JP2018054759A - Speckle eliminating optical system and optical device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve speckle eliminating performance of an optical system with speckle eliminating elements.SOLUTION: A speckle eliminating optical system comprises: a plurality of speckle eliminating elements disposed in an optical path of light emitted from a light source and configured to produce a speckle eliminating effect; and a speckle eliminating element drive unit configured to drive at least two of the speckle eliminating elements in a manner that provides temporal change in optical effect on the light from the light source.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a speckle elimination optical system including a speckle elimination element and an optical apparatus having such an optical system.

  The depolarization element is used as an optical component to eliminate polarized light, which is a problem in laser printers, and speckle reduction to reduce the generation of speckles in optical systems such as optical exposure devices and optical measuring instruments. It is used as an element.

  When splitting a light beam into multiple beams by passing the light from the laser through a microlens array or fly-eye lens, the split light is aligned in the same direction. When the specific condition is satisfied, there is a case where a point (speckle) where the divided light is caused to cause interference and the light is strengthened in the middle of the optical system. Speckle is known to occur in various optical systems that use laser light, and various methods have been proposed to eliminate this, but no effective solution has been established.

  One method of eliminating speckle includes a so-called random polarization state in which the polarization state of light is varied. This is because if the polarization is uneven, light interference is unlikely to occur because it approaches the state of natural light with low directivity.

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

  The periodic structure of grooves having a pitch shorter than the wavelength of light has different effective refractive indexes nTE and nTM in directions with and without periods, and behaves as if they are birefringent materials (so-called structural birefringence). Structure). Because the difference in effective refractive index can cause a difference in the propagation speed of light in each polarization direction, the polarization state of light passing through the sub-wavelength structure changes. The sub-wavelength structure can freely control birefringence and their dispersion depending on the design of the structure. Various products such as a polarizing plate, a wave plate, and a wavelength separation element have been developed using this characteristic of the sub-wavelength structure.

  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 depolarizing element is driven in a plane so that light scans each sub-wavelength structure region. As a result, the polarization direction of the light transmitted through the depolarizing element is changed in various directions according to time, and the light obtained by combining them becomes light having various polarization directions. Since the light transmitted through the depolarizer has various polarization directions, speckle due to interference of light having the same polarization direction is alleviated.

JP 2011-180581 A

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

  The speckle canceling optical system according to the present invention includes a plurality of speckle canceling elements that are arranged on an optical path of light emitted from a light source to produce a speckle canceling effect, and at least two of the speckle canceling elements are A speckle canceling element driving 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 an effect of causing a phase difference in light if the speckle eliminating element is a wave plate, for example.

  A wave plate having a function of causing a phase difference in light may be included as the speckle eliminating element, and the wave 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 wave 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, thereby improving the speckle elimination effect. A half-wave plate that converts the polarization direction of light tends to be expensive because the sub-wavelength structure is not easy to manufacture, but for example, by using a plurality of wave plates such as a quarter-wave plate, The function as a / 2 wavelength plate can be realized, and thereby the function of the 1/2 wavelength 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 plate and the light diffusing plate may be driven by the speckle eliminating element driving unit. The light diffusion plate is a light-transmitting speckle eliminating element having a microlens array and a fly-eye lens. By using such a speckle eliminating element together with a wave plate, the polarization direction of light can be not only temporally divided by the wave plate but also spatially divided by the light diffusion plate. Furthermore, by driving these, it is possible to improve both the time division function and the space division function in the polarization direction of light, and the speckle elimination effect is improved.

  The speckle canceling element driving unit may be configured to rotate at least two of the speckle canceling elements. The mechanism for rotating the speckle canceling element is less expensive than the mechanism for causing the speckle canceling element to perform other motions such as a vibration motion, and the cost can be reduced.

