KR910007718B1 - Achromatic holographic element - Google Patents

Abstract

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Description

Achromatic holographic optical element and manufacturing method thereof

1 is a schematic diagram of an optical input into a recording medium used to construct a holographic optical element.

2 through 4 are cross-sectional views of interference phenomena associated with the various recording media of FIG.

5 is a schematic diagram of the diffraction characteristics of a conventional holographic optical element.

6 is a schematic diagram of an optical input to a recording medium for use in manufacturing a holographic optical element according to the present invention.

7 is a schematic diagram of the diffraction graph diffraction characteristics of the holographic optical element according to the present invention.

8 is a diagram showing interference characteristics of a thick recording medium according to the present invention.

9 is a schematic representation of a preferred embodiment of the device according to the invention.

10 is a fragmentary view of another embodiment of a device according to the invention.

11 is a schematic diagram of another embodiment of the device according to the invention.

12 is a schematic diagram of the diffraction characteristics of a thick medium according to the present invention.

* Explanation of symbols for main parts of the drawings

14 substrate 54 laser

56: output beam 58: beam splitter

10: input beam 36: reference beam

38: recording plate 40: signal beam

64: aiming lens system 66: mirror

70: recording medium 72: glass plate

76: short focal length lens 80: adjusting means

82: control pin hole assembly 136: holographic diffraction grating

142: independent focus

The present invention relates to a chromatic holographic optical element and a method of manufacturing the same.

The term hologram is used to describe an increasingly popular photographic process. Unlike conventional photographs that record a three-dimensional scene as a two-dimensional image, the holographic process does not record an image of a subject to be photographed, but forms a reference beam and an interference light pattern generated by a reflected light wave from the same light source. When the reflected light wave itself is recorded. Thus, the hologram contains all the information that characterizes the object through which light waves pass or reflect or scatter light waves. When the object is an optical element such as a lens, matching filter or diffraction grating, the hologram will exhibit all the phenomena and properties of this optical element. Representative characteristics of holographic optical elements are focus, scale size and declination.

Conventionally, holograms containing holographic optical elements were made using a special wavelength laser called the constituent (C) wavelength, and regeneration (PB) or reconstruction wavelengths of the holographic elements were completed using lasers of the same or different wavelengths. . In the conventional hologram, when lasers of different wavelengths are used for regeneration, the main characteristics of the holographic optical elements, including declination, focus and scale size, are changed.

In application of holographic optical elements, it may be desirable to maintain performance parameters regardless of the wavelength of the laser used for the regeneration function. It is an object of the present invention to provide means for substantially reducing the wavelength dependence of holographic optical elements and a method of making such means uniquely.

In constructing the holographic optical element, as shown in FIG. 1, on the recording medium on which an input beam 10 called a signal beam S can be coated or installed on a suitable substrate 14 such as a glass plate, a thin film, or the like. Project it to enter As is already known, the recording medium 12 may be a photographic emulsion, dichromate gelatin, photopolymer, or the like. At the same time, since the second coherent electron radiation source, preferably a second beam called the reference beam R, is guided from the laser at an angle θ ₁ , the second beam overlaps the signal beam 10 in the medium. Incident on the recording medium 12 as much as possible. This results in optical interference which is recorded as the amplitude or phase distribution of tightly spaced lines in the medium. This pre-array is shown in FIG. 2 as the cross section in the amplitude distribution of the clear region 18 and the light absorbing region 20 in the recording medium 12 or in the recording medium 12 as shown in FIG. It can take various forms, such as phase distribution caused by the difference in refractive index 22 within, or spatial or undulating fluctuations 24 on the surface of the recording medium 12 as shown in FIG. As is well known, these forms exhibit different phenomena, the first form representing absorption through silver halides, the second form diffraction due to refractive index variation, and the third form diffraction through variation of surface relief. In the last case, the absorption area or the refractive index fluctuation area may be accompanied by the surface relief pattern of the recording medium or the plate.

