Digital holographic reconstruction device and method using single generation phase shifting method

Abstract

A time delay error occurring in the case of acquiring two holograms (object hologram and reference hologram) necessary for reconstruction in the related art or in the case of acquiring four physical holograms having different phase shift degrees may be removed. DC noise (including background noise) may be completely removed by using a software-implemented phase shifting method.

Claims

1. A digital holographic reconstruction device using a single generation phase shifting method, the digital holographic reconstruction device comprising: a light source unit emitting a single-wavelength light; a collimator collimating the single-wavelength light emitted from the light source unit; a light splitter splitting the single-wavelength light passed through the collimator into an object beam and a reference beam; an object beam objective lens transmitting the object beam generated by the light splitter; a reference beam objective lens transmitting the reference beam generated by the light splitter; an optical mirror reflecting the reference beam passed through the reference beam objective lens; a recording medium recording an interference pattern formed when an object beam passed through the object beam objective lens and then reflected from a surface of a measurement target object and a reference beam reflected by the optical mirror pass through the object beam objective lens and the reference beam objective lens respectively and then are transmitted to the light splitter; and a processor receiving and storing an image file generated by converting the interference pattern from the recording medium, wherein the processor generates first to fourth phase-shifted object holograms from an object hologram acquired from the image file by using a wave optics-based interference equation, generates a complex conjugate hologram by removing direct current (DC) noise and virtual image information by using the generated first to fourth phase-shifted object holograms and a software-implemented phase shifting method, extracts phase information of the measurement target object by using the generated complex conjugate hologram, and then reconstructs three-dimensional (3D) information of the measurement target object.

2. A digital holographic reconstruction device using a single generation phase shifting method, the digital holographic reconstruction device comprising: a light source unit emitting a single-wavelength light; a collimator collimating the single-wavelength light emitted from the light source unit; a light splitter splitting the single-wavelength light passed through the collimator into an object beam and a reference beam; an object beam objective lens transmitting an object-transmitted beam including information of a measurement target object after the object beam generated by the light splitter passes through the measurement target object; a second optical mirror reflecting the object-transmitted beam passed through the object beam objective lens; a reference beam objective lens transmitting the reference beam generated by the light splitter; a first optical mirror reflecting the reference beam passed through the reference beam objective lens; a second light splitter to which the reference beam reflected by the first optical mirror and the object-transmitted beam reflected by the second optical mirror are transmitted; a recording medium recording an interference pattern formed by the reference beam and the object-transmitted beam both transmitted to the second light splitter; and a processor receiving and storing an image file generated by converting the interference pattern from the recording medium, wherein the processor generates first to fourth phase-shifted object holograms from an object hologram acquired from the image file by using a wave optics-based interference equation, generates a complex conjugate hologram by removing direct current (DC) noise and virtual image information by using the generated first to fourth phase-shifted object holograms and a software-implemented phase shifting method, extracts phase information of the measurement target object by using the generated complex conjugate hologram, and then reconstructs three-dimensional (3D) information of the measurement target object.

3. The digital holographic reconstruction device of claim 1, wherein the processor separates and extracts the object beam information and the reference beam information by using a phase delay method in a frequency domain of the acquired object hologram.

4. The digital holographic reconstruction device of claim 2, wherein the processor separates and extracts the object beam information and the reference beam information by using a phase delay method in a frequency domain of the acquired object hologram.

5. The digital holographic reconstruction device of claim 3, wherein the processor phase-shifts the reference beam information by 0, 90, 180, and 270 and then generates the first to fourth phase-shifted object holograms by combining the 0, 90, 180, and 270 phase-shifted reference beam information with the extracted object beam information by using a wave optics-based interference equation.

6. The digital holographic reconstruction device of claim 4, wherein the processor phase-shifts the reference beam information by 0, 90, 180, and 270 and then generates the first to fourth phase-shifted object holograms by combining the 0, 90, 180, and 270 phase-shifted reference beam information with the extracted object beam information by using a wave optics-based interference equation.

7. The digital holographic reconstruction device of claim 5, wherein the processor simultaneously generates the second to fourth phase-shifted object holograms.

