KR102625948B1 - Device of optical coherence tomography - Google Patents

Abstract

An optical coherence tomography apparatus having a variable transmittance absorption filter capable of adjusting the brightness of the reference reflected light (R1) according to the brightness of the reflected light of the inspection object (5) is disclosed. A light source 10 that generates measurement light L irradiated into the inspection object 5, divides the measurement light L into a reference light R and a measurement light L, and divides the measurement light L into the reference light R. Irradiated by the reference mirror 30, the measurement light (L) is irradiated to the inspection object (5), and the reference reflected light (R1) reflected from the reference mirror (30) and the signal reflected light (S) reflected from the inspection object (5) ) a light splitter (20) that generates interference light (I) by overlapping them, a scan unit (40) that guides the measurement light (L) split by the light splitter (20) to the inspection position of the inspection object (5), It is mounted in the path of the reflected light reflected from the reference mirror 30, and by tilting it at a predetermined angle and adjusting the thickness, the light absorption rate for absorbing the light of the reference reflected light R1 reflected from the reference mirror 30 is adjusted. , an absorption filter 35 that adjusts the amount of light of the reference reflected light (R1) transmitted to the light splitter 20, and an optical detector 50 that detects the interference light (I) and obtains an internal image signal of the inspection object (5). ) and an optical coherence tomography device including an optical coherence tomography device.

Description

Device of optical coherence tomography having a variable transmittance absorption filter

The present invention relates to an optical coherence tomography apparatus having a variable transmittance absorption filter, and more specifically, to an optical coherence tomography apparatus having a variable transmittance absorption filter capable of adjusting the brightness of the reference reflected light (R1) according to the brightness of the reflected light of the inspection object (5). It relates to an optical coherence tomography device.

Modern electronic devices such as smartphones, tablet computers, and monitors are manufactured by laminating various materials such as synthetic resin films, glass substrates, metal components, and pigments in multiple layers. Recently, as the performance of electronic devices has improved, the structures of these multi-layered products are also developing into highly multi-layered, ultra-thin, ultra-fine patterning, and chip-package integration. At each manufacturing stage of a multi-layer laminated product, a method of extracting some product samples, destroying the samples, and visually inspecting the product for defects, such as the inflow of external foreign substances or damage, is generally used to check for product defects. there is. However, this destructive testing method not only has the problem of damaging expensive semi-finished or finished products, but also makes it impossible to inspect all products and effectively inspect internal defects in ultra-thin and ultra-fine patterned electronic devices. There is.

In order to non-destructively inspect multi-layer laminated products, a non-destructive inspection method using optical coherence tomography (OCT) is disclosed in Patent Publication No. 10-2015-0056713, etc.

In optical coherence tomography (OCT), the light emitted from the light source 10 is distributed and transmitted to the sample unit and the reference unit where the measurement object is located by an optical splitter (beam splitter or optical coupler). The light traveling to the sample unit passes through a galvanometer that scans the horizontal axis to obtain a 2D image of the measurement object, and then is focused on the sample, which is the measurement object, through an objective lens. The light reflected from the sample passes through the objective lens again to the light splitter. It returns and combines with the reference light reflected from the reference unit. Optical interference occurs due to the difference in optical paths between the two stages, and this interference light (I) is transmitted to the detection unit and converted into a digital signal. Through the signals detected in this way, the surface shape and internal layer structure of the sample are observed.

At this time, an effective light detection signal can be created only when the brightness of the light reflected from the sample and the light reflected from the reference unit match at an appropriate ratio. However, since the brightness of the reflected light of the measurement object varies depending on the characteristics of the measurement object, the standard It is necessary to adjust the amount of sub-reflected light accordingly.

Conventionally, when the amount of light desired by the user is different, the absorption filter 35 with a different transmittance must be replaced or an aperture must be added to change the light amount, which is cumbersome and complicated.

Therefore, the purpose of the present invention is to provide an optical coherence tomography apparatus having a variable transmittance absorption filter that can be adjusted (changed) to the amount of light desired by the user using one absorption filter 35.

Another object of the present invention is to provide an optical coherence tomography apparatus having a variable transmittance absorption filter that can adjust the amount of light according to the thickness of the absorption filter 35 by varying the angle of incidence of one absorption filter 35.

