Diffractive optical assembly and head mounted display having the same

Abstract

To provide a diffractive optical assembly and a head-mounted display having the same.SOLUTION: A diffractive optical assembly includes an input coupler, an output coupler, and an image source. The output coupler is next to the input coupler. One of the input coupler and the output coupler has a most critical holographic optical element (HOE), and another one has a diffractive optical element (DOE). Bragg condition of the most critical HOE is more sensitive than Bragg condition of the DOE. The image source is configured to generate image light that is incident to the input coupler and then propagates to the output coupler. The image light has incident angles to the input coupler and wavelengths corresponding to the incident angles. The wavelengths of the image light on the image source have a two-dimensional spatial distribution, such that relationships between the incident angles and the wavelengths of the image light comply with Bragg selectivity of the most critical HOE.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a diffractive optical assembly and a head mounted display including a diffractive optical assembly. [Background technology]

[0002] Currently, in head mounted displays, exit pupil expansion (EPE) is achieved by utilizing diffractive optical elements (DOEs) as couplers to planar waveguides, and DOEs include surface relief gratings (SRGs), metasurfaces, thin and volume holographic optical elements (HOEs). When a volume HOE acts as a coupler in a head mounted display to diffract a plane wave from an image source, the diffraction efficiency of the volume HOE depends on the wavelength and incident angle of the plane wave, which is called the Bragg selectivity.

[0003] Therefore, for a plane wave of a certain wavelength, the tolerance of the incidence angle is less than 10 degrees, limiting the field of view (FOV) of the head-mounted display. Conversely, for a plane wave from a broadband source, only a portion of the plane wave can be diffracted at each incidence angle, and the energy loss of the plane wave is more than 90%, resulting in a low optical efficiency. Summary of the Invention

[0004] One aspect of the present disclosure provides a diffractive optical assembly.

[0005] According to some embodiments of the present disclosure, a diffractive optical assembly includes an input coupler, an output coupler, and an image source. In the optical path, the output coupler is behind the input coupler. One of the input coupler and the output coupler has a prime holographic optical element (HOE), and another of the input coupler and the output coupler has a diffractive optical element (DOE). The Bragg condition of the prime HOE is more sensitive than the Bragg condition of the DOE. The image source is configured to generate image light incident on the input coupler and propagate to the output coupler. The image light has a plurality of angles of incidence on the input coupler and a plurality of wavelengths corresponding to the angles of incidence. The wavelengths of the image light on the image source have a two-dimensional spatial distribution such that the relationship between the angles of incidence and the wavelengths of the image light matches the Bragg selectivity of the prime HOE of the input coupler or the output coupler.

[0006] In some embodiments, the image source includes multiple regions, each region producing image light having angles of incidence in multiple non-overlapping ranges, and the portions of the two-dimensional spatial distribution of wavelengths of the image light in each region of the image source are continuous.

[0007] In some embodiments, the primary HOE of the input coupler or the output coupler includes a plurality of first holographic gratings, each configured to diffract image light having an incident angle within a range.

[0008] In some embodiments, the primary HOE of the input coupler or the output coupler includes a plurality of first sub-HOEs, each of which is configured to diffract image light having an incident angle within a range.

[0009] In some embodiments, the image source includes a light source and a plurality of quantum dots disposed on the light source, the size of the quantum dots varying across the plane of the image source such that the wavelengths of the image light on the image source have a two-dimensional spatial distribution.

[0010] In some embodiments, the image source includes a spatial light modulator (SLM), a light source generating source light, and a number of quantum dots located on the light source, the sizes of the quantum dots being different such that the wavelength of the source light illuminating the SLM through the quantum dots has a two-dimensional spatial distribution on the face of the SLM.

[0011] In some embodiments, the image source comprises a spatial light modulator (SLM), a light source generating a source light, and a dispersive element.

[0012] In some embodiments, the light source is disposed next to a dispersive element comprising a transmission grating, the dispersive element being configured to disperse the source light passing through the dispersive element to illuminate the SLM, where the wavelengths of the source light on the SLM have a two-dimensional spatial distribution.

[0013] In some embodiments, the light source is disposed on a side of the dispersive element facing the SLM, the dispersive element being configured to disperse the source light to illuminate the SLM, where the wavelengths of the source light on the SLM have a two-dimensional spatial distribution.

[0014] In some embodiments, the image source further comprises a bandpass filter disposed between the SLM and the dispersive element.

[0015] In some embodiments, the dispersive element of the image source comprises a surface relief grating, a metasurface, a metalens, a holographic grating, or a volume holographic optical element.