8. The digital holographic reconstruction device of claim 6, wherein the processor simultaneously generates the second to fourth phase-shifted object holograms.

9. The digital holographic reconstruction device of claim 1, wherein the phase information of the measurement target object is represented by an equation of (x,y)=tan.sup.1[I.sub.4(x,y)I.sub.2(x,y)]/[I.sub.1(x,y)I.sub.3(x,y)], where x and y denote spatial coordinates, (x,y) denotes phase information of the measurement target object, and I.sub.1(x,y), I.sub.2(x,y), I.sub.3(x,y), and I.sub.4(x,y) respectively denote intensity information of the first to fourth phase-shifted object holograms.

10. The digital holographic reconstruction device of claim 2, wherein the phase information of the measurement target object is represented by an equation of (x,y)=tan.sup.1[I.sub.4(x,y)I.sub.2(x,y)]/[I.sub.1(x,y)I.sub.3(x,y)], where x and y denote spatial coordinates, (x,y) denotes phase information of the measurement target object, and I.sub.1(x,y), I.sub.2(x,y), I.sub.3(x,y), and I.sub.4(x,y) respectively denote intensity information of the first to fourth phase-shifted object holograms.

11. The digital holographic reconstruction device of claim 1, wherein quantitative thickness information of the measurement target object is represented by an equation of L=(x,y)/2n(x,y), where L denotes quantitative thickness information of the measurement target object, denotes a wavelength of the light source unit, (x,y) denotes phase information of the measurement target object, and n(x,y) denotes a refractive index difference between a background and the measurement target object.

12. The digital holographic reconstruction device of claim 2, wherein quantitative thickness information of the measurement target object is represented by an equation of L=(x,y)/2n(x,y), where L denotes quantitative thickness information of the measurement target object, denotes a wavelength of the light source unit, (x,y) denotes phase information of the measurement target object, and n(x,y) denotes a refractive index difference between a background and the measurement target object.

13. A digital holographic reconstruction method using a single generation phase shifting method, the digital holographic reconstruction method comprising: an operation a) of acquiring an object hologram of a measurement target object; an operation b) of generating a first phase-shifted object hologram from the acquired object hologram by separately extracting object beam information having phase information of the measurement target object and reference beam information having no phase information of the measurement target object; an operation c) of generating a second phase-shifted object hologram by phase-shifting the extracted reference beam information by 90; an operation d) of generating a third phase-shifted object hologram by phase-shifting the extracted reference beam information by 180; an operation e) of generating a fourth phase-shifted object hologram by phase-shifting the extracted reference beam information by 270; an operation f) of extracting phase information of the measurement target object by removing direct current (DC) information, DC noise, and virtual image information by using the generated first to fourth phase-shifted object holograms and a phase shifting method; and an operation g) of compensating the extracted phase information for distorted phase information and reconstructing quantitative thickness information and three-dimensional (3D) shape information of the measurement target object by calculating quantitative thickness information of the measurement target object by using the compensated phase information.

14. The digital holographic reconstruction method of claim 13, wherein the operations c) to e) are simultaneously performed.

15. The digital holographic reconstruction method of claim 13, wherein in the operation c), the object beam information and the reference beam information are separated and extracted by using a phase delay method in a frequency domain of the acquired object hologram.

16. The digital holographic reconstruction method of claim 13, wherein the first to fourth phase-shifted object holograms are respectively generated by combining the 0, 90, 180, and 270 phase-shifted reference beam information with the extracted object beam information by using a wave optics-based interference equation.

17. The digital holographic reconstruction method of claim 13, wherein the phase information of the measurement target object is represented by an equation of (x,y)=tan.sup.1[I.sub.4(x,y)I.sub.2(x,y)]/[I.sub.1(x,y)I.sub.3(x,y)], where x and y denote spatial coordinates, (x,y) denotes phase information of the measurement target object, and I.sub.1(x,y), I.sub.2(x,y), I.sub.3(x,y), and I.sub.4(x,y) respectively denote intensity information of the first to fourth phase-shifted object holograms.