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

  In the speckle canceling optical system according to the present invention, a plurality of speckle canceling elements having a speckle canceling effect are operated so as to change the optical effect given to the light from the light source over time. Compared to the 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 apparatus provided with the speckle cancellation optical system of one Example. It is sectional drawing which shows roughly an example of the wavelength plate which is 1 type of the speckle cancellation element of the speckle cancellation optical system of the Example. It is sectional drawing which shows roughly an example of the light diffusing plate which is 1 type of the speckle cancellation element of the speckle cancellation optical system of the Example. It is a conceptual diagram for demonstrating an example of the combination of a speckle cancellation element. It is a conceptual diagram for demonstrating the other example of the combination of a speckle cancellation element. It is a conceptual diagram for demonstrating the further another example of the combination of a speckle cancellation element. It is a conceptual diagram for demonstrating the further another example of the combination of a speckle cancellation element. It is a conceptual diagram for demonstrating the further another example of the combination of a speckle cancellation element. It is a conceptual diagram for demonstrating the further another example of the combination of a speckle cancellation element. It is a conceptual diagram for demonstrating the further another example of the combination of a speckle cancellation element. It is a conceptual diagram for demonstrating the further another example of the combination of a speckle cancellation element. It is sectional drawing which shows the structure which radiate | emits light as parallel light. It is a conceptual diagram explaining the concept which radiate | emits light as parallel light. It is sectional drawing which shows an example of the speckle cancellation optical system incorporating the structure which radiate | emits light as parallel light. It is sectional drawing which shows the other example of the speckle cancellation optical system incorporating the structure which radiate | emits light as parallel light. It is sectional drawing which shows the further another example of the speckle elimination optical system incorporating the structure which radiate | emits light as parallel light. It is sectional drawing which shows the further another example of the speckle elimination optical system incorporating the structure which radiate | emits light as parallel light. It is a schematic block diagram which shows the structure of the projector as another example of the optical apparatus provided with the speckle cancellation optical system.

  Hereinafter, a speckle elimination 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 apparatus using the speckle elimination optical system of one embodiment.

  The screen projection apparatus 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, and 4c made of laser diodes (LD) or light emitting diodes (LEDs) that emit light of three colors of red, green, and blue, respectively. The generated light is synthesized by the half mirrors 6 and 8 and emitted through the lens 10. In addition, the light source which comprises the light source part 2 is not restricted to LD or LED, Other light sources may be sufficient.

A speckle eliminating optical system 12 is disposed on the optical axis of the light emitted from the light source unit 2. The speckle canceling optical system 12 includes a plurality of speckle canceling elements 14 having a speckle canceling effect. At least two of the speckle canceling elements 14 of the speckle canceling optical system 12 are within a plane perpendicular to the optical axis of the light emitted from the light source unit 2 by the speckle canceling element driving unit 16. Can be exercised.
Although not described in detail here, in the case of a “reflective speckle canceling element”, the speckle canceling optical system 12 may not be disposed 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 convex portions 30 and grooves 32 are periodically provided at a pitch shorter than the wavelength of light as shown in FIG. An example of the wave plate 14a is a speckle eliminating element. 2 is provided with a sub-wavelength structure only on one surface of the substrate, the sub-wavelength structure may be provided on both surfaces of the substrate. By moving such a wave plate 14a in a plane perpendicular to the optical axis of light, a time division function for temporally converting the polarization state into light can be obtained. In particular, if the light causes a phase difference of approximately ½ wavelength (a ½ wavelength plate), the polarization direction of the light can be temporally converted. Even a wave plate that produces a small phase difference in light can reduce the coherence of light. For example, in the case of a “reflective speckle eliminating element”, the phase difference amount passes through the optical element portion of the λ / 4 wavelength plate twice (λ / 4 wavelength plate) + (λ / 4 wavelength plate) = The function of (λ / 2 wavelength plate) is expressed. For this reason, the same effect as what produces the phase difference for 1/2 wavelength (1/2 wavelength plate) is expressed.

  The wave plate 14a is a region division type wave plate in which the substrate surface is divided into a plurality of regions and sub-wavelength structures having different optical axis directions (arrangement directions of the convex portions 30 and the grooves 32) are provided in these regions. There may be a non-dividing type wavelength plate in which the entire sub-wavelength region (region where the sub-wavelength structure is provided) on the substrate surface has the same optical axis direction. The region non-dividing wave plate can exhibit a time division function by rotating. An area non-dividing type wave plate is easier to manufacture than an area dividing type wave plate, and the manufacturing cost is low.

