CN112180594A

CN112180594A - Holographic waveguide display device

Info

Publication number: CN112180594A
Application number: CN201910598949.9A
Authority: CN
Inventors: 于超; 江丽; 蔡宏; 毛慧; 浦世亮
Original assignee: Hangzhou Hikvision Digital Technology Co Ltd
Current assignee: Hangzhou Hikvision Digital Technology Co Ltd
Priority date: 2019-07-04
Filing date: 2019-07-04
Publication date: 2021-01-05

Abstract

The application provides a holographic waveguide display device, the device includes: the optical-mechanical module comprises a plurality of light-emitting diodes, wherein at least two light-emitting diodes have wavelengths with the same spectral energy value and larger than zero, and the central wavelengths of the at least two light-emitting diodes are different; a holographic waveguide module comprising at least one first volume holographic optical device, at least one second volume holographic optical device, an optical waveguide in contact with the at least one first volume holographic optical device and the at least one second volume holographic optical device. The light that a plurality of emitting diode sent in this application device has the light of at least part the same wave band, can improve the spectral energy distribution degree of consistency of above-mentioned wave band light for the ray machine module can send the light that has the broad spectral bandwidth, makes holographic waveguide display device have the Bragg angle bandwidth of broad, and then effectively increases holographic waveguide display device's visual field.

Description

Holographic waveguide display device

Technical Field

The application relates to the technical field of display, in particular to a holographic waveguide display device.

Background

Augmented Reality (AR) technology is a technology for fusing information of a real world and information of a virtual world, so that a human can better recognize the world and make a judgment. The potential application of the method is very wide and extends to various fields of military affairs, education, navigation, logistics, inspection, security protection, entertainment and the like. The near-eye display technology is a main hardware carrier for enhancing the display technology, and has a crucial influence on the user experience, so that the near-eye display technology has recently attracted wide attention all over the world.

The near-eye display technology has various technical routes, mainly including a free-form surface prism, an off-axis reflection technology, a waveguide technology and the like. Waveguide technology is now the best technology seen, including holographic waveguide technology. The holographic waveguide is a waveguide near-eye display technology using a volume holographic optical device as a coupling device, and has relatively low production cost, but has a relatively small field of view (FOV), that is, an angle range of an image which can be seen by a user is small, and the use requirement cannot be completely met.

Disclosure of Invention

The embodiment of the application provides a holographic waveguide display device, which at least can solve the problem that the field of view of the holographic waveguide display device is small.

The application provides a holographic waveguide display device comprising:

the optical-mechanical module comprises a plurality of light-emitting diodes, wherein at least two light-emitting diodes have wavelengths with the same spectral energy value and larger than zero, and the central wavelengths of the at least two light-emitting diodes are different;

the holographic waveguide module comprises at least one first volume holographic optical device, at least one second volume holographic optical device and an optical waveguide which is in contact with the at least one volume holographic optical device and the at least one second volume holographic optical device, wherein the at least one first volume holographic optical device is used for guiding light emitted by the optical machine module into the optical waveguide, and the at least one second volume holographic optical device is used for guiding out the light in the optical waveguide.

In an embodiment of the present application, the holographic waveguide display device includes an optical-mechanical module, wherein at least two light emitting diodes are included, and there exist wavelengths with equal spectral energy values and larger than zero, and center wavelengths of the at least two light emitting diodes are different. The apparatus provided herein also includes a holographic waveguide module comprising at least one first volume holographic optical device, at least one second volume holographic optical device, and an optical waveguide. The optical-mechanical module is used for receiving light emitted by the optical-mechanical module, and the optical-mechanical module is used for receiving the light emitted by the optical-mechanical module and outputting the light to the outside. The optical machine module of the device comprises a plurality of light-emitting diodes with the same spectral energy value and the wavelength larger than zero, and the central wavelengths of the at least two light-emitting diodes are different, namely, the light rays emitted by the light-emitting diodes have at least part of light with the same waveband. The light that a plurality of diodes in the ray apparatus module sent can improve the spectral energy distribution degree of consistency of above-mentioned wave band light, and then makes the ray apparatus module can send the light that has the broad spectral bandwidth. The light then passes through the volume holographic optical device with a wider bragg angular bandwidth. In addition, the view field of the holographic waveguide display device is positively correlated with the Bragg angular bandwidth, so that the view field of the holographic waveguide display device can be effectively increased by the scheme provided by the application.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:

