Holographic grating preparation system and method

Abstract

The invention discloses a holographic grating preparation system and method, and belongs to the technical field of optics. The holographic grating preparation system comprises an exposure device which is used for generating a wavelength-tunable emergent light beam, dividing the emergent light beam into two light beams and enabling the two light beams to enter a holographic material layer so as to carry out interference exposure on the holographic material layer and form a holographic grating; the control device is used for determining a first interference wavelength according to the reproduction wavelength and the diffraction angle of the reproduction light beam and the refractive index of the holographic material layer; determining a first incident angle and a second incident angle according to the reproduction wavelength, the diffraction angle, the refractive index and the first interference wavelength; adjusting the wavelength of the emergent light beam to be the first interference wavelength, and correspondingly adjusting the incident angles of the two light beams to be the first incident angle and the second incident angle respectively. The manufacturing difficulty of the holographic grating can be reduced, and the diffraction efficiency uniformity of the holographic grating is improved.

Description

Technical Field

[0001] This application belongs to the field of optical technologies, and particularly relates to a holographic grating preparation system and method. Background Art

[0002] Currently, when fabricating the holographic grating 101 in an optical waveguide, a coupling prism 102 needs to be provided at the holographic grating, as Figure 1 shown. The light beams A1 and A2 interfere at the holographic grating 101, where the light beam A1 is perpendicularly incident on the holographic grating 101, and the incident angle of the light beam A2 is determined by the angle of the diffracted light A3. Additionally, a refractive index matching liquid 104 is filled between the coupling prism 102, the holographic grating 101, and the waveguide 103 to prevent total internal reflection of light at the interface between the coupling prism 102 and the holographic grating.

[0003] However, the setting of the coupling prism increases the difficulty of fabricating the holographic grating, thereby increasing the difficulty of mass-producing the optical waveguide. Moreover, problems such as air bubbles and uneven fitting exist in the refractive index matching liquid, which easily affect the interference effect of the light beams, thereby affecting the diffraction efficiency uniformity of the holographic grating. Summary of the Invention

[0004] This application aims to at least solve one of the technical problems existing in the prior art. For this purpose, this application provides a holographic grating preparation system and method, which can reduce the difficulty of fabricating the holographic grating and improve the diffraction efficiency uniformity of the holographic grating.

[0005] In a first aspect, this application provides a holographic grating preparation system, including:

[0006] An exposure device, configured to generate an output light beam with a tunable wavelength, divide the output light beam into two light beams, and incident the two light beams on a holographic material layer to perform interference exposure on the holographic material layer to form a holographic grating;

[0007] A control device, configured to determine a first interference wavelength according to the reproduction wavelength and diffraction angle of a reproduction light beam and the refractive index of the holographic material layer; determine a first incident angle and a second incident angle according to the reproduction wavelength, the diffraction angle, the refractive index, and the first interference wavelength; adjust the wavelength of the output light beam to the first interference wavelength, and respectively adjust the incident angles of the two light beams to the first incident angle and the second incident angle.

[0008] For the holographic grating preparation system according to the present application, the first interference wavelength, the first incident angle, and the second incident angle are determined based on the reproduction wavelength and diffraction angle of the reproduction beam and the refractive index of the holographic material layer, so as to adjust the wavelength of the light beam emitted by the exposure device to the first interference wavelength, and respectively adjust the incident angles of the two light beams into which the light beam is divided to the first incident angle and the second incident angle, so that the two light beams interfere at the holographic material layer to expose and form a holographic grating. There is no need to set a coupling prism, which reduces the difficulty of manufacturing the holographic grating, thereby reducing the difficulty of mass-producing optical waveguides. Moreover, there is no need to set a refractive index matching liquid, which improves the uniformity of the diffraction efficiency distribution of the holographic grating.

[0009] According to an embodiment of the present application, when the two light beams are respectively incident on opposite sides of the holographic material layer, the range of the first interference wavelength is:

[0010]

[0011] wherein, λ w is the first interference wavelength, λ r is the reproduction wavelength, θ is the diffraction angle, and n is the refractive index;

[0012] When the two light beams are incident on the same side of the holographic material layer, the range of the first interference wavelength is:

[0013]

[0014] According to an embodiment of the present application, the control device is further configured to:

[0015] Determine the wave vector of the reproduction wavelength according to the reproduction wavelength and the refractive index;

[0016] Determine the grating vector according to the wave vector of the reproduction wavelength and the diffraction angle;

[0017] Determine the wave vector of the first interference wavelength according to the first interference wavelength and the refractive index;

[0018] Determine the first incident angle and the second incident angle according to the wave vector of the first interference wavelength, the grating vector, the diffraction angle, and the refractive index.

[0019] According to an embodiment of the present application, the first incident angle and the second incident angle are respectively:

[0020]

[0021]

[0022]

[0023] Wherein, θ1 is the first incident angle, and θ2 is the second incident angle. is the grating vector. is the wave vector of the first interference wavelength, λ w is the first interference wavelength, λ r is the reproduction wavelength, θ is the diffraction angle, and n is the refractive index.

[0024] According to an embodiment of the present application, the control device is further configured to:

[0025] Obtain the refractive index of the holographic grating after exposure;

[0026] Determine a second interference wavelength according to the refractive index after exposure and the first interference wavelength;

[0027] Adjust the wavelength of the outgoing light beam to the second interference wavelength.

[0028] According to an embodiment of the present application, the second interference wavelength is:

[0029]

[0030] Wherein, λ' w is the second interference wavelength, λ w is the first interference wavelength, n is the refractive index of the holographic material layer before exposure, and n' is the refractive index of the holographic material layer after exposure.

[0031] According to an embodiment of the present application, when the two light beams are respectively incident on opposite sides of the holographic material layer, the control device is further configured to:

[0032] Obtain the material shrinkage rate of the holographic grating after exposure;

[0033] Determine a third interference wavelength, a third incident angle, and a fourth incident angle according to the material shrinkage rate;

[0034] Adjust the wavelength of the outgoing light beam to the third interference wavelength, adjust the incident angles of the two light beams to the third incident angle and the fourth incident angle respectively, and the included angle between the incident directions of the two light beams is 180°.

