A holographic sight based on volume Bragg grating

Abstract

The invention discloses a holographic sight based on a volume Bragg grating, and belongs to the field of holographic optics. The holographic sight comprises a sight housing, a semiconductor laser, a wave-locking element, a beam expander, an off-axis parabolic reflector and a holographic grating. The wave-locking element is a reflective volume Bragg grating, and the holographic grating is a transmissive volume Bragg grating. Both have excellent selectivity for the wavelength and incident angle of light. At the same time, both are made of photothermorefractive glass, which is less affected by the external temperature and can effectively reduce the deviation of the output wavelength, thereby reducing the deviation of the holographic grating mark image and increasing the accuracy and stability of the holographic sight. The photothermorefractive glass has a high refractive index modulation degree, which achieves a higher holographic diffraction efficiency, making the displayed holographic image brighter and more recognizable. In addition, the components of the beam expander and the off-axis parabolic reflector are used to shorten the optical path and reduce the overall structural size of the sight.

Description

Technical Field

[0001] The invention belongs to the field of holographic optics, and in particular relates to a holographic sight based on a volume Bragg grating. Background Art

[0002] With the emergence and development of laser technology, holography has been greatly promoted and gradually applied to image display, information storage, information encryption and other fields. At the end of the 20th century, the emergence of holographic sights applied holography to light weapons for the first time and showed superior performance to other types of sights. It has the advantages of fast aiming speed, bright field of view, wide field of view, etc. Even if the observation window is partially blocked or contaminated, it can complete the aiming work. It has been equipped in the troops of many countries.

[0003] Holographic sights generally face two major problems. One is that the wavelength of the light source drifts due to temperature changes, which in turn causes the holographic sight to shift; the other is that due to the size of the device, the system optical path cannot be too large. In view of the holographic recording element used in traditional holographic sights, the article "Application of photo-thermo-refractive glass as a holographic medium for holographic collimator gun sights" proposes a feasible optimization solution. This solution uses a volume Bragg grating holographic grating made of photothermo-refractive glass material to replace the traditional organic photosensitive holographic recording medium. It is selective for the wavelength and incident angle of the light source, thereby solving the problem of wavelength temperature drift to a certain extent. The photothermo-refractive glass material has good mechanical stability, thermal stability, chemical stability and high transmittance, so it does not need to be sealed during storage. However, due to the low refractive index modulation of the material, the effective thickness of the grating needs to be increased to improve the diffraction efficiency. In addition, the semiconductor light source of the current holographic sight causes wavelength drift as the external temperature changes, which causes the holographic sight to shift.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a holographic sight based on a volume Bragg grating, which can improve the accuracy and reliability of the sight and aims to solve the problem that the semiconductor light source of the existing holographic sight causes wavelength drift as the external temperature changes, thereby causing the holographic aiming mark to shift.

[0006] The technical solution of the present invention is as follows:

[0007] A holographic sight based on a volume Bragg grating, wherein the holographic sight comprises: a sight housing, an illumination light system, and a holographic graticule;

[0008] The illumination light system and the holographic reticle are arranged inside the sight housing;

[0009] The sighting scope housing is provided with a sighting scope window;

[0010] The illumination optical system comprises: a semiconductor laser, a wave-locking element, a beam expander, and an off-axis parabolic reflector;

[0011] The holographic reticle has a hologram of aiming reticle marks;

[0012] The wave-locking element is a reflective volume Bragg grating, and the holographic grating is a transmissive volume Bragg grating;

[0013] The light emitted by the semiconductor laser passes through a wave-locking element, and the wave-locking element returns the parallel light part with an incident angle of 0° to the semiconductor laser cavity to form a resonant wave-locking. The parallel light is transmitted through the wave-locking element, and then sequentially passes through the beam expansion of a beam expander and the collimation of an off-axis parabolic reflector to obtain collimated parallel light, and the collimated parallel light is irradiated onto a holographic graticule to form a holographic image of the graticule mark.

[0014] Preferably, the materials of the wave-locking element and the holographic grating plate are both photothermorefractive glass.

