Multi-gear optical fiber channel fusion depth detection OCT system, optical path matching method and application

Abstract

The invention discloses a multi-gear optical fiber channel fusion depth detection OCT (optical coherence tomography) system, an optical path matching method and application, an optical fiber coupler is respectively connected with a reference optical path and a sample optical path system, in the reference optical path system, the optical fiber coupler is connected with a multi-gear optical fiber switching port through a reference optical path optical fiber, each interface of the port is connected with a switching optical fiber with a specific optical path length, and the switching optical fiber is connected with the sample optical path system. The other end of the switching optical fiber is connected with an optical fiber beam combiner and then sequentially passes through a reference arm beam expanding collimator and a focusing lens to a fixed reflecting mirror to form a reference light beam, a sample light path system passes through a sample arm beam expanding collimator, a two-dimensional scanning galvanometer and a field lens to reach a tested sample, and the tested sample returns to form a sample light beam; the preset lengths of the switching optical fibers are in one-to-one correspondence with the working distances of different field lenses, and when the field lenses are replaced, the reference optical path optical fibers are inserted into the corresponding interfaces so as to compensate the optical path difference caused by replacement of the field lenses. According to the invention, the optical path adjusting function is compressed to be within the size of a standard optical fiber device, and the optical path conversion from tens of centimeters to meters is realized in a small volume.

Description

Technical Field

[0001] This invention relates to the field of optical coherence tomography (OCT) technology, and particularly to a multi-level fiber optic channel OCT system for detecting fusion depth, an optical path matching method, and its applications. Background Technology

[0002] Optical coherence tomography (OCT) technology has become a key method for monitoring molten pool depth due to its ability to achieve real-time imaging of depth profiles with micron-level resolution. Its working principle is based on a Michelson interferometer: light emitted from a broadband light source is split into a reference beam and a sample beam. The sample beam travels along a path coaxial with the processing laser and is focused onto the workpiece by a field lens; the reference beam propagates in the reference arm and returns. The two beams converge to produce interference, and by analyzing and demodulating the interference spectrum, the scattered signal from the sample surface to a specified depth can be obtained. To ensure precise alignment between the measurement and processing positions, the OCT probe beam must be combined with the high-power laser beam through a beam splitter and pass together through the final focusing field lens of the laser processing head. The effective operation of an OCT system depends on a high degree of matching between the optical path lengths of the reference arm and the sample arm. In industrial applications such as laser welding and cladding, to adapt to different material thicknesses, welding speeds, and penetration depth requirements, it is often necessary to replace the focusing field lens with one of different focal lengths to change the laser spot size and energy density distribution. This process change results in a stepwise change in the laser focus position (i.e., the OCT detection focus position) by tens of centimeters or even meters, causing a similarly abrupt change in the optical path of the sample arm. Therefore, the reference arm must have a corresponding wide-range, high-precision optical path adjustment capability to real-time rematch the optical paths of the two arms. This is a necessary prerequisite for the application of OCT technology in various industrial processes.

[0003] Traditional OCT optical path adjustment methods primarily rely on linear motor platforms. To achieve a wide range of optical path adjustments, several methods exist: 1. Long-stroke precision electric translation stage direct adjustment: This method uses a high-precision electric translation stage with a stroke matching the expected optical path variation range, directly supporting the end mirror of the reference arm. Continuous, wide-range adjustment of the reference optical path is achieved by controlling the long-distance linear motion of the translation stage. This method is simple in principle, but the stroke is typically small, making it difficult to adapt to the large-scale requirements of field lens replacement. 2. Foldable multi-reflection delay line optical path scheme: The core of this scheme is to construct an optical folding cavity within the reference arm, specifically designed to obtain a larger optical delay within a limited mechanical stroke. Structurally, two sets of parallel mirrors are typically used, one fixed and the other mounted on a relatively short-stroke translation stage. The incident beam undergoes multiple round-trip reflections between the two mirror sets. When the moving mirror set produces a physical displacement ΔL, the total effective optical path change is 2NΔL because the beam travels back and forth N times. By designing the number of reflections, a translation stage with a movement range of only centimeters can be used to achieve optical path adjustment at the decimeter or even meter level.

