal processing process is simpler, more intuitive, and faster, which effectively improves the measurement efficiency.

Description of drawings

FIG. 1 is a device for extracting low-coherence interference center fringes based on two-dimensional images according to the present invention.

Fig. 2 is a schematic diagram of the distance between the two optical fibers and the lens of the CMOS camera in the present invention.

Fig. 3 is a schematic interface diagram of the low-coherence interference central fringe extraction module of the present invention.

Fig. 4 is a black-and-white image with central fringe information after binarization processing in the present invention.

Fig. 5 is a black and white image with outline information stripes obtained by the present invention.

Fig. 6 is a black-and-white image of the present invention with stripe center mark.

In the figure: 1. Low coherent light source 2.3dB fiber coupler 3. The first single-mode fiber 4. The second single-mode fiber 5. CMOS camera 6. Computer

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings.

Referring to Fig. 1, shown in Fig. 2, the present invention is a kind of extraction device of the low-coherence interference center fringe based on two-dimensional image, and this device is made of low-coherence light source 1, 3dB optical fiber coupler 2, the first single-mode fiber 3, the first Two single-mode optical fibers 4, a CMOS camera 5 and a computer 6 are formed, wherein a low-coherence light source 1, a 3dB fiber coupler 2, a first single-mode optical fiber 3 and a second single-mode optical fiber 4 form an optical fiber Young's interferometer, and the optical fiber Young's interferometer The interferometer is the measured object; the low-coherence interference center fringe extraction module is stored in the hard disk of the computer 6, and the low-coherence interference center fringe extraction module is written under the VC 6.0 compilation environment, based on OpenCV (opensource computer vision library). In the present invention, the low-coherence interference fringe acquisition and processing software interface written based on the low-coherence interference signal two-dimensional image processing method as shown in Figure 3, it is under the VC 6.0 compilation environment, based on OpenCV (open source computer vision library) implemented. The left half of the interface can display the collected fringe images in real time (as shown in FIG. 6 ), and the right half can display and save the interference fringe images captured by the CMOS camera 5 . After the interference fringe image is collected, the central fringe in the low-coherence fringe image can be extracted, identified, and tracked, and the coordinate value of the reference point can be obtained, which is the circle in Figure 6. In addition, this system can also set the size and brightness of the image and save the collected fringe image as a video.

In the present invention, the minimum configuration of computer 6 is CPU 2GHz, memory 2GB, hard disk 180GB; operating system is windows 2000/2003/XP.

The connection of each part in the extraction device of the present invention is (seeing Fig. 1, shown in Fig. 2): the A end of 3dB fiber optic coupler 2 is connected with low coherence light source 1, the B end of 3dB fiber optic coupler 2 is connected with the first single-mode One end of the optical fiber 3 is connected, there is a gap d ₃ (d ₃ =2cm～4cm) between the other end of the first single-mode optical fiber 3 and the lens 51 of the CMOS camera 5, the C end of the 3dB fiber coupler 2 is connected to the second single-mode optical fiber One end of the mode fiber 4 is connected, and there is a gap d ₄ (d ₄ =2cm～4cm) between the other end of the second single mode fiber 4 and the lens 51 of the CMOS camera 5, and a CMOS camera is adopted between the CMOS camera 5 and the computer 6 5. The USB data transmission line that comes with it is connected on the USB interface of the computer 6. The distance d ₀ between the first single-mode fiber 3 and the second single-mode fiber 4 is ≤0.5mm.

The optical path of the extraction device of the present invention is as follows: the light emitted by the low-coherence light source 1 with a center wavelength of 820nm, a line width spectrum of 39.6nm, and an optical power of 14mW is divided into two beams of light after being passed through a 3dB fiber coupler 2, and one beam of light is passed through After the first single-mode fiber 3 is irradiated on the lens 51 of the CMOS camera 5, another beam of light is irradiated on the lens 51 of the CMOS camera 5 through the second single-mode fiber 4, and the two beams of light are in the CMOS camera 5 When interference occurs, a low-coherence interference fringe image is formed and output to the computer 6. The low-coherence interference center fringe extraction module in the computer 6 performs center fringe extraction on the received low-coherence interference fringe image.

In the present invention, the low-coherence interference center fringe extraction module includes a binary image unit, a contour extraction unit, a contour area comparison unit and a reference point coordinate analysis unit.

After the binary image unit adopts the binary method to process the image output by the CMOS camera 5, the binary image is obtained and output to the contour extraction unit; the binary image is a black-and-white image containing part of the central stripe information, as shown in Figure 4 shown.

The contour extraction unit adopts the function cvFindContours to search for the contour in the binary image, and then outputs the fringe contour (as shown in Figure 5) found to the contour area comparison unit;

The contour area comparison unit compares the size of the two-dimensional area of all fringe contours in the binary image, thereby obtaining the contour S with the largest area;

The reference point coordinate analysis unit adopts two-dimensional contour relation $\begin{array}{c}x=\frac{x_1+x_2+\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;+x_{N-1}+x_N}{N}\\ \mathrm{the\; y}=\frac{{\mathrm{the\; <figure-callout\; id="1"\; label="y"\; filenames="H200910092494XE00011.png"\; state="\{\{state\}\}">y</figure-callout>}}_1+{\mathrm{the\; y}}_2+\&Center\; Dot;\&CenterDot;\&Center\; Dot;+{\mathrm{the\; y}}_{N-1}+{\mathrm{the\; y}}_N}{N}\end{array}$ The coordinates of the reference point are calculated for the contour S with the largest area, so as to obtain the central fringe information of the low-coherence interference fringe, as shown in Figure 6, the circle in the figure is the logo of the central fringe of the low-coherence interference fringe.

