Pancake lens assembly and optical system thereof

An optical lens assembly and an optical system is provided. The optical lens assembly includes a first optical element including a partial reflector and a quarter-wave plate and a second optical element including a reflective polarizer. The first optical element and the second optical element form a cavity. The pancake lens assembly further includes a varifocal lens having an adjustable optical power, and the varifocal lens is disposed inside or outside the cavity.

BACKGROUND

Head-Mounted Display (HMD) has been widely used in, e.g., video playback, gaming, and sports. One major application of HMD is to realize at least one of virtual reality (VR), augmented reality (AR), or mixed reality (MR). An HMD is highly desired to be compact and light weight, and have high resolution, large field of view (FOV), and small form factors. An HMD generally has a display element configured to generate image light that passes through a lens system to reach a user's eyes. The lens system includes multiple optical elements, such as lenses, waveplates, reflectors, etc., for focusing the image light to the user's eyes. To achieve a compact size and light weight but maintain good optical characteristics, an HMD often uses a pancake lens in the lens system.

Further, current VR/AR/MR HMDs are often having the so-called vergence-accommodation conflict, where a stereoscopic image pair drives the vergence state of a user's human visual system to arbitrary distances, but the accommodation or focusing state of the user's eyes is optically driven towards a fixed distance. The vergence-accommodation conflict causes eye strain or headaches during prolonged VR/AR/MR sessions, significantly degrading the visual experience of the users. The disclosed pancake lens assembly and optical system thereof are directed to solve one or more problems set forth above and other problems.

BRIEF SUMMARY OF THE DISCLOSURE

One aspect of the present disclosure provides an optical lens assembly. The optical lens assembly includes a first optical element including a partial reflector and a quarter-wave plate and a second optical element including a reflective polarizer. The first optical element and the second optical element form a cavity. The pancake lens assembly further includes a varifocal lens having an adjustable optical power, and the varifocal lens is disposed inside or outside the cavity.

Another aspect of the present disclosure provides an optical lens system. The optical lens assembly includes a light source; a first optical element including a partial reflector and a quarter-wave plate; a second optical element including a reflective polarizer; a varifocal lens having an adjustable optical power; and a detector. The first optical element and the second optical element form a cavity, and the varifocal lens is disposed inside or outside the cavity. The first optical element, the second first optical element and the varifocal lens are configured to direct a light from the light source to the detector.

DETAILED DESCRIPTION

Hereinafter, embodiments consistent with the disclosure will be described with reference to drawings, which are merely examples for illustrative purposes and are not intended to limit the scope of the disclosure. In the drawings, the shape and size may be exaggerated, distorted, or simplified for clarity. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts, and a detailed description thereof may be omitted.

Further, in the present disclosure, the disclosed embodiments and the features of the disclosed embodiments may be combined under conditions without conflicts. The described embodiments are some but not all of the embodiments of the present disclosure. Based on the disclosed embodiments, persons of ordinary skill in the art may derive other embodiments consistent with the present disclosure, all of which are within the scope of the present disclosure.

The present disclosure provides a pancake lens assembly, which is capable of folding the optical path and solving vergence-accommodation conflict in head-mounted displays (HMDs). The pancake lens assembly may include a first optical element including a partial reflector and a quarter-wave plate and a second optical element including a reflective polarizer. The first optical element and the second optical element may form a cavity. The pancake lens assembly may further include a varifocal lens having an adjustable optical power. In some embodiments, the varifocal lens may be disposed inside the cavity. In some embodiments, the varifocal lens may be disposed outside the cavity. The varifocal lens may enable the pancake lens assembly to be a variable pancake lens assembly.

FIG. 1illustrates a schematic diagram of a pancake lens assembly100according to an embodiment of the disclosure. The pancake lens assembly100may be used in an optical system to fold the optical path from a light source to a detector. For example, the pancake lens assembly100may be used in a head-mounted display (HMD), to fold the optical path, thereby reducing the back focal distance in the HMD. As shown inFIG. 1, the pancake lens assembly100may focus light190from an electronic display110to an eye-box located at an exit pupil170. Hereinafter, the light190emitted by the electronic display110for forming images is also referred to as “image light.” The exit pupil170may be at a location where an eye180is positioned in an eye-box region when a user wears the HMD.

The pancake lens assembly100may include a first optical element120, a varifocal lens130, a second optical element140. The first optical element120and the second optical element140may form a cavity, and the varifocal lens130may be disposed inside or outside the cavity. For illustrative purposes,FIG. 1shows the varifocal lens130may be disposed inside the cavity formed by the first optical element120and the second optical element140. In some embodiments, the first optical element120, the varifocal lens130and the second optical element140may be coupled together by an adhesive. The first optical element120and/or the second optical element140may include one or more optical lenses. In some embodiments, the first optical element120may include a first surface120-1configured to receive the image light from the electronic display110and an opposing second surface120-2configured to output altered image light. The first optical element120may further include a mirrored surface122and a waveplate surface124, which are separate layers or coatings bonded to or formed on the first optical element120. In some embodiments, the waveplate surface124may be bonded to or formed on the second surface120-2of the first optical element120, and the mirrored surface122may be bonded to or formed on the first surface120-1of the first optical element120.

The mirrored surface122may include a partial reflector that is partially reflective to reflect a portion of the received light. In some embodiments, the mirrored surface122may be configured to transmit about 50% of incident light and reflect about 50% of the incident light. Such a mirrored surface is often referred to as a 50/50 mirror. In some embodiments, the waveplate surface124may include a quarter-wave plate (QWP) that alters the polarization of received light. A quarter-wave plate includes a polarization axis, and the polarization axis of the QWP may be oriented relative to incident linearly polarized light to convert the linearly polarized light into circularly polarized light or vice versa for a visible spectrum and/or infrared spectrum. In some embodiments, for an achromatic design, the quarter-wave plate may include a multilayer birefringent material (e.g., polymer or liquid crystals) to produce quarter wave birefringence across a wide spectral range. In some embodiments, for a simple monochrome design, an angle between the polarization axis (i.e., fast axis) of the quarter-wave plate and incident linearly polarized light may be approximately 45 degrees.

The second optical element140may have a first surface140-1facing the varifocal lens130and an opposing second surface140-2. The second optical element140may include a reflective polarizer surface142, which is a separate layer or coating bonded to or formed on the second optical element140. In some embodiments, the reflective polarizer surface142may be bonded to or formed on the first surface140-1of the second optical element140. The reflective polarizer surface142may include a partially reflective mirror configured to reflect a received light of a first linear polarization and transmit a received light of a second linear polarization. For example, the reflective polarizer surface142may reflect light polarized in a blocking direction (e.g., x-axis direction), and transmit light polarized in an orthogonal direction (e.g., y-axis direction). In the disclosed embodiments, the blocking direction is referred to as a direction of a blocking axis or a blocking axis direction of the reflective polarizer surface142, and the perpendicular direction is referred to as a direction of a transmission axis or a transmission axis direction of the reflective polarizer surface142.

