Laser speckle suppression device and method

Abstract

The application discloses a kind of laser speckle suppression device and method, belong to optical technology field, by laser light source, collimating lens, half-transmission half-reflection mirror, light splitting film layer array, detector is formed, laser light source output coherent laser;Collimating lens is collimated after laser beam, again by half-transmission half-reflection mirror vertical injection light splitting film layer array;Light splitting film layer array will incident beam be divided into multiple non-coherent and light intensity equal sub-beam.The present application is static speckle suppression device, does not need power supply and drive, device structure is compact, small in size, low energy consumption, long service life;This device structure is simple, and the effect of speckle suppression is good, can be divided into N beam light intensity equal non-coherent light for laser beam, at most the speckle contrast of laser is reduced to 1 / N of original 1 / 2 .

Description

Technical Field

[0001] This invention relates to the field of optical technology, and more specifically to a laser speckle suppression device and method. Background Technology

[0002] Lasers possess advantages such as high monochromaticity, strong directionality, high brightness, long lifespan, and high integration, making them widely applicable across various fields. When used in the display industry, lasers offer unique advantages as a light source: high color saturation, rich spectral lines, and high brightness, enabling high-brightness, large-screen displays and improving energy efficiency. However, the high monochromaticity of laser light sources also leads to strong coherence. When laser light is projected onto a rough screen, speckle appears. The image perceived by the human eye is obscured by speckle, which degrades image quality and makes it difficult for the human eye to extract useful information. Therefore, suppressing speckle has always been a research hotspot in the fields of laser projection and laser technology.

[0003] To suppress laser speckle, methods such as wavelength diversity, angle diversity, and polarization diversity can be introduced. Wavelength diversity involves rapidly changing the laser wavelength by introducing multiple single-wavelength light sources or a single broadband light source, thus suppressing speckle. However, this method has limited effectiveness and is not suitable for fields such as laser displays. Angle diversity involves rapidly changing the illumination or viewing angle of the light source, such as using an array of light sources at different angles. However, this method has the drawback of only suppressing speckle in the overlapping beam area; light in other areas cannot be utilized, resulting in very low light energy utilization. Polarization diversity involves introducing the superposition of two orthogonally polarized beams to suppress speckle. The drawback of this method is that it can only reduce speckle contrast by a maximum of half.

[0004] Therefore, providing a laser speckle suppression device and method that can improve light energy utilization and reduce speckle contrast is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a laser speckle suppression device and method, which employs a method of destroying spatial coherence to suppress speckle. This is achieved by dividing the light source into an array of N incoherent sub-beams of equal intensity, with a certain time delay between each sub-beam. When the time delay is greater than or equal to the coherence time, the spatial coherence of the entire light source is destroyed. Using this method, dividing the light source into N incoherent sub-beams of equal intensity can reduce the speckle contrast to at most 1 / N of its original value. 1 / 2 .

[0006] To achieve the above objectives, the present invention provides a laser speckle suppression device, comprising a laser source, a collimating lens, a semi-transparent and semi-reflective mirror, a beam-splitting film array, and a detector arranged sequentially.

[0007] The laser source is used to output a coherent laser beam;

[0008] The collimating lens is used to shape the coherent laser beam output from the laser source into a collimated beam;

[0009] The semi-transparent and semi-reflective mirror is used to vertically incident the collimated beam into the beam-splitting film array, and to reflect several sub-beams output after being processed by the beam-splitting film array into the detector.

[0010] The beam-splitting array is used to split the incident beam into several incoherent sub-beams with equal intensity.

[0011] Preferably, the laser source is a semiconductor laser, and the operating wavelength is the visible light band or the near-infrared band.

[0012] Preferably, the beam-splitting array consists of several beam-splitting layers. After passing through the beam-splitting layers, the light beam is split into several sub-beams, and the number of sub-beams is consistent with the number of beam-splitting layers. To ensure that the intensity of the sub-beams after beam splitting is equal, the transmittance-reflection ratios of the several beam-splitting layers are different, and the transmittance-reflection ratio of each beam-splitting layer in the beam-splitting array is specifically designed.