FIG. 1 is a schematic diagram of a holographic waveguide display device according to an embodiment of the present disclosure;

FIG. 2 is a diagram illustrating normalized spectral energy values of a holographic waveguide display device according to an embodiment of the present disclosure;

fig. 3 is a second schematic structural diagram of a holographic waveguide display device according to an embodiment of the present disclosure;

FIG. 4 is a schematic diagram of light propagation for a holographic waveguide display device according to embodiments of the present disclosure;

FIG. 5 is a schematic diagram of two light rays satisfying the Bragg condition for VHOE at different angles;

FIG. 6 is a diagram illustrating diffraction efficiency curves of a predetermined wavelength band according to an embodiment of the present disclosure;

fig. 7 is a schematic structural diagram of a light source sub-module provided in an embodiment of the present application;

FIG. 8 is a second illustration of normalized spectral energy values for a holographic waveguide display device according to an embodiment of the present disclosure;

FIG. 9 is a graphical representation of the relationship between VHOE thickness and index modulation for achieving the same Bragg diffraction efficiency;

FIG. 10 is a graphical representation of the diffraction efficiency of VHOE versus the number of exit orders.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application. The reference numbers in the present application are only used for distinguishing the steps in the scheme and are not used for limiting the execution sequence of the steps, and the specific execution sequence is described in the specification.

In order to increase the FOV of the display device, a splicing approach may be used to obtain a larger FOV. Specifically, two groups of coupling-in volume holographic optical devices and two groups of coupling-out volume holographic optical devices can be adopted in the display device, then the two groups of coupling-in volume holographic optical devices are spliced together by adopting a relatively complex process, and the two groups of coupling-out volume holographic optical devices are spliced together, so that the display device has a relatively large FOV as a whole. In the mode, a larger FOV can be obtained theoretically, but in the actual operation process, higher process precision is needed, the whole splicing process is more complex, the process difficulty is higher, and in addition, various defects exist in the aspects of sub-cost, design and the like, so the realization is more difficult.

In order to solve the problems of the prior art, the application provides a holographic waveguide display device, which may be a device capable of being worn on the head of a user, for example, the device may be worn in front of the eyes of the user like glasses, or may be worn on the head of the user like a helmet. The holographic waveguide display device provided by the application is shown in fig. 1 and comprises:

an optical module 11 comprising a plurality of light emitting diodes, wherein at least two light emitting diodes have wavelengths with equal spectral energy values and greater than zero, and the central wavelengths of the at least two light emitting diodes are different;

the holographic waveguide module 12 includes at least one first volume holographic optical device 121, at least one second volume holographic optical device 122, and an optical waveguide 123 in contact with the at least one first volume holographic optical device 121 and the at least one second volume holographic optical device 122, where the at least one first volume holographic optical device 121 is configured to guide light emitted by the optical-mechanical module into the optical waveguide 123, and the at least one second volume holographic optical device 122 is configured to guide light out of the optical waveguide 123.

Fig. 1 shows a structure of a holographic waveguide display device, which mainly includes an optical-mechanical module 11 and a holographic waveguide module 12. The optical module 11 includes a plurality of Light Emitting Diodes (LEDs), and Light emitted from the LEDs can be transmitted to the eyes E through the holographic waveguide module 12. Preferably, the spacing distance between adjacent light emitting diodes in the light engine module is not greater than 1 cm. The first holographic optical device 121 in the holographic waveguide module 12 is used for guiding light emitted from the optical machine module 11 into the optical waveguide 123, so that the light propagates inside the optical waveguide 123. When the light in the optical waveguide 123 reaches the second volume hologram optical device 122, the second volume hologram optical device 122 serves to guide out the light. In this embodiment, the second volume hologram optical device 122 is configured to guide light to the outside of the optical waveguide 123 and to emit the light to the human eye E. The path of the light rays propagating is schematically indicated by arrows in fig. 1.

Since the volume holographic optical device described in the embodiment of the present application has wavelength selectivity and angle selectivity, the volume holographic optical device does not block light of the real world, and the optical waveguide has high transparency, so that a user can see a picture of the real world through the volume holographic optical device and the optical waveguide. In addition, the light emitted by the optical-mechanical module can be transmitted to human eyes through the holographic waveguide module, so that a user can see a virtual picture. Therefore, the device provided by the application can enable the user to see pictures of the real world and the virtual world at the same time.