[0004] For example, the patent with application number CN202311417334.4 uses a large-range linear electric displacement stage to achieve large-range optical path switching, enabling rapid optical path registration. This design is typically used for small-range optical path changes that may be needed in the medical field. However, for applications like laser welding that may require optical path adjustments of tens or even hundreds of centimeters, using linear optical path adjustment usually results in a large volume structure; furthermore, because the adjustment spatial optical path is long, large-range movement of the reference arm can cause the return beam to deviate, leading to changes in OCT imaging quality.

[0005] As in the patent application CN200720111382.0, although the delay line reference optical path based on multiple folding reflections greatly reduces the spatial structure of the reference arm, the multiple reflection optical path is extremely sensitive to the alignment of the mirror angles. Even minor vibrations or thermal deformations can easily lead to optical path misalignment or even failure, resulting in poor adaptability to industrial environments. Furthermore, due to the introduction of multiple mirror angle deviations in the optical path, the returned light intensity may change significantly during the movement of the reference arm, impairing the signal-to-noise ratio and stability of the OCT signal and failing to guarantee consistent imaging quality before and after the reference arm movement. Particularly noteworthy is that in laser deep penetration welding, the key signal detected by the OCT system comes from the weak scattered light from the keyhole at the bottom of the molten pool. This signal itself is extremely weak and highly sensitive to changes in optical path transmission efficiency and the intensity of light returning to the detector. Therefore, during large-scale optical path adjustments, the reference arm must maintain stable optical path efficiency to ensure that the returned signal intensity does not fluctuate significantly. This places more stringent requirements on the optical path adjustment device: it must achieve large-span, rapid optical path switching while maintaining a high degree of consistency in the optical performance of the optical path before, during, and after the switching process. This is to avoid interference from intensity changes introduced by the adjustment action itself in judging the keyhole status, and to ensure the accuracy and reliability of the melt depth measurement results. Existing mechanical adjustment schemes cannot simultaneously meet the above requirements of "large range, rapid speed, and stability," constituting a technical bottleneck. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention aims to provide a multi-level fiber optic channel fusion depth detection OCT system, optical path matching method, and application, which can compress the optical path adjustment function into the size of standard fiber optic devices, and achieve optical path conversion from tens of centimeters to meters in a small volume.

[0007] To achieve the above objectives, this invention proposes a multi-level fiber channel fusion depth detection OCT system, including a light source and a fiber coupler connected to each other, and a reference optical path system and a sample optical path system respectively connected to the output end of the fiber coupler.

[0008] The reference optical path system includes a multi-position fiber optic adapter port. One end of the reference optical fiber is connected to the output of a fiber optic coupler, and the other end can be selectively connected to one of the interfaces of the multi-position fiber optic adapter port. The other end of each interface of the multi-position fiber optic adapter port is fixedly connected to an adapter fiber with a specific optical path length, where the optical path lengths of each adapter fiber are δ1, δ2, δ3, ..., δ... n Together, they constitute a set of preset optical path compensation values ​​δ iThe other ends of all the connecting optical fibers are connected to the input ends of an optical fiber combiner. The reference optical path system also includes a reference arm beam expander collimator, a focusing lens and a fixed mirror arranged sequentially along the optical path. The common output end of the optical fiber combiner is connected to the reference arm beam expander collimator. After the reference arm beam expander collimator expands the beam, the beam can be focused by the focusing lens onto the surface of the fixed mirror, and then reflected by the fixed mirror to form a reference beam.

[0009] The sample optical path system includes a sample arm beam expander and collimator, a two-dimensional scanning galvanometer, a focusing field lens, and a sample under test arranged sequentially along the optical path. The fiber coupler is connected to the sample arm beam expander and collimator through a sample optical path fiber. After the sample arm beam expander and collimator expands the beam, the beam can be deflected by the two-dimensional scanning galvanometer and then focused by the focusing field lens onto the sample under test. After being blocked by the sample under test, the beam returns to form a sample beam.

[0010] The reference beam and the sample beam return to the same fiber coupler, which combines the two beams and sends them to the detector. Since the two beams originate from the same source, they are coherent. When they superimpose at the detector, an interference signal is generated.

