KR20220035890A - An Improved Holographic Reconstruction Apparatus and Method - Google Patents

Abstract

The disclosed holographic restoration device includes a first light splitter that splits single-wavelength light from a light source into first and second transmitted split lights; a plurality of optical mirrors reflecting the first transmitted split light; a second light splitter splitting the second transmission split light into first and second reflection split lights; a reference light objective lens through which the second reflected split light passes; a position adjustment mirror through which the first reflected split light passing through the reference light objective lens is transmitted; The first transmission split light passing through the object to be measured or the first reflected split light reflected from the object to be measured passes through the object light objective lens, and the second reflected split light reflected from the position adjustment mirror is a recording medium that records an interference pattern formed by passing the reference light objective lens and being transmitted to the second light splitter; and a processor that receives and stores the image file generated by converting the interference pattern, and selectively acquires a light-transmitting or reflective object hologram according to the mode. Various embodiments are possible.

Description

An Improved Holographic Reconstruction Apparatus and Method}

The present invention relates to an improved holographic restoration device and method.

More specifically, the present invention is an integrated system that integrates a transmissive system that measures an object that transmits light and a reflective system that measures an object that reflects light, and is an integrated system that integrates the optical system of the object to be measured. The present invention relates to an improved hologram restoration device and method that can measure a digital hologram regardless of its characteristics.

As is well known, holography is an imaging method invented for the purpose of improving the resolving power of electron microscopes. While conventional photography records only the distribution of the bright and dark sides of an object, holography records all the information contained in light as a wave. In other words, it accumulates and reproduces amplitude and phase simultaneously. The principle is that coherent light from a laser light source divides the beam splitter into two and lets one of them illuminate the subject, causing diffuse reflection on the subject's surface. The reflected light reaches the holographic photosensitive material. This ray is called object light. The other ray is diffused by a lens and shines directly on the front of the holographic photosensitive material. This ray is called reference light or reference light (hereinafter referred to as “reference light”). In this way, object light and reference light interfere with each other on the holographic photosensitive material, creating a very delicate and complex interference pattern of about 500 to 1,500 per mm. A photo recording this interference pattern is called a hologram. When a hologram created in this way is illuminated with the same light as the reference light, the interference pattern acts as a diffraction grid and the light is diffracted in a position different from the direction from which the reference light entered. We become together. In this way, the initial object light is reproduced in the hologram.

Therefore, when you look inside the reproduced wave front, you can see the object for the first time, but it looks as if the object is inside. Then, if you move the viewing point again, the position where the object is visible also changes, making it seem as if you are looking at a three-dimensional photo. Additionally, because the wavefront of the original object is reproduced, it can also interfere with the wavefront from a slightly modified object. Therefore, these characteristics of holography are applied and used in various fields.

For example, a digital holographic microscope is a microscope that measures the shape of an object using digital holographic technology. A general microscope usually measures the shape of an object by shining a general light source on the object and measuring the intensity of light reflected or transmitted from the object. If it is a measuring device, a digital holographic microscope is a device that measures the interference and diffraction phenomenon of light that occurs when light shines on an object, records it digitally, and restores the shape information of the object from this information.

In other words, digital holography technology generates light of a single wavelength, such as a laser, and splits it into two lights using an optical splitter, so that one light (reference light) shines directly on the image sensor, and the other light (object light) is As the light transmitted or reflected from the object to be measured is illuminated on the image sensor, interference occurs between the reference light and the object light in the image sensor, and the interference pattern information of this light is recorded by the digital image sensor. This is a technology that restores the shape of the object to be measured using a computer using the recorded interference pattern information.

Meanwhile, in the case of existing optical holography technology rather than digital holography, the interference pattern information of the light is recorded on a special film, and the reference light is shined on the special film on which the interference pattern is recorded to restore the shape of the object to be measured. This is a method in which the shape of the virtual object to be measured is restored to the original location of the object to be measured.

Compared to the existing optical holography method, the digital holographic microscope measures the interference pattern information of light with a digital image sensor and stores it digitally, and uses the stored interference pattern information as a numerical calculation method using a computer device, etc., rather than an optical method. The difference is that the shape of the object being measured is restored through processing.

Existing digital holographic microscopes sometimes use a single-wavelength laser light source. However, when using a single laser light source, there is a problem that the measurement resolution of the object, that is, the minimum measurement unit, is limited to the wavelength of the laser light source used. In addition, when using a dual-wavelength or multi-wavelength laser light source among existing digital holographic microscopes, the cost increases due to the use of light sources with different wavelengths, or holographic images must be acquired sequentially using light sources of different wavelengths. Therefore, there is a problem in that it is difficult to measure three-dimensional change information of the object to be measured in real time.