[0016] In some embodiments, the image source further includes a spatial light modulator (SLM), a light source generating source light, a dispersive element, a light guide, and a regular HOE. The dispersive element is disposed on the light guide. The light source is disposed on a side of the dispersive element that does not face the light guide. The SLM and the regular HOE are disposed on two opposite sides of the light guide, respectively. The regular HOE is in contact with the light guide. The dispersive element is configured to disperse the source light. The light guide is configured to propagate the source light from the dispersive element to the regular HOE. The regular HOE is configured to reflect a portion of the wavelengths of the source light to illuminate the SLM, and the wavelengths of the source light on the SLM have a two-dimensional spatial distribution.

[0017] In some embodiments, a conventional HOE of the image source is placed on one of two opposite sides of the light guide facing the dispersive element.

[0018] In some embodiments, a conventional HOE of the image source is placed on one of two opposite sides of the light guide opposite the dispersive element.

[0019] In some embodiments, the normal HOE of the image source includes multiple second sub-HOEs arranged side by side.

[0020] In some embodiments, the typical HOE of the image source comprises a volume holographic optical element, and the dispersive element of the image source comprises a holographic grating or a prism.

[0021] In some embodiments, the image source includes a plurality of color channels, each of which is configured to generate a portion of the image light.

[0022] In some embodiments, the most important HOE of the input coupler or the output coupler includes a plurality of first holographic gratings, each configured to diffract the image light generated by a color channel.

[0023] In some embodiments, the primary HOE of the input coupler or the output coupler includes a plurality of first sub-HOEs, each of which is configured to diffract a portion of the image light generated by a color channel.

[0024] In some embodiments, the diffractive optical assembly further includes a lens disposed between the input coupler and the image source, the image source being located on a focal plane of the lens.

[0025] Another aspect of the present disclosure provides a head mounted display.

[0026] According to some embodiments of the present disclosure, a head mounted display includes a diffractive optical assembly and a light guide. The diffractive optical assembly includes an input coupler, an output coupler, and an image source. In the optical path, the output coupler is behind the input coupler. One of the input coupler and the output coupler has a most significant holographic optical element (HOE), and another of the input coupler and the output coupler has a diffractive optical element (DOE). The Bragg condition of the most significant HOE is more sensitive than the Bragg condition of the DOE. The image source is configured to generate image light incident on the input coupler and propagating to the output coupler. The image light has a plurality of angles of incidence on the input coupler and a plurality of wavelengths corresponding to the angles of incidence. The wavelengths of the image light on the image source have a two-dimensional spatial distribution such that the relationship between the angles of incidence and the wavelengths of the image light matches the Bragg selectivity of the most significant HOE of the input coupler or the output coupler. The light guide is connected to the input coupler and the output coupler of the diffractive optical assembly and is disposed between the input coupler and the image source of the diffractive optical assembly.

[0027] In some embodiments, the head mounted display further includes a two-dimensional grating disposed on the light guide between the input coupler and the output coupler, the length and width of the input coupler being smaller than the length and width of the output coupler, respectively.

[0028] In some embodiments, the head mounted display further comprises a surface relief grating disposed on the light guide such that the surface relief grating is aligned with the input couplers along the length of the light guide and aligned with the output couplers along the width of the light guide.

[0029] In the above-mentioned embodiment of the present disclosure, since the wavelength of the image light on the image source has a two-dimensional spatial distribution, and the relationship between the incident angle and the wavelength of the image light matches the Bragg selectivity of the most important HOE, the energy of the image light is preserved even after the image light is diffracted by the most important HOE, and the diffractive optical assembly can have a higher diffraction efficiency compared with the conventional diffractive optical element. Furthermore, the head mounted display having the diffractive optical assembly can widen the field of view (FOV) while maintaining the optical efficiency, thus improving the energy utilization rate of the head mounted display. [Brief description of the drawings]

[0030] Aspects of the present disclosure are best understood by reading the following detailed description in conjunction with the accompanying drawings, in which: It should be noted that, in accordance with standard industry practice, the various features have not been drawn to scale, and in fact the dimensions of the various features may be arbitrarily increased or decreased for clarity of illustration.

