Patent Description:
Recently, as electronic devices and display devices capable of realizing virtual reality (VR) have been developed, interest in VR has increased. As a next step of VR, technologies (methods) that may realize augmented reality (AR) and mixed reality (MR) have also been studied.

Unlike VR that presents a complete virtual world, AR is a display technique that further increases an effect of reality by overlapping (combining) virtual objects or information on an environment of the real world. Considering that VR is limitedly applicable to fields such as games or virtual experiences, AR may be applicable to various real environments. In particular, AR is drawing the attention as a next generation display technique suitable for a ubiquitous environment or an Internet-of-Things (IoT) environment. AR may be an example of MR in that AR mixes the real world and additional information such as virtual world information.

In the case where a see-through display device includes a holographic optical element as a combiner, the see-through display device may have a narrow eye box. Static methods for solving the narrow eye box issue include a method of generating multiple spots by additionally using high-order diffraction other than ±<NUM>-order diffraction or adjusting a reference beam when exposing a holographic optical element. Dynamic methods for solving the narrow eye box issue include a method of adjusting an optical path of an image entering a pupil of a user by arranging a projection optical system (e.g., a microelectromechanical systems (MEMS) mirror) on the optical path between a display unit and a combiner. <CIT> discloses a microelectromechanical resonant device, comprising: a base; a movable body coupled to the base for resonant motion relative to the base about a pivot axis; an enclosure surrounding the movable body and at least a portion of the base; a flexible member extending between the movable body and the base, the flexible member including a gas absorbing material, the gas absorbing material having material properties responsive to a partial pressure of a selected gas within the enclosure wherein the responsive material properties define a resonant frequency of the resonant motion; and an electrically activated pressure controller, coupled to the enclosure and responsive to an electrical signal to increase or decrease the partial pressure of the gas. <CIT> discloses an electrode for use with an electroactive polymer, the electrode comprising: a compliant portion in contact with the electroactive polymer, wherein the electrode comprises a conductive material having an aspect ratio greater than about <NUM> and an electrode thickness less than about <NUM> micrometers. <CIT> discloses a see-through display device comprising: an image generation unit configured to emit a virtual image light; a light combining unit configured to combine the virtual image light with an actual image light; and a driving unit comprising a deformation unit and a bridge unit disposed between the deformation unit and the image generation unit, and configured to control a distance between the image generation unit and the light combining unit through the deformation unit and the bridge unit. <CIT> discloses a transducer comprising: a frame structure defining an opening and at least two electroactive polymer layers extending within the opening of the frame, the electroactive polymer layers each having an elastic modulus below about <NUM> MPa and a central portion, wherein the electroactive polymer layers are stretched to join at each central portion of the electroactive polymer layers to each form a concave shape; wherein the central portions of the electroactive polymer layers actuate in at least two component directions upon application of a voltage across the electroactive polymer material.

The size and the driving speed of a MEMS mirror have a trade-off relationship. As the size of the MEMS mirror increases, the driving speed of the MEMS mirror decreases, and thus, the size of the MEMS mirror needs to be decreased to increase the driving speed of the MEMS mirror. Therefore, it may be difficult to increase the size or area of a MEMS mirror to reach a required level.

The invention is set out in the claims. An object of the disclosure is to provide a projection optical system having a large area and a high driving speed.

Another object of the disclosure is to provide a see-through display device including a projection optical system having a large area and a high driving speed.

However, the objects of the disclosure are not limited thereto.

According to one aspect of the invention there is provided a projection optical system including: a base; a mirror; and a pair of first actuators provided between the base and the mirror, the pair of first actuators configured to face each other in a first direction, wherein each of the pair of first actuators comprises a first electroactive polymer film having structural flexibility such that a size of the first electroactive polymer film is changeable based on an applied voltage, and wherein the mirror is adjustable based on a change in the size of the first electroactive polymer film, wherein the first electroactive polymer film has a first surface and a second surface, and each of the pair of first actuators further comprises: a first electrode provided on the first surface; a second electrode provided on the second surface; a first stretch maintaining film provided to surround the first electrode; and a pair of first hinge elements provided on the first stretch maintaining wherein the first stretch maintaining film comprises a hole, and the first electrode is provided in the hole.

The pair of first hinge elements may be spaced apart from each other, and wherein the first electrode is provided between the pair of first hinge elements in a second direction from the base toward the mirror.

The second surfaces of the pair of first actuators may face each other.

In a region adjacent to the mirror, the first electroactive polymer film may have a first width that decreases toward the mirror.

The projection optical system may further include a pair of second actuators which are between the pair of first actuators and face each other in a third direction intersecting with the first direction, wherein each of the pair of second actuators includes: a second electroactive polymer film having a third surface and a fourth surface; a third electrode provided on the third surface; a fourth electrode provided on the fourth surface; a second stretch maintaining film provided to surround the third electrode; and a pair of second hinge elements provided on the second stretch maintaining film.

Each of the pair of first actuators further may include a serpentine spring, and the first electroactive polymer film is provided on the serpentine spring to deform the serpentine spring.

The serpentine spring may include a hole, and the first electroactive polymer film covers the hole.

The first electroactive polymer film may have a first surface and a second surface, and each of the pair of first actuators includes: a first electrode provided on the first surface; a second electrode provided on the second surface; a first frame provided on the first surface and surrounding the first electrode; and a second frame provided on the second surface and surrounding the second electrode.

Each of the first frame and the second frame may have a rhombic shape in which a first corner and a second corner, which are opposite to each other in a direction from the base toward the mirror, are in contact with the base and the mirror, respectively.

Each of the pair of first actuators may further include a lift element provided at a side opposite to the mirror with respect to the base, and wherein the lift element is configured to push or pull the base.

The lift element may include: a lift base facing the base; a restoring element configured to apply a force to the base and the lift base to increase a distance between the base and the lift base; and a deformation element provided between the lift base and the base, wherein a length of the deformation element varies according to a temperature of the deformation element, and a distance between the base and the lift base is adjusted by the restoring element and the deformation element.

The projection optical system may further include a support film between the base, the mirror, and the pair of first actuators, wherein the support film extends along surfaces of the base, the mirror, and the pair of first actuators.

The projection optical system may further include a pivot pillar between the base and the mirror, wherein one end of the pivot pillar is in contact with the base, and another end of the pivot pillar is in contact with the mirror.

According to another aspect of the disclosure, there is provided a see-through display device including: an image generator configured to generate virtual image light comprising virtual image information; a combiner configured to concentrate the virtual image light to a first spot; and a projection optical system configured to project, to the combiner, the virtual image light provided from the image generator, wherein the projection optical system includes: a base, a mirror, and a pair of actuators provided between the base and the mirror, the pair of actuators configured to face each other in a first direction, wherein each of the pair of actuators comprises an electroactive polymer film having structural flexibility such that a size of the electroactive polymer film is changeable based on an applied voltage, and wherein the mirror is adjustable based on a change in the size of the electroactive polymer film.

