KR102516526B1 - Wavelength compensation method and system of hologrpahic optical element - Google Patents

Abstract

An optical structure capable of preventing distortion of reproduction light by pre-compensating for a difference from reproduction light during optical recording and a manufacturing method thereof are provided. A wavelength compensation method for a holographic optical element according to an embodiment of the present invention includes: dividing, by a manufacturing apparatus, a region of interest within a holographic optical element into a plurality of local regions; deriving, by a fabrication device, local reference beams and local signal beams for individual local regions; deriving, by a manufacturing device, a compensation reference wavefront and a compensation signal wavefront required for final recording by synthesizing the derived local reference beam and local signal beam; Performing, by a manufacturing device, wavefront approximation of the compensation reference wavefront and the compensation signal wavefront; and performing, by the fabrication device, optical recording of the holographic optical element based on the approximation result. Accordingly, it is possible to record a desired grating by adjusting the light incident condition of the possessed laser, and thus, a holographic optical element-based head-mounted display (HMD), HUD ( Head-up Display), etc., it is possible to use an inexpensive and small projection module, so advanced development is possible through the introduction of miniaturized light sources and low-cost light sources.

Description

Wavelength compensation method and system of holographic optical element {Wavelength compensation method and system of hologrpahic optical element}

The present invention relates to a technology related to a holographic optical element for providing an image, and more particularly, to an optical structure capable of preventing distortion of reproduction light by pre-compensating for a difference from reproduction light during optical recording and a manufacturing method thereof. .

Since the holographic optical element operates correctly only under the same light input conditions as the optical properties such as the wavelength and radiation angle of the laser used when recording through optical recording and outputs distortion-free reproduction light, conventional lasers with the same characteristics as the reproduction conditions Several times it has been used for optical recording of holographic optical elements.

However, laser diodes or LEDs that can be supplied in the form of chips are preferred for light sources used in applications where small/low power characteristics such as HMD (Head-mounted Display) must be satisfied, and high-power lasers with the same characteristics as these reproduction lights are to be realized. Since it is very difficult, HOE (Hologrpahic optical element) recording technology through pre-compensation for reproduction light having an arbitrary wavelength and wavefront is required.

The present invention has been made to solve the above problems, and an object of the present invention is to develop a see-through display using a hologrpahic optical element (HOE), and the difference between recording light and reproduction light (wavelength , light incident direction, etc.) and medium shrinkage, it is an object of the present invention to provide an optical compensation recording method and apparatus capable of reproducing a light wave intended by a user in a reproducing step without distortion and efficiency degradation.

According to an embodiment of the present invention for achieving the above object, a wavelength compensation method for a holographic optical element includes: dividing, by a manufacturing apparatus, a region of interest within the holographic optical element into a plurality of local regions; deriving, by a fabrication device, local reference beams and local signal beams for individual local regions; deriving, by a manufacturing device, a compensation reference wavefront and a compensation signal wavefront required for final recording by synthesizing the derived local reference beam and local signal beam; Performing, by a manufacturing device, wavefront approximation of the compensation reference wavefront and the compensation signal wavefront; and performing, by the fabrication device, optical recording of the holographic optical element based on the approximation result.

The step of deriving the local reference beam and the local signal beam may include performing grating modeling to be generated through interference between reproduction lights in individual local regions; converting the modeled grating into a compensation grating required for recording according to medium shrinkage and wavelength deviation compensation; and deriving a local reference beam and a local signal beam capable of generating a transformed compensation grating.

Also, in the step of performing grating modeling, when deflecting a projected beam of a wavelength incident on a holographic optical element, a required grating vector may be a vector that satisfies a predetermined grating inclination angle in a holographic recording medium.

And, for the incident light angles of the local reference beam and the local signal beam, λ _d is the wavelength of light incident to the holographic optical element at θ _1,d , θ _2,d is the projection beam with the wavelength λ _d , and θ _1,r is the local If it is the incident angle of the reference beam and θ _2,r is the incident angle of the local signal beam, it can be arranged according to Equation 1 below.

(Equation 1)

인 경우, 하기 수식 2에 따라 정리될 수 있다. In addition, for the incident angles of the local reference beam and the local signal beam, θ _1,r is the incident angle of the local reference beam, θ _2,r is the incident angle of the local signal beam, and λ _d is θ ₁ to the holographic optical element. _,d is the incident light wavelength, θ _2,d is the projection beam with _the wavelength λd ,

In the case of , it can be arranged according to Equation 2 below.

(Formula 2)

In addition, in the step of performing the optical recording, the local reference beam and the local signal beam derived for each local area are incident on the individual local area to perform the optical recording, but for the entire area of the holographic optical element, optical recording By repeatedly performing, it is possible to implement the finally required compensation reference wavefront and compensation signal wavefront.

