RU162200U1 - OPTICAL SCHEME OF THE HOLOGRAPHIC INDICATOR OF SIGN-SYMBOL INFORMATION BASED ON THE COMBINED DIFFRACTION OPTICAL ELEMENT - Google Patents

Abstract

Optical design of a holographic indicator of symbolic information information, comprising an OLED display sequentially installed on the optical axis as a radiation source of symbolic information, a collimating lens, a light guide plate, a Bragg reflective diffraction grating for introducing radiation of the symbolic information into the specified plate for subsequent distribution inside the plate under the action of total internal reflection and obtained on two opposite surfaces of the plate component combined diffraction optical element in the form of diffraction gratings of variable diffraction efficiency for outputting radiation from the plate to the observer’s pupil on one side of the plate and a holographic mirror with the function of transmitting light from the environment to the observer’s pupil through the plate on its other side, characterized in that in the optical the scheme contains a combination of a holographic mirror and an introductory Bragg reflection diffraction grating, operating as a spectral filter due to the high spectral and angular selectivity.

Description

Technical field

The utility model relates to the field of holographic displays that form an image, and, more specifically, to collimator optical indicators that form sign-symbolic information for the observer’s pupil against the background of the surrounding environment.

State of the art

The use of diffractive optical elements (DOEs) in the current information display systems brought them to a qualitatively new stage of development, which made it possible to significantly reduce the weight and size parameters with an increase in the exit pupil of such systems. Displays and indicators based on light guide plates and DOEs are currently becoming an important and integral part of many information display and visualization systems, especially in display systems for cars, airplanes and systems where the observed image is superimposed on the image of a real scene. The advantage of information display systems based on DOEs and light guide plates is that they provide a large exit pupil with a relatively small size of the collimating optical system, which can significantly reduce the weight and size parameters of a holographic display or indicator.

In foreign patents (Russian patents on the subject of a utility model are not found), various options are proposed for constructing displays and indicators based on diffractive optical elements.

US patent application Korean company SAMSUNG ELECTRONICS - US 2004004767 WEARABLE DISPLAY SYSTEM ADJUSTING MAGNIFICATION OF AN IMAGE (IPC G02B 27/01; G02B 27/02; G02B 27/22; G02B 5/18; G02B 5/32; H04N 5/64 ; G02B 27/00; G02B 6/00; (IPC 1-7): G02B 27/44; G02B 5/18, publ. 2004-01-08) presents a diagram of a color display based on a glass plate, through which formed by the optical system The image is transmitted to the observer. This display consists of an image forming source 450, an optical system 400 with a variable focal length, diffraction gratings 410 and 430 for input and output of radiation from a glass substrate 420. Due to the fact that the radiation propagates inside the substrate, it is possible to reduce the longitudinal dimensions of such a display. To minimize the loss of total internal reflection (TIR) when radiation passes inside the substrate, an opaque reflective aluminum coating is applied to both of its surfaces.

The disadvantage of this display is the limited size of the exit pupil, as well as the presence of an opaque aluminum coating, which can limit the field of view of the observer.

In the US patent of the Israeli company YEDA RESEARCH & DEVELOPMENT - US 5966223 PLANAR HOLOGRAPHIC OPTICAL DEVICE (IPC G02B 5/32; G02B 6/124; G02B 6/26; G02B 6/28; G02B 6/34; G03H 1/00; G03H 1 / 22; G03H 1/24; G02B 6/43; (IPC 1-7): G02B 27/44; G02B 5/18; G02B 5/32, publ. 1999-10-12) and US patent of Israeli companies YEDA RESEARCH AND DEVELOPMENT and ELOP ELECTRO OPTICS INDUSTRIES - US 6580529 HOLOGRAPHIC OPTICAL DEVICES (IPC G02B 5/32; (IPC1-7): G02B 5/32; G03H 1/00; G03H 1/22, publ. 2003-06-17) presented monochrome display, comprising a radiation source 2 for the formation of the necessary information, collimating lens 4, and the glass plate 6 on which three gratings are obtained (DR) H _1, H ₂ and H ₃ azlichnogo period. The first DR H ₁ introduces radiation into the substrate at an angle of total internal reflection. The second H ₂ lattice “unfolds” the radiation incident on it by 90 degrees, while realizing the principle of pupil multiplexing along one coordinate. The third DR N ₃ provides the output of radiation from the substrate in the direction of the observer, and also implements the principle of multiplexing pupils in a different coordinate. The diffraction efficiency of the second and third gratings is variable to ensure equal intensity of the radiation beams emerging from the plate 6. An opaque reflective coating 10 and 12 is applied to both surfaces of the plate in order to avoid extraneous illumination and unwanted reflections.