  Further, as the speckle canceling element 14 of the speckle canceling optical system 12, a light diffusing plate 14b having a microlens array or a fly-eye lens composed of a plurality of lens portions 34 as shown in FIG. . When light enters such a light diffusing plate 14b, one light beam is divided into a plurality of light beams. 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 depicted as being evenly arranged. However, the effective diameter and focal length of the lens portions 34 are uniform, but not uniform. May be. As the light diffusing plate in which the effective diameter and focal length of the microlens are not uniform, those disclosed in Japanese Patent Application Laid-Open No. 2014-203032 can be used.

  Further, as the speckle canceling element 14 of the speckle canceling optical system 12, a wave plate as shown in FIG. 2 and a light diffusing plate as shown in FIG. 3 may be integrated. Good. Such an element is disclosed in, for example, Japanese Patent Application Laid-Open No. 2011-180581.

  Any of the above-described wavelength plate 14a, light diffusing plate 14b, or those in which they are integrated has a time division function or a space division function of light, and has a speckle elimination effect. The speckle canceling optical system 12 is realized by combining a plurality of speckle canceling elements having such a speckle canceling effect.

  In FIG. 1, the speckle canceling elements 14 of the speckle canceling optical system 12 are shown to be arranged side by side. However, the speckle canceling elements 14 are separated from each other, that is, the speckle canceling elements 14. Other optical elements may be present between the two. In short, a plurality of speckle canceling 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. Any arrangement is possible as long as at least two speckle canceling elements 14 can be moved by the speckle canceling element driving unit 16.

  The light that has passed through the speckle elimination 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 composed of MEMS elements (MEMS mirror) or a MEMS mirror array. In the present invention, in order to avoid complications, the above is collectively referred to as a MEMS mirror. The MEMS mirror includes one or a plurality of micromirrors that can be electrically driven, and the tilt state of the micromirror can be changed by turning on / off driving of an electrode provided in the lower portion of the micromirror. Therefore, light projection can be controlled for each display pixel by individually driving the mirrors.

  Various combinations of speckle canceling elements 14 constituting the speckle canceling optical system 12 are conceivable. Below, the typical example is demonstrated below.

  First, as shown in FIG. 4, it is conceivable that the speckle canceling optical system 12 is composed of two speckle canceling elements 14-1 and 14-2. In the embodiment of FIG. 4, the speckle canceling elements 14-1 and 14-2 are both disk-shaped elements and are arranged on the same axis and are rotated in the same direction by the speckle canceling element 16. The rotational speeds of the speckle eliminating 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 of the speckle canceling elements 14-1 and 14-2 are wave plates, the speckle canceling elements 14-1 and 14-2 are each set to a substantially quarter wave plate, for example. It is preferable that the canceling elements 14-1 and 14-2 have a function as one half-wave plate. If it does so, it can have a function which changes the polarization direction of light by the speckle cancellation elements 14-1 and 14-2. And by moving these speckle cancellation elements 14-1 and 14-2 simultaneously, the speckle cancellation effect is improved as compared with the case where the speckle cancellation elements are used alone.

  In addition, 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 half wave plate. In that case, a light diffusing plate as shown in FIG. 3 can be used for the other speckle eliminating element. By combining a light diffusing plate having a space division function of light with a half-wave plate having a time division function in the polarization direction of light and moving them simultaneously, both the time division function and the space division function are improved. The speckle elimination effect is improved compared to the case where the speckle elimination element is used alone. Further, any of the speckle eliminating elements 14-1 and 14-2 may be a light diffusing plate as shown in FIG.

  In addition, as FIG. 5 shows, the rotation direction of the speckle cancellation elements 14-1 and 14-2 may be mutually reverse. If it does so, the relative motion speed of the optical axis passage area | region of each speckle cancellation element 14-1 and 14-2 will become high, the time division function of light will improve, and the speckle cancellation effect will further improve.