[0013] Preferably, the distance between adjacent beam-splitting layers is greater than half the coherence length of the laser source. The spacing between adjacent beam-splitting layers ensures that the time delay of the beam passing through different beam-splitting layers is greater than or equal to the coherence length of the laser, thereby disrupting the spatial coherence of the laser beam and suppressing speckle. After the laser speckle suppression device designed in this scheme is applied, the laser beam is split into N sub-beams of equal intensity, which can reduce the speckle contrast of the laser source to at most 1 / N of its original value. 1 / 2 .

[0014] Preferably, the spectrophotometer layer comprises a dielectric thin film layer and a substrate material. The dielectric thin film layer is composed of a single-layer dielectric thin film or multiple-layer dielectric thin films, and the material of the dielectric thin film is SiO2 film, TiO2 film, Ta2O5 film, TiO2 / SiO2 film system, etc. Its transmittance-to-reflection ratio is determined by the refractive index of the film material and the thickness of the film layer.

[0015] On the other hand, the present invention provides a laser speckle suppression method, comprising:

[0016] The incident laser beam output from the laser source is collimated by the collimating lens and then perpendicularly incident into the beam splitting film array through the semi-transparent and semi-reflective mirror.

[0017] The incident laser beam is split into several incoherent sub-beams of equal intensity through reflection and transmission by the beam-splitting array; this can reduce the speckle contrast of the laser to at most 1 / N of its original value. 1 / 2 .

[0018] The sub-beams are then reflected into the detector by the semi-transparent mirror. After the laser beam is split by the beam-splitting film array, each sub-beam is emitted coaxially after passing through the semi-transparent mirror. The emitted beam has good collimation and high energy utilization.

[0019] Preferably, the incident laser beam is split into several incoherent sub-beams of equal intensity by the reflection and transmission of the beam-splitting film array, including:

[0020] The processed incident laser beam is incident perpendicularly into a beam-splitting layer array, which includes several beam-splitting layers arranged in sequence. When the incident laser beam passes through the first beam-splitting layer, a first sub-beam is separated. The first sub-beam returns to the semi-transparent mirror, and the remaining incident laser beam is transmitted through the first beam-splitting layer to the adjacent beam-splitting layer.

[0021] The adjacent beam-splitting layers split the remaining incident laser beam into a second sub-beam and a remaining laser beam. The second sub-beam returns to the semi-transparent mirror through the first beam-splitting layer, and so on until the last beam-splitting layer, resulting in multiple incoherent sub-beams with equal intensity.

[0022] Preferably, the transmittance-reflection ratios of the plurality of beam-splitting layers are all different, and the distance between adjacent beam-splitting layers is greater than half the coherence length of the laser beam.

[0023] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a laser speckle suppression device and method, which is a static speckle suppression device that does not require a power supply or drive. The device has a compact structure, small size, low energy consumption, and long service life. In this invention, a beam-splitting array is used to split the laser beam. The beam-splitting array contains beam-splitting layers with different transmittance-reflection ratios, which can divide the laser beam into several sub-beams of equal intensity. The optical path difference generated by the sub-beams passing through adjacent beam-splitting layers is greater than or equal to the coherence length of the laser beam, which can destroy the temporal coherence of the laser. The sub-beams after splitting are coaxially emitted, and the emitted beams have good collimation and energy utilization. This device has a simple structure, good speckle suppression effect, and can divide the laser beam into N incoherent beams of equal intensity, reducing the laser speckle contrast to at most 1 / N of the original. 1 / 2 . Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the overall structure of the laser speckle suppression device disclosed in this invention.

[0026] Figure 2 This is a schematic diagram of the principle of generating sub-beams of the same intensity in the laser speckle suppression device disclosed in this invention.

[0027] Figure 3 This is a schematic diagram showing the setting of the distance between adjacent beam-splitting film layers in the laser speckle suppression device disclosed in this invention.

