Spectral domain OCT reference arm structure for adjusting optical path length

Abstract

The utility model discloses a kind of spectrum domain OCT reference arm structures of optical path adjustment, the spectrum domain OCT includes light source, coupler, reference arm, sample arm, reference mirror, the reference arm and reference mirror correspond to each other, the sample arm is equipped with laser welding head, and laser focal point is used to align sample weld seam, the light emitted by light source is divided into two ways by coupler, one light returns by original road after reference arm, reference mirror in turn, another light returns by original road after sample arm, sample weld seam in turn, collimating assembly, waveguide element and focusing assembly are sequentially provided in the reference arm along light direction, the waveguide element is installed on mobile platform one, waveguide element is used to in-couple the light after collimating assembly collimation, and after reflection increase optical path, it is coupled out to focusing assembly, waveguide element can adjust the optical path length before and after in-coupling waveguide element and coupling out waveguide element by itself movement, with the advantages, such as reference arm optical path precision adjustment, flexible and convenient adjustment.

Description

Technical Field

[0001] This invention belongs to the field of spectral OCT technology, specifically relating to a spectral OCT reference arm structure for adjusting optical path. Background Technology

[0002] Spectral-domain optical coherence tomography (SD-OCT) utilizes the principle of low-coherence interference. Light emitted from a source passes through a beam splitter and enters the reference arm and sample arm separately. The reflected light returning along the original path interferes with the sample light carrying depth information within the beam splitter. The interference signal enters a spectrometer for detection. After image processing, the interference spectrum carrying sample structural information can reconstruct the depth direction information of the sample under test. SD-OCT technology is primarily used in the medical field, but due to its non-contact, non-destructive testing characteristics, it has recently begun to be applied in industrial fields, such as in combination with laser welding for weld inspection. When applied to industrial inspection, considering machine size and sample characteristics, long optical path detection is often required. Generally, a coupler using optical fiber connects to the sample arm, which reduces light energy loss and can adapt to different machine sizes and positional requirements. According to the principle of SD-OCT technology, the reference light and sample light must be within the coherence length to interfere. Meanwhile, during laser welding, the sample arm is often coupled to the laser welding head. The sample to be welded should be placed at the laser focal point according to the requirements of laser welding, so optical path matching cannot be achieved by adjusting the distance between the sample and the sample arm. Therefore, the only option is to equip the arm with a function to fine-tune the optical path. Currently, there is a need to increase and fine-tune the optical path by moving a combination of triangular prisms, but since it requires passing through multiple triangular prisms, it inevitably leads to problems such as light energy loss and complicated assembly and adjustment. Utility Model Content

[0003] The present invention aims to provide a spectral domain OCT reference arm structure for adjusting the optical path, which meets the requirements for fine-tuning the optical path of the reference arm and solves the problems of light energy loss and complicated assembly and adjustment caused by the current method of fine-tuning the optical path by moving multiple triangular prisms.

[0004] Therefore, the technical solution adopted by this utility model is as follows: a spectral domain OCT reference arm structure for adjusting optical path length, the spectral domain OCT including a light source, a coupler, a reference arm, a sample arm, and a reference mirror, the reference arm and the reference mirror corresponding to each other, the sample arm is equipped with a laser welding head, and the laser focus is used to align with the sample weld, the light emitted by the light source is split into two paths by the coupler, one path of light passes through the reference arm and the reference mirror and then returns along the original path, the other path of light passes through the sample arm and the sample weld and then returns along the original path, the reference arm is provided with a collimation component, a waveguide element and a focusing component in sequence along the light direction, the waveguide element is used to couple in the light after it has been collimated by the collimation component, and after reflection to increase the optical path length, it is coupled out to the focusing component, the waveguide element is mounted on a moving platform, and the optical path length before the light enters the waveguide element and after the light exits the waveguide element can be adjusted by moving the moving platform.

[0005] As a preferred embodiment of the above scheme, the waveguide element adopts a geometric waveguide with reasonable selection, which couples light into the glass substrate of the waveguide. The light travels back and forth between the upper and lower surfaces of the glass through "total internal reflection", thereby increasing the optical path and effectively reducing dispersion and energy loss.

[0006] A further preferred embodiment is that the waveguide element is a trapezoidal prism, which is a reasonable selection and provides stable fine-tuning effect.