The electroactive polymer film may have a first surface and a second surface, and each of the pair of actuators further includes: a first electrode provided on the first surface, a second electrode provided on the second surface, a stretch maintaining film provided to surround the first electrode, and a pair of hinge elements provided on the stretch maintaining film.

The combiner may be further configured to concentrate the image light further to a second spot which is different from the first spot based on the change in the size of the electroactive polymer film.

The see-through display device may further include an eye tracker configured to measure a pupil position of a user.

According to another aspect of the disclosure, there is provide a see-through display device including: a lens frame having a pair of holes; a pair of temples connected to both ends of the lens frame, respectively; a pair of combiners inserted into the pair of holes, respectively; and electronic system provided in the pair of temples, wherein the electronic system comprises an image generator configured to generate virtual image light comprising virtual image information, and a projection optical system configured to project, to the combiner, the virtual image light provided from the image generator, and wherein the projection optical system comprises: a base, a mirror, and a pair of actuators provided between the base and the mirror, the pair of actuators configured to face each other in a first direction, wherein each of the pair of actuators comprises an electroactive polymer film having structural flexibility such that a size of the electroactive polymer film is changeable based on an applied voltage, and |wherein the mirror is adjustable based on a change in the size of the electroactive polymer film.

According to another aspect of the disclosure, there is provide a projection optical system including: a base portion; a mirror; and at least one actuator provided between the base portion at the mirror, the at least one actuator comprising an electroactive polymer film having a malleable structure, which is changeable based on an applied voltage, wherein the mirror is adjustable based on a change in the structure of electroactive polymer film.

A position or a direction of the mirror may be adjustable based on a change in the structure of electroactive polymer film.

According to another aspect of the disclosure, there is provide a display device including: a controller configured to apply a voltage; and a projection optical system including: a base portion; a mirror; and at least one actuator provided between the base portion at the mirror, the at least one actuator comprising an electroactive polymer film having a malleable structure, which is changeable based on the applied voltage, wherein the mirror is adjustable based on a change in the structure of first electroactive polymer film.

Based on a first voltage applied to the electroactive polymer film, the mirror may be adjusted to face a first direction, and based on a second voltage applied to the electroactive polymer film, the mirror may be adjusted to face a second direction.

In the following drawings, like reference numerals refer to like elements, and sizes of elements in the drawings may be exaggerated for clarity and convenience of description. Meanwhile, embodiments described below are merely illustrative, and various modifications may be made from these embodiments.

Hereinafter, an expression "on" used herein may include not only "immediately on in a contact manner" (e.g., "direct contact") but also "on in a non-contact manner".

The singular expression also includes the plural meaning as long as it is not inconsistent with the context. In addition, when an element is referred to as "including" a constituent element, other constituent elements may be further included not excluded unless there is any other particular mention on it.

<FIG> is a conceptual diagram of a see-through display device <NUM>, according to an example embodiment. <FIG> is a perspective view of a projection optical system <NUM> of <FIG>. <FIG> is a cross-sectional view taken along line I-I' of the projection optical system <NUM> of <FIG>. <FIG> is an exploded perspective view of an actuator <NUM> (hereinafter, also referred to as the left actuator <NUM> and the right actuator <NUM>) of the projection optical system <NUM> of <FIG>.

Referring to <FIG>, according to an example embodiment, the see-through display device <NUM> may include an image generator <NUM>, the projection optical system <NUM>, a combiner <NUM>, and an eye tracker <NUM>. The see-through display device <NUM> may be a device that combines real image light with virtual image light and provides the combined light to a user. The real image light may be light that is emitted from a real object and includes image information about the real object. The virtual image light may be, for example, light that is emitted from a display device such as a spatial light modulator (SLM), and includes required virtual image information.

The image generator <NUM> may emit virtual image light. For example, the image generator <NUM> may include a light source, a liquid crystal on silicon (LCoS), and a polarization beam splitter. However, the disclosure is not limited thereto. As such, according to another example embodiment, image generator <NUM> may be an electronic device including components capable of outputting a virtual image.

The projection optical system <NUM> may be on an optical path between the image generator <NUM> and the combiner <NUM>. The projection optical system <NUM> may include a mirror layer <NUM>. The projection optical system <NUM> may reflect the virtual image light emitted from the image generator <NUM> and project the reflected virtual image light to the combiner <NUM>. The projection optical system <NUM> may adjust the slope and/or position of the mirror layer <NUM> to change the position to which virtual image light is concentrated. The projection optical system <NUM> will be described below.

The combiner <NUM> may combine real image light with virtual image light and provide the combined light to a user <NUM>. The combiner <NUM> may include a photosensitive film on which an interference pattern is formed. The virtual image light may be reflected by the combiner <NUM>. The virtual image light IL, when reflected, may be diffracted and concentrated by the interference pattern. For example, the virtual image light IL may be concentrated to a pupil of the user <NUM>. The real image light may pass through the combiner <NUM> and then reach the user <NUM>.

The eye tracker <NUM> may measure a pupil position of the user <NUM> to generate information about a user pupil position. The slope and/or position of a mirror of the projection optical system <NUM> may be adjusted based on the information about the user pupil position generated by the eye tracker <NUM>.

The pupil of the user <NUM> may receive the virtual image light IL within a certain range. In other words, the user <NUM> may view the virtual image light IL within the certain range. A region through which the user <NUM> may view a virtual image may be referred to as an eye box EB.

Referring to <FIG>, according to an example embodiment, the projection optical system <NUM> may include a base <NUM>, the mirror layer <NUM>, a plurality of actuators <NUM>, a support film <NUM>, and a pivot pillar <NUM>. The base <NUM> may have a flat plate shape extending in a first direction DR1 and a second direction DR2. For example, the base <NUM> may have a quadrangular flat plate shape. For example, the base <NUM> may include polyethylene terephthalate (PET) or FR4 glass epoxy laminate. The base <NUM> may be sufficiently thick to be rigid.

The mirror layer <NUM> may be spaced apart from the base <NUM>. The mirror layer <NUM> may face the base <NUM>. According to an example embodiment, the mirror layer <NUM> may be provided in a direction perpendicular to the flat plate surface of the base <NUM>. For instance, the mirror layer <NUM> may be above the base <NUM>. The mirror layer <NUM> may have a flat plate shape. For example, the mirror layer <NUM> may have a quadrangular flat plate shape. When the plurality of actuators <NUM> are not driven, the mirror layer <NUM> may be parallel to the base <NUM>. The mirror layer <NUM> may include a mirror base <NUM> and a mirror <NUM> on the mirror base <NUM>. For example, the mirror base <NUM> may include PET or FR4 glass epoxy laminate. The mirror base <NUM> may be sufficiently thick to be rigid.