[0031] [Figure 1] FIG. 1 is a 3D perspective view of a head mounted display having a diffractive optical assembly according to an embodiment of the present disclosure. [Diagram 2] 2 is a schematic side view of the head mounted display of FIG. 1 in operation. FIG. [Diagram 3] 3(a) and 3(b) are 3D schematic diagrams of the most important HOE of the diffractive optical assembly of FIG. 1 in the recording and reading states, respectively. [Figure 4] 2 is a schematic side view of an image source of the diffractive optical assembly of FIG. 1. [Diagram 5] FIG. 2 is a schematic side view of an image source according to another embodiment of the present disclosure. [Figure 6]FIG. 13 is a schematic side view of an image source according to yet another embodiment of the present disclosure. [Figure 7] FIG. 13 is a schematic side view of an image source according to yet another embodiment of the present disclosure. [Figure 8] FIG. 2 is a schematic side view of an image source according to one embodiment of the present disclosure. [Figure 9] FIG. 2 is a schematic side view of an image source according to another embodiment of the present disclosure. [Figure 10] FIG. 13 is a schematic side view of an image source according to yet another embodiment of the present disclosure. [Figure 11] 1 is a schematic side view of a head mounted display having a diffractive optical assembly in operation according to another embodiment of the present disclosure. [Figure 12] FIG. 2 is a 3D perspective view of a head mounted display having a diffractive optical assembly according to yet another embodiment of the present disclosure. [Figure 13] FIG. 13 is a schematic side view of the head mounted display of FIG. 12 in operation. [Figure 14] FIG. 13 is a schematic side view of an image source of the diffractive optical assembly of FIG. [Figure 15] FIG. 2 is a schematic side view of an image source according to one embodiment of the present disclosure. [Figure 16] FIG. 2 is a top view of the head mounted display of FIG. [Figure 17] FIG. 2 is a top view of a head mounted display according to an embodiment of the present disclosure. [Figure 18] FIG. 2 is a top view of a head mounted display according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The following disclosure provides many different embodiments or examples for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. Furthermore, the disclosure may repeat reference numbers and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself indicate a relationship between the various embodiments and / or configurations described.

[0033] Additionally, spatially relative terms such as above and below ("below," "lower," "lower," "upper," "top," etc.) are intended to describe the relationship of one element or feature to another element or feature as illustrated in the figures and may be used herein for ease of description. The spatially relative terms are intended to encompass different orientations of the device during use or operation in addition to the orientation shown in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted similarly.

[0034] FIG. 1 is a 3D perspective view of a head mounted display 200 having a diffractive optical assembly 100 according to an embodiment of the present disclosure. FIG. 2 is a schematic side view of the head mounted display 200 of FIG. 1 in operation. As shown in FIG. 1 and FIG. 2, the head mounted display 200 includes a diffractive optical assembly 100 and a light guide 210. The diffractive optical assembly 100 includes an input coupler 110, an output coupler 150, and an image source 120. In the optical path, the output coupler 150 is behind the input coupler 110. In this embodiment, the output coupler 150 is next to the input coupler 110. One of the input coupler 110 and the output coupler 150 has a most important holographic optical element (HOE) 160, and the other of the input coupler 110 and the output coupler 150 has a diffractive optical element (DOE) 170, and the Bragg condition of the most important HOE 160 is more sensitive than the Bragg condition of the DOE 170. The image source 120 is configured to generate an image light L1 that is incident on the input coupler 110 and propagates to the output coupler 150. The image light L1 has a plurality of angles of incidence θ1 on the input coupler 110 and a plurality of wavelengths λ1 corresponding to the angles of incidence θ1. The wavelengths λ1 of the image light L1 on the image source 120 have a two-dimensional spatial distribution D1 such that the relationship between the angle of incidence θ1 and the wavelengths λ1 of the image light L1 matches the Bragg selectivity of the most significant HOE 160 of the input coupler 110 or the output coupler 150. For example, in this embodiment, the input coupler 110 has the most significant HOE 160, and the output coupler 150 has the DOE 170. In such a configuration, the energy of the image light L1 is preserved after the image light L1 is diffracted by the input coupler 110, and the diffractive optical assembly 100 may have a higher diffraction efficiency compared to a conventional diffractive optical element. Furthermore, the head mounted display 200 having the diffractive optical assembly 100 can increase the field of view (FOV) while maintaining optical efficiency, thus improving the energy utilization of the head mounted display 200.

[0035] In some embodiments, the diffractive optical assembly 100 further includes a lens 130 disposed between the input coupler 110 and the image source 120 to collimate the image light L1, where the image source 120 is located on a focal plane of the lens 130. Also, since the incident angle θ1 of the image light L1 has a tolerance, the two-dimensional spatial distribution D1 of the wavelength λ1 has multiple intervals as shown in FIG. 1, and the darker the interval, the longer the wavelength λ1.