The varifocal lens130may have a variable focal length, for example, an adjustable optical power. The varifocal lens130may include any suitable lenses, such as a glass lens, a polymer lens, a liquid lens, a liquid crystal (LC) lens, or some combination thereof. The varifocal lens130may adjust an orientation of light emitted from the electronic display110, such that the light emitted from the electronic display110appears at particular focal distances/image planes from the user. In some embodiments, the varifocal lens130may include an LC lens130, which is capable of adjusting the optical power sufficiently fast to keep pace with eye accommodation (e.g., accommodation occurs in around 300 ms), such that the vergence-accommodation conflict in the HMD can be resolved.

The pancake lens assembly100shown inFIG. 1is merely for illustrative purposes. In some embodiments, one or more of the first surface120-1and the second surface120-2of the first optical element120and the first surface140-1and the second surface140-2of the second optical element140may be curved surface(s). In some embodiments, the pancake lens assembly100consistent with the disclosure can have one optical element or more than two optical elements. In some embodiments, the pancake lens assembly100may further include other optical elements arranged between the electronic display110and the eye180, such as a linear polarizer, a quarter-wave plate, which is not limited by the present disclosure.

In some embodiments, the LC lens130may have a Fresnel structure, i.e., a Fresnel LC lens. The Fresnel LC lens may include any appropriate type of Fresnel structure, such as a Fresnel zone plate lens including areas that have a phase difference of a half-wave to adjacent areas, a diffractive Fresnel lens having a segmented parabolic phase profile where the segments are small and can result in significant diffraction, or a refractive Fresnel lens having a segmented parabolic profile where the segments are large enough so that diffraction effects are minimized. Other structures may also be used. In some embodiments, the varifocal lens130may include a refractive Fresnel LC lens having a segmented parabolic profile, where the segments are large enough such that the diffraction angle is smaller than the angular resolution of human eyes, i.e., diffraction effects are not observable by human eyes. Such a refractive Fresnel LC lens is referred to as a segmented phase profile (SPP) LC lens.

FIG. 2illustrate a schematic diagram of an SPP LC lens200according to an embodiment of the disclosure. As shown inFIG. 2, the Fresnel structure of the SPP LC lens200is represented by a plurality of concentric ring-shaped zones202of increasing radii, which are referred as Fresnel segments or Fresnel resets. For a positive thin lens, optical path difference (“OPD”) is approximated with Maclaurin series to a parabolic profile as shown in Equation (1)

OPD⁡(r)=-r22⁢f,(1)
where r is the lens radius (i.e., half of the lens aperture) and f is the focal length. The OPD of an LC lens is proportional to the cell thickness d and the birefringence Δn of the LC material as shown in Equation (2)
OPD=d*Δn,(2)
The response time τ of an Electrically Controlled Birefringence (ECB) LC cell, which is the time the material requires to recover to its original state, is quadratically dependent on cell thickness d (τ∝d2) as shown in Equation (3)

τ=γ×d2K1⁢1×π2,(3)
where γ and K11are the rotational viscosity and the splay elastic constant of the LC material, respectively. Equations (1)-(3) show there is a tradeoff between the aperture size and response time, and thus designing an LC lens with large aperture and reasonable response time is an uphill task. In the disclosed embodiments, though introducing phase resets in the parabolic phase profile, e.g., using a SPP LC lens, a large aperture size of the LC lens may be allowed without compromising the response time.

FIG. 3Aillustrates a desired phase profile for ±0.375 Diopter (D) LC lens that does not include any phase resets, where the OPD equals to 35λ. The aperture of the LC lens is 20 mm, and the thickness of the LC cell is about 70 μm for LC materials with a birefringence Δn of 0.27. To decrease the effective thickness of the LC cell, resets or segments may be introduced into the lens phase profile.FIG. 3Billustrates 2D phase map of the SPP LC lens200that includes 5 resets, where the thickness of the LC cell would be reduced up to 5 times and, accordingly, the response time would be improved by a factor of 25. That is, through introducing the segments in the lens phase profile, the optical power of the SPP LC lens200may be adjusted sufficiently fast to keep pace with eye accommodation (e.g., accommodation occurs in around 300 ms), such that the vergence-accommodation conflict would be resolved.

The number of the resets may be determined based on specific configurations of the Fresnel structure and the SPP LC lens200requirements, such as the desired optical power, lens aperture, switching time, image quality of the LC lens. A large number of phase steps within one wavelength of OPD (i.e., per wavelength) may be desired for accurate representation of phase profile. Meanwhile, to configure the SPP LC lens with negligible diffraction angle for near eye applications, the minimum width of the Fresnel segments (i.e., the minimum Fresnel segment width) of the SPP LC lens200is desired to be larger than about 1 mm for green light having a wavelength of 543.5 nm.

FIG. 4Aillustrates a schematic diagram of an SPP LC lens400according to an embodiment of the disclosure. The SPP LC lens400may be the SPP LC lens200inFIG. 2. As shown inFIG. 4A, the SPP LC lens400may include a plurality of first electrodes412, one or more second electrode410, a liquid crystal (LC) layer414, and substrates416. The substrates416may be substantially transparent in the visible band (˜380 nm to 750 nm). In certain embodiments, the substrates416may also be transparent in some or all of the infrared (IR) band (˜750 nm to 1 mm). The substrate layers may be composed of, e.g., SiO2, plastic, sapphire, etc. The first electrodes412and second electrodes410may be transparent electrodes (e.g., indium tin oxide electrodes) disposed on the substrates416to generate electric fields, which reorients the LC molecules in the LC layer414to form a lens having a desired phase profile.

In some embodiments, the first electrodes412may include discrete ring-shaped electrodes corresponding to the Fresnel structures in the SPP LC lens400, and the ring-shaped electrodes may be concentric with identical area. With this electrode geometry, when the phase difference between adjacent first electrodes412is the same, a parabolic phase profile may be obtained. If the phase is proportional to the applied voltage, a linear change in the voltage across the first electrodes412(same difference in voltage between any two first electrodes412) may yield a desired parabolic phase profile.

In some embodiments, the gaps between the first electrodes412can cause scattering and thus image degradation. To address that image degradation, a plurality of floating electrodes may be introduced.FIG. 4Billustrates a schematic diagram of an SPP LC lens450having floating electrodes according to an embodiment of the disclosure. As shown inFIG. 4B, a plurality of floating electrodes418may be disposed on the substrate416having the first electrodes412. The floating electrodes418may include discrete and concentric ring electrodes which are not driven by ohmic connection but are capacitively coupled to the first electrodes412. The floating electrodes418may be configured to cover half of the area of each of neighboring first electrodes412. An insulating layer420may be disposed between the floating electrodes418and the first electrodes412to achieve the electrical insulation.

