A high-resolution speckle wavelength measurement device and method

Abstract

The application belongs to the technical field of wavelength measurement, and is especially a high-resolution speckle wavelength measurement device and method. The device comprises a shell, a first optical fiber incident port and a second optical fiber incident port are arranged on the outer wall of the shell, an optical switch, a light splitting coupler, a calibration light source and a test light path are arranged in the shell, and the test light path is composed of a multimode optical fiber, an optical fiber mode enhancement device and a surface array detector. The application enhances the coupling and phase delay between different modes by applying mechanical disturbance to the scattering medium, increases the number of excited modes, and solves the problems that the resolution of the speckle wavelength meter is limited by the light path length of the transmission medium and the insufficient information density of the speckle per unit area. The method can improve the wavelength resolution, and effectively improve the sampling speed of the speckle wavelength meter by reducing the size of the photosensitive camera target surface.

Description

Technical Field

[0001] This invention relates to the field of wavelength measurement technology, specifically to a high-resolution speckle wavelength measurement device and method. Background Technology

[0002] Wavelength is a fundamental parameter characterizing the spatial periodicity of electromagnetic waves, defined as the distance between two adjacent points with the same phase along the wave propagation direction. As a type of electromagnetic wave, light's wavelength information carries key physical characteristics of the light source, playing a decisive role in precision measurement fields such as chemical analysis, astronomy, quantum physics, and biomedicine. While traditional dispersive spectrometers (such as grating spectrometers) offer advantages in wide spectrum and multi-wavelength detection, their resolution and size parameters are insufficient for some application requirements. Traditional interferometer methods require precision moving parts and high-reflectivity lenses to ensure measurement accuracy, making them unsuitable for applications requiring high-speed wavelength information.

[0003] Emerging speckle wavelength meters utilize the deterministic speckle pattern generated after light waves pass through a fixed scattering medium, and achieve wavelength demodulation by establishing a mapping relationship between wavelength and speckle. Wavelength meters built using this method exhibit advantages such as miniaturization, high precision, and fast response. However, their wavelength accuracy and size can still be further improved. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0006] A high-resolution speckle wavelength measurement device includes a housing with a first fiber optic port and a second fiber optic port on its outer wall. Inside the housing are an optical switch, a beam splitter, a calibration light source, and a test optical path. The test optical path consists of a multimode fiber, a fiber mode enhancement device, and an area array detector. The calibration light source compensates for speckle pattern drift in the multimode fiber caused by environmental disturbances. The beam splitter, used in combination with the optical switch, enables optical path switching. The multimode fiber, as the speckle generation medium, is integrated into the optical path. The fiber mode enhancement device directly acts on the multimode fiber to enhance optical path coupling within the medium. The area array detector receives the speckle pattern. The fiber mode enhancement device has a supporting fiber structure for generating small macrobending in the multimode fiber and a tunable mechanism for controlling the degree of macrobending in the multimode fiber.

[0007] In a preferred embodiment of the high-resolution speckle wavelength measurement device of the present invention, the calibration light source adopts a light source with narrow linewidth and highly stable output wavelength, and the calibration light source is a helium-neon laser or an acetylene frequency-stabilized light source.

[0008] As a preferred embodiment of the high-resolution speckle wavelength measurement device of the present invention, the operating bandwidth of the beam splitter and the optical switch covers the visible light band or the near-infrared band, and the operating wavelength range of the beam splitter and the optical switch is configured to simultaneously cover the band of the light source under test and the wavelength of the calibration light source.

[0009] As a preferred embodiment of the high-resolution speckle wavelength measurement device of the present invention, the operating wavelength range of the multimode optical fiber covers the measurement bandwidth, and the multimode optical fiber is a step-index multimode optical fiber with a core diameter between 50μm and 60μm and a length greater than 0.5m.

[0010] As a preferred embodiment of the high-resolution speckle wavelength measurement device described in this invention, the fiber mode enhancement device is further provided with a temperature control device and a vibration attenuation device.