18. The digital holographic reconstruction method of claim 13, wherein in the operation g), the extracted phase information of the measurement target object is compensated for the distorted phase information by using a two-dimensional (2D) phase unwrapping algorithm.

19. The digital holographic reconstruction method of claim 13, wherein quantitative thickness information of the measurement target object is represented by an equation of L=(x,y)/2n(x,y), where L denotes quantitative thickness information of the measurement target object, denotes a wavelength of a light source unit used to acquire the object hologram, (x,y) denotes phase information of the measurement target object, and n(x,y) denotes a refractive index difference between a background and the measurement target object.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram illustrating a configuration of a 3D measurement device using digital holography, according to Related Art 1.

(2) FIG. 2A is a schematic block diagram of a digital holographic reconstruction device using a single generation phase shifting method, according to an embodiment of the present disclosure.

(3) FIG. 2B is a schematic block diagram of a digital holographic reconstruction device using a single generation phase shifting method, according to another embodiment of the present disclosure.

(4) FIG. 2C is a schematic flowchart illustrating a digital holographic reconstruction method using a single generation phase shifting method, according to an embodiment of the present disclosure.

(5) FIG. 2D is a diagram illustrating an object hologram of steps having different thicknesses of three levels and first to fourth phase-shifted holograms generated in the object hologram, in an off-axis holographic method according to an embodiment of the present disclosure.

(6) FIG. 2E is a diagram illustrating an object hologram of steps having different thicknesses of three levels and first to fourth phase-shifted holograms generated in the object hologram, in an on-axis holographic method according to an embodiment of the present disclosure.

(7) FIG. 2F is a diagram illustrating a 3D object hologram of steps having different thicknesses of three levels, which is obtained by reconstructing four phase-shifted holograms illustrated in FIG. 2D by using a software-based phase shifting method, in an off-axis holographic method according to an embodiment of the present disclosure.

(8) FIG. 2G is a diagram illustrating a 3D object hologram of steps having different thicknesses of three levels, which is obtained by reconstructing four phase-shifted holograms illustrated in FIG. 2E by using a software-based phase shifting method, in an on-axis holographic method according to an embodiment of the present disclosure.

(9) FIG. 2H is a diagram illustrating a comparison between a 3D object hologram reconstructed by using an off-axis optical holographic method of the related art and a 3D object hologram (see FIG. 2F) reconstructed by using an off-axis holographic method according to an embodiment of the present disclosure, with respect to steps having different thicknesses of three levels.

(10) FIG. 2I is a diagram illustrating a comparison table between the characteristics of off-axis reconstruction and on-axis reconstruction of holograms according to the related art and the present disclosure.

BEST MODE

(11) Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

(12) FIG. 2A is a schematic block diagram of a digital holographic reconstruction device using a single generation phase shifting method, according to an embodiment of the present disclosure.

(13) Referring to FIG. 2A, a digital holographic reconstruction device 200a using a single generation phase shifting method according to an embodiment of the present disclosure may include: a light source unit 210 emitting a single-wavelength light; a collimator 220 collimating the single-wavelength light emitted from the light source unit 210; a light splitter 230 splitting the single-wavelength light passed through the collimator 220 into an object beam O and a reference beam R; an object beam objective lens 240 transmitting the object beam O generated by the light splitter 230; a reference beam objective lens 260 transmitting the reference beam R generated by the light splitter 230; an optical mirror 270 reflecting the reference beam R passed through the reference beam objective lens 260; a recording medium 280 recording an interference pattern formed when an object beam O passed through the object beam objective lens 240 and then reflected from a surface of a measurement target object 250 and a reference beam R reflected by the optical mirror 270 pass through the object beam objective lens 240 and the reference beam objective lens 260 respectively and then are transmitted to the light splitter 230; and a processor 290 receiving and storing an image file generated by converting the interference pattern from the recording medium 280, wherein the processor 290 may generate first to fourth phase-shifted object holograms from an object hologram acquired from the image file by using a wave optics-based interference equation, generate a complex conjugate hologram by removing DC information, DC noise, and virtual image information by using the generated first to fourth phase-shifted object holograms and a software-implemented phase shifting method, extract phase information of the measurement target object 250 by using the generated complex conjugate hologram, and then reconstruct 3D information of the measurement target object 250.