[0015] The wave-locking element and the holographic grating described in the present invention are two types of volume Bragg gratings. The former is a reflective volume Bragg grating, and the latter is a transmissive volume Bragg grating. Both have excellent selectivity for the wavelength and incident angle of light. At the same time, the material of the volume Bragg grating is photothermorefractive glass, and its wavelength drift coefficient reaches 0.01nm / ℃. When the wavelength of the light source shifts by 2nm, the output wavelength shift can be controlled to 0.067nm. At this time, the shift of the holographic grating image is reduced to 5×10 -3 m, effectively suppressing the influence of wavelength drift on the holographic imaging position, increasing the accuracy and stability of the holographic sight; and the photothermal refracting glass has a high refractive index modulation degree, achieving a higher holographic diffraction efficiency, making the displayed holographic image brighter and more recognizable.

[0016] Preferably, the material of the holographic grating is photothermorefractive glass with a refractive index modulation degree of up to 500 ppm.

[0017] The present invention adopts a photothermorefractive glass material with a refractive index modulation degree of up to 500 ppm as a holographic recording medium, and can achieve higher diffraction efficiency without increasing the material thickness.

[0018] In addition, the present invention uses a beam expander and an off-axis parabolic reflector to expand and collimate the light source, shortening the system optical path and effectively reducing the size of the holographic sight. Compared with the existing holographic sight, the size is smaller and the assembly space is saved.

[0019] Preferably, the dimensions of the holographic sight are: length L = 85-90 nm, width W = 55 nm, height H = 65-70 nm.

[0020] Preferably, the normal direction of the wave-locking element is placed at 0° to the direction of the light emitted by the semiconductor laser, so that the parallel light part with an incident angle of 0° returns to the semiconductor laser cavity along the original path to form a resonant wave-locking.

[0021] Preferably, the main optical axis of the beam expander is placed parallel to the direction of the transmitted light, and the beam expander is a biconcave lens.

[0022] Preferably, the off-axis parabolic reflector is placed in the emitting direction of the beam expander, and the angle between the irradiation direction of the collimated parallel light and the normal direction of the holographic graticule is 40-80°.

[0023] More preferably, the off-axis parabolic reflector is placed in the emission direction of the beam expander, and the angle between the collimated parallel light irradiation direction and the normal direction of the holographic graticule is 60°. By designing the optical path in this way, the size of the holographic sight can be made as small as possible.

[0024] Preferably, the thickness of the reflective volume Bragg grating is 1-3 mm, and the thickness of the transmissive volume Bragg grating is 0.5-3 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the optical path structure of an existing holographic sight;

[0026] Figure 2 This is a graph showing the relationship between the imaging angle deviation of the traditional holographic graticule and the wavelength of light;

[0027] Figure 3 Schematic diagram of the optical path structure of the holographic sight in an embodiment of the present invention;

[0028] Figure 4 is a graph showing the angle selection of the volume Bragg grating as its effective thickness changes;

[0029] Figure 5 This is a graph showing the wavelength selection of a volume Bragg grating as its effective thickness varies. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the described scope.

[0031] See also Figure 1 As shown, Figure 1 In the optical path structure of the existing holographic sight, the laser diode emits a light beam that passes through a reflector and a collimating reflector and then irradiates the holographic diffraction grating as a plane wave. The holographic diffraction grating deflects the light beam to a fixed angle and irradiates the hologram to form a diffraction image. The light beam that does not participate in the diffraction is blocked by the structure. The existing holographic sight uses a laser diode as the illumination light source. The central wavelength of the light source will shift with temperature changes, causing the position of the holographic image to change. Figure 2 As shown in the figure, a 2nm change in the wavelength of the light source irradiating the holographic grating will cause the imaging angle to change by 0.086°. When the aiming distance is 100m, the holographic grating image will shift by 0.15m. Therefore, a holographic diffraction grating is generally used in the optical path structure to compensate for the influence of wavelength changes. This method can reduce the imaging angle change to 0.0038°. When the aiming distance is 100m, the holographic grating image will shift by 6.7×10 -3 However, due to the limitation of the size of the device structure, it is difficult to place the holographic diffraction grating parallel to the holographic grating, which reduces the compensation effect.