[0036] 3(a) is a 3D schematic diagram of the most important HOE 160 of the diffractive optical assembly 100 of FIG. 1 in a recording state. As shown in FIG. 3(a), during recording, the reference beam RL and the signal beam SL are irradiated onto two opposite surfaces of the most important HOE 160, respectively. The incident angle of the reference beam RL is θ R and the incident angle of the signal light SL is θ S The angle of incidence is determined by the deviations from the x, y, and z axes, i.e., θ R =(θ Rx ,θ Ry ,θ Rz ) and θ S =(θ Sx ,θ Sy ,θ Sz The coordinate system is defined such that the reference light RL and the signal light SL are both in the x, z plane, i.e., they have no y component (θ Sy =θ Ry =0).

[0037] 3(b) is a 3D schematic diagram of the most important HOE 160 of the diffractive optical assembly 100 of FIG. 1 in a reading state. As shown in FIG. 3(b), the reading light PL is diffracted by the most important HOE 160 and converted into a diffracted light DL. The reading light PL is incident at an incident angle θ P The diffracted light DL has a diffraction angle θ D The diffraction angle θ of the diffracted light DL D and the incident angle θ of the reading light PL P are the deviations from the x, y, and z axes, that is, θ P =(θ Px ,θ Py ,θ Pz ) and θ D =(θ Dx ,θ Dy,θ Dz ) Referring to FIG. 3(a) and FIG. 3(b), in order to increase the diffraction efficiency of the most important HOE 160, the read light PL incident on the most important HOE 160 must follow the Bragg selectivity of the most important HOE 160. Therefore, if the wavelength of the signal light SL and the wavelength of the reference light RL are the same λ0, the wavelength of the read light PL λ P and the incidence angle θ P The relationship between

number

[0038] 2 and 3(b), the most important image light L1 incident on the HOE 160 can act as the reading light PL, so the incident angle θ1 and wavelength λ1 of the image light L1 are set to the incident angle θ P and wavelength λ P The incident angle θ1 of the image light L1 is expressed as θ1=(θ 1x ,θ 1y ,θ 1z ) and depends on the position within image source 120 where image light L1 originates, and can be expressed as:

number

number

number

number

number

[0039] 4 is a schematic side view of the image source 120 of the diffractive optical assembly 100 of FIG. 1. The image source 120 can include a plurality of quantum dots 121 and a light source 123. The light source 123 can generate image light L1. The quantum dots 121 are disposed on the light source 123. The size of the quantum dots 121 varies along the plane of the image source 120 such that the wavelength of the image light L1 on the image source 120 has a two-dimensional spatial distribution D1. In some embodiments, the light source 123 is a chip of a micro light emitting diode (micro LED) that emits ultraviolet or blue light, so the image source 120 can be a micro LED display.

[0040] 5 is a schematic side view of an image source 120 according to another embodiment of the present disclosure. The image source 120 of FIG. 5 may include a spatial light modulator (SLM) 122, a light source 123 that generates source light L2, and a number of quantum dots 121 located on the light source 123. The quantum dots 121 have different sizes, so that the wavelength λ2 of the source light L2 irradiating the SLM 122 through the quantum dots 121 has a two-dimensional spatial distribution D2 along the face of the SLM 122. Furthermore, the image source 120 of FIG. 5 may further include a light guide 125 configured to transmit the source light L2 to the SLM 122. In some embodiments, the two-dimensional spatial distribution D2 of the wavelength λ2 of the source light L2 of FIG. 5 is the same as the aforementioned two-dimensional spatial distribution D1 of the wavelength λ1 of the image light L1 of FIG. 2, so that the source light L2 of FIG. 5 passing through the SLM 122 of FIG. 5 may function as the image light L1 of FIG. 2.

[0041] It should be noted that the connections and advantages of the above-mentioned elements will not be repeated in the following description.Other types of image sources are described in the following description.

[0042] FIG. 6 is a schematic side view of an image source 120 according to yet another embodiment of the present disclosure. The image source 120 of FIG. 6 may include an SLM 122, a light source 123 generating source light L2, and a dispersive element 124. The light source 123 of FIG. 6 may be disposed on the opposite side of the dispersive element 124 from the SLM 122. The dispersive element 124 may be configured to split the source light L2 passing through the dispersive element 124 along a horizontal plane of the dispersive element 124 to illuminate the SLM 122. The wavelength λ2 of the source light L2 on the SLM 122 has a two-dimensional spatial distribution D2. In some embodiments, the dispersive element 124 of FIG. 6 includes a surface relief grating, a metasurface, a metalens, a holographic grating, or a volume holographic optical element. In this embodiment, the dispersive element 124 is transmissive.