In two-dimensional contour relation $\begin{array}{c}x=\frac{x_1+x_2+\&CenterDot;\&CenterDot;\&CenterDot;+x_{N-1}+x_N}{N}\\ \mathrm{the\; y}=\frac{{\mathrm{the\; <figure-callout\; id="1"\; label="y"\; filenames="H200910092494XE00011.png"\; state="\{\{state\}\}">y</figure-callout>}}_1+{\mathrm{the\; y}}_2+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{the\; y}}_{N-1}+{\mathrm{the\; y}}_N}{N}\end{array}$ middle:

x represents the abscissa of the center of the circle;

y represents the vertical coordinate of the center of the circle;

N represents the total number of contour points in the contour S with the largest area;

x ₁ represents the abscissa of the first point among the contour points of the contour S with the largest area;

y ₁ represents the ordinate of the first point among the contour points of the contour S with the largest area;

x ₂ represents the abscissa of the second point among the contour points of the contour S with the largest area;

y ₂ represents the ordinate of the second point among the contour points of the contour S with the largest area;

x _N-1 represents the abscissa of the N-1th point among the contour points of the contour S with the largest area;

y _N-1 represents the ordinate of the N-1th point among the contour points of the contour S with the largest area;

x _N represents the abscissa of the Nth point among the contour points of the contour S with the largest area;

y _N represents the ordinate of the Nth point among the contour points of the contour S with the largest area.

A device and method for extracting low-coherence interference center fringes based on two-dimensional images of the present invention, the inventor uses a CMOS camera to obtain optical information, changing the traditional form of optical signal conversion using photodetectors. Using the mature computing power of the existing computer and the low-coherence interference central fringe extraction module embedded in the computer hard disk, the central fringe in the fringe image can be effectively extracted and tracked, and the coordinates of the reference point can be obtained and displayed at the same time. Combining a CMOS camera with a computer (a low-coherence interference center fringe extraction module is stored in the computer), it has strong anti-electromagnetic interference ability. Since the interference fringe acquisition and processing parts do not contain signal amplification, filtering and other circuits, the anti-electromagnetic interference ability is relatively good. powerful.

Claims (2)

1. A device for extracting low-coherence interference center fringes based on two-dimensional images, characterized in that: the device consists of low-coherence light source (1), 3dB fiber coupler (2), the first single-mode fiber (3), the first Two single-mode optical fibers (4), CMOS camera (5) and computer (6) constitute; The low-coherence interference center fringe extraction module is stored in the hard disk of the computer (6); the low-coherence interference center fringe extraction module includes a binary image unit, a contour extraction unit, a contour area comparison unit and reference point coordinate analysis unit; after the binarization image unit adopts the binarization method to process the image output by the CMOS camera (5), the binary image is obtained and output to the contour extraction unit; the binary image is a black-and-white image containing part of the central stripe information The contour extraction unit adopts the function cvFindContours to find contours in the binary image, and then outputs the fringe contours found to the contour area comparison unit; the contour area comparison unit carries out the size comparison of the two-dimensional area to all the fringe contours in the binary image, In order to obtain the contour S with the largest area; the reference point coordinate analysis unit adopts the two-dimensional contour relation

Calculate the coordinates of the reference point on the contour S with the largest area, so as to obtain the central fringe information of the low-coherence interference fringe; The A end of the 3dB fiber coupler (2) is connected to the low-coherence light source (1), the B end of the 3dB fiber coupler (2) is connected to one end of the first single-mode fiber (3), and the first single-mode fiber (3) There is a gap d ₃ =2cm～4cm between the other end of the CMOS camera (5) and the lens (51) of the CMOS camera (5), and the C end of the 3dB fiber optic coupler (2) is connected with one end of the second single-mode optical fiber (4). Leave gap d ₄ =2cm～4cm between the other end of the single-mode optical fiber (4) and the lens (51) of the CMOS camera (5), adopt the CMOS camera (5) between the CMOS camera (5) and the computer (6) ) the USB data transmission cable that comes with it is connected on the USB interface of the computer (6); The distance d ₀ between the first single-mode fiber (3) and the second single-mode fiber (4) is ≤0.5mm. 2. A method for extracting low-coherence interference center fringes based on a two-dimensional image, characterized in that: the central wavelength emitted from the low-coherence light source (1) is 820nm, the line width spectrum is 39.6nm, and the light power is 14mW After the 3dB fiber coupler (2), it is divided into two beams of light, one beam of light is irradiated on the lens (51) of the CMOS camera (5) after passing through the first single-mode optical fiber (3), and the other beam of light passes through the second single-mode optical fiber (3). After the optical fiber (4) is irradiated on the lens (51) of the CMOS camera (5), the two beams of light interfere in the CMOS camera (5), forming a low-coherence interference fringe image output to the computer (6). The coherent interference center fringe extraction module extracts the center fringe of the received low-coherence interference fringe image, and the extraction steps of the center fringe are: After the binarization image unit adopts the binarization method to process the image output by the CMOS camera (5), the binary image is obtained and output to the contour extraction unit; the binary image is a black-and-white image containing part of the central stripe information; The contour extraction unit uses the function cvFindContours to find the contour in the binary image, and then outputs the fringe contour found to the contour area comparison unit; The contour area comparison unit compares the size of the two-dimensional area of all fringe contours in the binary image, thereby obtaining the contour S with the largest area; The reference point coordinate analysis unit adopts two-dimensional contour relation

The coordinates of the reference point are calculated for the contour S with the largest area, so as to obtain the central fringe information of the low-coherence interference fringes.

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