In addition, in the conventional digital holography technology described above, in order to restore the shape of the object to be measured, a CGH (Computer Generated Hologram) is generated with a computer, displayed on a spatial light modulator (SLM), and then illuminated with reference light. , a three-dimensional holographic image of an object is obtained by diffraction of reference light. In this case, the use of an expensive spatial light modulator (SLM) (tens of millions of won or more) is required, which poses considerable difficulties in practical application.

A number of patent documents to solve the problems of such conventional digital holography technology are disclosed as follows.

According to these patent documents, the effect of increasing the measurement resolution of the object to be measured and restoring the three-dimensional shape information of the object to be measured in real time by measuring and recording a hologram of the object to be measured in real time that changes over time. is achieved, but the following problems still occur.

More specifically, Patent Document 1, whose invention title is “Digital Holographic Microscope and Digital Holographic Image Generation Method,” is a two-wavelength digital holographic microscope device, and as shown in FIG. 1, a mixed light source unit 100 and a wavelength splitting unit. (200), an interference pattern acquisition unit 300, an objective unit 400, an image sensor unit 500, an image storage unit 600, a control unit 700, and an object shape restoration unit 800.

The mixed light source unit 100 includes a mixed light source light emitting unit 110 and a light source lens 120. The mixed light source light emitting unit 110 emits mixed light having wavelength bands distributed in several bands rather than a single light source unit. The lens 120 optically adjusts the mixed light generated by the mixed light source light emitting unit 110 and makes it incident on the wavelength splitting unit 200.

The wavelength splitter 200 includes a first light splitter 210, a first light filter plate 220, a second light filter plate 230, and a first reflector 240. The first light splitter 210 receives the mixed light incident from the mixed light source unit 100 and splits it into two lights. At this time, the first light splitter 210 serves to divide and advance the incident mixed light into different directions. The first light filter 220 receives one light from among the lights split by the first light splitter 210 and obtains a first light ray having a predetermined single wavelength. Here, the light input to the first light filter plate 220 is filtered while passing through the first light filter plate 220, and a first light beam having a single wavelength determined according to the characteristics of the first light filter plate 220 is obtained. The second light filter 230 receives the remaining light among the lights split by the first light splitter 210 in the same manner as the first light filter 220, and generates a second light having a wavelength different from that of the first light beam. Obtain a ray of light. And the second light beam is sent to the interference pattern acquisition unit 300. The first reflector 240 serves to receive the first light ray obtained from the first light filter 220 and reflect it to the interference pattern acquisition unit 300.

The interference pattern acquisition unit 300 includes a second light splitter 310, a third light splitter 320, a second reflector 330, a third light filter plate 340, and a third reflector 350. The second light splitter 310 receives the first light beam input from the wavelength splitter 200 and splits it into first object light and first reference light. At this time, the second light splitter 210 serves to divide and advance the incident first light beam in different directions. The third light splitter 320 also receives the second light beam in the same manner as the second light splitter 310 and splits it into a second object light and a second reference light. The second reflector 330 receives the first reference light and sends the reflected first reflected reference light to the second light splitter 310. The third light filter 340 receives the first reference light split by the second light splitter 310 and sends it to the second reflector 330, and receives the reflected first reflected reference light and sends it to the second light splitter 310. You can. In addition, the third light filter 340 prevents the second object light from reaching the second reflector 330 when the second object light is split by the second light splitter 310 and a portion of the light proceeds in the direction of the second reflector 330. . To this end, the third light filter plate 340 is a light filter plate that has the same characteristics as the first light filter plate 220 in transmitting light. The third reflector 350 receives the second reference light and sends the reflected second reference light to the third light splitter 320, where the second reflector 330 and the third reflector 350 are connected to the control unit 700. ), it is possible to implement an off-axis hologram by configuring the angle to be adjustable according to the control.

Meanwhile, the first object light and the second object light obtained as described above are converted into first reflective object light and second reflective object light through the following process and are sent to the image sensor unit 500. The second light splitter 310 makes the first object light split as described above incident on the object to be measured mounted on the objective unit 400, and also makes the second object light split and sent from the third light splitter 320. Light is incident on the object to be measured. In this case, the reflected light that reflects the first object light incident on the object to be measured is called first reflected object light. In addition, the reflected light that reflects the second object light incident on the object to be measured is called second reflected object light. The second light splitter 310 receives the reflected first and second reflective object lights as described above and sends them to the third light splitter 320. The third light splitter 320 sends the first reflective object light and the second reflective object light input as described above back to the image sensor unit 500.

In addition, the first reflection reference light and the second reflection reference light obtained as described above are sent to the image sensor unit 500 through the following process. Specifically, the second light splitter 310 receives the first reflected reference light reflected from the second reflector 330 and sends it to the third light splitter 320. As described above, the third light splitter 320 receives the first reflected reference light sent from the second light splitter 310 and the second reflected reference light reflected from the third reflector 350 and returns it to the image sensor unit 500. send to Accordingly, from the third light splitter 320, the first reflective object light, the first reflected reference light, the second reflected object light, and the second reflected reference light are all equally sent toward the image sensor unit 500, and then interfere with each other. An interference pattern is created.

