JPH08136856A - Device and method for optical collimation - Google Patents

Abstract

PURPOSE: To provide a small image light collimating device as well as an image light collimating method, ensuring an improved image transfer function. CONSTITUTION: A light collimating device 10 utilizes an optical (concave) mirror 16 and a cholestric liquid crystal element 14 for efficiently projecting image light within the line of sight of an observer O. Furthermore, the image light is generated, using a light component having the prescribed circularly polarized light rotating direction within the prescribed band width. In this case, the light image is transmitted, so as to be reflected from the concave mirror 16 acting for the enlargement (collimation) of the image light and for the projection of an image light component existing within band width B and having a proper circularly polarized light rotating direction, toward the cholestric liquid crystal element 14. Thus, the cholestric liquid crystal element 14 substantially reflects a returned image toward the observer O.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention generally relates to, for example,
The field of visual display systems for purposes such as entertainment, training, simulation, vehicle status display, virtual reality, machine maintenance, etc. In particular, the present invention collimates the generated image light to focus it within the line of sight of an observer so that it appears at or near infinity and yet provides a high degree of transmission of the image incident thereon. Regarding

[0002]

Optical collimating devices have been known for some time. An example of image light collimation is 1972 May 5.
Reissued March 9, US Pat. No. Re27,356, which uses a single spherical compound mirror as the imaging element. The primary image is sent to the convex surface of the mirror, which sends the image to a birefringent beam splitter array located on the concave surface of the mirror. The array reflects the image back to the spherical mirror, which collimates the image for viewing by an observer. Some polarization filters in the optical path
Selectively send the part of the primary image that returns to the spherical mirror. However, filtering and reflection of the primary image tends to progressively reduce the intensity of the image. The result is a final transmission near 0.5 to 1.0% of the initial intensity of the primary image.
Therefore, the image source must have sufficient power to produce an image of acceptable brightness when viewed.

Another collimating system described in US Pat. No. 3,940,203 issued Feb. 24, 1976 is that the spherical mirror is replaced by a reflective holographic analogue of the spherical mirror. This is a modification of the above-mentioned US Pat. No. Re27,356.
Again, a relatively large number of reflections and transmissions are used to properly control the image light reaching the observer. By using the improved reflection and transmission of the holographic element, efficiencies on the order of 6-10% of the original intensity of the image are achieved.

Collimation devices are also found in head-up display (HUD) systems cooperatively associated with a combiner element that superimposes the generated image on the forward field of view. In many configurations, the combiner element and the collimation device require multiple filtering and reflection of the generated image, which can affect transmission and have a negative effect on image brightness, as described above. An example of a modern system of this type is found in U.S. Pat. No. 4,859,031 issued Aug. 22, 1989. There, a system that utilizes the properties of cholesteric liquid crystals as an efficient reflector to a semi-reflecting concave mirror, and then an efficient transmitter of the collimated image to the observer, in order to get a good effect. Is explained. The image collimating device is arranged between the image source and the observer, and the generated image is first polarized into circularly polarized light in a particular rotational direction. When so polarized, the image is transmitted to a semi-reflecting mirror which is then reflected by the mirror. This configuration has a transmission efficiency higher than that of the prior art, and at best 12.
Although improving to 5%, the multiple reflection paths of the polarizing and semi-reflecting concave mirrors can still negatively affect the image intensity.

[0005]

Therefore, there is currently a need in the art for an optical collimating device having improved transmission of images. In addition, applications of such optical devices include head-mounted display systems or other applications where size and weight are important.
A need currently exists for such an optical collimating device that is small and lightweight.

[0006]

SUMMARY OF THE INVENTION The present invention is a compact image light having improved image transmission for forming an image within the line of sight of an observer, preferably at or near infinity. The present invention relates to a collimating device. Another embodiment of the invention enables collimation with a combiner, also with improved image intensity, to optically superimpose multiple images for viewing by an observer.

According to an embodiment of the present invention, a collimation device includes an image source for generating image light having a component within a predetermined bandwidth and having circularly polarized light in a specific rotation direction, a cholesteric liquid crystal element, and a concave surface. And an optical mirror. The cholesteric liquid crystal element is arranged so as to receive the image light and send the image light to the curved (concave) surface of the optical mirror. The optical mirror expands (collimates) the image light and returns it to the cholesteric liquid crystal element, and when doing so, reverses the rotation direction of the circularly polarized light of the image. The component of the returned image light that is within the predetermined bandwidth and has the specific circular polarization is then reflected by the cholesteric liquid crystal element into the line of sight of the observer.

