KR20220043305A - Wavelength compensation method and system of hologrpahic optical element - Google Patents

Abstract

Provided are an optical structure, capable of preventing distortion of reproduced light by pre-compensating for the difference from the reproduced light during optical recording, and a manufacturing method thereof. According to an embodiment of the present invention, a wavelength compensation method of a holographic optical element, comprises the steps of: dividing, by a manufacturing device, a region of interest within a holographic optical element into a plurality of local regions; deriving, by the manufacturing device, local reference beams and local signal beams for individual local regions; deriving, by the manufacturing device, a compensation reference wavefront and a compensation signal wavefront required for final recording by aggregating the derived local reference beams and local signal beams; performing, by the 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 on the basis of an approximation result. Accordingly, a desired grid can be recorded by adjusting a light incident condition of an owned laser to relieve a requiring condition for matching recorded light and reproduced light, such that a manufactured holographic optical element-based head-mounted display (HMD) and head-up display (HUD) are low costs and can be used for a small projection module to allow advanced development through an introduction of a miniaturized light source and a low-cost light source.

Description

Wavelength compensation method and system of holographic optical element

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

Since the holographic optical element operates correctly only under the same light incident conditions as the optical characteristics such as the wavelength and radiation angle of the laser used when recording through optical recording, and outputs reproducing light without distortion, in the past, a laser having the same characteristics as the reproduction condition was used. It has been used for optical recording of holographic optical devices.

However, laser diodes or LEDs that can be supplied in chip form are preferred for light sources used in applications that need to satisfy small/low power characteristics such as head-mounted displays (HMDs). is very difficult, so a HOE (Hologrpahic optical element) recording technique through pre-compensation for reproduction light having an arbitrary wavelength and wavefront is required.

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

According to an embodiment of the present invention for achieving the above object, there is provided a method for compensating a wavelength of a holographic optical device, comprising: dividing, by a manufacturing apparatus, a region of interest in the holographic optical device into a plurality of local regions; deriving, by the fabrication apparatus, a local reference beam and a local signal beam for each local area; deriving, by the manufacturing apparatus, a compensation reference wavefront and a compensation signal wavefront necessary for final recording by synthesizing the derived local reference beam and local signal beam; performing, by the manufacturing device, wavefront approximation of the compensation reference wavefront and the compensation signal wavefront; and performing, by the manufacturing apparatus, optical recording of the holographic optical device based on the approximation result.

And deriving the local reference beam and the local signal beam may include: performing grating modeling to be generated through interference between reproduced lights in individual local areas; converting the modeled grating into a compensating 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 the converted compensation grating.

Also, in the step of performing grating modeling, when a projection beam having a wavelength incident on the holographic optical device is deflected, a required grating vector may be a vector satisfying a predetermined grating tilt angle in the holographic recording medium.

Incident angles of the local reference beam and the local signal beam are: λ _d is the wavelength incident to the holographic optical element at θ _1,d , θ _2,d is the projection beam of the wavelength λ _d , θ _1,r is the local If θ 2,r 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.

(Formula 1)

인 경우, 하기 수식 2에 따라 정리될 수 있다. Incidentally, as 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, λ _d is θ ₁ to the holographic optical element _{, d} is the incident wavelength, θ _2,d is the projected beam of wavelength λ _d ,

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

(Equation 2)

In addition, in the performing optical recording, the optical recording is performed by allowing the local reference beam and the local signal beam derived for each local area to be incident on the individual local areas, but with respect to 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.

In the step of performing optical recording, 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, thereby becoming a target 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 area on the surface of the holographic recording medium.

Meanwhile, according to another embodiment of the present invention, an apparatus for manufacturing a holographic optical device includes: a division unit for dividing a region of interest in the holographic optical device into a plurality of local regions; a local reference beam pass for deriving a local reference beam for an individual local area; a local signal beam path for deriving a local signal beam for an individual local area; a plurality of direction adjustment units for adjusting respective directions 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 compensatingly 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, a desired grating can be recorded by adjusting the light incident condition of the laser, so that the holographic optical element base manufactured by alleviating the requirement for recording light-reproducing light matching Inexpensive and small projection module can be used for HMD (Head-mounted Display) and HUD (Head-up Display) of

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

1 is a view provided for the explanation of a reproduction beam distortion problem due to wavelength deviation in an HOE lens-based see-through display;
2 is a flowchart provided for explaining a wavelength compensation method of a holographic optical device according to an embodiment of the present invention;
3 is a view 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 the description of a process for deriving a compensating recording wavefront from a local reference beam and a local signal beam;
5 is a view 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.

1 is a view provided for explanation of a reproduction beam distortion problem due to wavelength deviation in an HOE lens-based see-through display.

In general, a holographic optical element (HOE) records the interference pattern of two light waves (reference beam and signal beam) incident from different directions onto a recording medium (eg, photopolymer, photorefractive polymer, silver halide, etc.). created by recording.