In the optical interference phenomenon shown in FIG. 1, the interval between optical interference lines, also known as fringe lines, is obtained by the following equation regarding the case where the signal beam 10 is a normal to the recording plate.

When the latter condition is not true, the general formula is

The negative sign prevails when two beams are on the same side of the recording plate normal, and the positive sign prevails on the opposite side. However, if θ _S = 0 is assumed, generality is not lost, and it can be explained using Equation (1).

If the object is complex or enlarged, equation (1a)

This indicates that the signal beam incidence angle depends on the two-dimensional distribution of the origin.

The angles θ ₂ are different, but if the reference beams 26 having the same wavelength are used, the recording fringe patterns will be different fringe spacings. In other words,

Here, it is assumed that the common wavelength? Is used, only the angle? Is changed, and it is assumed that the two fringe patterns are sequentially recorded in the same recording medium.

)을 통하여 회절되고, 입력빔(28)의 λ_PB2의 출력빔(34)은 각(W)을 통하여 회절될 것이다.In FIG. 5, it is assumed that the input beam 38 incident on the recording plate 30 is a combination of two wavelengths, the incident beam is recorded, and the recording medium is properly processed. In the reconstruction process, the wavelength including the input beam may be represented as λ _PB1 or λ _PB2 . One of the two wavelengths may be the constituent wavelength λ ₁ , but since such conditions are not critical, it can be assumed that this wavelength is absent for this description. In regeneration, the normal condition is that different wavelengths are diffracted through different angles. Therefore, the input beam 28 is the output beam 32 of λ _PB1 is an angle (

), And the output beam 34 of λ _PB2 of the input beam 28 will be diffracted through the angle W.

In constructing a chromatic optical element such as a diffraction grating, whether or not the two wavelengths can be incident simultaneously on the diffraction grating or similar diffractive elements (when θ _S = 0) and still provide the same diffraction angle to be.

The diffraction equation is as follows.

Here, m is an order of the diffraction gratings, and D is a diffraction angle when a beam of wavelength lambda is normally incident on the diffraction grating of the fringe spacing d.

Since the common angle (D) is preferred,

In other words, the two wavelengths will be diffracted at the same angle D by the diffraction grating when they are related to each other inversely of the sine ratio of their constituent angles. This can be extended even if the number of wavelengths is larger if the following conditions are met in equation (2).

(A) The beam should enter the diffraction grating normally.

(B) The beam shall be made at one wavelength (λ ₁ ).

(C) The following general formula shall be established.

In the case where there is a wavelength other than a single wave, the diffraction grating does not need to be made at one wavelength as long as it is compensated by the equation (1d). The latter is rare, but cannot be ruled out in advance.

Now consider the following relationship with respect to the focal length of the holographic lens HL.

Here, F and λ are focal lengths and wavelengths applicable to the construction of the holographic optical element and the reconstruction or reproduction using the holographic optical element.

For both wavelengths,

F _PB1 = F _PB2 is required for playback or reconstruction.

In the above, it was found that λ _C1 = λ _PB1 ,

Or λ _C1 can be made equal to λ _C2 ,

λ _C1 = λ _C2 Thus,

This formula seems to be similar to equation (2).

Here is a special example with the parameters selected:

λ _C = 4880Å

F _C1 = 360mm

θ ₁ = 30˚

λ _PB1 = 4880 Å (choose both because of the common laser wavelength)

λ _PB2 = 6328Å

F _C1 = 360mm (since constituent wavelength and one reconstruction wavelength are one and the same)

F _C2 = 466.8mm

FIG. 6 shows that one reference beam 36 interacts with the signal beam 40 as long as the focal length 42 of the recording plate 38 is F _C1 . The second signal beam 44 whose focal length 46 is F _C2 also interacts with the reference beam 36 in the recording plate 38 to exhibit an interference pattern in the recording plate. Beams 36 and 40 should have the same wavelength and beams 36 and 44 should have a second common wavelength. If these wavelengths are not the same, the angle of incidence θREF of the reference beam should be adjusted according to the equation given earlier. The recording plate forms a holographic lens after conventional processing. If the numerical condition set forth above is met, the holographic lens 38a thus formed will function as shown in FIG. The input beams 48 and 50 of different wavelengths will be diffracted by the holographic lens 38a so that the combined output beams 48a and 50a actually converge at the co-focus 52.

