JP6832107B2 - Speckle-resolving optical system and optical equipment equipped with the speckle-resolving optical system - Google Patents

Description

The present invention relates to a speckle-eliminating optical system including a speckle-eliminating element and an optical device having such an optical system.

The depolarizing element is used as an optical component for eliminating polarized light, which is a problem in laser printers, etc., and speckle reduction that reduces the occurrence of speckle in the optical system of optical equipment such as optical exposure equipment and optical measuring instruments. It is used as an element.

When one light beam is divided into multiple light rays by passing the light from the laser through a microlens array or fly-eye lens, the divided light has the same polarization direction, and is included in the speckle-eliminating optical system. When specific conditions are met, the divided light may cause interference, and a point (speckle) in which the light strengthens each other may occur in the middle of the optical system. Speckle is known to occur in various optical systems that use laser light, and various methods for solving this have been proposed, but no effective solution has been established.

One of the methods to eliminate the speckle is to make the so-called random polarization state in which the polarization state of light is various. This is because if the polarized light is not uniform, light interference is unlikely to occur because it approaches the state of natural light having low directivity.

As a depolarizing element, an element having a sub-wavelength structure (SWS) is known (see, for example, Patent Document 1). The sub-wavelength structure is a periodic structure of grooves that are repeatedly arranged at a period shorter than the wavelength of light used.

The periodic structure of the groove having a pitch shorter than the wavelength of light has effective refractive indexes nTE and nTM different from each other in the direction having the period and the direction having no period, and behaves as if it is a birefringent material (so-called structural birefringence). Structure). Since the propagation speed of light in each polarization direction is different due to this difference in effective refractive index, the polarization state of light passing through the sub-wavelength structure changes. The sub-wavelength structure can freely control birefringence and their dispersion by designing the structure. Utilizing this characteristic of the sub-wavelength structure, various products such as polarizing plates, wave plates, and wavelength separation elements have been developed.

In a depolarizing element using a sub-wavelength structure, a portion that transmits light is divided into a plurality of regions, and sub-wavelength structures having various optical axis directions are formed in each region. Hereinafter, this region is referred to as a sub-wavelength structure region. The optical axis direction is the arrangement direction of the grooves of the sub-wavelength structure. The depolarization element is driven in a plane so that light scans each sub-wavelength structural region. As a result, the polarization directions of the light transmitted through the depolarizing element are changed in various directions with time, and the combined light becomes light having various polarization directions. Since the light transmitted through the depolarizing element has various polarization directions, the speckle due to the interference of the light having the same polarization direction is alleviated.

Japanese Unexamined Patent Publication No. 2011-180581

An object of the present invention is to improve the speckle elimination effect of an optical system including the speckle elimination element described above.

The speckle-eliminating optical system according to the present invention includes a plurality of speckle-eliminating elements arranged on the optical path of light emitted from a light source to produce a speckle-eliminating effect, and at least two of the speckle-eliminating elements. It is equipped with a speckle elimination element drive unit that operates so as to change the optical effect given to the light from the light source over time. The optical effect given to light means, for example, an effect of causing a phase difference in light if the speckle eliminating element is a wave plate.

A wavelength plate having a function of causing a phase difference in light may be included as the speckle eliminating element, and the wavelength plate may be driven by the speckle eliminating element driving unit.

A plurality of wave plates may be included as the speckle eliminating element, and at least two of the wavelength plates may be driven by the speckle eliminating element driving unit. By driving at least two wave plates, the time division effect of the phase difference of light by the wave plates is improved, and thereby the speckle elimination effect is improved. A 1/2 wave plate that converts the polarization direction of light tends to be expensive because its sub-wave plate structure is not easy to manufacture. For example, by using a plurality of wave plates such as a 1/4 wave plate, 1 The function as a / 2 wave plate can be realized, and thereby the function of the 1/2 wave plate can be realized at low cost.

A light diffusing plate having a light diffusing function may be included as the speckle eliminating element, and at least one of the wavelength plates and the light diffusing plate may be driven by the speckle eliminating element driving unit. The light diffusing plate is a light-transmitting speckle-eliminating element having a microlens array or a fly-eye lens. By using such a speckle-eliminating element together with the wave plate, the polarization direction of light can be not only temporally divided by the wave plate but also spatially divided by the light diffusing plate. Further, by driving these, both the time division function and the space division function in the polarization direction of light can be improved, and the speckle elimination effect is improved.