And, in the step of performing the optical recording, if it is difficult to implement the compensation recording wavefront through a single optical element, the laser beam is complex-modulated using a spatial light modulator (SLM) to target the compensation recording wavefront. , and the wavefront complex-modulated by the spatial light modulator can satisfy the compensation reference beam and compensation signal beam of each local region on the surface of the holographic recording medium.

Meanwhile, an apparatus for fabricating a holographic optical element according to another embodiment of the present invention includes a dividing unit dividing a region of interest in the holographic optical element into a plurality of local regions; a local reference beam path that derives a local reference beam for each local area; a local signal beam path for deriving local signal beams for individual local areas; a plurality of direction adjusting units for adjusting directions of each of the local reference beam path and the local signal beam path; and a plurality of wavefront adjusting units for converting the parallel light of the laser into a compensation designed light wave for each of the local reference beam path and the local signal beam path.

As described above, according to the embodiments of the present invention, it is possible to record a desired grating by adjusting the incident light conditions of the possessed laser, thereby relieving the requirements for matching recording light and reproducing light based on a holographic optical element. Since inexpensive and small projection modules can be used in HMD (Head-mounted Display) and HUD (Head-up Display), advanced development is possible through the introduction of miniaturized light sources and low-cost light sources.

In addition, according to the embodiments of the present invention, it is possible to manufacture a high-efficiency HOE optical device capable of operating under a Bragg condition under an arbitrary target wavefront condition.

1 is a diagram provided for explanation of a reproduction beam distortion problem due to a wavelength deviation in an HOE lens-based see-through display;
2 is a flowchart provided to explain a method for compensating a wavelength of a holographic optical element according to an embodiment of the present invention;
3 is a diagram provided for explanation of reproduction light conditions and recording light conditions in the process of deriving a local reference beam and a local signal beam;
4 is a diagram provided for explanation of a process of deriving a compensating recording wavefront from a local reference beam and a local signal beam;
5 is a diagram provided for explanation of an apparatus for manufacturing a wavelength-compensated holographic optical element.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a diagram provided to explain the reproduction beam distortion problem due to wavelength deviation in a see-through display based on an HOE lens.

In general, a holographic optical element (HOE) transfers the interference patterns of two light waves (a reference beam and a signal beam) incident from different directions to a recording medium (e.g., photopolymer, photorefractive polymer, silver halide, etc.) created by recording

At this time, the recorded interference pattern forms a periodically repeated volume grating in the holographic recording medium, and diffraction occurs when the incident beam in a later reproduction step satisfies the Bragg condition of the volume grating. A reproduction beam is output through the development. This is because if the incident light deviates from the Bragg condition of the recorded volume grating, problems such as a decrease in the intensity of diffracted light and distortion of the outgoing light direction occur.

1 is a representative example of a see-through display using an HOE with a lens function.

Specifically, FIG. 1A is a diagram illustrating a system for projecting a virtual image onto a user's pupil by diffracting and condensing a virtual image starting from a projection system through an HOE lens in front of the user's eyeball.

If the wavelength of the projected beam ( λ _d ) is different from the recording light wavelength ( λ _r ) of the HOE lens, as illustrated in FIG. Or, in some cases, observation may not be possible.

In order to compensate for this, a method for compensating the wavelength of the holographic optical element according to the present embodiment is proposed in the optical recording of the HOE lens.

2 is a flowchart provided to explain a method for compensating a wavelength of a holographic optical element according to an embodiment of the present invention.

The wavelength compensation method of the holographic optical element according to the present embodiment considers the difference between recording light and reproduction light (wavelength, incident light direction, etc.) and medium shrinkage in the development of a see-through display using HOE. , in the reproduction step, the light wave intended by the user can be reproduced without distortion and efficiency degradation.

To this end, the method for compensating the wavelength of the holographic optical element according to the present embodiment divides the region of interest in the holographic optical element into a plurality of local regions using an apparatus for manufacturing a wavelength-compensated holographic optical element (S210). , local reference beams and local signal beams can be derived for individual local regions.

Specifically, in the wavelength compensation method of the holographic optical element, in the process of deriving a local reference beam and a local signal beam, grating modeling to be generated through interference between reproduction lights in individual local areas is performed (S220), and the modeled The grating is converted into a compensation grating required for recording according to medium shrinkage and wavelength deviation compensation (S230), and a local reference beam and a local signal beam capable of generating the converted compensation grating can be derived (S240).