To further improve the response time of the SPP LC lens, in some embodiments, multiple SPP LC lens (e.g., multiple lens layers) may be optically coupled to form a stack of SPP LC lens, i.e., an SPP LC lens stack, such that given a same tunable optical power range, the thickness of each SPP LC lens may be reduced and, accordingly, the response of each SPP LC lens may be reduced.FIG. 5illustrates a schematic diagram of an SPP LC lens stack500according to an embodiment of the disclosure. For illustrative purposes,FIG. 5shows a pair of SPP LC lenses may be optically coupled to form the SPP LC lens stack500. Provided that each SPP LC lens has 5 resets in the phase profile, considering the effect of the pair of lenses and the Fresnel resets, the thickness of the LC cell may be reduced up to 10 times (5 resets×2) and, accordingly, the response speed may be improved by a factor of 100. Moreover, the two SPP LC lenses may have opposite alignment directions (e.g., rubbing directions) on the corresponding LC surfaces of the two SPP LC lens, so as to improve the viewing angle. That is, for viewing angle improvement, two of SPP LC lenses with the same configuration but opposite rubbing directions may be optically coupled.

In addition, the polarization insensitivity is also very important for HMDs for AR applications. Most LC materials are birefringent and, thus, are polarization sensitive. When the light propagating in a direction parallel to the LC director is incident onto the LC cell, the light will experience ordinary refractive index n0of the LC material for any polarization states. However, when the light propagating in a direction perpendicular to the LC director is incident onto the LC cell, the light will experience refractive index between the ordinary refractive index n0and extraordinary refractive index neof the LC material, depending on the polarization state of light.

Cholesteric LC materials can be made polarization insensitive as discussed by Clarke et al. in Electro-active lens U.S. Pat. No. 7,728,949B2. In this case the pitch of cholesteric LCs can be made in the range of the wavelength of incident light and, therefore, when no voltage is applied to the LC cell, the light will experience an average refractive index

(no+ne2)
for any polarization states of light. For nematic LCs, the SPP LC lenses may be configured to be polarization insensitive by optically coupling cells of orthogonal polarization, in which each cell may focus one polarization state of light, for example, one cell focuses s polarization and the other focuses p polarization.

FIG. 6Aillustrates a schematic diagram of an SPP LC lens stack600without Fresnel resets offset according to an embodiment of the disclosure. As shown inFIG. 6A, the SPP LC lens stack600may include a plurality of SPP LC lenses or SPP LC lens layers610stacked in a z-direction. Each SPP LC lens610may have a Fresnel structure including a plurality of concentric ring-shaped zones of increasing radii. Each SPP LC lens610may have a same configuration of the concentric ring-shaped zones or Fresnel resets, for example, the radius of the corresponding ring-shaped zones in the SPP LC lenses610may be the same. For illustrative purposes,FIG. 6Ashows the SPP LC lens stack600may include eight SPP LC lenses610, and each SPP LC lens610may include three concentric ring-shaped zones of increasing radii: a first zone610-1, a second zone610-2and a third zone610-3. The first zones610-1of the eight SPP LC lenses610may have the same radius, the second zones610-2of the eight SPP LC lenses610may have the same radius, and the third zones610-3of the eight SPP LC lenses610may have the same radius.

A problem of such an SPP LC lens stack600is that chief rays (ray from an off-axis point in an object passing through the center of an aperture stop) from different off-axis points in the object may experience different phase after transmitted through the SPP LC lens stack600due to the unmatched Fresnel resets. For example, shown inFIG. 6A, a chief ray601may propagate through eight second zones610-2, a chief ray603may propagate through seven second zones610-2and one first zone610-1, a chief ray605may propagate through six second zones610-2and two first zone610-1, and so on, a chief ray613may propagate through eight first zones610-1. That is, chief rays601,603,605,607,609,611and613each may experience a different phase after transmitted through the SPP LC lens stack600due to the unmatched Fresnel resets. As a result, when cutting up the pupil with unmatched Fresnel resets, each slide may have a different phase.

In view of this, in the disclosed embodiments, the SPP LC lens stack may be configured to have Fresnel resets offset.FIG. 6Billustrates a schematic diagram of an SPP LC lens stack650having Fresnel resets offset according to an embodiment of the disclosure. For illustrative purposes,FIG. 6Bshows the SPP LC lens stack650may include eight SPP LC lenses660, and each SPP LC lens660may include three concentric ring-shaped zones or Fresnel resets of increasing radii: a first zone660-1, a second zone660-2and a third zone660-3. The Fresnel resets may be offset by following chief ray from nominal eye relief, such that the number of cuts may be reduced. For example, as shown inFIG. 6B, the first zones660-1of the eight SPP LC lenses660may be offset by following the chief ray607from nominal eye relief, the second zones660-2of the eight SPP LC lenses660may be offset by following the chief ray601from nominal eye relief. Thus, the chief rays601,603and605may experience the same phase, and the chief rays607,609,611and613may experience the same phase. Thus, the number of cuts in the pupil may be reduced. For example, the pupil could still be cut up by 1 mm slices at edge of field.

FIG. 7illustrates a schematic diagram of a light propagation700in a pancake lens assembly100according to an embodiment of the disclosure. The varifocal lens130may be any one of the disclosed SPP LC lens or SPP LC lens stack. InFIG. 7, s denotes s-polarized light, p denotes p-polarized light, R denotes right-handed circularly polarized light, and L denotes left-handed circularly polarized light. In one embodiment, as shown inFIG. 7, light171emitted from the electronic display110may be left-handed circularly polarized light (L) and transmitted to the mirrored surface122. After the left-handed circularly polarized light (L)171reaches the mirrored surface122, a first portion of the light171may be reflected by the mirrored surface122, and a second portion of the light171may be transmitted by the mirrored surface122, becoming left-handed circularly polarized light (L)172propagating towards the waveplate surface124. The waveplate surface124may be a quarter-wave plate that converts the left-handed circularly polarized light (L)172to s-polarized light173, which is incident onto the LC lens130then transmitted as s-polarized light174.

The reflective polarizer surface142may reflect light that is polarized in a blocking direction (e.g., x-axis direction), and transmit light that is polarized in a perpendicular direction (e.g., y-axis direction). That is, the reflective polarizer surface142may transmit p-polarized light and reflect s-polarized light. Thus, the s-polarized light174traveling in the positive z-direction from the LC lens130may be reflected by the reflective polarizer surface142to be s-polarized light175traveling in the negative z-direction. The reflected s-polarized light175may be transmitted through the LC lens130for a second time to be s-polarized light176, which is transmitted through the waveplate surface124for a second time and converted to left-handed circularly polarized light (L)177traveling in the negative z-direction. The left-handed circularly polarized light (L)177traveling in the negative z-direction may be reflect by the mirrored surface122to be right-handed circularly polarized light (R)178, which is then transmitted through the waveplate surface124and converted to be p-polarized light179. The p-polarized light179may be transmitted through the LC lens130for a third time to be p-polarized light180, which is transmitted through the reflective polarizer surface142to be p-polarized light181. The p-polarized light181may be transmitted through the second surface140-2of the second optical element to be incident into the user eye.

