Laser self-mixing interference system

Abstract

The utility model discloses a kind of laser self-mixing interference systems, including laser, first lens, attenuating sheet and second lens arranged in sequence, the laser of laser projector is transmitted through first lens, attenuating sheet and second lens in sequence, and is focused by first lens, attenuated light intensity by attenuating sheet and collimated after second lens, it is reflected by the object to be measured and along original light path returns into laser and occurs self-mixing interference.The laser self-mixing interference system of the utility model, attenuating sheet is combined with lens, good light path correction and attenuation effect are realized, so that the laser spot size on attenuating sheet can be adjusted, for common attenuating sheet product, attenuating sheet can be placed in the focal point close to first lens, at this time, the laser spot on attenuating sheet is very small, can avoid the interference caused by uneven local attenuation intensity of attenuating sheet.For attenuating sheet, attenuation intensity gradually reduces from center to edge, attenuation degree to laser can also be conveniently adjusted.

Description

Technical Field

[0001] This utility model belongs to the field of precision measurement technology, specifically relating to a laser self-mixing interferometry system. Background Technology

[0002] Laser self-mixing interference effect is a phenomenon in which the feedback light carrying information about the object interferes with the light inside the cavity after the laser output light is reflected by an external object, thus modulating the laser output characteristics. This phenomenon can be used to achieve precise measurement of physical quantities such as velocity, displacement, vibration, and distance.

[0003] like Figure 1 As shown, when the distance between the object under test and the laser is less than half the coherence length of a single-tube laser, the self-mixing interferometry system can be regarded as a coincident resonant cavity, which is equivalent to a three-mirror cavity model. Here, M1 and M2 are the front and rear resonant cavity surfaces of the laser, M is the external surface of the object under test, Ld is the laser cavity, and Le is the external cavity length.

[0004] In a dual-cavity laser system without optical feedback, standing wave generation can lead to excitation. The gain of the medium is sufficient to overcome absorption loss and geometric loss propagating at the cavity surface. The excitation condition is that the light wave has the same frequency after one round trip within the cavity. With optical feedback, assuming the light wave propagates to the right, the light wave is denoted as: u = Eexp[i(wt + kx + ψ)], where E is the amplitude of the light wave, x represents the direction of propagation, w is the frequency of the light wave, and ψ is the initial phase.

[0005] The light wave is split into two beams. One beam travels back and forth within the cavity, while the other beam passes through M2, is reflected by M, and is coupled back into the cavity. The two beams eventually superimpose at M1. When the system is stable, the superimposed wave should have the same frequency as the initial wave. The relevant formulas for the interference model can be calculated, and the beam pattern can be analyzed.

[0006] In laser self-mixing interferometry systems, the intensity of the feedback light also affects the waveform processing of the interference signal. Generally, weak feedback is required to make it easier to recover distance information from the waveform and achieve more accurate measurements. Therefore, the intensity of the emitted laser light needs to be attenuated in the system.

[0007] The information disclosed in this background section is intended only to enhance the understanding of the overall background of this utility model and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Utility Model Content

[0008] The purpose of this invention is to provide a laser self-mixing interference system that can achieve good optical path correction and attenuation effects.

[0009] To achieve the above objectives, the technical solution provided by a specific embodiment of this utility model is as follows:

[0010] A laser self-mixing interferometry system includes a laser, a first lens, an attenuator, and a second lens arranged in sequence. The laser emitted from the laser passes through the first lens, the attenuator, and the second lens in sequence, and is focused by the first lens, attenuated by the attenuator, and collimated by the second lens. After being reflected by the object under test, the laser returns to the laser along the original optical path and undergoes self-mixing interference.

[0011] In one or more embodiments of this invention, the attenuation intensity of the attenuator gradually decreases from the center to the edge.

[0012] In one or more embodiments of this utility model, a light-blocking area is provided at the center of the attenuator.

[0013] In one or more embodiments of this utility model, the diameter of the light-blocking area is greater than or equal to the diameter of the laser spot at the focal point of the first lens.

[0014] In one or more embodiments of the present invention, the laser self-mixing interferometry system further includes a first displacement mechanism, which is fixedly installed with the attenuator. The first displacement mechanism is used to adjust the distance between the attenuator and the focal point of the first lens to adjust the degree of attenuation of the laser.

[0015] In one or more embodiments of the present invention, the laser self-mixing interferometry system further includes a second displacement mechanism, which is fixedly installed with the first lens and the second lens. The second displacement mechanism is used to synchronously move the first lens and the second lens to adjust the distance between the focal point of the first lens and the attenuator, so as to adjust the degree of attenuation of the laser.

