Methods and apparatuses for casting optical polymer films

In an example method of forming an optical film for an eyepiece, a curable material is dispensed into a space between a first and a second mold surface. A position of the first mold surface relative to the second mold surface is measured using a plurality of sensors. Each sensor measures a respective relative distance along a respective measurement axis between a respective point on a planar portion of the first mold surface and a respective point on a planar portion of the second mold surface. The measurement axes are parallel to each other, and the points define corresponding triangles on the first and second mold surfaces, respectively. The position of the first mold surface is adjusted relative to the second mold surface based on the measured position, and the curable material is cured to form the optical film.

TECHNICAL FIELD

This disclosure relates to optical polymer films and methods for producing the same.

BACKGROUND

Optical imaging systems, such as wearable imaging headsets, can include one or more eyepieces that present projected images to a user. Eyepieces can be constructed using thin layers of one or more highly refractive materials. As examples, eyepieces can be constructed from one or more layers of highly refractive glass, silicon, metal, or polymer substrates.

In some cases, an eyepiece can be patterned (e.g., with one or more light diffractive nanostructures), such that it projects an image according to a particular focal depth. For an example, to a user viewing a patterned eyepiece, the projected image can appear to be a particular distance away from the user.

Further, multiple eyepieces can be used in conjunction to project a simulated three-dimensional image. For example, multiple eyepieces—each having a different pattern—can be layered one atop another, and each eyepiece can project a different depth layer of a volumetric image. Thus, the eyepieces can collectively present the volumetric image to the user across three-dimensions. This can be useful, for example, in presenting the user with a “virtual reality” environment or an “augmented reality” environment.

To improve the quality of a projected image, an eyepiece can be constructed such that unintended variations in the eyepiece are eliminated, or otherwise reduced. For example, an eyepiece can be constructed such that it does not exhibit any wrinkles, uneven thicknesses, or other physical distortions that might negatively affect the performance of the eyepiece.

SUMMARY

System and techniques for producing polymer films are described herein. One or more of the described implementations can be used to produce polymer film in a highly precise, controlled, and reproducible manner. The resulting polymer films can be used in a variety of variation-sensitive applications in which extremely tight tolerances on film dimensions are desired. For instance, the polymer films can be used in optical applications (e.g., as a part of eyepieces in a head mounted display device, such as one used for presenting virtual reality content and/or augmented reality content) in which material homogeneity and dimensional constraints are on the order of optical wavelengths or smaller.

In general, polymer films are produced by enclosing a photocurable material (e.g., a photopolymer or light-activated resin that hardens when exposed to light) between two mold structures, and curing the material (e.g., by exposing the material to light and/or heat). The physical characteristics of the polymer film (e.g., the thickness and shape of the polymer film) can be controlled, at least in part, by controlling the position of the mold structures relative to one another during the curing process. To facilitate accurate positioning of the mold structures, a system can measure the positions of at least three points on each of the mold structures (e.g., three non-linear points that form a notional triangle on a planar surface of the mold structure). Based on this information, the system can determine the position of the mold structures in space, and adjust the position of one or more of the mold structures to reduce or eliminate misalignment between the opposing mold surfaces that contact the polymer film. For example, where surfaces of the mold structures are to be arranged parallel to one another, the system can reduce or eliminate any deviation of the surfaces from parallel. Accordingly, variations in thickness and/or distortions in the resulting polymer film may be reduced.

In an aspect, method of forming an optical film for an eyepiece includes dispensing a curable material into a space between a first mold surface and a second mold surface opposite the first mold surface, and measuring, using a plurality of sensors, a position of the first mold surface relative to the second mold surface, Measuring the position of the first mold surface relative to the second mold surface includes determining a first relative distance along a first measurement axis between a first point on a planar portion of the first mold surface and a first point on a planar portion of the second mold surface using a first of the sensors, determining a second relative distance along a second measurement axis between a second point on the planar portion of the first mold surface and a second point on the planar portion of the second mold surface using a second of the sensors, and determining a third relative distance along a third measurement axis between a third point on the planar portion of the first mold surface and a third point on the planar portion of the second mold surface using a third of the sensors. The first, second, and third measurement axes are parallel to each other. The first, second, and third points define corresponding triangles on the first and second mold surfaces, respectively. The space between the first and second mold surfaces is located within the triangles. The method also includes adjusting the position of the first mold surface relative to the second mold surface based on the measured position, and curing the curable material in the space to form the optical film.