[0043] Fig. 7 is a schematic side view of an image source 120 according to yet another embodiment of the present disclosure. The image source 120 in Fig. 7 may include an SLM 122, a light source 123 generating source light L2, and a dispersive element 124. The difference between this embodiment and the embodiment in Fig. 6 is that the light source 123 in Fig. 7 is disposed on the side of the dispersive element 124 facing the SLM 122. The dispersive element 124 is configured to reflect and split the source light L2 along the horizontal plane of the dispersive element 124 to illuminate the SLM 122. In this embodiment, the dispersive element 124 is reflective.

[0044] FIG. 8 is a schematic side view of an image source 120 according to an embodiment of the present disclosure. The image source 120 of FIG. 8 may include an SLM 122, a light source 123 generating source light L2, a dispersive element 124, a light guide 125, and a regular HOE 126. The dispersive element 124 of FIG. 8 is disposed on the light guide 125. The light source 123 of FIG. 8 is disposed on the side of the dispersive element 124 that does not face the light guide 125. The SLM 122 and the regular HOE 126 of FIG. 8 are disposed on two opposite sides of the light guide 125, respectively. The regular HOE 126 is in contact with the light guide 125 and disposed on the side of the light guide 125 where the dispersive element 124 is disposed. The dispersive element 124 is configured to disperse the source light L2 emitted from the light source 123 along the side of the dispersive element 124. The light guide 125 is configured to propagate the source light L2 from the dispersive element 124 to the regular HOE 126. The conventional HOE 126 is configured to reflect and reshape the source light L2 transmitted in the light guide 125 to illuminate the SLM 122, so that the wavelength λ2 of the source light L2 on the SLM 122 has a two-dimensional spatial distribution D2. In some embodiments, the dispersive element 124 includes a holographic grating or a prism, and the conventional HOE 126 includes a volume holographic optical element. Compared with the image source 120 of FIG. 6 or FIG. 7, the image source 120 of FIG. 8 can further save space.

[0045] 9 is a schematic side view of an image source 120 according to another embodiment of the present disclosure. The image source 120 in FIG. 9 includes an SLM 122, a light source 123 generating a source light L2, a dispersive element 124, a light guide 125, and a conventional HOE 126. The dispersive element 124 is disposed on the light guide 125. The difference between this embodiment and the embodiment in FIG. 8 is that the conventional HOE 126 in FIG. 9 is disposed on the opposite side of the light guide 125 from the dispersive element 124.

[0046] Fig. 10 is a schematic side view of an image source 120 according to yet another embodiment of the present disclosure. The image source 120 in Fig. 10 includes an SLM 122, a light source 123 generating a source light L2, a dispersive element 124, a light guide 125, and a conventional HOE 126. The dispersive element 124 is disposed on the light guide 125. The difference between this embodiment and the embodiment in Fig. 9 is that the conventional HOE 126 in Fig. 10 includes multiple second sub-HOEs 127 arranged side by side.

[0047] 11 is a schematic side view of a head mounted display 200a having a diffractive optical assembly 100a in operation according to an embodiment of the present disclosure. The head mounted display 200a includes a diffractive optical assembly 100a and a light guide 210. The diffractive optical assembly 100a includes an input coupler 110a, an image source 120a, and an output coupler 150. In this embodiment, the input coupler 110a has a most significant HOE 160a, the output coupler 150 has a DOE 170, and the Bragg condition of the most significant HOE 160a is more sensitive than the Bragg condition of the DOE 170. Alternatively, in other embodiments, the input coupler 110a may have a DOE 170, and the output coupler 150 may have a most significant HOE 160a. The image source 120a is configured to generate an image light L1a that is incident on the input coupler 110a. The difference between the head mounted display 200a of FIG. 11 and the head mounted display 200 of FIG. 1 is that the image source 120a includes multiple color channels 128, each of which is configured to generate a portion of the image light L1a, such that the image source 120a can function as a color image source.

[0048] In some embodiments, the primary HOE 160a may be a volume HOE including multiple holographic gratings, each configured to diffract the image light L1a generated by the color channels 128. Alternatively, the primary HOE 160a may include multiple sub-HOEs 162, each configured to diffract the image light L1a generated by the color channels 128.