In another version of the above-described embodiment of the present invention, the cholesteric liquid crystal element emits image light from the image source having circular polarization and wavelength in a predetermined rotation direction,
Formed and arranged to reflect onto the concave optical mirror. The optical mirror returns the collimated image light to the cholesteric liquid crystal element by reversing the rotation direction of the circularly polarized light of the image, and the returned image light is then viewed by an observer by the cholesteric liquid crystal element. It is made transparent on the line. Also in this case, the image light projected from the image source having the rotation direction opposite to the rotation direction of the circularly polarized light reflected by the cholesteric liquid crystal element, if any, is transmitted out of the line of sight of the observer.

According to the present invention, the generated image light is transmitted to the observer 100 times.
It can be sent with a strength near%. In another configuration of the invention, where the image light is superimposed on the front field of view of the observer,
The strength is reduced by about 50%.

The image source is, of the many possible technologies, preferably a liquid crystal display (LCD), but other image sources such as a cathode ray tube (CRT) may also be used. A liquid crystal display as an image source produces image light which is linearly polarized and can be easily and efficiently converted into circularly polarized light by a quarter-wave delay device having substantially no intensity loss. Such an arrangement would give the observer at best 25% of the original image intensity.
Gives the image intensity of.

One feature of any of the embodiments of the present invention is that the image transmission through the semi-reflecting mirror and the subsequent reflection from the semi-reflecting mirror, which was done in the prior art, is
It has been avoided. The present invention reduces the effect of the focusing mirror on image transmission over that of the prior art. The transmission efficiency of the image is increased because the cholesteric liquid crystal element can transmit and / or reflect a higher percentage of the incident light.

A second advantage of the present invention is that additional sources, or sensors, may be combined with the present invention. For example,
In another embodiment of the invention, the additional source may be located opposite the original image source from the cholesteric liquid crystal element. The additional source may effectively superimpose additional information into the line of sight of the observer, and / or if, for example, the image source is a reflective device or a photo-actinic device.
It can be used to illuminate the image source as desired if an iv photonic device. The sensor may be used to record the image produced by the image source and / or the observer's eye and / or the produced image reflected by the observer's eye, for example for the purpose of eye tracking.

In another embodiment of the invention, two separate image sources are provided to produce the image projected onto the cholesteric liquid crystal device. One has an image light portion with a predetermined rotation direction which is reflected by the cholesteric liquid crystal device to a focusing mirror. The mirror is then arranged to reflect the image light back to the cholesteric liquid crystal device and reverses the direction of rotation of the image light so that the image light is within the line of sight of the observer by the cholesteric liquid crystal device. Is transmitted to. The other image has a predetermined image light projected directly into the line of sight of the observer. In this way, the present invention
Used to give multiple images for observation, one collimated and magnified, the other not.

In yet another embodiment of the invention, an LCD is illuminated by a light source to produce a light image projected onto a cholesteric liquid crystal device. These and other advantages and features of the invention will be apparent to those of skill in the art upon reading the following description of an embodiment of the invention and other embodiments with reference to the accompanying drawings. It should be clear.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes certain properties of cholesteric liquid crystal (CLC) devices known to those skilled in the relevant arts of the present invention. For a detailed description of their properties, see US Pat. No. 4,859,031 or 4,90.
See the discussion in No. 0,133. For the sake of completeness, but rather to assure an understanding of the invention in this single document, some of their nature is outlined here before discussing the details of the invention.

A cholesteric liquid crystal (CLC) device is (1) within a specific bandwidth projected onto the device,
(2) It may be configured to reflect a component of light, which is circularly polarized light in a specific rotation direction. For example, a CLC device may be configured to reflect light components that are within bandwidth B and that have right circular polarization (RHCP). The reflected light retains its original direction of rotation (RHCP). On the other hand, CL
Left circularly polarized light within the bandwidth B (LHC
All other components of the image light, including the light component with P), pass through the CLC device unchanged. Of course, conversely, the CLC may also be configured to pass, i.e., transmit, light components having an RHCP rotation direction within the bandwidth B and reflect light components having an LHCP rotation direction.

Referring now to the drawings, and in particular to FIG. 1A, there is shown an embodiment of the optical collimating device of the present invention. A light collimating device, generally designated by reference numeral 10, is a type of cholesteric liquid crystal (CLC) configured to reflect an image light component having a particular circular polarization within a bandwidth B.
It is shown to include the device 14. The reflected light is
Retain its original direction of rotation, as described above. However, it is not within bandwidth B and / or even if bandwidth B
The incident image light component on the CLC device 14, which does not have the specific circularly polarized light inside, is transmitted through the CLC device 14 without change.