[0035] According to an embodiment of the present application, the control device is further configured to:

[0036] Determine the third interference wavelength according to the material shrinkage rate, the reproduction wavelength, and the diffraction angle;

[0037] Determine the third incident angle and the fourth incident angle according to the material shrinkage rate, the diffraction angle, and the refractive index.

[0038] According to an embodiment of the present application, the third interference wavelength is:

[0039]

[0040] where λ” w is the third interference wavelength, λ r is the reproduction wavelength, θ is the diffraction angle, and k is the material shrinkage rate;

[0041] The third incident angle and the fourth incident angle are respectively:

[0042]

[0043] where θ1′ is the third incident angle, θ2′ is the fourth incident angle, θ is the diffraction angle, k is the material shrinkage rate, and n is the refractive index.

[0044] According to an embodiment of the present application, when the two light beams are incident on the same side of the holographic material layer, the control device is further configured to:

[0045] Obtain the material shrinkage rate of the holographic grating after exposure;

[0046] Determine the third incident angle and the fourth incident angle according to the material shrinkage rate, the first interference wavelength, the reproduction wavelength, the refractive index, and the diffraction angle;

[0047] Adjust the incident angles of the two light beams to the third incident angle and the fourth incident angle respectively.

[0048] According to an embodiment of the present application, the third incident angle and the fourth incident angle are respectively:

[0049]

[0050]

[0051] where θ1′ is the third incident angle, θ2′ is the fourth incident angle, θ is the diffraction angle, k is the material shrinkage rate, n is the refractive index, and λ w is the first interference wavelength, and λ r is the reproduction wavelength.

[0052] According to an embodiment of the present application, the exposure device includes:

[0053] A laser for generating an output light beam with a tunable wavelength;

[0054] A polarization beam splitter for splitting the output light beam into two light beams;

[0055] A rearview mirror with an adjustable angle is used to reflect the two light beams respectively so as to make the two light beams incident on the holographic material layer;

[0056] The angle of the holographic material layer is adjustable. The control device is further configured to control the laser to adjust the wavelength of the emitted light beam, and control the angle of the rearview mirror and / or the holographic material layer to adjust the incident angles of the two light beams.

[0057] According to an embodiment of the present application, the exposure device further includes:

[0058] A shutter for controlling the on / off duration of the emitted light beam;

[0059] A polarization controller for controlling the polarization direction of the emitted light beam;

[0060] A spatial filter for filtering out high-order modes in the two light beams;

[0061] A collimation system for collimating the two light beams.

[0062] In a second aspect, the present application provides a method for preparing a holographic grating, including:

[0063] Determining a first interference wavelength according to the reproduction wavelength and diffraction angle of the reproduction light beam and the refractive index of the holographic material layer;

[0064] Determining a first incident angle and a second incident angle according to the reproduction wavelength, the diffraction angle, the refractive index and the first interference wavelength;

[0065] Controlling an exposure device to generate an emitted light beam with the first interference wavelength, splitting the emitted light beam into two light beams, and respectively making the two light beams incident on the holographic material layer at the first incident angle and the second incident angle to perform interference exposure on the holographic material layer to form a holographic grating.

[0066] One or more of the above technical solutions in the embodiments of the present application have at least one of the following technical effects:

[0067] By reproducing the reproduction wavelength and diffraction angle of the beam and the refractive index of the holographic material layer, the first interference wavelength, the first incident angle, and the second incident angle are determined, so as to adjust the wavelength of the outgoing light beam generated by the exposure device to the first interference wavelength, and respectively adjust the incident angles of the two light beams into which the outgoing light beam is divided to the first incident angle and the second incident angle, so that the two light beams interfere at the holographic material layer to expose and form a holographic grating. There is no need to set a coupling prism, which reduces the difficulty of manufacturing the holographic grating, thereby reducing the difficulty of mass-producing optical waveguides. Moreover, there is no need to set a refractive index matching liquid, which improves the uniformity of the diffraction efficiency distribution of the holographic grating.

[0068] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Description of the Drawings

[0069] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0070] Figure 1 is the exposure schematic diagram of the holographic grating in the related art;

[0071] Figure 2 is the structural schematic diagram of the holographic grating preparation system provided by the embodiment of the present application;

[0072] Figure 3 is the structural schematic diagram of the exposure device in the holographic grating preparation system provided by the embodiment of the present application;

[0073] Figure 4 is one of the k-vector diagrams in the holographic grating preparation system provided by the embodiment of the present application;

[0074] Figure 5 is another k-vector diagram in the holographic grating preparation system provided by the embodiment of the present application;

[0075] Figure 6 is yet another k-vector diagram in the holographic grating preparation system provided by the embodiment of the present application;

[0076] Figure 7 is still another k-vector diagram in the holographic grating preparation system provided by the embodiment of the present application;

[0077] Figure 8 is yet another k-vector diagram in the holographic grating preparation system provided by the embodiment of the present application;

[0078] Figure 9 is still another k-vector diagram in the holographic grating preparation system provided by the embodiment of the present application;

[0079] Figure 10It is the seventh k-vector diagram in the holographic grating preparation system provided by the embodiments of the present application;

[0080] Figure 11 It is a schematic flowchart of the holographic grating preparation method provided by the embodiments of the present application. Detailed implementation manners

[0081] Next, the technical solutions in the embodiments of the present application will be clearly described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present application.

[0082] The terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, rather than to describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. generally belong to the same category, and the number of objects is not limited. For example, the first object can be one or multiple. In addition, "and / or" in the specification and claims means at least one of the connected objects, and the character " / " generally represents an "or" relationship between the associated objects before and after.

[0083] Next, the holographic grating preparation system and method provided by the embodiments of the present application will be described in detail in conjunction with the accompanying drawings through specific embodiments and their application scenarios.

[0084] Figure 2 It is a schematic structural diagram of the holographic grating preparation system provided by the embodiments of the present application.

[0085] As Figure 2 shown, the holographic grating preparation system includes an exposure device 1 and a control device 2, and the exposure device 1 is connected to the control device 2.