Thus, this display does not allow to simultaneously monitor the displayed information and the environment, which is its serious drawback.

In the US patent of the Finnish company NOKIA - US 6805490 METHOD AND SYSTEM FOR BEAM EXPANSION IN A DISPLAY DEVICE (IPC G02B 5/18; G02B 6/00; G02B 6/34; (IPC1-7): G02B 6/38, publ. 2004 -10-19) presents a planar waveguide structure for displays. It is a transparent substrate, on one surface of which a DR is obtained, as in previous cases, but a distinctive feature is the use of a polarization coating on the second side. Due to this, it is possible to direct radiation of a certain polarization to the grating, which allows one to reduce the back reflection by -1 and -2 orders of diffraction, thereby increasing the waveguide length, and, accordingly, the size of the exit pupil of the display.

Due to the use of diffraction gratings for input and output of radiation from the waveguide, the issue of dispersion blur of the image when using this structure in the display is not resolved.

In the same patent US 6805490 a substrate is presented, consisting of two glued plates with different refractive indices, with diffraction gratings obtained on the surface of the first plate for input and output of radiation from the substrate. Such a two-component structure can be used in two-color displays due to the presence of two glued plates 30 and 50. Due to the fact that they have different refractive indices, radiation with a longer wavelength experiences ATR already in the first plate (in the first layer 30), and the radiation is more a shorter wavelength, diffracted to a smaller angle, experiences air defense in the second layer 50. Additionally, a thin film 40 is deposited between the two layers, having a refractive index lower than the first layer 30, to reduce the losses in air defense at Agen to longer wavelength in the first layer. The radiation of a shorter wavelength in this case passes through the layer 30 and the film 40, without undergoing reflection. Such a structure, taking into account the exact selection of the thicknesses and refractive indices of both layers, makes it possible to ensure that radiation of different wavelengths, having undergone an air defense in its layer, falls onto the H ₂ diffraction grating at the same point and is removed from it by the observer. This eliminates ghosting when overlapping two-color images. Such a structure is transparent, allows to reduce the longitudinal dimensions of the display system and increase the exit pupil.

The disadvantage of this display is that due to the use of diffraction gratings for input and output of radiation from the waveguide, the issue of dispersive image blur can be solved only when using semiconductor lasers as radiation sources, which significantly increases the dimensions of the display itself. When using an OLED type radiation source with a wide emission spectrum, spectral smearing will be observed for each color component due to the sufficiently long plate length and the number of radiation re-reflections in it.

The US patent application of ROCKWELL COLLINS - US 2014140654 TRANSPARENT WAVEGUIDE DISPLAY (IPC G02F 1/29, published 2014-05-22) presents a diagram of a small-sized monochrome display based on Bragg gratings (mainly switchable, with the presence of electrodes for controlling the operating modes of the grating) . The display includes a microdisplay such as LCOS, LED, OLED, etc. depending on the embodiment, an optical unit for introducing radiation into the substrate and at least two glass substrates with switchable Bragg gratings obtained on their surface for input and output of radiation from the plates. Some of the options for implementing these gratings can work in a passive (non-switchable) mode, i.e. without applying voltage to them. A thin half-wave film is also located between the substrates to provide a certain type of polarization of the radiation propagating in the substrates. Switchable Bragg gratings have a high (up to 90%) diffraction efficiency and good transmittance, but unlike static non-switchable gratings (whose parameters do not change), switchable gratings are much more difficult to manufacture, because require electrodes. In various implementations, switchable Bragg gratings up to 3 μm thick can be used as transmission gratings to remove radiation (due to diffraction) from the substrate (mainly in the passive mode of operation), to expand the beam in one direction (in the active mode of operation), and also as reflective gratings such as holographic mirrors. In addition, there is the possibility of constructing multi-color displays according to this scheme if only a certain spectral component will propagate and output in each plate, and the RGB layers of switched Bragg gratings must be consistent with the RGB radiation source and switched sequentially.