[0028] Figure 4 This is a schematic diagram of the optical path of the beam incident when the beam-splitting film is coated with a single layer in the laser speckle suppression device disclosed in this invention.

[0029] Figure 5 This is a schematic diagram of the optical path of the beam incident when the beam-splitting film is coated with multiple films in the laser speckle suppression device disclosed in this invention.

[0030] Figure Labels

[0031] 1-Laser source, 2-Collimating lens, 3-Semi-transparent mirror, 4-Beam-splitting film array, 5-Beam-splitting film, 6-Incident laser beam, 7-Sub-laser beam, 8-Detector, 9-Substrate material, 10-Dielectric thin film, 11-Dielectric thin film layer. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention discloses a laser speckle suppression device, such as... Figure 1 As shown, the laser speckle suppression device includes a laser source 1, a collimating lens 2, a semi-transparent and semi-reflective mirror 3, a beam splitting film array 4, a beam splitting film 5, an incident laser beam 6, a sub-laser beam 7, and a detector 8.

[0034] Laser source 1 is a semiconductor laser that outputs a coherent incident laser beam 6. Collimating lens 2 shapes the incident laser beam 6 output by laser source 1 into a collimated beam. After passing through a semi-transparent and semi-reflective mirror 3, it is perpendicularly incident into a beam splitting layer array 4. The beam splitting layer array 4 is composed of several beam splitting layers 5 with different transmittance and reflection ratios, which are used to split the incident laser beam 6 into multiple incoherent sub-beams 7 with equal light intensity.

[0035] In laser speckle suppression devices, the beam-splitting film can be achieved by depositing a single-layer or multi-layer film. Its transmittance-to-reflectance ratio is determined by the refractive index and thickness of the film material. The film material can be SiO2, TiO2, Ta2O5, or a TiO2 / SiO2 film system, etc. The distance between adjacent beam-splitting films is set to be greater than or equal to the coherence length of the laser source, thereby disrupting the coherence between the split sub-beams.

[0036] This invention also discloses a laser speckle suppression method, such as... Figure 1 As shown, an incident laser beam 6 is emitted from a laser source 1, collimated by a collimating lens 2, and then perpendicularly incident on a beam-splitting array 4 after passing through a semi-transparent mirror 3. The beam-splitting array 4 consists of several beam-splitting layers 5 with different transmittance-to-reflection ratios. The incident laser 6 undergoes reflection and transmission through these layers 5, generating several sub-laser beams. These sub-laser beams exit from one side of the laser speckle suppression device after passing through the semi-transparent mirror 3 and are received by a detector 8. The emitted beam 7 is composed of several split sub-beams that are coaxial. The distance between adjacent beam-splitting layers is not less than half the coherence length of the laser source, ensuring that the time delay of the beam passing through different beam-splitting layers is greater than or equal to the coherence length of the laser, thereby disrupting the coherence of the incident laser beam and ensuring that the emitted sub-laser beams have equal intensity.

[0037] When the light source is split into multiple incoherent laser beams, the speckle contrast C of the laser beams... t The formula for calculating can be used as follows:

[0038]

[0039] Among them, I n Let N be the intensity of the nth laser beam; N be the total number of laser beams; and n be a positive integer less than N.

[0040] According to the above formula, when the intensity of each split laser beam is the same, the speckle contrast will reach its minimum value, which is [value missing]. The following describes in detail how to obtain multiple incoherent laser beams with equal intensity using the laser speckle suppression device of this invention.

[0041] Specifically, when the incident laser beam is incident perpendicularly into the beam-splitting array, after entering the first beam-splitting layer, part of the incident beam is reflected and part is transmitted. The transmitted light, upon passing through the second beam-splitting layer, is also partially reflected and partially transmitted. This process continues until the incident beam returns after passing through the last beam-splitting layer, at which point it has been divided into several sub-beams, and these sub-beams are coaxial.