The plurality of actuators <NUM> may be between the base <NUM> and the mirror layer <NUM>. Four actuators <NUM> are illustrated, but this is an example. The number of actuators <NUM> may be determined as necessary. Among the plurality of actuators <NUM>, a pair of first actuators <NUM>-<NUM> may face each other in the first direction DR1, and a pair of second actuators <NUM>-<NUM> may face each other in the second direction DR2. The four actuators <NUM> may be substantially the same as each other. For brevity of description, one actuator <NUM> is described.

The actuator <NUM> may include an electroactive polymer film(first electroactive polymer film for the first actuator, and second electroactive polymer film for the second actuator) <NUM>, a stretch maintaining film(first stretch maintaining film for the first actuator, and second stretch maintaining for the second actuator) <NUM>, a pair of hinge elements(first hinge elements for the first actuator, and second hinge elements for the second actuator) <NUM>, a first electrode(first electrode for the first actuator, and third electrode for the second actuator) <NUM>, and a second electrode(second electrode for the first actuator, and fourth electrode for the second actuator) <NUM>. The electroactive polymer film <NUM> may have a size or area that varies according to an electric field applied to the electroactive polymer film <NUM>. In detail, when a voltage is applied to both surfaces of the electroactive polymer film <NUM> (e.g., a voltage difference is generated) and thus an electric field is generated in the electroactive polymer film <NUM>, the thickness of the electroactive polymer film <NUM> is decreased, and accordingly, the size or area of the electroactive polymer film <NUM> may be increased. As the voltage difference applied to the electroactive polymer film <NUM> increases, the area or size of the electroactive polymer film <NUM> may be increased. The electroactive polymer film <NUM> may include an electronic electroactive polymer. For example, the electroactive polymer film <NUM> may include a dielectric elastomer. For example, the electroactive polymer film <NUM> may include a silicone elastomer. The electroactive polymer film <NUM> may have elasticity. When the electroactive polymer film <NUM> is stretched, the electroactive polymer film <NUM> may have a restoring force to return to a state before being stretched. The electroactive polymer film <NUM> may include a first surface(first surface for the first actuator, and third surface for the second actuator) and a second surface(second surface for the first actuator, and fourth surface for the second actuator) which face opposite directions. The first surface may face the outside of the projection optical system <NUM>, and the second surface may face the inside of the projection optical system <NUM>.

The stretch maintaining film <NUM> may be on the first surface of the electroactive polymer film <NUM>. For example, the stretch maintaining film <NUM> may be adhered to the first surface of the electroactive polymer film <NUM>. Before the stretch maintaining film <NUM> is adhered to the electroactive polymer film <NUM>, the electroactive polymer film <NUM> may be pre-stretched. When the stretch maintaining film <NUM> is adhered to the pre-stretched electroactive polymer film <NUM>, the stretch maintaining film <NUM> may hinder the restoration of the electroactive polymer film <NUM>, thereby maintaining the pre-stretched state of the electroactive polymer film <NUM>. For example, the stretch maintaining film <NUM> may include a PET film. The stretch maintaining film <NUM> may have a sufficiently low thickness to have flexibility. For example, the thickness of the stretch maintaining film <NUM> may be about <NUM> to about <NUM>. The stretch maintaining film <NUM> may have a hole exposing the first surface of the electroactive polymer film <NUM>.

The first electrode <NUM> may be on the first surface of the electroactive polymer film <NUM>. The first electrode <NUM> may be in the hole of the stretch maintaining film <NUM>. The second electrode <NUM> may be on the second surface of the electroactive polymer film <NUM>. The first electrode <NUM> and the second electrode <NUM> may face each other with the electroactive polymer film <NUM> therebetween. The first electrode <NUM> and the second electrode <NUM> may apply a voltage to the electroactive polymer film <NUM>. The first electrode <NUM> and the second electrode <NUM> may be stretchable electrodes. Voltages applied to the plurality of actuators <NUM> may be adjusted independently of each other.

A first conductive line 234P may be at one side of the first electrode <NUM>. The first conductive line 234P may protrude from the first electrode <NUM>. The first conductive line 234P may pass between the electroactive polymer film <NUM> and the stretch maintaining film <NUM>. The first conductive line 234P may be between the first electrode <NUM> and a controller, which applies a voltage to the first electrode <NUM>, to electrically connect the first electrode <NUM> to the controller. The voltage applied to the first electrode <NUM> may be adjusted by the controller. The first conductive line 234P may include a stretchable electrode material. In an example, the first conductive line 234P may include substantially the same material as that of the first electrode <NUM>.

A second conductive line 235P may be at one side of the second electrode <NUM>. The second conductive line 235P may protrude from the second electrode <NUM>. The second conductive line 235P may pass between the electroactive polymer film <NUM> and the support film <NUM>. The second conductive line 235P may be between the second electrode <NUM> and the controller, which applies a voltage to the second electrode <NUM>, to electrically connect the second electrode <NUM> to the controller. The voltage applied to the second electrode <NUM> may be adjusted by the controller. The second conductive line 235P may include a stretchable electrode material. In an example, the second conductive line 235P may include substantially the same material as that of the second electrode <NUM>.

The pair of hinge elements <NUM> may be on the stretch maintaining film <NUM>. The pair of hinge elements <NUM> may be spaced apart from each other with the first electrode <NUM> therebetween. The pair of hinge elements <NUM> may be arranged in a third direction DR3 which is toward the mirror layer <NUM> from the base <NUM>. One of the pair of hinge elements <NUM> may be adjacent to the base <NUM>, and the other may be adjacent to the mirror layer <NUM>. The pair of hinge elements <NUM> may be configured to fold or unfold the electroactive polymer film <NUM> when the electroactive polymer film <NUM> is stretched or contracted. When the pair of hinge elements <NUM> fold the electroactive polymer film <NUM>, the pair of hinge elements <NUM> may become closer to each other. When the pair of hinge elements <NUM> unfold the electroactive polymer film <NUM>, the pair of hinge elements <NUM> may be moved apart from each other. As the voltage difference generated in the electroactive polymer film <NUM> increases, the size or area of the electroactive polymer film <NUM> may be increased, and accordingly, the pair of hinge elements <NUM> may unfold the electroactive polymer film <NUM> to a large degree. As the voltage difference generated in the electroactive polymer film <NUM> decreases, the size or area of the electroactive polymer film <NUM> may be decreased, and the pair of hinge elements <NUM> may fold the electroactive polymer film <NUM> to a large degree. The size or area of the electroactive polymer film <NUM> may be lowest when no voltage difference is generated in the electroactive polymer film <NUM>. When the size or area of the electroactive polymer film <NUM> is lowest, the pair of hinge elements <NUM> may fold the electroactive polymer film <NUM> to the greatest degree. A degree of unfolding or folding the electroactive polymer film <NUM> by the pair of hinge elements <NUM> may be adjusted by adjusting a magnitude of the voltage applied to the electroactive polymer film <NUM> by the first electrode <NUM> and the second electrode <NUM>. For example, the pair of hinge elements <NUM> may include PET. The pair of hinge elements <NUM> may be sufficiently thick to be rigid. For example, the thickness of the pair of hinge elements <NUM> may be about <NUM> to about <NUM>.