[0049] Fig. 12 is a 3D perspective view of a head mounted display 200b having a diffractive optical assembly 100b according to yet another embodiment of the present disclosure. Fig. 13 is a schematic side view of the head mounted display 200b of Fig. 12 during operation. As shown in Figs. 12 and 13, the head mounted display 200b includes a diffractive optical assembly 100b and a light guide 210. The diffractive optical assembly 100b includes an input coupler 110b, an image source 120b, and an output coupler 150. The image source 120b is configured to generate an image light L1b that is incident on the input coupler 110b. The difference between head mounted display 200b in FIG. 12 and head mounted display 200 in FIG. 1 is that image source 120b includes multiple regions 129, which generate image light L1b having an incident angle θ1 in multiple ranges that do not overlap with each other, and portions P1 of two-dimensional spatial distribution D1b of wavelength λ1 of image light L1b located in each of the regions 129 of image source 120b are continuous.

[0050] In some embodiments, the most important HOE 160b of the input coupler 110b may be a volume HOE including multiple holographic gratings. The holographic gratings may be configured to diffract the image light L1b having an incident angle θ1 within the range R, respectively. Alternatively, the most important HOE 160b of the input coupler 110b may include multiple sub-HOEs 162. The sub-HOEs 162 are configured to diffract the image light L1b having an incident angle θ1 within the range R, respectively. In such a configuration, the head mounted display 200b may have higher chromaticity and saturation, thereby improving the performance of the color mixing capability of the head mounted display 200b.

[0051] FIG. 14 is a schematic side view of the image source 120b of the diffractive optical assembly 100b of FIG. 12. As shown in FIG. 14, the image source 120b can include an SLM 122, a light source 123 that generates the source light L2b, and a dispersive element 124b. The difference between this image source 120b and the image source 120 of FIG. 6 is that the dispersive element 124b is configured to split the source light L2b, and the portions P2 located in each region 129 of the two-dimensional spatial distribution D2b of the wavelength λ2 of the source light L2b that illuminates the SLM 122 are continuous. Also, the portions P2 of the two-dimensional spatial distribution D2b of the wavelength λ2 of the source light L2b located in each region 129 may be identical to each other. In some embodiments, the image source 120b can further include a bandpass filter 140 disposed between the SLM 122 and the dispersive element 124b to prevent the portions of the source light L2b in the region 129 from interfering with each other. Furthermore, the two-dimensional spatial distribution D2b of the wavelength λ2 of the source light L2b is the same as the two-dimensional spatial distribution D1b (see FIG. 12) of the wavelength λ1 of the image light L1b (see FIG. 12) on the image source 120b, and the source light L2b that has passed through the SLM 122 becomes the image light L1b. In this embodiment, the dispersion element 124 is a transmissive DOE.

[0052] Fig. 15 is a schematic side view of an image source 120b according to another embodiment of the present disclosure. As shown in Fig. 15, the image source 120b of Fig. 15 can include an SLM 122, a light source 123 that generates a source light L2b, and a dispersive element 124b. The difference between this embodiment and the embodiment of Fig. 14 is that the light source 123 of the image source 120b of Fig. 15 is disposed on the side of the dispersive element 124b that faces the SLM 122. In this embodiment, the dispersive element 124 is a reflective DOE.

[0053] 16 is a top view of the head mounted display 200 of FIG. 1. As shown in FIG. 2 and FIG. 16, the light guide 210 is connected to the input coupler 110 and the output coupler 150 of the diffractive optical assembly 100, and is disposed between the input coupler 110 of the diffractive optical assembly 100 and the image source 120. Furthermore, along the longitudinal direction LD of the light guide 210, the length 152 of the output coupler 150 is longer than the length 113 of the input coupler 110. In such a configuration, the head mounted display 200 can achieve an exit pupil expansion (EPE) with lower energy loss.

[0054] Fig. 17 is a top view of a head mounted display 200c according to an embodiment of the present disclosure. As shown in Fig. 17, the difference between the head mounted display 200c and the head mounted display 200 of Fig. 16 is that the head mounted display 200c further includes a two-dimensional grating 230 disposed between the input coupler 110 and the output coupler 150 on the light guide 210. Furthermore, the length 113 and width 114 of the input coupler 110 are smaller than the length 152 and width 153 of the output coupler 150, respectively, so that the head mounted display 200c can realize a 2D EPE.