Through configuring the light from the electronic display110to be transmitted through the LC lens130three times by polarization controlling, the optical power added to the pancake lens assembly100by the LC lens130may be at least tripled. For example, provided that the first optical element120, the second optical element140and the LC lens130have an optical power of D1, D2 and D3, respectively, the LC lens130may add an optical power of at least tripled D3 to the pancake lens assembly100. That is, the total optical power of the pancake lens assembly100may be equal to at least (D1+D2+3*D3).

For illustrative purposes,FIG. 7shows the light171emitted from the electronic display110is left-handed circularly polarized light (L). In some embodiments, light emitted from the electronic display110may be right-handed circularly polarized light (R). In some embodiments, light emitted from the electronic display110may be linearly polarized light, and a quarter-wave plate may be arranged between the electronic display110and the mirrored surface122, or bonded to or formed on the mirrored surface122to convert the linearly polarized light to circularly polarized light. In some embodiments, light emitted from the electronic display110may be unpolarized light, and a linear polarizer and a quarter-wave plate may be arranged between the electronic display110and the mirrored surface122, or bonded to or formed on the mirrored surface122. The linear polarizer may convert the unpolarized light from the electronic display110to be linear polarized light, and the quarter-wave plate may be orientated relative to the linear polarizer to convert the linear polarized light received from the linear polarizer to circularly polarized light.

In some embodiments, the varifocal lens130, e.g., an SPP LC lens130, may be disposed outside the cavity formed by the first optical element and the second optical element.FIG. 8illustrates a schematic diagram of a pancake lens assembly800according to an embodiment of the disclosure. The similarities betweenFIG. 8andFIG. 1are not explained, while certain difference may be explained. As shown inFIG. 8, the SPP LC lens130may be disposed outside the cavity formed by the first optical element120and the second optical element140. In some embodiments, the SPP LC lens130may be disposed between the first optical element120and the electronic display110, i.e., disposed before the first optical element120in optical series.

Optical series refers to relative positioning of a plurality of optical elements, such that light, for each optical element of the plurality of optical elements, is transmitted by that optical element before being transmitted by another optical element of the plurality of optical elements. Moreover, ordering of the optical elements does not matter. For example, optical element A placed before optical element B, or optical element B placed before optical element A, are both in optical series. Similar to electric circuitry design, optical series represents optical elements with their optical properties compounded when placed in series.

The pancake lens assembly800may further include a quarter-wave plate135disposed between the SPP LC lens130and the first optical element120, and configured to receive a linearly polarized light from the SPP LC lens130. A polarization axis of the quarter-wave plate135may be orientated relative to the polarization direction of the linearly polarized light received from the SPP LC lens130to convert the linearly polarized light to a circularly polarized light to be incident onto the first optical element120.

In some embodiments, when the light190emitted from the electronic display110is a circularly polarized light, a quarter-wave plate may be disposed between the SPP LC lens130and the electronic display110to convert the circularly polarized light to a linearly polarized light that is incident onto the SPP LC lens130. In some embodiments, the SPP LC lens130(e.g., the alignment direction of the SPP LC lens130) may be oriented relative to the polarization direction of the linearly polarized incident light to provide an adjustable optical power to the pancake lens assembly800, thereby realizing a varifocal pancake lens assembly. In some embodiments, when the light190emitted from the electronic display110is a linearly polarized light, the SPP LC lens130(e.g., the alignment direction of the SPP LC lens130) may be oriented relative to the polarization direction of the linearly polarized light to provide an adjustable optical power to the pancake lens assembly800. In some embodiments, when the light190emitted from the electronic display110is a unpolarized light, a linear polarizer may be disposed between the SPP LC lens130and the electronic display110to convert the unpolarized light to a linearly polarized light.

For illustrative purposes,FIG. 8shows the SPP LC lens130is disposed outside the cavity formed by the first optical element120and the second optical element140, and disposed at a side of the cavity facing the electronic display110. In another embodiment, the SPP LC lens130may be disposed at a side of the cavity far away from the electronic display110. For example, the SPP LC lens130may be disposed between the second optical element140and the eye180to receive a linearly polarized light from the second optical element140. That is, the SPP LC lens130may be disposed after the second optical element140in optical series. In some embodiments, the SPP LC lens130(e.g., the alignment direction of the SPP LC lens130) may be oriented relative to the polarization direction of the linearly polarized light to provide an adjustable optical power to the pancake lens assembly800.

In some embodiments, the varifocal lens130may include a Pancharatnam Berry Phase (PBP) LC lens stack.FIG. 9Aillustrates a schematic diagram of a pancake lens assembly900according to an embodiment of the disclosure. The similarities betweenFIG. 9AandFIG. 1are not explained, while certain difference may be explained. As shown inFIG. 9A, the varifocal lens130may include a Pancharatnam Berry Phase (PBP) LC lens stack150, which is arranged outside the cavity formed by the first optical element120and the second optical element140. The PBP LC lens stack150may be disposed at a side of the cavity facing the electronic display110, for example, between the first optical element120and the electronic display110. That is, the PBP LC lens stack150may be disposed before the first optical element120in optical series. The PBP LC lens stack150may provide a plurality of discrete focal states (or optical states).

FIG. 10illustrates a schematic diagram of a Pancharatnam Berry Phase (PBP) LC lens stack1000according to an embodiment of the disclosure. As shown inFIG. 10, the PBP LC lens stack1000may include a plurality of PBP LC lenses and a plurality of switchable half-wave plates (SHWPs). The PBP LC lenses and SHWPs may be alternately arranged. For illustrative purposes,FIG. 10shows the PBP LC lens stack1000may include SHWPs1010,1030,1050and PBP LC lenses1020,1040,1060alternately arranged. The SHWP1010,1030,1050may be a half-waveplate that transmits a polarized light of a specific handedness in accordance with a switching state of the SHWP. The PBP LC lens1020,1040,1060may provide an optical power according to the handedness of circularly polarized light incident on the PBP LC lens1020,1040,1060.