[0016] In one or more embodiments of the present invention, the laser self-mixing interferometry system further includes a reflector, which is positioned toward the object under test. The laser is reflected by the object under test to the reflector and then reflected between the reflector and the object under test before returning to the laser along the original optical path.

[0017] In one or more embodiments of this utility model, the angle between the reflector and the surface of the object to be measured satisfies:

[0018]

[0019] in, The angle between the laser and the surface of the object being measured is... Let k be the acute angle between the reflector and the surface of the object to be measured, where k is a positive integer.

[0020] In one or more embodiments of this utility model, the surface of the reflector is provided with an anti-reflection film.

[0021] In one or more embodiments of the present invention, the laser self-mixing interferometry system further includes a collimating lens disposed between the laser and the first lens, the collimating lens being used to collimate the laser; and / or the laser self-mixing interferometry system further includes a photoelectric converter disposed inside the laser to perform photoelectric conversion on the laser after self-mixing interferometry to generate an output signal.

[0022] Compared with existing technologies, the laser self-mixing interferometry system of this invention combines an attenuator with a lens to achieve excellent optical path correction and attenuation effects. The emitted laser is focused by a first lens, and then the attenuator is placed behind the first lens, making the size of the laser spot illuminating the attenuator adjustable. For common attenuator products, the attenuator can be placed close to the focal point of the first lens, resulting in a very small laser spot on the attenuator, thus avoiding interference caused by uneven local attenuation intensity.

[0023] If an attenuator with a gradually decreasing attenuation intensity from the center to the edge is used, the degree of laser attenuation can be easily adjusted by changing the relative distance between the attenuator and the focal point of the first lens, i.e., changing the size of the laser spot illuminating the attenuator. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the model of a laser self-mixing interferometry system in the existing technology.

[0026] Figure 2 This is a schematic diagram of the structure of a laser self-mixing interference system in one embodiment of the present invention.

[0027] Figure 3 This is a partial structural schematic diagram of a laser self-mixing interference system in one embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram of the attenuator structure in one embodiment of the present invention.

[0029] Figure 5This is a schematic diagram of the optical path of a laser self-mixing interference system in one embodiment of the present invention.

[0030] Figure 6 This is a partial structural schematic diagram of a laser self-mixing interference system in another embodiment of the present invention. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0032] The terms "coupled," "connected," or "linked" in this specification include both direct and indirect connections. Indirect connections are those made through an intermediate medium, such as those made through an electrically conductive medium, which may have parasitic inductance or capacitance. Indirect connections may also include connections made through other active or passive devices to achieve the same or similar functional purpose, such as connections through switches, follower circuits, or other circuits or components. Furthermore, in this specification, terms such as "first" and "second" are primarily used to distinguish one technical feature from another, and do not necessarily require or imply any actual relationship, quantity, or order between these technical features.

[0033] In the detailed description of this specification, reference is made to the accompanying drawings, which form a part thereof, wherein like reference numerals always denote like parts, and wherein exemplary embodiments are shown by way of example that may be implemented. It should be understood that other embodiments may be utilized, and structural or logical changes may be made, without departing from the scope of this application. Therefore, the following detailed description should not be considered limiting.

[0034] The various operations in the specification may be described sequentially as multiple discrete actions or operations in a manner most conducive to understanding the claimed subject matter. However, the order of description should not be construed as implying that these operations must be sequentially related. Specifically, these operations may not be performed in the order presented. The described operations may be performed in a different order than in the described embodiments. Various additional operations may be performed in additional embodiments and / or the described operations may be omitted.

[0035] For the purposes of this application, the phrase "A and / or B" means (A), (B), or (A and B). For the purposes of this application, the phrase "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0036] Various components and devices may be mentioned or shown in the singular form herein, but only for the convenience of discussion, and any element mentioned in the singular form may include multiple such elements as taught herein.

[0037] The description uses the phrases "in one embodiment," "in other embodiments," or "in some embodiments," each of which can refer to one or more of the same or different embodiments. Furthermore, the terms "comprising," "including," "having," etc., used in relation to embodiments of this application are synonymous.

[0038] Example 1

[0039] like Figure 2 As shown, a laser self-mixing interference system in one embodiment of the present invention includes a laser 10, a collimating lens 20, a first lens 30, an attenuator 40, a second lens 50, a first displacement mechanism 60, a reflector 70, and a photoelectric converter 80.

