All-fiber three-dimensional tomography system

Abstract

The application discloses a full-optical fiber three-dimensional tomography system, which comprises a sweep-frequency laser, a first optical coupler, a first optical circulator, a first optical collimator, a first convex lens, an electrically-controlled attenuator, a second optical circulator, a second optical collimator, a second convex lens, a second optical coupler and a balance detector. The sweep-frequency laser of the full-optical fiber three-dimensional tomography system can utilize the technology of acquiring optical signals to obtain images and adopt a full-optical fiber circuit architecture, so that linear or plane scanning can be rapidly performed on optical scattering media such as biological tissues, and high-resolution three-dimensional images can be obtained.

Description

Technical Field

[0001] This invention relates to an optical inspection system, and more particularly to an all-fiber three-dimensional tomography system, which can acquire images by capturing optical signals and adopts an all-fiber circuit architecture, and can quickly perform line or surface scanning on optical scattering media such as biological tissues to obtain high-resolution three-dimensional images. Background Technology

[0002] In many current industries, examining the surfaces of minute structures or obtaining three-dimensional information is crucial. In the field of optical interferometry, interference occurs when the path lengths of the reference beam and the scanning beam are aligned. More specifically, the condition for interference is the coherence length of the light source. Optical interference will occur when the path length difference is less than the coherence length of the light source. Non-transparent specimens can be examined using a Michelson interferometer or a Mirau interferometer. Transparent samples can also be measured using interferometry.

[0003] The Michelson interferometer is one of the most commonly used configurations in optical interferometers. By using a beamsplitter, the light source is split into two paths. Both beams are reflected back to the beamsplitter, which then combines them to produce interference. The resulting interference pattern, not guided back to the light source, is typically directed to some type of photodetector or camera. Depending on the application of the interferometer, the two optical paths can have different lengths, or they can contain optical elements or even the material being measured. The light source provides an initial beam to the beamsplitter, which splits the initial light into two beams. One of the two beams is directed onto the sample, and the other beam is directed into a mirror to form a reference path. After the two beams are reflected back to the beamsplitter, they are combined and directed to the detector, thus generating an interference pattern on the detector.

[0004] The Mira interferometer is another commonly used optical interferometer configuration. The Mira interferometer operates on the same principle as the Michelson interferometer. The difference lies in the actual position of the reference arm. In the Mira interferometer, the reference arm is located within the microscope objective assembly. The light source generates an initial beam towards lens L, which refracts the beam to a beam splitter to produce two beams. One beam is incident on the sample, and the other beam is reflected back to a semi-reflective mirror on lens L. Another optical system can be applied to combine the two beams to generate an interference pattern. For example, if the sample can be transparent, another optical system is configured below the sample. If the sample is opaque, an optical system with a mirror should be configured above the sample to collect the two beams.

[0005] Although both Michelson and Milau interferometers are widely used, they both rely on a single beam to probe the sample, and the use of a reference beam introduces interference. Therefore, in both cases, at most half of the light from the source reaches the sample surface. This significantly limits the ability to detect fine features on the sample surface. Furthermore, the reference path is crucial to the system, which contributes to the complexity of the Michelson interferometer. While interference results can be obtained using a Milau interferometer, in non-transparent samples, the use of backscattered light for interference further reduces the intensity of light illuminating the sample and easily leads to the loss of information about sample depth and thickness.

[0006] Therefore, how to solve the problems and deficiencies of the existing technologies is the research topic that relevant industry players are eager to develop. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide an all-fiber three-dimensional tomography system.