[0086] The exposure device 1 is used to generate an output light beam with tunable wavelength, divide the output light beam into two light beams, and make the two light beams incident on the holographic material layer to perform interference exposure on the holographic material layer to form a holographic grating.

[0087] Combined with Figure 3 shown, the exposure device 1 can generate an output light beam and divide the output light beam into two light beams, namely a first light beam B1 and a second light beam B2. Among them, the first light beam B1 and the second light beam B2 can be incident on the same side of the holographic material layer 3, or can be respectively incident on the opposite sides of the holographic material layer 3. For example Figure 3As shown, the first light beam B1 is incident on the first side of the holographic material layer 3, and the second light beam B2 is incident on the second side of the holographic material layer 3. The first side and the second side are oppositely arranged. The first light beam B1 and the second light beam B2 perform interference exposure on the holographic material layer 3, and the holographic material layer 3 records interference fringes to form a holographic grating. Among them, the holographic grating can be a volume holographic grating. The holographic grating can be applied to an optical waveguide.

[0088] The control device 2 is used to determine the first interference wavelength, the first incident angle, and the second incident angle according to the reproduction wavelength and diffraction angle of the reproduction light beam and the refractive index of the holographic material layer, adjust the wavelength of the output light beam to the first interference wavelength, and respectively adjust the incident angles of the two light beams to the first incident angle and the second incident angle.

[0089] Since the holographic grating in the optical waveguide and its diffracted light are totally reflected in the waveguide, the exposure wavelength (i.e., the interference wavelength) needs to be consistent with the operating wavelength of the optical waveguide (i.e., the reproduction wavelength of the reproduction light beam). The reproduction wavelength and diffraction angle of the reproduction light beam can be preset according to the usage requirements of the optical waveguide. The control device 2 can determine the wavelengths of the two light beams that interfere during exposure (i.e., the first interference wavelength) and the incident angles of the two light beams incident on the holographic material layer (i.e., the first incident angle and the second incident angle) according to the reproduction wavelength and diffraction angle of the reproduction light beam and the refractive index of the holographic material layer.

[0090] The control device 2 controls the exposure device 1 according to the first interference wavelength, the first incident angle, and the second incident angle, so as to adjust the wavelength of the output light beam generated by the exposure device 1 to the first interference wavelength, and respectively adjust the incident angles of the two light beams to the first incident angle and the second incident angle, that is, adjust the incident angle of the first light beam B1 incident on the holographic material layer to the first incident angle, and adjust the incident angle of the second light beam B2 incident on the holographic material layer 3 to the second incident angle, so as to ensure that the holographic grating formed by the interference exposure of the first light beam B1 and the second light beam B2 on the holographic material layer 3 meets the usage requirements of the optical waveguide.

[0091] In this embodiment, the laser device 1 can generate an output light beam with a tunable wavelength, and the incident angles of the two light beams into which the output light beam is divided can be adjusted. After the control device 2 determines the first interference wavelength, the first incident angle, and the second incident angle according to the reproduction light beam, the exposure device 1 can adjust the wavelength of the output light beam to the first wavelength and adjust the incident angles of the two light beams to the first incident angle and the second incident angle respectively, so that the two light beams interfere at the holographic material layer 3 to form a holographic grating by exposure. There is no need to set a coupling prism, which reduces the difficulty of manufacturing the holographic grating, thereby reducing the difficulty of mass-producing optical waveguides. At the same time, there is no need to set a refractive index matching liquid, which improves the uniformity of the diffraction efficiency distribution of the holographic grating. When the optical waveguide is applied to an Augmented Reality (AR) near-eye display system, the improvement of the uniformity of the diffraction efficiency distribution of the holographic grating in the optical waveguide can improve the display effect of the AR display screen.

[0092] In some embodiments, the control device 2 is further configured to:

[0093] Determine the first interference wavelength according to the reproduction wavelength, the diffraction angle, and the refractive index;

[0094] Determine the first incident angle and the second incident angle according to the reproduction wavelength, the diffraction angle, the refractive index, and the first interference wavelength.

[0095] After the control device 2 obtains the reproduction wavelength and diffraction angle of the reproduction light beam and the refractive index of the holographic material layer, it can first determine the first interference wavelength according to the reproduction wavelength and diffraction angle of the reproduction light beam and the refractive index of the holographic material layer. Then, according to the first interference wavelength, the reproduction wavelength and diffraction angle of the reproduction light beam, and the refractive index of the holographic material layer, determine the first incident angle and the second incident angle.

[0096] In some embodiments, the control device 2 is further configured to:

[0097] Determine the wave vector of the reproduction wavelength according to the reproduction wavelength and the refractive index;

[0098] Determine the grating vector according to the wave vector of the reproduction wavelength and the diffraction angle;

[0099] Determine the wave vector of the first interference wavelength according to the first interference wavelength and the refractive index;

[0100] Determine the first incident angle and the second incident angle according to the wave vector of the first interference wavelength, the grating vector, the diffraction angle, and the refractive index.

[0101] The main parameter of the holographic grating is the grating vector, which is determined by the wavelength and the incident angle of the interfering beams. After determining the first interference wavelength, the grating vector can be determined first according to the reproduction wavelength and diffraction angle of the reproduction beam and the refractive index of the holographic material layer. Then, according to the first interference wavelength, the grating vector, the diffraction angle of the reproduction beam and the refractive index of the holographic material layer, the first incident angle and the second incident angle are determined.

[0102] For example, the reproduction wavelength of the reproduction beam is λ r , the diffraction angle is θ, and the refractive index of the holographic material layer is n. According to the reproduction wavelength λ r of the reproduction beam and the refractive index n of the holographic material layer, the wave vector of the reproduction wavelength is determined as It should be noted that the wave vector of the reproduction wavelength refers to the wave vector of the reproduction wavelength in the holographic grating. As shown in the k-vector diagrams of Figure 4 and Figure 5 , the wave vector of the reproduction wavelength is mainly on the k-vector circle 41. In the case where the two beams are incident on the opposite sides of the holographic material layer respectively, the wave vector of the reproduction wavelength is as shown in Figure 4 ; in the case where the two beams are incident on the same side of the holographic material layer, the wave vector of the reproduction wavelength is as shown in Figure 5 .

