KR101192256B1 - Apparatus and method of optical path difference compensation using Fringe locking system - Google Patents

Abstract

According to an aspect of the present invention, there is provided a light-receiving unit, which periodically photographs an interference pattern to collect image information of a region to be examined; Extracting the position information of the valley or the floor point of the interference pattern from the collected image information, measuring the change and the degree of change of the interference pattern from the position information, calculating the compensation value, and sends the compensation value as a signal to the controller A calculator; And a controller configured to compensate an optical path according to the signal of the output unit.

In addition, the present invention collects the image information of the inspection area in the light receiving unit and transmits to the operation unit, extracting the position information of the valley or the floor of the interference pattern from the transmitted image information, the extracted information and the initial information Determining whether the pattern is changed by comparison, if it is determined that a change has occurred in the pattern, measuring a position change amount of the valley or floor point, calculating a compensation value from the position change amount, and transmitting the compensation value as a signal step; And generating a phase change in the control unit according to the signal.

Fringe Locking System, Optical Path Compensation, Interference Pattern, Fringe Pattern

Description

Fringe locking system and optical path compensation method using the same {Apparatus and method of optical path difference compensation using Fringe locking system}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fringe locking system and a phase compensation method using the same. More particularly, the present invention relates to a fringe locking system and an optical path compensation method that can be used in manufacturing holography or interference fringes.

Holography is a technique of recording information of a three-dimensional image on a photographic film by using interference of light.

In normal general photography, image information is recorded as an amount of change in the intensity of light reflected from an object (subject). In other words, the portion having less reflected light is dark and the portion having more reflected light is displayed brightly. Therefore, the shape of the object is represented by two-dimensional shadows. On the other hand, holography technology is a technology that can reproduce the subject as a three-dimensional image by recording the phase of the light by the wave with the intensity of light. At this time, the phase of the light can be represented by the interference fringe generated by the light reflected from the object and other light. When two lights meet, an interference fringe consisting of many bright and dark lines is generated by the difference in the phase of the object wave reflected from each part of the object, and the amplitude and phase of the object are recorded together in this interference fringe.

However, when such interference fringes are formed, a change occurs in the optical path difference due to the external environment. If the optical path difference is changed in this manner, the interference fringe is shaken, and as a result, the sharpness of the interference fringe is reduced. Therefore, by periodically monitoring the change in the interference fringe, and to compensate for the change occurs, there is a need for a system that does not change the interference pattern, called a fringe locking system (fringe locking system).

In the conventional fringe locking system, the intensity of two fixed points is periodically monitored, the difference between the two points is checked to see if a change occurs in the interference pattern, and when the change occurs, the difference between the two points is different. Has been used to calculate the degree of movement of the pattern by comparing it with previous data and to compensate for it.

This conventional method responds relatively well when the pattern is minutely changed, but does not respond to errors or generate errors when half-wavelength change does not occur, and the period is shifted a lot or the intensity distribution of the pattern is changed. If it is not constant, an error occurs.

The present invention provides a fringe locking system and an optical path compensation method using the same, so that accurate compensation can be made even when the pattern changes by half wavelength or the intensity distribution of the pattern is not fixed to solve the above problems, It is an object of the present invention to stably provide a clear interference pattern.

To this end, the present invention is a light-receiving unit for collecting the image information of the inspection area by periodically imaging the interference pattern; Extracting the location information of the valley and the floor of the interference pattern from the collected image information, measuring whether or not the interference pattern is changed and the degree of change from the position information, calculates a compensation value, and sends the compensation value as a signal to the controller A calculator; And a controller configured to compensate an optical path according to the signal of the output unit.

In this case, the light receiving unit is preferably made of a photodiode, a CCD camera or a CMOS imaging device.

In addition, the image information preferably includes location information and light intensity.

Moreover, it is preferable that the said imaging is performed with respect to the whole test | inspection area | region.

In addition, the control unit preferably comprises a Pockel's cell, a PZT piezoelectric element, or a temperature controller.

In addition, the present invention collects the image information of the inspection area in the light receiving unit and transmits to the operation unit, extracting the location information of the valleys and the floor of the interference pattern from the transmitted image information, the extracted information and the initial information Determining whether the pattern is changed by comparison, if it is determined that a change has occurred in the pattern, measuring a position change amount of a point of a valley and a floor, calculating a compensation value from the position change amount, and transmitting the compensation value as a signal Making; And generating a phase change in the control unit according to the signal.

At this time, it is preferable that the collection of the image information is performed for the entire inspection area.

In addition, the image information preferably includes location information and light intensity.

In addition, it is preferable to extract the valleys and valleys of the interference pattern by using light intensity information.

In addition, the phase change is preferably generated using a Pockel's cell, a PZT piezoelectric element, or a temperature controller.

In addition, the steps are preferably performed repeatedly at regular intervals.

The present invention grasps the location point of the valley and the floor of the interference pattern, and calculates a compensation value from the amount of change in the location, so that accurate compensation can be achieved even when a sudden half wavelength change occurs or the intensity of the wavelength is not constant. Thus, it was possible to stably provide a clear interference pattern.