(14) FIG. 2B is a schematic block diagram of a digital holographic reconstruction device using a single generation phase shifting method, according to another embodiment of the present disclosure.

(15) Referring to FIG. 2B, a digital holographic reconstruction device 200b using a single generation phase shifting method according to another embodiment of the present disclosure may include: a light source unit 210 emitting a single-wavelength light; a collimator 220 collimating the single-wavelength light emitted from the light source unit 210; a light splitter 230 splitting the single-wavelength light passed through the collimator 220 into an object beam O and a reference beam R; an object beam objective lens 240 transmitting an object-transmitted beam T including information of a measurement target object 250 after the object beam O generated by the light splitter 230 passes through the measurement target object 250; a second optical mirror 272 reflecting the object-transmitted beam T passed through the object beam objective lens 240; a reference beam objective lens 260 transmitting the reference beam R generated by the light splitter 230; a first optical mirror 270 reflecting the reference beam R passed through the reference beam objective lens 260; a second light splitter 232 to which the reference beam R reflected by the first optical mirror 270 and the object-transmitted beam T reflected by the second optical mirror 272 are transmitted; a recording medium 280 recording an interference pattern formed by the reference beam R and the object-transmitted beam T both transmitted to the second light splitter 232; and a processor 290 receiving and storing an image file generated by converting the interference pattern from the recording medium 280, wherein the processor may generate first to fourth phase-shifted object holograms from an object hologram acquired from the image file by using a wave optics-based interference equation, generate a complex conjugate hologram by removing DC information, DC noise, and virtual image information by using the generated first to fourth phase-shifted object holograms and a software-implemented phase shifting method, extract phase information of the measurement target object 250 by using the generated complex conjugate hologram, and then reconstruct 3D information of the measurement target object 250.

(16) The digital holographic reconstruction device 200a using a single generation phase shifting method according to an embodiment of the present disclosure illustrated in FIG. 2A and the digital holographic reconstruction device 200b using a single generation phase shifting method according to another embodiment of the present disclosure illustrated in FIG. 2B may have substantially the same configuration except that the object beam O is reflected from the measurement target object 250 (the embodiment of FIG. 2A) or the object beam O is transmitted through the measurement target object 250 (the embodiment of FIG. 2B) and except the additional use of some components (e.g., the second optical mirror 272 and the second light splitter 232 of the embodiment of FIG. 2B) according thereto and the arrangement of some components according thereto, and may have the same feature in that the interference pattern is recorded on the recording medium 280 and a digital reference hologram is calculated from the object hologram acquired in the form of an image file from the recorded interference pattern by the processor 290. Hereinafter, the digital holographic reconstruction devices 200a and 200b using a single generation phase shifting method according to the embodiments of the present disclosure will be collectively referred to as a digital holographic reconstruction device 200 using a single generation phase shifting method according to an embodiment of the present disclosure.

(17) The processor 290 of the digital holographic reconstruction device 200 using a single generation phase shifting method according to an embodiment of the present disclosure may be implemented, for example, as an device capable of arithmetical operations, such as a microprocessor or a personal computer (PC), and the recording medium 280 may be implemented, for example, as an image sensor such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS).

(18) Also, the information of the object hologram acquired by the processor 290 of the digital holographic reconstruction device 200 using a single generation phase shifting method according to an embodiment of the present disclosure may include wavelength, interference angle, phase, and aberration of the object beam objective lens 240 and may further include noise.

