Patent Description:
The present disclosure relates to systems and techniques for providing images of different focal lengths from a single micro-display of an HMD by employing a multifocal module having one or more voltage controlled optical elements. By changing the voltage applied to the one or more optical elements, the HMD can change the focal length of an image generated by the micro-display. According to the invention, the multifocal module comprises carr a cholesteric liquid crystal (CLC) element and a polarizer switch. By controlling the voltage applied to each of the CLC element and the polarizer switch, the HMD can change the focal length of the image passed through the multifocal module. The HMD can thereby change the focal length of any image generated by the micro-display.

The images fields of different focal lengths can be employed to support a variety of uses and applications. For example, in some embodiments, the images of different focal lengths can be used to display objects at different image planes, increasing the immersiveness of VR and AR content. Further, the multifocal module can be constructed of optical elements, such as the CLC element, having a small form factor, thereby allowing the multifocal to be used in a variety of HMD systems.

The proposed solution relates to a head-mound display system of claim <NUM> and a method of claim <NUM>.

<FIG> illustrate systems and techniques for providing images of different focal lengths from a single micro-display of an HMD by employing a multifocal module having one or more voltage controlled optical elements.

<FIG> illustrates an HMD <NUM> in accordance with some embodiments. In the depicted example the HMD <NUM> has an eyeglass form factor and includes two seethrough eyepieces <NUM> and <NUM> that each provide image light to a user in a viewing region (e.g. viewing region <NUM>) along with a view of the surrounding environment. The image light may be augmented reality data that provides information of one or more objects in the surrounding environment. Additionally, the image light provides other information to the user such as text messages, email messages, phone call information, etc..

The HMD <NUM> includes electronics and a micro-display (not shown at <FIG>) to project the image light to the user. The electronics are either coupled to a secondary electronics device, such as a computer or cell phone, that provides the data for generating the image light, or the electronics include wireless communication technology that allows for the receipt of the information via a wireless network, such as Bluetooth, Wi-Fi or cellular. In some embodiments, each eyepiece includes a lightguide or other element that provides an optical pathway for the image light to propagate from a micro-display to the image light viewing region <NUM>, which is arranged to be aligned with the user's eye. The lightguide relies on total internal reflection (TIR) for propagating the image light from an input coupler to an output coupler, which redirects the light out of the HMD <NUM> and toward the eye of the user in the image light viewing region. The eyepieces may additionally include vision correction lensing for the user or absorbing sunglass coatings.

As described further below, between the micro-display and the optical pathway the HMD <NUM> can include a multifocal module that can change the focal length of an image generated at the micro-display. The multifocal module includes one or more voltage controlled optical elements. By changing the voltage applied to the optical elements (e.g., by changing states of a CLC element), the HMD changes the focal length of the image.

<FIG> illustrates a block diagram of portions of the HMD <NUM> in accordance with some embodiments. In the depicted example, the HMD <NUM> includes a micro-display <NUM>, a multifocal module <NUM>, an optical path <NUM> and a controller <NUM>. The micro-display is generally configured to generate image light <NUM> based on image frames received from a graphics processing unit (GPU) or other image frame generator (not shown). The optical path <NUM> includes one or more optical elements, such as a lightguide, to propagate image light generated by the multifocal module <NUM> to a user's eye.

The multifocal module <NUM> includes one or more voltage controlled optical elements that can set the focal length of images based on the image light <NUM>, as described further herein. For example, in some embodiments the multifocal module <NUM> includes a CLC element and a polarizer switch, each controllable by an associated control signal generated by the controller <NUM>. Depending on the state of the control signal, the optical path through optical elements of the multifocal module is changed, as described further below, thereby changing the focal length of the image associated with the image light <NUM>. In other embodiments the multifocal module <NUM> includes a voltage-controlled phase modulator. The controller <NUM> can generate the voltage to control the phase modulator to change the focal length of the image associated with the image light <NUM> as described further below. Thus, the multifocal module <NUM> is configured to generate light representing images (e.g. image <NUM> and image <NUM>) wherein the focal length associated with each image is based on the control signal(s) generated by the controller <NUM>. Thus, for example, the images <NUM> and <NUM> have different focal lengths (designated FL1 and FL2), based on the control signals generated by the controller <NUM>.