The support film <NUM> may be in an internal region of the projection optical system <NUM> defined by the base <NUM>, the mirror layer <NUM>, and the plurality of actuators <NUM>. The support film <NUM> may cover surfaces of the base <NUM>, the mirror layer <NUM>, and the plurality of actuators <NUM>, which face the inner region of the projection optical system <NUM>. For example, the support film <NUM> may extend along the surfaces of the base <NUM>, the mirror base <NUM>, the electroactive polymer films <NUM>, and the second electrodes <NUM>, which face the inner region of the projection optical system <NUM>. For example, a surface of the support film <NUM> may be in contact with the surfaces of the base <NUM>, the mirror base <NUM>, the electroactive polymer films <NUM>, and the second electrodes <NUM>. The second electrodes <NUM> may be between the support film <NUM> and the electroactive polymer films <NUM>. For example, the support film <NUM> may include polyimide. The support film <NUM> may have a sufficiently low thickness to have flexibility. For example, the thickness of the support film <NUM> may be <NUM> or less.

The pivot pillar <NUM> may be between the base <NUM> and the mirror layer <NUM>. The pivot pillar <NUM> may penetrate the support film <NUM>. The pivot pillar <NUM> may extend from the base <NUM> to the mirror layer <NUM>. A first end of the pivot pillar <NUM> may be in contact with the base <NUM>, and a second of the pivot pillar <NUM> may be in contact with the mirror base <NUM>. The first end and the second end of the pivot pillar <NUM> may be spaced apart from each other in the direction in which the pivot pillar <NUM> extends. The pivot pillar <NUM> may be fixed to a central portion of the mirror layer <NUM>. The central portion of the mirror layer <NUM> in contact with the pivot pillar <NUM> may be a reference by which the slope of the mirror layer <NUM> is adjusted. Adjustment of the slope of the mirror layer <NUM> will be described below.

A rotational drive of about <NUM> is required for effective dynamic eye box expansion in see-through display devices. According to the conventional MEMS-based mirror driving device, a driving speed is limited depending on the size of the mirror. For example, in the case of a mirror having a diameter of <NUM>, the rotational driving speed is limited to about <NUM>, and it is expected that the rotational driving speed is further reduced when the diameter of the mirror is <NUM> or more. The actuator <NUM> according to an example embodiment of disclosure is a dielectric elastomer actuator (DEA) employing the active polymer film <NUM>. According to the DEA type actuator <NUM>, when the mirror diameter is about <NUM>, a rotational driving speed of about <NUM> may be implemented. A conventional MEMS-based mirror driving device has a low degree of freedom for the size of the mirror, so there is a limitation in that the mirror should be disposed near a focal length of the lens. According to the dielectric elastomer actuator (DEA) of the example embodiment, since the degree of freedom for the size of the mirror is relatively high, the freedom of arrangement of the actuator <NUM> may also be increased. Therefore, both the inside and outside of the focal length of the lens may be an appropriate position for the rotation actuator including the mirror and the actuator <NUM>.

<FIG> is a cross-sectional view corresponding to line I-I' of the projection optical system <NUM> of <FIG> for describing an operation of the projection optical system <NUM>. <FIG> is a cross-sectional view corresponding to line I-I' of the projection optical system <NUM> of <FIG> for describing an operation of the projection optical system <NUM>.

Referring to <FIG>, a voltage may be applied to the first electrode <NUM> and the second electrode <NUM> of a first one (hereinafter, referred to as a left actuator) of the pair of actuators <NUM> facing each other in the first direction DR1, and thus, a voltage difference may be generated in the electroactive polymer film <NUM> of the left actuator <NUM>. No voltage may be applied to the first electrode <NUM> and the second electrode <NUM> of a second (or the other) one (hereinafter, referred to as a right actuator) of the pair of actuators <NUM> facing each other in the first direction DR1. The terms `left actuator' and `right actuator' are only used to indicate different actuators, and do not refer to an actuator actually on the left side and an actuator on the right side. The size or area of the electroactive polymer film <NUM> of the left actuator <NUM> may be increased. Accordingly, the pair of hinge elements <NUM> may unfold the electroactive polymer film <NUM>. Accordingly, the length of the left actuator <NUM> in the third direction DR3 may become greater than the length of the right actuator <NUM> in the third direction DR3.

The support film <NUM> in contact with the left actuator <NUM> may be moved in response to the unfolding of the left actuator <NUM>. Force by which the left actuator <NUM> is unfolded (e.g., the force by which the pair of hinge elements <NUM> unfold the electroactive polymer film <NUM> as the size or area of the electroactive polymer film <NUM> increases) may be transferred to the mirror layer <NUM> and the base <NUM> through the support film <NUM>. The support film <NUM> in contact with the left actuator <NUM> may increase the distance between the mirror layer <NUM> and the base <NUM>.

The mirror layer <NUM> may be inclined with respect to a portion at which the pivot pillar <NUM> is in contact with the mirror base <NUM>. A first portion (P1) of the mirror layer <NUM>, which is adjacent to the left actuator <NUM>, may be moved away from the base <NUM>, and a second portion (P2) of the mirror layer <NUM>, which is adjacent to the right actuator <NUM>, may be moved toward the base <NUM>. Because the electroactive polymer film <NUM> of the right actuator <NUM> has a restoring force to return to the size or area before being pre-stretched, the right actuator <NUM> may be folded as the second portion of the mirror layer <NUM> is moved toward the base <NUM>.

Referring to <FIG>, unlike as illustrated in <FIG>, a voltage may be applied to the first electrode <NUM> and the second electrode <NUM> of the right actuator <NUM>, and thus, a voltage difference may be generated in the electroactive polymer film <NUM> of the right actuator <NUM>. No voltage may be applied to the first electrode <NUM> and the second electrode <NUM> of the left actuator <NUM>. The pair of hinge elements <NUM> of the right actuator <NUM> may unfold the electroactive polymer film <NUM>. Accordingly, the length of the right actuator <NUM> in the third direction DR3 may become greater than the length of the left actuator <NUM> in the third direction DR3.