Meanwhile, the second reflector 330 and the third reflector 350 change angles according to the control of the control unit 700 to form an off-axis system in which light rays of different wavelengths form different interference patterns. It is characterized by being able to be adjusted in multiple directions.

That is, as the angles of the second reflector 330 and the third reflector 350 become different from each other, the first reflected reference light reflected from the second reflector 330 and the second reference light reflected from the third reflector 350 When a separation occurs in the direction of light and the first reflected reference light and the second reflected reference light are combined with the first reflected object light and the second reflected object light reaching the image sensor unit 500 to form an interference pattern, each wavelength Differently deaxial interference patterns are formed.

The objective unit 400 includes an object holder 410 and an objective lens 420. The object holder 410 fixes the object to be measured to the holder so that it can be measured, and the objective lens 420 is an object that is incident on the object to be measured. The first object light and the second object light are optically adjusted.

The image sensor unit 500 projects the interference pattern obtained by the interference pattern acquisition unit 300 onto a digital image sensor, measures the projected interference pattern using the digital image sensor, and converts the measured value into a discrete signal. Convert to Usually, the recording of the interference pattern is called a hologram. Various image sensors such as CCD can be used as such digital image sensors.

The image storage unit 600 stores the interference pattern information converted into discrete signals in the image sensor unit 500 in various storage media such as memory or a disk device.

The control unit 700 implements the above-described off-axis system and controls the interference pattern acquisition unit 300 by adjusting the positions and angles of the second reflector 330 and the third reflector 350 to obtain the interference pattern. ) is controlled, and the objective part 400 is controlled, such as by adjusting the objective lens 420 to adjust the first object light and the second object light incident on the object to be measured, and the interference pattern is measured and The image sensor unit 500 is controlled to convert information into discrete signals, and the image storage unit 600 is controlled to store interference pattern information converted into discrete signals.

The object shape restoration unit 800 includes a phase information acquisition unit 810, a thickness information acquisition unit 820, and a shape restoration unit 830, and the phase information acquisition unit 810 uses the interference pattern information to The phase information of the interference pattern for the first ray and the phase information of the interference pattern for the second ray are respectively acquired, and the thickness information acquisition unit 820 uses the phase information to obtain thickness information of the object to be measured. , the shape restoration unit 830 restores the real-time three-dimensional shape of the object to be measured using the thickness information. At this time, the thickness information of the object to be measured includes information on the difference between the paths taken by the object light and the reference light. Due to the difference in optical paths between the object light and the reference light, the interference pattern is formed when the object light and the reference light overlap.

In Patent Document 1 disclosed as above, a mixed light source having wavelength bands distributed in several non-single bands is used, so in order to obtain at least two or more single wavelengths, the wavelength splitter divides the first and second light rays with different wavelengths. For segmentation, a first light filter plate, a second light filter plate, and a first reflector must be used. In addition, the interference pattern acquisition unit further includes a third light splitter for splitting the second light beam, a third reflector for reflecting the second light beam, and a third light filter plate for blocking the second light beam from being incident on the second reflector. Must use. Accordingly, problems still exist in that the structure of the entire device becomes complex, optical noise in the entire device increases due to an increase in the use of optical elements, and the overall manufacturing cost is high.

Accordingly, as new methods are required to solve the above-mentioned problems while using a light source of a single wavelength, a number of patent documents corresponding thereto have been disclosed.

However, the optical systems in most of the disclosed patent documents can be broadly classified into a transmission type system that measures an object that transmits light to measure a digital hologram, or a reflective system that reflects light.

More specifically, Patent Documents 2, 3, 5, and 6 are reflective measurement devices using two wavelengths and can only measure objects that reflect light, but Patent Document 2 requires lasers with two different wavelengths. The optical interferometer system is complex, and Patent Document 3 requires two image sensors and uses white light with low coherence. Like Patent Document 2, the optical interferometer system is complex, and Patent Document 5, like Patent Document 2, , Not only are lasers with two different wavelengths required and the optical interferometer system is complicated, but the configuration of the proposed system makes it impossible to create a hologram. Patent Document 6, like Patent Document 2, uses two different wavelengths. Eggplant requires a laser and the optical interferometry system has complex problems.

In addition, Patent Document 4 is a transmission type measuring device using a single wavelength and can only measure objects that transmit light. However, since it requires two images to be taken, there is a problem in that errors occur due to time delay.