<FIG> illustrates a block diagram of the multifocal module <NUM> in accordance with some embodiments. In the depicted example, the multifocal module <NUM> includes a right-handed polarizer <NUM>, a plane-parallel plate <NUM> having a <NUM>/<NUM> beamsplitting coating <NUM>, a polarizer switch <NUM> and a cholesteric liquid crystal (CLC) element <NUM>. The right-handed polarizer <NUM> and the plane parallel plate <NUM> together pass right-handed circularly polarized light based on the image light <NUM>. The polarizer switch <NUM> is generally configured to pass light of a specified polarization based on the state of a received control signal (not shown). Thus, for example, in response to the control signal having a first state, the polarizer switch <NUM> passes right-hand (R)-polarized light and in response to the control signal having a second state, the polarizer switch <NUM> switches the R-polarized light to left-hand (L)-polarized light. In some embodiments, the polarizer switch <NUM> is a liquid crystal display (LCD) cell and the control signal is a voltage provided by the controller <NUM>.

The CLC element <NUM> is an element that, depending on an applied voltage, is transparent to or reflects light of a specified polarization. When there is no voltage applied to the CLC element <NUM>, the liquid crystal molecules have a helical structure with a pitch that results in a Bragg reflection. When the incident unpolarized light hits the cholesteric liquid crystal (left-handed), the left-handed circularly polarized light will be reflected. When the CLC element <NUM> is switched by an electric field, the CLC molecules are unwound such that all the molecules are aligned along the electric field. Thus, the helical structure disappears so does the Bragg reflection. Therefore, they become transparent to any polarization light.

In operation, the controller <NUM> controls the voltages applied to the polarizer switch <NUM> and the CLC element <NUM> to alternately change the optical path for the image light <NUM> through the elements of the multifocal module <NUM>. In particular, the controller <NUM> alternates a relatively short optical path with a relatively long optical path, thereby changing the focal length associated with the image light. This can be better understood with reference to <FIG>.

<FIG> illustrates two different states of the multifocal module <NUM> in accordance with some embodiments, designated states <NUM> and <NUM>. The state <NUM> represents the state when the controller <NUM> has applied control signals (voltages) to place the polarizer switch <NUM> and the CLC element <NUM> in "off" states. Accordingly, in state <NUM> the polarizer switch passes R-polarized light without changing the light's polarization, and the CLC element <NUM> passes all polarized light. Thus, in the illustrated example, an unpolarized light ray <NUM> is converted to R-polarized light, and that light is passed through the remaining optical elements.

The state <NUM> represents the state when the controller <NUM> has applied control signals to place the polarizer switch <NUM> and the CLC element <NUM> in "on" states. Thus, in state <NUM> the polarizer switch <NUM> converts R-polarized light to L-polarized light and R-polarized light to L-polarized light and the CLC element <NUM> reflects L-polarized light and passes R-polarized light. The path of light through the optical elements of the multifocal module <NUM> in state <NUM> is illustrated by a ray <NUM>. In the depicted example, R-polarized light is designated with the label "R" and L-polarized light is designated with the label "L".

As shown, the ray <NUM> first passes through the polarizer <NUM>, and thus becomes R-polarized light. Because the polarizer switch <NUM> is in the on state, the ray <NUM> is converted from R-polarized to L-polarized light and, because the CLC element <NUM> is in the on state, the L-polarized light is reflected. Accordingly, the ray <NUM> passes back through the polarizer switch <NUM> and is converted to R-polarized light. The ray <NUM> then passes through the plane parallel plate <NUM>, which reflects the ray <NUM> as L-polarized light. The ray <NUM> is then converted to R-polarized light by the polarizer switch <NUM>, and the R-polarized light is passed by the CLC element <NUM>.

As is understood in the art, the focal lengths associated with the rays <NUM> and <NUM> at the output of the multifocal module <NUM>, after the rays <NUM> and <NUM> pass through the CLC element <NUM>, is governed in part by the thickness of the optical elements through which each ray passes. By increasing the length of the optical path for the ray <NUM>, relative to the ray <NUM>, the multifocal module changes the focal length of the ray <NUM> as compared to the ray <NUM>. Thus, by alternating the states <NUM> and <NUM> (by alternating the voltages applied to the polarizer switch <NUM> and CLC element <NUM>, the controller <NUM> can change the focal length associated with images generated from image light <NUM>.

In some embodiments, the multifocal module <NUM> is coupled to additional optical elements that form at least a portion of the optical path <NUM> to direct light to a user's eye. These additional optical elements can also change the focal length and image plane associated with each image provided by the multifocal module <NUM> in order to present a satisfactory visual experience to a user. An example of these optical elements is illustrated at <FIG> in accordance with some embodiments. In the depicted example, the multifocal module <NUM> is disposed between the micro-display <NUM> and a filter stack formed by a quarter waveplate <NUM>, a beamsplitter <NUM>, a quarter waveplate <NUM>, a polarization beamsplitter <NUM>, and a linear polarizer <NUM>.