[0103] According to the wave vector of the reproduction wavelength and the diffraction angle θ of the reproduction beam, the grating vector is determined, where the diffraction angle θ is the angle between the diffracted light of the reproduction beam and the k z axis (negative half-axis), and the k z axis is perpendicular to the holographic material layer. As shown in the k-vector diagrams of Figure 4 and Figure 5 , the grating vector is inscribed in the k-vector circle 41, and at this time, the Bragg condition of the reproduction wavelength is satisfied.

[0104] The first interference wavelength is λ w , λ r >λ w . The wave vector of the first interference wavelength is mainly on the k-vector circle 42. Translate the grating vector so that the grating vector is inscribed in the k-vector circle 42. The line connecting the center of the circle to the point where the grating vector is tangent to the k-vector circle 42 is the wave vector of the first interference wavelength. It should be noted that the wave vector of the first interference wavelength is the wave vector of the first interference wavelength in the holographic grating.

[0105] The wave vector of the first interference wavelength is related to the first interference wavelength λ w and the refractive index n of the holographic material layer. The wave vector of the first interference wavelength is calculated by the formula According to the geometric relationship, the incident angles of the two interfering light beams in the holographic grating can be obtained as follows:

[0106]

[0107]

[0108] where θ wn1 and θ wn2 are the incident angles of the two light beams in the holographic grating respectively, and θ w is the angle between the wave vector of the first interference wavelength and the grating vector , satisfying

[0109] The wave vector of the first interference wavelength in air is mainly on the k-vector circle 43. Extend the wave vector of the first interference wavelength towards the k x axis (the k x axis is parallel to the entire material layer) to intersect with the k-vector circle 43. The line connecting the center of the circle to the intersection point is the wave vector of the first interference wavelength in air. According to the refraction law, the incident angles of the two interfering light beams (such as the first light beam B1 and the second light beam B2 in Figure 2 ) in air are respectively:

[0110]

[0111]

[0112] where θ1 is the first incident angle and θ2 is the second incident angle.

[0113] In the case where the two light beams (such as the first light beam B1 and the second light beam B2 in Figure 2 ) are respectively incident on the opposite sides of the holographic material layer, as shown in Figure 4 , according to the total reflection law of the optical waveguide, the range of the first interference wavelength λ w is:

[0114]

[0115] It should be noted that the first interference wavelength λ wWithin this range, the first incident angle θ1 and the second incident angle θ2 can both be between 0° and 90° to ensure that the two interfering light beams can be incident on the holographic material layer.

[0116] In some embodiments, the first interference wavelength λ w is At this time, the included angle between the incident directions of the two interfering light beams incident on the holographic material layer is 180°, that is, the incident directions of the two light beams are exactly opposite, reducing the angle control of the two light beams, thereby reducing the complexity of the exposure device 1.

[0117] In the case where the two light beams are incident on the same side of the holographic material layer, combined with Figure 5 shown, according to the total reflection law of the optical waveguide, the range of the first interference wavelength λ w is:

[0118]

[0119] In some embodiments, as Figure 3 shown, the exposure device 1 includes:

[0120] A laser 11 for generating an output light beam with a tunable wavelength;

[0121] A polarization beam splitter 12 for splitting the output light beam into two light beams;

[0122] A reflecting mirror 13 with an adjustable angle, used to reflect the two light beams respectively to make the two light beams incident on the holographic material layer;

[0123] The angle of the holographic material layer is adjustable. The control device 2 is further configured to control the laser 11 to adjust the wavelength of the output light beam, and control the angle of the reflecting mirror 13 and / or the holographic material layer 3 to adjust the incident angles of the two light beams.

[0124] Among them, the laser 11 is a wavelength continuously tunable laser, and the output light beam generated by the laser 11 can be a continuous laser with any wavelength within the visible light range. The wavelength range can be 400 nm to 760 nm. After determining the first interference wavelength, the control device 2 can control the wavelength of the output light beam generated by the laser 11 to be the first interference wavelength λ w .

[0125] The polarization beam splitter 12 can split the output light beam generated by the laser 11 into two perpendicularly propagating light beams. The two light beams propagate along two splitting optical paths respectively.

[0126] Two reflecting mirrors 13 are respectively provided on the two splitting optical paths to respectively reflect the two light beams so that the two light beams are incident on the holographic material layer 3. Among them, the two light beams can be incident on the same side of the holographic material layer 3, or the two light beams can be respectively incident on the opposite sides of the holographic material layer 3. The angles of the reflecting mirrors 13 are adjustable, and the angle of the holographic material layer 3 is adjustable. After determining the first incident angle θ1 and the second incident angle θ2, the control device 2 adjusts the angles of the two reflecting mirrors 13 and / or the angle of the holographic material layer 3 so that the two light beams are respectively incident on the opposite sides of the holographic material layer 3 at the first incident angle θ1 and the second incident angle θ2.

[0127] The position of the holographic material layer 3 is also adjustable. The control device 2 can adjust the position of the holographic material layer 3 so that the two light beams interfere at a specific position of the holographic material layer 3.

[0128] In some embodiments, the exposure device 2 further includes:

[0129] A shutter 14 for controlling the on-off duration of the outgoing light beam;

[0130] A polarization controller 15 for controlling the polarization direction of the outgoing light beam;

[0131] A spatial filter 16 for filtering out the high-order modes in the two light beams;

[0132] A collimation system 17 for collimating the two light beams.

[0133] Among them, the shutter 14 can be located on the outgoing light side of the laser 11. The shutter 14 can control the on-off of the outgoing light beam, thereby controlling the exposure time of the holographic grating. The polarization controller 15 can control the polarization direction of the outgoing light beam so that the polarization directions of the two light beams split from the outgoing light beam are kept consistent. In addition, the polarization beam splitter 12 can control the intensity ratio of the two light beams through the polarization controller 15. In some embodiments, the polarization controller 15 can be a half-wave plate.

