CN115657314A - AR diffraction optical waveguide device based on light field wave front phase modulation - Google Patents

Abstract

The invention provides an AR diffraction light waveguide device based on light field wave front phase modulation, which comprises: a light source, a coupling exit grating, a first diffractive optical element, a second diffractive optical element, and a waveguide; the light source emits an incident beam with an initial wave front to irradiate the first diffractive optical element, the incident beam forms a plane wave front after being modulated and is vertically incident to the second diffractive optical element, the incident beam is subjected to wave front phase modulation by the second diffractive optical element and then is reflected along a diffraction angle theta to enter the inside of the waveguide, and the plane wave front phase is continuously kept to be continuously propagated in the waveguide by utilizing total reflection; the incident light beams are coupled through the coupling emergent gratings at different positions to form emergent light beams of different orders to be emergent and enter human eyes, and the imaging process is completed. The invention solves the problem that the original light with different orders experiences crosstalk between emergent lights with different orders due to the increase of the size of a light spot.

Description

AR Diffractive Optical Waveguide Device Based on Optical Field Wavefront Phase Modulation

technical field

The invention relates to the technical field of diffractive optics, in particular to an AR diffractive optical waveguide device based on optical field wavefront phase modulation.

Background technique

Augmented reality technology or AR technology is to provide users with virtual information through images, videos, 3D models and other technologies while displaying real scenes, so as to realize the integration of the surrounding visual environment and virtual graphic information, that is, to integrate the real environment and virtual Objects are superimposed on the same screen or space in real time, presenting users with a new environment with richer perceptual effects. Therefore, augmented reality technology has been widely used in the fields of military, industrial design and manufacturing, medical treatment, entertainment and education by virtue of its unique feature of superimposing the projected image on the real environment perceived by the user, affecting and even changing all walks of life. Some information interaction methods in the production and life of various industries have huge potential application value. At present, the relatively mature optical display schemes in augmented reality technology are mainly divided into prism schemes, birdbath schemes, free-form surface schemes, off-axis holographic lens schemes and waveguide (Lightguide) schemes.

At present, solutions other than waveguides have problems such as large system size and heavy equipment quality. The waveguide solution can greatly reduce the size and weight of the equipment while ensuring the imaging quality. The waveguide using diffractive optics is currently the mainstream development and research direction in the market. Although companies such as Microsoft (Microsoft) and Magic Leap have product output, the products on the market all use a two-piece optical waveguide structure to integrate light of different wavelengths. (Red+Green&Green+Blue) input into different waveguides for image or optical information transmission. In the optical waveguide, using the diffraction effect of the blue light and part of the green light on the coupling incident grating (diffractive optical element 1), the propagation direction of this part of light is deflected by a specific angle, and it can be used in the optical waveguide medium. The properties of reflection are propagated. Similarly, using the diffraction effect of the remaining green light and red light coupled to the incident grating (diffractive optical element 2) on the second optical waveguide, the propagation direction of this part of light is deflected by a specific angle, and it can be transmitted in the light In the waveguide medium, the characteristics of total reflection are used for propagation. After propagating to a specific position, in each waveguide, the light propagating in the waveguide is used to couple the diffraction effect of the outgoing grating (diffractive optical element 3) to deflect the propagating light by a certain angle, away from the total reflection of the waveguide After confinement, the light entering the human eye is finally imaged on the retina.

As shown in Figure 1, the light emitted by the light source enters the optical waveguide at different angles after being coupled to the incident grating, and the total reflection effect of the light at the interface between the waveguide material and the outside world (air) is used to make the light in the optical waveguide The interface is totally reflected and propagated to the right. After propagating to a certain distance, the light is incident on the coupling-out grating on the surface, a part of the light is acted on by the coupling-out grating and leaves the optical waveguide, and the other part is reflected and split to make part of the light leave the optical waveguide during the next incident coupling-out grating, and the other part The reflection continues to propagate in the optical waveguide. Light coupled out at different positions is regarded as outgoing light of different orders.