The speckle elimination element driving unit may be configured to rotate at least two speckle elimination elements. The mechanism for rotating the speckle-eliminating element is cheaper than the mechanism for causing the speckle-eliminating element to perform other movements such as vibration, and the cost can be reduced.

The rotation speeds of the speckle-eliminating elements that rotate may be different from each other. Since the rotation speeds of the speckle elimination elements are different from each other, the time division function in the polarization direction of light is improved, and the speckle elimination effect is improved.

Since the speckle-eliminating optical system according to the present invention operates a plurality of speckle-eliminating elements having a speckle-eliminating effect so as to change the optical effect given to the light from the light source with time, the speckle-eliminating element can be used independently. Compared to the case of operation, the time division function in the polarization direction of light is improved, and the speckle elimination effect is improved.

It is a schematic block diagram which shows the structure of the screen projection apparatus as an example of the optical device provided with the speckle elimination optical system of one Example. It is sectional drawing which shows typically an example of the wavelength plate which is one kind of the speckle elimination element of the speckle elimination optical system of the same Example. It is sectional drawing which shows typically an example of the light diffusing plate which is one kind of the speckle elimination element of the speckle elimination optical system of the same Example. It is a conceptual diagram for demonstrating an example of the combination of speckle elimination elements. It is a conceptual diagram for demonstrating another example of a combination of speckle elimination elements. It is a conceptual diagram for demonstrating still another example of the combination of speckle elimination elements. It is a conceptual diagram for demonstrating still another example of the combination of speckle elimination elements. It is a conceptual diagram for demonstrating still another example of the combination of speckle elimination elements. It is a conceptual diagram for demonstrating still another example of the combination of speckle elimination elements. It is a conceptual diagram for demonstrating still another example of the combination of speckle elimination elements. It is a conceptual diagram for demonstrating still another example of the combination of speckle elimination elements. It is sectional drawing which shows the structure which emits light as parallel light. It is a conceptual diagram explaining the concept which emits light as parallel light. It is sectional drawing which shows an example of the speckle elimination optical system which incorporated the structure which emits light as parallel light. It is sectional drawing which shows the other example of the speckle elimination optical system which included the structure which emits light as parallel light. It is sectional drawing which shows the further example of the speckle elimination optical system which incorporates the structure which emits light as parallel light. It is sectional drawing which shows the further example of the speckle elimination optical system which incorporates the structure which emits light as parallel light. It is a schematic block diagram which shows the structure of the projector as another example of the optical device provided with the speckle elimination optical system.

Hereinafter, the speckle-eliminating optical system according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a screen projection device using the speckle-eliminating optical system of one embodiment.

This screen projection device includes a light source unit 2, a speckle elimination optical system 12, a mirror 18, a lens 20, a MEMS element 22, a projection lens 24, and a screen 26. The light source unit 2 includes light sources 4a, 4b, 4c composed of a laser diode (LD) or a light emitting diode (LED) that emit light of three colors of red, green, and blue, respectively, and emits light from the light sources 4a, 4b, 4c. The light to be generated is combined by the half mirrors 6 and 8 and emitted through the lens 10. The light source constituting the light source unit 2 is not limited to the LD and the LED, and may be another light source.

The speckle-eliminating optical system 12 is arranged on the optical axis of the light emitted from the light source unit 2. The speckle-eliminating optical system 12 includes a plurality of speckle-eliminating elements 14 having a speckle-eliminating effect. At least two of the speckle-eliminating elements 14 of the speckle-eliminating optical system 12 are in a plane perpendicular to the optical axis of the light emitted from the light source unit 2 by the speckle-eliminating element driving unit 16. Can be exercised with.
Although not described in detail here, in the case of the "reflection type speckle elimination element", the speckle elimination optical system 12 may not be arranged on the optical axis of the light emitted from the light source unit 2.