[0134] Spatial filters 16 are also respectively provided on the two splitting optical paths. The spatial filters 16 can filter out the high-order modes in the two light beams and improve the spot quality of the two light beams. In some embodiments, the spatial filter 16 can be a small hole.

[0135] Collimation systems 17 are also respectively provided on the two splitting optical paths. The collimation systems 17 can collimate the light beams passing through the spatial filters 16. In some embodiments, the collimation system 17 can be an aspherical achromatic lens.

[0136] It should be noted that the exposure device 2 may further include other devices, which are not specifically limited here.

[0137] In some embodiments, the control device 2 is further used for:

[0138] Obtain the refractive index of the holographic grating after exposure;

[0139] Determine the second interference wavelength according to the refractive index after exposure and the first interference wavelength;

[0140] Adjust the wavelength of the outgoing light beam to the second interference wavelength.

[0141] The refractive index of the holographic material after exposure increases, resulting in an offset of the grating vector angle, that is, the deviation of the Bragg angle before and after exposure. As Figure 6 shown in the k-vector diagram, the two interfering light beams 111 and 112 and the grating vector 132 form a Bragg vector triangle on the k-vector circle 52. Due to the increase in the refractive index of the holographic material after exposure, the reproduced light beams of the same wavelength will form a Bragg vector triangle at a larger k-vector circle 51. Since the increase in the refractive index does not affect the grating vector, the grating vector 132 is translated and inscribed in the k-vector circle 51 to obtain the grating vector 131. The line connecting the center of the circle to the point where the grating vector 131 touches the k-vector circle 51 is the reproduced light beams 121 and 122. It can be seen that the reproduced light beams 121 and 122 are angularly offset compared to the two light beams 111 and 112, affecting the final optical waveguide effect.

[0142] In this embodiment, after the control device 2 obtains the refractive index after exposure, it determines the second interference wavelength according to the refractive index after exposure and the first interference wavelength, and adjusts the wavelength of the outgoing light beam generated by the laser 11 to the second interference wavelength, that is, the wavelengths of the two light beams into which the outgoing light beam is divided are the second interference wavelength, so as to solve the problem of the deviation of the Bragg angle before and after exposure.

[0143] For example, the refractive index of the holographic grating after exposure is n' = n + δn. In the case where the two light beams are respectively incident on the opposite sides of the holographic material layer, as Figure 7 shown in the k-vector diagram, the size of the k-vector circle 61 formed by the reproduced wavelength is If it is necessary to ensure that the directions of the reproduced light beams 221 and 222 are respectively the same as the directions of the two interfering light beams 211 and 212, it is necessary to ensure that the Bragg vector triangle formed by the grating vector 232, the reproduced light beams 221 and 222 is similar to the Bragg vector triangle formed by the grating vector 231, the two light beams 211 and 212. By adjusting the wavelengths of the two interfering light beams to the second interference wavelength λ' w , that is, adjusting the wavelength of the outgoing light beam generated by the laser to the second interference wavelength λ' w , so that the second interference wavelength λ' w forms a k-vector circle 62 with a size of Thereby ensuring that the Bragg angle before and after exposure does not deviate.

[0144] In the case where the two light beams are incident on the same side of the holographic material layer, the wavelength of the output light beam generated by the laser is also adjusted to the second interference wavelength. Thereby ensuring that the Bragg angle before and after exposure does not deviate.

[0145] In some embodiments, in the case where the two light beams are respectively incident on the opposite sides of the holographic material layer, the control device 2 is further configured to:

[0146] Obtain the material shrinkage rate of the holographic grating after exposure;

[0147] Determine the third interference wavelength, the third incident angle, and the fourth incident angle according to the material shrinkage rate;

[0148] Adjust the wavelength of the output light beam to the third interference wavelength, and adjust the incident angles of the two light beams to the third incident angle and the fourth incident angle respectively, and the included angle between the incident directions of the two light beams is 180°.

[0149] The polymerization of the holographic material monomers after exposure will cause the volume of the holographic material to shrink, which will in turn cause the deviation of the Bragg angle before and after exposure. As Figure 8 In the k-vector diagram shown, the two interfering light beams 311 and 312 and the grating vector 331 form a Bragg vector triangle on the k-vector circle 71. Since the holographic material shrinks in its thickness direction, the grating vector 331 will extend in the direction of the k z axis to obtain the grating vector 332. Translate the grating vector 332 to be inscribed in the k-vector circle 71 to obtain the grating vector 333. The line connecting the center of the circle to the contact point of the grating vector 333 and the k-vector circle 71 is the reproduced light beams 321 and 322. It can be seen that the reproduced light beams 321 and 322 deviate from the initial design values.

[0150] In this embodiment, in the case where the two light beams are respectively incident on the opposite sides of the holographic material layer, after the control device 2 obtains the material shrinkage rate of the holographic grating after exposure, it determines the third interference wavelength, the third incident angle, and the fourth incident angle according to the material shrinkage rate, and adjusts the wavelength of the output light beam of the laser 11 to the third interference wavelength. At the same time, the angles of the reflecting mirror and / or the holographic grating are controlled so that the incident angles of the two interfering light beams incident on the holographic grating are respectively adjusted to the third incident angle and the fourth incident angle, and the included angle between the incident directions of the two light beams is 180°, so as to solve the problem of the deviation of the Bragg angle before and after exposure.

[0151] In some embodiments, the control device 2 is further configured to:

[0152] Determine the third interference wavelength according to the material shrinkage rate, the reproduction wavelength, and the diffraction angle;

[0153] Determine the third incident angle and the fourth incident angle according to the material shrinkage rate, diffraction angle, and refractive index.

[0154] As Figure 9 In the k-vector diagram shown, the reproduced beams 411 and 412 and the grating vector 431 after material shrinkage form a Bragg vector triangle on the k-vector circle 81. The grating vector 432 is obtained by expanding the grating vector 431, and the grating vector 432 is translated to the center of the k-vector circle 81 to obtain the grating vector 433. Determine the third interference wavelength so that the diameter of the k-vector circle 82 corresponding to the third interference wavelength is the same as the length of the grating vector 433. The line connecting the center to the intersection of the grating vector 433 and the k-vector circle 82 is the two interfering beams 421 and 422.