In the existing AR diffractive optical waveguide optical system, there are problems of separation of different colors of light due to the dispersion characteristics of the medium material, and different reflections caused by the gradual increase of the beam size due to the different diffraction angles corresponding to different viewing angles. The problem of mutual crosstalk between stages, and the problem that the coupling efficiency of the light position at the edge of the field of view caused by the original in-coupling grating structure decreases significantly at large field of view.

Contents of the invention

In view of the above problems, the object of the present invention is to propose an AR diffractive optical waveguide device based on optical field wavefront phase modulation. The microstructure of the diffractive optical element at each position is used to realize the modulation requirements of each diffractive optical element on the light field at different positions (wavefront modulation/shaping, and direction deflection), and then realize the transmission of optical information under a large field of view.

To achieve the above object, the present invention adopts the following specific technical solutions:

The present invention provides an AR diffractive optical waveguide device based on optical field wavefront phase modulation, including: a light source, a coupling output grating, a first diffractive optical element, a second diffractive optical element, and a waveguide;

The light source emits an incident light beam with an initial wavefront to irradiate the first diffractive optical element located on the upper surface of the waveguide. The incident beam is modulated by the first diffractive optical element to form a plane wavefront, and is perpendicularly incident on the second diffractive optical element located on the lower surface of the waveguide. The optical element has a plane wavefront incident light beam that is modulated by the second diffractive optical element and then reflected along the diffraction angle θ into the interior of the waveguide with high diffraction efficiency, and continues to maintain the plane wavefront phase and continues to propagate in the waveguide by total reflection ; Different positions on the lower surface of the waveguide are respectively provided with coupling output gratings, and the incident light beams are coupled through the coupling output gratings at different positions to form different levels of output light beams to enter the human eye to complete the imaging process.

Preferably, the upper and lower surfaces of the waveguide are parallel to each other.

Preferably, a part of the incident beam is coupled through a coupling output grating to form a first-order output beam for output;

The other part of the beam is reflected by the coupling output grating and is incident on the coupling output grating at the next position in the next propagation to be coupled to form the second secondary output beam for output, and the other part of the beam is reflected by the coupling output grating and continues to be used in the waveguide using the full Reflection propagates.

Preferably, the design process of the first diffractive optical element 4 is:

局部线性近似光栅周期

与出射波前

之间的关系；Established at a certain position (x,y) by a local linear grating approximation method, the incident wavefront

locally linear approximate grating period

and outgoing wavefront

The relationship between;

According to the wavefront direction of the outgoing beam, it can be determined:

与对应位置的入射波前

之间的关系式为：Then the local linear approximate grating period can be established at each position

The incident wavefront corresponding to the position

The relationship between is:

Among them, θ is the angle between the incident wavefront and the grating normal;

之后，进而的带刻线密度函数N(x，y)＝1/d(x，y)；Solve the local linear approximation grating period

Then, the further band density function N(x, y)=1/d(x, y);

Then solve the preliminary structure of the first diffractive optical element;

Then optimize the design of the preliminary structural groove shape of the first diffractive optical element, improve the diffraction efficiency results at each position, and finally obtain the optimized structural parameters of the first diffractive optical element.

Preferably, the design process of the second diffractive optical element is:

Establishing the relationship ε(x, y, z) between the dielectric constant and the spatial position for the groove distribution in the grating period d of the second diffractive optical element by a rigorous coupled wave analysis method;

and using the periodic distribution of the groove shape of the second diffractive optical element in the nearby space to solve Maxwell's equations in the nearby space of the second diffractive optical element;

According to the rigorous coupled wave analysis method, when the electrolyte constant presents a periodic distribution, the light field satisfies the following characteristic equation in the spatial frequency domain:

in,

κ=(k _x , k _y ) is the coordinate in the space frequency domain space;

E _i (κ) (i=x, y) is the X component and Y component of the vertical propagation direction of the light field;

Then the distribution of the light field in the nearby space is:

in,

为特征向量对应的不全为零的比例系数；

is the proportional coefficient corresponding to the feature vector that is not all zero;