The speckle-eliminating element 14 of the speckle-eliminating optical system 12 has a sub-wavelength structure in which a convex portion 30 and a groove 32 are periodically provided at a pitch shorter than the wavelength of light, as shown in FIG. A speckle-eliminating element may be used for the wavelength plate 14a. Although the wave plate of FIG. 2 is provided with a sub-wavelength structure only on one surface of the substrate, it may be provided with sub-wavelength structures on both sides of the substrate. By moving such a wave plate 14a in a plane perpendicular to the optical axis of light, it is possible to obtain a time division function for temporally converting a polarized state into light. In particular, if the light has a phase difference of about 1/2 wavelength (1/2 wavelength plate), the polarization direction of the light can be changed in time, but it is more than 1/2 wavelength. Even with a wave plate that causes a small phase difference in light, the coherence of light can be reduced. For example, in the case of a "reflection type speckle elimination element", the amount of phase difference passes through the optical element portion of the λ / 4 wave plate twice, so that (λ / 4 wave plate) + (λ / 4 wave plate) = It expresses the function of (λ / 2 wave plate). Therefore, the same effect as that which causes a phase difference of 1/2 wavelength (1/2 wavelength plate) is exhibited.

The wave plate 14a is a region-divided wave plate in which the surface of the substrate is divided into a plurality of regions and sub-wavelength structures having different optical axis directions (arrangement directions of the convex portion 30 and the groove 32) are provided in those regions. It may be a region-undivided wave plate in which the entire sub-wavelength region (region in which the sub-wavelength structure is provided) on the surface of the substrate has the same optical axis direction. The region-undivided wave plate can exhibit a time-dividing function by rotating it. The region-divided wave plate is easier to manufacture than the region-divided wave plate, and the manufacturing cost is low.

Further, as the speckle eliminating element 14 of the speckle eliminating optical system 12, a light diffusing plate 14b provided with a microlens array composed of a plurality of lens portions 34 and a fly-eye lens as shown in FIG. 3 can be mentioned. .. When light is incident on such a light diffusing plate 14b, one light flux is divided into a plurality of light fluxes. That is, the light diffusing plate 14b has a space dividing function for spatially dividing light.

In FIG. 3, a plurality of lens portions 34 having the same size are drawn so as to be evenly arranged, but the effective diameter and focal length of the lens portions 34 are not uniform even if they are uniform. You may. As the light diffusing plate having a non-uniform effective diameter and focal length of the microlens, those disclosed in Japanese Patent Application Laid-Open No. 2014-203032 can be used.

Further, even if the speckle-eliminating element 14 of the speckle-eliminating optical system 12 is an integrated wave plate as shown in FIG. 2 and a light diffusing plate as shown in FIG. Good. Such an element is disclosed in, for example, Japanese Patent Application Laid-Open No. 2011-180581.

The wavelength plate 14a, the light diffusing plate 14b, or a combination thereof all have a light time dividing function or a space dividing function, and have a speckle elimination effect. The speckle-eliminating optical system 12 is realized by combining a plurality of speckle-eliminating elements having such a speckle-eliminating effect.

In FIG. 1, the speckle-eliminating elements 14 of the speckle-eliminating optical system 12 are shown to be arranged side by side, but the speckle-eliminating elements 14 are located at positions separated from each other, that is, the speckle-eliminating elements 14. Other optical elements may be present between the two. In short, a plurality of speckle-eliminating elements 14 including at least a wave plate that causes a phase difference in the light from the light source unit 2 are provided on the optical axis of the light from the light source unit 2, and the speckle-eliminating elements 14 are provided. Any arrangement may be used as long as at least two speckle-eliminating elements 14 are moved by the speckle-eliminating element driving unit 16.

The light that has passed through the speckle-eliminating optical system 12 is projected onto the screen 26 via the mirror 18, the lens 20, the mirror 22, and the projection lens 24. The mirror 22 may be a mirror made of a MEMS element (MEMS mirror) or a MEMS mirror array. In addition, in order to avoid complication in the present invention, the above are collectively referred to as MEMS mirrors. The MEMS mirror includes a single or a plurality of micromirrors that can be electrically driven, and the tilted state of the micromirrors can be changed by turning on / off the drive of electrodes provided under the micromirrors. Therefore, by driving the mirrors individually, it is possible to control the projection of light for each display pixel.