[0011] In a preferred embodiment of the high-resolution speckle wavelength measurement device of the present invention, the fiber mode enhancement device has a toothed structure, the multimode fiber is clamped inside the fiber mode enhancement device, the fiber mode enhancement device includes a rotary tuning structure, a moving rod, a fixed rod, a fiber coupler, and a surface array detector coupler, the multimode fiber is coiled on the fixed rod, the rotary tuning structure is connected to the moving rod, the rotary tuning structure is used to tune the distance between the moving rod and the fixed rod, the fiber coupler is used to connect to the light source under test, and the surface array detector coupler is used to assemble with the surface array detector.

[0012] A high-resolution speckle wavelength measurement method includes the following steps:

[0013] S1: When the laser propagates in the optical fiber, the multimode fiber is processed using a tunable compression method. After being mechanically disturbed, the internal mode coupling mode of the multimode fiber changes, thereby causing a greater difference in the speckle pattern with wavelength variation. During this process, the light under test... When propagating in a multimode optical fiber, the electric field is expressed as: The modal superposition can be calculated using the following formula:

[0014]

[0015] In the formula Let a(z) be the spatial distribution of the electric field of light throughout the optical fiber, a(z) be the amplitude of the mode, and m be the intensity of mode m in the propagation direction z. Transverse electric field mode, Modal propagation factor in the z-direction;

[0016] S2: After being subjected to mechanical disturbance, the orthogonality of some paths is disrupted, and energy exchange occurs between different paths, causing modal coupling, such as the two modes of propagation. , When passing through this disturbance point, the modal electric field is calculated according to the following formula:

[0017]

[0018] When the degree of disturbance increases, if As the disturbance decreases, Then, as the disturbance increases, the energy will decrease from... Flow direction In a similar process, energy can also flow to inefficient modes, making them efficient transmission modes, thereby increasing the degree of intermodal coupling.

[0019] S3: The fiber mode enhancement device adds a mode coupling drive to the propagation of light in a multimode fiber. During propagation, the fiber refractive index becomes:

[0020]

[0021] In the formula The refractive index when undisturbed. This represents the perturbation to the refractive index in the z-direction, under which the mode enhancement of the multimode fiber is:

[0022]

[0023] in:

[0024] , representing the fiber perturbation enhancement coefficient;

[0025] S4: The mode enhancement method can be designed, and the perturbation structure is designed as a tooth shape. The mode enhancement form of the optical fiber is as follows:

[0026] In the formula The small change in the square of the refractive index of the optical fiber The transverse distribution function representing the disturbance. Represents the magnitude of the disturbance. This represents the periodic variation of the disturbance in the direction of light propagation. It is the spatial frequency of the fiber optic disturbance;

[0027] Mode enhancement in multimode fiber tends to be:

[0028]

[0029] In the formula The difference between the propagation constants of the two modes. The length of the disturbance region.

[0030] Compared with existing technologies, the advantages of this invention are as follows: By applying mechanical perturbation to the scattering medium, this invention enhances the coupling and phase delay between different modes, increases the number of excitation modes, and thus solves the problem that the resolution of speckle wavelength meters is limited by the optical path length of the transmission medium and the insufficient speckle information density per unit area. This method, while improving wavelength resolution, can effectively increase the sampling speed of the speckle wavelength meter by reducing the target surface size of the photosensitive camera. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0032] Figure 1 This is a schematic diagram of the structure of a high-resolution speckle wavelength measurement device according to the present invention;

[0033] Figure 2 This is a schematic diagram of the fiber mode enhancement device structure of a high-resolution speckle wavelength measurement device according to the present invention;

[0034] Figure 3 This is a schematic diagram of the internal structure of the fiber mode enhancement device of the high-resolution speckle wavelength measurement device of the present invention.