[0040] The laser 10, collimating lens 20, first lens 30, attenuator 40, and second lens 50 are arranged sequentially, with a reflector 70 facing the object to be measured. The laser emitted from the laser 10 passes sequentially through the collimating lens 20, first lens 30, attenuator 40, and second lens 50. After being focused by the collimating lens 20 and first lens 30, attenuated by the attenuator 40, and collimated by the second lens 50, the laser is reflected by the object to be measured to the reflector 70. After reflection between the reflector 70 and the object, the laser returns to the laser 10 along its original path, undergoing self-mixing interference. A photoelectric converter 80 is located inside the laser 10 to perform photoelectric conversion on the self-mixing interference laser to generate an output signal.

[0041] Specifically, the laser 10 uses a laser diode (LD) as the laser source, which has advantages such as low cost, high integration, and easy adjustment. The typical output wavelength of the laser diode is 1550nm. The laser 10 also includes a three-position adjustment bracket, on which the laser diode is fixed. After positioning, the screws are tightened, which facilitates the adjustment of the laser emission direction and angle to achieve optical path alignment, so that the reflected light can be smoothly coupled and returned to the resonant cavity of the laser 10.

[0042] Collimating lens 20 can be mounted on the emission window of laser 10. Due to the asymmetric structure of the active region of the laser diode's emitting area, the emitted beam's fast and slow axes form a cone with astigmatism, asymmetry, and high divergence. Its far field is elliptical, with its major and minor axes corresponding to the lateral and sideways directions, respectively. The divergence angle parallel to the junction plane (slow axis) is generally 5°~10°, while the divergence angle perpendicular to the junction plane (fast axis) can reach 10°~20°, which does not adequately meet the application requirements. To obtain a practical laser, an optical system is needed to collimate and correct the elliptical far-field spot in applications. By adding collimating lens 20 to collimate the laser beam, a beam with a small divergence angle and high collimation can be obtained, improving the efficiency of light energy utilization.

[0043] In other embodiments, the collimating lens 20 may not be provided.

[0044] Combination Figure 3 As shown, in one embodiment, the front focal point of the second lens 50 coincides with the rear focal point of the first lens 30 (point A in the figure) to ensure that the emitted laser can be restored to a collimated beam output by the second lens 50 (the front and rear focal points are determined according to the laser emission direction).

[0045] Combination Figure 4 As shown, in one embodiment, the attenuation intensity of the attenuator 40 gradually decreases from the center to the edge. A first displacement mechanism 60 is fixedly installed with the attenuator 40, and the first displacement mechanism 60 is used to adjust the distance between the attenuator 40 and the focal point of the first lens 30, so as to adjust the degree of laser attenuation by the attenuator 40.

[0046] In one embodiment, the attenuator 40 is typically made of a transparent material with a specific optical thin film coated on its surface. The effect of controlling the light attenuation intensity is achieved by controlling parameters such as the thickness and refractive index of the thin film.

[0047] In one embodiment, the first adjustment mechanism includes a first slide rail 61 and a first slider 62 slidably mounted along the first slide rail 61, with the attenuator 40 fixedly mounted on the first slider 62. A first displacement mechanism 60 moves the attenuator 40 back and forth along the laser optical axis. In other embodiments, the first adjustment mechanism may also employ methods including, but not limited to, a motor, a lead screw, or a movable mounting bracket to adjust the position of the attenuator 40.

[0048] When the attenuator 40 is close to the focal point of the first lens 30, the size of the laser spot illuminating the attenuator 40 is smaller, and the laser spot is concentrated in the area of ​​stronger attenuation intensity at the center of the attenuator 40, making the attenuator 40's attenuation effect stronger. Conversely, the farther the attenuator 40 is from the focal point of the first lens 30, the larger the size of the laser spot illuminating the attenuator 40, and the laser is more dispersed in the area of ​​weaker attenuation intensity on the attenuator 40, making the attenuation effect weaker. The degree of laser attenuation can be easily adjusted by changing the position of the attenuator 40. Furthermore, since the attenuator 40 is positioned between the first lens 30 and the second lens 50, and the distance between the first lens 30 and the second lens 50 is determined by their optical parameters, the attenuator 40 does not introduce additional installation space, which is beneficial for system miniaturization.

[0049] Preferably, the attenuator 40 has a light-blocking area 41 at its center, and the attenuation intensity of the light-blocking area 41 is 100% to achieve complete laser attenuation.