[0155] For example, the reproduction wavelengths of the reproduced beams 411 and 412 are λ r , the angle between the reproduced beam 412 and the k z axis (negative half-axis) is θ (diffraction angle), and the grating vector 431 is The material shrinkage rate is k. According to geometric relations, the grating vector 432 is The angle with the k z axis (negative half-axis) is Therefore, the third interference wavelength is The angles between the two interfering beams 421 and 422 and the k z axis (negative half-axis) (i.e., the third incident angle θ1' and the fourth incident angle θ2') are And the directions of the two beams 421 and 422 are opposite, so as to ensure that the Bragg angles before and after exposure do not deviate.

[0156] In some embodiments, when the two beams are incident on the same side of the holographic material layer, the control device is further configured to:

[0157] Obtain the material shrinkage rate of the holographic grating after exposure;

[0158] Determine the third incident angle and the fourth incident angle according to the material shrinkage rate, the first interference wavelength, the reproduction wavelength, the refractive index, and the diffraction angle;

[0159] Correspondingly adjust the incident angles of the two beams to the third incident angle and the fourth incident angle respectively.

[0160] After exposure, the polymerization of the holographic material monomers causes the volume of the holographic material to shrink, which in turn leads to the deviation of the Bragg angle before and after exposure. In this embodiment, when two beams are incident on the same side of the holographic material layer, after obtaining the material shrinkage rate of the holographic grating after exposure, the control device 2 determines the third incident angle and the fourth incident angle according to the material shrinkage rate, the first interference wavelength, the reproduction wavelength, the refractive index, and the diffraction angle. The angles of the control mirror and / or the holographic grating are adjusted so that the incident angles of the two interfering beams on the holographic grating are respectively adjusted to the third incident angle and the fourth incident angle to solve the problem of the deviation of the Bragg angle before and after exposure. It should be noted that the wavelength of the light beam emitted by the laser 11 does not need to be adjusted, that is, the wavelength of the light beam emitted by the laser 11 remains the first interference wavelength

[0161] For example, the reproduction wavelength of the reproduction beam is λ r , and the refractive index of the holographic material layer is n. According to the reproduction wavelength λ r of the reproduction beam and the refractive index n of the holographic material layer, the wave vector of the reproduction wavelength is determined to be It should be noted that the wave vector of the reproduction wavelength refers to the wave vector of the reproduction wavelength in the holographic grating. As Figure 10 shown, the wave vector of the reproduction wavelength is mainly on the k-vector circle 91

[0162] According to the wave vector of the reproduction wavelength and the diffraction angle θ of the reproduction beam, the grating vector is determined. The material shrinkage rate is k. According to the geometric relationship, the grating vector is The angle between the z axis and k The wave vector of the first interference wavelength is mainly on the k-vector circle 92. The grating vector is translated so that the grating vector is inscribed in the k-vector circle 92. The line connecting the center of the circle to the point where the grating vector touches the k-vector circle 92 is the wave vector of the first interference wavelength. It should be noted that the wave vector of the first interference wavelength is the wave vector of the first interference wavelength in the holographic grating

[0163] According to the geometric relationship, the incident angles of the two interfering beams in the holographic grating can be obtained as follows

[0164]

[0165]

[0166] Among them, λ2 is the first interference wavelength, which needs to satisfy θ wn1 ′ and θ wn2 ′ are respectively the incident angles of the two light beams in the holographic grating,

[0167] The wave vector of the first interference wavelength in air is mainly on the k-vector circle 93. Extend the wave vector of the first interference wavelength towards the k x axis to intersect with the k-vector circle 93. The line connecting the center of the circle to the intersection point is the wave vector of the first interference wavelength in air. According to the refraction law, the incident angles of the two interfering light beams in air (i.e., the third incident angle θ1′ and the fourth incident angle θ2′) are respectively:

[0168]

[0169]

[0170] According to the holographic grating manufacturing system provided by the embodiments of the present application, the first interference wavelength, the first incident angle and the second incident angle can be determined according to the reproduction wavelength and diffraction angle of the reproduction light beam and the refractive index of the holographic material layer. During the exposure process, the laser is controlled to adjust the wavelength of the output light beam to the first interference wavelength, and the angles of the reflecting mirror and / or the holographic material layer are controlled to adjust the incident angles of the two light beams incident on the holographic material layer to be the first incident angle and the second incident angle respectively, so that the two light beams interfere at the holographic material layer, and a holographic grating is formed by exposure. There is no need to set a coupling prism, which reduces the manufacturing difficulty of the holographic grating, thereby reducing the difficulty of mass-producing optical waveguides;

[0171] At the same time, there is no need to set a refractive index matching liquid, which improves the uniformity of the diffraction efficiency distribution of the holographic grating. When the optical waveguide is applied to an AR near-eye display system, the improvement of the uniformity of the diffraction efficiency distribution of the holographic grating in the optical waveguide can improve the display effect of the AR display screen. Moreover, the holographic grating manufacturing system can provide different ranges of exposure wavelengths, is suitable for different exposure requirements, and has a wide application range.

[0172] In addition, after exposure, the laser is controlled to adjust the wavelength of the output light beam to the second interference wavelength to improve the grating vector offset problem caused by the change in the refractive index of the holographic material layer after exposure. After exposure, the laser is controlled to adjust the wavelength of the output light beam to the third interference wavelength, and the angles of the reflecting mirror and / or the holographic material layer are controlled to adjust the incident angles of the two light beams incident on the holographic material layer to be the third incident angle respectively, so as to improve the grating vector offset problem caused by the volume shrinkage of the holographic material after exposure.

[0173] Accordingly, the present application also provides a method for preparing a holographic grating, which can be applied to the above-mentioned holographic grating preparation system.

[0174] Figure 11 It is a schematic flow chart of a method for preparing a holographic grating provided by an embodiment of the present application.

[0175] As Figure 11 shown, the method for preparing a holographic grating includes: step 110, step 120, and step 130.