(19) FIG. 2C is a schematic flowchart illustrating a digital holographic reconstruction method using a single generation phase shifting method, according to an embodiment of the present disclosure. FIG. 2D is a diagram illustrating an object hologram of steps having different thicknesses of three levels and first to fourth phase-shifted holograms generated in the object hologram, in an off-axis holographic method according to an embodiment of the present disclosure. FIG. 2E is a diagram illustrating an object hologram of steps having different thicknesses of three levels and first to fourth phase-shifted holograms generated in the object hologram, in an on-axis holographic method according to an embodiment of the present disclosure. FIG. 2F is a diagram illustrating a 3D object hologram of steps having different thicknesses of three levels, which is obtained by reconstructing four phase-shifted holograms illustrated in FIG. 2D by using a software-based phase shifting method, in an off-axis holographic method according to an embodiment of the present disclosure. FIG. 2G is a diagram illustrating a 3D object hologram of steps having different thicknesses of three levels, which is obtained by reconstructing four phase-shifted holograms illustrated in FIG. 2E by using a software-based phase shifting method, in an on-axis holographic method according to an embodiment of the present disclosure.

(20) Referring to FIGS. 2C to 2G and FIGS. 2A and 2B, the processor 290 of the digital holographic reconstruction device 200 using a single generation phase shifting method according to an embodiment of the present disclosure may acquire an object hologram 310a or 310b from the image file generated and stored by the processor 290 (operation S1). In the following description, it should be noted that a is used to represent a reference numeral associated with an off-axis hologram and b is used to represent a reference numeral associated with an on-axis hologram.

(21) More particularly, when the angle formed between two beams (i.e., the object beam O and the reference beam R) is zero (that is, when they are on the same axis), the acquired object hologram 310a or 310b is an on-axis hologram 310b, and when the angle formed between the two beams is not zero (that is, when they are not on the same axis), the acquired object hologram 310a or 310b is an off-axis hologram 310a. The acquired object hologram 310a or 310b is a complex conjugate hologram and may be expressed as Equation 1 below.
|U.sub.o(x,y,0)|.sup.2=|O(x,y)|.sup.2=|R(x,y)|.sup.2+O*(x,y)R(x,y)+O(x,y)R*(x,y)Equation 1:

(22) In Equation 1, x and y denote spatial coordinates, U.sub.o(x,y,0) denotes the acquired object hologram, O(x,y) and R(x,y) respectively denote the object beam O and the reference beam R, and O*(x,y) and R*(x,y) respectively denote the complex conjugates of the object beam O and the reference beam R.

(23) Thereafter, the processor 290 may generate a first phase-shifted object hologram 312a or 312b from the acquired object hologram 310a or 310b (operation S2).

(24) More particularly, the acquired object hologram 310a or 310b may include an interference pattern of the object beam O having phase information of the measurement target object 250 and the reference beam R having no phase information of the measurement target object 250, and the processor 290 may separately extract object beam information having phase information of the measurement target object 250 and reference beam information having no phase information of the measurement target object 250 by using a phase delay method in a frequency domain of the acquired object hologram 310a or 310b. Thereafter, the extracted reference beam information may be phase-shifted by 0, and then the first phase-shifted object hologram 312a or 312b may be generated by combining the 0 phase-shifted reference beam information with the extracted object beam information by using a known wave optics-based interference equation (U.sub.H(r)=|O(r)+R(r)|). The generated first phase-shifted object hologram 312a or 312b may be expressed as Equation 2 below.
U.sub.1ps(r)=|O(r)+R(r+0)|Equation 2:

(25) In Equation 2, r denotes a spatial coordinate vector, U.sub.1ps(r) denotes the first phase-shifted object hologram, O(r) denotes the object beam information, and R(r+0) denotes the 0 phase-shifted reference beam information.

(26) Thereafter, the processor 290 may phase-shift the extracted reference beam information (in operation S2) by 90 and then generate a second phase-shifted object hologram 314a or 314b by combining the 90 phase-shifted reference beam information with the extracted object beam information by using the above wave optics-based interference equation (operation S3). The generated second phase-shifted object hologram 314a or 314b may be expressed as Equation 3 below.
U.sub.2ps(r)=|O(r)+R(r+/2)|Equation 3:

(27) In Equation 3, r denotes a spatial coordinate vector, U.sub.2ps(r) denotes the second phase-shifted object hologram, O(r) denotes the object beam information, and R(r+/2) denotes the 90 phase-shifted reference beam information.

