WO2015102145A1

WO2015102145A1 - Polarization-sensitive full-field optical coherence tomography system, and control system and control method thereof

Info

Publication number: WO2015102145A1
Application number: PCT/KR2014/000762
Authority: WO
Inventors: 이병하; 엄태중; 박관섭; 최우준
Original assignee: 광주과학기술원
Priority date: 2013-12-30
Filing date: 2014-01-27
Publication date: 2015-07-09
Also published as: KR20150078335A; KR101538044B1

Abstract

A polarization-sensitive full-field optical coherence tomography system according to the present invention may include: a light source unit for emitting light; a beam splitter that separates the light emitted from the light source unit, emits the light to a sample side and a reference side, and enables the light that has been reflected from the reference side and the sample side to be incident; an imaging unit for acquiring the image of an interference light reflected from the beam splitter; a linear polarizer for linearly polarizing the light of the light source unit; a quarter-wave plate for converting the linearly polarized light passed through the linear polarizer into an elliptically polarized light and then for providing the converted light to the sample side and the reference side; and a selected polarized light transmission device for, provided in the imaging unit, temporally selecting and passing a horizontal component and a vertical component of the polarized light, wherein the imaging unit has a single camera. The present invention can achieve advantages of eliminating an inconvenience of matching error alignment between image pixels, an inconvenience of pixel response rate correction of a camera, and an inconvenience of a strict adjustment of optical alignment, and significantly reducing the unit price of a product and reducing the size of a system.

Description

Polarization sensitive global optical tomography device and its control system and control method

The present invention relates to a full-field optical coherence tomography, a control system and a control method thereof. More specifically, the present invention relates to a polarization-sensitive global optical tomography device capable of detecting the birefringence of an object under test together with the shape of the object under test.

Optical coherence tomography (OCT) is a non-destructive and non-invasive technique for acquiring an image of a predetermined depth of a sample, and mainly photographing its internal structure at submicron resolution with respect to a biological sample. It is used to

In recent years, the scope of use of OCT has been widely increased due to medical diagnosis and the identification of jewelry. Among them, a full-field optical coherence tomography system (FFOCT) has an advantage that a cross-sectional image of a sample as well as an image of a longitudinal section of a sample can be obtained at high resolution. In addition, in the case of using a two-dimensional sensor arrangement, there is an advantage that only depth scanning (C-scanning) is required as one dimension. By such a global optical tomography imaging apparatus, relatively high mechanical error can be achieved with a high speed two-dimensional image. Equipment for obtaining polarization sensitivity information among the FFOCT has also been proposed, which is called a polarization sensitive full-field optical coherence tomography system, for example, G. Moneron, A-C. Boccara, A. Dubois, “Polarization-sensitive full-field optical coherence tomography,” Opt. Lett. 32, 2058-2060 (2007).

The polarization sensitive global optical tomography device is practically never commercialized due to various problems as follows. For example, the polarization sensitive global optical tomography device separates beams to obtain two orthogonal polarization component values from the light reflected from the sample and reference ends, and uses two CCD cameras to capture each separated light. do. However, in the case of using two CCD cameras, the pixel-to-pixel matching of the image obtained from each camera is distorted, so that an error occurs in the image and it is difficult to construct a practically applicable system. In addition, there is an inconvenience in that the pixel response rate of the camera must be corrected every time the object to be measured is measured. In addition, there is an inconvenience in that a process of accurately matching the optical paths separated by polarization components through optical alignment is required.

Due to such a problem, a polarization sensitive global optical tomography device has not been introduced yet, and the present invention proposes a polarization sensitive global optical tomography device, a control system, and a control method thereof, which solves the above problems by improving such a problem.

The present invention is proposed to solve the above problems, and proposes a polarization sensitive global optical tomography device which can acquire birefringence information of a sample stably, accurately and conveniently, and can be commercialized.