Therefore, in order to solve this problem, measurement was possible only by using a transmissive system or a reflective system depending on the optical characteristics of the object to be measured, such as an object that transmits light or an object that reflects light. However, regardless of the characteristics of the object to be measured, digital In order to measure holograms, expensive equipment worth hundreds of millions of won per unit must be purchased, resulting in additional cost issues.

[Prior patent literature]

[Patent Document]

1. Korean Patent No. 10-1634170 (registered on June 22, 2016)

2. Korean Patent No. 10-1152798 (registered on May 29, 2012)

3. Korean Patent No. 10-1139178 (registered on April 16, 2012)

4. Korean Patent No. 10-1203699 (registered on November 15, 2012)

5. Korean Patent No. 10-1441245 (registered on September 5, 2014)

6. Korean Patent No. 10-1716452 (registered on March 8, 2017)

The present invention was devised to solve the above-described conventional problems. The purpose of the present invention is to provide a transmission-type system for measuring objects that transmit light and a reflective system for measuring objects that reflect light. The aim is to provide an improved holographic restoration device that can measure a digital hologram regardless of the optical characteristics of the object being measured by an integrated system.

In addition, another object of the present invention is to measure a digital hologram regardless of the optical characteristics of the object being measured, and a transmission mode for measuring an object that transmits light and a reflection mode for measuring an object that reflects light. The purpose is to provide an improved holographic restoration method to select .

In order to achieve the above object, an improved holographic restoration device according to one aspect of the present invention includes a light source unit emitting single wavelength light; a first light splitter that splits the single-wavelength light emitted from the light source into first and second transmission split lights; a plurality of optical mirrors that reflect the first transmitted split light split by the first light splitter; a second light splitter splitting the second transmitted light split by the first light splitter into a first reflection split light and a second reflection split light; a multi-body light objective lens that passes the first transmission split light that is reflected by the plurality of optical mirrors and then passes through the object to be measured, or the first reflection split light split by the second light splitter; a reference light objective lens that passes the second reflected split light split by the second light splitter; a position adjustment mirror through which the second reflected split light passing through the reference light objective lens is transmitted; The first transmission split light that passes through the object to be measured or the first reflected split light reflected from the surface of the object to be measured, and the second reflected split light that passes through the reference light objective lens and is reflected by the position adjustment mirror. a recording medium for recording an interference pattern formed by passing through the object light objective lens and the reference light objective lens respectively and being transmitted to the second light splitter; and a processor that receives and stores an image file generated by converting the interference pattern transmitted from the recording medium, wherein the processor converts a light transmission object hologram and a light reflection object hologram into a transmission mode. and is selectively acquired according to the reflective mode.

An improved holographic restoration method according to another aspect of the present invention includes the steps of a) selecting two measurement modes of the object hologram of the object to be measured (S1); b) measuring the object hologram according to the selected mode (S2); c) removing direct current, virtual image, and aberration information from the measured object hologram (S3); d) extracting phase information of the object hologram (S4); and e) a step (S5) of restoring the three-dimensional shape information and quantitative size (thickness) information of the object to be measured.

By solving the above problems, the improved holographic restoration device and method of the present invention provides the following effects.

1. The problem of the complex optical device structure and the correspondingly high cost required for one-shot digital holography restoration using a single object holographic image in the prior art can be solved.

2. Holographic restoration is possible with a simple structure and low cost.

3. It has the versatility to be applied to both reflective and transmissive hologram restoration devices of the prior art.

4. In particular, the use of reference light is unnecessary when restoring holograms, and quantitative 3D image restoration of the object to be measured is possible in real time.

5. Detection, confirmation or display in various fields, including devices for detecting defects in ultra-fine structures such as TFTs and semiconductors, medical devices requiring display of precise three-dimensional images, and detection of refractive index errors in transparent objects such as other lenses. Applicable to devices.

6. Digital holograms can be measured regardless of the optical properties of the object to be measured by selectively selecting transmission mode and reflection mode by one integrated system that integrates the reflection type and transmission type hologram restoration device of the prior art, thereby reducing additional costs. The problem can be resolved.

Additional advantages of the present invention will become apparent from the following description with reference to the accompanying drawings in which like or similar reference numerals designate like elements.

Figure 1 is a block diagram showing in detail a two-wavelength digital holography microscope device according to the disclosed prior art.
Figure 2 is a schematic block diagram showing an improved holographic restoration device according to a preferred embodiment of the present invention.
Figure 3 is a flowchart showing an improved holographic restoration method according to an embodiment of the present invention.
FIG. 4 is a flowchart showing in detail the specific implementation steps of step S3 of the improved holographic restoration method of FIG. 3.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. At this time, it should be noted that in the attached drawings, identical components are indicated by identical symbols whenever possible. In describing the present invention, if a detailed description of a related configuration or function is deemed unnecessary, the detailed description will be omitted.