The support film <NUM> in contact with the right actuator <NUM> may be moved in response to the unfolding of the left actuator <NUM>. Force by which the right actuator <NUM> is unfolded may be transferred to the mirror layer <NUM> and the base <NUM> through the support film <NUM>. The support film <NUM> in contact with the right actuator <NUM> may increase the distance between the mirror layer <NUM> and the base <NUM>.

The mirror layer <NUM> may be inclined with respect to a portion P1 at which the pivot pillar <NUM> is in contact with the mirror base <NUM>. The second portion P2 of the mirror layer <NUM>, which is adjacent to the right actuator <NUM>, may be moved away from the base <NUM>, and the second portion of the mirror layer <NUM>, which is adjacent to the left actuator <NUM>, may be moved toward the base <NUM>. Because the electroactive polymer film <NUM> of the left actuator <NUM> has a restoring force to return to the size or area before being pre-stretched, the left actuator <NUM> may be folded as the first portion of the mirror layer <NUM> is moved toward the base <NUM>.

<FIG> illustrates a state in which no voltage is applied to the first electrode <NUM> and the second electrode <NUM> of the pair of actuators <NUM> facing each other in the first direction DR1. Unlike the mirror layer <NUM> of <FIG>, which is substantially parallel to the base <NUM>, the mirror layer <NUM> of <FIG> and the mirror layer <NUM> of <FIG> may be inclined with respect to the base <NUM>. The pair of actuators <NUM> facing each other in the second direction DR2 may also be driven in the same manner as the pair of actuators <NUM> facing each other in the first direction DR1 to adjust the slope of the mirror layer <NUM>.

The disclosure may provide the projection optical system <NUM> capable of adjusting the direction of projection of the virtual image light IL by using the pair of actuators <NUM> facing each other in the first direction DR1 and the pair of actuators <NUM> facing each other in the second direction DR2. A process of adjusting the direction of projection of the virtual image light IL will be described below.

<FIG> is a conceptual diagram of a see-through display device for describing a process of adjusting the direction of projection of virtual image light. <FIG> is a conceptual diagram of a see-through display device for describing a process of adjusting the direction of projection of virtual image light. <FIG> is a conceptual diagram of a see-through display device for describing a process of adjusting the direction of projection of virtual image light.

Referring to <FIG>, the image generator <NUM>, the projection optical system <NUM>, the combiner <NUM>, and the eye tracker <NUM> may be provided. The image generation unit <NUM>, the projection optical system <NUM>, the combiner <NUM>, and the eye tracker <NUM> may be substantially the same as the image generator <NUM>, the projection optical system <NUM>, the combiner <NUM>, and the eye tracker <NUM>, which are described with reference to <FIG>, respectively. The projection optical system <NUM> may be substantially the same as the projection optical system <NUM> described with reference to <FIG>.

As illustrated in <FIG>, the pupil of the user <NUM> may be at a first position. For example, the first position may be the position of the pupil of the user <NUM> looking at a central portion of the combiner <NUM>. No voltage may be applied to the plurality of actuators <NUM> of the projection optical system <NUM>. The projection optical system <NUM> may reflect, to a first region on the combiner <NUM>, the virtual image light IL emitted from the image generator <NUM>. The combiner <NUM> may concentrate, to the pupil of the user <NUM> looking at the central portion of the combiner <NUM>, the virtual image light IL incident to the first region from the projection optical system <NUM>. When no voltage is applied to the plurality of actuators <NUM>, an eye box through which the user <NUM> may view a virtual image may be referred to as a first eye box EB <NUM>.

As illustrated in <FIG>, the pupil of the user <NUM> may move to a second position. For example, the second position may be the position of the pupil of the user <NUM> looking at a region (hereinafter, a right region) at the right of the central portion of the combiner <NUM>. A voltage may be applied to one (hereinafter, referred to as a left actuator) of the plurality of actuators <NUM>, and no voltage may be applied to the other actuators <NUM>. The magnitude of the voltage applied to the left actuator <NUM> may be adjusted as necessary. The projection optical system <NUM> may reflect, to the right region of the combiner <NUM>, the virtual image light IL emitted from the image generator <NUM>. The combiner <NUM> may concentrate, to the pupil of the user <NUM> looking at the right region of the combiner <NUM>, the virtual image light IL incident to the right region from the projection optical system <NUM>. When the voltage is applied to the left actuator <NUM>, an eye box through which the user <NUM> may view a virtual image may be referred to as a second eye box EB2. The second eye box EB2 may be at the right of the first eye box EB1. When a voltage is applied to the left actuator <NUM> and no voltage is applied to the other actuators <NUM>, the eye box may move to the right. That is, the eye box may be dynamically expanded.

As illustrated in <FIG>, the pupil of the user <NUM> may be at a third position. For example, the third position may be the position of the pupil of the user <NUM> looking at a region (hereinafter, referred to as a left region) at the left of the central portion of the combiner <NUM>. A voltage may be applied to the other one (hereinafter, the right actuator <NUM>) of the plurality of actuators <NUM>, and no voltage may be applied to the other actuators <NUM>. The magnitude of the voltage applied to the right actuator <NUM> may be adjusted as necessary. The projection optical system <NUM> may reflect, to the left region of the combiner <NUM>, the virtual image light IL emitted from the image generator <NUM>. The combiner <NUM> may concentrate, to the pupil of the user <NUM> looking at the left region of the combiner <NUM>, the virtual image light IL incident to the left region from the projection optical system <NUM>. When the voltage is applied to the right actuator <NUM>, an eye box through which the user <NUM> may view a virtual image may be referred to as a third eye box EB3. The third eye box EB3 may be at the left of the first eye box EB <NUM>. When a voltage is applied to the right actuator <NUM> and no voltage is applied to the other actuators <NUM>, the eye box may move to the left. That is, the eye box may be dynamically expanded.

According to the disclosure, an eye box may be dynamically expanded by adjusting the slope of the mirror <NUM>. The slope of the mirror <NUM> may be adjusted according to a change in the length of the actuators <NUM> each including the electroactive polymer film <NUM>.

The mirror <NUM> controlled by the actuators <NUM> each including the electroactive polymer film <NUM> may have a higher driving speed than that of a MEMS mirror having the same size. The disclosure may provide the projection optical system <NUM> having a required driving speed even when the mirror <NUM> has a sufficiently large size or area, and the see-through display device <NUM> including the same.

<FIG> is a perspective view of a projection optical system <NUM>, according to an example embodiment. For brevity of description, substantially the same descriptions as provided with reference to <FIG> may not be provided.