[0008] This invention provides an all-fiber 3D tomography system, particularly for high-speed 3D tomographic scanning of an object. The all-fiber 3D tomography system includes a swept-frequency laser, a first optical coupler, a first optical scanning module, a second optical scanning module, a second optical coupler, and a balanced detector. The swept-frequency laser emits laser light of different wavelengths. The first optical coupler is connected to the swept-frequency laser via optical fiber. The first optical coupler receives the initial incident light emitted by the swept-frequency laser and splits it into a first incident light and a second incident light, wherein the number of first incident light rays is 40 to 60 times that of the second incident light rays. The first optical scanning module is connected to the first optical coupler via optical fiber to receive the first incident light, which is directed towards the object to generate a first reflected light. The second optical scanning module is connected to the first optical coupler via optical fiber to receive the second incident light, which is directed towards a plane mirror to generate a second reflected light. The second optical coupler is connected to the first and second optical scanning modules via optical fiber to combine the first and second reflected rays, respectively. The two output ports of the second optical coupler output the same number of first and second target rays, which interfere with each other optically. The balanced detector is connected to the two output ports of the second optical coupler via optical fiber to receive the first and second target rays and outputs an optical measurement signal after signal processing.

[0009] In one embodiment of the present invention, the first optical scanning module includes a first optical circulator, a first optical collimator, a first convex lens, and an electrically controlled attenuator. The first optical circulator is connected to a first optical coupler via an optical fiber to receive a first incident light beam, wherein the first incident light beam enters from a first port of the first optical circulator and exits from a second port. The first optical collimator is connected to a second port of the first optical circulator via an optical fiber, and is used to convert the diverging light of the first incident light beam into parallel light. The first convex lens is disposed in front of the first optical collimator, wherein the first incident light beam passes through the first optical collimator and the first convex lens and is directed toward the object to be observed to generate a first reflected light beam. The electrically controlled attenuator has its input port connected to a third port of the first optical circulator via an optical fiber to receive the first reflected light beam and attenuate it according to an attenuation parameter value.

[0010] In one embodiment of the present invention, the second optical scanning module includes a second optical circulator, a second optical collimator, and a second convex lens. The second optical circulator is connected to a first optical coupler via an optical fiber to receive a second incident light beam, wherein the second incident light beam enters from a first port of the second optical circulator and exits from a second port. The second optical collimator is connected to a second port of the second optical circulator via an optical fiber, and is used to convert the diverging light of the second incident light beam into parallel light. The second convex lens is disposed in front of the second optical collimator, wherein the second incident light beam passes through the second optical collimator and the second convex lens and is directed towards a plane mirror to generate a second reflected light beam.

[0011] In one embodiment of the present invention, the two input ports of the second optical coupler are respectively connected by optical fibers to the output port of the electronically controlled attenuator and the third port of the second optical circulator to combine the first reflected light and the second reflected light respectively.

[0012] In one embodiment of the present invention, the first incident ray and the second incident ray arrive at the object to be observed and the plane mirror simultaneously, respectively.

[0013] In one embodiment of the present invention, the first reflected light and the second reflected light arrive at the second optical coupler simultaneously.

[0014] In one embodiment of the present invention, the attenuation parameter value of the electronically controlled attenuator is set manually or automatically according to the type of object to be observed.

[0015] In summary, the all-fiber 3D tomography system provided by this invention can bring the following benefits:

[0016] 1. It can rapidly perform line or surface scanning on optically scattering media such as biological tissues to obtain high-resolution three-dimensional images;

[0017] 2. The entire optical tomography system can be set up more easily and accurately using fiber optic cables; and

[0018] 3. It has highly flexible expansion capabilities, high scanning resolution, and high efficiency.

[0019] The following detailed description through specific embodiments will make it easier to understand the purpose, technical content, features and effects achieved by the present invention. Attached Figure Description

[0020] Figure 1 This is a block diagram of the all-fiber three-dimensional tomography system of the present invention.

[0021] Figure 2 This is a detailed block diagram of the all-fiber three-dimensional tomography system of the present invention.