Referring to FIG. 2 showing an improved holographic restoration device according to an embodiment of the present invention, the improved holographic restoration device 1 according to an embodiment of the present invention measures an object that transmits light. It may be an all-in-one type digital holographic microscope that selectively executes a transmission mode that measures objects that reflect light and a reflection mode that measures objects that reflect light.

An improved holographic restoration device (1) according to an embodiment of the present invention includes a light source unit (10) that emits single wavelength light; a first light splitter (20) that splits the single-wavelength light emitted from the light source unit (10) into a first transmitted split light (T1) and a second object transmitted light (T2); a plurality of optical mirrors (30, 31) that reflect the first transmission split light (T1) split by the first light splitter (20); a second light splitter (60) splitting the second transmission split light (T2) split by the first light splitter (20) into a first reflection split light (R1) and a second reflection split light (R2); The first transmitted split light (T1) that is reflected by the plurality of optical mirrors (30, 31) and then passes through the object to be measured (40) or the first split light (T1) split by the second light splitter (60) an object light objective lens 50 that passes the reflected split light R1; a reference light objective lens 51 that passes the second reflection split light R2 split by the second light splitter 60; a position adjustment mirror 70 through which the second reflected split light R2 passing through the reference light objective lens 51 is transmitted; The first transmission split light T1 that passes through the object to be measured 40 or the first reflected split light R1 reflected from the surface of the object to be measured 40, and the reference light objective lens 51. The second reflection split light R2 reflected from the position adjustment mirror 70 passes through the object light objective lens 50 and the reference light objective lens 51, respectively, to the second light splitter 60. a recording medium 80 that records the interference pattern formed by being transmitted to; and a processor 90 that receives and stores an image file generated by converting the interference pattern transmitted from the recording medium 80.

The processor 90 of the holographic restoration device 1 according to the above-described embodiment of the present invention is implemented as a device capable of arithmetic operations, such as a microprocessor or a personal computer (PC), and also includes a recording medium 80. ) can be implemented, for example, with an image sensor such as a Charge Coupled Device (CCD) or Complimentary Metal-Oxide Semiconductor (CMOS).

The improved holographic restoration device 1 according to an embodiment of the present invention uses the processor 90 to produce a light transmission object hologram and a light reflection object hologram according to a transmission mode and a reflection mode. It can be obtained selectively. That is, the processor 90 of the integrated improved holographic restoration device 1 according to an embodiment of the present invention variably adjusts the position of the position adjustment mirror 70, thereby adjusting the position of the light in the transmissive mode and the reflective mode. Corrects the optical path difference. Accordingly, the light-transmitting object hologram or the light-reflecting object hologram may be transmitted to the processor 90 through the recording medium 80 (eg, CCD) and obtained in the form of an image file.

More specifically, in the holographic restoration device 1 according to an embodiment of the present invention, in a transmission mode that measures an object that transmits light, light emitted from the laser, which is the light source unit 10, passes through the first light splitter 20. It is divided into a first transmission split light T1 and a second transmission split light T2.

The first transmitted split light T1 is reflected by each of the plurality of optical mirrors 30 and 31 and transmitted to the object to be measured 40, then passes through the object to be measured 40, and then is transmitted to the object light objective lens ( 50) and heads to the second optical splitter 60. In the embodiment of the present invention, the plurality of optical mirrors 30 and 31 are illustrated as being implemented with two optical mirrors, but those skilled in the art will fully understand that they can be implemented with three or more optical mirrors. Meanwhile, the second transmission split light T2 passes through the second light splitter 60 and the reference light objective lens 51, is reflected by the positioning optical mirror 70, and then passes through the reference light objective lens 51 again to form the second light splitter 60. Head to the optical splitter (60).

The first and second transmitted split lights T1 and T2 encountered in the second light splitter 60 form an interference pattern (light-transmitting object hologram) for the light-transmitting portion of the object to be measured 40. . Here, the first transmission split light T1 corresponds to the object light of the light transmission object hologram, and the second transmission split light T2 corresponds to the reference light of the light transmission object hologram.

Meanwhile, in the reflective mode that measures an object that reflects light, light from the laser, which is the light source unit 10, passes through the first light splitter 20 into a first transmission split light (T1) and a second transmission split light (T2). is divided into

The second transmitted light T2 is divided into a first reflection split light R1 and a second reflection split light R2 by the second light splitter 60. The first reflected split light R1 passes through the object light objective lens 50, is reflected from the object to be measured 40, passes through the object light objective lens 50 again, and heads to the second light splitter 60. The second reflected split light (R2) passes through the reference light objective lens 51 and is reflected by the positioning optical mirror 70, and the reflected light again passes through the reference light objective lens 51 to the second light splitter 60. Head to

The first reflection split light (R1) and the second reflection split light (R2) met at the second light splitter 60 produce an interference pattern (light reflection object hologram) for the light-reflecting part of the measurement target object 40. is formed. Here, the first reflection split light R1 corresponds to the object light of the light reflecting object hologram, and the second reflection split light R2 corresponds to the reference light of the light reflecting object hologram.