이다.The recording medium used in the holographic process is 1 to 20 microns thick. However, it is generally advantageous to use a thick medium of about 20 to 100 microns in thickness for the process. Thick media for record gratings are characterized by Kline's Q criterion, which is Q =

to be.

If the angle of incidence in the diffraction grating is Q '= Q / cos where λ is the free-space wavelength, d is the thickness of the recording medium, n ₀ is the average refractive index, and λ ² is the diffraction grating spacing (assuming that the spacing is uniform here Is).

When the diffraction grating is recorded in a thick medium, not only the angle of incidence of reproduction should be taken into account but also the angle of incidence based only on the diffraction grating interval and this gap. This is due to the Bragg effect. The angle of incidence according to the Brac law is a high efficiency beam, otherwise the angle of incidence is inefficient and may be attenuated beam. The Brack's law is 2d N sin θ = λ. Where N is the refractive index.

In FIG. 8, when two beams interfere at angles θ _C1 and θ ′ _C1 , a fringe 96 is formed in the thick recording medium 97, and the reproduction angle of maximum efficiency is θ _PB1 (98). Should be. Here, if θ _PB1 is obtained from equation (4),

Using a second set of angles (and initially a second wavelength),

Or using equation (5) for both cases,

If λ _C1 = λ _C2 , (normal but unnecessary procedure)

If sinθ _C1 = 0 (common but unnecessary procedure)

The above equation is similar to equation (2a).

To regenerate at the joint break angle, the wavelength must be within the ratio given for equation (7b). For example, the reproduction wavelength is 6328Å, 4880Å,

Or sinθ _C2 ± sinθ _C2 '= · 65

θ _C2 = 10 °, θ ' _C2 = 27 ° 18', and many other combinations.

When the cavity regeneration angle is obtained from equation (5), sin ⁻¹ · 325 = 18 ° 35 '.

θ _C2 and θ ′ _cz can not be arbitrarily determined, and the _reproduction angle is common with the _reproduction angles of the configuration angles θ _C1 and θ ′ _C1 .

U.S. Patent Application No. 3,586,412 exposes the recording medium at different angles to the two intersecting input beams so that the individual non-aberration band plates are configured for each exposure angle in a single three-dimensional recording medium for scanning virtually any object. We have disclosed a method of constructing a holographic lens that can obtain a composite image of an object without using it. This patent implies that the lens can also be used at multiple wavelengths, but it does not specify the conditions necessary for obtaining hydrochromic regeneration. Another U.S. Patent Application No. 3,503,050 discloses an improvement in the riffman-type process, in which an interfering wave of coherent light detects a layer of photosensitive emulsion at the breaking of standing waves in the emulsion to form a periodic reflecting surface structure. do. This structure is formed at a different angle at one point in the emulsion and is read by the angle of the reflected light. However, as in the case of the aforementioned patents, it has not proved here that the recorded beam angles must be a set of angles specified so that the entire wavelength or white light can be co-focused. In addition, this patent does not indicate that fringe arrangements on the surface of thin recording media in white light reproduction should be particularly specified.

Therefore, the main object of the present invention is to provide a holographic optical element with low aberration while operating at multiple wavelengths. It is another object of the present invention to provide a method for manufacturing such a chromatic holographic optical element.

It is another object of the present invention to use a thick recording medium capable of generating a pair of symmetrical output beams having two independent focal points as a single input beam.

The present invention will be described in more detail with reference to the accompanying drawings.