Due to the chemical nature of the CLC material, the CLC device 14 can reflect circularly polarized light with either direction of rotation, that is, left-right, and for the purposes of this discussion, the CLC device 14 will have a bandwidth within the bandwidth B. Reflects left circularly polarized (LHCP) image light and appears to be transparent to image light including RHCP image light within the wavelength bandwidth of electromagnetic radiation significantly larger than (but including bandwidth B) Are described as being configured. However, in essence, L in bandwidth B
All visible spectrum electromagnetic radiation, excluding the HCP component, passes through the CLC device 14.

Thus, FIG. 1A shows the CLC device 14
Are arranged to transmit the image light from the image source 12 (as viewed from the CLC device 14) to the concave mirror 16 and reflect the LHCP image light having the bandwidth B out of the line of sight of the observer O. ing. The concave mirror 16 has a function of enlarging (collimating) the image light received from the CLC device 14, and reverses the rotation direction of the image light thus collimated to obtain C
It is arranged so as to be reflected back to the LC device 14. In this way, the RHCP component of the image light from the CLC device 14 is converted to the LHCP component when reflected back to the CLC device 14. Those LHCP components within the bandwidth B of the image light reflected by the mirror are then reflected by the CLC device 14 into the line of sight of the observer O for observation. All other components of the image light reflected by the concave mirror 16 (for example, RHCP image light) are observed by the observer O by the CLC device 14.
It is transmitted outside the line of sight of.

As FIG. 1B further shows, the CLC
The device 14 is also arranged to transmit the anterior field of view excluding the RHCP component in the bandwidth B to the observer O.
Therefore, the collimator device of FIG. 1B superimposes the image produced by the image source 12 onto the observer O and onto the front field of view (observed through the CLC device 14) with a very small loss of produced image light. To present.

Of course, the invention taught herein has various alternative embodiments, some of which are illustrated in FIGS. 1B and 2-4. Referring now to FIG. 1B, this alternate embodiment of the present invention illustrates a CLC device 14
And the mirror 16 repositioned from the position shown in FIG. 1A.
And both are located within the line of sight of the observer O.
The image source 12 and the CLC device 14 are arranged so that R of the image light within the bandwidth B is
The HCP component is arranged by the CLC device 14 to be reflected by the concave mirror 16 without reversing the rotation direction. The mirror 16 is then arranged to magnify (collimate) the image, reflect the collimated image light back along the path to the CLC device 14, and reverse its direction of rotation from RHCP to LHCP. . The reflected image light, now having the LHCP rotation direction, is transmitted by the CLC device 14 to the observer O.

In any of the embodiments of the invention shown in FIGS. 1A and 1B, the image source 12 may be of the type that produces a monochromatic image, in which case a portion (bandwidth) of the image light is generated. Only the RHCP component within the width B) is reflected, passes through the concave mirror 16 and the CLC 14 as described above, and finally reaches the observer O.
Is transmitted to All other components of the image light are CLC device 1
The image is transmitted outside the line of sight of the observer O by 4. However, preferably the image source 12 is a liquid crystal display 20 which produces a linearly polarized image. In the embodiment of FIG. 1A of the present invention, the generated image is then a quarter wavelength delay 22
, And the delay device 22 circularly polarizes the image light so that the rotation direction is LHCP. FIG. 1B of the present invention
In this embodiment, the 1/4 wavelength delay device transmits the image light to the RH
Circularly polarized light having a CP rotation direction.

Due to the nature of the optical components used in the light collimating device, the CLC device 14 will have a CL within the bandwidth B and at the corner where the cholesteric liquid crystal element is formed.
Reflects substantially all of the RHCP light that is incident on the C device 14. Alternatively, CLC device 14 transmits substantially all of the LHCP light component incident on it, if present. The optical concave mirror 16 reflects substantially all light incident on it. Therefore, in each of the embodiments of the optical collimator device 10 of FIGS. 1A and 1B, nearly 100% of the initial intensity of the RHCP image light can be sent to the observer O. A linearly polarized light configured as described above and capable of producing originally circularly polarized light (or, as in the case of LCD 20, can be converted to substantially circularly polarized light by transmission through quarter-wave retarder 22). Can generate light)
When shared with an image source, the visual display system using the image collimating device 10 becomes substantially efficient. If the image source 20 is otherwise, producing unpolarized light, or equally mixed polarized light, the visual display system using the image collimating device 10 is substantially 50% efficient.