In most applications of such displays constructed according to such a scheme, it is preferable to use a laser radiation source in combination with an LCOS display or a narrow-band microdisplay (within ± 5 nm) as a radiation source. At the same time, an OLED display can be used as a radiation source in cases where the optical characteristics of the device (resolution, brightness, color gamut) are not so important. This is a disadvantage of using such a display implementation since the use of a broadband OLED source causes spectral smearing of the image projected to the observer and reduces the resolution of the device as a whole.

One of the options for this device is the closest analogue (prototype) to the proposed topographic indicator, because It may contain an OLED type microdisplay, an optical radiation input unit and a transmission two-component structure, including glass substrates with diffraction gratings, connected (or glued) to each other. These gratings are Bragg diffraction gratings (basically switchable with the ability to work in active and passive modes, including the ability to work as a holographic mirror), designed to output radiation from the substrate.

The main disadvantages of this prototype scheme include the complexity of manufacturing switchable Bragg gratings due to the presence of electrodes on them, which are supplied with voltage in the active mode of their operation, which additionally complicates the display circuit and, accordingly, significantly increases its cost compared to static diffraction gratings. Another disadvantage of this device when using an OLED display as a radiation source is the deterioration of its optical characteristics (resolution, brightness, color blur).

Utility Model Disclosure

The objective of the utility model was to create a holographic indicator of symbolic information with the elimination of the lack of a prototype, namely: preservation of its optical characteristics (ensuring high resolution and the absence of color blur) when using an OLED display with a wide radiation spectrum as a source of information formation.

To eliminate the disadvantages of the prototype, it is necessary, on the one hand, to use traditional (non-switchable, i.e., without electrodes) diffraction gratings, which can be not only Bragg, but multi-level relief-phase, which will further reduce the complexity of manufacturing the display. Together with diffraction gratings for radiation output, it is proposed to additionally use a spectral filter in the indicator to reduce chromatic aberration and color blur, and, on the other hand, to preserve a mirror or similar coating on the light guide substrate to reduce reflection loss, but ensuring its transparency. This can be achieved through the use of a two-component combined DOE structure, which includes a transmission diffraction grating on one surface of the substrate to remove radiation from the plate and a holographic mirror with high spectral-angular selectivity on the other to obtain pure colors. This will significantly reduce chromatic aberration and color blur of monochrome image display systems arising due to the large number of re-reflections of radiation inside the light guide plate of the substrate when using an OLED display as a source for generating the necessary information. This, in turn, allows, in contrast to the prototype circuit, to maintain an acceptable indicator resolution when using an OLED display.

The technical result of the utility model is the construction of an optical holographic indicator based on a glass substrate (light guide plate) with a combined two-component DOE consisting of a diffraction grating (which can be both Bragg and phase-relief) on one side of the substrate and a holographic mirror on the other. The presence of a holographic mirror indicator and a Bragg reflection diffraction grating for radiation input, operating as spectral filters due to high spectral selectivity, allows the use of an OLED display with a wide radiation spectrum (up to 60 nm) as a source for generating sign-symbol information without compromising optical characteristics of the device, as it compensates for the dispersion blurring of the image that occurs in conventional schemes when using light sources such as OLED with relatively a wide spectral band of radiation.

The technical result is achieved due to the fact that the optical scheme of the holographic indicator of symbolic information contains an OLED display sequentially installed on the optical axis as a radiation source of the symbolic information, a collimating lens, a light guide plate, a Bragg reflection diffraction grating for inputting the radiation of the symbolic symbol information in the specified plate for the subsequent propagation of radiation inside the plate under the action of total internal reflection and obtained a two-component combined diffractive optical element on two opposite working surfaces of the plate in the form of diffraction gratings of variable diffraction efficiency for outputting radiation from the plate to the observer’s pupil on one side of the plate and a holographic mirror with the function of transmitting light from the surrounding environment to the observer’s pupil through the plate on the other side . Moreover, the optical scheme contains a combination of a holographic mirror and an introductory Bragg reflection diffraction grating, operating as spectral filters due to high spectral-angular selectivity.