Referring to <FIG>, the projection optical system <NUM> may include the base <NUM>, the mirror layer <NUM>, the plurality of actuators <NUM>, the support film <NUM>, and the pivot pillar <NUM>. The base <NUM>, the mirror layer <NUM>, and the pivot pillar <NUM> may be substantially the same as the base <NUM>, the mirror layer <NUM>, and the pivot pillar <NUM>, which are described with reference to <FIG>, respectively.

Unlike that described with reference to <FIG>, the plurality of actuators <NUM> may have a width that narrows toward the mirror layer <NUM>, in a region adjacent to the mirror layer <NUM>. A first width of the electroactive polymer film <NUM> of each of the plurality of actuators <NUM> may decrease toward the mirror layer <NUM>, in the region adjacent to the mirror layer <NUM>. The plurality of actuators <NUM> may be respectively on four sides of the base <NUM> having a quadrangular flat plate shape. By reducing the first width of the electroactive polymer film <NUM> in contact with the mirror layer <NUM>, crosstalk between the actuators <NUM> adjacent to each other is reduced, and the mirror layer <NUM> can be rotated about an accurate rotation axis.

The support film <NUM> in contact with the actuators <NUM> may be inside the projection optical system <NUM>. The support film <NUM> may have a shape corresponding to the actuators <NUM>. The support film <NUM> in contact with the actuators <NUM> may have a width that narrows toward the mirror layer <NUM>, in a region adjacent to the mirror layer <NUM>.

The disclosure may provide the projection optical system <NUM> having a required drive speed even when the mirror <NUM> has a sufficiently large size or area.

<FIG> is a cross-sectional view of a projection optical system <NUM>, according to an example embodiment. <FIG> is a diagram illustrating an embodiment of the projection optical system <NUM> of <FIG>. <FIG> is a diagram illustrating another embodiment of the projection optical system <NUM> of <FIG>. For brevity of description, substantially the same descriptions as provided with reference to <FIG> may not be provided.

Referring to <FIG>, the projection optical system <NUM> may include the base <NUM>, the mirror layer <NUM>, the plurality of actuators <NUM>, the support film <NUM>, the pivot pillar <NUM>, and a lift element <NUM>. The base <NUM>, the mirror layer <NUM>, the plurality of actuators <NUM>, the support film <NUM>, and the pivot pillar <NUM> may be substantially the same as the base <NUM>, the mirror layer <NUM>, the plurality of actuators <NUM>, the support film <NUM>, and the pivot pillar <NUM>, which are described with reference to <FIG>, respectively.

The lift element <NUM> may be at the side opposite to the support film <NUM> with respect to the base <NUM>. The lift element <NUM> may be in contact with a surface of the base <NUM>. The lift element <NUM> may push the base <NUM> toward the mirror layer <NUM>. By the pivot pillar <NUM>, the distance between the base <NUM> and the mirror layer <NUM> may be maintained, and the position of the mirror <NUM> with respect to the third direction DR3 may be changed. For example, the lift element <NUM> may include a shape memory alloy (SMA) having a length that varies depending on the temperature.

Referring to <FIG>, the lift element <NUM> may include a bridge element <NUM> and a first deformation element <NUM>. The bridge element <NUM> may have elasticity and may be long in one direction. Both ends of the bridge element <NUM> may be wound by the first deformation element <NUM> having a ring shape. In other words, both ends of the bridge element <NUM> may be inside the ring shape of the first deformation element <NUM>. The bridge element <NUM> may have an arch shape bent toward the base <NUM>. In an example, the bridge element <NUM> may be adhered to the base <NUM>. When not wound by the first deformation element <NUM>, the bridge element <NUM> may have a straight shape (e.g., an unbent shape). The bridge element <NUM>, when bent, may apply a force to the first deformation element <NUM> in a direction from the inside toward the outside of the first deformation element <NUM> (e.g., a direction from the inside toward the outside of the ring shape of the first deformation element <NUM>).

The first deformation element <NUM> may be a ring having a variable length. The first deformation element <NUM> may include an SMA. The length of the first deformation element <NUM> may be increased by the force exerted by the bridge element <NUM> at a temperature less than a threshold temperature, and may be decreased back at a temperature greater than or equal to the threshold temperature. The temperature of the first deformation element <NUM> may be adjusted by a voltage applied to the first deformation element <NUM>. As the voltage applied to the first deformation element <NUM> increases, the temperature of the first deformation element <NUM> may be increased.

The curvature of the bridge element <NUM> may be changed according to a change in the length of the first deformation element <NUM>. When the length of the first deformation element <NUM> is decreased, the curvature of the bridge element <NUM> may be increased, and the bridge element <NUM> may push the base <NUM>. When the length of the first deformation element <NUM> is increased, the curvature of the bridge element <NUM> may be decreased, and the bridge element <NUM> may pull the base <NUM>.

Referring to <FIG>, the lift element <NUM> may include a lift base <NUM> and a plurality of second deformation elements <NUM>. The lift base <NUM> may have a fixed position. For example, the lift base <NUM> may include substantially the same material as that of the base <NUM>.

A pair of second deformation elements <NUM> may be between the base <NUM> and the lift base <NUM>. One end of each of the pair of second deformation elements <NUM> may be in contact with the base <NUM> and the other end thereof may be in contact with the lift base <NUM>. In an example, a restoring element may be further provided to apply a force to the base <NUM> and the lift base <NUM> to increase the distance between the base <NUM> and the lift base <NUM>. The pair of second deformation elements <NUM> may include an SMA. The length of the pair of second deforming elements <NUM> may be increased by the force exerted by the restoring element to the base <NUM> and the lift base <NUM> at a temperature less than a threshold temperature, and may be decreased back at a temperature greater than or equal to the threshold temperature. At a temperature less than the threshold temperature of the pair of second deforming elements <NUM>, the base <NUM> may be moved away from the lift base <NUM> by the restoring element. At a temperature greater than or equal to the threshold temperature of the pair of second deforming elements <NUM>, the base <NUM> may be moved toward the lift base <NUM> by the restoring element. The temperature of the pair of second deformation elements <NUM> may be adjusted by a voltage applied to the pair of second deformation elements <NUM>. As the voltage applied to the pair of second deformation elements <NUM> increases, the temperature of the pair of second deformation elements <NUM> may be increased.

The lift element <NUM> of the disclosure may adjust the position of the mirror <NUM> with respect to the third direction DR3. When the position of the mirror <NUM> with respect to the third direction DR3 is changed, the position of a virtual image formed by virtual image light may be changed. When the distance along an optical path between the mirror <NUM> and the combiner <NUM> is decreased, the distance between the virtual image and the combiner <NUM> may also be decreased. When the distance along the optical path between the mirror <NUM> and the combiner <NUM> is increased, the distance between the virtual image and the combiner <NUM> may also be increased.