Hereinafter, the present invention will be described in more detail.

The fringe locking system of the present invention includes a light receiving unit 10, a calculating unit 20, and a control unit 30, and operates in conjunction with a pattern generator for forming an interference pattern.

First, the process of forming the interference pattern will be briefly described. The interference pattern can be formed by dividing the beam emitted from the laser into two paths by a beam splitter and allowing the two beams to reach the sample through different paths. 1 illustrates a process of forming an interference pattern. As shown in FIG. 1, when the beam is first irradiated from the laser 40, the irradiated beam is divided into two by the beam splitter 60. The beams divided into two proceed in different paths, and in this case, the paths of the beams are adjusted using the reflection mirror 70 mounted in the middle of the paths of the beams. A lens 80 for enlarging the size of the beam is mounted on the path of the beam. The two beams reach the sample 50 through different paths, and the interference pattern is formed on the surface of the sample by the path difference generated in the process.

When the interference pattern is formed on the surface of the sample 50 through the above process, the light receiving unit 10 captures the interference pattern. The light receiver 10 collects image information of an interference pattern, and may include a photodiode, a CCD camera, a CMOS image sensor, and the like.

On the other hand, the present invention is characterized in that the light receiving unit 10 collects the image information for all coordinate points of the inspection area (sample), which is to recognize the interference pattern in the form of a waveform. In this case, it is preferable that the collected image information includes light intensity information together with the position information.

The imaging is repeated at regular intervals, and the collected image information is sent to the calculating unit 20.

On the other hand, the calculation unit 20 is to determine the change of the interference pattern and calculate the optical path compensation value, the change of the interference pattern and the calculation of the optical path compensation value is made based on the location information of the valley and the floor of the interference pattern. .

This will be described in detail below.

First, when image information is first transmitted from the light receiving unit 10, the calculation unit 20 extracts a point (floor) with the highest light intensity and / or a point (valley) with the lowest light intensity among the image information. Recognize location information and store as initial value.

After a certain time, the second light receiver 10 collects the second image information and transmits the second image information to the calculator 20. The calculator 20 extracts the valley and / or floor points from the second image information in the light receiver 10 again, recognizes the location information, and compares the location information with the stored initial value. If the result of the comparison is the same as the initial value, it is stored.

If the positional information is different from the initial value as a result of the comparison, the degree of change is calculated, and the optical path compensation value is calculated based on the calculated amount of change. In this case, the optical path compensation value may be obtained by using the position change amount of the valley and / or the floor.

For example, assume that the distance from the goal to the goal (ie, the period or repetition distance) in the initial interference pattern is L, and that the pattern has moved by ΔL. The distance from the goal to the goal, or period, corresponds to 2π in phase. Therefore, when ΔL, which is the moving distance of the pattern, is represented in phase, the amount of phase change x = 2π ΔL / L is obtained. In this case, L and ΔL are preferably used as the average value for each pattern period in consideration of the measurement error.

After calculating the amount of phase change as described above, it is substituted into the conversion equation or conversion equation of the controller to calculate the optical path compensation value. For example, assuming that the phase change amount of the interference pattern is π / 10, and the Pockel's cell of the controller assumes that the phase shift conversion formula per driving voltage is π radian / 5V, the optical path compensation value is 0.5V.

In this way, when the optical path compensation value is calculated with the amount of change in the valley and the floor of the interference pattern, even if there is a half-wavelength change unlike in the prior art, the change is clearly recognized. In addition, in the conventional method, since the optical path compensation value is calculated with the difference in intensity between two points, there is a problem that the error becomes large when the period of the pattern is not constant or when there is a change in intensity. With the variation of the position of the floor and the floor, the error is much smaller because the compensation is calculated.

Next, the calculated optical path compensation value is sent to the control unit 30 as a signal. The controller 30 is preferably located on one path of two beams separated from the beam splitter. The controller 30 compensates the optical path by generating a phase change according to the signal transmitted from the calculation unit 20, thereby reducing the interference pattern. To remain the same.

The controller 30 may include a Pockel's cell, a PZT piezoelectric element, a temperature controller, or the like.

Next, the optical path compensation method using the fringe locking system made as described above will be described.

The optical path compensation method of the present invention comprises the steps of collecting the image information for the inspection area in the light receiving unit and sending it to the operation unit, extracting the position information of the valley or the floor of the interference pattern from the transmitted image information, the extracted information Determining the change of the pattern by comparing with the previously stored initial value, if it is determined that a change has occurred in the pattern, measuring a change in the position of the point of the valley or the floor, calculating a compensation value from the change in the position, Transmitting the compensation value as a signal; And generating a phase change in the control unit according to the signal.

That is, the light receiving portion picks up the interference pattern of the inspection region with a photodiode, a CCD camera, or a CMOS to obtain image information. This image information includes the positional information of the interference pattern, the degree of light intensity, and the like, and the obtained image information is sent to the calculation unit.

