Phase calculation method and phase calculation apparatus

Abstract

The objective is to obtain a phase calculation method and a phase calculation apparatus that can fix the position of the detector. [Solution] The phase calculation method according to the present disclosure involves irradiating an optical component with multiple light beams of different wavelengths through a measurement target, fixing the position of the detector, and using the detector to obtain the intensity of the multiple light beams that propagate through the optical component along different paths, and calculating the phase from the intensity of the multiple light beams.

Description

Technical Field

[0001] The present disclosure relates to a phase calculation method and a phase calculation device.

Background Art

[0002] Patent Document 1 discloses a method for calculating the phase of propagating light. In this method, the intensity of the propagating light is acquired in multiple types by changing the propagation distance, and an intensity transport equation is calculated from the information of the multiple types of intensities and the propagation distance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the method of Patent Document 1, in order to acquire the intensity of the propagating light in multiple types by changing the propagation distance, it is necessary to shift the detector in the direction of light propagation. Therefore, there is a possibility that high-precision alignment in the optical axis direction is required. In addition, the imaging speed may be limited by the operation of the device.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to obtain a moving phase calculation method and a phase calculation device capable of fixing the position of the detector.

Means for Solving the Problems

[0006] The phase calculation method according to the present disclosure irradiates a plurality of lights having different wavelengths onto an optical component through a measurement object, and in a state where the position of the detector is fixed, the detector acquires the intensities of the plurality of lights that propagate through different paths by passing through the optical component, and calculates a phase from the intensities of the plurality of lights.

[0007] The phase calculation device according to this disclosure comprises an optical component configured to receive a plurality of light beams of different wavelengths that have passed through a target to be measured; a detector configured to detect the intensity of the plurality of light beams that propagate along different paths by passing through the optical component; and a calculation circuit configured to calculate a phase from the intensities of the plurality of light beams. [Effects of the Invention]

[0008] The phase calculation method and phase calculation apparatus described herein calculate the phase from the intensities of multiple light beams that propagate through different paths by passing through an optical component. Therefore, the position of the detector can be fixed. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram illustrates a method for calculating the phase using the intensity transport equation. [Figure 2] This figure shows examples of light intensity distribution and phase distribution. [Figure 3] This diagram illustrates the configuration of the phase calculation device according to Embodiment 1. [Figure 4] This is a diagram illustrating the propagation of multiple light sources according to Embodiment 1. [Figure 5] This is a flowchart showing the phase calculation method according to Embodiment 1. [Figure 6] This is a hardware configuration diagram of the arithmetic circuit according to Embodiment 1. [Figure 7] This diagram illustrates the configuration of the phase calculation device according to Embodiment 2. [Figure 8] This is a diagram illustrating the propagation of multiple light sources according to Embodiment 2. [Figure 9] This is a flowchart showing the phase calculation method according to Embodiment 2. [Figure 10] This diagram illustrates the configuration of the phase calculation device according to Embodiment 3. [Figure 11] This is a diagram illustrating the propagation of multiple light sources according to Embodiment 3. [Figure 12]Perspective view of the color filter according to Embodiment 3. [Figure 13] It is a diagram for explaining the configuration of the phase calculation device according to Embodiment 4. [Figure 14] It is a diagram showing the +1st order diffracted light component and the -1st order diffracted light component detected by the detector according to Embodiment 4.

Mode for Carrying Out the Invention

[0010] The phase calculation method and the phase calculation device according to each embodiment will be described with reference to the drawings. The same or corresponding components may be denoted by the same reference numerals, and repeated descriptions may be omitted.

[0011] Embodiment 1. First, the Transport of Intensity Equation (TIE) will be described. TIE is represented by the following equation (1).

[0012]

Equation

[0013] φ

[0015] (x, y) is the phase distribution, and ∇ ⊥ is the two-dimensional gradient operator. k is the wave number, and I0 is the intensity of the in-focus image. I z (x, y) is the intensity distribution. That is, the partial derivative on the right side of Equation (1) indicates the intensity change in the optical axis direction. Equation (2) shows the phase solution of TIE.

[0014]

Equation

[0015] <着 FT[···] is the Fourier transform operator, and IFT[···] is the inverse Fourier transform operator. μ and ν are the spatial frequencies in the x and y directions, respectively. Equation (3) is derived from the difference approximation of Equation (2).