(28) Thereafter, the processor 290 may phase-shift the extracted reference beam information (in operation S2) by 180 and then generate a third phase-shifted object hologram 316a or 316b by combining the 180 phase-shifted reference beam information with the extracted object beam information by using the above wave optics-based interference equation (operation S4). The generated third phase-shifted object hologram 316a or 316b may be expressed as Equation 4 below.
U.sub.3ps(r)=|O(r)+R(r+)|Equation 4:

(29) In Equation 4, r denotes a spatial coordinate vector, U.sub.3ps(r) denotes the third phase-shifted object hologram, O(r) denotes the object beam information, and R(r+) denotes the 180 phase-shifted reference beam information.

(30) Thereafter, the processor 290 may phase-shift the extracted reference beam information (in operation S2) by 270 and then generate a fourth phase-shifted object hologram 318a or 318b by combining the 270 phase-shifted reference beam information with the extracted object beam information by using the above wave optics-based interference equation (operation S5). The generated fourth phase-shifted object hologram 318a or 318b may be expressed as Equation 5 below.
U.sub.4ps(r)=|O(r)+R(r+3/2)|Equation 5:

(31) In Equation 5, r denotes a spatial coordinate vector, U.sub.4ps(r) denotes the fourth phase-shifted object hologram, O(r) denotes the object beam information, and R(r+3/2) denotes the 270 phase-shifted reference beam information.

(32) In the above embodiment of the present disclosure, the processor 290 sequentially performs the operations S3, S4, and S5; however, it should be noted that the operations S3, S4, and S5 may be simultaneously performed by a parallel processing method to generate the second to fourth phase-shifted object holograms 314a or 314b; 316a or 316b; and 318a or 318b by phase-shifting the extracted reference beam information (in operation S2) by 90, 180, and 270, respectively.

(33) Thereafter, the processor 290 may remove DC information, DC noise (including background noise), and virtual image information by using four phase-shifted object holograms (i.e., the first to fourth phase-shifted object holograms 312a or 312b; 314a or 314b; 316a or 316b; and 318a or 318b) respectively generated in the operations S2 to S5 and a known phase shifting method implemented by software installed in the processor 290 (operation S6). This process may be expressed as Equation 6 below.

(34) $\begin{array}{cc}\frac{I_4\left(x,y\right)-I_2\left(x,y\right)}{I_1\left(x,y\right)-I_3\left(x,y\right)}=\frac{\begin{array}{c}\left[I_{\mathrm{DC}}\left(x,y\right)+2\sqrt{I_{\mathrm{DC}}\left(x,y\right)}\sin \left\{\left(x,y\right)\right\}\right]-\\ \left[I_{\mathrm{DC}}\left(x,y\right)-2\sqrt{I_{\mathrm{DC}}\left(x,y\right)}\sin \left\{\left(x,y\right)\right\}\right]\end{array}}{\begin{array}{c}\left[I_{\mathrm{DC}}\left(x,y\right)+2\sqrt{I_{\mathrm{DC}}\left(x,y\right)}\cos \left\{\left(x,y\right)\right\}\right]-\\ \left[I_{\mathrm{DC}}\left(x,y\right)-2\sqrt{I_{\mathrm{DC}}\left(x,y\right)}\cos \left\{\left(x,y\right)\right\}\right]\end{array}}& \mathrm{Equation}6\end{array}$

(35) In Equation 6, x and y denote spatial coordinates, I.sub.DC(x,y) denotes DC information and DC noise, (x,y) denotes phase information of the measurement target object 250, I.sub.1(x,y) denotes intensity information of the first phase-shifted object hologram 312a or 312b, I.sub.2(x,y) denotes intensity information of the second phase-shifted object hologram 314a or 314b, I.sub.3(x,y) denotes intensity information of the third phase-shifted object hologram 316a or 316b, and I.sub.4(x,y) denotes intensity information of the fourth phase-shifted object hologram 318a or 318b.

