RU2332694C1 - Device for suppressing speckles (versions) - Google Patents

Abstract

FIELD: lighting.

SUBSTANCE: invention pertains to lighting and formation of an image, and specifically to devices for suppressing speckles. The device contains a generator of alternating voltage, a polarisation controller, and two birefringent optical wedges. The outer surfaces of the optical wedges are parallel to each other and are at the same distance from each other with formation of a gap. The polarisation controller is made with provision for changing polarisation of a laser beam depending on the frequency of the alternating voltage generator. The first optical wedge is made with provision for dividing the laser beam into two orthogonal polarised beams, the intensity of which changes depending on the direction of polarisation of the laser beam entering the wedge. The second wedge is made with provision for parallelisation of the beams coming out of the first wedge.

EFFECT: device can be used in laser systems of imaging optical information.

10 cl, 3 dwg

Description

The invention relates to the field of lighting and image formation, and in particular to speckle suppression devices, and can be used in laser optical information display systems.

The main problem of lighting systems based on laser sources is the speckle noise on the illuminated surface.

There are a number of speckle suppression devices.

The published international application WO 0065401 [1] describes a speckle reduction device with a mechanical drive of a part of a lighting system, in which speckle effects are washed out and become invisible to the user due to vibrational disturbances of the moving mirror. In one embodiment, a mirror directing a beam of light along a broken path can be moved mechanically using several piezoelectric drives.

In US Patent Application Laid-Open No. 2005195508 [2], to improve image quality and eliminate speckle noise, a vibrating mirror is located between the light source and the screen, due to the vibration of which the speckle pattern is smeared.

The disadvantage of these devices is the presence of moving parts, which reduces their reliability.

The published international application WO 2004008225 [3] describes a speckle reduction device without moving parts, which is based on the idea of dividing a laser beam into several beams with an optical path difference greater than the coherence length of the incoming laser beam. This idea was implemented using an inclined plate with semi-reflective and reflective surfaces.

The disadvantage of this device is the need for additional homogenizing elements for the output beams, which increases the dimensions of the device.

Closest to the claimed invention is a speckle reduction system for fiber optic illumination described in USH2045H (US Statutory Invention Registration) [4], which deflects the initial light beam so that its path and speckle distribution changes with time. This solution is selected as a prototype of the claimed invention.

The disadvantage of the design of the prototype [4] is that it is not compact enough due to the presence of a large number of constituent elements.

The task of the invention is to provide a device for suppressing speckles of small size with increased reliability.

The problem is solved by creating three versions of a device for suppressing speckle noise, combined by a single inventive concept.

Option 1. The inventive device for suppressing speckle noise includes an alternating voltage generator, as well as a polarization controller arranged in series along the laser beam path connected to an alternating voltage generator, and two birefringent optical wedges, the outer surfaces of the optical wedges being parallel to one another, the beveled inner surfaces are also parallel to each other and located at a distance from one another with the formation of a gap, while the polarization controller made with the possibility of changing the polarization of the laser beam depending on the frequency of the generator voltage, the first optical wedge is configured to split the laser beam into two orthogonally polarized beams, the intensity of which varies depending on the direction of polarization of the laser beam entering the wedge, and the second wedge is made with the possibility parallelization of the beams emerging from the first wedge.

For the operation of the device according to option 1, it is important that the polarization controller is made in the form of an element selected from the group of elements, which includes a liquid crystal cell, an electro-optical and acousto-optical crystal.

Option 2. The inventive device for suppressing speckle noise includes an alternating voltage generator, as well as two birefringent optical wedges arranged in series along the laser beam propagation path, each of which is connected to an alternating voltage generator, the outer surfaces of the optical wedges being parallel to one another, the beveled inner surfaces are also parallel one another and are located at a distance from one another with the formation of a gap, while the first optical wedge is made in the possibility of dividing the laser beam into two orthogonally polarized beams (hereinafter referred to as “ordinary” and “extraordinary” beams) and changing the deflection angle of the “extraordinary” beam due to a change in the refractive index under the action of the voltage from the alternating voltage generator, and the second wedge is made with the possibility of parallelization Beams emerging from the first wedge due to a change in the refractive index under the action of voltage from an alternating voltage generator.