Various combinations of speckle-eliminating elements 14 constituting the speckle-eliminating optical system 12 can be considered. A typical example thereof will be described below.

First, as shown in FIG. 4, it is conceivable that the speckle elimination optical system 12 is composed of two speckle elimination elements 14-1 and 14-2. In the embodiment of FIG. 4, both the speckle eliminating elements 14-1 and 14-2 are disk-shaped elements, are arranged coaxially, and are rotated in the same direction by the speckle eliminating element 16. The rotation speeds of the speckle elimination elements 14-1 and 14-2 may be the same or different.

At least one of the speckle-eliminating elements 14-1 and 14-2 is a wave plate as shown in FIG. When both the speckle elimination elements 14-1 and 14-2 are wave plates, the speckle elimination elements 14-1 and 14-2 are each made into a substantially 1/4 wavelength plate, and the speckle is used. It is preferable that the elimination elements 14-1 and 14-2 have a function as one 1/2 wave plate. Then, the speckle eliminating elements 14-1 and 14-2 can have a function of converting the polarization direction of light. Then, by simultaneously moving these speckle-eliminating elements 14-1 and 14-2, the speckle-eliminating effect is improved as compared with the case where the speckle-eliminating element is used alone.

Further, when only one of the speckle eliminating elements 14-1 and 14-2 is a wave plate, it is preferable that the wave plate has a function as a 1/2 wavelength plate. In that case, a light diffusing plate as shown in FIG. 3 can be used as the other speckle eliminating element. By combining a 1/2 wave plate having a time dividing function in the polarization direction of light with a light diffusing plate having a space dividing function of light and moving them at the same time, both the time dividing function and the space dividing function are improved. The speckle elimination effect is improved as compared with the case where the speckle elimination element is used alone. Further, both the speckle eliminating elements 14-1 and 14-2 may be light diffusing plates as shown in FIG.

As shown in FIG. 5, the rotation directions of the speckle eliminating elements 14-1 and 14-2 may be opposite to each other. By doing so, the relative moving speeds of the optical axis passing regions of the speckle-eliminating elements 14-1 and 14-2 are increased, the time division function of light is improved, and the speckle-eliminating effect is further improved.

Further, as shown in FIGS. 6 and 7, the speckle elimination elements 14-1 and 14-2 may be arranged so as to overlap each other's partial regions, not coaxially. In the examples of FIGS. 6 and 7, the lower end portion of the speckle elimination element 14-1 and the upper end portion of the speckle elimination element 14-2 are arranged on the optical axis of the light from the light source unit 2. In this case, as shown in FIG. 6, when the speckle eliminating elements 14-1 and 14-2 rotate in opposite directions, the region through which the light passes moves in the same direction, and FIG. 7 shows. As shown, when the speckle eliminating elements 14-1 and 14-2 rotate in the same direction, the region through which light passes moves in the opposite direction.

Further, as shown in FIGS. 8 and 9, the speckle eliminating elements 14-1 and 14-2 may have a shape other than the disk type, for example, a flat plate type, and such speckle eliminating elements may be formed. May be made to perform an exercise other than the rotational exercise. Examples of the motion other than the rotary motion include a vibration motion in two directions orthogonal to each other in a plane perpendicular to the optical axis, a figure eight motion, an elliptical motion, and the like.

Further, as shown in FIGS. 10 and 11, the speckle-eliminating optical system 12 may include three or more speckle-eliminating elements 14-1, 14-2, and 14-3. In the example of FIG. 10, among the three speckle elimination elements 14-1, 14-2 and 14-3, the speckle elimination elements 14-1 and 14-2 are moved in a plane perpendicular to the optical axis. The speckle elimination element 14-3 is stationary. In the example of FIG. 11, all speckle eliminating elements 14-1, 14-2, and 14-3 are moved in a plane perpendicular to the optical axis.