At this time, the recorded interference pattern forms a periodically repeating volume grating in the holographic recording medium, and diffraction when the incident beam satisfies the Bragg condition of the volume grating in the subsequent reproduction step. Outputs a playback beam through 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 the diffracted light and distortion of the outgoing light direction occur.

1 is a diagram representatively exemplified of a see-through display using an HOE of a lens function.

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

If the wavelength ( λ _d ) of the projection beam is different from the wavelength of recording light ( λ _r ) of the HOE lens, as illustrated in FIG. 1B , the converging position of the HOE lens is changed according to the corresponding wavelength deviation, and the color of the image is blurred Or, in some cases, observation may not be possible.

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

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

The wavelength compensation method of the holographic optical device according to this embodiment considers the difference (wavelength, incident direction, etc.) between the recording light and the reproduction light and the medium shrinkage in the development of a see-through display using HOE. , it is possible to reproduce the light wave intended by the user in the reproduction stage without distortion or degradation of efficiency.

To this end, the wavelength compensation method of the holographic optical device according to the present embodiment divides the region of interest in the holographic optical device into a plurality of local regions using the wavelength-compensated holographic optical device manufacturing apparatus (S210). , it is possible to derive a local reference beam and a local signal beam for each local area.

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

And, the wavelength compensation method of the holographic optical device derives the compensation reference wavefront and compensation signal wavefront necessary for final recording by synthesizing the derived local reference beam and the local signal beam using a wavelength-compensated holographic optical device manufacturing apparatus. and (S250), perform wavefront approximation of the compensation reference wavefront and the compensation signal wavefront (S260), implement 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 device divides the entire area of the holographic optical device into a set of very few local areas, and then models the grating to be generated in each local area and compensates for it in the form of a plane wave. A reference beam and a local signal beam are derived.

This is because, although the grating in the entire holographic optical device is complex and non-periodic, if it is divided into a sufficiently large number of local regions, each local region can be approximated with a periodic and simple grating.

Therefore, wavelength and contraction compensation in individual local areas can be quickly performed based on periodic gratings, and compensation wavefront (compensation) necessary for actual recording by synthesizing the derived local reference beam and local signal beam over the entire HOE area. 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.

3 is a view provided for explanation of the reproduction light condition and the recording light condition in the process of deriving the local reference beam and the local signal beam.

Referring to FIG. 3 , if the projection beam of wavelength λ _d incident on the HOE at θ _1,d in the reproduction step is to be deflected to θ _2,d , the required grating vector is θ _g,d in the holographic recording medium. The grid tilt angle must be satisfied.

Based on this, the grating required in the recording step is derived in consideration of the contraction of the medium (the grating vector tilted to θ _g,r in Fig. 3), and two vector pairs of wavelength λ _r that satisfy the Bragg condition of the grating required for recording to save

In this case, the vector pair means the incident directions of the local reference beam and the local signal beam, respectively, and the incident angles θ _1,r , θ _2,r are different from the reproduction stage depending on the wavelength and the degree of contraction.

For example, λ _d is the wavelength incident to the holographic optical element at θ _1,d , θ _2,d is the projection beam of the wavelength λ _d , θ _1,r is the incident angle of the local reference beam, and θ ₂ If _,r is the incident angle of the local signal beam and the medium contraction is very small, the incident angles of the local reference beam and the local signal beam can be arranged according to Equation 1 below.

(Formula 1)

인 경우, 하기 수식 2에 따라 정리될 수 있다. Incidentally, as 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, λ _d is θ ₁ to the holographic optical element _{, d} is the incident wavelength, θ _2,d is the projected beam of wavelength λ _d ,

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

(Equation 2)

4 is a diagram provided for explanation of a process for 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 incident on individual local areas during the HOE fabrication and optical recording process, by repeating this for the entire HOE area, the finally required compensation reference wavefront and compensation signal wavefront can be realized. there is.

However, the compensating recording wavefront that has undergone such a process has a complex shape, so it may be difficult to implement through a single optical element.

In this case, a spatial light modulator (SLM) and the principle of holography can be used to reproduce a complex type of light wave in the recording process.

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

In addition, if necessary, it is of course possible to approximate a recording-needed light wave having a complex wavefront in a simple form for easy implementation of the manufacturing apparatus.

For example, when light waves converging to the compensating recording wavefront are required as shown in FIG. 4 , the wavelength-compensated holographic optical device manufacturing apparatus by approximating to a spherical wave (or spherical wave array) each having one (or multiple) focal points implementation cost can be reduced.

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

Generally, in manufacturing a holographic optical device operating in full color, the degree of wavelength deviation between the reproduction light and the recording light is different in each red, green, blue, and blue band.

Therefore, when recording a holographic optical element, sequential recording is suitable for each wavelength of red, green, and blue, and since the scheme for realizing a compensating recording wavefront for each wavelength may be different, as illustrated in FIG. There is a need for an optical recording device capable of finely adjusting the direction and focal position of incident light from both sides of the signal beam.