为特征方程的特征向量；

is the eigenvector of the characteristic equation;

The light field transmission matrix M of the light field in the grating structure is obtained as:

M(x,y)=M[d,z(x,y),ε(x,y,z)]

in,

d is the grating period;

z(x,y) is the height distribution function within a single period;

ε(x,y,z) is the electrolyte constant distribution function;

When the light field passes through the multilayer film structure, the light field passing through the i-th film is:

in,

E _i is the light field behind the i-th film;

E _i-1 is the light field behind the i-1th film;

A _i , B _i , C _i , D _i are four coefficients determined by the multi-dimensional structure parameters (refractive index of the medium, film thickness) of the i-th film, respectively.

Then the outgoing light field function E ^output through the multilayer dielectric film is:

in,

M _i is the modulation matrix of the i-th film to the light field;

Then the relationship between the outgoing light field function E ^output and the incident light field function E ^input of the second diffractive optical element is obtained as:

E ^output = M2 M1 E ^input

Wherein, M ₁ is the first light field transmission matrix; M ₂ is the second light field transmission matrix.

Compared with the existing technology, the present invention modulates the wavefront phase of the light field to be coupled into the optical waveguide into a plane wavefront phase by designing the novel diffractive optical element 1 . After the phase is modulated into the phase of the plane wavefront, the diffraction characteristics of the diffractive optical element 2 (high diffraction efficiency of a specific order) are used to make the light beam of the plane wavefront reflect and diffract along the direction of the specific order, and the phase of the plane wavefront is still satisfied, and the diffraction The angle satisfies the limit condition of total reflection at the boundary, which can ensure that the light propagates backward in the optical waveguide by the total reflection at the upper and lower surfaces.

After being modulated into the phase of the plane wave front, the size of the beam can be sufficiently limited, and in the subsequent propagation process, the phase of the plane wave front can still be maintained, and the original beam size can be maintained for propagation. Under the condition that the beam size is fixed, the original problem of crosstalk between different orders of light due to the increase of the spot size is solved.

Description of drawings

FIG. 1 is a schematic diagram of a one-dimensional optical path structure of the existing AR diffractive optical waveguide technology.

Fig. 2 is a schematic diagram of a three-dimensional optical path structure of an AR diffractive optical waveguide device based on optical field wavefront phase modulation provided according to an embodiment of the present invention.

3 is a schematic diagram of a two-dimensional optical path structure of an AR diffractive optical waveguide device based on optical field wavefront phase modulation provided according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of the structure of the coupled outgoing optical path of the AR diffractive optical waveguide device based on optical field wavefront phase modulation provided according to an embodiment of the present invention.

Reference numerals therein include: illumination area 1 , light source 11 , coupling-incoming grating 2 , coupling-outgoing grating 3 , first diffractive optical element 4 , second diffractive optical element 5 and waveguide 6 .

Detailed ways

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same blocks are denoted by the same reference numerals. With the same reference numerals, their names and functions are also the same. Therefore, its detailed description will not be repeated.

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention.

FIG. 2 shows a schematic diagram of a three-dimensional optical path structure of an AR diffractive optical waveguide device based on optical field wavefront phase modulation provided according to an embodiment of the present invention.

FIG. 3 shows a schematic diagram of a two-dimensional optical path structure of an AR diffractive optical waveguide device based on optical field wavefront phase modulation provided according to an embodiment of the present invention.

As shown in Figures 2-3, the AR diffractive optical waveguide device based on light field wavefront phase modulation provided by the embodiment of the present invention includes: an illumination area 1, a light source 11, an incident coupling grating 2, an outgoing coupling grating 3, a first diffractive optical Element 4 , second diffractive optical element 5 and waveguide 6 .

The light source 11 emits an incident light beam with an initial wavefront to irradiate the upper surface of the waveguide 6 , modulated by the coupling incident grating 2 located on the upper surface of the waveguide 6 , and then vertically incident on the lower surface of the waveguide 6 . The upper and lower surfaces of the waveguide 6 are parallel to each other.