<FIG> illustrates a projection optical system <NUM>, according to an example embodiment. <FIG> is an enlarged view of region AA of <FIG> for describing driving of the projection optical system <NUM> of <FIG>. <FIG> is an enlarged view corresponding to region AA of <FIG> for describing driving of the projection optical system <NUM> of <FIG>. For brevity of description, substantially the same descriptions as provided with reference to <FIG> may not be provided.

Referring to <FIG>, the projection optical system <NUM> may include the mirror layer <NUM>, a plurality of serpentine springs <NUM>, and a plurality of electroactive polymer films <NUM>. The mirror layer <NUM> may be substantially the same as the mirror layer <NUM> described with reference to <FIG>.

The plurality of serpentine springs <NUM> may be at four sides of the mirror layer <NUM>, respectively. The plurality of serpentine springs <NUM> may be substantially the same as each other. For brevity of description, one serpentine spring <NUM> is described. The serpentine spring <NUM> may include a plurality of flat plates. The plurality of flat plates may extend in one direction. The plurality of flat plates may be connected to each other to constitute a zigzag shape. The plurality of flat plates may have a plurality of holes <NUM>, respectively. Each of the plurality of holes <NUM> may penetrate the plurality of flat plates. When no force is applied to the serpentine spring <NUM>, the plurality of flat plates may be arranged parallel to each other on a plane. For example, one end and the other end of the serpentine spring <NUM> may be at the same height. When a force is applied to bend the plurality of flat plates in the same direction, the one end and the other end of the serpentine spring <NUM> may be at different heights. When one end of the serpentine spring <NUM> is coupled to a base and the other end thereof is coupled to an object, the plurality of flat plates may be bent to lift the object from the base.

The plurality of electroactive polymer films <NUM> may be on the plurality of flat plates, respectively. A pair of electrodes may be respectively on both surfaces of each of the electroactive polymer films <NUM>. The electroactive polymer film <NUM> may be pre-stretched and adhered to each flat plate. The plurality of serpentine springs <NUM>, the plurality of electroactive polymer films <NUM>, and the electrodes may constitute an actuator.

When no voltage is applied to the pair of electrodes, the size or area of the electroactive polymer film <NUM> may be decreased. The electroactive polymer film <NUM> may pull the flat plate. As illustrated in <FIG>, the flat plate may be bent.

When a voltage is applied to the pair of electrodes, the size or area of the electroactive polymer film <NUM> may be increased. The force with which the electroactive polymer film pulls the flat plate may be decreased. When the magnitude of the voltage applied to the pair of electrodes is sufficiently high, the electroactive polymer film <NUM> may not pull the flat plate. In this case, as illustrated in <FIG>, the electroactive polymer film <NUM> may be in a straight state (e.g., an unbent state).

The disclosure may provide the projection optical system <NUM> including the serpentine spring driven by using the electroactive polymer film <NUM>.

<FIG> is a perspective view of a projection optical system <NUM>, according to an example embodiment. <FIG> is a side view of the projection optical system <NUM> of <FIG>. <FIG> is an exploded perspective view of an actuator <NUM> of the projection optical system <NUM> of <FIG>. For brevity of description, substantially the same descriptions as provided with reference to <FIG> may not be provided.

Referring to <FIG>, the projection optical system <NUM> may be provided. The projection optical system <NUM> may include the base <NUM>, the mirror layer <NUM>, and a plurality of actuators <NUM>. The base <NUM> and the mirror layer <NUM> may be substantially the same as the base <NUM> and the mirror layer <NUM>, which are described with reference to <FIG>, respectively.

The plurality of actuators <NUM> may be substantially the same as each other. For brevity of description, one actuator <NUM> will be described. The actuator <NUM> may include an electroactive polymer film <NUM>, a pair of frames <NUM>, and a pair of electrodes <NUM>. The electroactive polymer film <NUM> may be substantially the same as the electroactive polymer film <NUM> described with reference to <FIG>, except for its shape. The electroactive polymer film <NUM> may have a rhombic shape. One corner of the electroactive polymer film <NUM> may be adjacent to the base <NUM>, and another corner opposite to the one corner may be adjacent to the mirror layer <NUM>. The electroactive polymer film <NUM> may be pre-stretched. The electroactive polymer film <NUM> includes a first surface and a second surface opposite to each other.

The pair of frames(first and second frames) <NUM> may be on the first and second surfaces of the electroactive polymer film <NUM>, respectively. The pair of frames <NUM> may have a rhombic ring shape. A first corner and a second corner in each of the pair of frames <NUM>, which are opposite to each other in a direction from the base <NUM> toward the mirror <NUM>, are in contact with the base <NUM> and the mirror <NUM>, respectively. The pair of frames <NUM> may extend along the edge of the electroactive polymer film <NUM>. Both surfaces of the electroactive polymer film <NUM> may be exposed inside the pair of frames <NUM>. The pair of frames <NUM> may be adhered to the surfaces of the pre-stretched electroactive polymer film <NUM> to maintain the stretched state of the electroactive polymer film <NUM>. The pair of frames <NUM> may be rigid. However, the pair of frames <NUM> may be deformed. The deformation of the pair of frames <NUM> will be described below.

The pair of electrodes(first and second electrodes) <NUM> may be on the first and second surfaces of the electroactive polymer film <NUM>, respectively. Each of the pair of electrodes <NUM> may be surrounded by the pair of frames(first and second frames) <NUM>, respectively, on the first and second surfaces of the electroactive polymer film <NUM>. The pair of electrodes <NUM> may be spaced apart from the pair of frames <NUM>. The pair of electrodes <NUM> may be respectively on both surfaces of the electroactive polymer film <NUM> exposed by the pair of frames <NUM>. The pair of electrodes <NUM> may include substantially the same material as those of the first electrode <NUM> and the second electrode <NUM>, which are described with reference to <FIG>.

<FIG> are diagrams for describing an operation of the actuator <NUM> of <FIG>.

Referring to <FIG>, no voltage may be applied to the actuator <NUM>. The electroactive polymer film <NUM> is in a pre-stretched state, and thus may have a property of being restored to its original shape. Accordingly, the electroactive polymer film <NUM> may pull the pair of frames <NUM>. The actuator <NUM> may have a first vertical length Loff in the third direction DR3.

Referring to <FIG>, a voltage may be applied to the actuator <NUM>. Because the size or area of the electroactive polymer film <NUM> is increased, the force exerted by the electroactive polymer film <NUM> to pull the pair of frames <NUM> may be decreased or removed. The actuator <NUM> may have a second vertical length Lon in the third direction DR3. The second vertical length Lon may be greater than the first vertical length Loff.