In addition, the wavelength compensation method of the holographic optical element derives the compensation reference wavefront and compensation signal wavefront required for final recording by synthesizing the derived local reference beam and local signal beam using a manufacturing apparatus for the wavelength-compensated holographic optical element. (S250), performs wavefront approximation of the compensation reference wavefront and compensation signal wavefront (S260), implements the optical recording setup of the holographic optical element for the approximated compensation wavefront (S270), and based on the approximation result, Optical recording of the graphic optical element may be performed (S280).

That is, the wavelength compensation method of the holographic optical element divides the entire area of the holographic optical element into a set of very few local areas, models a grating to be generated in each local area, and then models a local area in the form of a plane wave to compensate for it. A reference beam and a local signal beam are derived.

This is because even if the grating in the entire holographic optical element is complex and non-periodic, when divided into a sufficiently large number of local areas, individual local areas can be approximated with periodic and simple gratings.

Therefore, wavelength and shrinkage compensation in individual local regions can be quickly performed based on the periodic grating, and the derived local reference beam and local signal beam are synthesized over the entire HOE region to obtain a compensation wavefront (compensation reference wavefront and compensation signal wavefront) can be derived.

Through this, it is possible to compensate for the difference by modulating the angle and the wavefront between the recording beams in the recording step in consideration of the reproduction beams having different optical characteristics such as wavelength and radiation angle.

FIG. 3 is a diagram provided for explanation of reproduction light conditions and recording light conditions in the process of deriving local reference beams and local signal beams.

Referring to FIG. 3, if a projected beam with a wavelength λ _d entering the HOE at θ _1, d is deflected to θ _2,d in the regeneration step, the required grating vector is θ _g,d within the holographic recording medium. The grid tilt angle must be satisfied.

Based on this, a grating required in the recording step is derived in consideration of the shrinkage of the medium (the grating vector tilted at θ _{g,r in} FIG. save

At this time, the vector pair means the light incident direction of the local reference beam and the local signal beam, respectively, and the light incident angles θ _1,r and θ _2,r vary according to the wavelength and contraction degree from the regeneration stage.

For example, λd is the wavelength of light incident on the holographic optical element at θ _1,d , _{θ 2,d} is the projection beam of wavelength λd , θ _1,r is the incident angle of the local reference beam, _and θ _{2 , r} is the light incident angle of the local signal beam and the medium shrinkage is very small, the light incident angles of the local reference beam and the local signal beam can be arranged according to Equation 1 below.

(Equation 1)

인 경우, 하기 수식 2에 따라 정리될 수 있다. In addition, for the incident angles of the local reference beam and the local signal beam, θ _1,r is the incident angle of the local reference beam, θ _2,r is the incident angle of the local signal beam, and λ _d is θ ₁ to the holographic optical element. _,d is the incident light wavelength, θ _2,d is the projection beam with _the wavelength λd ,

In the case of , it can be arranged according to Equation 2 below.

(Formula 2)

4 is a diagram provided for explanation of a process of deriving a compensation recording wavefront from a local reference beam and a local signal beam.

Since the local reference beam and the local signal beam are conditions that must be received in individual local regions in the HOE fabrication and optical recording process, by repeating this for the entire HOE region, the finally required compensation reference wavefront and compensation signal wavefront can be implemented. there is.

However, the compensating recording wavefront that has undergone this process has a complicated shape and may be difficult to implement using a single optical device.

In this case, a Spatial Light Modulator (SLM) and the principle of holography may be used to reproduce a complex light wave in a recording process.

At this time, the target compensation recording wavefront can be implemented by complex-modulating the laser beam. In this case, the complex-modulated wavefront in the SLM must satisfy the compensation reference beam and compensation signal beam of each local region on the surface of the holographic recording medium. do.

In addition, it goes without saying that a recording-required light wave having a complicated wavefront can be approximated in a simple form for easy implementation of a manufacturing device when necessary.

For example, when a light wave converging to a compensation recording wavefront is required as shown in FIG. 4, a device for producing a wavelength-compensated holographic optical element by approximating a spherical wave (or spherical wave array) each having one (or multiple) focal points implementation cost can be reduced.

5 is a diagram provided for explanation of an apparatus for manufacturing a wavelength-compensated holographic optical element.

In manufacturing a holographic optical element that normally operates in full color, the wavelength deviation between reproduction light and recording light is different in each band of red, green and blue.

Therefore, when recording a holographic optical element, sequential recording is suitable for each wavelength of red, green, and blue, and since the scheme for implementing a compensation recording wavefront for each wavelength may be different, as illustrated in FIG. 5, the reference beam and An optical recording device capable of finely adjusting the direction and focus position of incident light on both sides of a signal beam is required.