According to the present invention, there is provided a polarization sensitive global optical tomography device comprising: a light source unit for irradiating light; A beam splitter which separates the light irradiated from the light source unit and irradiates the sample side and the reference side, and receives the light reflected from the sample side and the reference side; An imaging unit which acquires an image of interference light reflected from the beam splitter; A linear polarizer for linearly polarizing light of the light source unit; A quarter-wave plate which makes the linearly polarized light that has passed through the linear polarizer into elliptical polarization and provides it to the sample side and the reference side; And a selective polarization transmitting device provided in the imaging unit to pass the horizontal component and the vertical component of polarized light by time selection, wherein the imaging unit is provided with a single camera. According to the present invention, there is no need for optical alignment, pixel matching, and camera response rate correction, and the optical tomography device can be used more conveniently. In addition, it is possible to overcome the above-mentioned inconvenience or impossible circumstances to commercialize.

In the optical monolayer device, the major axis of the quarter wave plate provided on the sample side is inclined 45 degrees with the optical axis of the linearly polarized light, and the major axis of the quarter wave plate provided on the reference side is 22.5 degrees with the optical axis of the linear polarization. It characterized in that the inclined, the selective polarization transmission device includes a polarization switch in which the polarization state is changed by the external force, and a linear flat polarizer to which the light passing through the polarization switch is incident. This makes it possible to conveniently adjust the selection for polarization. Here, a ferroelectric liquid crystal may be used for the polarization switch. According to this, there is an advantage that the response to the polarization switch is further improved.

In the optical tomography device, the camera photographs eight times when the selective polarization transmitting device operates one cycle. According to the present invention, there is an advantage that the birefringence information can be obtained completely.

According to another aspect of the present invention, there is provided a control system of a polarized civilian global optical tomography device, comprising: a control device to which at least an arithmetic function, a communication function, and a storage function can be given; A phase modulator controlled by the controller and providing a phase modulated interference signal; A selective polarization transmitting device controlled by the control device and configured to rotate the optical axis of the elliptical polarization provided as interference light so that the vertical component or the horizontal component of the polarization is selectively passed; And a camera controlled by the control device and photographing the light passing through the selective polarization transmitting device, wherein the control device comprises a half cycle of the polarization switch during one period of the phase modulator. do. According to the said control apparatus, by controlling an optical tomographic apparatus, it can drive completely, meeting timing. Here, the camera may perform four shots during one period of the phase modulator. In this way, the timing of shooting can be precisely adjusted.

According to another aspect of the present invention, there is provided a method of controlling a polarization sensitive global optical tomography device, comprising: obtaining interference light in which reflected light from a sample side and a reference side interfere with each other; Imaging the vertical component and the horizontal component of the interference light in time; And adding the vertical components and the horizontal components to provide single image information, and comparing the single image information to obtain birefringence. This method eliminates the need for optical alignment, pixel matching, and camera response rate correction, making it easier to use optical tomographic devices. In addition, it is possible to overcome the above-mentioned inconvenience or impossible circumstances to commercialize.

In the above method, the birefringence information may be obtained by dividing the single image information of a horizontal component and the single image information of a vertical component and taking a square root and an arc tangent. According to the present invention, birefringence information can be obtained conveniently.

According to the present invention, the inconvenience of mismatching between pixel matching of an image, the inconvenience of correcting pixel response rate of a camera, and the inconvenience of strict alignment of light alignment can be eliminated, and the unit cost of the product can be significantly lowered, and the size of the system is You can get the advantage of shrinking.

1 is a block diagram of a polarization sensitive global optical tomography device according to an embodiment.

2 and 3 are views illustrating the operation of the selective polarization transmitting device, Figure 2 is a case where the vertical component of the elliptical polarization passes, and Figure 3 is a view showing a case where the horizontal component of the elliptical polarization passes.

4 illustrates a control system of a polarization sensitive global optical tomographic device.

5 is a timing diagram of a phase modulator, a polarization switch, and a camera provided in FIG. 4;

6 is a flowchart for explaining a method of controlling a polarization sensitive global optical tomography device;

Hereinafter, with reference to the drawings will be described in detail a specific embodiment of the present invention. However, the spirit of the present invention is not limited to the following embodiments, and those skilled in the art who understand the spirit of the present invention can easily add, change, delete, and add other embodiments that fall within the scope of the same spirit. It may be proposed, but this is also included within the scope of the present invention.