The disclosure may provide the projection optical system <NUM> capable of controlling the slope of the mirror <NUM> by independently adjusting vertical distances of the plurality of actuators <NUM>.

<FIG> is a conceptual diagram of a see-through display device <NUM>, according to an example embodiment. For brevity of description, substantially the same descriptions as provided with reference to <FIG> may not be provided.

Referring to <FIG>, the see-through display device <NUM> may be provided. The see-through display device <NUM> may include the image generator <NUM>, the projection optical system <NUM>, the combiner <NUM>, and the eye tracker <NUM>. The image generator <NUM>, the projection optical system <NUM>, and the eye tracker <NUM> may be substantially the same as those described with reference to <FIG>. The projection optical system <NUM> may be one of the projection optical systems <NUM>, <NUM>, <NUM>, and <NUM> described above, instead of the projection optical system <NUM> described with reference to <FIG>.

Unlike that described with reference to <FIG>, the combiner <NUM> may concentrate, to a first spot S1 and a second spot other than the first spot S1, the virtual image light IL projected from the projection optical system <NUM>. For example, the second spot may be S2, S3, or S4. Accordingly, the eye box may be expanded statically as well as dynamically.

<FIG> is a perspective view of a see-through display device <NUM> according to an example embodiment. For brevity of description, substantially the same descriptions as provided with reference to <FIG> may not be provided.

Referring to <FIG>, the see-through display device <NUM> may be provided. For example, the see-through display device <NUM> may be a glasses-type augmented reality device. The see-through display device <NUM> may include a pair of temples <NUM>, a lens frame <NUM>, an electronic system <NUM>, and a pair of combiners <NUM>. The pair of templates <NUM> may be connected to both ends of the lens frame <NUM>, respectively. The pair of temples <NUM> may be put on the ears of a user.

The lens frame <NUM> may include a pair of holes. The pair of combiners <NUM> may be inserted into the pair of holes, respectively. When the user wears the see-through display device <NUM>, both eyes of the user may face the pair of combiners <NUM>, respectively.

The electronic system <NUM> may include the image generator, the projection optical system, and the eye tracker, which are described with reference to <FIG>. Virtual image light may be emitted from the electronic system <NUM> to the combiner <NUM>. The virtual image light may be reflected and concentrated by the combiner <NUM>. For example, the virtual image light concentrated by the combiner <NUM> facing the left eye of the user may be concentrated to a left spot SL, and the virtual image light concentrated by the combiner <NUM> facing the right eye of the user may be concentrated to a right spot SR. Real image light may pass through the pair of combiners <NUM> to reach both eyes of the user. Accordingly, the user may view the virtual image and the real image at the same time. In another example, as described with reference to <FIG>, the combiner <NUM> may concentrate, to a plurality of spots, the virtual image light provided from the electronic system <NUM>.

Referring to <FIG>, the projection optical system <NUM> may be provided with the base <NUM>, the mirror layer <NUM>, the plurality of actuators <NUM>, the support film <NUM>, and the pivot pillar <NUM>. The base <NUM>, the mirror layer <NUM>, and the pivot pillar <NUM> may be substantially the same as the base <NUM>, the mirror layer <NUM>, and the pivot pillar <NUM>, which are described with reference to <FIG>, respectively.

Unlike as illustrated in <FIG>, the plurality of actuators <NUM> may be a pair of actuators <NUM> facing each other in the first direction DR1. Each of the plurality of actuators <NUM> may be substantially the same as each of the plurality of actuators <NUM> described with reference to <FIG>. Because the projection optical system <NUM> includes two actuators <NUM>, the projection optical system <NUM> may have one degree of freedom with respect to inclination of the mirror layer <NUM>. For example, the mirror layer <NUM> may be inclined on a virtual plane parallel to the first direction DR1 and the third direction DR3.

The disclosure may provide a projection optical system having a large area and a high driving speed.

The disclosure may provide a see-through display device including a projection optical system having a large area and a high driving speed.

However, the effects of the disclosure are not limited to those described above.

According to an example embodiment, the methods and/or operations illustrated in <FIG>, <FIG>, <FIG>, <FIG> and <FIG> may be performed by an electronic device including a memory and a processor. For instance, according to an example embodiment, a display device may include a memory, a processor and a projection optical system according to any of the embodiments of the disclosure. According to an example embodiment, the processor (in combination with a memory) may control the projection optical system. According to another example embodiment, the display device may include a controller configured to control the projection optical system.

At least one of the components, elements, modules or units (collectively "components" in this paragraph) represented by a block in the drawings, such as the image generator, may be embodied as various numbers of hardware, software and/or firmware structures that execute respective functions described above, according to an exemplary embodiment. For example, at least one of these components may use a direct circuit structure, such as a memory, a processor, a logic circuit, a look-up table, etc. that may execute the respective functions through controls of one or more microprocessors or other control apparatuses. Also, at least one of these components may be specifically embodied by a module, a program, or a part of code, which contains one or more executable instructions for performing specified logic functions, and executed by one or more microprocessors or other control apparatuses. Further, at least one of these components may include or may be implemented by a processor such as a central processing unit (CPU) that performs the respective functions, a microprocessor, or the like. Two or more of these components may be combined into one single component which performs all operations or functions of the combined two or more components. Also, at least part of functions of at least one of these components may be performed by another of these components. Functional aspects of the above exemplary embodiments may be implemented in algorithms that execute on one or more processors. According to an example embodiment, the algorithms or computer programs may be stored in a memory or a storage device. Furthermore, the components represented by a block or processing steps may employ any number of related art techniques for electronics configuration, signal processing and/or control, data processing and the like.

Claim 1:
A projection optical system comprising:
a base (<NUM>);
a mirror (<NUM>); and
a pair of first actuators (<NUM>-<NUM>) provided between the base (<NUM>) and the mirror (<NUM>), the pair of first actuators (<NUM>-<NUM>) configured to face each other in a first direction,
characterised in that each of the pair of first actuators (<NUM>-<NUM>) comprises a first electroactive polymer film having structural flexibility such that a size of the first electroactive polymer film is changeable based on an applied voltage, and
wherein the mirror (<NUM>) is adjustable based on a change in the size of the first electroactive polymer film,
wherein the first electroactive polymer film has a first surface and a second surface, and
each of the pair of first actuators (<NUM>-<NUM>) further comprises:
a first electrode (<NUM>) provided on the first surface;
a second electrode (<NUM>) provided on the second surface;
a first stretch maintaining film (<NUM>) provided to surround the first electrode (<NUM>); and
a pair of first hinge elements (<NUM>) provided on the first stretch maintaining film (<NUM>);
wherein the first stretch maintaining film (<NUM>) comprises a hole, and
the first electrode (<NUM>) is provided in the hole.