In order to achieve the above object, the present invention includes a light source (10) that generates measurement light (L) irradiated into the interior of the inspection object (5), and the measurement light (L) is divided into a reference light (R) and a measurement light (L). Divided into , the reference light (R) is irradiated to the reference mirror 30, the measurement light (L) is irradiated to the inspection object (5), and the reference reflected light (R1) reflected from the reference mirror 30 and the inspection object ( 5) A light splitter (20) that generates interference light (I) by overlapping the signal reflection light (S) reflected from the light splitter (20), and sends the measurement light (L) split by the light splitter (20) to the inspection position of the inspection object (5). The scanning unit 40, which guides the reference mirror 30, is mounted in the path of the reflected light reflected from the reference mirror 30, and tilts it at a predetermined angle to adjust the thickness of the reference reflected light R1 reflected from the reference mirror 30. An absorption filter 35 that adjusts the amount of light of the reference reflected light (R1) transmitted to the light splitter 20 by adjusting the light absorption rate that absorbs light, and detects the interference light (I) of the inspection object (5) An optical coherence tomography device is provided having a variable transmittance absorption filter including an optical detector (50) to obtain an internal image signal.

The optical coherence tomography device having a variable transmittance absorption filter according to the present invention adjusts the incident angle of the absorption filter 35 to adjust the brightness of the reference reflected light (R1) according to the brightness of the signal reflected light (S) of the measurement object. By varying the length of the light path passing through the absorption filter 35, the amount of light can be adjusted.

1 is a diagram showing an optical coherence tomography apparatus having a variable transmittance absorption filter according to an embodiment of the present invention.
FIG. 2 is a diagram showing a method of controlling the amount of light using the absorption filter 35 of an optical coherence tomography device having a variable transmittance absorption filter according to an embodiment of the present invention.

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

FIG. 1 is a diagram showing an optical coherence tomography device having a variable transmittance absorption filter according to an embodiment of the present invention. As shown in FIG. 1, the optical coherence tomography device is directed to the inside of the inspection object 5. A light source (10) that generates irradiated measurement light (L), splits the measurement light (L) into reference light (R) and measurement light (L), and radiates the reference light (R) to the reference mirror (30), The measurement light (L) is irradiated to the inspection object (5), and the reference reflected light (R1) reflected from the reference mirror 30 and the signal reflection light (S) reflected from the inspection object (5) are overlapped to produce interference light (I). A light splitter 20 that generates a light splitter 20, a scanning unit 40 that guides the measurement light L split by the light splitter 20 to the inspection position of the inspection object 5, and a light beam reflected from the reference mirror 30. It is mounted in the path of the reflected light, tilted at a random angle, and adjusts the thickness to adjust the light absorption rate of absorbing the light of the reference reflected light (R1) reflected from the reference mirror (30), which is transmitted to the light splitter (20). It includes an absorption filter 35 that adjusts the amount of light of the reference reflected light (R1) and a light detector 50 that detects the interference light (I) and obtains an internal image signal of the inspection object (5).

The light source 10 generates measurement light L that is irradiated into the interior of the inspection object 5. In general, the measurement light L used in optical coherence tomography (OCT) is usually broadband low-coherence light with a short coherence distance, for example, near-infrared light with a wavelength of 750 nm to 1500 nm. May include light.

The light splitter 20 (also referred to as a beam splitter) splits the measurement light (L) into the reference light (R) and the measurement light (L), irradiates the reference light (R) to the reference mirror 30, and performs measurement. The light (L) is irradiated to the inspection object (5), and the reference reflected light (R1) reflected by the reference mirror 30 and the signal reflected light (S) reflected from the inspection object (5) are overlapped to produce interference light (I). Creates (interference light, I). Generally, optical interference occurs due to an optical path difference between the reference reflected light (R1) reflected from the reference mirror 30 and the signal reflected light (S) reflected from the inspection object 5. The light splitter 20 serves to overlap the reference reflected light (R1) and the signal reflected light (S), so it is also called an optical coupler. The generated interference light (I) is guided to the light detector 50. The light splitter 20 can split the measurement light into reference light and measurement light with an intensity of 50:50.