[0007] A further preferred embodiment is that the first half of the waveguide element employs a trapezoidal prism total internal reflection structure, while the second half incorporates a semi-transparent, semi-reflective mirror structure arranged in parallel at intervals to form a semi-transparent, semi-reflective structure. The semi-transparent, semi-reflective mirrors form a surface at a specific angle with the transmitted light. Each mirror reflects a portion of the light out of the waveguide element, while the remaining light is transmitted through and continues its journey within the waveguide element. This transmitted light then encounters another semi-transparent, semi-reflective mirror, repeating the "reflection-transmission" process until the last mirror in the mirror array reflects all the remaining light out of the waveguide element. During this process, the output light energy decreases progressively with the number of mirrors that pass through.

[0008] The focusing component and the reference mirror are respectively mounted on their respective mobile platforms and move synchronously through the mobile platforms to receive light of different energy levels from the semi-transparent and semi-reflective region, thereby controlling the energy ratio of the light reflected by the reference mirror and the light reflected by the sample weld. At the same time, the optical path in the waveguide element can be adjusted to achieve more precise optical path adjustment.

[0009] More preferably, the waveguide element is a surface relief grating waveguide or a volume holographic grating waveguide. The surface relief grating is manufactured using traditional semiconductor micro-nano manufacturing, and the holographic grating is made using holographic interference technology. The surface relief grating or holographic grating is used as a light coupling structure. After the light enters the waveguide element, it is transmitted by total internal reflection. The diffraction waveguide has low cost potential and is suitable for industrial machine assembly. It has a high degree of design freedom and the angle of the coupled light can be controlled by optimizing the grating design.

[0010] Further preferably, both the first mobile platform and the second mobile platform are mounted on slide rails and equipped with corresponding moving drive components, resulting in a reasonable structural design.

[0011] More preferably, the coupler is connected to the reference arm and the sample arm via optical fiber, and the coupler is connected to the light source via optical fiber. The light from the light source returns along its original path and then interferes, and the interference light energy is analyzed by a spectrometer.

[0012] The beneficial effects of this utility model are as follows: Compared with the current method of fine-tuning the optical path by moving multiple triangular prisms, this application uses waveguide elements inserted into the collimation and focusing components of the reference arm and combines the waveguide elements with the reference arm. The waveguide is a medium device that guides light waves to propagate in it. By installing the waveguide elements on the moving platform, the optical path of the reference arm can be increased or decreased, thereby achieving precise control and meeting the long optical path matching requirements of SD-OCT technology. It has the advantages of precise adjustment of the optical path of the reference arm and flexible and convenient adjustment. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of spectral domain OCT.

[0014] Figure 2 This is a schematic diagram of a waveguide element where a trapezoidal prism is used to couple light out from inside the reference arm to the reference mirror.

[0015] Figure 3 This is a schematic diagram of a waveguide structure where light is coupled out from inside the reference arm to the reference mirror when a diffractive waveguide is used for waveguide elements.

[0016] Figure 4 This is a schematic diagram of a waveguide element where a trapezoidal prism is used in the first half of the waveguide and a semi-transparent, semi-reflective mirror is used in the second half, with the light being coupled out from inside the reference arm to the reference mirror. Detailed Implementation

[0017] The present invention will be further described below with reference to embodiments and accompanying drawings:

[0018] Combination Figure 1 — Figure 4 As shown, a spectral domain OCT reference arm structure for adjusting optical path is presented. The spectral domain OCT consists of a light source 1, a coupler 2, a reference arm 3, a sample arm 4, and a reference mirror 5.

[0019] Reference arm 3 and reference mirror 5 correspond to each other. Sample arm 4 is equipped with a laser welding head, and the laser focus is used to align with the weld seam of sample 6. The light emitted by light source 1 is split into two paths through coupler 2. One path passes through reference arm 3 and reference mirror 5 and then returns along the same path. The other path passes through sample arm 4 and the weld seam of sample 6 and then returns along the same path.

[0020] Coupler 2 is connected to reference arm 3 and sample arm 4 via optical fiber, and coupler 2 is connected to light source 1 via optical fiber. The light from light source 1 returns along its original path and interferes, and the interference light energy is analyzed by spectrometer 9.

[0021] The reference arm 3 is provided with a collimation component 31, a waveguide element 32 and a focusing component 33 in sequence along the light path.

[0022] Waveguide element 32 is used to couple in light that has been collimated by collimation component 31, and after reflection to increase the optical path, it is coupled out to focusing component 33.

[0023] The waveguide element 32 is mounted on the moving platform 7, and the optical path length before and after the optical coupler enters the waveguide element 32 can be adjusted by moving the moving platform 7.

[0024] Waveguide element 32 is preferably a geometric waveguide.