To this end, an apparatus for manufacturing a holographic optical element according to the present embodiment includes a division unit 501 for dividing a region of interest in the holographic optical element into a plurality of local regions, and a division unit 501 for deriving a local reference beam for each local region. A local reference beam path 502, a local signal beam path 503 for deriving local signal beams for individual local areas, a plurality of direction adjusting units 510 for adjusting the direction of each of the local reference beam path and the local signal beam path, and It includes a plurality of wavefront adjusting units 520 for converting the parallel light of the laser into light waves of compensation design for each of the local reference beam path and the local signal beam path.

That is, the apparatus for manufacturing a holographic optical element is designed to cause interference at a location of a holographic medium including a local signal beam path and a local reference beam path.

In each beam pass, a direction adjuster 510 for adjusting the direction of the beam pass and a wavefront adjuster 520 for converting the parallel light of the laser into a light wave with a compensation design are used to record the position of the focal point 530 of the light wave according to the step-by-step wavelength to be recorded. It plays a role in moving.

The direction adjusting unit 510 must support a fine rotation function of at least one axis in order to support vertical and horizontal rotational movement.

For example, the direction adjusting unit 510 may be implemented as a two-axis electric scanning device using a galvo mirror, MEMS mirror, or the like.

The wavefront adjusting unit 520 should support movement in one axis direction, and may be composed of a single lens or a group of lenses such as a spherical surface, an aspheric surface, and a free curved surface associated with a motorized stage.

Specifically, in the process of performing optical recording, the wavefront adjusting unit 520 supports finely adjustable translation of one axis or more and finely adjustable rotation of the entire direction of each beam path in one or more axes. will support

As described above, if a complex compensation recording wavefront is not approximated, the wavefront adjuster 520 may be implemented as a system that performs a complex modulation function through an SLM and a filtering optical system instead of a lens/lens group.

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the specific embodiments described above, and is common in the art to which the present invention pertains without departing from the gist of the present invention claimed in the claims. Of course, various modifications are possible by those who have knowledge of, and these modifications should not be individually understood from the technical spirit or prospect of the present invention.

501: division part
502: local reference beam pass
503: local signal beam pass
510: direction adjustment unit
520: wave front adjustment unit
530: focus of light wave

Claims (8)

Dividing, by a fabrication device, a region of interest within the holographic optical element into a plurality of local regions;
deriving, by a fabrication device, local reference beams and local signal beams for individual local regions;
deriving, by a manufacturing device, a compensation reference wavefront and a compensation signal wavefront required for final recording by synthesizing the derived local reference beam and local signal beam;
Performing, by a manufacturing device, wavefront approximation of the compensation reference wavefront and the compensation signal wavefront; and
Performing, by the manufacturing device, optical recording of the holographic optical element based on the approximation result;
The step of deriving a local reference beam and a local signal beam,
performing grating modeling to be generated through interference between reproduction lights in individual local regions;
converting the modeled grating into a compensation grating required for recording according to medium shrinkage and wavelength deviation compensation; and
Deriving a local reference beam and a local signal beam capable of generating a transformed compensation grating;
The step of performing lattice modeling is,
When deflecting a projected beam of a wavelength entering a holographic optical element, a required grating vector is a vector that satisfies a predetermined grating tilt angle in a holographic recording medium,
The incident angles of the local reference beam and the local signal beam are
λ _d is the wavelength of light incident on the holographic optical element at θ _1,d , θ _2,d is the projection beam of wavelength λ _d , θ _1,r is the incident angle of the local reference beam, and θ _2,r is the local reference beam. If the angle of incidence of the signal beam is arranged according to Equation 1 below,
The incident angles of the local reference beam and the local signal beam are
θ _1,r is the incident angle of the local reference beam, θ _2,r is the incident angle of the local signal beam, λ _d is the wavelength of light incident on the holographic optical element at θ _1,d , and θ _2,d is the wavelength It is a projection beam of λ _d ,

If , it is arranged according to Equation 2 below,
The steps of performing optical recording include:
Optical recording is performed by allowing the local reference beam and the local signal beam derived for each local area to enter the individual local area, and the optical recording is repeatedly performed for the entire area of the holographic optical element, so that finally required ensure that a compensation reference wavefront and a compensation signal wavefront are implemented;
The steps of performing optical recording include:
When it is difficult to implement a compensation recording wavefront through a single optical element, a spatial light modulator (SLM) is used to complex-modulate a laser beam to implement a compensation recording wavefront as a target,
The wavefront complex modulated by the spatial light modulator is
Satisfying the compensation reference beam and compensation signal beam of each local area on the surface of the holographic recording medium,
The wavefront complex modulated by the spatial light modulator is
A wavelength compensation method for a holographic optical element, characterized in that, when a light wave converging to a compensation recording wavefront is required, it is approximated with a spherical wave having one focus or an array of spherical waves having a plurality of focus points.
(Equation 1)

(Formula 2)

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