It should be noted that fig. 1 shows only the structure of one type of holographic waveguide display device. The optical engine module 11 and the holographic waveguide module 12 may be combined in other positional relationships. For example, in fig. 1, the opto-mechanical module 11 is located on the opposite side of the volume hologram optical device based on the optical waveguide 123, however, the opto-mechanical module 11 may also be located on the same side of the optical waveguide 123 as the volume hologram optical device. In addition, in fig. 1, the first volume hologram optical device 121 and the second volume hologram optical device 122 in the hologram waveguide module 12 are located on the same side of the optical waveguide 123, however, the first volume hologram optical device 121 and the second volume hologram optical device 122 may be located on different sides of the optical waveguide 123. The specific structure of the holographic waveguide display device may be determined according to the type of the internal volume holographic optical device, the type of the optical waveguide, the power and the type of the optical-mechanical module, and the like, and is not limited in this embodiment.

In the embodiment of the present application, the optical mechanical module includes a plurality of light emitting diodes having wavelengths with equal spectral energy values and greater than zero, and the at least two light emitting diodes have different center wavelengths, that is, the light emitted by the plurality of light emitting diodes has at least part of light with the same wavelength band. Fig. 2 shows a diagram of normalized spectral energy values for an LED under normal operating conditions, with wavelength on the abscissa and normalized spectral energy on the ordinate in nanometers.

If the opto-mechanical module includes only one LED or a plurality of LEDs with the same center wavelength, the spectral energy curve of the light emitted by the opto-mechanical module is shown as curve 21.

In the embodiment of the application, at least two LEDs in the optical mechanical module have wavelengths with equal spectral energy values and larger than zero. It is assumed that the spectral energy curves of the two LEDs included in the opto-mechanical module of the embodiment of the present application are respectively shown as curve 22 and curve 23, and the curve 22 and the curve 23 intersect at the point M. At point M, the ordinate values of curve 22 and curve 23 are equal and are the ordinate values of point M, and the ordinate value of point M is greater than 0. In this case, the total spectral power curve of the light emitted from the LED corresponding to curve 22 and the LED corresponding to curve 23 is shown as curve 24.

Comparing the curve 21 and the curve 24 in the figure, it can be seen that the spectral bandwidth of the curve 24 is wider than that of the curve 21, and the spectral energy distribution uniformity is better. Therefore, the light emitted by the optical-mechanical module in the embodiment of the application has the characteristics of wider spectral bandwidth and better spectral energy distribution uniformity. Specifically, the brightness uniformity of the holographic waveguide display device is related to the spectral energy uniformity of the light emitted by the optical-mechanical module. Because the light that a plurality of emitting diode sent in this application embodiment have the light of at least some the same wave band, so the light that a plurality of LED in the ray apparatus module sent can improve the spectral energy distribution degree of consistency of above-mentioned wave band light, and then makes the ray apparatus module can send the light that has the broad spectral bandwidth, and meanwhile, can also guarantee that the light that sends has better luminance degree of consistency. In addition, the optical-mechanical module of the embodiment of the application adopts a plurality of LEDs, and the structural complexity of the whole device can be reduced.

Based on the apparatus provided in the foregoing embodiment, preferably, as shown in fig. 3, the optical module 11 includes:

at least one projection sub-module 31;

at least one light source sub-module 32, wherein each light source sub-module 32 includes a plurality of light emitting diodes, at least two light emitting diodes in each light source sub-module 32 have wavelengths with equal spectral energy values and greater than zero, and center wavelengths of the at least two light emitting diodes are different, and light emitted from the at least one light source sub-module 32 is projected to the at least one first volume hologram optical device 121 through the projection sub-module 31.

In fig. 3, the Light source sub-module 32 includes at least two Light emitting diodes having wavelengths with equal spectral energy values and greater than zero, and the at least two Light emitting diodes have different center wavelengths, and may further include a spatial Light modulator, such as an lcd (liquid Crystal display), an lcos (liquid Crystal on silicon), a dlp (digital Light processing), and the like. In the embodiment of the present application, the holographic waveguide display device shown in fig. 3 includes only one light source sub-module, actually, one holographic waveguide display device may include a plurality of light source sub-modules, and the actual positions of the light source sub-modules may be preset according to requirements.