List of figures

In FIG. 1 is a diagram of a holographic indicator of symbolic information based on a combined two-component DOE.

In FIG. Figure 2 shows a layered diagram of a combined two-component DOE consisting of a diffraction grating for outputting radiation from a substrate and a holographic mirror.

In FIG. Figure 3 shows experimental graphs of the reflection spectrum of a holographic mirror for different wavelengths of light and different angles of incidence.

Implementation of the utility model As the source of the formation of the symbolic information in the proposed holographic indicator (FIG. 1), the OLED display 1 is used, which emits in the green region of the spectrum with a fairly wide spectral band (up to 60 nm). The beam of radiation emitted by the radiation source 1 is collimated by the lens 2, and then, through the introductory Bragg reflection grating (DR) 5, it is introduced into a glass substrate (light guide plate) 3, inside which the radiation propagates under the influence of air defense. A feature of this system is that on the surface of the substrate, combined two-component DOEs (FIG. 2) are obtained, which are diffraction gratings (DR) 6 for outputting radiation into the pupil 8 of the observer on one side of the substrate and a holographic mirror 7 as a spectral filter on the other The holographic mirror is usually covered with protective glass 4.

Reflective DR 5 is designed to enter the radiation beams coming after the collimating lens 2 into the plate 3 at angles of air defense. This DR 5 has spectral and angular selectivity, i.e. introduces radiation at a certain angle and a specific spectral composition into plate 3, therefore, like a holographic mirror, it acts as a spectral filter when radiation is introduced into plate 3. DR 5 was obtained on a layer of bichromated gelatin (BCL). Specific operating parameters of DR 5: thickness - 35 microns; working radiation wavelength - 530 nm; diffraction efficiency is above 0.7.

Once inside the surface of the plate 3, on which the DR 6 is located, part of the radiation diffracts into the “+1” order going towards the pupil 8 of the observer. The “0” radiation order continues to propagate in the plate 3. To align with the brightness field of the observed image, DR 6 must have variable diffraction efficiency, which is ensured by changing the depth of the surface relief of grating 6. Thus, the output grating 6 is divided into zones, in each from which a lattice with a certain relief depth is obtained. In these zonal gratings, diffraction efficiency depends on the zone of location of the grating in the overall structure.

In FIG. 2, a layer-by-layer diagram of a combined two-component DOE consisting of a diffraction grating 6 with variable efficiency η increasing as the radiation propagates inside the substrate to its edge, for outputting radiation from the substrate 3, holographic mirror 7 and protective glass 4. is shown in layers. The holographic mirror 7 has a reflection coefficient ρ (λ, θ), depending on the wavelength and angle of incidence of the radiation (see FIG. 3). Thus, when a certain wavelength λ with a wide spectral range λ ± Δλ _{1 is} incident on a mirror, the mirror reflects radiation of a narrower spectral range λ ± Δλ ₂ .

The holographic mirror 7 is a transparent glass plate with a structure obtained on a bichromated gelatin layer. The thickness of the mirror material is 35 microns; working radiation wavelength - 530 nm; the reflection coefficient at the working wavelength is above 0.75. Such a holographic mirror is transparent to the lumen, but due to the spectral and angular selectivity of the material, it is able to reflect radiation incident at a working angle with a narrow (about 20 nm) spectral range Δλ ₂ .

The use of a holographic mirror 7 and an introductory Bragg reflective grating 5 with high spectral-angular selectivity reduces the chromatic aberration and dispersion blur of monochrome image systems resulting from a large number of radiation re-reflections inside light guide plate 3 when using a broadband OLED display 1 as a source the formation of the necessary symbolic information.

A holographic mirror has a narrow reflection spectrum for a specific spectral component. The spectral selectivity of the holographic mirror δ _λ is determined by the relation (1):

where δ _α is the magnitude of angular selectivity, which can be determined from relation (2);

where n is the average refractive index of the recording medium (n = 1.52);

T is the thickness of the recording medium (T = 35 μm);

Θ ₀ is the Bragg angle in the recording medium (for a reflective mirror, in which the direction of the antinode planes is parallel to the photographic material layer Θ ₀ = 90 °);

ξ _r - coefficient proportional to the angular deviation yes from the Bragg angle

The coefficient ξ _r varies in the range from 0 to 3. In the first case, the maximum possible diffraction efficiency is provided - 100%, and in the second it is 0. For a preliminary assessment of the spectral selectivity of a holographic mirror, we take ξ _r = 1.5.