[0055] FIG. 18 is a top view of a head mounted display 200d according to another embodiment of the present disclosure. As shown in FIG. 18, the difference between the head mounted display 200d and the head mounted display 200 of FIG. 16 is that the head mounted display 200d further includes a surface relief grating 240 disposed on the light guide 210. The surface relief grating 240 is aligned with the input coupler 110 along the longitudinal direction LD of the light guide 210, and is aligned with the output coupler 150 along the width direction WD of the light guide 210. In such a configuration, the head mounted display 200d can realize a 2D EPE.

[0056] The above outlines features of some embodiments to enable those skilled in the art to better understand aspects of the present disclosure. Those skilled in the art should appreciate that they can readily use this disclosure as a basis for designing or modifying other processes and structures to carry out the same purposes and / or achieve the same advantages as the embodiments introduced herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that those skilled in the art can make various changes, substitutions, and alterations without departing from the spirit and scope of the present disclosure.

Claims

1. An input coupler; an output coupler next to the input coupler, the output coupler and the input coupler being disposed on a first side of a light guide, one of the input coupler and the output coupler having a most significant holographic optical element (HOE) and another of the input coupler and the output coupler having a diffractive optical element (DOE), the Bragg condition of the most significant HOE being more sensitive than the Bragg condition of the DOE, the more sensitive the Bragg condition is the lower the wavelength tolerance, and the wavelength tolerance that satisfies Bragg selectivity is: [0010] from [0025] The range is where λ pk is the wavelength distribution with the peak diffraction efficiency, λ 0 is the wavelength of the reference light which is the same as the wavelength of the signal light, θ Rx and θ Rz are the angles of incidence of the reference light expressed as the offset components from the x-axis and the z-axis, θ Sx and θ Sz are the angles of incidence of the signal light expressed as the offset components from the x-axis and the z-axis, θ Px and θ Pz are the angles of incidence of the read light expressed as the offset components from the x-axis and the z-axis, and T is the thickness of the most important HOE; and an image source disposed proximate a second side of the light guide opposite the input coupler and configured to generate image light that enters the input coupler after passing through the light guide and is propagated by the light guide to the output coupler, where the image light has a plurality of angles of incidence on the input coupler and a plurality of wavelengths corresponding to the angles of incidence, and the wavelengths of the image light on the image source have a two-dimensional spatial distribution such that a relationship between the angles of incidence and the wavelengths of the image light matches a Bragg selectivity of a most significant HOE of the input coupler or the output coupler; 1. A diffractive optical assembly comprising:

2. the image source includes a plurality of regions, the regions generating the image light having the angle of incidence in a plurality of non-overlapping ranges, and a portion of the two-dimensional spatial distribution of the wavelengths of the image light in each of the regions of the image source is continuous; and 2. The diffractive optical assembly of claim 1, comprising:

3. 3. The diffractive optical assembly of claim 2, wherein the most significant HOE of the input coupler or the output coupler includes a plurality of first holographic gratings, each of the first holographic gratings configured to diffract the image light having the incidence angle within the range.

4. 3. The diffractive optical assembly of claim 2, wherein the most significant HOE of the input coupler or the output coupler includes a plurality of sub-HOEs, each of which is configured to diffract the image light having the incidence angle within the range.

5. 2. The diffractive optical assembly of claim 1, wherein the image source comprises a light source and a plurality of quantum dots disposed on the light source, the size of the quantum dots varying along a horizontal plane of the image source such that the wavelengths of the image light on the image source have the two-dimensional spatial distribution.

6. 2. The diffractive optical assembly of claim 1, wherein the image source includes a spatial light modulator (SLM), a light source that generates source light, and a plurality of quantum dots located on the light source, the quantum dots having different sizes such that the wavelengths of the source light irradiated onto the SLM through the quantum dots have a two-dimensional spatial distribution along a horizontal plane of the SLM.

7. 10. The diffractive optical assembly of claim 1, wherein the image source comprises a spatial light modulator (SLM), a light source generating a source light, and a dispersive element.

8. 8. The diffractive optical assembly of claim 7, wherein the light source is disposed on an opposite side of the dispersive element from the SLM, the dispersive element is configured to disperse the source light passing through the dispersive element along a horizontal plane of the dispersive element to illuminate the SLM, and the wavelengths of the source light on the SLM have a two-dimensional spatial distribution.

9. 8. The diffractive optical assembly of claim 7, wherein the light source is disposed on a side of the dispersive element facing the SLM, the dispersive element is configured to disperse the source light and split it along a horizontal plane of the dispersive element to illuminate the SLM, and the wavelengths of the source light on the SLM have a two-dimensional spatial distribution.

10. 8. The diffractive optical assembly of claim 7, wherein the image source further comprises a bandpass filter disposed between the SLM and the dispersive element.