[0035] Figure 4 These are diagrams illustrating the resolution improvement effects of different levels of disturbance on optical fibers provided in this embodiment of the invention.

[0036] Figure 5 This is a diagram illustrating the long-term wavelength monitoring effect in an embodiment of the present invention.

[0037] Figure 6 This is a comparison diagram showing the effect of having and not having a resolution-enhancing structure when the wavelength changes by 0.03 nm in an embodiment of the present invention.

[0038] In the figure: 1. Outer shell; 2. First fiber optic inlet; 3. Second fiber optic inlet; 4. Optical switch; 5. Optical splitter coupler; 6. Calibration light source; 7. Multimode fiber; 8. Fiber optic mode enhancement device; 9. Area array detector; 10. Temperature control device; 11. Vibration attenuation device; 12. Rotary tuning structure; 13. Moving rod; 14. Fixed rod; 15. Area array detector coupler; 16. Fiber optic coupler. Detailed Implementation

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0040] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0041] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0042] This invention proposes for the first time a mechanical perturbation method to process the scattering medium of a speckle wavelength meter, enhancing the coupling between different modes, increasing the phase delay in the scattering medium, and increasing the number of excitation modes. This improves the resolution and speckle information density per unit area of ​​the speckle wavelength meter. The increased speckle information density allows for a smaller target area for the photosensitive camera, thereby increasing the sampling speed of the speckle wavelength meter.

[0043] For details, please refer to Figure 1 A high-resolution speckle wavelength measurement device includes a housing 1. The outer wall of the housing 1 has a first optical fiber inlet 2 and a second optical fiber inlet 3. Inside the housing 1 are an optical switch 4, a beam splitter 5, a calibration light source 6, and a test optical path. The test optical path consists of a multimode fiber 7, an optical fiber mode enhancement device 8, and an array detector 9. The entire calibration and measurement process involves three light sources: a calibration light source, a standardization light source, and a light source under test, referred to as the first beam, the second beam, and the third beam, respectively. All three beams pass through the test optical path. The calibration light source 6 is used to compensate for speckle pattern drift in the multimode fiber 7 caused by environmental disturbances. The optical splitter 5 is used in combination with the optical switch 4 to achieve optical path switching. The multimode fiber 7, as the speckle generation medium, is integrated into the optical path. The fiber mode enhancement device 8 acts directly on the multimode fiber 7 to enhance the optical path coupling in the medium. The area array detector 9 is used to receive the speckle pattern, and its spectral response range covers the measurement bandwidth required by the system. A high frame rate area array detector is used for speckle acquisition to ensure that the speckle wavelength meter has a high sampling rate. The fiber mode enhancement device 8 has a supporting fiber structure for generating small macrobending in the multimode fiber 7 and a tunable mechanism for controlling the degree of macrobending in the multimode fiber 7.

[0044] The calibration light source 6 is a light source with narrow linewidth and highly stable output wavelength. The calibration light source 6 is a helium-neon laser or an acetylene frequency-stabilized light source.

[0045] The operating bandwidth of the beam splitter 5 and the optical switch 4 covers the visible light band or the near-infrared band, and the operating wavelength range of the beam splitter 5 and the optical switch 4 is configured to simultaneously cover the band of the light source under test and the wavelength of the calibration light source.

[0046] The operating wavelength range of the multimode fiber 7 covers the measurement bandwidth (including the visible light band or near-infrared band). The multimode fiber 7 is a step-index multimode fiber with a core diameter between 50μm and 60μm and a length greater than 0.5m.

[0047] Please see Figure 2 The fiber optic mode enhancement device 8 is also equipped with a temperature control device 10 and a vibration attenuation device 11. The temperature control device 10 is specifically in the form of a temperature control box or similar structure. The temperature control method is PID (proportional-integral-derivative) control to reduce wavelength drift caused by changes in the external environment of the measuring device. The vibration attenuation device 11 is in the form of a vibration isolation pad or similar structure to reduce wavelength drift caused by changes in external vibration of the measuring device.