(36) Thereafter, the phase information of the measurement target object 250 may be extracted by using the complex conjugate hologram generated by removing the DC information, the DC noise, and the virtual image information. The extracted phase information of the measurement target object 250 may be expressed as Equation 7 below.
(x,y)=tan.sup.1[I.sub.4(x,y)I.sub.2(x,y)]/[I.sub.1(x,y)I.sub.3(x,y)]Equation 7:

(37) In Equation 7, x and y denote spatial coordinates, (x,y) denotes phase information of the measurement target object 250, I.sub.1(x,y) denotes intensity information of the first phase-shifted object hologram 312a or 312b, I.sub.2(x,y) denotes intensity information of the second phase-shifted object hologram 314a or 314b, I.sub.3(x,y) denotes intensity information of the third phase-shifted object hologram 316a or 316b, and I.sub.4(x,y) denotes intensity information of the fourth phase-shifted object hologram 318a or 318b.

(38) Thereafter, the processor 290 may compensate the extracted phase information of the measurement target object 250 for distorted phase information by using a two-dimensional (2D) phase unwrapping algorithm and calculate quantitative thickness information of the measurement target object 250 by using the compensated phase information. The quantitative thickness information of the measurement target object 250 calculated by the processor 290 may be expressed as Equation 8 below.
L=(x,y)/2n(x,y)Equation 8:

(39) In Equation 8, L denotes quantitative thickness information of the measurement target object 250, denotes a wavelength of the light source unit 210 used to acquire the object hologram, (x,y) denotes phase information of the measurement target object 250, and n(x,y) denotes a refractive index difference between a background and the measurement target object 250.

(40) Thereafter, the processor 290 may reconstruct the 3D shape of the measurement target object 250 by using the quantitative thickness information of the measurement target object 250 calculated according to Equation 8 (operation S7: see 320a and 320b in FIGS. 2F and 2G). The 3D shape reconstructed by the processor 290 may be displayed on a separate monitor (not illustrated) such as a display of a PC.

(41) FIG. 2H is a diagram illustrating a comparison between a 3D object hologram reconstructed by using an off-axis optical holographic method of the related art and a 3D object hologram (see FIG. 2F) reconstructed by using an off-axis holographic method according to an embodiment of the present disclosure, with respect to steps having different thicknesses of three levels.

(42) Referring to FIG. 2H, it may be seen that a 3D object hologram 320a reconstructed according to an embodiment of the present disclosure is much clearer than that reconstructed according to the related art.

(43) FIG. 2I is a diagram illustrating a comparison table between the characteristics of off-axis reconstruction and on-axis reconstruction of holograms according to the related art and the present disclosure.

(44) Referring to FIG. 2I, it may be seen that the off-axis reconstruction of the hologram according to the present disclosure is significantly improved in comparison with the related art in terms of the information loss degree, the noise removal degree, the time delay error, and the number of required holograms, and it may be seen that the on-axis reconstruction of the hologram according to the present disclosure is significantly improved in comparison with the related art in terms of the information loss degree, the device manufacturing cost, the time delay error, and the number of required holograms.

(45) Hereinafter, a digital holographic reconstruction method using a single generation phase shifting method according to an embodiment of the present disclosure will be described.

(46) Referring to FIGS. 2A to 2I, a digital holographic reconstruction method using a single generation phase shifting method according to an embodiment of the present disclosure may include: an operation a) of acquiring an object hologram 310a or 310b of a measurement target object 250 (S1); an operation b) of generating a first phase-shifted object hologram 312a or 312b from the acquired object hologram 310a or 310b by separately extracting object beam information having phase information of the measurement target object 250 and reference beam information having no phase information of the measurement target object 250 (S2); an operation c) of generating a second phase-shifted object hologram 314a or 314b by phase-shifting the extracted reference beam information by 90 (S3); an operation d) of generating a third phase-shifted object hologram 316a or 316b by phase-shifting the extracted reference beam information by 180 (S4); an operation e) of generating a fourth phase-shifted object hologram 318a or 318b by phase-shifting the extracted reference beam information by 270 (S5); an operation f) of extracting the phase information of the measurement target object 250 by removing DC information, DC noise, and virtual image information by using the generated first to fourth phase-shifted object holograms 312a or 312b; 314a or 314b; 316a or 316b; and 318a or 318b and a phase shifting method (S6); and an operation g) of compensating the extracted phase information for distorted phase information and reconstructing quantitative thickness information and 3D shape information of the measurement target object 250 by calculating quantitative thickness information of the measurement target object 250 by using the compensated phase information (S7).