[0176] Step 110: Determine a first interference wavelength according to the reproduction wavelength and diffraction angle of the reproduction beam and the refractive index of the holographic material layer.

[0177] Step 120: Determine a first incident angle and a second incident angle according to the reproduction wavelength, diffraction angle, refractive index, and first interference wavelength.

[0178] Step 130: Control the exposure device to generate an outgoing light beam with the first interference wavelength, divide the outgoing light beam into two light beams, and respectively make the two light beams incident on the holographic material layer at the first incident angle and the second incident angle, so as to perform interference exposure on the holographic material layer to form a holographic grating.

[0179] According to the method for preparing a holographic grating provided by an embodiment of the present application, the first interference wavelength, the first incident angle, and the second incident angle are determined through the reproduction wavelength and diffraction angle of the reproduction beam and the refractive index of the holographic material layer, so as to adjust the wavelength of the outgoing light beam generated by the exposure device to the first interference wavelength, and respectively adjust the incident angles of the two light beams divided from the outgoing light beam to the first incident angle and the second incident angle, so that the two light beams interfere at the holographic material layer to expose and form a holographic grating. There is no need to set a coupling prism, which reduces the manufacturing difficulty of the holographic grating, thereby reducing the difficulty of mass-producing optical waveguides. Moreover, there is no need to set a refractive index matching liquid, which improves the uniformity of the diffraction efficiency distribution of the holographic grating.

[0180] In some embodiments, when the two light beams are respectively incident on opposite sides of the holographic material layer, the range of the first interference wavelength is:

[0181]

[0182] where, λ w is the first interference wavelength, λ r is the reproduction wavelength, θ is the diffraction angle, and n is the refractive index;

[0183] When the two light beams are incident on the same side of the holographic material layer, the range of the first interference wavelength is:

[0184]

[0185] In some embodiments, the step of determining the first incident angle and the second incident angle according to the reproduction wavelength, the diffraction angle, the refractive index, and the first interference wavelength includes:

[0186] Determining the wave vector of the reproduction wavelength according to the reproduction wavelength and the refractive index;

[0187] Determining the grating vector according to the wave vector of the reproduction wavelength and the diffraction angle;

[0188] Determining the wave vector of the first interference wavelength according to the first interference wavelength and the refractive index;

[0189] Determining the first incident angle and the second incident angle according to the wave vector of the first interference wavelength, the grating vector, the diffraction angle, and the refractive index.

[0190] In some embodiments, the first incident angle and the second incident angle are respectively:

[0191]

[0192]

[0193]

[0194] where θ1 is the first incident angle, θ2 is the second incident angle, is the grating vector, is the wave vector of the first interference wavelength, λ w is the first interference wavelength, λ r is the reproduction wavelength, θ is the diffraction angle, and n is the refractive index.

[0195] In some embodiments, the method for preparing the holographic grating further includes:

[0196] Obtaining the refractive index of the holographic grating after exposure;

[0197] Determining a second interference wavelength according to the refractive index after exposure and the first interference wavelength;

[0198] Adjusting the wavelength of the outgoing light beam to the second interference wavelength.

[0199] In some embodiments, the second interference wavelength is:

[0200]

[0201] where λ' w is the second interference wavelength, λ wis the first interference wavelength, n is the refractive index of the holographic material layer before exposure, and n' is the refractive index of the holographic material layer after exposure.

[0202] In some embodiments, when the two light beams are respectively incident on opposite sides of the holographic material layer, the holographic grating preparation method further includes:

[0203] Obtaining the material shrinkage rate of the holographic grating after exposure;

[0204] Determining a third interference wavelength, a third incident angle, and a fourth incident angle according to the material shrinkage rate;

[0205] Adjusting the wavelength of the outgoing light beam to the third interference wavelength, and respectively adjusting the incident angles of the two light beams to the third incident angle and the fourth incident angle, and the included angle between the incident directions of the two light beams is 180°.

[0206] In some embodiments, the step of determining a third interference wavelength, a third incident angle, and a fourth incident angle according to the material shrinkage rate includes:

[0207] Determining the third interference wavelength according to the material shrinkage rate, the reproduction wavelength, and the diffraction angle;

[0208] Determining the third incident angle and the fourth incident angle according to the material shrinkage rate, the diffraction angle, and the refractive index.

[0209] In some embodiments, the third interference wavelength is:

[0210]

[0211] where λ” w is the third interference wavelength, λ r is the reproduction wavelength, θ is the diffraction angle, and k is the material shrinkage rate;

[0212] The third incident angle and the fourth incident angle are respectively:

[0213]

[0214] where θ1′ is the third incident angle, θ2′ is the fourth incident angle, θ is the diffraction angle, k is the material shrinkage rate, and n is the refractive index.

[0215] In some embodiments, when the two light beams are incident on the same side of the holographic material layer, the holographic grating preparation method further includes:

[0216] Obtaining the material shrinkage rate of the holographic grating after exposure;

[0217] Determine a third incident angle and a fourth incident angle according to the material shrinkage rate, the first interference wavelength, the reproduction wavelength, the refractive index, and the diffraction angle;

[0218] Respectively adjust the incident angles of the two light beams to the third incident angle and the fourth incident angle.

[0219] In some embodiments, the third incident angle and the fourth incident angle are respectively:

[0220]

[0221]

[0222] where θ1′ is the third incident angle, θ2′ is the fourth incident angle, θ is the diffraction angle, k is the material shrinkage rate, n is the refractive index, λ w is the first interference wavelength, λ r is the reproduction wavelength.

[0223] It should be noted that in this text, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device. Without more limitations, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including that element. In addition, it should be pointed out that the methods and devices in the embodiments of the present application are not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may also be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0224] Through the description of the above embodiments, those skilled in the art can clearly understand that the above-described embodiment methods can be implemented by means of software plus a necessary general hardware platform. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art, can be embodied in the form of a computer software product. The computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disc) and includes several instructions for causing a terminal (which may be a mobile phone, computer, server, or network device, etc.) to execute the methods described in the various embodiments of the present application.