At this time, the position of the position adjustment mirror 70 is adjusted by the processor 90 implemented in a PC, for example, to correct the difference in the optical path of light occurring in the transmissive mode and the reflective mode. The light-transmitting object hologram and the light-reflecting object hologram are each transmitted to the PC, which is the processor 90, through the CCD, which is the recording medium 80, and are acquired in the form of an image file.

When measuring by selecting the light transmission mode by the holographic restoration device 1 according to the above-described embodiment of the present invention, the obtained light-transmitting object hologram is located in the light-transmitting part of the object 40 to be measured. This is the interference pattern for The light-transmitting object hologram obtained in this way can be expressed as a complex conjugate hologram as shown in Equation 1 below.

Equation 1:

*Here, x and y represent spatial coordinates, represents the obtained hologram of a light-transmitting object, represents the object light and reference light of the light-transmitting object hologram, represents the complex conjugate of the object light and reference light of the light-transmitting object hologram.

On the other hand, when measuring by selecting the light reflection mode, the obtained hologram of the light reflecting object is an interference pattern for the light reflecting portion of the object 40 to be measured. The light reflecting object hologram obtained in this way can be expressed as a complex conjugate hologram as shown in Equation 2 below.

Equation 2:

Here, x and y represent spatial coordinates, represents the obtained hologram of a light-reflecting object, represents the object light and reference light of the light-reflecting object hologram, represents the complex conjugate of the object light and reference light of the light-reflecting object hologram.

Hereinafter, a specific method for restoring the three-dimensional shape of an object from the two types of object holograms obtained above will be described.

Specifically, referring again to FIGS. 2 to 4, as described above, the transmissive mode is selected by the processor 90 to remove direct current and virtual image information from the obtained light-transmitting object hologram (S21 in FIG. 3). A 2D Fourier Transform is performed (S3 in FIG. 3).

In the case of transmissive mode, the frequency spectrum of the light-transmitting object hologram obtained by two-dimensional Fourier transform is divided into the real image of the light-transmitting object hologram, the virtual image of the light-transmitting object hologram, and direct current (DC) information. It appears separated (S31 in Figure 4). To remove virtual images and direct current (DC) information from separated light-transmitting object holograms, for example, an automatic real image spot-position extraction algorithm is used from real image spot-position. Apply to extract phase information (S3 in Figure 3 and S32 in Figure 4).

Afterwards, reference light information of the light-transmitting object hologram is extracted using a frequency filtering algorithm (S33 in FIG. 4).

In order to calculate the compensation term (Term) of the extracted reference light information, the wavenumber vector constant of the extracted reference light information is calculated (S34 in FIG. 4). The compensation term (Term) of the extracted reference light information is calculated using the calculated wavenumber vector constant (S35 in FIG. 4). In this case, the compensation term of the extracted reference light information is the conjugate term of the light-transmitting object hologram.

Afterwards, aberration information is extracted from the light-transmitting object hologram to compensate for the aberration of the object light objective lens 51 used when measuring the hologram (S36 in FIG. 4). For this purpose, for example, a curvature information compensation term is generated using an automatic frequency curvature compensation algorithm.

The compensation term of the extracted reference light information and the compensation term of the aberration information are multiplied by the light-transmitting object hologram to obtain a compensated light-transmitting object hologram (S5 in Fig. 3 and S37 in Fig. 4).

Meanwhile, in the case of the reflective mode, the same method as the above-described transmissive mode is applied to the hologram of the light-reflecting object obtained by two-dimensional Fourier transform to obtain a compensated hologram of the light-reflecting object. The compensated light-transmitting object hologram and the compensated light-reflecting object hologram obtained in this way can be expressed as Equation 3 and Equation 4 below, respectively.

Equation 3:

Equation 4:

here, and are a compensated light-transmitting object hologram and a compensated light-reflecting object hologram, respectively, is the object light and reference light of the light-transmitting object hologram, is the object light and reference light of the light reflection hologram, is the compensation term of the reference light information of the light-transmitting object hologram, is the aberration information compensation term of the light-transmitting object hologram, is the compensation term of the reference light information of the light reflecting object hologram, refers to the aberration information compensation term of the hologram of a light-reflecting object.

The compensated light-transmitting object hologram represented by Equation 3 above is converted into information on a reconstruction image plane using an Angular Spectrum Propagation algorithm.

Phase information is extracted from the transformation-compensated object hologram through the Inverse 2D Fourier Transform. The phase information acquired at this time is the remaining information (i.e., information of light, information of the object light objective lens 50) excluding the phase information of the light-transmitting part of the measurement object 40 contained in the acquired light-transmitting object hologram. It is a form in which aberration information) is removed and only includes phase information of the light-transmitting part of the measurement target object 40.