The scanning unit 40 serves to guide the measurement light split by the light splitter 20 to the inspection position of the inspection object 5. The scanning unit 40 includes a galbinomirror that performs transverse scanning to obtain a two-dimensional (2D) image of the inspection object 5 and an objective that condenses the measurement light scanned by the galbinomirror onto the inspection object 5. Includes a lens 42. For example, the measurement light scans the surface of the inspection object 5 two-dimensionally by sequentially changing the reflection angle of the measurement light by the galbino mirror. The measurement light is irradiated into the interior of the inspection object 5. For example, if the inspection object 5 includes a multi-layer structure, the measurement light is scattered and reflected in each layer, producing a fine signal reflected light (S). Create. The generated fine signal reflected light S is guided to the light splitter 20 through the objective lens 42. The scanning unit 40 may use a reflecting mirror whose reflection angle is adjusted by a galvanometer and has a scanning function of the measurement light.

The optical detector 50 detects the interference light (I) in which the signal reflected light (S) and the reference reflected light (R1) reflected from the reference mirror 30 overlap to obtain an internal image signal of the inspection object 5. . The generated interference light (I) is transmitted to the detection unit and converted into a digital signal. Through the signal of the interference light (I) detected by the optical detector 50, the surface shape and internal layer structure of the inspection object 5 are observed.

The brightness of the signal reflected light (S) reflected from the inspection object 5 and the reference reflected light (R1) reflected from the reference mirror 30 must match at an appropriate ratio to create an effective light detection signal (interference light (I)). You can. However, in general, since the brightness (light quantity) of the signal reflected light (S) generated is different depending on the characteristics of the inspection object (5), the light quantity of the reference reflected light (R1) needs to be adjusted to match the light quantity of the signal reflected light (S). There is. Generally, in order to control the amount of light of the reference reflected light (R1) using a filter made of the same material, the absorbing filter is replaced with an absorption filter of various thicknesses, or an aperture is used to adjust the amount of light to an appropriate amount. In addition, a general optical coherence tomography device is used by manually replacing the absorption filter with an appropriate thickness according to the signal reflected light (S) of the inspection object (5), so a method of replacing the absorption filter according to the inspection object (5) This was cumbersome, and it was difficult to precisely control the thickness of the absorption filter. For example, it was not possible to finely adjust the thickness of the absorption filter 35 (for example, 1.12 mm to 1.15 mm, etc.), making more accurate observation difficult.

According to the present invention, the optical coherence tomography apparatus having a variable transmittance absorption filter is equipped with an absorption filter 35 on the optical path of the reference mirror 30, and varies the inclination of the absorption filter 35 to filter the absorption filter. By adjusting the light absorption or light transmittance of (35), the amount of light of the reference reflected light (R1) is adjusted. The absorption filter 35 has a flat, flat shape with a predetermined thickness. However, as long as it is in a form that can perform the above functions, it can be used without limitation.

FIG. 2 is a diagram showing a change in the absorption filter 35 according to a change in the slope of the absorption filter 35 of an optical coherence tomography device having a variable transmittance absorption filter according to an embodiment of the present invention. As shown in FIG. 2, the absorption filter 35 absorbs light within the filter material, and the amount of light ultimately emitted decreases, so depending on the length of the optical path passing through the absorption filter 35, The light absorption rate is determined, and thereby the light amount is adjusted.

By tilting (positioning) the absorption filter 35 at an arbitrary angle, the length of the reference reflected light (R1) passing through the absorption filter 35 and the thickness of the filter itself are adjusted. Specifically, when the absorption filter 35 is tilted at a certain angle, the absorption filter 35 gains a thickness corresponding to the diagonal direction, which has an increased length compared to the thickness of the existing filter. In addition, since the optical path length of the reference reflected light R1 passing through the absorption filter 35 increases, tilting the absorption filter 35 at a certain angle has the effect of increasing the thickness of the filter itself.

According to the thickness of the absorption filter 35 and the length of the light path passing through it, the light absorption rate absorbed by the absorption filter 35 is adjusted, and thus the amount of light transmitted to the light splitter 20 is ultimately adjusted.