In some implementations, the position of the first mold surface relative to the second mold surface can be measured prior to curing the curable material.

In some implementations, the position of the first mold surface relative to the second mold surface can be measured concurrently with curing the curable material.

In some implementations, the position of the first mold surface relative to the second mold surface can be measured continuously over time.

In some implementations, the position of the first mold surface relative to the second mold surface can be adjusted prior to curing the curable material.

In some implementations, the position of the first mold surface relative to the second mold surface can be adjusted concurrently with curing the curable material.

In some implementations, the position of the first mold surface relative to the second mold surface is adjusted continuously over time.

In some implementations, adjusting the position of the first mold surface relative to the second mold surface can include determining, based on the position of the first mold surface relative to the second mold surface, one or more adjustments to at least one of a position of the first mold surface or a position of the second mold surface to reduce an angle between the planar portion of the first mold surface and the planar portion of the second mold surface. Adjusting the position of the first mold surface relative to the second mold surface can also include activating one or more actuators to move the at least one of the first mold surface or the second mold surface according to the one or more determined adjustments.

In some implementations, the one or more adjustments can include at least one of a translation of at least one of the first mold surface or the second mold surface along an axis of translation, or a rotation of at least one of the first mold surface or the second mold surface about an axis of rotation.

In some implementations, the axis of translation can be substantially parallel to the first, second, and third measurement axes.

In some implementations, the axis of rotation can be substantially orthogonal to the first, second, and third measurement axes.

In some implementations, adjusting the position of the first mold surface relative to the second mold surface can include determining, based on the first relative distance along a first measurement axis, the second relative distance along a second measurement axis, and the third relative distance along a third measurement axis: coordinates (x1, y1, z1) of the first point on the planar portion of the first mold surface or the first point on the planar portion of the second mold surface with respect to a Cartesian coordinate system, coordinates (x2, y2, z2) of the second point on the planar portion of the first mold surface or the second point on the planar portion of the second mold surface with respect to the Cartesian coordinate system, and coordinates (x3, y3, z3) of the third point on the planar portion of the first mold surface or the third point on the planar portion of the second mold surface with respect to the Cartesian coordinate system.

In some implementations, adjusting the position of the first mold surface relative to the second mold surface can include determining the one or more adjustments are determined according to a relationship

[y⁢1-x⁢11y⁢2-x⁢21y⁢3-x⁢31][R⁢xR⁢yZ]=[z⁢1z⁢2z⁢3],
where Z corresponds to the translation of at least one of the first mold surface or the second mold surface along an axis of translation, where Rx corresponds to the rotation of at least one of the first mold surface or the second mold surface about a first axis of rotation, and where Ry corresponds to the rotation of at least one of the first mold surface or the second mold surface about a second axis of rotation.

In some implementations, the plurality of sensors can include one or more low-coherence interferometry (LCI) sensors.

In some implementations, the one or more LCI sensors can be mounted on a first mold portion that includes the first mold surface or a second mold portion that comprises the second mold surface. Measuring the position of the first mold surface relative to the second mold surface can include directing an optical beam from each of the one or more LCI sensors along a corresponding measurement axis so that, for each LCI sensor, a first portion of the optical beam reflects from the first mold surface and a second portion of the optical beam reflects from the second mold surface, The reflected portions of the optical beam can be detected by the LCI sensor.

In some implementations, the one or more LCI sensors can be mounted remote from the first mold surface or the second mold portion. Directing the optical beam from at least one of the LCI sensors can include reflecting the optical beam with a mirror toward the first and second mold surfaces.

In some implementations, the curable material can include a photocurable material. Curing the curable material to form the optical film can include irradiating the photocurable material with radiation suitable for photocuring the photocurable material.

In some implementations, the curable material can be confined entirety within the space between the first mold surface and the second mold surface during the curing of the curable material.

In some implementations, the method further include separating the optical film from the first mold portion and the second mold portion.