The same method is applied to the compensated light-reflecting object hologram to extract phase information. The phase information acquired at this time is the remaining information (i.e., information of light, information of the object light objective lens 50) excluding the phase information of the light-reflecting part of the measurement object 40 contained in the acquired light-reflecting object hologram. It is a form in which aberration information) is removed and only includes phase information of the part that reflects light of the measurement target object 40.

The phase information of the part that transmits the extracted light and the phase information of the part that reflects the extracted light of the object 40 to be measured are distorted phase information using a 2D phase unwrapping algorithm. are compensated for, and quantitative thickness information of the object to be measured 40 is calculated using this (S5 in FIG. 3). This quantitative thickness information can be expressed as Equation 5 below.

Equation 5:

*

here, is quantitative thickness information of the object to be measured 40, is the wavelength of the light source used when acquiring the object hologram, is the phase information of the light-transmitting part of the measurement object 40, is the phase information of the light-reflecting part of the measurement object 40, means the difference in refractive index between the measurement target object 40 and air. The three-dimensional shape of the object is restored using the calculated quantitative thickness information of the object.

Figure 3 is a flowchart showing an improved holographic restoration method according to an embodiment of the present invention.

2 and 3, the improved holographic restoration method according to an embodiment of the present invention includes a) selecting two measurement modes of the object hologram of the measurement target object 40 (S1); b) measuring the object hologram according to the selected measurement mode (S2); c) removing direct current, virtual image, and aberration information of the measured object hologram (S3); d) extracting phase information of the object hologram (S4); and e) a step (S5) of restoring the three-dimensional shape information and quantitative size (thickness) information of the measurement object 40.

In the holographic restoration method according to an embodiment of the present invention described above, step b) includes measuring an object hologram in a light transmission mode (S21) or measuring an object hologram in a light reflection mode (S22). can do.

In addition, the light-transmitting object hologram obtained in the light-transmitting mode measurement step (S21) is a complex conjugate hologram corresponding to the interference pattern of the light-transmitting portion of the measurement target object 40, expressed by Equation 1 below: It can be.

Equation 1:

Here, x and y represent spatial coordinates, represents the obtained hologram of a light-transmitting object, represents the object light and reference light of the light-transmitting object hologram, represents the complex conjugate of the object light and reference light of the light-transmitting object hologram.

On the other hand, the light reflecting object hologram obtained in the light reflection mode measurement step (S22) is a complex conjugate hologram corresponding to the interference pattern of the light reflecting part of the measurement target object 40, and is expressed by Equation 2 below: It can be.

Equation 2:

Here, x and y represent spatial coordinates, represents the obtained hologram of a light-reflecting object, represents the object light and reference light of the light-reflecting object hologram, represents the complex conjugate of the object light and reference light of the light-reflecting object hologram.

In the holographic restoration method according to an embodiment of the present invention described above, when the measured object hologram is a light-transmitting object hologram, step c) is performed to remove direct current and virtual image information from the light-transmitting object hologram. Separating the frequency spectrum of the light-transmitting object hologram obtained by performing 2D Fourier Transform into real image, virtual image, and direct current information of the light-transmitting object hologram. step; c2) In order to remove the virtual image and direct current (DC) information of the separated light-transmitting object hologram, the real image spot-position is extracted using an automatic real image spot-position extraction algorithm. applying and extracting; c3) extracting reference light information of the light-transmitting object hologram using a frequency filtering algorithm; c4) calculating a wavenumber vector constant of the extracted reference light information; c5) calculating a compensation term (Term) of the extracted reference light information using the calculated wavenumber vector constant; c6) extracting aberration information from the light-transmitting object hologram to compensate for the aberration of the object light objective lens 50 used when measuring the object hologram; and c7) converting the light-transmitting object hologram for which the compensation term and the aberration information have been compensated into information on a reconstruction image plane using an Angular Spectrum Propagation algorithm. .

At this time, step c6) generates an aberration information compensation term (Term) using an automatic frequency curvature compensation algorithm; and obtaining the compensated light-transmitting object hologram by multiplying the compensation term of the extracted reference light information and the aberration information compensation term by the light-transmitting object hologram.

Meanwhile, in the case of the reflective mode, the same method as the above-described transmissive mode is applied to the hologram of the light-reflecting object obtained by two-dimensional Fourier transform to obtain a compensated hologram of the light-reflecting object.

*In the holographic restoration method according to an embodiment of the present invention, the compensated light-transmitting object hologram or the compensated light-reflecting object hologram may be expressed by Equation 3 or Equation 4 below.