The light from the opto-mechanical module then reaches a first Volume Holographic Optical Element (VHOE) that directs the light from the opto-mechanical module into the Optical waveguide, which may also be coupled into the VHOE. While a second bulk holographic optical device, which may also employ a coupling-out VHOE, is used to bring the light in the optical waveguide out to the outside of the device. The apparatus provided in the present application will be described in detail below assuming that the first bulk holographic optical device employs a coupling-in VHOE and the second bulk holographic optical device employs a coupling-out VHOE.

For further explanation of the embodiments of the present application, fig. 4 shows a schematic diagram of a light propagation path. Light is emitted from the light source submodule 32, and the light emitted from the light source submodule 32 is incident on the coupling-in VHOE after passing through the projection submodule 31. In fact, there are many kinds of VHOE, and the coupling-in VHOE and the coupling-out VHOE provided in this embodiment may be reflective volume holographic gratings, and according to actual requirements, the coupling-in VHOE and the coupling-out VHOE may be transmissive volume holographic gratings, or other types of VHOE. Even at least part of the functionality of the projection sub-module can be integrated, e.g. using a graded grating or comprising a certain optical power. In addition, multiple coupled-in VHOEs or multiple coupled-out VHOEs may be included in a holographic waveguide module, and the types of the multiple coupled-in VHOEs or the multiple coupled-out VHOEs may be the same or different.

The coupling-in VHOE couples at least a part of light emitted by the optical-mechanical module into the optical waveguide, and makes at least a part of the light propagate in the optical waveguide in the direction of the coupling-out VHOE in the form of total reflection. Since the diffraction angles of incident light at different angles are different, and the diffraction angles of light of different wavelengths are also different. The lights are reflected in the optical waveguide for different times and reach the coupled-out VHOE, the coupled-out VHOE diffracts a part of the lights, the angle of light propagation is changed, the lights do not meet the total reflection condition any more, and therefore the lights are guided out of the device and enter human eyes, and a user can see a virtual picture.

For the same grating, when the wavelength and the incident angle of the incident light satisfy a specific relationship, the bragg condition can be satisfied. Specifically, θ is an incident angle, λ is a wavelength, Λ is a grating period, and n is an average refractive index of the hologram recording material, and when 2 Λ · cos (θ) ═ λ/n is satisfied, the bragg condition is satisfied.

For a specific wavelength band of light, when the bragg condition is satisfied, each wavelength in the wavelength band corresponds to one incident angle. The angle range value of the incident angle satisfying the Bragg condition is a Bragg Angle Bandwidth (BAB). When the spectral bandwidth of the light emitted by the optical-mechanical module is wide, the incidence angle which can satisfy the Bragg condition has a wide range, so that the whole device can have a large BAB.

The bragg conditions are illustrated below, and fig. 5 shows a schematic diagram of two different wavelengths of light meeting the bragg conditions for VHOE at different angles.

Having a first wavelength λ₁At a first angle theta₁Incident on one face 302 of the VHOE, at point a, the light reflected by the first face 302 is a first reflected light ray 303. 301 passes through 302 and is incident on a second surface 304 at an incident point B and is reflected to obtain a second reflected ray 305, where the ray 305 intersects the ray 302 at a point C, and a perpendicular line is drawn from the point C to the ray 303, and the perpendicular line is denoted as a point D. The optical path difference between the light ray 303 and the light ray 305 is L₁＝AB+BC-_AD. The distance between the

rays

302 and 304 isThe period d of the grating. From the geometric relationship, L₁＝2·d·cos(θ₁) When L is present₁＝m·λ₁Where m is an integer, the bragg condition is satisfied, and the diffraction efficiency of VHOE pair 301 is the highest.

For the same reason, having a second wavelength λ₂At a second angle theta₂Incident on one face 302 of the VHOE, at point a, the light reflected by the first face 302 is a third reflected light ray 307. The light ray 306 passes through the surface 302 and is incident on the second surface 304, the incident point is E, and is reflected to obtain a fourth reflected light ray 308, the light ray 308 intersects the light ray 302 at a point F, a perpendicular line is drawn from the point F to the light ray 307, and the perpendicular line is a point G. The optical path difference between the light ray 307 and the light ray 308 is L₂AE + EF-AG. From the geometric relationship, L₂＝2·d·cos(θ₂) When L is present₂＝n·λ₂Where n is an integer, satisfying the bragg condition, the diffraction efficiency of VHOE to light 306 is the highest.