[0016]

number

[0017] Δz is the defocus distance. In the following, the position where the intensity in the optical axis direction is obtained may be referred to as the defocus distance.

[0018] Figure 1 is a diagram illustrating the phase calculation method using the intensity transport equation. Figure 2 is a diagram showing an example of the light intensity distribution and phase distribution. Figure 2 shows an example of the light intensity distribution and phase distribution at the position z=0. According to equations (2) and (3), the intensity I of light propagated ±Δz from z=0 is Δz ,I -Δz By obtaining and performing difference approximation, the phase φ z This allows us to calculate the phase distribution. If there are at least two intensity distributions with different defocus distances, the phase distribution can be calculated. Furthermore, the more intensity distributions with different defocus distances there are, the better the accuracy of the phase calculation. This is called higher-order TIE.

[0019] Figure 3 is a diagram illustrating the configuration of the phase calculation device 100 according to Embodiment 1. The light source 10 is a tunable light source. The light source 10 emits multiple light beams of different wavelengths in sequence. The light source 10 is, for example, a TLD (Tunable Laser Diode). The light emitted from the light source 10 becomes parallel light through a spatial filter 11 and a lens 12. The spatial filter 11 and lens 12 together are called a collimator. The light that passes through the lens 12 passes through the object 50 that is to be measured. The light that passes through the object 50 further passes through optical components, which are lenses 14 and 16, and its intensity is acquired by the detector 20. The detector 20 is, for example, a monochrome camera. The calculation circuit 30 is configured to calculate the phase from the intensities of the multiple light beams acquired by the detector 20.

[0020] Figure 4 is a diagram illustrating the propagation of multiple light sources according to Embodiment 1. Figure 4 shows examples of paths for multiple light sources of different wavelengths propagating from the object surface 51 of object 50. The solid line shows an example of the path for blue light, the dashed line shows an example of the path for green light, and the dashed line shows an example of the path for red light. Also, f1 and f2 indicate the focal lengths of lenses 14 and 16, respectively. Note that the collimator is omitted in Figure 4. Also, for convenience, Figure 4 shows how the image is formed when object 50 is a simple point light source. Lenses 14 and 16 transmit and refract light. Here, the refractive indices of lenses 14 and 16 differ depending on the wavelength of light. For this reason, as shown in Figure 4, when multiple light sources of different wavelengths pass through lenses 14 and 16, they disperse and chromatic aberration occurs. In Figure 4, an example of chromatic aberration is shown as Δf.

[0021] In this embodiment, this chromatic aberration is used to capture multiple images with different defocus distances while keeping the position of the detector 20 fixed. In other words, the intensities of multiple dispersed light sources with different optical paths are measured with the detector 20 fixed. This allows for imaging equivalent to imaging at two or more locations on the z-axis. From the above, the phase can be calculated using equations (2) and (3).

[0022] In the phase calculation device 100 of this embodiment, lenses 14 and 16 are configured to receive multiple light beams of different wavelengths that have passed through the object 50. The detector 20 is configured to detect the intensity of multiple light beams that propagate along different paths after passing through lenses 14 and 16. The position of the detector 20 is fixed when detecting the intensity of multiple light beams.

[0023] Figure 5 is a flowchart showing the phase calculation method according to Embodiment 1. First, light of a first wavelength from among multiple lights of different wavelengths is shone onto the lenses 14 and 16 via object 50 (Step 1). Next, with the position of the detector 20 fixed, the intensity of the light of the first wavelength is obtained by the detector 20 (Step 2). Steps 1 and 2 are repeated for light of all wavelengths (Step 3).

[0024] In other words, after the measurement at the first wavelength is completed, light of the second wavelength from among the multiple lights is shone onto the lenses 14 and 16 via object 50 (Step 1). At this time, the light of the first wavelength and the light of the second wavelength propagate through lenses 14 and 16, following different paths. Next, without moving the position of the detector 20 from the previous measurement, the intensity of the light of the second wavelength is obtained by the detector 20 (Step 2).

[0025] In this way, multiple light sources are sequentially shone onto lenses 14 and 16 to obtain the intensities of multiple light sources with different focusing positions. Next, the phase is calculated from the intensities of the multiple light sources (step 4).