[0225] The embodiments of the present application have been described above in conjunction with the accompanying drawings. However, the present application is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present application, those of ordinary skill in the art can also make many forms without departing from the purpose of the present application and the scope protected by the claims, and all of them fall within the protection scope of the present application.

[0226] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0227] Although the embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and purposes of the present application. The scope of the present application is defined by the claims and their equivalents.

Claims

1. A holographic grating preparation system, characterized in that, Comprising: An exposure device for generating an output light beam with tunable wavelength, splitting the output light beam into two light beams, and incidenting the two light beams onto a holographic material layer to perform interference exposure on the holographic material layer to form a holographic grating; A control device for determining a first interference wavelength according to the reproduction wavelength and diffraction angle of a reproduction light beam and the refractive index of the holographic material layer; determining a first incident angle and a second incident angle according to the reproduction wavelength, the diffraction angle, the refractive index and the first interference wavelength; adjusting the wavelength of the output light beam to the first interference wavelength, and respectively adjusting the incident angles of the two light beams to the first incident angle and the second incident angle.

2. The holographic grating preparation system according to claim 1, characterized in that, When the two light beams are respectively incident on opposite sides of the holographic material layer, the range of the first interference wavelength is: where λ w is the first interference wavelength, λ r is the reproduction wavelength, θ is the diffraction angle, and n is the refractive index; When the two light beams are incident on the same side of the holographic material layer, the range of the first interference wavelength is:

3. The holographic grating preparation system according to claim 1, characterized in that, The control device is further configured to: Determine the wave vector of the reproduction wavelength according to the reproduction wavelength and the refractive index; Determine the grating vector according to the wave vector of the reproduction wavelength and the diffraction angle; Determine the wave vector of the first interference wavelength according to the first interference wavelength and the refractive index; Determine the first incident angle and the second incident angle according to the wave vector of the first interference wavelength, the grating vector, the diffraction angle and the refractive index.

4. The holographic grating preparation system according to claim 3, characterized in that, The first incident angle and the second incident angle are respectively: Where, θ1 is the first incident angle, and θ2 is the second incident angle. is the grating vector, is the wave vector of the first interference wavelength, λ w is the first interference wavelength, λ r is the reproduction wavelength, θ is the diffraction angle, and n is the refractive index.

5. The holographic grating preparation system according to claim 1, characterized in that, The control device is further configured to: Obtain the refractive index of the holographic grating after exposure; Determine a second interference wavelength according to the refractive index after exposure and the first interference wavelength; Adjust the wavelength of the output light beam to the second interference wavelength.

6. The holographic grating preparation system according to claim 5, characterized in that, The second interference wavelength is: where λ' w is the second interference wavelength, λ w is the first interference wavelength, n is the refractive index of the holographic material layer before exposure, and n' is the refractive index of the holographic grating after exposure.

7. The holographic grating preparation system according to claim 1, characterized in that, When the two light beams are respectively incident on opposite sides of the holographic material layer, the control device is further configured to: Obtain the material shrinkage rate of the holographic grating after exposure; Determine a third interference wavelength, a third incident angle and a fourth incident angle according to the material shrinkage rate; Adjust the wavelength of the output light beam to the third interference wavelength, and respectively adjust the incident angles of the two light beams to the third incident angle and the fourth incident angle, and the included angle between the incident directions of the two light beams is 180°.

8. The holographic grating preparation system according to claim 7, characterized in that, The control device is further configured to: Determine the third interference wavelength according to the material shrinkage rate, the reproduction wavelength and the diffraction angle; Determine the third incident angle and the fourth incident angle according to the material shrinkage rate, the diffraction angle and the refractive index.

9. The holographic grating preparation system according to claim 8, wherein The third interference wavelength is: where λ″ w is the third interference wavelength, λ r is the reproduction wavelength, θ is the diffraction angle, and k is the material shrinkage rate; The third incident angle and the fourth incident angle are respectively: Wherein, θ1′ is the third incident angle, θ2′ is the fourth incident angle, θ is the diffraction angle, k is the material shrinkage rate, and n is the refractive index.

10. The holographic grating preparation system according to claim 1, wherein When the two light beams are incident on the same side of the holographic material layer, the control device is further configured to: Obtain the material shrinkage rate of the holographic grating after exposure; Determine the third incident angle and the fourth incident angle according to the material shrinkage rate, the first interference wavelength, the reproduction wavelength, the refractive index and the diffraction angle; Adjust the incident angles of the two light beams to the third incident angle and the fourth incident angle respectively.

11. The holographic grating preparation system according to claim 10, wherein The third incident angle and the fourth incident angle are respectively: Wherein, θ1′ is the third incident angle, θ2′ is the fourth incident angle, θ is the diffraction angle, k is the material shrinkage rate, n is the refractive index, λ w is the first interference wavelength, λ r is the reproduction wavelength.

12. The holographic grating preparation system according to any one of claims 1-11, wherein The exposure device includes: A laser for generating an output light beam with a tunable wavelength; A polarization beam splitter for splitting the output light beam into two light beams; A reflecting mirror with an adjustable angle for reflecting the two light beams respectively to make the two light beams incident on the holographic material layer; The angle of the holographic material layer is adjustable. The control device is further configured to control the laser to adjust the wavelength of the output light beam, and control the angles of the reflecting mirror and / or the holographic material layer to adjust the incident angles of the two light beams.

13. The holographic grating preparation system according to claim 12, wherein The exposure device further includes: A shutter for controlling the on / off duration of the output light beam; A polarization controller for controlling the polarization direction of the output light beam; A spatial filter for filtering out the high-order modes in the two light beams; A collimation system for collimating the two light beams.

14. A method for preparing a holographic grating, wherein Includes: Determine a first interference wavelength according to the reproduction wavelength and diffraction angle of the reproduction light beam and the refractive index of the holographic material layer; Determine a first incident angle and a second incident angle according to the reproduction wavelength, the diffraction angle, the refractive index and the first interference wavelength; Control the exposure device to generate an output light beam with the first interference wavelength, split the output light beam into two light beams, and make the two light beams incident on the holographic material layer at the first incident angle and the second incident angle respectively to perform interference exposure on the holographic material layer to form a holographic grating.

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