As can be seen from the above, the spectral bandwidth of the light emitted from the optical-mechanical module in the device provided by the present application is wider, so that the device has a larger BAB as a whole. Next, the relationship between the BAB and the FOV is explained with reference to fig. 6. FIG. 6 is a graph showing diffraction efficiency curves of predetermined wavelength bands, where the ordinate is diffraction efficiency and the abscissa is incident angle λ₁，λ₂，λ₃Respectively the minimum wavelength, the center wavelength and the maximum wavelength in the waveband, for a certain VHOE, lambda₁，λ₂，λ₃Corresponding Bragg angles are respectively theta₁，θ₂，θ₃. The VHOE pair lambda₁，λ₂，λ₃The diffraction efficiency curve of (a) with the incident angle is shown as a curve in fig. 6.

When the wave band of the ray that the ray apparatus module of the device that this application provided jetted out is above-mentioned wave band of predetermineeing, the holistic FOV of device that this application provided is: DAB with FOV BAB +1/2_m+1/2DAB_o. Because the light that the ray machine module of the device that this application provided jetted out itself has the characteristics of spectral width broad, so this application device has great BAB, and then guarantees that the device is whole to have great FOV.

Based on the apparatus provided in the above embodiment, it is preferable that, referring to fig. 1, the at least one first bulk holographic optical device 121 and the at least one second bulk holographic optical device 122 are respectively in contact with the first side of the optical waveguide 123;

the opto-mechanical module 11 is located at the second side of the optical waveguide.

As shown in fig. 1, the first side of the optical waveguide is the upper side of the optical waveguide shown in the figure, and the second side of the optical waveguide is the lower side of the optical waveguide shown in the figure.

Based on the apparatus provided in the foregoing embodiment, preferably, as shown in fig. 7, the light source sub-module includes:

a square bar 707;

a lead-in lens 706 provided at one end of the square rod 707;

a lead-out lens 708 disposed at the other end of the square rod 707;

and the light emitting diode group 705 is arranged on the side, far away from the square rod 707, of the lead-in lens 706.

In this example, the LED group includes 4 LEDs, which are LED701, LED702, LED703, and LED 704. At least two of the LEDs have different center wavelengths, so that the at least two LEDs have wavelengths with equal spectral energy values and larger than zero, and the center wavelengths of the at least two LEDs are different. In the figure 712 is the optical axis of the light source sub-module. The introduction lens 706 may be a single lens or a lens group, in this example, the introduction lens 706 is a fresnel lens, and the light emitted from the light emitting diode group is introduced to the front end surface 710 of the square rod 707 through the introduction lens 706, so that the light enters the square rod 707 from the front end surface 710 and is reflected in the square rod 707 for multiple times, thereby forming a uniform light intensity distribution at the rear end surface 711 of the square rod. The exit lens 708 can direct and image the light at the rear face 711 to an image generator 709, where 709 can be a transmissive device such as an LCD. In addition, if a polarization beam splitter is added to the deriving lens 708 and some design is performed according to actual requirements, the image generator 709 may also be a reflective device, such as LCOS or DLP.

Based on the device provided by the above embodiment, preferably, the light emitting diode set includes a plurality of light emitting diodes arranged in an array of M rows and M columns, where M is an integer greater than 1.

As shown in fig. 7, the LED set in this example comprises 4 LEDs arranged in a 2 row and 2 column array. The device that this application provided enables the whole luminance of the light that the emitting diode group sent even, and then makes the light luminance of light source submodule piece outgoing even, improves the holistic luminance degree of consistency of device.

Based on the apparatus provided in the foregoing embodiment, preferably, a difference between maximum spectral energy values of the at least two light emitting diodes meets a preset spectral energy difference standard.

Fig. 8 shows a diagram of spectral energy values for a LED under normal operating conditions, with wavelength on the abscissa and normalized spectral energy on the ordinate.

If the opto-mechanical module includes only one LED or a plurality of LEDs with the same center wavelength, the spectral energy curve of the light emitted by the opto-mechanical module is shown as curve 81.

In order to improve the uniformity of the light emitted by the light source sub-module, the difference between the maximum spectral energy values of at least two light emitting diodes in the light source sub-module is not large. Referring to fig. 8, the spectral energy curves of the two LEDs included in the light source sub-module in this example are shown as curve 82 and curve 83 in fig. 8, respectively, and the spectral energy curves of the two LEDs intersect at N points where the spectral energy values of the two LEDs are equal and the ordinate of the N point is greater than 0. The peak of curve 82 is 0.8 and the peak of curve 83 is 1, the difference between the maximum spectral energy values of the two LEDs being 0.2 in this example.