Equation 3:

Equation 4:

here, is the compensated light-transmitting object hologram, is the compensated light reflection object hologram, is the object light and reference light of the light-transmitting object hologram, is the object light and reference light of the light reflection hologram, is the compensation term of the reference light information of the light-transmitting object hologram, is the aberration information compensation term of the light-transmitting object hologram, is the compensation term of the reference light information of the light reflecting object hologram, refers to the aberration information compensation term of the hologram of a light-reflecting object.

In the holographic restoration method according to an embodiment of the present invention described above, step d) is implemented as a step of extracting phase information from the transformation-compensated object hologram through an inverse 2D Fourier transform, The phase information obtained here is the remaining information (i.e., information of light, object It contains only phase information of the part that transmits or reflects light of the object to be measured 40 from which aberration information of the optical objective lens 50 has been removed.

In the holographic restoration method according to an embodiment of the present invention described above, step e) is the extracted phase information of the light-transmitting part or the extracted phase information of the light-reflecting part of the measurement target object 40. Compensating for each distorted phase information using a 2D phase unwrapping algorithm; calculating quantitative thickness information of the object to be measured (40) using the compensated phase information; And it may include restoring the three-dimensional shape of the object to be measured 40 using the calculated quantitative thickness information of the object.

The calculated thickness information can be expressed as Equation 5 below.

Equation 5:

here, is quantitative thickness information of the measurement target object 40, is the wavelength of the light source used when acquiring the object hologram, is the phase information of the light-transmitting part of the object, is the phase information of the light-reflecting part of the object, refers to the difference in refractive index between an object and air.

As described above, in the improved holographic restoration device 1 and method according to the present invention, a digital reference hologram calculated from the object hologram is directly generated using the processor 90, and 3 of the object 40 to be measured Since dimensional information can be restored, it is possible to solve the problem of the complex optical device structure and the correspondingly high cost required for one-shot digital holography restoration using a single object holographic image in the prior art.

In addition, according to the improved holographic restoration device 1 and method according to the present invention, since the restoration device additionally uses only the processor 90, the overall configuration is very simple and it is possible to restore holography at low cost. .

In addition, in the improved holographic restoration device 1 and method according to the present invention, other components except the processor 90 and the position adjustment mirror 70 are substantially the same as the reflective and transmissive holographic restoration devices of the prior art. Because it has a configuration, it has versatility that can be easily applied to both reflective and transmissive hologram restoration devices of the prior art.

In addition, in the improved holographic restoration device 1 and method according to the present invention, unlike the prior art, the use of reference light is not necessary when restoring the hologram, and quantitative three-dimensional image restoration of the measurement target object 40 is performed in real time. This is possible.

In addition, in the improved holographic restoration device 1 and method according to the present invention, as described above, quantitative three-dimensional image restoration of the object to be measured 40 in real time is possible without using the reference light, so that TFT and semiconductor It can be applied to detection, confirmation or display devices in various fields, including devices for detecting defects in ultra-fine structures, medical devices requiring display of precise three-dimensional images, and detection of refractive index errors in transparent objects such as lenses. possible.

Moreover, in the improved holographic restoration device (1) and method according to the present invention, transmission mode and reflection mode are selectively selected and measured by an integrated system that integrates the reflection type and transmission type hologram restoration device of the prior art. Since digital holograms can be measured regardless of the object's optical characteristics, additional cost issues can be resolved.

Although the present invention has been described above by way of examples, it is not necessarily limited thereto, and modifications and variations are possible within the scope of the technical idea of the present invention.

10: light source unit 20: first optical splitter
30: first optical mirror 31: second optical mirror
40: Object to be measured 50: Object light objective lens
51: Reference light objective lens 60: Second light splitter
70: Position adjustment mirror 80: Recording medium
90: processor

Claims (1)

In the holographic restoration device,
A light source unit emitting single wavelength light;
a first light splitter that splits the single-wavelength light emitted from the light source into first and second transmission split lights;
a plurality of optical mirrors reflecting the first transmitted split light;
a second light splitter splitting the second transmission split light into a first reflection split light and a second reflection split light;
The first transmission split light transmitted through the object to be measured after being reflected by the plurality of optical mirrors, and the first reflected split light reflected from the surface of the object to be measured after being split by the second light splitter. An objective lens that allows object light to pass through;
a reference light objective lens through which the second reflected split light passes;
a position adjustment mirror through which the second reflected split light passing through the reference light objective lens is transmitted;
The first transmission split light passing through the object to be measured or the first reflection split light reflected from the surface of the object to be measured passes through the object light objective lens, and the second reflection split light is reflected from the position adjustment mirror. a recording medium that records an interference pattern formed when light passes through the reference light objective lens and is transmitted to the second light splitter; and
A holographic restoration device comprising: a processor configured to receive and store an image file generated by converting the interference pattern transmitted from the recording medium.