  Further, as shown in FIGS. 6 and 7, the speckle eliminating elements 14-1 and 14-2 may not be coaxial but may be arranged so that their partial areas overlap each other. In the example of FIGS. 6 and 7, the lower end of the speckle canceling element 14-1 and the upper end of the speckle canceling 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 rotation directions of the speckle canceling elements 14-1 and 14-2 are opposite to each other, the region through which the light passes moves in the same direction, and FIG. 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.

  As shown in FIGS. 8 and 9, the speckle canceling elements 14-1 and 14-2 may have a shape other than a disk type, for example, a flat plate type. You may make the movement other than the rotational movement. Examples of the motion other than the rotational motion include a vibration motion in two directions orthogonal to each other in a plane perpendicular to the optical axis, an eight-shaped motion, and an elliptic motion.

  Further, as shown in FIGS. 10 and 11, the speckle canceling optical system 12 may include three or more speckle canceling elements 14-1, 14-2, and 14-3. In the example of FIG. 10, among the three speckle canceling elements 14-1, 14-2 and 14-3, the speckle canceling elements 14-1 and 14-2 are moved in a plane perpendicular to the optical axis. The speckle eliminating element 14-3 is stationary. In the example of FIG. 11, all the 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 canceling elements 14-1 and 14-2 are wave plates as shown in FIG. 2, and the speckle canceling element 14-3 is a light diffusing plate as shown in FIG. Can do. In that case, it is preferable that the speckle eliminating elements 14-1 and 14-2 cause a movement difference of approximately ½ wavelength in the light. Then, as the speckle eliminating 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 shown in the example of FIG. 11, the spatial resolution function of light can be further improved by moving the speckle eliminating element 14-3 made of a light diffusing plate in a plane perpendicular to the optical axis.

  In the example of FIG. 11, all three speckle eliminating elements 14-1 to 14-3 may be wave plates, or any two may be wave plates or light diffusing plates. The speckle elimination effect can be further improved by simultaneously moving the three speckle elimination elements 14-1 to 14-3 in a plane perpendicular to the optical axis.

  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 reversed. Further, the speckle eliminating elements 14-1 and 14-2 are not necessarily provided on the same axis, and may be arranged in the same manner as in FIGS.

  When the light diffusing plate 14b as shown in FIG. 3 is used as the speckle eliminating element 14 of the speckle eliminating optical system 12, as shown in FIG. 12, two light diffusing plates 14b are connected to each other's lens portion. It can arrange | position so that it may oppose. By making the lens portions face each other, as shown in FIG. 13, light incident as parallel light can be emitted as parallel light. In order to realize this principle in all the lens units, it is preferable to use a light diffusing plate as disclosed in JP 2014-203032 A 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 a focal length, and D is an 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 unit as parallel light.

  Examples of the configuration of the speckle resolution optical system 12 using the principle of FIG. 13 include the configurations shown in FIGS.

  In the example of FIG. 14, the wave plate 14 a is used as the speckle canceling element 14-1, and the two light diffusion plates 14 b are used as one speckle canceling element 14-2 with the lens portions facing each other. In this case, the two light diffusing plates 14b are united and simultaneously moved in a plane perpendicular to the optical axis. Thereby, the incident light as parallel light can be emitted as parallel light while improving the time division function and the space division function.

  Although detailed description is omitted here, the speckle eliminating element 14 shown in FIGS. 2, 14, 15, 16, and 17 allows light to enter the optical surface obliquely. However, the effect as a wave plate can be obtained. Therefore, each speckle eliminating element 14 is not necessarily arranged perpendicular to the optical axis of light, and may be arranged in an inclined state 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 fly-eye lens on the other surface is used as one speckle canceling element 14-1, and the lens portion of the element 14c. The light diffusing plate 14b is used as the second speckle canceling element 14-2 so as to face the surface provided with. Also with this structure, it is possible to emit the 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, the wavelength plate 14a may be added to the configuration of FIG. 15 as the third speckle canceling element 14-3. Further, as shown in FIG. 17, two elements 14c having a function as a wavelength plate and a function as a light diffusing plate are used, and they are respectively used as speckle eliminating elements 14-1 and 14-2. You may arrange | position so that the surface in which a mutual lens part is provided may oppose. 16 and FIG. 17, the incident light as the parallel light can be emitted as the parallel light while improving the time division function and the space division function.