The preset spectral energy difference criterion may be, for example, that the difference between the maximum spectral energy values of the two LEDs in the light source sub-module is smaller than a preset criterion value, and the preset criterion value may be a relative value or an absolute value. In the present embodiment, a normalized spectral energy curve is shown in fig. 8, wherein the normalized standard may be the spectral energy curve peak of the LED with the largest spectral energy curve peak in the light source sub-module. Taking the LED corresponding to the curve 82 and the LED corresponding to the curve 83 shown in fig. 8 as an example, when the peak value of the curve 83 is larger than the peak value of the curve 82, normalization is performed based on the peak value of the curve 83. That is, the peak of the curve 83 is defined as 1, and the relative value of the peak of the curve 82 to the peak of the curve 83 is defined as the peak of the curve 82.

In the practical application process, the spectral energy values of the LEDs can also be directly used as vertical coordinates, and whether the difference value of the maximum spectral energy values of the two LEDs meets the preset spectral energy difference value standard or not is determined according to the difference value of the actual spectral energy curve peak values of the different LEDs.

For example, the predetermined spectral energy difference criterion is that the normalized maximum spectral energy difference of the two LEDs is not greater than 0.4. The normalized maximum spectral energy difference between the LED corresponding to the curve 82 and the LED corresponding to the curve 83 shown in fig. 8 is 0.2, and since 0.2 is not greater than 0.4, the LED corresponding to the curve 82 and the LED corresponding to the curve 83 shown in fig. 8 meet the requirement.

The total spectral power curve for the light emitted by the LED corresponding to curve 82 and the LED corresponding to curve 83 is shown as curve 84 in fig. 8. Comparing curve 84 and curve 81, it can be seen that the spectral bandwidth of curve 84 is wider than the spectral bandwidth of curve 81, so that the light source sub-modules in the device provided by the present application can emit light rays with wider spectral bandwidths, and the device as a whole has a larger FOV.

Based on the apparatus provided in the foregoing embodiment, preferably, the preset spectral energy difference criterion includes:

the product of the larger value of the maximum spectral energy value of the first light-emitting diode and the maximum spectral energy value of the second light-emitting diode and a preset spectral energy ratio is larger than the absolute value of the difference value of the maximum spectral energy value of the first light-emitting diode and the maximum spectral energy value of the second light-emitting diode.

Referring to fig. 8, it is assumed that the normalized spectral energy curve of the first led is shown as curve 82 and the normalized spectral energy curve of the second led is shown as curve 83. Comparing the peak of the curve 82 with the peak of the curve 83, the peak of the curve 83 is larger. That is, the first light emitting diode has a larger maximum spectral energy value than the second light emitting diode is the maximum spectral energy value of the second light emitting diode. Assuming that the predetermined spectral energy ratio is 0.5 and the peak of the curve 83 is 1, the product of the maximum spectral energy value of the second led and the predetermined spectral energy ratio is 0.5.

As can be seen from the peak of the curve 82 and the peak of the curve 83, the absolute value of the difference between the maximum spectral energy value (0.8) of the first light-emitting diode and the maximum spectral energy value (1) of the second light-emitting diode is 0.2. Since 0.5 is greater than 0.2, the LED corresponding to curve 82 and the LED corresponding to curve 83 shown in FIG. 8 meet the above requirements.

In the device provided by the application, the difference between the maximum values of the spectral energy values of the two LEDs in the light source sub-module is small, so that the spectral bandwidth of the total light emitted by the light source sub-module is wide, and therefore, the device provided by the application has a large FOV as a whole.

Based on the apparatus provided in the foregoing embodiment, preferably, the preset spectral energy ratio is greater than or equal to 40% and less than or equal to 60%. For example, the predetermined spectral power ratio may be 50%. The embodiment that this application provided enables the difference of the maximum value of the spectral energy value of a plurality of LEDs in the light source submodule piece less, and then guarantees the spectral bandwidth broad of the total light that the light source submodule piece sent to make the whole great FOV that has of device.

Based on the device provided by the above embodiment, preferably, the center wavelength of each of the light emitting diodes is different.

In the embodiment of the present application, the light source sub-module may include a plurality of LEDs, where the center wavelength of each LED is different, which makes the spectral bandwidth of the light emitted by the light source sub-module wider, so that the device has a larger FOV as a whole.