9 shows an apparatus for use in manufacturing a holographic optical element according to the invention, such as a rotating lattice. A suitable coherent light source, such as laser 54 operating at wavelength λ _C1 , has an output beam 56, which passes through beam splitter 58 and has beams 60, 62 of approximately equal intensity. Generates. The beam 60 used as the holographic reference beam may pass through the aiming lens system 64 and then impinge on the recording medium 70 by the mirrors 66 and 68 at an appropriate angle θ ₁ . Are guided. As the recording medium, a well-known suitable photosensitive material can be used, and if necessary, a suitable means such as glass plate 72 can be provided as the support. The beam 62 used as the signal beam is guided by the mirror 74 to the short focal length lens 76, and the output beam 78 of the lens is guided to the recording medium 70. The beam 78 interferes with the reference beam 60 and this interference is recorded by the medium.

The devices described above are primarily for use in the process of manufacturing conventional holographic optical elements. However, in the process of the present invention, once the beam 60 is recorded at the incident angle θ ₁ , the mirror 68 is adjusted by suitable adjusting means 80, and the beam 60 is beamed at the incident angle θ ₂ . It is recorded while interfering with (78). When necessary to record the interference in the incident angle (θ ₃ ... θ _n) has to repeat this procedure.

라는 관계를 얻는다.When beams of different optical wavelengths by the above description of the present invention is related to each other in the ratio of the inverse of that configuration, each (θ _i θ _j ...) and it can be seen that the holes in the same diffraction angle by the graph optical element. As mentioned earlier, the beam is made at one wavelength, as long as it is normally incident on the element, and from equation (2)

Get a relationship.

일 때 일어난다.If the holographic optical element is a lens, the various wavelengths of the beam diffracted by the chromaticity should actually be concentrated at a common focal point. This action requires that the numerical conditions in the equations (3 to 3e) are met,

Happens when

To change the focal length required during the construction of the chromosomal lens of the present invention, the apparatus shown in FIG. 9 is changed as shown in FIG. 10 by inserting the adjusting pin hole assembly 82 in the passage of the signal beam. . Accordingly, although not shown, in the embodiment of FIG. 10, the light source, the beam splitter, the aiming lens system, and the first mirror shown in FIG. 9 for generating the reference beam 60 'and the signal beam 62' Will be. The reference beam 60 'is guided by the adjustment mirror 68' to impinge on the recording medium 70 'at an appropriate angle &thetas; ₁ . The signal beam 62 'is guided by the mirror 74' to the pinhole assembly 82 including the short focal length lens 84 and the pinhole diaphragm 86. As indicated by the arrow 90, the pinhole assembly is provided with an adjusting mechanism 88 which can be selectively adjusted in parallel movement. The output beam 78 'exiting the pinhole assembly is a spherical spherical wave. This beam is guided to the recording medium 70 'at the focal length F _C1 so that it can interfere with the reference beam 60' and this interference is recorded by the recording medium.

In the process of the present invention, once the reference beam 60 'is recorded at the incident angle θ ₁ and the signal beam 62' is recorded at the focus F _C1 , the mirror 68 'and the pinhole assembly 82 Are adjusted by the adjusting means 80 'and 88, respectively, and the beam 60' is recorded at the focal point F _C2 at the incident angle [theta] ₂ , respectively. When it is necessary to record in the beams 60 ', 62' angle of incidence of interference of (θ θ ₃ ... _n) and the focus (F F _C3 ... _Cn) may repeat this procedure.