Comparing this with the prior art, which has an efficiency of at most 50% or 25% in each of the two cases of generated image light considered, the benefit afforded by the present invention is clear. The improved transmission provided by the present invention requires that the image source 12 generate images at low power levels in order to maintain similar visibility, or if generated at the same power. , The image produced by the image source 12 has improved intensity and brightness over the prior art.

The curvature of the mirror 16 is preferably spherical, although other curvatures can be used and may even be suitable in certain applications. Furthermore, the mirror 16
It may be semi-silvered so that the observer O is thereby provided with a forward field of view on the horizon, on which the image produced by the image source 12 is superimposed. If the mirror 16 is partially reflective and partially transparent, the light collimating device 10 combines the collimator for the generated image with the image on the front horizon with the image generated by the image source 12. Function as both a synthesizer and a synthesizer.

Referring now to FIG. 2, another embodiment of the light collimating device 10 is shown. In FIG. 2, a light collimating device 10 configured as in FIG. 1B is used with a second image source 30 for superimposing a second image on the image from image source 12 for observation by an observer O. Has been. As shown in FIG. 2, the second image source 30
Is a second with component in the RHCP rotation direction within bandwidth B
It is arranged to generate a generated image. This second image is projected on the CLC device 14. Second image RHCP
Due to the direction of rotation, it is superimposed on the first image produced by the image source 12 and reflected in the line of sight of the observer O.

The second image is optionally collimated,
Or not collimated. If a collimated second image is desired or required, it may for example have a collimating lens between the image source 30 and the CLC device 14 that receives the image light and transmits it in a collimated form, etc. And then they have to be collimated.

As described above, the image source 12 and / or 3
0 is L having a backlight for generating image light
Advantageously it is a CD. In some environments, LC that does not have a backlight function in the optical collimator
It is desired to use the D device. If so,
The LCD device used must be illuminated to generate the image light and FIG. 3 shows an embodiment of the invention using such an LCD device. In this case, as shown in FIG. 3, the collimating device 10 collimates and is illuminated by the light source 42 because it uses an image source 40 that does not have a backlight function. So image source 4
The image produced by illuminating 0 is projected onto a cholesteric liquid crystal element 14 constructed and arranged to reflect an image having an RHCP component within bandwidth B. Of the image light generated by the image source 40,
The RHCP component within the bandwidth B is
It is reflected on the concave mirror 16 without reversing the rotation direction. Concave mirror 16 then reverses the image by reversing its direction of rotation to C
Since it is reflected back to the LC device 14, it is LHCP here.
Become light. The CLC device 14 transmits this image light into the line of sight of the observer O.

Although not shown in the embodiment of the invention of FIG. 3, 1 / used to circularly polarize (to RHCP) linearly polarized light reflected from liquid crystal display 40.
A four wavelength delay device is used.

Referring now to FIG. 4, there is shown an embodiment of the present invention in which the generated image is projected and collimated with substantially 100% of the generated light within the line of sight of the observer O. ing. As in the embodiments described above, the CLC device used in the embodiment of FIG.
It is configured to reflect light components having a RHCP rotation direction within and transmit all other components (in the visible region of the spectrum). Thus, as FIG. 4 shows, a collimator device, generally designated by the reference numeral 50, has an image source 52 that produces an image light having both LHCP and RHCP rotation directions within a bandwidth B. including. The generated image light is CL that is configured as described above.
It is projected so as to be incident on the C device 54. The RHCP rotation direction component of the generated image light is reflected by the CLC device 54 to the concave mirror 56. The concave mirror 56 reverses the rotation direction of the generated image light to collimate it, reflects it back to the CLC device 54, and the CLC device 54 transmits the image light into the line of sight of the observer O.

At the same time, the LHC of the generated image light from the image source 52 is
The P component is transmitted to the second concave mirror 58 by the CLC device 54. The concave mirror 58 reverses the rotation direction of the received image light from LHCP to RHCP, collimates it, and reflects it back to the CLC device 54. The CLC device 54 then reflects the RHCP component within the bandwidth B from the concave mirror 58 into the line of sight of the observer. Therefore, the observer receives both the LHCP and RHCP components of the generated image projected by the image source 52 into the collimating device 50, which components will reduce the image to one.
Supply with a transmission rate of near 00%.