[0032] Based on this, an embodiment of the present invention provides a holographic sight based on a volume Bragg grating, such as Figure 3 As shown, the holographic sight comprises: a sight housing 6, an illumination light system, and a holographic graticule 5;

[0033] The illumination light system and the holographic reticle 5 are arranged inside the sight housing 6;

[0034] The sighting scope housing 6 is provided with a sighting scope window;

[0035] The illumination optical system comprises: a semiconductor laser 1, a wave-locking element 2, a beam expander 3 and an off-axis parabolic reflector 4;

[0036] The holographic reticle 5 has a hologram of aiming reticle marks;

[0037] The wave-locking element 2 is a reflective volume Bragg grating, and the holographic grating 5 is a transmissive volume Bragg grating;

[0038] The light emitted by the semiconductor laser 1 passes through the wave-locking element 2, and the wave-locking element 2 returns the parallel light part with an incident angle of 0° to the cavity of the semiconductor laser 1 to form a resonant wave lock (wavelength locking). The parallel light is transmitted through the wave-locking element 2, and then sequentially passes through the beam expansion of the beam expander 3 and the collimation of the off-axis parabolic reflector 4 to obtain parallel light with a sufficiently large beam diameter after collimation, and the parallel light is irradiated onto the holographic graticule 5 (containing the holographic information of the graticule mark) to form a holographic image of the graticule mark; the aiming graticule mark is reproduced in the direction of human eye observation, and a virtual image of the graticule mark is generated at a distance approximately infinite from the human eye; when the human eye observes through the sight window, the virtual image of the graticule mark is overlapped with the aiming target, thereby realizing the aiming function.

[0039] In this embodiment, the wave-locking element 2 and the holographic grating 5 are two different volume Bragg gratings, the former is a reflective volume Bragg grating, and the latter is a transmissive volume Bragg grating, both of which are characterized in that the incident light will produce corresponding diffraction phenomena only when the wavelength and incident angle of the light meet the Bragg diffraction conditions, otherwise it will directly pass through the volume Bragg grating along the direction of the light beam without diffraction. Figure 4 and Figure 5 The selectivity of the volume Bragg grating thickness to the light source angle and wavelength is demonstrated respectively, indicating that the volume Bragg grating can effectively control the conditions for diffraction of the light source.

[0040] In this embodiment, the thickness of the reflective volume Bragg grating is 1-3 mm, and the thickness of the transmissive volume Bragg grating is 0.5-3 mm, so as to achieve higher wave locking performance and diffraction efficiency.

[0041] In this embodiment, the materials of the wave-locking element 2 and the holographic grating plate 5 are both photothermorefractive glass. Photothermorefractive glass is less affected by the external temperature. Generally, its wavelength drift coefficient is 0.01nm / ℃, while the wavelength drift coefficient of the semiconductor laser is 0.3nm / ℃. Under the same temperature change range, when the wavelength of the semiconductor laser shifts by 2nm, the output wavelength of the photothermorefractive glass shifts by only 0.067nm. Therefore, when the wavelength and angle of the light source are stable, the shift of the holographic image of the grating mark can be reduced from 0.15m in the above result to 5×10 -3 m.

[0042] In this embodiment, the normal direction of the wave-locking element 2 is placed at 0° to the direction of the light emitted by the semiconductor laser 1, so that the parallel light with an incident angle of 0° is partially reflected into the cavity of the semiconductor laser 1 to form wavelength locking.

[0043] In this embodiment, the main optical axis of the beam expander 3 is placed parallel to the direction of the transmitted light, and the beam expander 3 is a double concave lens.

[0044] In this embodiment, the emitted light of the semiconductor laser 1 is first irradiated onto the wave-locking element 2, and the normal direction of the wave-locking element 2 is placed parallel to the light source direction, so that the parallel light with an incident angle of 0° is partially reflected into the cavity of the semiconductor laser 1 to form a resonant wave-locking, and the parallel light transmitted through the wave-locking element 2 enters the beam expander 3, and the main optical axis of the beam expander 3 is placed parallel to the direction of the transmitted light. The off-axis parabolic reflector 4 is placed in the emission direction of the beam expander 3, and the light expanded (also called magnified) by the beam expander 3 is collimated to obtain parallel light with a sufficiently large beam diameter, and the parallel light is reflected along a direction with an angle of 40 to 80° (preferably 60°) with the normal direction of the holographic graticule, and finally irradiated onto the holographic graticule 5, and the aiming scale mark is reproduced in the direction of human eye observation, and a virtual image of the scale mark is generated at a distance approximately infinite from the human eye. When the human eye observes through the sight window, the virtual image of the scale mark coincides with the aiming target, and the aiming function can be achieved.