For the operation of the device according to option 2, it is important that the gap between the wedges is filled with a material with a refractive index, the value of which is between the highest and lowest values of the refractive index for the "unusual" beam of wedges.

Option 3. The inventive device for the suppression of speckle noise includes an alternating voltage generator arranged in series along the path of the laser beam two optical wedges, the outer surfaces of which are parallel to each other, and the beveled inner surfaces are parallel to each other and are located at some distance from each other with the formation of a gap, as well as at least one drive connected to an alternating voltage generator and configured to vary the gap between wedged surfaces of the wedges in accordance with the change in the voltage of the generator, at which there is a displacement of the laser beam emerging from this wedge.

For the operation of the device according to option 3, it is important that the drive was made in the form of a piezoelectric element.

For the operation of the device according to option 3, it is also important that it contains a drive located in the gap between the beveled inner surfaces of the wedges and configured to move the wedges parallel to the beam propagation direction in accordance with the change in the voltage of the alternating voltage generator.

For the operation of the device according to option 3, it is also important that it contains one drive located on one of the wedges and configured to move the wedge perpendicular to the beam propagation direction in accordance with the change in the voltage of the alternating voltage generator.

The technical result of the claimed invention is to reduce the size and increase reliability through the use of a compact and simple design, which contains simple and birefringent optical wedges connected to an alternating voltage generator, and allows the laser beam to be shifted with a high frequency for speckle erosion.

For a better understanding of the present invention, the following is a detailed description thereof with corresponding drawings.

Figure 1. Scheme of embodiment 1 of a speckle suppression device with a polarization rotator made according to the invention.

Figure 2. Scheme of variant 2 of the speckle suppression device with birefringent wedges connected to a common alternating voltage generator, made according to the invention: view 2.1 - with an empty gap between the wedges, view 2.2 - with a gap between the wedges filled with optical material.

Figure 3. Scheme of variant 3 of the speckle suppression device with optical wedges moved by an electrically controlled drive, made according to the invention: view 3.1 - with a drive located in the gap between the wedges, view 3.2 - with a drive located on one of the wedges.

In the embodiment with the polarization rotator (Fig. 1), the speckle suppression device includes an alternating voltage generator 1, and also a polarization rotator 2 arranged in series along the laser beam path connected to the alternating voltage generator 1, and two birefringent optical wedges 3, 4. External surfaces 5, 6 of the optical wedges are parallel to one another, the beveled inner surfaces 7, 8 are also parallel to one another and are located at a distance from one another to form a gap. The control signal in the form of an alternating voltage is applied to the polarization rotator 2 and, thus, the polarization state of the laser beam 9 is changed in time. The optical wedge 3 divides the laser beam 9 into two orthogonally polarized beams 10 and 11, the intensity of which depends on the polarization state of the incoming laser beam 12, and the wedge 4 directs them parallel to one another (beams 13 and 14).

Each of the emerging beams 13 and 14 has its own speckle distribution. By controlling the intensity of the emerging beams, the brightness of the speckle distribution is changed. If the frequency of the control signal (the frequency of the voltage change of the generator 1) is higher than 25 Hz, then the resulting speckle distribution will be blurred to the human eye.

The polarization rotator 2 can be made, for example, in the form of a liquid crystal cell that rotates the polarization direction of the outgoing beam 9, or in the form of an electro- or acousto-optical crystal that redistributes the intensities of the orthogonally polarized components of the beam 9.

The second embodiment of the inventive speckle suppression device with birefringent wedges 3 and 4 connected to a common alternating voltage generator 1 (FIG. 2) does not contain a polarization rotator, but wedges 2 and 3 have a refractive index that is variable by the voltage of the generator. When the voltage supplied to the wedges 3, 4 from the generator 1 changes, the refractive index of the wedges changes, while the "unusual" beam 11 deviates relative to the "ordinary" beam 10 at the exit of the first wedge 3, and in the second wedge, the beams 10 and 11. Controlling the amplitude and frequency of the control signal (voltage generator 1) change the blur distribution of the speckles.