Referring to FIG. 1, a light splitter (1) for irradiating light, a beam splitter (1) for separating light emitted from the light source unit, and the reflected light is incident, and a sample for splitting the beam splitter (1) as a center on an optical path A side and reference side, an imaging unit for obtaining the interference light reflected from the beam splitter 1, and a control unit 14 for controlling the components.

The light source unit includes a light source 2 exemplified by a halogen illuminator, a lens array 3 for focusing and aligning light, and a linear polarizer 4 for linearly polarizing light. The light source unit irradiates linearly polarized light through the configuration as described above. The linearly polarized light is incident on the beam splitter 1, and then separated and incident on the sample side and the reference side, respectively.

On the sample side, a quarter wave plate 5, an objective lens 6, and a stage 7 are provided. Therefore, the light transmitted to the sample side is circularly polarized and irradiated to the sample placed on the stage 7 through the objective lens 6. The light reflected by the sample is elliptically polarized and passes through the quarter wave plate 5 again to the beam splitter 1.

The quarter wave plate 5 may have an orientation of 45 degrees with the main axis of the quarter wave plate 5 so that the circularly polarized light may be circularly polarized when irradiated toward the sample side. According to this configuration, the circularly polarized light is irradiated onto the sample, and the circularly polarized light is elliptically polarized according to the degree of birefringence of the sample and then reflected. Therefore, the light reflected from the sample may include not only the image information of the sample but also the birefringence information of the sample.

The stage 7 may move in various directions including up and down. Therefore, the sample placed on it also moves up and down, and the measurement depth of a sample can be adjusted.

On the reference side, a quarter wave plate 8, an objective lens 9, and a reflecting mirror 10 are provided. Therefore, the light transmitted to the reference side is transmitted to the reflection mirror 10 through the objective lens 9, and the light reflected by the reflection mirror is transmitted to the beam splitter 1 again. In this case, the quarter wave plate may have an orientation of 22.5 degrees with respect to the main axis of polarization. According to this configuration, the light reflected by the reflecting mirror 10 and re-incident to the beam splitter 1 may be light of linear polarization.

The imaging unit includes a polarization switch 11 for adjusting a polarization state of light, a linear polarizer 12, and a camera 13. The polarization switch 11 may be exemplified by a liquid crystal, and preferably, a ferroelectric liquid crystal (FLC) having good reactivity may be used. The optical axis of the polarization switch may be changed by 45 degrees depending on the electric field applied from the outside. Therefore, the optical axis of the elliptical polarization incident from the beam splitter 1 to the polarization switch 11 may be changed, and then only the polarization component selected by the linear polarizer 12 passes through and enters the camera 13. Done. Therefore, the polarization switch 11 and the linear polarizer 12 may be referred to as a selective polarization transmission device. Another kind of polarizer may be used for the selective polarization transmitting device. The camera 13 may be, for example, a CCD camera. In addition, the controller 14 controls each component so as to obtain respective image information.

As will be explained, in the embodiment, a single camera is used to select and pass elliptical polarization for imaging. Therefore, there is no inconvenience in correcting pixel matching between pixels or pixel response rate of an image generated when using different cameras. In addition, since the light system is provided as one, there is no inconvenience to strictly match the light alignment. In addition, since there is no need to use a plurality of cameras reaching tens of thousands of won, there is an advantage of lowering the unit cost of the product, there is an advantage that the size of the product is reduced.

The selective polarization transmitting device will be described in more detail.

2 and 3 are views illustrating the operation of the selective polarization transmitting device, FIG. 2 shows a case where the vertical component of the elliptical polarization passes and FIG. 3 shows a case where the horizontal component of the elliptical polarization passes. However, the drawings are for explaining the concept, the size, shape and aspect may be exaggerated for the convenience of understanding.

Referring to FIG. 2, the elliptical polarization a incident from the beam splitter 1 passes through the polarization switch 11 so that vertical components are vertically aligned. The elliptical polarization b in which the vertical components are vertically aligned passes through the linear polarizer 12 so that the vertical component c of the elliptical polarization aligned with the optical axis of the linear polarizer 12 passes. Therefore, the light incident on the camera 13 becomes a vertical component of the elliptical polarization.