[0026] From the above, the phase calculation method and phase calculation device 100 according to this embodiment calculate the phase from the intensities of multiple light rays that propagate through optical components along different paths. Therefore, the position of the detector 20 can be fixed. In other words, it is unnecessary to mechanically move the position of the detector 20. As a result, the accuracy of alignment in the optical axis direction can be relaxed. In addition, manual errors in the defocus distance can be eliminated. Furthermore, it is possible to suppress the imaging speed from being limited by the operation of the equipment.

[0027] The phase distribution obtained by the above method allows for the calculation of, for example, the refractive index or thickness of the object 50 being measured. Furthermore, it enables the visualization of the colorless, transparent object 50. This information is used as important parameters during measurement and inspection, and is expected to have applications primarily in the following two fields.

[0028] The first application is the inspection of optical components such as lenses and prisms. Generally, inspecting optical components for defects requires the use of special components such as light sources outside the visible light range, such as X-rays, and detectors with corresponding wavelength sensitivity bands. This can lead to high costs for inspection equipment. In contrast, this embodiment enables inspection in the visible light range. Therefore, general-purpose components for the visible light range can be used, resulting in lower costs for inspection equipment. This embodiment may also be applied to the manufacturing methods of microscopes and other devices.

[0029] The second is the quantitative observation of colorless, transparent living cells. Methods using high-energy X-rays can damage and kill living cells. Therefore, cells are generally stained before observation in the visible light region. However, this method is limited to qualitative observation and cannot quantitatively evaluate the characteristics of living cells. Furthermore, in the field of regenerative medicine, such as with iPS cells, cells are transplanted into the human body after observation. For this reason, cell staining is undesirable. To address these problems, this embodiment allows for the calculation of quantitative values ​​in the low-energy visible light region. Moreover, it enables observation of living cells without staining.

[0030] Figure 6 is a hardware configuration diagram of the arithmetic circuit 30 according to Embodiment 1. The functions of the arithmetic circuit 30 are realized by one or more control circuits, such as a processor 31. The control circuits may be dedicated hardware. Alternatively, the control circuits may be a CPU (Central Processing Unit) that executes a program stored in memory 32. The CPU may be a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor).

[0031] If the control circuit is dedicated hardware, it may be, for example, a single circuit, a composite circuit, a programmed processor, or a parallel programmed processor. Alternatively, the control circuit may be an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). Furthermore, the control circuit may be a combination of these. Also, each function of the arithmetic circuit 30 may be implemented by a separate control circuit. Alternatively, the functions of each part may be implemented together by a single control circuit.

[0032] When the control device is a CPU, the functions of the arithmetic circuit 30 are realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in one or more memories 32. The control circuit realizes the functions of each part by reading and executing the programs stored in the memory 32.

[0033] In other words, memory 32 stores a program that calculates the phase from the intensities of multiple lights. These programs cause the computer to execute the procedures or methods in the arithmetic circuit 30.

[0034] Here, memory 32 may be non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, EEPROM, magnetic disk, flexible disk, optical disk, compact disk, minidisc, DVD, etc. RAM is an abbreviation for Random Access Memory. ROM is an abbreviation for Read Only Memory. EPROM is an abbreviation for Erasable Programmable Read Only Memory. EEPROM is an abbreviation for Electrically Erasable Programmable Read-Only Memory.

[0035] Furthermore, some of the functions of the arithmetic circuit 30 may be implemented using dedicated hardware, while others may be implemented using software or firmware. In this way, the control circuit can implement the above-mentioned functions using hardware, software, firmware, or a combination thereof.

[0036] The arrangement and types of each element in the phase calculation device 100 can be changed in any way, as long as the intensity of multiple light sources propagating through different paths by passing through optical components can be obtained while the position of the detector 20 is fixed.

[0037] The modifications described above can be appropriately applied to the phase calculation method and phase calculation apparatus according to the following embodiments. Since the phase calculation method and phase calculation apparatus according to the following embodiments have many similarities with Embodiment 1, the differences from Embodiment 1 will be the focus of this explanation.

[0038] Embodiment 2. Figure 7 is a diagram illustrating the configuration of the phase calculation device 200 according to Embodiment 2. In the phase calculation device 200, a prism 214 is provided as an optical component instead of lenses 14 and 16. The light source 210 is a multi-wavelength light source. The light source 210 simultaneously irradiates the prism 214 with multiple lights of different wavelengths. The light source 210 is, for example, an M / W (Multi Wavelength) LD. The other configurations are the same as those of Embodiment 1.