[0050] Furthermore, the diameter of the light-blocking area 41 is greater than or equal to the diameter of the laser spot at the focal point of the first lens 30, ensuring that the laser at the focal point of the attenuator 40 and the first lens 30 can be completely attenuated.

[0051] In other embodiments, the first adjustment mechanism may be omitted, and the position of the attenuator 40 may be changed manually.

[0052] In other embodiments, the attenuator 40 may also have a uniform overall attenuation intensity or exhibit other varying trends. Even when using a uniform attenuator, the size of the laser spot illuminating the attenuator can be changed by adjusting the position of the attenuator, thus avoiding interference caused by uneven local attenuation intensity of the attenuator.

[0053] Combination Figure 2 and Figure 5 As shown, the angle between the reflector 70 and the surface of the object to be measured satisfies:

[0054]

[0055] in, The angle between the laser and the surface of the object being measured. Let k be the acute angle between the reflector 70 and the surface of the object to be measured, and k be a positive integer. Here, the coefficient k represents the number of times the laser beam is reflected between the reflector 70 and the surface of the object to be measured. When the above formula is satisfied, after the laser beam is reflected k times between the reflector 70 and the surface of the object to be measured, it will be perpendicular to either the reflector 70 or the surface of the object to be measured, causing the laser beam to return along its original path.

[0056] In one embodiment, the surface of the object to be measured can be regarded as a reflective plane, which can be achieved by covering it with an anti-reflective film or other means. The laser self-mixing interferometry system of this solution can also be used to measure the liquid surface.

[0057] For example, , At this point, the laser beam is reflected three times between the surface of the object under test and the reflector 70, and then returns perpendicular to the reflector 70, following the original optical path. If the object under test is displaced by x along the incident direction of the laser, it can be seen that the optical path length has increased by 3.22x. Compared with the traditional scheme without a reflector module, this achieves a doubling of the optical path length for the same displacement, thus effectively amplifying the minute displacement of the object under test and improving the resolution.

[0058] In other embodiments, the angle between the reflector and the surface of the object to be measured can be set according to the actual required resolution.

[0059] Preferably, the surface of the reflector 70 is provided with an anti-reflection coating to improve the reflection effect and reduce light loss. The anti-reflection coating can be disposed on the side of the reflector 70 facing the object to be measured.

[0060] Preferably, the laser incident direction is parallel to the direction of translational movement of the object under test, and the reflector 70 remains stationary. As the object under test translates, the angle between it and the reflector 70 remains consistent, ensuring that the object exhibits the same waveform amplification under different displacements, thus more accurately recovering displacement information and improving the ability to resolve minute distances.

[0061] In other embodiments, the reflector 70 may not be provided. In this case, after the emitted laser shines on the surface of the object to be tested, it is directly reflected by the surface of the object to be tested and returns to the laser 10 along the original optical path to undergo self-mixing interference.

[0062] The photoelectric converter 80 may include a photodiode, which is built behind the resonant cavity of the laser 10 to ensure that the self-mixed interference laser signal can be received by the photodiode after escaping from the cavity surface of the resonant cavity and photoelectrically converted into an output signal by the photodiode.

[0063] The self-mixing interference laser signal, that is, the output signal is generally a tilted sawtooth waveform, can be used to calculate the displacement of the object under test using the following formula:

[0064]

[0065] In the formula, L0 is the initial external cavity length, k is the number of interference fringes between two adjacent inflection points of the displacement, and the sign of its coefficient depends on the tilt direction of the interference signal, i.e., the direction of motion of the object under test. λ is the laser wavelength, and a is the magnification factor of the optical path after adding a 70° reflector. At this time, the measurement resolution is improved to λ / 2a. It can also be seen that the number of fringes when the tilt direction of the output signal flips indicates the magnitude of the vibration of the object under test, and the frequency at which the tilt direction flips is the vibration frequency of the vibrating object.

[0066] In practical work, the data acquisition and analysis system can also be used to collect and analyze the output signals to accurately measure the displacement information of the object under test.

[0067] Example 2

[0068] like Figure 6 As shown, the laser self-mixing interferometry system in this embodiment differs from that in Embodiment 1 only in that the first displacement mechanism 60 is removed and a second displacement mechanism 90 is added; all other components remain unchanged. The second displacement mechanism 90 will be described below:

[0069] Specifically, the second displacement mechanism 90 is fixedly installed with the first lens 30 and the second lens 50. The second displacement mechanism 90 is used to synchronously move the first lens 30 and the second lens 50, and adjust the distance between the focal point of the first lens 30 and the attenuator 40 to adjust the degree of laser attenuation.