[0048] Please see Figure 3 The fiber mode enhancement device 8 has a toothed structure. The multimode fiber 7 is clamped inside the fiber mode enhancement device 8. The fiber mode enhancement device 8 includes a rotary tuning structure 12, a moving rod 13, a fixed rod 14, a fiber coupler 16, and a surface array detector coupler 15. The multimode fiber 7 is coiled on the fixed rod 14. The rotary tuning structure 12 is connected to the moving rod 13. The rotary tuning structure 12 is used to tune the distance between the moving rod 13 and the fixed rod 14. The distance between the moving rod 13 and the fixed rod 14 determines the degree of mode enhancement of the multimode fiber 7 by the fiber mode enhancement device 8. The fiber coupler 16 is used to connect to the light source under test. The surface array detector coupler 15 is used to assemble with the surface array detector 9.

[0049] A high-resolution speckle wavelength measurement method includes the following steps:

[0050] S1: When the laser propagates in the optical fiber, the multimode fiber 7 is processed by tunable compression. After being mechanically disturbed, the internal mode coupling mode of the multimode fiber 7 changes, thereby causing a greater difference in the speckle pattern with wavelength variation. During this process, the light under test... When propagating in a multimode optical fiber, the electric field is expressed as: The modal superposition can be calculated using the following formula:

[0051]

[0052] In the formula Let r be the spatial distribution of the electric field of light throughout the optical fiber (r = (x,y) cross section, z is the propagation direction), a(z) be the mode amplitude, and the intensity (including power and phase) of mode m in the propagation direction z. Transverse electric field mode, Modal propagation factor in the z-direction;

[0053] S2: After being subjected to mechanical disturbance, the orthogonality of some paths is disrupted, and energy exchange occurs between different paths, causing modal coupling, such as the two modes of propagation. , When passing through this disturbance point, the modal electric field is calculated according to the following formula:

[0054]

[0055] When the degree of disturbance increases, if As the disturbance decreases, Then, as the disturbance increases, the energy will decrease from... Flow direction In a similar process, energy can also flow to inefficient modes, making them efficient transmission modes, thereby increasing the degree of intermodal coupling.

[0056] S3: The fiber mode enhancement device 8 adds a mode coupling drive to the propagation of light in the multimode fiber 7. During propagation, the refractive index of the fiber becomes:

[0057]

[0058] In the formula The refractive index when undisturbed. This represents the perturbation to the refractive index in the z-direction, under which the mode enhancement of the multimode fiber is:

[0059]

[0060] in:

[0061] , representing the fiber perturbation enhancement coefficient;

[0062] S4: The mode enhancement method can be designed, and the perturbation structure is designed as a tooth shape. The mode enhancement form of the optical fiber is as follows:

[0063] In the formula The small change in the square of the refractive index of the optical fiber The transverse distribution function representing the disturbance. Represents the magnitude of the disturbance. This represents the periodic variation of the disturbance in the direction of light propagation. It is the spatial frequency of the fiber optic disturbance;

[0064] The mode enhancement of multimode fiber 7 approaches:

[0065]

[0066] In the formula The difference between the propagation constants of the two modes. The length of the disturbance region.

[0067] Example

[0068] In this embodiment, the difference between mode enhancement and speckle pattern in multimode fiber can be quantified using the following calculation method. This calculation method quantifies the evolution of the correlation of the speckle image with wavelength. Further, the wavelength half-width at half-maximum (HWHM) is defined as the wavelength offset corresponding to the speckle correlation coefficient decreasing to half its maximum value, denoted as the wavelength HWHM index, which reflects the sensitivity of the speckle wavelengthmeter to wavelength changes.

[0069]

[0070] In the formula, It is a function of the spectral correlation coefficient as a function of wavelength shift. This represents the light intensity detected at a spatial location (corresponding to the camera's pixel coordinates) on the plane of the area array detector at the center wavelength. This represents the new light intensity detected at the same spatial location after the laser wavelength has changed.