Referring to FIG. 3, the elliptical polarization a incident from the beam splitter 1 passes through the polarization switch 11 so that horizontal components are aligned vertically. The elliptical polarization b with the horizontal component aligned vertically passes through the linear polarizer 12 so that the horizontal component c of the elliptical polarization aligned with the optical axis of the linear polarizer 12 passes. Therefore, light incident on the camera 13 becomes a horizontal component of the elliptical polarization.

On the other hand, the state of FIGS. 2 and 3 may be a case where the direction of the electric field applied to the polarization switch 11 is reversed, for example ± 5V may be applied.

Referring back to FIG. 1, the light incident from the sample side and the reference side interferes with each other, and the reference side includes a phase modulator 10, and the interference signal phase modulated by the phase modulator 10. Will be provided. A piezolctric transducer (PZT) may be used as the phase modulator 10. Specifically, when the phase modulated interference signal is provided by the phase modulator 10, the interference fringe may be shifted while the shape of the sample is maintained. A tomographic image can be obtained. In this case, in order to acquire only a single tomographic image having no birefringent information, phase modulation may occur four times, and may be performed by obtaining four images. However, more information is needed to obtain the birefringence information of the sample.

An operation method of the polarization sensitive global optical tomographic device according to the embodiment, in which birefringence information can be obtained, will be briefly described. To obtain the tomographic image information of the sample and the birefringence information of the sample, four shifted images including the vertical component of the elliptical polarization and four shifted images including the horizontal component of the elliptical polarization are required. By adding four shifted images for each polarization component, one image for the vertical component and one image for the horizontal component can be obtained. The birefringent information of the sample can be obtained by comparing one image for the vertical component and one image for the horizontal component. Specifically, the result of phase delay can be obtained by dividing the horizontal component image and the vertical component image and taking the square root and arc tangent.

The above process may be performed by the controller 14 for processing the image obtained from the camera 13. After image information and birefringence information for any one layer of the sample are obtained, the stage 7 can be moved to obtain image information and birefringence information for different depths and positions of the sample.

In order to obtain the birefringence information and the image information as described above, the switching operation of the phase modulator 10, the polarization switch 11, and the camera 13 must be controlled. 4 is a view showing a control system of a polarization sensitive global optical tomography device for this purpose.

Referring to FIG. 4, a control device 14 to which a calculation function, a communication function, and a storage function can be given at least, a phase modulator 10 controlled by the control device 14, and a polarization switch 11 And a camera 13 are included. The phase modulator 10 is a device for providing a phase-modulated interference signal. The phase modulator 10 changes the optical path of the reference side, and consequently shifts the interference fringe. The polarization switch is a device provided in the imaging unit, and rotates the optical axis of the elliptical polarization so that the vertical component or the horizontal component of the polarization selectively passes through the linear polarizer. The camera is an apparatus provided in the imaging unit to acquire an image.

When the phase modulator is operated at 5 Hz, the polarization switch is operated at 2.5 Hz, and the camera is operated at 20 Hz. Therefore, when the polarization switch is operated for one period, the phase modulator is operated in two periods, and the camera takes eight shots.

5 is a timing diagram of a phase modulator, a polarization switch, and a camera provided in FIG. 4.

Referring to Fig. 5, the operation of the control system of the polarization sensitive global optical tomographic device will be described. One period of the phase modulator PZT corresponds to a half period of the polarization switch FLC, and the camera CCD may perform four photographs during one period of the phase modulator PZT. In order to obtain birefringence information, two images having different polarization states are required for a single position of a sample. Therefore, in order to obtain image information and birefringence information for a single position of the sample, eight shots will be required and one cycle of the polarization switch will take time.

In other words, during one period of the phase modulator, the electric field of the polarization switch is controlled in the positive direction to pass the vertical component of the polarization, and during the other period of the phase modulator, the electric field of the polarization switch is controlled in the negative direction. It can pass the horizontal component of the polarization.

By adding four shifted images for each polarization component obtained through the above process, one image for the vertical component and one image for the horizontal component can be obtained. And, by comparing one image of the vertical component and one image of the horizontal component, birefringent information of the sample can be obtained.

6 is a flowchart illustrating a method of controlling a polarization sensitive global optical tomography device according to an embodiment.