[0070] In one embodiment, the second adjustment mechanism includes a second slide rail 91 and a second slider 92 slidably mounted along the second slide rail 91. The first lens 30 and the second lens 50 are fixedly mounted on the second slider 92. The second displacement mechanism 90 moves the first lens 30 and the second lens 50 back and forth along the laser optical axis. In other embodiments, the second adjustment mechanism may also employ methods including, but not limited to, a motor, a lead screw, or a movable mounting bracket to adjust the position of the first lens 30 and the second lens 50.

[0071] In one embodiment, the second displacement mechanism 90 moves the first lens 30 and the second lens 50 back and forth along the laser optical axis. During the synchronous movement of the first lens 30 and the second lens 50, the front focal point of the second lens 50 always coincides with the rear focal point of the first lens 30 (the front and rear focal points are determined based on the laser emission direction), ensuring that the emitted laser beam can be restored to a parallel beam output by the second lens 50. Because the focal points of the two lenses coincide, the synchronous movement of the first lens 30 and the second lens 50 does not affect the focusing and collimation of the laser.

[0072] When the first lens 30 and the second lens 50 move closer to the focal point of the attenuator 40, the size of the laser spot illuminating the attenuator 40 becomes smaller, and the laser spot is concentrated in the central area of ​​the attenuator 40 where the attenuation intensity is stronger, making the attenuator 40's attenuation effect stronger. Conversely, when the attenuator 40 moves further away from the focal point of the first lens 30, the size of the laser spot illuminating the attenuator 40 becomes larger, and the laser light is more dispersed in the area of ​​the attenuator 40 where the attenuation intensity is less strong, making the attenuator 40's attenuation effect weaker.

[0073] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0074] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A laser self-mixing interferometry system, characterized in that, The system includes a laser, a first lens, an attenuator, and a second lens arranged in sequence. The laser emitted from the laser passes through the first lens, the attenuator, and the second lens in sequence. After being focused by the first lens, attenuated by the attenuator, and collimated by the second lens, the laser is reflected by the object under test and returns to the laser along the original optical path, resulting in self-mixing interference.

2. The laser self-mixing interferometry system according to claim 1, characterized in that, The attenuation intensity of the attenuator gradually decreases from the center to the edge.

3. The laser self-mixing interferometry system according to claim 1, characterized in that, The attenuator has a light-blocking area at its center.

4. The laser self-mixing interferometry system according to claim 3, characterized in that, The diameter of the light-blocking area is greater than or equal to the diameter of the laser spot at the focal point of the first lens.

5. The laser self-mixing interferometry system according to any one of claims 1 to 4, characterized in that, The laser self-mixing interferometry system further includes a first displacement mechanism, which is fixedly installed with the attenuator. The first displacement mechanism is used to adjust the distance between the attenuator and the focal point of the first lens to adjust the degree of attenuation of the laser.

6. The laser self-mixing interferometry system according to any one of claims 1 to 4, characterized in that, The laser self-mixing interferometry system further includes a second displacement mechanism, which is fixedly installed with the first lens and the second lens. The second displacement mechanism is used to synchronously move the first lens and the second lens to adjust the distance between the focal point of the first lens and the attenuator, so as to adjust the degree of attenuation of the laser.

7. The laser self-mixing interferometry system according to claim 1, characterized in that, The laser self-mixing interferometer system also includes a reflector, which is positioned facing the object under test. The laser is reflected by the object under test to the reflector, and after being reflected between the reflector and the object under test, it returns to the laser along the original optical path.

8. The laser self-mixing interferometry system according to claim 7, characterized in that, The angle between the reflector and the surface of the object to be measured satisfies: in, The angle between the laser and the surface of the object being measured is... Let k be the acute angle between the reflector and the surface of the object to be measured, where k is a positive integer.

9. The laser self-mixing interferometry system according to claim 7, characterized in that, The surface of the reflector is provided with an anti-reflective coating.

10. The laser self-mixing interferometry system according to claim 1, characterized in that, The laser self-mixing interferometry system further includes a collimating lens disposed between the laser and the first lens, the collimating lens being used to collimate the laser; and / or The laser self-mixing interferometry system also includes a photoelectric converter, which is disposed inside the laser to perform photoelectric conversion on the laser after self-mixing interferometry to generate an output signal.

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