(47) In the digital holographic reconstruction method using a single generation phase shifting method according to an embodiment of the present disclosure, the operations c) to e) may be simultaneously performed.

(48) Also, in the digital holographic reconstruction method using a single generation phase shifting method according to an embodiment of the present disclosure, in the operation c), the object beam information and the reference beam information may be separated and extracted by using a phase delay method in a frequency domain of the acquired object hologram 310a or 310b.

(49) Also, in the digital holographic reconstruction method using a single generation phase shifting method according to an embodiment of the present disclosure, the first to fourth phase-shifted object holograms 312a or 312b; 314a or 314b; 316a or 316b; and 318a or 318b may be respectively generated by combining the 0, 90, 180, and 270 phase-shifted reference beam information with the extracted object beam information by using a wave optics-based interference equation (U.sub.H(r)=|O(r)+R(r)|).

(50) Also, in the digital holographic reconstruction method using a single generation phase shifting method according to an embodiment of the present disclosure, the phase information of the measurement target object may be represented by an equation of (x,y)=tan.sup.1[I.sub.4(x,y)I.sub.2(x,y)]/[I.sub.1(x,y)I.sub.3(x,y)] as in Equation 7, where x and y denote spatial coordinates, (x,y) denotes phase information of the measurement target object, and I.sub.1(x,y) denotes intensity information of the first phase-shifted object hologram 312a or 312b, I.sub.2(x,y) denotes intensity information of the second phase-shifted object hologram 314a or 314b, I.sub.3(x,y) denotes intensity information of the third phase-shifted object hologram 316a or 316b, and I.sub.4(x,y) denotes intensity information of the fourth phase-shifted object hologram 318a or 318b.

(51) Also, in the digital holographic reconstruction method using a single generation phase shifting method according to an embodiment of the present disclosure, the extracted phase information of the measurement target object 250 may be compensated for the distorted phase information by using a 2D phase unwrapping algorithm.

(52) Also, in the digital holographic reconstruction method using a single generation phase shifting method according to an embodiment of the present disclosure, the quantitative thickness information of the measurement target object 250 may be represented by an equation of L=(x,y)/2n(x,y) as in Equation 8, where L denotes quantitative thickness information of the measurement target object 250, denotes a wavelength of the light source unit 210 used to acquire the object hologram, (x,y) denotes phase information of the measurement target object 250, and n(x,y) denotes a refractive index difference between a background and the measurement target object 250.

(53) As described above, according to the digital holographic reconstruction device (200) and method using a single generation phase shifting method according to the present disclosure, 1) a time delay error occurring in the case of acquiring two holograms (object hologram and reference hologram) necessary for reconstruction in the related art or in the case of acquiring four physical holograms having different phase shift degrees may be removed, 2) DC noise (including background noise) may be completely removed by using a software-implemented phase shifting method, 3) information loss caused by non-use of a filtering method according to the related art may be minimized, 4) optical elements (-wave plate and/or -wave plate) required in the related art may be unnecessary and thus the digital holographic reconstruction device may be simple in overall structure and may be implemented at low cost, 5) the digital holographic reconstruction device may be universally applied to both the reflection-type and transmission-type hologram reconstruction devices of the related art, and 6) the digital holographic reconstruction device may be applied to devices for detection of defects in ultrafine structures such as TFTs and semiconductors, medical devices requiring display of accurate 3D images, and devices for detection, identification, or display in various fields, including detection of refractive index errors in transparent objects such as lenses.

INDUSTRIAL APPLICABILITY

(54) It is to be understood that all included in the detailed descriptions or illustrated in the accompanying drawings are merely illustrative and are not intended to limit the present disclosure since various changes or modifications may be made therein without departing from the scope of the present disclosure. Thus, the scope of the present disclosure should not be limited to the above example embodiments but should be determined only by the following claims and their equivalents.