  In general, it has been found that the higher the operating speed of the speckle canceling element, the higher the speckle canceling effect. However, when using an optical system that reads an image using a sensor, etc., regular noise occurs when the relationship between the sensor size (dimensions) and the operating speed of the speckle canceling element becomes constant. Patterns may occur in the image. In the past, since a single speckle canceling element was operated, the adjustment range for preventing noise generation was small, and it was difficult to achieve both reduction of noise and improvement of speckle canceling effect.

  On the other hand, in the embodiment described above, since at least two of the speckle canceling elements 14 constituting the speckle canceling optical system 12 are operated, the adjustment range for preventing noise generation is wide, It is easy to achieve both reduction and improvement in speckle elimination effect.

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

  In this verification, speckle contrast values (hereinafter referred to as Cs values) were measured for various combinations using a standard speckle contrast measurement optical apparatus manufactured by Oxide Corporation. Since the Cs value becomes larger as more speckles appear, it can be evaluated that the speckle elimination effect is higher as the measured Cs value is lower.

  As can be seen from Table 1 above, the Cs value when the ½ wavelength plate and the light diffusing plate (microlens array) are both stationary is 0.8 to 1.0 (the 0 row in Table 1). The Cs value when the half-wave plate was rotated at the speed V and the light diffusion plate was stationary was 0.4 (see row 1 in Table 1). Even if only the light diffuser is used, it is difficult to obtain the effect of eliminating speckles. However, if each of the two light diffusers is moved, the Cs value is higher than that when the stationary half-wave plate and the light diffuser are used. (See rows 2 and 3 of Table 1). Further, when one half-wave plate and one light diffuser plate are moved, when two quarter-wave plates and one light diffuser plate are moved, one wavelength When the plate and the two light diffusion plates were moved, the Cs value was decreased (see rows 2 to 13 in Table 1). From this, it was found that the speckle elimination effect can be improved by simultaneously moving a plurality of speckle elimination elements.

  The speckle elimination optical system 12 described above can also be applied to optical systems 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, light of the three primary colors is extracted from the light emitted from the laser light source 40 in the divided image forming unit 46, and these lights are respectively guided to an LCD (liquid crystal display) panel, and 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 disposed between lenses 42 and 44 disposed between the laser light source 40 and the divided image forming unit 46.

2 Light source part 4a-4c Light source 6,8 Half mirror 10,20 Lens 12 Speckle cancellation optical system 14 Speckle cancellation element 14a Wavelength plate 14b Light diffusing plate 16 Speckle cancellation element drive part 18 Mirror 22 MEMS element 24 Projection lens 26 Screen 30 Convex part 32 Groove 34 Lens part

Claims (8)

A plurality of speckle canceling elements that are arranged on the optical path of light emitted from the light source to produce a speckle canceling effect;
A speckle canceling optical system, comprising: a speckle canceling element driving unit that operates so that an optical effect of giving at least two of the speckle canceling elements to light from the light source is changed with time.   The speckle canceling optical system according to claim 1, further comprising a wave plate having a function of causing a phase difference in light as the speckle canceling element, wherein the wavelength plate is driven by the speckle canceling element driving unit.   The speckle canceling optical system according to claim 2, comprising a plurality of wavelength plates as the speckle canceling element, wherein at least two of the wavelength plates are driven by the speckle canceling element driving unit.   4. A light diffusing plate having a light diffusing function is included as the speckle eliminating element, and at least one of the wave plate and the light diffusing plate is driven by the speckle eliminating element driving unit. The speckle eliminating optical system described in the item.   The speckle elimination optical system according to any one of claims 1 to 4, wherein the speckle elimination element driving unit is configured to rotationally move at least two of the speckle elimination elements.   6. The speckle canceling optical system according to claim 5, wherein the rotational speeds of the speckle canceling elements that rotate are different from each other.   The speckle elimination optical system according to claim 5 or 6, wherein the rotational directions of the speckle elimination elements that rotate are different from each other.   An optical apparatus comprising the speckle elimination optical system according to any one of claims 1 to 7.

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