In the example of FIG. 10, the speckle eliminating elements 14-1 and 14-2 are used as a wave plate as shown in FIG. 2, and the speckle eliminating elements 14-3 are used as a light diffusing plate as shown in FIG. Can be done. In that case, it is preferable that the speckle eliminating elements 14-1 and 14-2 cause a movement difference of about 1/2 wavelength in the light. Then, as the speckle elimination element 12, it is possible to obtain a time division function in the polarization direction of light and a space division function of light.

Further, as in the example of FIG. 11, by moving the speckle eliminating element 14-3 made of a light diffusing plate in a plane perpendicular to the optical axis, the spatial decomposition function of light can be further improved.

Further, in the example of FIG. 11, all three speckle eliminating elements 14-1 to 14-3 may be used as a wave plate, or any two of them may be used as a wave plate or a light diffusing plate. By simultaneously moving the three speckle-eliminating elements 14-1 to 14-3 in a plane perpendicular to the optical axis, the speckle-eliminating effect can be further improved.

In the examples of FIGS. 10 and 11, the rotation directions of the speckle eliminating elements 14-1 and 14-2 may be the same or may be opposite. Further, the speckle elimination elements 14-1 and 14-2 do not necessarily have to be provided coaxially, and may be arranged in the same manner as in FIGS. 6 and 7.

When a light diffusing plate 14b as shown in FIG. 3 is used as the speckle eliminating element 14 of the speckle-resolving optical system 12, as shown in FIG. 12, two light diffusing plates 14b are attached to each other's lens portions. It can be arranged so as to face each other. By making the lens portions face each other, as shown in FIG. 13, the light incident as parallel light can be emitted as parallel light. In order to realize this principle in all lens units, it is preferable to use a light diffusing plate as disclosed in Japanese Patent Application Laid-Open No. 2014-203032 as the light diffusing plate 14b. The light diffusing plate disclosed in Japanese Patent Application Laid-Open No. 2014-203032 is configured so that the F number (= f / D, f is the focal length, D is the effective diameter of each lens) of each lens is substantially uniform. Therefore, it is possible to emit light incident as parallel light in each lens portion as parallel light.

As an example of the configuration of the speckle-resolving optical system 12 using the principle of FIG. 13, the configurations shown in FIGS. 14 to 17 can be mentioned.

In the example of FIG. 14, the wavelength plate 14a is used as the speckle elimination element 14-1, and the two light diffusing plates 14b are used as one speckle elimination element 14-2 with the lens portions facing each other. In this case, the two light diffusing plates 14b are integrally made to move at the same time in a plane perpendicular to the optical axis. As a result, the light incident as parallel light can be emitted as parallel light while improving the time division function and the space division function.

Although detailed description thereof is omitted here, the specular elimination element 14 shown in FIGS. 2, 14, 15, 16 and 17 causes light to be obliquely incident on the optical surface. However, the effect as a wave plate can be obtained. Therefore, each speckle eliminating element 14 does not necessarily have to be arranged perpendicular to the optical axis of light, and may be arranged in a state of being inclined with respect to the optical axis.

In the example of FIG. 15, an element 14c having a sub-wavelength structure on one surface and a microlens array or a fly-eye lens on the other surface is used as one speckle elimination element 14-1, and the lens portion of the element 14c is used. The light diffusing plate 14b is used as the second speckle eliminating element 14-2 so as to face the surface on which the lens is provided. With this structure as well, it is possible to emit light incident as parallel light as parallel light while improving the time division function and the space division function.

Further, as in the example of FIG. 16, a wave plate 14a can be added as the third speckle eliminating element 14-3 to the configuration of FIG. Further, as shown in FIG. 17, two elements 14c having a function as a wave plate and a function as a light diffusing plate are used, and they are used as speckle elimination elements 14-1 and 14-2, respectively. The surfaces on which the lens portions are provided may be arranged so as to face each other. With the configurations of FIGS. 16 and 17, the light incident as parallel light can be emitted as parallel light while improving the time division function and the space division function.

In general, it is known that the higher the operating speed of the speckle elimination element, the higher the speckle elimination effect. However, when using an optical system that reads an image using a sensor or the like, regular noise occurs when the relationship between the sensor size (dimensions) and the operating speed of the speckle elimination element becomes a certain relationship. Patterns may occur in the image. In the past, since a single speckle elimination element was operated, the adjustment range for not generating noise was small, and it was difficult to achieve both reduction of noise and improvement of speckle elimination effect.