[0042] Each beam-splitting layer in the beam-splitting array has a different transmittance-to-reflection ratio, the purpose of which is to ensure that the emitted sub-laser beams have the same intensity. The distance between adjacent beam-splitting layers is greater than or equal to half the coherence length of the laser, the purpose of which is to destroy the coherence between the sub-beams.

[0043] like Figure 2 As shown, 6 represents the incident laser beam, and 7-1, 7-2, ..., 7-n-1, 7-n represent the sub-beams after being split by the 1st, 2nd, ..., (n-1)th, and nth beam splitting layers, respectively. Figure 2 The individual laser beams after beam splitting are coaxial; for ease of illustration, they are drawn separately.

[0044] If the initial intensity of the incident laser beam is set to I0, and after passing through the beam splitting array, the beam is divided into N beams, then the intensity of the emitted sub-laser beam should be I0 / N.

[0045] When the incident light beam strikes the first beam-splitting layer perpendicularly, let its transmittance be T1, its reflectance be R1, and the transmitted light energy be E. T1 The reflected light energy is E R1 Neglecting absorption by the beam-splitting film material, T1 + R1 = 1. The intensity of the emitted sub-laser beam is I0 / N, therefore the reflectivity, transmittance, transmitted light energy, and reflected light energy of the first beam-splitting film are as follows:

[0046]

[0047]

[0048]

[0049]

[0050] When the incident light beam perpendicularly illuminates the path from the first beam splitter layer to the second beam splitter layer, let its transmittance be T2, its reflectance be R2, and the transmitted light energy be E. T2 The reflected light energy is E R2Neglecting absorption by the beam-splitting film material, T2 + R2 = 1. The intensity of the emitted sub-laser beam is I0 / N, therefore the reflectivity, transmittance, transmitted light energy, and reflected light energy of the second beam-splitting film are as follows:

[0051]

[0052]

[0053]

[0054]

[0055] Similarly, when the incident beam perpendicularly illuminates the nth beam splitter layer from the (n-1)th to the nth beam splitter layer, let its transmittance be T. n The reflectance is R n The transmitted light energy is E Tn The reflected light energy is E Rn If we disregard the absorption of the spectrophotometer layer material, then T n +R n =1. The intensity of the emitted sub-laser beam is I0 / N, therefore the reflectivity, transmittance, transmitted light energy, and reflected light energy of the nth beam-splitting layer are as follows:

[0056]

[0057]

[0058]

[0059]

[0060] Based on the above design method, the reflectivity and transmittance of different beam-splitting layers in the beam-splitting layer array are calculated according to the above formula, and N sub-laser beams with equal intensity can be obtained.

[0061] like Figure 3 As shown, 5-1, 5-2, ..., 5-n-1, 5-n represent the 1st, 2nd, ..., (n-1)th, and nth beam-splitting layers, respectively. The distance between two beam-splitting layers is d. To destroy the coherence between the sub-laser beams after beam splitting, the distance between two beam-splitting layers should be greater than or equal to half the laser coherence length. The laser coherence length is... Where λ represents the wavelength of the laser, the distance d between the two beam-splitting layers should be: 2d ≥ L, that is...

[0062] After determining the reflectivity and transmittance of each beam-splitting layer in the beam-splitting array, their reflectivity and transmittance can be determined by coating. The coating method can be either a single-layer film or a multi-layer film.

[0063] like Figure 4 The diagram shown illustrates a single-layer film deposition process for a beam-splitting coating. The single-layer film primarily consists of a dielectric thin film 10 and a substrate material 9. Let the refractive index of the incident medium be n0, the refractive index of the dielectric thin film be n1, and the refractive index of the substrate material be n... g If the geometric thickness of the film is d, then the reflectivity of the optical element surface after coating a single-layer thin film can be expressed as:

[0064]

[0065] The above formula shows that by selecting film materials with different refractive indices and setting different film geometric thicknesses, the desired reflectivity and transmittance of the spectral splitting film can be obtained.