[0011] The multi-position fiber channel fusion depth detection OCT system is equipped with multiple focusing lenses of different focal lengths. The preset length of each adapter fiber is mapped one-to-one with the working distance of each focusing lens. When changing to a focusing lens with a different working distance, the reference optical path fiber is plugged into the interface corresponding to the focusing lens in the multi-position fiber adapter port, thereby switching the variable optical path portion of the reference optical path system to the corresponding optical path compensation value δ. i This is to compensate for the optical path difference caused by the change of the focusing field lens.

[0012] In the above scheme: the reference optical fiber is a pluggable patch cord, which makes it convenient to replace or adjust the connection position according to actual testing needs.

[0013] In the above solution, the multi-position fiber optic adapter port is a mechanical adapter with multiple interfaces, each of which is matched with a pluggable patch cord. Switching between adapter fibers can be achieved simply by plugging and unplugging the cable.

[0014] In the above scheme, each interface of the multi-position fiber optic adapter port is equipped with a unique identifier to facilitate accurate connection of the corresponding adapter fiber.

[0015] In the above scheme: the multi-position fiber optic adapter port is equipped with 5 interfaces, which can correspond to 5 focusing field lenses with different working distances.

[0016] In the above scheme, the light source is a low-coherence near-infrared broadband light source to meet the requirements of the OCT system for interferometric measurement.

[0017] In the above scheme, the optical fiber used in the reference optical path system and the sample optical path system is of the same type, which helps to ensure the quality of the interference signal and thus improve the accuracy of the melt depth detection.

[0018] In the above scheme: the multi-level fiber channel fusion depth detection OCT system is equipped with a sample detection platform. The multi-level fiber channel fusion depth detection OCT system is deployed on the sample detection platform, which facilitates the high integration of the system and has a simple structure and convenient deployment.

[0019] This invention also proposes an optical path matching method for a multi-stage fiber optic channel fusion depth detection OCT system. Before performing the optical path matching operation, the multi-stage fiber optic channel fusion depth detection OCT system is calibrated to determine the optical path compensation value δ corresponding to each focusing field lens. i The correspondence between the interfaces of the multi-position fiber optic adapter ports and the adapter fiber and focusing field lens is recorded and marked so that optical path matching can be performed quickly and accurately in the future.

[0020] This multi-level fiber optic channel depth-of-melt OCT system can be applied to the field of laser processing.

[0021] The beneficial effects of this invention are:

[0022] 1. By connecting fiber optic cables of different lengths through multi-position fiber optic adapter ports, each fiber corresponds to the working distance of a focusing field lens with a specific focal length, forming a library of optical path compensation values. When changing to a focusing field lens with a different working distance, the reference optical path fiber is directly plugged into the interface corresponding to that focusing field lens in the multi-position fiber optic adapter port, thereby switching the variable optical path portion of the reference optical path system to the corresponding optical path compensation value δ. i This compensates for optical path differences caused by changing the focusing field lens. This process requires no mechanical moving parts; optical path adjustment is completed internally within the fiber optic device, with a response speed in the millisecond range. 2. By employing multi-length fixed fiber optic channels as discrete optical path standards, the optical path adjustment function is compressed within the fiber optic device size, avoiding the large volume structure of traditional mechanical translation stages. A wide range of optical path transformations is achieved within a small volume structure, possessing optical path conversion capabilities from tens of centimeters to meters. 3. The structure is simple and easy to operate, reducing costs and allowing seamless integration into automated production lines, providing key technical support for the large-scale and intelligent application of laser processing melt depth detection.

[0023] In summary, this invention, through its multi-position fiber optic channel design, achieves discrete, rapid, and low-cost adjustment of the reference arm optical path, solving the problem of large-scale optical path mismatch caused by field lens replacement in laser processing, and has significant technical and economic advantages. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a multi-level fiber optic channel OCT system for measuring fusion depth. Detailed Implementation

[0025] like Figure 1 As shown, a multi-level fiber optic channel fusion depth detection OCT system mainly consists of a light source 101 and a fiber optic coupler 102 connected to each other, as well as a reference optical path system and a sample optical path system respectively connected to the output end of the fiber optic coupler 102.