For angles of radiation propagation in a plate of the order of 45 ... 55 degrees, the theoretical spectral selectivity of a holographic mirror obtained on a layer of dichromated gelatin with a thickness of 35 μm is about 5 nm, which indicates the possibility of its use as a spectral filter.

In FIG. Figure 3 shows an experimental plot of the reflection spectrum of a holographic mirror for different wavelengths and incidence angles. The graph shows that at an angle of incidence of 50 degrees, the reflection coefficient of the holographic mirror is maximum and is 0.75 for a radiation wavelength of 530 nm, and for angles of incidence of 45 and 55 degrees, the reflection coefficient is more than 0.6. The width of the reflected spectrum for an angle of incidence of 50 degrees is 25 nm, and for a range of angles from 45 to 55 degrees - 35 nm. For wavelengths less than 500 nm and more than 550 nm, this radiation is almost completely extinguished, and the reflection coefficient is less than 0.1, which indicates the possibility of using a holographic mirror as a spectral filter.

To compare the spectral blur values of the image observed through an indicator with and without a topographic mirror 7, we calculated by what angle the radiation beam with different spectral widths diffracts in the plate 3 with a normal incidence on the input grating 5, and the blur source size of the point source was estimated for each case . The calculation is carried out for the working wavelength and for the extreme wavelengths of the radiation of the OLED display 1 with a spectrum width of 60 nm and in the presence of a holographic mirror 7 with a reflection spectrum width of 35 nm.

We write the formula of the diffraction grating:

where λ is the working wavelength; n _article is the refractive index of glass; d _res - the period of the input and output lattices; m is the diffraction order (m = 1); θ is the angle of incidence of radiation on the plate (normal incidence θ = 90 °); n is the refractive index of air (n = 1); α _i - diffraction angle for the i-th radiation wavelength.

Respectively

The distance between adjacent reflections for the i-th wavelengths is

where d _PL - the thickness of the plate;

The number of reflections that the radiation undergoes while propagating in a plate of length L _PL under the influence of air defense is

For a light guide plate with a length of 80 mm, a glass refractive index of 1.51, a substrate thickness of 2 mm, a diffraction grating period of 0.5 μm, using formulas (4) - (7), it can be calculated that the image of a point source formed by an OLED display with a spectrum width 60 nm when observing it through the outermost, most remote from the input grating, region of the light guide plate 80 mm long will be smeared into a line 2.4 mm or more in length, and if there is a holographic mirror with a reflection spectrum width of 35 nm, this blur will be up to 1 7 mm (i.e. 30% less e).

Thus, it is shown that the combination in a single combined diffractive optical element of a diffraction grating with a variable efficiency necessary for outputting radiation from a light guide plate, a non-switchable Bragg reflection grating for introducing radiation into the plate, and a holographic mirror as an additional spectral filter, allows to achieve a technical result, namely, it allows the use of an OLED display with a wide spectrum of radiation (up to 60 nm) as a source of sign-symbolic formation information without compromising the optical characteristics of the device, while significantly reducing the dispersion blur of the image in monochrome indicators of symbolic information when using light sources such as OLED with a relatively wide spectral emission band.

Claims (1)

Optical design of a holographic indicator of symbolic information information, comprising an OLED display sequentially installed on the optical axis as a radiation source of symbolic information, a collimating lens, a light guide plate, a Bragg reflective diffraction grating for introducing radiation of the symbolic information into the specified plate for subsequent distribution inside the plate under the action of total internal reflection and obtained on two opposite surfaces of the plate component combined diffraction optical element in the form of diffraction gratings of variable diffraction efficiency for outputting radiation from the plate to the observer’s pupil on one side of the plate and a holographic mirror with the function of transmitting light from the environment to the observer’s pupil through the plate on its other side, characterized in that in the optical the scheme contains a combination of a holographic mirror and an introductory Bragg reflection diffraction grating, operating as a spectral filter due to the high spectral and angular selectivity.

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