[0022] Figure reference numerals: 100 - All-fiber 3D tomography system; 110 - Sweeping laser; 120 - First optical coupler; 130 - First optical scanning module; 132 - First optical circulator; 134 - First optical collimator; 136 - First convex lens; 138 - Electrically controlled attenuator; 140 - Second optical scanning module; 142 - Second optical circulator; 144 - Second optical collimator; 146 - Second convex lens; 150 - Second optical coupler; 160 - Balance detector; IL - Initial incident ray; TL1 - First incident ray; TL2 - Second incident ray; BL1 - First reflected ray; BL2 - Second reflected ray; PL1 - First target ray; PL2 - Second target ray; TML - Optical measurement signal; TA - Object to be observed; MA - Plane mirror. Detailed Implementation

[0023] To address the problems of existing technologies, the inventors have conducted years of research and development to improve upon the shortcomings of existing products. The following sections will detail how this invention achieves the most efficient functional requirements using an all-fiber 3D tomography system.

[0024] Optical coherence tomography (OCT) can produce non-invasive three-dimensional deep images of wafers or skin tissue. It is based on the principle of the Michelson interferometer, which uses the phase change produced when the reflected beam from the reference end and the reflected beam from the object under test coincide to form an interference phenomenon, which is used to form a three-dimensional deep image of the tissue under test. However, the quality of the interference image or the three-dimensional information of the object under test in traditional optical coherence tomography (OCT) still needs to be improved.

[0025] Please see Figure 1 , Figure 1This is a block diagram of the all-fiber 3D tomography system of the present invention. As shown in the figure, the all-fiber 3D tomography system 100 of the present invention uses an all-fiber circuit to structure the entire optical system to fully utilize the advantages of optical fibers, and is particularly suitable for fields requiring high-speed 3D tomography scanning of objects to be observed, which can significantly preserve the depth and thickness information of the objects to be observed. The all-fiber 3D tomography system 100 includes a swept-frequency laser 110, a first optical coupler 120, a first optical scanning module 130, a second optical scanning module 140, a second optical coupler 150, and a balanced detector 160.

[0026] Furthermore, the swept-frequency laser 110 is used to emit laser light of different wavelengths at different times (with a fairly wide spectrum), and the light source of the swept-frequency laser 110 is a low-coherence light source, which is mainly used to generate an initial beam that can achieve very high resolution. A first optical coupler 120 is connected to the swept-frequency laser 110 via an optical fiber. The first optical coupler 120 is used to receive the initial incident light IL emitted by the swept-frequency laser 110 and splits the initial incident light IL into a first incident light TL1 and a second incident light TL2. The number of rays in the first incident light TL1 is 40 to 60 times that of the second incident light TL2, and in this embodiment, it operates at 49 times, but is not limited to 49 times. A first optical scanning module 130 is connected to the first optical coupler 120 via an optical fiber to receive the first incident light TL1. The first incident light TL1 is directed towards the object to be observed TA to generate a first reflected light BL1. The object to be observed TA can be a wafer, skin, or other items, depending on the actual application.

[0027] Furthermore, the second optical scanning module 140 is connected to the first optical coupler 120 via optical fiber to receive the second incident light TL2, which is directed towards a plane mirror MA to generate a second reflected light BL2. The first incident light TL1 and the second incident light TL2 arrive at the object to be observed TA and the plane mirror MA simultaneously, or substantially simultaneously. The second optical coupler 150 is connected to the first optical scanning module 130 and the second optical scanning module 140 via optical fiber to combine the first reflected light BL1 and the second reflected light BL2, respectively. The two output ports of the second optical coupler 150 output the same number of first target light PL1 and second target light PL2, and the first target light PL1 and second target light PL2 interfere with each other optically. The first reflected light BL1 and the second reflected light BL2 arrive at the second optical coupler 150 simultaneously. The balanced detector 160 is connected to the two output ports of the second optical coupler 150 via optical fiber to receive the first target light PL1 and the second target light PL2, and outputs an optical measurement signal TML after signal processing, which is an interferometric image with three-dimensional information. As described above, the all-fiber three-dimensional tomography system 100 of the present invention utilizes the technique of capturing optical signals to acquire images and adopts an all-fiber circuit architecture, enabling rapid line or surface scanning of optically scattering media such as biological tissue to obtain high-resolution three-dimensional images.