Specifically, compared to the travel distance (distance of the optical path) of the reference reflected light (R1) passing through the absorption filter 35 mounted in the original position ((a) in FIG. 2), the absorption filter 35 is randomly selected. When tilted at an angle, the absorption filter 35 becomes as thick as the diagonal direction, and the distance through which the reference reflected light (R1) passes (the distance the light travels) increases, so this can be seen as an increase in the thickness of the filter (Figure 2 (b)).

As the thickness of the absorption filter 35 and the length of the optical path of the reference reflected light (R1) passing through the absorption filter 35 increase, the time for passing through the absorption filter 35 increases, so the absorption filter 35 The light absorption rate increases, and the light transmittance decreases. Accordingly, the amount of reference reflected light R1 incident on the light splitter 20 decreases.

Conversely, if the predetermined angle at which the absorption filter 35 is tilted is small (less tilted), the distance through which light passes (light travel distance) is relatively reduced, which can be seen as a relative decrease in the thickness of the filter. .

When the thickness of the absorption filter 35 and the length of the optical path of the reference reflected light R1 passing through the absorption filter 35 are reduced, the time passing through the absorption filter 35 becomes shorter, so the absorption filter 35 The light absorption rate decreases, and the light transmittance increases. Accordingly, the amount of reference reflected light R1 incident on the light splitter 20 relatively increases.

The optical coherence tomography device having a variable transmittance absorption filter according to the present invention uses only one absorption filter 35 at random, without frequently replacing the absorption filters 35 of various thicknesses depending on the inspection object 5. Since the thickness of the absorption filter 35 is adjusted by tilting it at an angle, precise thickness control is possible. Accordingly, the amount of light of the reference reflected light R1 transmitted to the light splitter 20 can be adjusted.

The absorption filter 35 of the optical coherence tomography device obeys Snell's law according to the following equation.

[Equation]

The length of the optical path within the absorption filter 35 can be obtained by modifying Snell's law and using the following equation.

Length of optical path in absorption filter 35 (L) = thickness of absorption filter 35 (T)/cosB

When the incident angle of the absorption filter 35 changes (increases) from 5° to 70°, assuming that there is no change in reflection amount depending on the angle, and assuming that the refractive index of the absorption filter 35 is 1.51, the above formula If calculated by substitution, the effect of increasing the thickness (optical path length) of the absorption filter 35 by about 27.6% can be seen.

If the absorption filter 35 is tilted at an arbitrary angle, the reflectance of the reference reflected light R1 may be affected depending on the tilt of the absorption filter 35. Specifically, the absorption filter 35 is inclined at an arbitrary angle. Accordingly, in the process where the reference reflected light (R1) reflected from the reference mirror 30 passes through the inclined absorption filter 35, the reflectance reflected from the surface of the absorption filter 35 is reduced by the non-slanted absorption filter 35. Compared to when passing, it increases. For example, the absorption filter 35 is generally designed to have maximum efficiency when used without tilting (for example, when designing a mirror coating for a device, it is optimized to obtain high light transmittance when light is incident at a desired angle of incidence). It is possible to produce an absorption filter with a given reflectance (reflection angle)). However, if the absorption filter 35 is tilted at an arbitrary angle (the angle of incidence changes), the set maximum efficiency is not satisfied. That is, because the reflectance increases from the initially set reflectance, the light transmittance of the absorption filter 35 decreases, ultimately reducing the amount of light transmitted to the light splitter 20.

As the absorption filter 35 is tilted at a certain angle, the direction of the optical path of the reference reflected light R1 changes. This may cause the direction of the optical path of the reference reflected light R1 to be bent. When the reference reflected light (R1) passes through the absorption filter 35 inclined at an arbitrary angle, the light may be transmitted to the next lens (e.g., focusing lens, light splitter, etc.) while the direction of the optical path is bent. there is. Since the reference reflected light R1 is transmitted to the next lens with the direction of the optical path changed, it cannot be transmitted to the entire area of the lens. That is, the direction of the optical path of the reference reflected light R1 is bent and may pass through only a portion of the lens. Accordingly, the amount of light of the reference reflected light R1 is reduced. The absorption filter 35 absorbs light and controls the amount of light by reducing the area through which the reference reflected light (R1) passes, thereby serving as an aperture.