The coupling-incident grating 2 provided in one embodiment of the present invention is a first diffractive optical element 4 .

The initial wavefront phase of the incident light beam is modulated by the first diffractive optical element 4 into a plane wavefront phase, that is, the wave vector directions of the incident light at each position of the incident light beam are parallel to each other and perpendicular to the waveguide 6, after being modulated by the first diffractive optical element 4 The wavefront is plane and is incident perpendicularly to the lower surface of the waveguide 6 . After the light with the planar wavefront phase is irradiated on the lower surface of the optical waveguide 6, after being modulated by the wavefront phase of the second diffractive optical element 5 again, it is reflected along a specific diffraction angle θ and enters the interior of the waveguide 6 with high diffraction efficiency, and continues to Maintaining the phase of the plane wavefront continues to propagate in the optical waveguide using total reflection.

Because the upper and lower surfaces of the waveguide 6 are in a parallel state, all the incident angles of light beams on the upper and lower surfaces of the waveguide 6 during propagation are equal to the diffraction angle θ at the second diffractive optical element 5 (this angle needs to satisfy the light on the optical waveguide material and the air surface The total reflection condition of :

n _waveguide (λ)*sinθ＞n _air (λ)/k _waveguide (λ)*sinθ＞k _air (λ)

When the incident beam propagates along the interior of the waveguide 6, it propagates to the position near the human eye in the form of a plane wavefront phase, and then is coupled and emitted by the wavefront phase modulation of the output coupling grating 3, and enters the human eye for imaging.

FIG. 4 shows a schematic structural diagram of a coupled outgoing optical path of an AR diffractive optical waveguide device based on optical field wavefront phase modulation provided according to an embodiment of the present invention.

The incident light beam propagates in the optical waveguide 6 by total reflection, passes through multiple illumination areas 1 during the propagation process, and after multiple times of total reflection propagation, the incident light beam enters the coupling output grating 3 located on the lower surface of the waveguide 6 . Out-coupling gratings 3 are arranged at different positions on the lower surface of the waveguide 6 , and the light coupled out through the out-coupling grating 3 is regarded as outgoing light of different orders.

A part of the incident beam is coupled through the coupling-out grating 3 to form the first-order exit light, and the other part is reflected and coupled to form the second-order exit light when it enters the coupling-exit grating 3 next time. The reflected light continues to propagate in the optical waveguide.

The design process of the first diffractive optical element 4 is:

The first diffractive optical element 4 is used to modulate the light field of the incident light beam with wave vectors in different directions at each position to the light field of the wave front with the wave vector in the same direction, and improve the diffraction efficiency at each position as much as possible .

局部线性近似光栅

以及出射波前

的关系。According to the above requirements, the local linear grating approximation method (Local Linear GratingApproximation) is used to establish the incident wavefront at a certain position (x, y).

locally linear approximation grating

and the outgoing wavefront

Relationship.

则可以建立各个位置上，局部线性近似光栅周期与对应位置波矢之间的方程式为：According to the required outgoing wavefront direction can be determined:

Then the equation between the local linear approximate grating period and the wave vector at the corresponding position can be established at each position as:

Among them, θ is the angle between the wave vector and the grating normal.

After solving the local period, then solve the reticle density function M(x, y)=1/d(x, y), and then solve the preliminary structure of the preliminary first diffractive optical element 4 (reticle distribution and local groove type width), and then optimize the groove type design to improve the diffraction efficiency results at each position. Finally, the optimized structural parameters of the first diffractive optical element 4 are obtained.