Based on the device provided by the above embodiment, preferably, the maximum spectral energy value of each of the light emitting diodes is equal.

In fact, when the maximum spectral energy values of the plurality of LEDs in the light source sub-module are equal, the spectral bandwidth of the light emitted by the light source sub-module is wide. When the maximum spectral energy values of the plurality of LEDs in the light source sub-module are different, the maximum spectral energy values of the LEDs can be adjusted by reducing the working voltage and/or the working current for the LEDs with the larger maximum spectral energy values, so that the maximum spectral energy values of the plurality of LEDs in the light source sub-module are equal. In addition, the maximum spectral energy value of the LED can also be adjusted by Pulse Width Modulation (PWM). In particular, the adjustment may be made by varying the pulse width or duty cycle. The embodiment that this application provided can further improve the spectral homogeneity of the light that the light source submodule piece sent to improve the holistic spectral homogeneity of device, optimize the display effect.

In addition to the effects described in the above embodiments, the device provided by the present application can also reduce the production cost and the production difficulty on the basis of increasing the FOV, which is described in detail below with reference to the accompanying drawings:

fig. 9 shows the relationship between the thickness of the VHOE and the modulation of the refractive index in microns on the abscissa and the modulation of the refractive index of the VHOE on the ordinate in order to achieve equivalent bragg diffraction efficiency. Specifically, fig. 9 shows the refractive index modulation degree versus thickness for bragg diffraction efficiencies of 0.3, 0.5, and 0.8. According to Kogelnik theory, VHOE diffracts its highest efficiency when the incident light satisfies the bragg condition. The value of the diffraction efficiency is related to the thickness of VHOE and the degree of modulation of the refractive index of VHOE, and the larger the thickness, the higher the diffraction efficiency, and the larger the degree of modulation of the refractive index, the higher the diffraction efficiency.

As shown in fig. 9, when the thickness is large, the refractive index modulation degree can take a relatively small value. Generally, the smaller the refractive index modulation, the easier the holographic recording material is to manufacture and the lower the process difficulty. On the other hand, since the thickness of holographic recording materials is typically on the order of a few microns, thickness control, and uniformity control, present a significant challenge to the manufacturer. As can be seen from fig. 9, when the thickness is large, the sensitivity of the diffraction efficiency to the variation of the thickness is greatly reduced, and thus the requirements for the production process are also greatly reduced.

As can be seen from fig. 6 and the related description, the entire apparatus has a large BAB, so that even if the DAB is narrowed, the width of the entire FOV can be secured. Therefore, the difficulty of the production process of the VHOE can be reduced at least from the two aspects of the thickness of the holographic recording material and the degree of modulation of the refractive index. Therefore, the device provided by the application is beneficial to reducing the cost and expanding the productivity.

In addition to the devices provided in the above embodiments, the display effect of the whole device may be optimized by performing region segmentation and modulation on VHOE. Fig. 10 shows the diffraction efficiency versus the number of exit times for coupling out of a VHOE. After light enters the optical waveguide through the coupling-in VHOE, multiple total reflections can occur in the optical waveguide until the light is led out of the coupling-out VHOE to the outside of the device.

In practice, since the diffraction efficiency is usually not 100%, the coupled-out VHOE will only guide out a part of the light propagating in the optical waveguide and reaching the coupled-out VHOE to the outside of the device at a time, and the other part will continue to propagate in the waveguide at the original angle. This part of the light will also propagate back to the out-coupling VHOE and be coupled out part of the energy. The energy will be lower and lower as the number of times to reach out of the coupled-out VHOE increases. If the light is guided out to the outside by the coupling-in VHOE when the light is transmitted to the coupling-out VHOE through the coupling-in VHOE entering optical waveguide, the coupling-out frequency is 1. If the light enters the optical waveguide through the coupling-in VHOE and propagates to the coupling-out VHOE, the light cannot be guided out of the coupling-out VHOE to the outside, the light continues to propagate in the optical waveguide, when the light propagates to the coupling-out VHOE for the second time, the light is guided out of the coupling-out VHOE to the outside, the coupling-out frequency is 2, and the like.

Referring to fig. 10, the intensity of light propagating in the waveguide becomes stronger the more forward the number of times of exit, and therefore, the lower the required diffraction efficiency. The intensity of light propagating through the optical waveguide is already low by the number of times of the latter emission, and higher diffraction efficiency is required to maintain the intensity of the former emission light.