Referring to FIG. 6, interfering light in which reflected light from the sample side and the reference side interferes with each other is obtained (S1). At this time, the reflected light from the sample side and the reference side is polarized. The vertical component and the horizontal component of the interference light are separated in time and imaged (S2). The selective polarization transmitting device may be used to separate the vertical component and the horizontal component of the interference light in time. The selective polarization transmitting device may use a polarization switch and a linear polarizer.

The vertical component and the horizontal component may be combined with each other and provided as single image information. The birefringence report may be obtained by comparing each single image provided as a vertical component and a horizontal component (S3).

After the image of a tomography has been acquired, it is determined whether the inspection of the sample has ended (S4), and if a sample to be photographed is left, a series of processes such as moving the sample and acquiring interference light again is performed. . When the inspection of the sample is finished, three-dimensional analysis is performed (S5).

According to the present invention, not only the image information of the sample but also the birefringence information of the sample can be obtained, and the user can conveniently obtain reliable information even in obtaining the birefringence information. In addition, the birefringence information of the sample can be known accurately without going through a complicated process.

Therefore, the birefringence inspection and the directionality of the cover glass used in the digital device are applied to the polarization-sensitive global optical tomography device according to the embodiment by applying an appropriate change in terms of mechanical, controllable, methodological or additional device. Eggplants may be used in a variety of equipment, such as tests for biological tissues, such as cancer cells, stress tests, such as films that are directional when stress is given.

According to the present invention, eliminating the inconvenience of correcting the pixel-to-pixel matching of the image, the inconvenience of correcting the pixel response rate of the camera, and the strict alignment of the light alignment, the unit cost of the product can be significantly lowered, and the size of the system is reduced. . Therefore, it can be applied to various devices that need to grasp the image information about the depth of the object along with the birefringence of the object. For example, it may be used in a variety of equipment, such as birefringence test of the cover glass of the camera, test for cancer tissue having a direction, stress test such as a film that has a direction when stress is given.

Claims

A light source unit for irradiating light;

A beam splitter which separates the light irradiated from the light source unit and irradiates the sample side and the reference side, and receives the light reflected from the sample side and the reference side;

An imaging unit which acquires an image of interference light reflected from the beam splitter;

A linear polarizer for linearly polarizing light of the light source unit;

A quarter-wave plate which makes the linearly polarized light that has passed through the linear polarizer into elliptical polarization and provides it to the sample side and the reference side; And

A selective polarization transmitting device provided in the imaging unit and configured to pass a horizontal component and a vertical component of polarized light by time,

The imaging unit is provided with a single camera polarization sensitive global optical tomography device.
The method of claim 1,

The main axis of the quarter-wave plate provided on the sample side is inclined 45 degrees with the optical axis of the linearly polarized light, and the main axis of the quarter-wave plate provided on the reference side is inclined 22.5 degrees with the optical axis of the linearly polarized light. Device.
The method of claim 1,

The selective polarization transmitting device includes a polarization switch whose polarization state is changed by a force applied from the outside, and a linear flat polarizer to which light passing through the polarization switch is incident.
The method of claim 3, wherein

A polarization sensitive global optical tomography device wherein ferroelectric liquid crystal is used for the polarization switch.
The method of claim 1,

And the camera photographs eight times when the selective polarization transmitting device operates one cycle.
A control device to which at least a calculation function, a communication function, and a storage function can be given;

A phase modulator controlled by the controller and providing a phase modulated interference signal;

A selective polarization transmitting device controlled by the control device and configured to rotate the optical axis of the elliptical polarization provided as interference light so that the vertical component or the horizontal component of the polarization is selectively passed; And

A camera which is controlled by the control device and which photographs the light passing through the selective polarizing light transmission device,

Wherein said control device is one period of said phase modulator, said polarization switch is a half cycle of a polarizing civilian global optical tomographic device.
The method of claim 6,

And the camera performs four shots during one cycle of the phase modulator.
Obtaining interfering light in which reflected light from the sample side and the reference side interferes with each other;

Imaging the vertical component and the horizontal component of the interference light in time; And

And combining the vertical components and the horizontal components to provide single image information, and comparing the single image information to obtain birefringence information.
The method of claim 8,

And the birefringence information is obtained by dividing the single image information of a horizontal component and the single image information of a vertical component and taking a square root and an arc tangent.