FIG. 11illustrates a schematic diagram of a PBP LC lens1100according to an embodiment of the disclosure. As shown inFIG. 11, the PBP LC lens1100may create a lens profile via an in-plane orientation (θ, azimuth angle) of liquid crystal (LC) molecules. The phase difference of the PBP LC lens1100may be calculated as T=2θ.FIG. 12Aillustrates LC orientations1200in the PBP LC lens1100shown inFIG. 11. As shown inFIG. 12A, in the PBP LC lens1100, an azimuth angle (θ) of an LC molecule1212may be continuously changed from a center12114to an edge1216of the PBP LC lens1100, with a varied pitch Λ. Pitch is defined in a way that the azimuth angle of LC is rotated 180° from the initial state.FIG. 12Billustrates a section of LC orientations1250taken along y-axis in the PBP LC lens1100shown inFIG. 11. As shown inFIG. 12B, a rate of pitch variation may be a function of distance from the lens center1214. The rate of pitch variation may increase with distance from the lens center. For example, the pitch at the lens center1214(Λ0) may be the slowest, and the pitch at the edge1216(Λr) may be the highest, i.e., Λ0>Λ1> . . . >Λr.

Returning toFIG. 11, in the x-y plane, to obtain a PBP LC lens with lens radius (r) and lens power (+/−f), the azimuth angle θ may satisfy:

2⁢θ=π⁢⁢r2f*λ,(2)
where λ is the wavelength of incident light. The PBP LC lens1100may be active (also referred to as an active element) or passive (also referred to as a passive element). An active PBP LC lens may have three discrete focal states (also referred to as optical states). The three optical states are an additive state, a neutral state, and a subtractive state. In particular, the additive state may add optical power to the system (i.e., have a positive focus of ‘f’), and the subtractive state may subtract optical power from the system (i.e., have a negative focus of ‘−f’). When not in the neutral state, the active PBP LC lens may reverse the handedness of circularly polarized light passing through the active PBP LC lens in addition to focusing/defocusing the incident light. When in the neutral state, the active PBP LC lens may not affect the optical power of the system, but may or may not affect the polarization of light transmitted through the active PBP LC lens.

The state of an active PBP LC lens may be determined by the handedness of polarization of light incident on the active PBP LC lens and an applied voltage. In some embodiments, as shown inFIG. 11, an active PBP LC lens may operate in an additive state that adds optical power to the system in response to incident light with a right-handed circular polarization and an applied voltage of zero (or more generally below some minimal value), operate in a subtractive state that removes optical power from the system in response to incident light with a left-handed circular polarization and the applied voltage of zero (or more generally below some minimal value), and operate in a neutral state (regardless of polarization) that does not affect the optical power of the system in response to an applied voltage larger than a threshold voltage that aligns LCs along with the electric field.

In contrast, a passive PBP LC lens may have two optical states: an additive state and a subtractive state. The state of a passive PBP LC lens may be determined by the handedness of circularly polarized light incident on the passive PBP LC lens. In some embodiments, referring toFIG. 11, a passive PBP LC lens may operate in an additive state that adds optical power to the system in response to incident light with a right-handed circular polarization, and operate in a subtractive state that removes optical power from the system in response to incident light with a left-handed circular polarization. A passive PBP LC lens may output light that has a handedness opposite that of the light input into the passive PBP LC lens.

Returning toFIG. 10, the PBP LC lens stack1000may control the handedness of a circularly polarized light incident onto a PBP LC lens in accordance with a switching state of a SHWP. The switching state of the SHWP is either active or non-active. When active, the SHWP may reverse the handedness of polarized light, and when non-active, the SHWP may transmit the circularly polarized light without affecting the handedness. As discussed above, in some embodiments, a PBP LC lens acts in an additive state when receiving right-handed circularly polarized (RCP) light, and conversely, acts in a subtractive state if when receiving left-handed circularly polarized (LCP) light. Accordingly, a SHWP placed before a PBP LC lens in optical series may be able to control whether the PBP LC lens acts in an additive or subtractive state by controlling the handedness of the circularly polarized light incident onto the PBP LC lens.

As shown inFIG. 10, input light1005may be left-handed circularly polarized (LCP) light or right-handed circularly polarized (RCP) light. The state of the SHWP1010,1030,1050may determine the handedness of the light output from the SHWP1010,1030,1050. When not in a neutral state, an active PBP LC lens may reverse the handedness of circularly polarized light in addition to focusing/defocusing the incident light. Hence, when the input light1005is left-handed circularly polarized (LCP) light and the SHWP1010is active, the PBP LC lens1020may receive right-handed circularly polarized (RCP) light and output left-handed circularly polarized (LCP) light with an increment of optical power of R. When the input light1005is right-handed circularly polarized (RCP) light and the SHWP1010is active, the PBP LC lens1020may receive left-handed circularly polarized (LCP) light and output right-handed circularly polarized (RCP) light with a reduction of optical power of −R. When non-active, the SHWP1010may transmit the input light1005without affecting the handedness. The operation principle of the SHWP1030,1050and PBP LC lens1040,1060may refer to that of the SHWP1010and the PBP LC lens1020, and the details are not repeated here. The design of the PBP LC lens stack shown inFIG. 10is merely for illustrative purposes, and other designs of the PBP LC lens stack may be used according to various application scenarios.

Referring toFIG. 10andFIG. 9A, design specifications for HMDs used for VR, AR, or MR applications typically requires a large range of optical power to adapt for human eye vergence-accommodation (e.g., ˜±2 Diopters or more), fast switching speed (about 300 ms), and a good quality image. A PBP LC lens is able to meet these design specifications using LC materials having a relatively high index of refraction. The PBP LC lens stack150may provide any number of focus planes from two focus planes to more than two focus planes. Further, through increasing the number of PBP LC lenses and SHWPs in the PBP LC lens stack150, the number of focal planes may be increased, and the focal length interval (i.e., the resolution step of the PBP LC lens stack) may be reduced, thereby providing a continuous varifocal optical power merely by the PBP LC lens stack150. In other words, a varifocal pancake lens assembly may be realized. Further, the response time of the PBP LC lens stack150may be limited by the response of the SHWP which can be less than 1 ms by using ferroelectric SHWP. The maximum response time of the SHWP may be less than 15 ms when using a twisted nematic (TN) SHWP.

In some embodiments, the PBP LC lens stack150may be disposed at a side of the cavity facing away from the electronic display110.FIG. 9Billustrates a schematic diagram of a pancake lens assembly950according to an embodiment of the disclosure. The similarities betweenFIG. 9BandFIG. 1are not explained, while certain difference may be explained. As shown inFIG. 9B, the PBP LC lens stack150may be disposed between the second optical element140and the eye180. That is, the PBP LC lens stack150may be disposed after the second optical element140in optical series.

The second optical element140may further include a waveplate surface144in addition to the reflective polarizer surface142, which is a separate layer or coating bonded to or formed on the second optical element140. In some embodiments, the waveplate surface144may be bonded to or formed on the second surface140-2of the second optical element140, and the reflective polarizer surface142may be bonded to or formed on the first surface140-1of the second optical element140. In some embodiments, the waveplate surface144may include a quarter-wave plate (QWP) similar to the waveplate surface124of the first optical element120. The waveplate surface144may convert a linearly polarized light received from the reflective polarizer surface142to a circularly polarized light, which is incident onto the PBP LC lens stack150.