[0039] Figure 8 is a diagram illustrating the propagation of multiple light sources according to Embodiment 2. Note that the collimator is omitted in Figure 8. Also, for convenience, Figure 8 shows how the image is formed when object 50 is a simple point light source. In this embodiment, multiple light sources of different wavelengths are dispersed by a dispersive element such as a prism 214. In Figure 8, the solid line shows an example of the path of blue light, and the dashed line shows an example of the path of red light.

[0040] In this embodiment, dispersion by the prism 214 is used to capture multiple images with different defocus distances in a single shot while keeping the position of the detector 20 fixed. In other words, the intensities of multiple dispersed light beams with different optical paths are acquired simultaneously while keeping the position of the detector 20 fixed. This enables imaging equivalent to imaging at two or more locations on the z-axis. Therefore, the phase can be calculated using equations (2) and (3).

[0041] Figure 9 is a flowchart showing the phase calculation method according to Embodiment 2. First, multiple light beams of different wavelengths are simultaneously shone onto the prism 214 via the object 50 to be measured (step 21). This disperses the multiple light beams. Next, with the position of the detector 20 fixed, the detector 20 measures the intensity of the multiple light beams that have dispersed and propagated along different paths (step 22). Next, the phase is calculated from the intensities of the multiple light beams (step 23).

[0042] In this embodiment as well, the position of the detector 20 can be fixed. Furthermore, in this embodiment, multiple light intensities can be acquired in a single exposure, i.e., in one image capture. In this case, dynamic changes in phase can be captured. In other words, since the object 50 can be continuously photographed with a single exposure, dynamic changes in phase can be reproduced.

[0043] Furthermore, this embodiment also allows for the application of high-order TIE in a single exposure. That is, it is possible to acquire three or more images with different defocus distances at once. However, in this embodiment, when dispersing light, the dispersion distance and dispersion number are limited by the size of the detector surface. For this reason, it is presumed that the limit is acquiring the intensity of light at 3 or 4 wavelengths in a single imaging.

[0044] Embodiment 3. Figure 10 is a diagram illustrating the configuration of the phase calculation device 300 according to Embodiment 3. The light source 210 is a multi-wavelength light source. The light source 210 simultaneously irradiates the lenses 14 and 16 with multiple lights of different wavelengths. The detector 320 is a color camera. The other configurations are the same as those of Embodiment 1.

[0045] Figure 11 is a diagram illustrating the propagation of multiple light sources according to Embodiment 3. Note that the collimator is omitted in Figure 11. Also, for convenience, Figure 11 shows how the image is formed when object 50 is a simple point light source. In this embodiment as in Embodiment 1, multiple light sources of different wavelengths disperse when they pass through lenses 14 and 16, resulting in chromatic aberration.

[0046] In this embodiment, similar to Embodiment 1, the intensities of multiple light sources with different optical paths due to chromatic aberration are measured with the detector 320 fixed. This allows for imaging equivalent to imaging at two or more locations on the z-axis. Therefore, the phase can be calculated using equations (2) and (3).

[0047] Furthermore, in this embodiment, the detector 320, which is a color camera, can acquire the intensity of multiple lights at different collection positions in a single image. Figure 12 is a perspective view of the color filter 322 according to Embodiment 3. The color filter 322 is provided on the imaging surface of the detector 320. The color filter 322 has a Bayer array. In the color filter 322, for example, one filter of red, green, or blue is placed in front of each sensor of the color camera. This allows the intensity for each wavelength to be acquired in a single shot. Pixels with unsupported wavelengths are interpolated.

[0048] The flow of the phase calculation method in this embodiment is the same as the flow in Embodiment 2. First, multiple lights of different wavelengths are simultaneously irradiated onto the lenses 14 and 16 through the object 50 to be measured (step 21). Next, with the position of the detector 320 fixed, the detector 320 measures the intensity of multiple lights that propagate along different paths due to chromatic aberration (step 22). Next, the phase is calculated from the intensities of the multiple lights (step 23).