On the other hand, in the embodiment described above, since at least two of the speckle elimination elements 14 constituting the speckle elimination optical system 12 are operated, the adjustment range for not generating noise is wide and the noise is increased. It is easy to achieve both reduction and improvement of speckle elimination effect.

The present inventor has verified the combination of the speckle elimination elements 14 constituting the speckle elimination optical system 12 and the speckle elimination effect at that time. The results are shown in Table 1.

In this verification, speckle contrast values (hereinafter, Cs values) were measured for various combinations with a standard speckle contrast measurement optical device of Oxide Co., Ltd. Since the Cs value becomes larger as more speckles appear, it can be evaluated that the lower the measured Cs value, the higher the speckle elimination effect.

As can be seen from Table 1 above, the Cs value when the 1/2 wave plate and the light diffusing plate (microlens array) are both stationary is 0.8 to 1.0 (row 0 in Table 1). The Cs value was 0.4 when the 1/2 wave plate was rotated at a speed V and the light diffusing plate was stationary (see row 1 in Table 1). It is difficult to obtain the speckle elimination effect by using only the light diffusing plate, but even so, when the two light diffusing plates are moved, the Cs value is higher than when the stationary 1/2 wave plate and the light diffusing plate are used. Has become smaller (see rows 2 and 3 in Table 1). Further, when one 1/2 wave plate and one light diffusing plate are moved, respectively, when two 1/4 wave plates and one light diffusing plate are moved, one wavelength. When the plate and the two light diffusing plates were moved, the Cs value became smaller (see rows 2 to 13 in Table 1). From this, it was found that the speckle elimination effect was improved by moving a plurality of speckle elimination elements at the same time.

The speckle-eliminating optical system 12 described above can also be applied to an optical system other than the optical system of the embodiment described with reference to FIG. FIG. 18 shows an example of another optical system to which the speckle-eliminating optical system 12 is applied. In the embodiment of FIG. 18, the light of the three primary colors is extracted from the light emitted from the laser light source 40 by the split imaging unit 46, and the light is guided to the LCD (liquid crystal display) panel, respectively, from the projection lens 48 to the screen 50. It is a projector that outputs. In this embodiment, the speckle-eliminating optical system 12 is arranged between the lenses 42 and 44 arranged between the laser light source 40 and the split imaging unit 46.

2 Light source 4a to 4c Light source 6,8 Half mirror 10,20 Lens 12 Speckle elimination optical system 14 Speckle elimination element 14a Wave plate 14b Light diffuser 16 Speckle elimination element Drive unit 18 Mirror 22 MEMS element 24 Projection lens 26 Screen 30 Convex part 32 Groove 34 Lens part

Claims (6)

Multiple speckle-eliminating elements that are placed on the optical path of light emitted from a light source to produce speckle-eliminating effects,
It is provided with a speckle-eliminating element drive unit that operates at least two of the speckle-eliminating elements so as to change the optical effect on the light from the light source over time.
The plurality of speckle-eliminating elements include a plurality of wave plates each having a function of causing a phase difference in the light, and the plurality of wavelength plates are each driven by the speckle-eliminating element driving unit.
A speckle-eliminating optical system in which the total phase difference generated by the plurality of wave plates in the light is approximately 1/2 wavelength of the light. It includes a light diffusion plate having a light diffusing function as the speckle depolarizer, speckle eliminating optical system according to claim 1 in which the pre-Symbol wavelength plate and the light diffusing plate is driven by the speckle eliminating device driving section .. The speckle-eliminating optical system according to claim 1 or 2 , wherein the speckle-eliminating element driving unit is configured to rotate at least two speckle-eliminating elements. The speckle-eliminating optical system according to claim 3 , wherein the rotational speeds of the speckle-eliminating elements that rotate are different from each other. The speckle-eliminating optical system according to claim 3 or 4 , wherein the speckle-eliminating elements that rotate and move in different directions of rotation. An optical device provided with the speckle-eliminating optical system according to any one of claims 1 to 5.

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