[0045] Compared with the prior art, the beneficial effects of this embodiment include:

[0046] 1) In this embodiment, on the basis of using a transmissive volume Bragg grating as a holographic recording medium, a reflective volume Bragg grating is used as a wave-locking element, which stabilizes the wavelength of the semiconductor laser, is beneficial to suppress the influence of wavelength drift on the holographic imaging position, and increases the accuracy and stability of the holographic sight;

[0047] 2) This embodiment uses photothermorefractive glass with a higher refractive index modulation to make a transmissive volume Bragg grating, which can achieve a higher diffraction efficiency when the thickness is constant, making the displayed holographic image brighter and more recognizable; at the same time, this material has good mechanical stability, thermal stability, chemical stability and high transmittance, and the holographic information is easy to preserve and is less affected by the external temperature. No additional coating or glue sealing protection is required, making the observation window bright;

[0048] 3) This embodiment uses a beam expander and an off-axis parabolic reflector to expand the light source and then collimate it, which shortens the system optical path and effectively reduces the size of the holographic sight. The size of the holographic sight can be: length L = 85 ~ 90nm, width W = 55nm, height H = 65 ~ 70nm. Compared with the existing holographic sight, the size is smaller and saves assembly space.

Claims

1. A holographic sight based on volume Bragg grating, characterized in that: The holographic sight comprises: a sight housing, an illumination light system, and a holographic reticle; The illumination light system and the holographic reticle are arranged inside the sight housing; The sighting scope housing is provided with a sighting scope window; The illumination optical system comprises: a semiconductor laser, a wave-locking element, a beam expander, and an off-axis parabolic reflector; The holographic reticle has a hologram of aiming reticle marks; The wave-locking element is a reflective volume Bragg grating, and the holographic grating is a transmissive volume Bragg grating; The light emitted by the semiconductor laser passes through a wave-locking element, and the wave-locking element returns the parallel light part with an incident angle of 0° to the semiconductor laser cavity along the original path to form a resonant wave-locking. The parallel light transmitted through the wave-locking element is sequentially expanded by a beam expander and collimated by an off-axis parabolic reflector to obtain collimated parallel light, and the collimated parallel light is irradiated onto a holographic graticule to form a holographic image of the graticule mark; the aiming graticule mark is reproduced in the direction of human eye observation, and a virtual image of the graticule mark is generated at a distance approximately infinite from the human eye; when the human eye observes through the sight window, the virtual image of the graticule mark is overlapped with the aiming target, thereby realizing the aiming function.

2. The holographic sight based on volume Bragg grating according to claim 1, characterized in that: The normal direction of the wave-locking element is placed at 0° to the direction of the light emitted by the semiconductor laser, so that the parallel light part with an incident angle of 0° returns to the semiconductor laser cavity along the original path to form a resonant wave-locking.

3. The holographic sight based on volume Bragg grating according to claim 1, characterized in that: The main optical axis of the beam expander is placed parallel to the direction of the transmitted light, and the beam expander is a double concave lens.

4. The holographic sight based on volume Bragg grating according to claim 1, characterized in that: The off-axis parabolic reflector is placed in the emitting direction of the beam expander, and the angle between the irradiation direction of the collimated parallel light and the normal direction of the holographic graticule is 40-80°.

5. The holographic sight based on volume Bragg grating according to claim 4, characterized in that: The off-axis parabolic reflector is placed in the emitting direction of the beam expander, and the angle between the irradiation direction of the collimated parallel light and the normal direction of the holographic graticule is 60°.

6. The holographic sight based on volume Bragg grating according to claim 1, characterized in that: The materials of the wave-locking element and the holographic grating plate are both photothermorefractive glass.

7. The holographic sight based on volume Bragg grating according to claim 6, characterized in that: The material of the holographic grating plate is photothermorefractive glass with a refractive index modulation degree of up to 500 ppm.

8. The holographic sight based on volume Bragg grating according to claim 1, characterized in that: The thickness of the reflective volume Bragg grating is 1 to 3 mm, and the thickness of the transmissive volume Bragg grating is 0.5 to 3 mm.

9. The holographic sight based on volume Bragg grating according to claim 1, characterized in that: The dimensions of the holographic sight are: length L=85-90 nm, width W=55 nm, and height H=65-70 nm.

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