In some implementations, the method can further include assembling a head mounted display including the optical film formed using one or more of the methods described herein.

In another aspect, a system for forming an optical film for an eyepiece includes system having a first mold portion, a second mold portion, a dispenser, a measurement apparatus, one or more actuators, and a curing apparatus. The first mold portion has a first mold surface. The second mold portion has a second mold surface, where the first mold surface is opposite the first mold surface. The measurement apparatus includes a plurality of sensors. The one or more actuators are coupled to at least one of the first mold portion or the second mold portion. The dispenser is configured, during operation of the system, to dispense a curable material into a space between the first mold surface. The measurement apparatus is configured, during operation of the system, to measure a position of the first mold surface relative to the second mold surface. Measuring the position of the first mold surface relative to the second mold surface comprises includes determining a first relative distance along a first measurement axis between a first point on a planar portion of the first mold surface and a first point on a planar portion of the second mold surface using a first of the sensors, determining a second relative distance along a second measurement axis between a second point on the planar portion of the first mold surface and a second point on the planar portion of the second mold surface using a second of the sensors, and determining a third relative distance along a third measurement axis between a third point on the planar portion of the first mold surface and a third point on the planar portion of the second mold surface using a third of the sensors. The first, second, and third measurement axes are parallel to each other. The first, second, and third points define corresponding triangles on the first and second mold surfaces, respectively. The space between the first and second mold surfaces is located within the triangles. The one or more actuators are configured, during operation of the system, to adjust the position of the first mold surface relative to the second mold surface based on the measured position. The curing apparatus is configured, during operation of the system, to cure the curable material in the space to form the optical film.

In some implementations, the measurement apparatus can be configured, during operation of the system, to measure the position of the first mold surface relative to the second mold surface is prior to the curing the curable material by the curing apparatus.

In some implementations, the measurement apparatus can be configured, during operation of the system, to measure the position of the first mold surface relative to the second mold surface concurrently with the curing the curable material by the curing apparatus.

In some implementations, the measurement apparatus can be configured, during operation of the system, to measure the position of the first mold surface relative to the second mold surface continuously over time.

In some implementations, the one or more actuators can be configured, during operation of the system, to adjust the position of the first mold surface relative to the second mold surface prior to the curing the curable material by the curing apparatus.

In some implementations, the one or more actuators can be configured, during operation of the system, to adjust the position of the first mold surface relative to the second mold surface concurrently with the curing the curable material by the curing apparatus.

In some implementations, the one or more actuators can be configured, during operation of the system, to adjust the position of the first mold surface relative to the second mold surface continuously over time.

In some implementations, the measurement apparatus can include a control module configured, during operation of the system, to determine, based on the position of the first mold surface relative to the second mold surface, one or more adjustments to at least one of a position of the first mold surface or a position of the second mold surface to reduce an angle between the planar portion of the first mold surface and the planar portion of the second mold surface. The control module also can configured, during operation of the system, to generate one or more control signals to activate the one or more actuators to move the at least one of the first mold surface or the second mold surface according to the one or more determined adjustments.

In some implementations, the one or more adjustments can include at least one of a translation of at least one of the first mold surface or the second mold surface along an axis of translation, or a rotation of at least one of the first mold surface or the second mold surface about an axis of rotation.

In some implementations, the axis of translation can be substantially parallel to the first, second, and third measurement axes.

In some implementations, the axis of rotation can be substantially orthogonal to the first, second, and third measurement axes.

In some implementations, the control module can be configured, during operation of the system, to determine, based on the first relative distance along a first measurement axis, the second relative distance along a second measurement axis, and the third relative distance along a third measurement axis: coordinates (x1, y1, z1) of the first point on the planar portion of the first mold surface or the first point on the planar portion of the second mold surface with respect to a Cartesian coordinate system, coordinates (x2, y2, z2) of the second point on the planar portion of the first mold surface or the second point on the planar portion of the second mold surface with respect to the Cartesian coordinate system, and coordinates (x3, y3, z3) of the third point on the planar portion of the first mold surface or the third point on the planar portion of the second mold surface with respect to the Cartesian coordinate system.