[0066] like Figure 5 The diagram shows a multilayer thin film deposition layer for a beam splitter. The multilayer thin film structure consists of a dielectric thin film layer 11 and a substrate material 9. The dielectric thin film layer 11 is composed of N dielectric thin films with refractive indices n1, n2, n3, ..., n... j n j+1 ... n N-1 n N The geometric thicknesses of the films are d1, d2, d3, ..., d j d j+1 , ......, d N-1 d N Let the refractive index of the incident medium be n0, and the refractive index of the substrate material be n... g Then, the characteristic matrix of the entire film system after the multilayer thin film structure is deposited can be expressed as:

[0067]

[0068] The combined admittance of the multilayer thin film and the substrate material is Y = B / C, where B represents the admittance of the multilayer thin film and C represents the admittance of the substrate material. Therefore, the reflection coefficient and reflectivity of the entire multilayer dielectric thin film can be expressed as:

[0069]

[0070] For a non-absorbing medium membrane, its permeability is T = 1 - R.

[0071] The above formula shows that by selecting film materials with different refractive indices, different numbers of film layers, and setting different geometric thicknesses of film layers, the desired reflectivity and transmittance of the spectral splitting film can be obtained.

[0072] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0073] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A laser speckle suppression device, characterized in that, It includes a laser source, a collimating lens, a semi-transparent and semi-reflective mirror, a beam-splitting film array, and a detector arranged in sequence; The laser source is used to output a coherent laser beam; The collimating lens is used to shape the coherent laser beam output from the laser source into a collimated beam; The semi-transparent and semi-reflective mirror is used to vertically incident the collimated beam into the beam-splitting film array, and to reflect the several sub-beams output after being processed by the beam-splitting film array into the detector; The beam-splitting array is used to split the incident beam into several incoherent sub-beams of equal intensity. The distance between adjacent beam-splitting layers is greater than half the coherence length of the laser beam. The specific process includes: The processed incident laser beam is incident perpendicularly into a beam-splitting layer array, which includes several beam-splitting layers arranged in sequence. When the incident laser beam passes through the first beam-splitting layer, a first sub-beam is separated. The first sub-beam returns to the semi-transparent mirror, and the remaining incident laser beam is transmitted through the first beam-splitting layer to the adjacent beam-splitting layer. The adjacent beam-splitting layers split the remaining incident laser beam into a second sub-beam and the remaining laser beam. The second sub-beam returns to the semi-transparent mirror through the first beam-splitting layer, and so on until the last beam-splitting layer, resulting in multiple incoherent sub-beams with equal intensity. The optical path difference generated by the sub-beams passing through adjacent beam-splitting layers is greater than or equal to the coherence length of the laser beam, and the individual sub-beams after beam splitting are emitted coaxially.

2. The laser speckle suppression device according to claim 1, characterized in that, The laser source is a semiconductor laser.

3. The laser speckle suppression device according to claim 1, characterized in that, The beam-splitting film array consists of several beam-splitting film layers, and the transmittance and reflectance ratios of the several beam-splitting film layers are different.

4. The laser speckle suppression device according to claim 3, characterized in that, The spectral splitting film layer is composed of a dielectric thin film layer and a substrate material, wherein the dielectric thin film layer is composed of a single-layer dielectric thin film or multiple-layer dielectric thin films.

5. A method using the laser speckle suppression device according to claim 1, characterized in that, include: The incident laser beam output from the laser source is collimated by the collimating lens and then perpendicularly incident into the beam splitting film array by the semi-transparent and semi-reflective mirror. The incident laser beam is split into several incoherent sub-beams of equal intensity through reflection and transmission by the beam-splitting film array. The incoherent sub-beam is then coaxially reflected back into the detector by the semi-transparent mirror.

6. The method according to claim 5, characterized in that, The beam-splitting array consists of several beam-splitting layers, each with a different transmittance-to-reflection ratio, and the distance between adjacent beam-splitting layers is greater than half the coherence length of the laser beam.

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