의 일반관계식을 얻게 된다. 재생에 있어서는 2개의 파장(λ_C1,λ_C2)은 기록매체(116)에서 전개되는 홀로그래프 광학요소에 의하여 여기에서 나오는 출력이 실제로 제7도에 도시된 바와같이, 공통촛점에 이르도록 회절될 것이다.Above, the process of constructing the achromatic holographic optical element using single wavelength coherent electron radiation has been described in detail. However, as long as the mathematical relationship of the present invention is maintained, more than one wavelength of radiation can be used to construct the optical element. In FIG. 11, the apparatus includes a light source, such as a laser 100 operating at a wavelength λ _C1 , which passes through a beam splitter 104 to the reference beam 106 and the signal beam 108. There is an output beam 102 which generates. The reference beam 106 passes through the aiming lens system 110 and is mounted on the support 118 by mirrors 112 and 114 at a suitable angle θ ₁ . The signal beam 108 is guided to the adjustment pinhole assembly 122 by the mirror 120, and the output beam 124 of the pinhole assembly is combined with the reference beam 106 to interfere with the recording medium 116. Is guided to. As can be understood from the description of another embodiment of the present invention illustrated above, when the constituting optical element is a lens, the pinhole assembly 122 focuses the focus of the signal beam 124 on the recording medium 116 (F). _C1 ). In the case where the constituent optical element is a diffraction grating, a lens such as that shown in the embodiment of FIG. 9 may be used instead of the pinhole assembly and the adjusting means to change the focal length of the signal beam. The second radiation source at wavelength λ _C2 can be a laser 126, the output beam 128 of which is through the beam splitter 104, and the light beam passing through it is in line with the signal beam 108. The light rays reflected therefrom are guided to be in line with the reference beam 106. Once the output of the second laser 126 is recorded, the mirror 144 and the pinhole assembly 122 are adjusted to record the interference of the light beam at the incident angle θ ₂ and the focal length F _C2 . If necessary, in order to record the reference beam and the signal beam interfere with the incident angle of (θ θ _c3 ... _Cn) and the focus (F _C3 ... _Cn Fθ) has to repeat this procedure. As mentioned earlier,

You get a general relation of. In reproduction, the two wavelengths λ _C1 , λ _C2 are diffracted by the holographic optical element developed on the recording medium 116 so that the output from it actually reaches a common focal point, as shown in FIG. will be.

Instead of adjusting the mirror 114 to vary the angle of incidence of the reference beam 106 with respect to the second or subsequent wavelengths, a supplementary mirror, such as mirror 130, may be inserted into the beam. In the present invention, conventional means other than those shown for generating coherent radiation in a plurality of discrete wavelengths can also be used. Typical of such devices include parametric converters or interactors as disclosed in US Patent Application No. 4,250,465 to the inventors of the present invention.

It is advantageous to use thick media for the process. As mentioned above, thick media generally have a thickness of about 20 μm to 100 μm. When the reference beam is guided on either side of the recording plate normal to record the hologram, there is a single angle that generates a pair of symmetrical output beams with the same energy, which simultaneously satisfies the Bragg angle. Thus, during regeneration, two independent focuses are obtained from the thick assembly (see FIG. 12). As shown in the figure, the input beams 132, 134, which are different wavelengths, are two output beams having two independent focuses 142, 144 by the holographic diffraction grating 136 of a thick medium. 138), 140 will be diffracted.

During the construction of the holographic element, the actual input angle depends on the equation given above and on the refractive index of the material used for the thick medium. For example, with dichromate gelatin having a refractive index of n = 1.54, the reference beam incident angle for regeneration will be about ± 10 degrees to achieve the conditions shown in FIG.

Claims (14)