[0028] Next, we will provide a more detailed description of the all-fiber 3D tomography system 100.

[0029] Please refer to Figure 2 , Figure 2This is a detailed block diagram of the all-fiber three-dimensional tomographic scanning system of the present invention. The first optical scanning module 130 includes a first optical circulator 132, a first optical collimator 134, a first convex lens 136, and an electrically controlled attenuator 138. The first optical circulator 132 is connected to a first optical coupler 120 via optical fiber to receive a first incident light TL1, wherein the first incident light TL1 enters from a first port of the first optical circulator 132 and exits from a second port. The first optical collimator 134 is connected to a second port of the first optical circulator 132 via optical fiber to receive the first incident light TL1, and the first optical collimator is used to convert the diverging light of the first incident light TL1 into parallel light. The first convex lens 136 for focusing is disposed in front of the first optical collimator 134, wherein the first incident light TL1 passes through the first optical collimator 134 and the first convex lens 136 and is directed toward the object to be observed TA to generate a first reflected light BL1. The input port of the electrically controlled attenuator 138 is connected via optical fiber to the third port of the first optical circulator 132 to receive the first reflected light BL1 and attenuate it according to an attenuation parameter value, that is, to reduce the amount of light. The attenuation parameter value of the electrically controlled attenuator 138 is set manually or automatically according to the type of the object to be observed TA, so as to flexibly adjust the amount of the first reflected light BL1, thereby optimizing the entire all-fiber three-dimensional tomography system 100.

[0030] Furthermore, the second optical scanning module 140 includes a second optical circulator 142, a second optical collimator 144, and a second convex lens 146. The second optical circulator 142 is connected to the first optical coupler 120 via optical fiber to receive a second incident light TL2, wherein the second incident light TL2 enters from a first port of the second optical circulator 142 and exits from a second port. The second optical collimator 144 is connected to the second port of the second optical circulator 142 via optical fiber to receive the second incident light TL2, and is used to convert the diverging light of the second incident light TL2 into parallel light. The second convex lens 146, used for focusing, is disposed in front of the second optical collimator 144, wherein the second incident light TL2 passes through the second optical collimator 144 and the second convex lens 146 and is directed towards a plane mirror MA to generate a second reflected light BL2. Next, the two input ports of the second optical coupler 150 are connected by optical fibers to the output port of the electronically controlled attenuator 138 and the third port of the second optical circulator 142 respectively to combine the first reflected light BL1 and the second reflected light BL2.

[0031] As described above, in a system environment where fiber optic lines are used as the main connection lines of the all-fiber 3D tomography system 100, the light paths of the first incident light TL1 and the second incident light TL2 are equivalent and identical, and the light paths of the first reflected light BL1 and the second reflected light BL2 are also equivalent and identical. More than 90% of the laser energy is concentrated on the sample, and only a single wavelength is output instantaneously. The laser energy is held by a single wavelength, unlike traditional OCT where laser energy is shared by multiple wavelengths. Therefore, the interference image detected by this invention is better than that of traditional OCT.

[0032] This invention employs an all-fiber optic tomography system applicable to optical coherence tomography of non-metallic objects. For example, it can be used in the semiconductor manufacturing industry for defect inspection and dimensional measurement of non-metallic objects such as wafers, transparent adhesives, glass, or plastic films. Due to the high tolerance of optics, this invention allows for the acquisition of information on the entire object at micrometer or even sub-micrometer dimensions. Furthermore, by using this invention, the flatness, surface roughness, or thickness of film surfaces can be inspected; other information about non-metallic objects can be obtained by constructing three-dimensional images.