To this end, the 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 method for deriving a local reference beam for each local region. A local reference beam path 502, a local signal beam path 503 for deriving a local signal beam for an individual local area, a plurality of direction adjustment units 510 for adjusting the directions of the local reference beam path and the local signal beam path, respectively; A plurality of wavefront adjustment units 520 for converting the parallel light of the laser into a compensatingly designed light wave for each of the local reference beam path and the local signal beam path is included.

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

And in each beam path, the direction adjusting unit 510 for adjusting the direction of the beam path, and the wavefront adjusting unit 520 for converting the parallel light of the laser into a compensated designed light wave are at the wavelength of each step to record the position of the focal point 530 of the light wave. It plays a role in moving.

The direction adjustment unit 510 must support a minute rotation function of at least one axis in order to support the rotation movement up, down, left, and right.

For example, the direction adjustment unit 510 may be implemented as a 2-axis electric scanning device using a Galvo Mirror, a MEMS Mirror, or the like.

The wavefront adjustment unit 520 must support movement in the uniaxial direction, and may be composed of a single lens or a lens group such as a spherical surface, an aspherical surface, a free-form surface, etc. linked to the motorized stage.

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

If the complex compensating recording wavefront is not approximated as described above, the wavefront adjusting unit 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.

In the above, preferred embodiments of the present invention have been illustrated and described, but the present invention is not limited to the specific embodiments described above, and it is common in the technical field to which the present invention pertains without departing from the gist of the present invention as claimed in the claims. Various modifications are possible by those having the knowledge of, of course, and these modifications should not be individually understood from the technical spirit or perspective of the present invention.

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

Claims (8)

dividing, by the manufacturing apparatus, the region of interest in the holographic optical device into a plurality of local regions;
deriving, by the fabrication apparatus, a local reference beam and a local signal beam for each local area;
deriving, by the manufacturing apparatus, a compensation reference wavefront and a compensation signal wavefront necessary for final recording by synthesizing the derived local reference beam and local signal beam;
performing, by the manufacturing device, wavefront approximation of the compensation reference wavefront and the compensation signal wavefront; and
A method of compensating for a wavelength of a holographic optical device, comprising: a manufacturing apparatus, performing optical recording of a holographic optical device based on the approximation result.
The method according to claim 1,
The step of deriving a local reference beam and a local signal beam includes:
performing lattice modeling to be generated through interference between the reproduced light in individual local regions;
converting the modeled grating into a compensating grating required for recording according to medium shrinkage and wavelength deviation compensation; and
and deriving a local reference beam and a local signal beam capable of generating a converted compensation grating.
3. The method according to claim 2,
The step of performing lattice modeling is,
A method of compensating for a wavelength of a holographic optical device, characterized in that when a projection beam of a wavelength incident on the holographic optical device is deflected, a required grating vector is a vector that satisfies a predetermined grating tilt angle in the holographic recording medium.
4. The method according to claim 3,
The incident angle of the local reference beam and the local signal beam is,
λ _d is the wavelength incident to the holographic optical element at θ _1,d , θ _2,d is the projection beam of the wavelength λ _d , θ _1,r is the incident angle of the local reference beam, and θ _2,r is the local If the incident angle of the signal beam, the wavelength compensation method of a holographic optical device, characterized in that it is arranged according to Equation 1 below.
(Formula 1)

4. The method according to claim 3,
The incident angle of the local reference beam and the local signal beam is,
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 incident to the holographic optical element at θ _1,d , θ _2,d is the wavelength is the projection beam of λ _d ,

In the case of , the wavelength compensation method of a holographic optical device, characterized in that it is arranged according to Equation 2 below.
(Equation 2)

The method according to claim 1,
The steps of performing optical recording include:
Optical recording is performed by allowing the local reference beam and local signal beam derived for each local area to be incident on the individual local area, but by repeatedly performing optical recording for the entire area of the holographic optical element, finally required A method of compensating for a wavelength of a holographic optical device, characterized in that a compensation reference wavefront and a compensation signal wavefront are implemented.
7. The method of claim 6,
The steps of performing optical recording include:
When it is difficult to implement a compensating recording wavefront through a single optical element, a spatial light modulator (SLM) is used to complex-modulate a laser beam to implement a target compensated recording wavefront,
The complex modulated wavefront by the spatial light modulator is
A method of compensating a wavelength for a holographic optical device, characterized in that it satisfies a compensation reference beam and a compensation signal beam of each local area on the surface of the holographic recording medium.
a division unit dividing the region of interest in the holographic optical device into a plurality of local regions;
a local reference beam pass for deriving a local reference beam for an individual local area;
a local signal beam path for deriving a local signal beam for an individual local area;
a plurality of direction adjustment units for adjusting respective directions of the local reference beam path and the local signal beam path; and
An apparatus for manufacturing a wavelength-compensated holographic optical device, comprising: a plurality of wavefront adjusting units for converting parallel light of a laser into a compensatingly designed light wave for each of a local reference beam path and a local signal beam path.

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