In some embodiments, the pancake lens assembly may include both an LC lens (e.g., an SPP LC lens) and a PBP LC lens stack. The PBP LC lens stack may provide a plurality of discrete focal states in a first step resolution, and the SPP LC lens may provide visually continuously variable focal states (i.e., a continuous range of adjustment of optical power) in a second step resolution. The first step resolution may be configured to be smaller than the second step resolution, such that when the PBP LC lens stack is switched between two discrete optical states, the LC lens may provide a continuous adjustment of optical power between the two discrete optical states. The PBP LC lens stack and the varifocal lens together may provide a continuous adjustment of optical power for the system (e.g., HMDs).

FIG. 13illustrates a schematic diagram of a pancake lens assembly1300having hybrid lenses according to an embodiment of the disclosure. The similarities betweenFIG. 13andFIG. 1are not explained, while certain difference may be explained. As shown inFIG. 13, the second optical element140may further include a waveplate surface144in addition to the reflective polarizer surface142, which is a separate layer or coating bonded to or formed on the second optical element140. In some embodiments, the waveplate surface144may be bonded to or formed on the second surface140-2of the second optical element140, and the reflective polarizer surface142may be bonded to or formed on the first surface140-1of the second optical element140. In some embodiments, the waveplate surface144may include a quarter-wave plate (QWP) similar to the waveplate surface124of the first optical element120. The SPP LC lens130may be arranged between the first optical element120and the second optical element140, and the PBP LC lens stack150may be arranged between the second optical element140and the eye180.

In some embodiments, the PBP LC lens stack150may be arranged between the first optical element120and the electronic display110. The PBP LC lens stack150may be configured to provide a plurality of discrete focal states in a relatively large step resolution. The SPP LC lens130may be configured to have a continuous adjustment range of optical power equal to or larger than the step resolution of the PBP LC lens stack150. Herein the continuous adjustment range of optical power of the SPP LC lens130refers to a range from the minimum optical power to the maximum optical power of the SPP LC lens130. Further, the SPP LC lens130may be configured to provide the continuous adjustment range of optical power in a relatively small step resolution when switching among the discrete focal states of the PBP LC lens stack150. Because the step resolution of the SPP LC lens130is often too small to be perceived by human eyes, for example, the step resolution of the SPP LC lens130may be smaller than 1/10 of the second step resolution of PBP LC lens stack150, the PBP LC lens stack150and the SPP LC lens130together may provide continuously variable focal states (i.e., a continuous adjustment range of optical power) for the system. Thus, when switching among the discrete focusing states of the PBP LC lens stack150, the image distortion caused by large step resolution of the PBP LC lens stack150may be suppressed, and smoother transition between different focal states may be perceived by the human eyes. The continuous adjustment range of optical power of the PBP lens assembly800may be determined by the optical power of the PBP LC lens stack150, for example, a range from the maximum optical power to the minimum optical power of the PBP LC lens stack150.

FIG. 14illustrates a schematic diagram of a light propagation1400in the pancake lens assembly1300inFIG. 13. The similarities betweenFIG. 14andFIG. 7are not explained, while certain difference may be explained. As shown inFIG. 14, when the waveplate surface144is a quarter-wave plate, the p-polarized181may be converted to right-handed circularly polarized light (R)182after transmitted through the waveplate surface144. The right-handed circularly polarized light (R)182may be incident on the PBP LC lens stack150. Through controlling the switching state of the SWHPs in the PBP LC lens stack150, the pancake lens assembly800may provide a continuous adjustment of optical power to the system.

In some embodiments, the PBP LC lens stack and the SPP LC lens may be disposed outside the cavity and disposed at different sides of the cavity.FIG. 15Aillustrates a schematic diagram of a pancake lens assembly1500according to an embodiment of the disclosure. The similarities betweenFIG. 15AandFIG. 8are not explained, while certain difference may be explained. As shown inFIG. 15A, in the pancake lens assembly1500, the SPP LC lens130may be disposed between the first optical element120and the electronic display110, the quarter-wave plate135may be disposed between the first optical element120and the SPP LC lens130. The second optical element140may further include the reflective polarizer surface144, and the PBP LC lens stack150may be disposed between the second optical element140and the eye180. The details can be referred to the descriptions ofFIG. 8andFIG. 9b, and are not repeated here.

FIG. 15Billustrates a schematic diagram of a pancake lens assembly1550according to an embodiment of the disclosure. The similarities betweenFIG. 15BandFIG. 9Aare not explained, while certain difference may be explained. As shown inFIG. 15B, in the pancake lens assembly1550, the PBP LC lens stack150may be disposed between the first optical element120and the electronic display110, and the SPP LC lens130may be disposed between the second optical element140and the eye180.

In some embodiments, the SPP LC lens130and the PBP LC lens stack150may be disposed outside the cavity and disposed at the same side of the cavity.FIG. 16Aillustrates a schematic diagram of a pancake lens assembly1600according to an embodiment of the disclosure. The similarities betweenFIG. 16AandFIG. 9Bare not explained, while certain difference may be explained. As shown inFIG. 16A, in the pancake lens assembly1600, both the SPP LC lens130and the PBP LC lens stack150may be disposed between the second optical element140and the eye180. The SPP LC lens130may be disposed between the PBP LC lens stack150and the eye180. Further, a quarter-wave plate145may be disposed between the PBP LC lens stack150and the SPP LC lens130to convert a circularly polarized light received from the PBP LC lens stack150to a linearly polarized light, which is incident to the SPP LC lens130. In some embodiments, the SPP LC lens130(e.g., the alignment direction of the SPP LC lens130) may be oriented relative to the polarization direction of the linearly polarized incident light to provide an adjustable optical power.

FIG. 16Billustrates a schematic diagram of a pancake lens assembly1650according to an embodiment of the disclosure. The similarities betweenFIG. 16BandFIG. 16Aare not explained, while certain difference may be explained. As shown inFIG. 16B, in the pancake lens assembly1650, the SPP LC lens130and the PBP LC lens stack150may be both disposed between the second optical element140and the eye180, and the PBP LC lens stack150may be disposed between the SPP LC lens130and the eye180. The quarter-wave plate145may be disposed between the PBP LC lens stack150and the SPP LC lens130, and the polarization axis of the quarter-wave plate145may be oriented relative to the polarization direction of a linearly polarized light received from the SPP LC lens130to convert the linearly polarized light to a circularly polarized light, which is incident onto the PBP LC lens stack150.