[0033] In summary, the all-fiber 3D tomography system provided by this invention can bring the following benefits:

[0034] 1. It can rapidly perform line or surface scanning on optically scattering media such as biological tissues to obtain high-resolution three-dimensional images;

[0035] 2. The entire optical tomography system can be set up more easily and accurately using fiber optic cables; and

[0036] 3. It has highly flexible expansion capabilities, high scanning resolution, and high efficiency.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Therefore, all equivalent variations or modifications made in accordance with the features and spirit described in the claims of the present invention should be included within the protection scope of the present invention.

Claims

1. A full-fiber 3D tomography system for high-speed 3D tomography of an object to be observed, characterized in that, This all-fiber 3D tomography system includes: A frequency-sweeping laser is used to emit laser light of different wavelengths; A first optical coupler is connected to the swept laser via an optical fiber. The first optical coupler is used to receive an initial incident light emitted by the swept laser and split it into a first incident light and a second incident light, wherein the number of the first incident light is 40 to 60 times that of the second incident light. A first optical scanning module, connected to the first optical coupler via an optical fiber to receive the first incident light, wherein the first incident light is directed toward the object to be observed to generate a first reflected light, comprising: a first optical circulator connected to the first optical coupler via an optical fiber to receive the first incident light, wherein the first incident light enters from a first port of the first optical circulator and exits from a second port; and an electrically controlled attenuator, the input of which is connected to a third port of the first optical circulator via an optical fiber to receive the first reflected light and attenuate it according to an attenuation parameter value; A second optical scanning module is connected to the first optical coupler by an optical fiber to receive the second incident light, wherein the second incident light is directed toward a plane mirror to generate a second reflected light. A second optical coupler, connected by optical fiber to the first and second optical scanning modules, combines the first and second reflected rays respectively. The two output ports of the second optical coupler output the same number of first and second target rays, which then undergo optical interference. A balanced detector is connected by optical fiber to the two output ports of the second optical coupler to receive the first target light and the second target light, and outputs an optical measurement signal after signal processing.

2. The all-fiber three-dimensional tomography system as described in claim 1, characterized in that, The first optical scanning module also includes: A first optical collimator, connected by an optical fiber to a second port of the first optical circulator, is used to convert the diverging light of the first incident ray into parallel light; and A first convex lens is disposed in front of the first optical collimator, wherein the first incident light ray passes through the first optical collimator and the first convex lens and is directed toward the object to be observed, so as to generate a first reflected light ray.

3. The all-fiber three-dimensional tomography system as described in claim 1 or 2, characterized in that, The second optical scanning module includes: A second optical circulator is connected to the first optical coupler by optical fiber to receive the second incident light, wherein the second incident light enters from a first port of the second optical circulator and exits from a second port; A second optical collimator, connected by an optical fiber to a second port of the second optical circulator, is used to convert the diverging light of the second incident beam into parallel light; and A second convex lens is disposed in front of the second optical collimator, wherein the second incident light ray passes through the second optical collimator and the second convex lens and is directed toward a plane mirror to generate a second reflected light ray.

4. The all-fiber three-dimensional tomography system as described in claim 3, characterized in that, The two input ports of the second optical coupler are connected by optical fibers to the output port of the electronically controlled attenuator and the third port of the second optical circulator, respectively, so as to combine the first reflected light and the second reflected light.

5. The all-fiber three-dimensional tomography system as described in claim 1, characterized in that, The first incident ray and the second incident ray arrive at the object to be observed and the plane mirror simultaneously, respectively.

6. The all-fiber three-dimensional tomography system as described in claim 1, characterized in that, The first reflected ray and the second reflected ray arrive at the second optical coupler simultaneously.

7. The all-fiber three-dimensional tomography system as described in claim 2, characterized in that, The attenuation parameter value of the electronically controlled attenuator is set manually or automatically depending on the type of object to be observed.

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