In operation, the multifocal module <NUM> generates, based on image light provided by the micro-display <NUM>, images of different focal length. The light of the images generated by the multifocal module <NUM> is then passed through the filter stack and directed to the user's eye. In particular, the light is passed through the quarter waveplate <NUM> which generates L-polarized light. The L-polarized light is then passed through the beamsplitter <NUM>, and is translated to linearly polarized light (with polarization designated as x-polarization) by the quarter waveplate <NUM>. The x-polarized light is reflected by the polarization beamsplitter <NUM>. The reflected x-polarized light is translated to L-polarized light by the quarter waveplate <NUM>. This reflected L-polarized light is then reflected again as R-polarized light by the beamsplitter <NUM>. The R-polarized light is translated to linearly polarized light, with polarization designated as y-polarization that is orthogonal to x-polarization. The y-polarized light passes through the polarization beamsplitter <NUM> and the linear polarizer <NUM> and is directed towards the user's eye.

The filter stack illustrated at <FIG> can be manufactured with relatively small optical elements, such that the overall form factor of the filter stack, together with the multifocal module, is also small. The small form factor allows the depicted embodiment to be comfortably placed in a variety of HMD form factors while generating images associated with different focal lengths, and therefore having different image planes, and enhancing the overall user experience.

<FIG> illustrates a block diagram of the HMD <NUM> of <FIG> including a display system to display content via multiple image planes in accordance with some embodiments. To support display of images with different image planes, the HMD <NUM> includes a display control module <NUM>, a graphics processing unit (GPU) <NUM>, and the multifocal module. The GPU <NUM> is generally configured to generate frames (e.g., frames <NUM> and <NUM>) for display at the HMD <NUM> based on commands received from another processor (not shown) such as a central processing unit (CPU) of an external device (e.g. a computer or cell phone) or a CPU of the HMD <NUM>. The display control module <NUM> is generally configured to control operation of the multifocal module <NUM> to time multiplex the provision of light of different focal lengths to the user. In some embodiments, the display control module <NUM> controls provision of the frames from the GPU <NUM> to the micro-display <NUM> and synchronizes provision and display of the frames at the micro-display <NUM> with control of the multifocal module <NUM> so that different frames are associated with different focal planes, and are displayed with different image planes.

By displaying different frames via different image planes, the HMD <NUM> supports flexible and immersive display of information to the user. For example, in some embodiments the display control module <NUM> selects the frame to display via at a particular image plane to create an overall image that appears to the user to have depth, creating a more immersive VR or AR environment. In some embodiments, the image planes for the different frames are based on a set of user settings <NUM>. The user can adjust the user settings <NUM> (via, e.g., a graphical user interface (GUI) or other interface so that the display control module displays frames associated with different applications, or different types of information, at different image planes. For example, in some embodiments the user can adjust the user settings <NUM> so that a video is displayed at one image plane and notification information (e.g. email or chat notifications) are displayed via a different image plane.

Such storage media can include, but is not limited to, optical media (e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media (e.g., floppy disc , magnetic tape, or magnetic hard drive), volatile memory (e.g., random access memory (RAM) or cache), non-volatile memory (e.g., read-only memory (ROM) or Flash memory), or microelectromechanical systems (MEMS)-based storage media.

Claim 1:
A head mounted display, HMD, system comprising:
a micro-display (<NUM>) to emit display light (<NUM>);
a multifocal module (<NUM>) coupled to the micro-display, the multifocal module
to generate a plurality of images (<NUM>, <NUM>) based on the display light, each of the plurality of images being associated with a different focal length,
wherein the multifocal module further comprises:
a voltage controlled optical element (<NUM>, <NUM>) comprising a voltage-controlled cholesteric liquid crystal, CLC, element (<NUM>) and a voltage-controlled polarizer switch (<NUM>) coupled to the CLC element,
and
a controller (<NUM>) configured to control the voltage applied to each of the CLC element and the polarizer switch to change the focal length associated with the image light passed through the multifocal module, wherein a filter stack is coupled to the multifocal module and the filter stack comprises a first quarter waveplate (<NUM>), a beamsplitter (<NUM>) coupled to the first quarter waveplate, and a second quarter waveplate (<NUM>) coupled to the beamsplitter.