[0025] Waveguide element 32 is preferably a trapezoidal prism. The collimated light emitted by collimation component 31 is coupled into the geometric waveguide, and the coupling angle satisfies the total internal reflection condition.

[0026] Total internal reflection of light within waveguide elements can reduce dispersion and energy loss.

[0027] The waveguide element 32 adopts a trapezoidal prism total reflection structure in the first half and a semi-transparent and semi-reflective mirror structure with spaced parallel arrangement in the second half to form a semi-transparent and semi-reflective structure.

[0028] After entering the first half of the waveguide element 32, the light undergoes total internal reflection. When it reaches the second half, a portion of the light is coupled out proportionally as it passes through each "semi-transparent and semi-reflective" mirror, while the other portion continues to travel in the second half until the last portion is completely coupled out.

[0029] A waveguide element with a "semi-transparent and semi-reflective" mirror array is added, and the focusing assembly 33 is mounted on the moving platform 28. The energy of the reference light can be controlled by controlling the position of the focusing assembly 33 to receive the waveguide emitted light, thereby controlling the energy ratio of the reference light and the sample light. At the same time, the optical path length within the waveguide element can also be changed.

[0030] Waveguide element 32 is preferably a surface relief grating waveguide or a volume holographic grating waveguide of a diffraction waveguide. The collimated light emitted by collimation component 31 is coupled into the diffraction waveguide through the grating, undergoes total internal reflection inside, and is then coupled out by the grating and transmitted to focusing component 33.

[0031] Diffractive waveguides have low cost potential and are suitable for industrial machine assembly. They also offer high design freedom, allowing for control of the coupled light angle through optimized grating design.

[0032] The focusing component 33 and the reference mirror 5 are respectively mounted on their respective mobile platforms 2 and 8 and move synchronously through the mobile platforms 2 and 8.

[0033] Both mobile platform 7 and mobile platform 8 are mounted on slide rails and equipped with corresponding moving drive components, such as hydraulic cylinders.

Claims

1. A spectral domain OCT reference arm structure for adjusting optical path, the spectral domain OCT comprising a light source (1), a coupler (2), a reference arm (3), a sample arm (4), and a reference mirror (5), wherein the reference arm (3) and the reference mirror (5) correspond to each other, the sample arm (4) is equipped with a laser welding head, and the laser focus is used to align with the weld seam of the sample (6), the light emitted by the light source (1) is split into two paths by the coupler (2), one path of light passes through the reference arm (3) and the reference mirror (5) and then returns along the original path, and the other path of light passes through the sample arm (4) and the weld seam of the sample (6) and then returns along the original path, characterized in that: The reference arm (3) is provided with a collimation component (31), a waveguide element (32) and a focusing component (33) in sequence along the light direction. The waveguide element (32) is used to couple in the light after it has been collimated by the collimation component (31), and after reflection to increase the optical path, it is coupled out to the focusing component (33). The waveguide element (32) is mounted on the moving platform (7) and can be moved and adjusted by the moving platform (7) before the light is coupled into the waveguide element (32) and after it is coupled out of the waveguide element (32).

2. The spectral domain OCT reference arm structure for adjusting optical path length according to claim 1, characterized in that: The waveguide element (32) adopts a geometric waveguide.

3. The spectral domain OCT reference arm structure for adjusting optical path length according to claim 2, characterized in that: The waveguide element (32) is a trapezoidal prism.

4. The spectral domain OCT reference arm structure for adjusting optical path length according to claim 2, characterized in that: The waveguide element (32) adopts a trapezoidal prism total reflection structure in the first half and a semi-transparent and semi-reflective structure embedded in the second half. The focusing component (33) and the reference mirror (5) are respectively mounted on their respective mobile platforms (8) and move synchronously through the mobile platforms (8).

5. The spectral domain OCT reference arm structure for adjusting optical path length according to claim 1, characterized in that: The waveguide element (32) is a surface relief grating waveguide or a volume holographic grating waveguide.

6. The spectral domain OCT reference arm structure for adjusting optical path length according to claim 1, characterized in that: Both the first mobile platform (7) and the second mobile platform (8) are mounted on slide rails and equipped with corresponding moving drive components.

7. The spectral domain OCT reference arm structure for adjusting optical path length according to claim 1, characterized in that: The coupler (2) is connected to the reference arm (3) and the sample arm (4) by optical fiber. The coupler (2) is connected to the light source (1) by optical fiber. The light from the light source (1) returns along its original path and interferes. The interference light energy is analyzed by the spectrometer (9).

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