[0049] In this embodiment as well, the position of the detector 320 can be fixed. Furthermore, in this embodiment as well, since the intensity of multiple lights can be acquired in a single imaging, dynamic changes in phase can be captured.

[0050] Furthermore, in this embodiment, high-order TIE can also be applied in a single exposure. However, in this embodiment, the number of intensities that can be acquired in a single image is limited by the number of pixel divisions of the color camera. Generally, the number of pixel divisions is around 3 or 4. Therefore, it is presumed that the limit is acquiring the intensities of 3 or 4 wavelengths of light in a single image.

[0051] Embodiment 4. Figure 13 is a diagram illustrating the configuration of the phase calculation device 400 according to Embodiment 4. In the phase calculation device 400, a diffraction grating 418 is provided between the lens 14 and the detector 320. Specifically, the diffraction grating 418 is provided between the lens 14 and the lens 16. The detector 320 acquires the intensity of multiple beams of light that have passed through the diffraction grating 418. The other configurations are the same as those of Embodiment 1.

[0052] Figure 14 shows the first-order diffracted light component and the -1st-order diffracted light component detected by the detector 320 according to Embodiment 4. In this embodiment, the diffraction grating 418 generates a first-order diffracted light component and a -1st-order diffracted light component on the detector surface. These correspond to intensity distributions with positive and negative defocus distances, respectively. In other words, the diffraction grating 418 allows for the acquisition of two images with different defocus distances. Furthermore, in this embodiment, as in Embodiment 3, multiple lights of different wavelengths disperse when transmitted through lenses 14 and 16, resulting in chromatic aberration. That is, the intensity distribution obtained is equal to the number obtained by multiplying the two images from the diffraction grating 418 by the dispersion number due to chromatic aberration in Embodiment 3. Pixels with out-of-corresponding polarization and wavelengths are interpolated.

[0053] Based on the above, in this embodiment, in addition to the effects of Embodiment 3, higher-order TIE can be applied in a single exposure. In this embodiment, it is possible to obtain more than twice the number of light intensities compared to Embodiment 3 in a single image. Higher-order TIE can improve the accuracy of the difference approximation of TIE. It also enables fitting of intensity changes. This makes it possible to calculate a more accurate phase distribution. Furthermore, it is possible to improve noise immunity in phase calculation.

[0054] The technical features described in each embodiment may be used in combination as appropriate. [Explanation of Symbols]

[0055] 10 Light source, 11 Spatial filter, 12, 14, 16 Lens, 20 Detector, 30 Arithmetic circuit, 31 Processor, 32 Memory, 50 Object, 51 Object plane, 100 Phase calculation device, 200 Phase calculation device, 210 Light source, 214 Prism, 300 Phase calculation device, 320 Detector, 322 Color filter, 400 Phase calculation device, 418 Diffraction grating

Claims

1. Multiple light sources of different wavelengths are shone onto the optical component through the object to be measured. With the position of the detector fixed, the detector acquires the intensity of the multiple light beams that propagate through the optical component along different paths. A phase calculation method characterized by calculating the phase from the intensities of the plurality of lights.

2. The phase calculation method according to claim 1, characterized in that the plurality of lights are sequentially irradiated onto the lens, which is an optical component, to obtain the intensity of the plurality of lights at different focusing positions.

3. The plurality of lights are simultaneously shone onto the prism, which is an optical component, to disperse the plurality of lights. The phase calculation method according to claim 1, characterized in that the intensity of the dispersed plurality of lights is obtained by the detector.

4. The plurality of lights are simultaneously shone onto the lens, which is an optical component. The phase calculation method according to claim 1, characterized in that the intensity of the plurality of lights with different collection positions is acquired by the detector, which is a color camera.

5. A diffraction grating is provided between the lens and the color camera. The phase calculation method according to claim 4, characterized in that the intensity of the plurality of light beams transmitted through the diffraction grating is obtained using the color camera.

6. The phase calculation method according to any one of claims 3 to 5, characterized in that the detector acquires the intensity of the plurality of lights in a single imaging.

7. An optical component configured to receive multiple light beams of different wavelengths that have passed through the object to be measured, A detector configured to detect the intensity of multiple lights that propagate through different paths by passing through the aforementioned optical component, A calculation circuit configured to calculate the phase from the intensity of the plurality of lights, A phase calculation device characterized by comprising the following:

Images