FIG. 17Aillustrates a schematic diagram of a pancake lens assembly1700according to an embodiment of the disclosure. The similarities betweenFIG. 17AandFIG. 8are not explained, while certain difference may be explained. As shown inFIG. 17A, in the pancake lens assembly1700, both the SPP LC lens130and the PBP LC lens stack150may be disposed between the first optical element120and the electronic display110, and the PBP LC lens stack150may be disposed between the first optical element120and the SPP LC lens130. Further, a quarter-wave plate155may be disposed between the SPP LC lens130and the PBP LC lens stack150. The quarter-wave plate155may convert a circularly polarized light received from the PBP LC lens stack150to a linearly polarized light, which is incident onto the SPP LC lens130.

FIG. 17Billustrates a schematic diagram of a pancake lens assembly1750according to an embodiment of the disclosure. The similarities betweenFIG. 17BandFIG. 8are not explained, while certain difference may be explained. As shown inFIG. 17B, in the pancake lens assembly1750, the PBP LC lens stack150may be disposed between the first optical element120and the SPP LC lens130, and the quarter-wave plate135may be disposed between the SPP LC lens130and the PBP LC lens stack150. Provide that the light190emitted from the electronic display110is a circularly polarized light, a quarter-wave plate165may be disposed between the SPP LC lens130and the electronic display110to convert the circularly polarized light to a linearly polarized light, which is incident onto the SPP LC lens130. The quarter-wave plate135that is disposed between the SPP LC lens130and the PBP LC lens stack150may convert a linearly polarized light received from the SPP LC lens130to a circularly polarized light, which is incident onto the PBP LC lens stack150.

FIG. 18illustrates a block diagram of a system environment1800according to an embodiment of the disclosure. As shown inFIG. 18, the system environment1800may include an HMD1805, a console1810, an imaging device1835, and an input/output interface1840. The HMD1805, the imaging device1835, and the input/output interface1840may be coupled to the console1810. AlthoughFIG. 18shows an example system1800including one HMD1805, one imaging device1835, and one input interface1840, in some other embodiments, any number of these components may be included in the system environment1800. For example, the system environment1800may include multiple HMDs1805each having an associated input interface1840and being monitored by one or more imaging devices1835, and each HMD1805, input interface1840, and imaging device1835may communicate with the console1810. In some embodiments, different and/or additional components may be included in the system environment1800. The system environment1800may operate in a VR system environment, an AR system environment, a MR system environment, or some combination thereof.

The HMD1805may be a head-mounted display that presents media to a user. Examples of media presented by the HMD include one or more images, video, audio, or some combination thereof. In some embodiments, audio may be presented via an external device (e.g., speakers and/or headphones) which receives audio information from the HMD1805, the console1810or both, and presents audio data based on the audio information. An example of the HMD1805may be further described below in connection withFIGS. 19A and 19B.

The HMD1805may include one or more rigid bodies, which may be rigidly or non-rigidly coupled to each other. A rigid coupling between rigid bodies may cause the coupled rigid bodies to act as a single rigid entity. In contrast, a non-rigid coupling between rigid bodies may allow the rigid bodies to move relative to each other. In some embodiments, the HMD1805may present VR, AR, MR, or some combination thereof to the user. In the VR, AR and/or MR embodiments, the HMD1805may augment views of a physical, real-world environment with computer-generated elements (e.g., images, video, sound, etc.).

As shown inFIG. 18, the HMD1805may include an electronic display block1815, a pancake lens assembly1817, one or more locators1820, one or more position sensors1825, and an inertial measurement unit (IMU)1830. The electronic display block1815may display images to the user in accordance with data received from the console1810. In some embodiments, the electronic display block1815may include an electronic display and an optics block. The electronic display may generate image light. In some embodiments, the electronic display may include a single electronic display or multiple electronic displays (e.g., a display for each eye of a user). Examples of the electronic display may include: a liquid crystal display (LCD), an organic light emitting diode (OLED) display, an active-matrix organic light-emitting diode display (AMOLED), a transparent organic light emitting diode display (TOLED), some other display, a projector, or a combination thereof.

The optics block may include combinations of different optical elements. An optical element may be an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, or any other suitable optical element that affects the image light emitted from the electronic display. In some embodiments, one or more of the optical elements in the optics block may have one or more coatings, such as anti-reflective coatings. Magnification of the image light by the optics block may allow elements of the electronic display to be physically smaller, weigh less, and consume less power than larger displays. Additionally, magnification may increase a field of view of the displayed media. For example, the field of view of the displayed media may be widened, such that the displayed media may be presented using almost all (e.g., 110 degrees diagonal), and in some cases all, of the user's field of view. In some embodiments, the optics block may be designed to have an effective focal length larger than the spacing to the electronic display, thereby magnifying the image light projected by the electronic display. Additionally, in some embodiments, the amount of magnification may be adjusted by adding or removing optical elements.

The pancake lens assembly1817may be any one of the disclosed pancake lens assembly which is achromatic due to the compensation of the PBP LC lens. In some embodiments, the pancake lens assembly1817may be configured as a monolithic pancake lens assembly without any air gaps between optical elements of the pancake lens assembly. The pancake lens assembly1817may also magnify received light from the electronic display, correct optical aberrations associated with the image light, and the corrected image light may be presented to a user of the HMD1805.

The locators1820may be objects located at various positions on the HMD1805relative to one another and relative to a specific reference point on the HMD1805. A locator1820may be a light emitting diode (LED), a corner cube reflector, a reflective marker, a type of light source that contrasts with an environment in which the HMD1805operates, or a combination thereof. In some embodiments, when the locators1820may be active (i.e., an LED or other type of light-emitting device) elements, the locators1820may emit light in the visible band (about 380 nm to about 1850 nm), in the infrared (IR) band (about 1850 nm to about 1 mm), in the ultraviolet band (about 10 nm to about 380 nm), another portion of the electromagnetic spectrum, or a combination thereof.

In some embodiments, the locators1820may be located beneath an outer surface of the HMD1805, which can be transparent to the wavelengths of light emitted or reflected by the locators1820or can be thin enough to not substantially attenuate the wavelengths of light emitted or reflected by the locators1820. In some embodiments, the outer surface or other portions of the HMD1805may be opaque in the visible band of wavelengths of light. Thus, the locators1820may emit light in the IR band under an outer surface that may be transparent in the IR band but opaque in the visible band.

The IMU1830may be an electronic device that generates fast calibration data based on measurement signals received from one or more of the position sensors1825. A position sensor1825may generates one or more measurement signals in response to motion of the HMD1805. Examples of position sensors1825may include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU1830, or one or more combinations thereof. The position sensors1825may be located external to the IMU1830, internal to the IMU1830, or a combination thereof.