[0026] The reference optical path system includes a multi-position fiber optic adapter port 105. One end of the reference optical fiber 103 is connected to the output of the fiber optic coupler 102, and the other end can be selectively connected to one of the interfaces of the multi-position fiber optic adapter port 105. The other end of each interface of the multi-position fiber optic adapter port 105 is fixedly connected to an adapter fiber 106 with a specific optical path length, wherein the optical path lengths of each adapter fiber 106 are δ1, δ2, δ3, ..., δ... n Together, they constitute a set of preset optical path compensation values ​​δ i The other ends of all the adapter fibers 106 are connected to the input ends of a fiber optic combiner 107, which is an n×1 fiber optic combiner.

[0027] The reference optical path system also includes a reference arm beam expander collimator 108, a focusing lens 109, and a fixed reflector 110 arranged sequentially along the optical path. The common output end of the fiber optic combiner 107 is connected to the reference arm beam expander collimator 108. After the reference arm beam expander collimator 108 expands the beam, the beam can be focused by the focusing lens 109 onto the surface of the fixed reflector 110, and then reflected by the fixed reflector 110 to form a reference beam.

[0028] The sample optical path system includes a sample arm beam expander and collimator 111, a two-dimensional scanning galvanometer 112, a focusing field lens 113, and a sample under test 114, arranged sequentially along the optical path. An optical fiber coupler 102 is connected to the sample arm beam expander and collimator 111 via a sample optical fiber 104. After the sample arm beam expander and collimator 111 expands the beam, the beam is deflected by the two-dimensional scanning galvanometer 112 and then focused by the focusing field lens 113 onto the sample under test 114. The beam is then blocked by the sample under test 114 and returns, forming the sample beam.

[0029] The reference beam and the sample beam return to the same fiber coupler 102, which combines the two beams and sends them to the detector. Since the two beams originate from the same source, they are coherent. When they superimpose at the detector, an interference signal is generated.

[0030] The multi-position fiber channel fusion depth detection OCT system is equipped with multiple focusing lenses 113 with different focal lengths. The preset length of each adapter fiber 106 is mapped one-to-one with the working distance of each focusing lens 113. When changing to a focusing lens 113 with a different working distance, the reference optical path fiber 103 is plugged into the interface corresponding to the focusing lens 113 in the multi-position fiber adapter port 105, thereby switching the variable optical path part in the reference optical path system to the corresponding optical path compensation value δ. i This is to compensate for the optical path difference caused by the replacement of the focusing field lens 113.

[0031] Ideally, the reference optical fiber 103 should be a pluggable patch cord, which allows for easy replacement or adjustment of the connection position according to actual testing needs.

[0032] Ideally, the multi-position fiber optic adapter port 105 is a mechanical adapter with multiple interfaces, each of which is matched with a pluggable patch cord. The number of interfaces n≥2, and the switching of the adapter fiber optic cable 106 can be achieved simply by plugging and unplugging.

[0033] Ideally, each interface of the multi-position fiber optic adapter port 105 should have a unique identifier to facilitate accurate connection to the corresponding adapter fiber optic cable 106.

[0034] Ideally, the multi-position fiber optic adapter port should have 5 interfaces to accommodate 5 focusing lenses with different working distances.

[0035] Ideally, light source 101 should be a low-coherence near-infrared broadband light source to meet the requirements of the OCT system for interferometric measurements.

[0036] Ideally, the reference optical path system and the sample optical path system should use the same type of optical fiber, which helps to ensure the quality of the interference signal and thus improve the accuracy of the melt depth detection.

[0037] Ideally, the multi-channel fiber optic OCT system for measuring fusion depth is equipped with a sample testing platform. The multi-channel fiber optic OCT system is deployed on the sample testing platform, which facilitates high system integration and has a simple structure and is easy to deploy.

[0038] An optical path matching method for a multi-channel fiber optic depth-sensing OCT system involves calibrating the system before performing the optical path matching operation to determine the optical path compensation value δ corresponding to each focusing field lens 113. i The correspondence between the interface of the multi-position fiber optic adapter port 105 and the adapter fiber 106 and the focusing field lens 113 is recorded and marked so that optical path matching can be performed quickly and accurately in the future.

[0039] This multi-level fiber optic channel depth-of-melt OCT system can be applied to the field of laser processing.