When the image information is sent to the calculating unit, the calculating unit extracts the position information of the valley and / or the floor point of the interference pattern from the transmitted image information. In this case, the valley and / or the floor point may be extracted using light intensity information.

Next, the location information of the extracted bone and / or floor points is compared with the previously stored initial values. If it is determined that there is no change as a result of the comparison, the value is stored, and when the new information is sent from the light receiving unit, the process is repeated.

However, as a result of the comparison, when the location information value is different from the previously stored initial value, it is determined that a change has occurred in the interference pattern. In this case, the position change amount of the point of the valley and / or the floor is measured based on the initial value. When the position change amount is measured, the value is substituted into a conversion equation or conversion table to calculate a necessary compensation value, and the calculated compensation value is transmitted as a signal to the controller.

The controller generates a phase change by manipulating a Pockel's cell, a PZT piezoelectric element, or a temperature controller according to the transmitted signal.

By repeatedly performing all the above steps at regular intervals, it is possible to keep the interference pattern the same by monitoring whether the interference pattern fluctuates and properly compensating for the variation when it occurs.

Hereinafter, the optical path compensation method will be described in more detail with reference to specific examples.

Example

Assume that the initial interference fringe pattern by the image information collected by the light receiving unit is the same as the red line in FIG. 3. At this time, the light intensity is represented by the following equation.

Where A (x) represents the magnitude of the wave, Λ represents the period of the interference fringe, x is the displacement in the axial direction, and φ represents the externally given phase displacement.

When the image information appearing as described above in the light receiving unit is transmitted to the calculating unit, the calculating unit converts the size of the data into a graph with A (x) = 1 through Normalize. The graph of FIG. 4 converts the image information of FIG. 3 into the graph whose A (x) = 1. Then, the lowest point (a valley) or the highest point (floor) is extracted from the converted graph, and the average interval length of the highest point or the lowest point is obtained to obtain a period Λ of the interference fringe. Then, the period Λ is substituted into the above equation, φ ₁ is obtained from the x position of the minimum or maximum point, and then stored.

It is then assumed that the interference fringe pattern has moved like the orange line in FIG. 3. After a certain period of time, the light receiving unit picks up the interference pattern again to collect image information, and the collected image information is transmitted to the calculating unit. Then, the calculating unit extracts the x-axis values of the highest point and the lowest point through the same process as described above to obtain a value of φ ₂ .

Then, the value of φ _{1 and the} value of φ ₂ are compared to determine whether the two values are the same. If the two values are equal, store the φ ₂ value. However, if the two values are not the same, the amount of change is extracted, and then the phase compensation value is calculated by substituting the amount of change into a conversion equation or a conversion table.

Then, an appropriate input is applied to the controller based on the phase compensation value. For example, if the phase displacement conversion equation per driving voltage of Pockel's cell is π radian / 5V and Δφ is measured as π / 10, phase compensation can be performed by applying 0.5V to the Pockels cell.

1 is a view showing a fringe locking system of the present invention.

2 is a flowchart showing an optical path compensation method of the present invention.

3 is a view showing an interference fringe pattern of an embodiment of the present invention.

FIG. 4 is a graph obtained by normalizing the interference fringe pattern of FIG. 3 to A (x) = 1.

* Symbol *

10: light receiver 20: calculator

30 control unit 40 laser beam

50: sample 60: beam splitter

70: reflection mirror 80: lens

Claims (11)

A light receiving unit which periodically picks up an interference pattern and collects image information of a test region; Extracting the position information of the valley or the floor point of the interference pattern from the collected image information, measuring the change and the degree of change of the interference pattern from the position information, calculating the compensation value, and sending the value to the controller as a signal A calculator; And And a controller configured to compensate the optical path according to the compensation value signal transmitted from the calculator. The method of claim 1, The light receiving unit is a fringe locking system, characterized in that consisting of a photodiode, CCD camera or CMOS. The method of claim 1, The image capturing is performed on the entire inspection region. The method of claim 1, The image information includes position information and light intensity. The method of claim 1, The control unit is a fringe locking system, characterized in that consisting of a Pockel's cell (Pockel's cell), a PZT piezoelectric element or a temperature controller. Collecting, by the light receiving unit, image information of the inspection region and sending the image information to the operation unit; Extracting location information of a valley or a floor of an interference pattern from the transmitted image information; Determining whether a pattern is changed by comparing the extracted information with a previously stored initial value; If it is determined that a change has occurred in the pattern, measuring a change in the position of the point of the valley or the floor; Calculating a compensation value from the position change amount; Transmitting the compensation value as a signal to a controller; And And generating a phase change in the control unit according to the signal. The method according to claim 6, And the collection of the image information is performed for the entire inspected area. The method of claim 6, And the image information includes location information and light intensity. The method according to claim 6, The valley or the floor of the interference pattern is extracted using the light intensity information. The method according to claim 6, The phase shift is generated using a Pockel's cell, a PZT piezoelectric element or a temperature controller. The method of claim 6, And repeating the steps at regular intervals.

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