If the polarization direction of the incoming beam 9 is parallel or perpendicular to the optical axis of the wedge 3, then only one output beam is present, and this beam is shifted by changing the control signal of the generator 1.

The gap 15 between the wedges 3 and 4 in the second embodiment of the claimed invention is preferably filled with a material with a refractive index, the value of which is between the highest and lowest values of the refractive index for the "extraordinary" beam in wedges 3 and 4 (Figure 2, view 2.2).

In a third embodiment of the claimed speckle suppression device (Figure 3), the optical wedges 3 and 4 are made of ordinary optical material, which does not change under the influence of voltage. In this embodiment, the shift of the incoming laser beam occurs due to the movement of the wedges by at least one mechanical drive 15, which is connected to the alternator 1.

The device comprises a drive 16 located in the gap between the wedges 3, 4 and mutually moving the wedges in the longitudinal direction (Figure 3, view 3.1). In an equivalent alternative, the device includes a drive 15, mutually moving the wedges in the transverse direction (Figure 3, view 3.2).

The drive 15, 16 is performed mainly in the form of a piezoelectric element.

The inventive speckle suppression device can be used in lighting and imaging systems with a laser source, namely in handheld display devices, projectors, projection displays, etc.

Although the above embodiment of the invention has been set forth to illustrate the present invention, it is clear to those skilled in the art that various modifications, additions and substitutions are possible without departing from the scope and meaning of the present invention disclosed in the attached claims.

Claims (8)

1. The device for the suppression of speckle noise, containing an alternating voltage generator, as well as a polarization controller connected in series with the alternating voltage generator, and two birefringent optical wedges arranged in series along the laser beam propagation path, the outer surfaces of the optical wedges being parallel to one another, the beveled inner surfaces are also parallel one another and are located at a distance from one another to form a gap, while the polarization controller is configured to By changing the polarization of the laser beam depending on the frequency of the generator voltage, the first optical wedge is capable of dividing the laser beam into two orthogonally polarized beams, the intensity of which varies depending on the direction of polarization of the laser beam entering the wedge, and the second wedge is designed to parallelize the outgoing from the first wedge of beams. 2. The device according to claim 1, characterized in that the polarization controller is made in the form of an element selected from the group of elements consisting of a liquid crystal cell, electro-optical and acousto-optical crystal. 3. A speckle noise suppression device comprising an alternating voltage generator, as well as two birefringent optical wedges arranged in series along the laser beam propagation path, each of which is connected to an alternating voltage generator, the outer surfaces of the optical wedges being parallel to one another, the beveled inner surfaces are also parallel to one another and are located at a distance from one another with the formation of a gap, while the first optical wedge is arranged to separate dividing the laser beam into two orthogonally polarized beams - “ordinary” and “extraordinary” - and changing the angle of deviation of the “extraordinary” beam by changing the refractive index under the action of voltage from the alternating voltage generator, and the second wedge is made with the possibility of parallelization of the beams emerging from the first wedge due to changes in the refractive index under the action of voltage from an alternating voltage generator. 4. The device according to claim 3, characterized in that the gap between the wedges is filled with a material with a refractive index, the value of which is between the higher and lower values of the refractive index for the "unusual" beam of wedges. 5. A device for suppressing speckle noise, comprising an alternating voltage generator, two optical wedges located in series along the laser beam propagation path, the outer surfaces of which are parallel to each other, and the beveled internal surfaces are parallel to each other and are located at some distance from each other to form a gap, and at least one drive connected to an alternating voltage generator and configured to vary the gap between the beveled surfaces wedges in accordance with the change in the voltage of the generator, at which there is a displacement of the laser beam emerging from this wedge. 6. The device according to claim 5, characterized in that the actuator is made in the form of a piezoelectric element. 7. The device according to claim 5, characterized in that it comprises a drive located in the gap between the chamfered inner surfaces of the wedges and configured to shift the wedges parallel to the beam propagation direction in accordance with a change in the voltage of the alternating voltage generator. 8. The device according to claim 5, characterized in that it contains one drive located on one of the wedges and configured to move the wedge perpendicular to the beam propagation direction in accordance with the change in voltage of the alternating voltage generator.

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