In general, one of ordinary skill in the relevant arts of the present invention will recognize that many modifications in construction and various different embodiments may be made without departing from the spirit and scope of the invention. It should be profitable. For example, the composition of a cholesteric liquid crystal device can be such that the maximum reflection bandwidth of the device is centered at the selected wavelength. Similarly, the bandwidth of maximum reflection near the wavelength can also be varied as a function of the composition of the cholesteric liquid crystal. Also, several cholesteric liquid crystal elements covering different bandwidths can be deposited together to achieve wider bandwidth operation.

Further, the physical arrangement of the components of the present invention is
It can be modified to get special results. For example, the cholesteric liquid crystal element 14 may be formed on a curved surface to provide optical magnification to the image, thereby improving the optical performance of a system using the present invention, or for the same performance, an optical concave mirror. It is possible to reduce the optical magnification used.

In addition, the mirrors used in the various embodiments of the invention described herein may be of various aspheric, planar, or convex shapes to meet the different requirements of the particular display system contemplated. It can be formed into a shape.

Furthermore, it has been realized by the property of the cholesteric element that the wavelength of maximum reflection is angle-sensitive (that is, the wavelength of maximum reflection shifts to a shorter wavelength as the incident angle increases). The wavelength of maximum reflection of the cholesteric liquid crystal element for incident light at the nominal angle of the system design can be increased to compensate for the shift of the reflection at other angles of incidence towards shorter or longer wavelengths. This property is used to correct for chromatic aberration, where there is chromatic aberration in the system using the invention that results from the chromatic effect of any refractive material in the system without correction, or , If the color effect is the same, it is used to reduce the requirement of other refractive materials.

The above disclosure and description are purely illustrative and are not intended to be in any sense limiting.

[Brief description of drawings]

FIG. 1A shows an embodiment of the optical collimation system of the present invention, and B shows another embodiment of the optical collimation system of the present invention.

2 shows another embodiment of the invention in which a second generated image is superimposed on the collimated image generated by the imaging system of FIG. 1B.

FIG. 3 illustrates yet another embodiment of the present invention in which an image produced by illuminating an image source with a light source is projected onto the collimating device of FIG. 1B.

FIG. 4 illustrates yet another embodiment of the present invention, a collimating device capable of collimating unpolarized light with a transmission rate near 100%.

[Explanation of symbols]

 10 Optical collimator device 12 Image source 14 Cholesteric liquid crystal device 16 Concave mirror O Observer

Claims (4)

[Claims] 1. An optical collimating device for focusing an image at infinity or a desired finite distance as viewed by an observer, said image being formed by image means and having a component within a predetermined bandwidth. A cholesteric liquid crystal device of the type that includes circularly polarized image light that is circularly polarized in a rotational direction, wherein the device is reflective to light that is circularly polarized in a first rotational direction within the predetermined bandwidth; An optical mirror arranged to receive the image light and reflect it to the cholesteric liquid crystal element, and to reverse the rotation direction of the circularly polarized light by the reflection; and the image light from the image means is received by the optical mirror. The cholesteric liquid crystal element and the optical mirror are arranged so as to be reflected to the cholesteric liquid crystal element with the reversal of the rotation direction of the image light component and into the line of sight of the observer. Collimation Device. 2. The optical collimator device according to claim 1, wherein the cholesteric liquid crystal element sends the image light component reflected by the optical mirror to the element into the line of sight of the observer. 3. A light collimating device for focusing an image at infinity or a desired finite distance as viewed by an observer, the image being formed by image means, having a component within a predetermined bandwidth and having a predetermined rotation. A cholesteric liquid crystal element of a type including image light that is circularly polarized light in a predetermined direction, the device having a predetermined bandwidth and being reflective to light that is circularly polarized light in the predetermined rotation direction, and an optical mirror. The image light from the image means is projected onto the cholesteric liquid crystal element, and the component of the image light having the predetermined bandwidth and the rotation direction is reflected to the optical mirror. An optical collimating device in which the cholesteric liquid crystal element and the optical mirror are arranged so that the light is reflected back to the cholesteric liquid crystal element and into the line of sight of the observer. 4. A method of optically collimating an image at infinity or a desired finite distance from an observer, the image light having an image light component within a predetermined bandwidth and being circularly polarized light in a predetermined rotation direction. To enter a cholesteric liquid crystal element configured to be reflective to an image light component having the predetermined bandwidth and the predetermined rotation direction; and reflecting the image light component to a light focusing mirror. As such, the step of disposing the cholesteric liquid crystal element, the step of disposing the light focusing mirror so as to reflect back the image light component toward the cholesteric liquid crystal element, and the image light reflected from the light focusing mirror. Sending a component to said observer.