An achromatic holographic diffractive optical element, comprising a photosensitive recording medium containing particles arranged to form a periodic structure by combining a plurality of parallel planes successively spaced at equal intervals, wherein each combination of the periodic structures includes the recording. A chromatic holographic diffractive optical element comprising a pair of lift reflecting surfaces having equal intervals extending over the entire thickness of the medium, the angles being inversely related to each other. An achromatic holographic diffractive optical element, comprising a photosensitive recording medium having a combination of a plurality of parallel optical diffraction surfaces arranged at equal intervals to form a periodic structure on a surface, wherein the constituent angles of the structures differ from each other in terms of their sine ratio. An achromatic holographic optical element, which is inversely related. 2. The achromatic holographic optical element of claim 1, wherein the recording medium has a thickness of about 20 to 100 microns. 3. The light-colored holographic optical element of claim 2, wherein the recording medium has a thickness of 20 microns or less. A method of manufacturing a light-receiving optical element that diffracts radiation of wavelengths λ ₁ ..., _{N n} , wherein in a three-dimensional photosensitive recording medium, a pair of first interconnections each having a wavelength of λ ₁ and including a signal beam and a reference beam A common portion of the coherent magnetic beam is first exposed, and the beam is incident on the recording medium, wherein the signal beam is an incidence normal to the surface of the medium, and the reference beam is an angle of incidence (θ) relative to the surface normal. ₁ ) forming a first diffraction means having a periodic structure in the medium by the exposure, and another pair of wavelengths in the recording medium having a wavelength of ₁ and including a signal beam and a reference beam. The second portion of the common portion of the interfering electron beam is secondly exposed, and the reference beam is incident on the recording medium at angles θ ₂ to θ _n, respectively, and another overlapping _circuit having a periodic structure in the medium is caused by the exposure. A cutting means is formed, and the angles (θ ₁ ... θ _n ) are related to each other in the inverse of their sine ratio, and the optical element emits radiation of the wavelengths (λ ₁ ... λ _n ) by a common angle.

A diffractive holographic optical device manufacturing method comprising the step of diffraction to be established. 6. The method of claim 5, wherein the signal beam becomes a diverging beam of focal length F ₁ during the first exposure in the recording medium, and a diverging beam of focal length F ₂ during the second exposure. each is one another (θ ₁ ... θ _n) is related to the sine of the ratio of reverse, the optical element is a wavelength radiation in the general equation for (λ ₁ ... λ _n) to a common focal

A diffractive holographic optical element manufacturing method, characterized in that the diffraction to achieve this. 6. The method of manufacturing a chromatic holographic optical element according to claim 5, wherein the optical element to be manufactured is a diffraction grating. The method of manufacturing a chromic optical element according to claim 5, wherein the optical element to be manufactured is a lens. 7. A method according to claim 5 or 6, wherein the recording medium has a thickness of about 20 to 100 microns. 6. The water repellency according to claim 5, wherein the periodic structure of the diffraction means formed by exposure is in the surface of the recording medium, and the optical element diffracts the radiation of wavelengths lambda ₁ ... lambda _n through a common angle. Holographic optical device manufacturing method. 7. A method according to claim 6, characterized in that the periodic structure of the diffraction means formed by exposure is a band plate in the surface of the recording medium, and the optical element diffracts radiation of wavelengths lambda ₁ ... lambda _n to a common focus. A method for manufacturing a chromatic holographic optical element. The method of claim 10 or 11, wherein the recording medium has a thickness of 20 microns or less. A method of manufacturing a chromatic holographic optical element that diffracts radiation of wavelengths λ ₁ ..., _{N n} , wherein a pair of mutually having a signal beam and a reference beam having a wavelength of λ ₁ in a thick three-dimensional photosensitive recording medium A common portion of the coherent electron beam is first exposed, the signal beam being an incidence normal to the surface of the medium, and the reference beam from the side of the medium normal to the medium thick at an incident angle θ ₁ with respect to the surface normal. Forming a first band plate having a periodic structure in the medium by the exposure, and another pair of interfering magnetisms having a wavelength λ _{1 in} the recording medium and including a signal beam and a reference beam. the intersection of the beam and the second exposure, each wavelength θ ₂ of the reference beam from either side of the medium normal ... sikimyeo abscisic the thicker the medium in the incident angle of θ _n, sikidoe by the exposure to form a second overlap zone plate having periodic structures in said medium, respectively (θ ₁ ... θ _n) is to be related to each other as the inverse of the sign ratio and the thick optical element is a wavelength (λ ₁ ... λ _n) the general equation for a copy of the two output beams with a common focus of the medium

A diffractive holographic optical device manufacturing method comprising the step of diffraction to be established. 14. The method of claim 13, wherein the recording medium has a thickness of about 20 to 100 microns.

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