[0071] Please see Figure 4 The figure shows the correlation coefficient curve of the speckle image as a function of wavelength. In the simulation example, the calculated speckle gradually increases with the degree of mechanical disturbance. Based on the above simulation data and characteristic parameters, it can be seen that the perturbation structure of the optical fiber can improve the speckle pattern intensity under the same wavelength change, thereby improving the resolution of the speckle wavelength meter.

[0072] In actual testing, the calibration process is performed first. The first beam from the calibration light source enters the first fiber optic port 2. At this time, the optical switch 4 isolates the second and third beams from the optical path under test. After the first beam enters the test optical path, the first beam is tuned with a wide bandwidth and small step size. During this process, the speckle pattern after each tuning is continuously recorded as a wavelength information database.

[0073] After calibration, the second beam of the calibration light source 6 and the third beam of the light source under test are respectively connected to the optical switch 4 and the second optical fiber input port 3. The two beams are time-division multiplexed in the optical fiber coupling. After long-term use or after the measuring device is moved, the second beam of the calibration light source 6 can be connected to the measuring optical path and compared with the wavelength information database of the same wavelength to calculate the wavelength offset and perform data compensation.

[0074] During measurement, the third beam of the laser to be measured is connected to the device, and its speckle pattern is collected.

[0075] The matching degree between the speckle pattern under test and each reference speckle pattern in the calibration database is calculated using the transfer matrix method (existing technology is used here and will not be elaborated further). , The higher the value, the closer the wavelength to be measured is to the reference wavelength. The closer.

[0076] The wavelength to be measured is predicted using an interpolation algorithm, and the formula is as follows:

[0077]

[0078] in, For similarity, For reference wavelength, The wavelength to be measured, This represents the number of reference wavelength points.

[0079] Actual test results are as follows Figure 5 As shown, when measuring a high-stability laser source with a known wavelength of 1388nm, the standard deviation of the output results of the system within one hour is 0.00023nm. This result fully demonstrates that the device provided in this embodiment has high-precision and high-stability wavelength measurement capabilities.

[0080] like Figure 6 As shown, the multi-dimensional quantitative comparison of the similarity comparison criteria reveals that the peak and mean values ​​of the similarity comparison criteria for the enhanced multimode fiber are higher than those for the ordinary multimode fiber. Combined with the positive correlation between the similarity comparison criteria and structural fidelity and resolution, it can be concluded that the misaligned fusion spliced ​​multimode fiber outperforms the ordinary multimode fiber in terms of resolution. The greater difference in the similarity comparison criteria under the same wavelength tuning also indicates high sensitivity to the fine structure of the speckle pattern, further supporting the conclusion of improved resolution of the speckle wavelength meter.