11. 8. The diffractive optical assembly of claim 7, wherein the dispersive element of the image source comprises a surface relief grating, a metasurface, a metalens, a holographic grating, or a volume holographic optical element.

12. 2. The diffractive optical assembly of claim 1, wherein the image source comprises a spatial light modulator (SLM), a light source generating source light, a dispersive element, another light guide, and a regular HOE, the dispersive element being disposed on the other light guide, the light source being disposed on a side of the dispersive element that does not face the other light guide, the SLM and the regular HOE being disposed on two opposite sides of the other light guide, respectively, the regular HOE being in contact with the other light guide, the dispersive element being configured to split the source light, the other light guide being configured to transmit the source light from the dispersive element to the regular HOE, the regular HOE being configured to reflect and reshape the source light to illuminate the SLM, and the wavelengths of the source light on the SLM have a two-dimensional spatial distribution.

13. 13. The diffractive optical assembly of claim 12, wherein the normal HOE of the image source is disposed on one of two opposite sides of the other light guide facing the dispersive element.

14. 13. The diffractive optical assembly of claim 12, wherein the conventional HOE of the image source is disposed on one of two opposing sides of the other light guide opposite the dispersive element.

15. 13. The diffractive optical assembly of claim 12, wherein the normal HOE of the image source comprises a plurality of second sub-HOEs arranged side by side.

16. 13. The diffractive optical assembly of claim 12, wherein the conventional HOE of the image source comprises a volume holographic optical element, and the dispersive element of the image source comprises a holographic grating or a prism.

17. 2. The diffractive optical assembly of claim 1, wherein the image source includes a plurality of color channels, each of the color channels configured to generate a portion of the image light.

18. 20. The diffractive optical assembly of claim 17, wherein the most significant HOE of the input coupler or the output coupler includes a plurality of holographic gratings, each of the holographic gratings configured to diffract the image light generated by the color channel.

19. 20. The diffractive optical assembly of claim 17, wherein the most significant HOE of the input coupler or the output coupler includes a plurality of sub-HOEs, each of which is configured to diffract a portion of the image light generated by the color channel.

20. 2. The diffractive optical assembly of claim 1, wherein a lens is disposed between the input coupler and the image source, the image source being located on a focal plane of the lens.

21. 1. A diffractive optical assembly, comprising: An input coupler; an output coupler adjacent to the input coupler, one of the input coupler and the output coupler having a most significant holographic optical element (HOE), and another of the input coupler and the output coupler having a diffractive optical element (DOE); the Bragg condition of the most significant HOE is more sensitive than the Bragg condition of the DOE; the more sensitive the Bragg condition is, the lower the wavelength tolerance is; and the wavelength tolerance that satisfies Bragg selectivity is: [0030] from [0045] The range is where λ pk is the wavelength distribution with the peak diffraction efficiency, λ 0 is the wavelength of the reference light which is the same as the wavelength of the signal light, θ Rx and θ Rz are the angles of incidence of the reference light expressed as the offset components from the x-axis and the z-axis, θ Sx and θ Sz are the angles of incidence of the signal light expressed as the offset components from the x-axis and the z-axis, θ Px and θ Pz are the angles of incidence of the read light expressed as the offset components from the x-axis and the z-axis, and T is the thickness of the most important HOE; and an image source configured to generate image light incident on the input coupler and propagating to the output coupler, where the image light has a plurality of angles of incidence on the input coupler and a plurality of wavelengths corresponding to the angles of incidence, the wavelengths of the image light on the image source having a two-dimensional spatial distribution such that a relationship between the angles of incidence and the wavelengths of the image light matches a Bragg selectivity of a most significant HOE of the input coupler or the output coupler; a diffractive optical assembly including: a light guide connected to the input coupler and the output coupler of the diffractive optical assembly and disposed between the input coupler and the image source of the diffractive optical assembly; Equipped with the output coupler and the input coupler are disposed on a first side of the light guide, and the image source is disposed proximate a second side of the light guide opposite the input coupler; A head mounted display configured such that the image light passes through the light guide, enters the input coupler, and is propagated by the light guide to the output coupler.

22. 22. The head mounted display of claim 21, comprising a two dimensional grating disposed on the light guide between the input coupler and the output coupler.

23. 22. The head mounted display of claim 21, further comprising a surface relief grating disposed on the light guide, the surface relief grating aligned with the input coupler along the length of the light guide and aligned with the output coupler along the width of the light guide.

Images