The design process of the second diffractive optical element 5 is:

Establishing the relationship ε(x, y, z) between the dielectric constant and the spatial position for the groove distribution (height function z(x, y)) within the single period d of the second diffractive optical element by a rigorous coupled wave analysis method;

and using the periodic distribution of the groove shape of the second diffractive optical element in space to solve Maxwell's equations in the space near the second diffractive optical element;

According to the rigorous coupled wave analysis method, when the electrolyte constant presents a periodic distribution, the light field satisfies the following characteristic equation in the space (k-domain) of the spatial frequency domain:

In the formula, κ=(k _x , _ky ) represents the coordinates in the spatial frequency domain space, and E _i (κ)(i=x, y) represents the two components of the light field perpendicular to the direction of propagation. Since the remaining four light fields The components E _z , H _x , H _y , and H _z can all be calculated by Maxwell's equations combined with E _x & E _y , so they are not reflected in the formula.

Then the distribution of the light field in this space can be expressed as:

代表各特征向量对应的不全为零的比例系数，

为整数数集；

代表特征方程的特征向量，根据光的传输需求，消去κ≥2π/λ所代表的消逝波的部分，实际代表计算时仅包含κ＜2π/λ的特征向量。其中，特征向量由入射光场及电介质常数分布函数ε(x,y,z)决定，比例系数由入射光场决定的边界条件确定。各个特征向量实际代表了在光传输过程中发生衍射效应对应的不同衍射级次。In the formula

Represents the proportional coefficients corresponding to each eigenvector that are not all zero,

is an integer number set;

The eigenvector representing the characteristic equation, according to the transmission requirements of light, eliminates the part of the evanescent wave represented by κ≥2π/λ, and actually represents only the eigenvector of κ<2π/λ in the calculation. Among them, the eigenvector is determined by the incident light field and the dielectric constant distribution function ε(x, y, z), and the proportional coefficient is determined by the boundary conditions determined by the incident light field. Each eigenvector actually represents the different diffraction orders corresponding to the diffraction effect in the light transmission process.

At the same time, according to the grating period d, the height distribution function z(x,y) in a single period and the electrolyte constant distribution function ε(x,y,z), determine the light field transmission matrix M(x,y) of the light field in the grating structure =M[d,z(x,y),ε(x,y,z)].

The diffracted light of the required order is regarded as the direction information is determined by the light field transfer matrix M containing the grating structure information on the energy distribution ratio of the diffraction order determined by the corresponding eigenvector and the energy information is determined by the incident light (related to σ _i ) result. Its overall effect can be represented by a light field modulation matrix M1.

The process of the light field passing through the single-layer dielectric film structure can be expressed in matrix form:

Then, under the multi-layer film structure, the process of passing through the i-th film can be expressed as:

Where E _i represents the light field behind the i-th film, which is the light field in front of the i+1 film. Similarly, E _i-1 represents the light field behind the i-1 film, which is the light field in front of the i-th film. field; A _i , B _i , C _i , D _i are four coefficients determined by the multi-dimensional structure parameters (refractive index of the medium, film thickness) of the i-th film.

Then the light field before and after the light field passes through the entire multilayer dielectric film can be connected by multiple matrices:

In the formula, M _i represents the modulation matrix of the i-th film to the light field. This result shows that the corresponding light field modulation effect under the multilayer dielectric film structure can be expressed by a matrix M2.

Furthermore, the relationship between the light field function E ^output of the required diffraction order and the incident light field function E ^input of the second diffractive optical element is obtained as follows:

E ^output = M2 M1 E ^input

By optimizing the groove structure of the grating and optimizing the parameters of the dielectric film structure, the energy of the light field of the required order can be maximized.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention, those skilled in the art can make the above-mentioned The embodiments are subject to changes, modifications, substitutions and variations.

The above specific implementation manners of the present invention do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (5)

1. An AR diffractive optical waveguide device based on optical field wavefront phase modulation, comprising: a light source, a coupling exit grating, a first diffractive optical element, a second diffractive optical element, and a waveguide;

the light source emits an incident beam with an initial wave front to irradiate a first diffractive optical element on the upper surface of the waveguide, the incident beam is modulated by the first diffractive optical element to form a plane wave front and is vertically incident to a second diffractive optical element on the lower surface of the waveguide, the incident beam with the plane wave front is subjected to wave front phase modulation by the second diffractive optical element and then is reflected along a diffraction angle theta with high diffraction efficiency to enter the waveguide, and the plane wave front phase is continuously maintained to be continuously transmitted in the waveguide by means of total reflection; the coupling emergent gratings are respectively arranged at different positions of the lower surface of the waveguide, and the incident light beams are coupled through the coupling emergent gratings at different positions to form emergent light beams of different orders to be emitted into human eyes, so that the imaging process is completed.