Based on the one or more measurement signals from one or more position sensors1825, the IMU1830may generates fast calibration data indicating an estimated position of the HMD1805relative to an initial position of the HMD1805. For example, the position sensors1825may include multiple accelerometers to measure translational motion (forward/back, up/down, left/right) and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, roll). In some embodiments, the IMU1830may rapidly samples the measurement signals and calculates the estimated position of the HMD1805from the sampled data. For example, the IMU1830may integrate the measurement signals received from the accelerometers over time to estimate a velocity vector and integrates the velocity vector over time to determine an estimated position of a reference point on the HMD1805. In some embodiments, the IMU1830may provide the sampled measurement signals to the console1810, which determines the fast calibration data. The reference point may be a point that may be used to describe the position of the HMD1805. While the reference point may generally be defined as a point in space; however, in practice the reference point may be defined as a point within the HMD1805(e.g., a center of the IMU1830).

The IMU1830may receive one or more calibration parameters from the console1810. As further discussed below, the one or more calibration parameters may be used to maintain tracking of the HMD1805. Based on a received calibration parameter, the IMU1830may adjust one or more IMU parameters (e.g., sample rate). In some embodiments, certain calibration parameters may cause the IMU1830to update an initial position of the reference point, so it corresponds to a next calibrated position of the reference point. Updating the initial position of the reference point as the next calibrated position of the reference point may help reduce accumulated error associated with the determined estimated position. The accumulated error, also referred to as drift error, may cause the estimated position of the reference point to “drift” away from the actual position of the reference point over time.

The imaging device1835may generate slow calibration data in accordance with calibration parameters received from the console1810. Slow calibration data may include one or more images showing observed positions of the locators1820that may be detectable by the imaging device1835. The imaging device1835may include one or more cameras, one or more video cameras, any other device capable of capturing images including one or more of the locators1820, or some combination thereof. Additionally, the imaging device1835may include one or more filters (e.g., used to increase signal to noise ratio). The imaging device1835may be configured to detect light emitted or reflected from locators1820in a field of view of the imaging device1835.

In some embodiments, when the locators1820include passive elements (e.g., a retroreflector), the imaging device1835may include a light source that illuminates some or all of the locators1820, which retro-reflect the light towards the light source in the imaging device1835. Slow calibration data may be communicated from the imaging device1835to the console1810, and the imaging device183may receive one or more calibration parameters from the console1810to adjust one or more imaging parameters (e.g., focal length, focus, frame rate, ISO, sensor temperature, shutter speed, aperture, etc.).

The input interface1840may be a device that allows a user to send action requests to the console1810. An action request may be a request to perform a particular action. For example, an action request may be to start or end an application or to perform a particular action within the application. The input interface1840may include one or more input devices. Example input devices may include: a keyboard, a mouse, a game controller, or any other suitable device for receiving action requests and communicating the received action requests to the console1810. An action request received by the input interface1840may be communicated to the console1810, which performs an action corresponding to the action request. In some embodiments, the input interface1840may provide haptic feedback to the user in accordance with instructions received from the console1810. For example, haptic feedback may be provided when an action request may be received, or the console1810may communicate instructions to the input interface1840causing the input interface1840to generate haptic feedback when the console1810performs an action.

The console1810may provide media to the HMD1805for presentation to the user in accordance with information received from one or more of: the imaging device1835, the HMD1805, and the input interface1840. In some embodiments, as shown inFIG. 18, the console1810may include an application store1845, a tracking module1850, and a virtual reality (VR) engine1855. In some embodiments, the console1810may include modules different from those described in conjunction withFIG. 18. Similarly, the functions further described below may be distributed among components of the console1810in a different manner than may be described here.

The application store1845may store one or more applications for execution by the console1810. An application may be a group of instructions, that when executed by a processor, may generate content for presentation to the user. Content generated by an application may be in response to inputs received from the user via movement of the HMD1805or the input interface1840. Examples of applications may include gaming applications, conferencing applications, video playback application, or other suitable applications.

The tracking module1850may calibrate the system1800using one or more calibration parameters and may adjust one or more calibration parameters to reduce error in determination of the position of the HMD1805. For example, the tracking module1850may adjust the focus of the imaging device1835to obtain a more accurate position for observed locators on the HMD1805. Moreover, calibration performed by the tracking module1850may also account for information received from the IMU1830. Additionally, when tracking of the HMD1805may be lost (e.g., the imaging device1835loses line of sight of at least a threshold number of the locators1820), the tracking module1850may re-calibrate some or all of the system environment1800.

The tracking module1850may track movements of the HMD1805using slow calibration information from the imaging device1835. The tracking module1850may determine positions of a reference point of the HMD1805using observed locators from the slow calibration information and a model of the HMD1805. The tracking module1850may also determine positions of a reference point of the HMD1805using position information from the fast calibration information. Additionally, in some embodiments, the tracking module1850may use portions of the fast calibration information, the slow calibration information, or some combination thereof, to predict a future location of the HMD1805. The tracking module1850may provide the estimated or predicted future position of the HMD1805to the engine1855.

The engine1855may execute applications within the system environment1800and receives position information, acceleration information, velocity information, predicted future positions, or some combination thereof of the HMD1805from the tracking module1850. Based on the received information, the engine1855may determine content to provide to the HMD1805for presentation to the user. For example, when the received information indicates that the user has looked to the left, the engine1855may generate content for the HMD1805that mirrors the user's movement in a virtual environment. Additionally, the engine1855may perform an action within an application executing on the console1810in response to an action request received from the input interface1840, and provide feedback to the user that the action was performed. The provided feedback may be visual or audible feedback via the HMD1805or haptic feedback via the input interface1840.

FIG. 19Aillustrates a schematic diagram of the HMD1805inFIG. 18. Referring toFIG. 19AandFIG. 18, the HMD1805may include a front rigid body1905and a band1910. The front rigid body1905may include one or more electronic display elements of the electronic display and optics block (not shown inFIG. 19A), the IMU1830, the one or more position sensors1825, and the locators1820. In the embodiment shown inFIG. 19A, the position sensors1825may be located within the IMU1830, and neither the IMU1830nor the position sensors1825may be visible to the user.

The locators1820may be located at fixed positions on the front rigid body1905relative to one another and relative to a reference point1915. In the embodiment shown inFIG. 19A, the reference point1915may be located at the center of the IMU1830. Each of the locators1820may emit light that may be detectable by the imaging device1835. The locators1820, or some of the locators1820, may be located on a front side1920A, a top side1920B, a bottom side1920C, a right side1920D, and a left side1920E of the front rigid body1905.

FIG. 19Billustrates a schematic diagram of the front rigid body1905of the HMD1805shown inFIG. 19A. As shown inFIG. 19B, the front rigid body1905may include an electronic display1928and the pancake lens assembly1817that provides altered image light to an exit pupil1935. The exit pupil1935may be at a location of the front rigid body1905where a user's eye1940may be positioned. For illustrative purposes,FIG. 19Bshows a cross-section of the front rigid body1905associated with a single eye1940, while another electronic display, separate from the electronic display1928, can provide image light altered by the optics block to another eye of the user.

The foregoing description of the embodiments of the disclosure have been presented for the purpose of illustration. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.