[0081] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, as long as there is no structural conflict, the features in the disclosed embodiments can be combined with each other in any manner. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A high-resolution speckle wavelength measurement device, characterized in that, The device includes a housing (1), the outer wall of which is provided with a first optical fiber inlet (2) and a second optical fiber inlet (3). Inside the housing (1) are an optical switch (4), a beam splitter (5), a calibration light source (6), and a test optical path. The test optical path consists of a multimode fiber (7), an optical fiber mode enhancement device (8), and an array detector (9). The calibration light source (6) is used to compensate for the speckle pattern drift of the multimode fiber (7) caused by environmental disturbances. The beam splitter (5) is used in combination with the optical switch (4) to realize optical path switching. The multimode fiber (7) is integrated into the optical path as a speckle generation medium. The optical fiber mode enhancement device (8) acts directly on the multimode fiber (7) to enhance the optical path coupling in the medium. The array detector (9) is used to receive the speckle pattern. The optical fiber mode enhancement device (8) has a supporting fiber structure for generating small macrobending in the multimode fiber (7) and a tunable mechanism for controlling the degree of macrobending in the multimode fiber (7). The measurement method of this high-resolution speckle wavelength measurement device includes the following steps: S1: When the laser propagates in the optical fiber, the multimode fiber (7) is processed by tunable extrusion. After being mechanically disturbed, the internal mode coupling mode of the multimode fiber (7) changes, thereby causing the speckle pattern to produce greater differences in wavelength variation. During this process, the light under test... When propagating in a multimode optical fiber, the electric field is expressed as: The modal superposition can be calculated using the following formula: In the formula Let a(z) be the spatial distribution of the electric field of light throughout the optical fiber, a(z) be the amplitude of the mode, and m be the intensity of mode m in the propagation direction z. Transverse electric field mode, Modal propagation factor in the z-direction; S2: After being subjected to mechanical disturbance, the orthogonality of some paths is disrupted, and energy exchange occurs between different paths, causing modal coupling, such as the two modes of propagation. , When passing through this disturbance point, the modal electric field is calculated according to the following formula: When the degree of disturbance increases, if As the disturbance decreases, Then, as the disturbance increases, the energy will decrease from... Flow direction In a similar process, energy can also flow to inefficient modes, making them efficient transmission modes, thereby increasing the degree of intermodal coupling. S3: The fiber mode enhancement device (8) adds a mode coupling drive to the propagation of light in the multimode fiber (7). During propagation, the refractive index of the fiber becomes: In the formula The refractive index when undisturbed. This represents the perturbation to the refractive index in the z-direction, under which the mode enhancement of the multimode fiber is: in: , representing the fiber perturbation enhancement coefficient; S4: The mode enhancement method can be designed, and the perturbation structure is designed as a tooth shape. The mode enhancement form of the optical fiber is as follows: In the formula The small change in the square of the refractive index of the optical fiber The transverse distribution function representing the disturbance. Represents the magnitude of the disturbance. This represents the periodic variation of the disturbance in the direction of light propagation. It is the spatial frequency of the fiber optic disturbance; The mode enhancement of multimode fiber (7) approaches: In the formula The difference between the propagation constants of the two modes. The length of the disturbance region.

2. The high-resolution speckle wavelength measurement device according to claim 1, characterized in that, The calibration light source (6) adopts a narrow linewidth and highly stable output wavelength light source, and the calibration light source (6) is a helium-neon laser or an acetylene frequency-stabilized light source.

3. The high-resolution speckle wavelength measurement device according to claim 1, characterized in that, The operating bandwidth of the beam splitter (5) and the optical switch (4) covers the visible light band or the near-infrared band, and the operating wavelength range of the beam splitter (5) and the optical switch (4) is configured to simultaneously cover the band of the light source under test and the wavelength of the calibration light source.

4. The high-resolution speckle wavelength measurement device according to claim 1, characterized in that, The operating wavelength range of the multimode fiber (7) covers the measurement bandwidth. The multimode fiber (7) is a step-index multimode fiber with a core diameter between 50μm and 60μm and a length greater than 0.5m.

5. The high-resolution speckle wavelength measurement device according to claim 1, characterized in that, The fiber optic mode enhancement device (8) is also equipped with a temperature control device (10) and a vibration attenuation device (11).

6. The high-resolution speckle wavelength measurement device according to claim 1, characterized in that, The fiber mode enhancement device (8) has a toothed structure. The multimode fiber (7) is clamped inside the fiber mode enhancement device (8). The fiber mode enhancement device (8) includes a rotary tuning structure (12), a moving rod (13), a fixed rod (14), a fiber coupler (16), and an array detector coupler (15). The multimode fiber (7) is coiled on the fixed rod (14). The rotary tuning structure (12) is connected to the moving rod (13). The rotary tuning structure (12) is used to tune the distance between the moving rod (13) and the fixed rod (14). The fiber coupler (16) is used to connect to the light source under test. The array detector coupler (15) is used to assemble with the array detector (9).

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