2. The AR diffractive optical waveguide device based on optical field wavefront phase modulation according to claim 1, wherein the upper and lower surfaces of the waveguide are parallel to each other.

3. The AR diffractive optical waveguide device based on light field wavefront phase modulation according to claim 2, wherein a part of the incident light beams are coupled through the coupling exit grating to form a first-order exit light beam for exiting;

and the other part of the light beam is reflected by the coupling exit grating and is incident to the coupling exit grating at the next position in the next transmission to form a second-level exit light beam for exiting, and the other part of the light beam is reflected by the coupling exit grating and is continuously transmitted in the waveguide by utilizing total reflection.

4. The AR diffractive optical waveguide device based on optical field wavefront phase modulation according to claim 3, characterized in that the first diffractive optical element 4 is designed by the process of:

built at a certain position (x, y) by local linear grating approximation

Local linear approximation of grating period

And the front of the emergent wave

The relationship between;

from the direction of the outgoing beam wavefront it can be determined:

local linear approximation of the grating period at each position can be established

Incident wavefront with corresponding position

The relationship between them is:

wherein, theta is an included angle between an incident wavefront and a grating normal;

solving out local linear approximate grating period

Then, the further band scribe density function N (x, y) =1/d (x, y);

then solving a preliminary structure of the first diffractive optical element;

and then, carrying out optimization design on the initial structure groove type of the first diffractive optical element, improving the diffraction efficiency result of each position, and finally obtaining the optimized structure parameters of the first diffractive optical element.

5. The AR diffractive optical waveguide device based on light field wavefront phase modulation according to claim 4, wherein the second diffractive optical element is designed by the process of:

establishing a relation epsilon (x, y, z) between a dielectric constant and a spatial position for the groove type distribution in the grating period d of the second diffractive optical element by a strict coupled wave analysis method;

solving Maxwell equations in the space near the second diffractive optical element by utilizing the periodic distribution of the groove type of the second diffractive optical element in the near space;

according to the rigorous coupled-wave analysis method, when the electrolyte constant exhibits a periodic distribution, the optical field satisfies the following characteristic equation in the spatial frequency domain:

wherein,

κ＝(k _x ,k _y ) Is a coordinate in the spatial frequency domain space;

E _i (κ) (i = X, Y) is the X and Y components of the light field perpendicular to the direction of propagation;

the distribution of the light field in said nearby space is then:

wherein,

σ _i ，

the scale coefficients corresponding to the feature vectors are not all zero;

E _i,⊥ (κ)，

is a feature vector of a feature equation;

obtaining a light field transmission matrix M of the light field in the grating structure as follows:

M(x,y)＝M[d,z(x,y),ε(x,y,z)]

wherein,

d is the grating period;

z (x, y) is a height distribution function within a single period;

ε (x, y, z) is the electrolyte constant distribution function;

when the light field passes through the multilayer film structure, the light field passing through the ith film is:

wherein,

E _i is the light field after the ith film;

E _i-1 the optical field after the i-1 th film;

A _i ,B _i ,C _i ,D _i 4 coefficients determined by the multi-dimensional structure parameters of the ith film respectively;

then the emergent light field function E passing through the multilayer dielectric film ^output Comprises the following steps:

wherein,

M _i a modulation matrix of the ith film to the optical field;

further obtain the emergent light field function E ^output Incident light field function E with said second diffractive optical element ^input The relationship between them is:

E ^output ＝M2·M1·E ^input

wherein M is ₁ A first light field transmission matrix; m is a group of ₂ A second light field transmission matrix.

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