The absorption filter 35 may further include a motor shaft that mechanically drives the absorption filter 35 at a predetermined angle and a driving means including a motor or lever that drives the motor shaft.

If necessary, the optical coherence tomography apparatus may further include one or more focusing lenses on the optical path. Necessary to transmit the reference reflected light (R1) that has passed through the absorption filter (35) inclined at a predetermined angle to the light splitter (20) and to transmit the signal light overlapped with the signal reflected light (S) to the photo detector (50). It may further include a focusing lens on the optical path, and the signal of the interference light (I) transmitted to the optical detector 50 is converted into a digital signal that can observe the surface and internal layer structure of the inspection object 5. converted.

The optical coherence tomography device having a variable transmittance absorption filter according to the present invention can be used in various fields such as industrial and medical fields (for example, equipment used in ophthalmology, etc.), and is especially used for industrial purposes. More useful, but not limited to this.

The optical coherence tomography device with a variable transmittance absorption filter according to the present invention varies the optical path length of the reference reflected light (R1) passing through the absorption filter 35, and as a result, does not replace different filters of various thicknesses. The same effect can be reproduced by using a single filter. Therefore, the optical coherence tomography device can respond to a wide range of reflection characteristics of various inspection objects by using a single absorption filter, and replacement of the absorption filter is not necessary depending on the application, compared to the existing method. , it is compact and the implementation method is also simple. In addition, since it is possible to control the thickness more precisely than the conventional absorption filter replacement method, a more optimized light amount can be found, and since it can be adjusted while observing the inspection object, production and light amount brightness adjustment work is also easy.

Claims (6)

A light source (10) that generates measurement light (L) irradiated into the interior of the inspection object (5);
The measurement light (L) is divided into reference light (R) and measurement light (L), the reference light (R) is irradiated to the reference mirror 30, and the measurement light (L) is irradiated to the inspection object 5, A light splitter (20) that generates interference light (I) by overlapping the reference reflected light (R1) reflected from the reference mirror (30) and the signal reflected light (S) reflected from the inspection object (5);
a scanning unit 40 that guides the measurement light L split by the light splitter 20 to the inspection position of the inspection object 5;
It is mounted in the path of the reflected light reflected from the reference mirror 30, tilted at a random angle, and adjusts the thickness to adjust the light absorption rate of absorbing the reference reflected light R1 reflected from the reference mirror 30, thereby adjusting the light absorption rate. An absorption filter 35 that adjusts the amount of reference reflected light (R1) transmitted to the splitter 20; and
It includes a light detector (50) that detects the interference light (I) and obtains an internal image signal of the inspection object (5),
The absorption filter 35 has a flat flat shape with a predetermined thickness, and as it is tilted at a random angle, the length of the optical path through which the reference reflected light (R1) passes increases, so that the reference reflected light (R1) passes through it. An optical coherence tomography device with a variable transmittance absorption filter, wherein the thickness of the absorption filter (35) is also increased. delete The method of claim 1, wherein when the length of the optical path through which the reference reflected light (R1) passes and the thickness of the filter (35) increase, the light transmittance of the reference reflected light (R1) passing through the absorption filter (35) decreases. In, optical coherence tomography apparatus. According to claim 1, when the length of the optical path of the reference reflected light (R1) passing through the absorption filter (35) increases, the light absorption rate of the absorption filter (35) increases, and the reference light incident on the light splitter (20) increases. An optical coherence tomography device in which the amount of reflected light (R1) is reduced. The method of claim 1, wherein when the length of the optical path of the reference reflected light (R1) passing through the absorption filter (35) increases, the refractive index of the reference reflected light (R1) increases, so that the amount of light transmitted to the light splitter (20) increases. Optical coherence tomography device, wherein the optical coherence tomography device is reduced. The method of claim 1, wherein as the absorption filter 35 is tilted at a random angle, the reflectance of the reference reflected light (R1) reflected on the surface of the absorption filter 35 increases, thereby increasing the light transmittance of the absorption filter 35. An optical coherence tomography device in which this is reduced.