The diffraction efficiency can be changed by changing the modulation degree of the refractive index of the holographic material, and the change of the modulation degree of the refractive index of the holographic material can be controlled by the exposure amount when the holographic grating is recorded. For light rays propagating at different angles in the optical waveguide, the positions on the VHOE corresponding to the same number of times of emergence are different. On the contrary, for the same position on the VHOE, the emission times are different for different angles of light. To achieve an overall optimization for light at all angles, the light at all angles can be globally optimized by slicing the positions on the grating.

The VHOE of the device provided by the application is subjected to segmentation and optimization, and the diffraction efficiency of light rays at all angles is different, so that the brightness of the whole emergent light rays of the device is stable, and a better display effect is achieved.

The device provided by the embodiments of the present application comprises a plurality of LEDs, and a larger FOV and higher brightness uniformity can be achieved using a set of in-and out-coupling VHOE. Moreover, because the light emitted by the optical-mechanical module has larger spectral width, the whole device has larger FOV, and further the requirement on the angular bandwidth of single wavelength is very low, so that the volume holographic recording material with larger thickness can be used, the requirement on the thickness control precision is reduced, and the process difficulty and the cost for manufacturing the volume holographic recording material are favorably reduced. In addition, because the thickness is larger, the refractive index modulation degree required for ensuring certain diffraction efficiency is also reduced, so that more choices are provided in the aspects of materials, formulas and the like, and the process difficulty and the cost are further reduced. In addition, the light emitted by the optical machine module of the device has uniform spectrum, which is beneficial to improving the integral brightness uniformity of the device.

It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.

Through the above description of the embodiments, those skilled in the art will clearly understand that the method of the above embodiments can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware, but in many cases, the former is a better implementation manner. Based on such understanding, the technical solutions of the present application may be embodied in the form of a software product, which is stored in a storage medium (such as ROM/RAM, magnetic disk, optical disk) and includes instructions for enabling a terminal (such as a mobile phone, a computer, a server, an air conditioner, or a network device) to execute the method according to the embodiments of the present application.

While the present embodiments have been described with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiments described above, which are meant to be illustrative and not restrictive, and that various changes may be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A holographic waveguide display, comprising:

the holographic waveguide module comprises at least one first volume holographic optical device, at least one second volume holographic optical device and an optical waveguide which is in contact with the at least one first volume holographic optical device and the at least one second volume holographic optical device, wherein the at least one first volume holographic optical device is used for guiding light emitted by the optical machine module into the optical waveguide, and the at least one second volume holographic optical device is used for guiding out light in the optical waveguide.

2. The apparatus of claim 1, wherein the opto-mechanical module comprises:

at least one projection sub-module;

at least one light source sub-module, wherein each light source sub-module comprises a plurality of light emitting diodes, at least two light emitting diodes in each light source sub-module have wavelengths with equal spectral energy values and larger than zero, the center wavelengths of the at least two light emitting diodes are different, and light emitted by the at least one light source sub-module is projected to the at least one first integral holographic optical device through the projection sub-module.

3. The apparatus of claim 2,

the at least one first bulk holographic optical device and the at least one second bulk holographic optical device are each in contact with a first side of the optical waveguide;

the optical-mechanical module is located on the second side of the optical waveguide.

4. The apparatus of claim 2, wherein the light source sub-module comprises:

a square bar;

the lead-in lens is arranged at one end of the square rod;

the guiding lens is arranged at the other end of the square rod;

and the light emitting diode group is arranged on one side of the lead-in lens, which is far away from the square rod.

5. The apparatus of claim 4, wherein the set of light emitting diodes comprises a plurality of light emitting diodes arranged in an array of M rows and M columns, M being an integer greater than 1.

6. The device according to any one of claims 1 to 5, wherein the difference of the maximum spectral energy values of the at least two light emitting diodes meets a predetermined spectral energy difference criterion.

7. The apparatus of claim 6, wherein the predetermined spectral energy difference criteria comprises:

8. The apparatus of claim 7, wherein the predetermined spectral power ratio is greater than or equal to 40% and less than or equal to 60%.

9. The apparatus of any of claims 1 to 5, wherein adjacent light emitting diodes in the opto-mechanical module are spaced apart by a distance of no more than 1 cm.

10. The device of any one of claims 1 to 5, wherein the maximum spectral energy values of each of said LEDs are equal.