Claims

1. A multi-level fiber optic channel fusion depth detection OCT system, comprising a light source (101) and a fiber optic coupler (102) connected to each other, and a reference optical path system and a sample optical path system respectively connected to the output end of the fiber optic coupler (102), characterized in that: The reference optical path system includes a multi-position fiber optic adapter port (105). One end of the reference optical path fiber (103) is connected to the output end of the fiber optic coupler (102), and the other end can be selectively connected to one of the interfaces of the multi-position fiber optic adapter port (105). The other end of each interface of the multi-position fiber optic adapter port (105) is fixedly connected to an adapter fiber (106) with a specific optical path length. The optical path lengths of each adapter fiber (106) are δ1, δ2, δ3, ..., δ n Together, they constitute a set of preset optical path compensation values ​​δ i The other ends of all the connecting optical fibers (106) are connected to the input ends of an optical fiber combiner (107). The reference optical path system also includes a reference arm beam expander collimator (108), a focusing lens (109) and a fixed mirror (110) arranged sequentially along the optical path. The common output end of the optical fiber combiner (107) is connected to the reference arm beam expander collimator (108). After the reference arm beam expander collimator (108) expands the beam, the beam can be focused by the focusing lens (109) onto the surface of the fixed mirror (110) and then reflected by the fixed mirror (110) to form a reference beam. The sample optical path system includes a sample arm beam expander collimator (111), a two-dimensional scanning galvanometer (112), a focusing field lens (113), and a sample under test (114) arranged sequentially along the optical path. The fiber coupler (102) is connected to the sample arm beam expander collimator (111) through a sample optical path fiber (104). After the sample arm beam expander collimator (111) expands the beam, the beam can be deflected by the two-dimensional scanning galvanometer (112) and then focused by the focusing field lens (113) onto the sample under test (114). After being blocked by the sample under test (114), the beam returns to form a sample beam. The multi-stage fiber channel fusion depth detection OCT system is equipped with multiple focusing lenses (113) with different focal lengths. The preset length of each adapter fiber (106) is mapped one-to-one with the working distance of each focusing lens (113). When changing the focusing lens (113) with a different working distance, the reference optical path fiber (103) is plugged into the interface corresponding to the focusing lens (113) in the multi-stage fiber adapter port (105), thereby switching the variable optical path part in the reference optical path system to the corresponding optical path compensation value δ. i This is to compensate for the optical path difference caused by the replacement of the focusing field lens (113).

2. The multi-level fiber optic channel fusion depth detection OCT system according to claim 1, characterized in that: The reference optical fiber (103) is a pluggable jumper.

3. The multi-level fiber optic channel fusion depth detection OCT system according to claim 2, characterized in that: The multi-position fiber optic adapter port (105) is a mechanical adapter with multiple interfaces, each of which is matched with a pluggable patch cord.

4. The multi-level fiber optic channel fusion depth detection OCT system according to claim 3, characterized in that: Each interface of the multi-position fiber optic adapter port (105) is equipped with a unique identifier.

5. The multi-level fiber optic channel fusion depth detection OCT system according to claim 4, characterized in that: The multi-position fiber optic adapter port (105) is equipped with 5 interfaces.

6. The multi-level fiber optic channel fusion depth detection OCT system according to claim 1, characterized in that: The light source (101) is a low-coherence near-infrared broadband light source.

7. The multi-level fiber optic channel fusion depth detection OCT system according to claim 1, characterized in that: The reference optical path system and the sample optical path system use the same type of optical fiber.

8. The multi-level fiber optic channel fusion depth detection OCT system according to claim 1, characterized in that: The multi-level fiber optic channel melt depth detection OCT system is equipped with a sample detection platform, and the multi-level fiber optic channel melt depth detection OCT system is deployed on the sample detection platform.

9. An optical path matching method for a multi-level fiber optic channel fusion depth detection OCT system as described in any one of claims 1-8, characterized in that: Before performing optical path matching, the OCT system for detecting the fusion depth of the multi-position fiber channel is calibrated to determine the optical path compensation value δ corresponding to each focusing field lens (113). i The correspondence between the interface of the multi-position fiber optic adapter port (105) and the adapter fiber (106) and the focusing field lens (113) is recorded and marked.

10. The application of a multi-level fiber optic channel OCT system for detecting weld depth as described in any one of claims 1-8 in laser processing.

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