In some implementations, the control module can be configured, during operation of the system, to determine the one or more adjustments according to a relationship

[y⁢1-x⁢11y⁢2-x⁢21y⁢3-x⁢31][R⁢xR⁢yZ]=[z⁢1z⁢2z⁢3],
where Z corresponds to the translation of at least one of the first mold surface or the second mold surface along an axis of translation, where Rx corresponds to the rotation of at least one of the first mold surface or the second mold surface about a first axis of rotation, and where Ry corresponds to the rotation of at least one of the first mold surface or the second mold surface about a second axis of rotation.

In some implementations, the plurality of sensors can include one or more low-coherence interferometry (LCI) sensors.

In some implementations, the one or more LCI sensors can be mounted on the first mold portion or the second mold portion. The measurement apparatus can be configured, during operation of the system, to direct an optical beam from each of the one or more LCI sensors along a corresponding measurement axis so that, for each LCI sensor, a first portion of the optical beam reflects from the first mold surface and a second portion of the optical beam reflects from the second mold surface. The reflected portions of the optical beam can be detected by the LCI sensor.

In some implementations, the one or more LCI sensors can be mounted remote from the first mold surface or the second mold portion. The measurement apparatus can be configured, during operation of the system, to reflect the optical beam with a mirror toward the first and second mold surfaces.

In some implementations, the curable material can include a photocurable material. The curing apparatus can include a radiation source. The curing apparatus can be configured, during operation of the system, to irradiate, using the radiation source, the photocurable material with radiation suitable for photocuring the photocurable material.

DETAILED DESCRIPTION

System and techniques for producing polymer film are described herein. One or more of the described implementations can be used to produce polymer film in a highly precise, controlled, and reproducible manner. The resulting polymer films can be used in a variety of variation-sensitive applications (e.g., as a part of eyepieces in an optical imaging system).

In some implementations, polymer films can be produced such that wrinkles, uneven thicknesses, or other unintended physical distortions are eliminated or otherwise reduced. This can be useful, for example, as the resulting polymer film may exhibit more predictable physical and/or optical properties. For example, polymer films produced in this manner can guide and diffract light in a more predictable and consistent manner, and thus, may be more suitable for use a high-resolution optical imaging system. In some implementations, optical imaging systems using these polymer films can produce sharper and/or higher resolution images than might otherwise be possible with other polymer films.

An example system100for producing polymer film is shown inFIG.1. The system100includes two actuable stages102aand102b, two mold structures104aand104b, two light sources106aand106b, a support frame108, a control module110, and a position determination module150.

During operation of the system100, the two mold structures104aand104b(also referred to as “optical flats”) are secured to the actuable stages102aand102b, respectively (e.g., through clamps112aand112b). In some implementations, the clamps112aand112bcan be magnetic (e.g., electromagnets) and/or pneumatic clamps that enable the mold structures104aand104bto be reversibly mounted to and removed from the actuable stages102aand102b. In some implementations, the clamps112aand112bcan be controlled by a switch and/or by the control module110(e.g., by selectively applying electricity to the electromagnets of the clamps112aand112band/or selectively actuating pneumatic mechanisms to engage or disengage the molds structures).

A photocurable material114(e.g., a photopolymer or light-activated resin that hardens when exposed to light) is deposited into the mold structure104b. The mold structures104aand104bare moved into proximity with one another (e.g., by moving the actuable stages102aand/or102bvertically along the support frame108), such that the photocurable material114is enclosed by the mold structures104aand104b. The photocurable material114is then cured (e.g., by exposing the photocurable material114to light from the light sources106aand/or106b), forming a thin film having one or more features defined by the mold structures104aand104b. To facilitate curing, the mold structures104aand104bcan be partially or fully transparent to radiation at one or more wavelengths suitable for photocuring the photocurable material114(e.g., between 315 nm and 430 nm). After the photocurable material114has been cured, the mold structures104aand104bare moved away from each other (e.g., by moving the actuable stages102aand/or102bvertically along the support frame108), and the film is extracted.

The actuable stages102aand102bare configured to support the mold structures104aand104b, respectively. Further, the actuable stages102aand102bare configured to manipulate the mold structures104aand104b, respectively, in one or more dimensions to control a gap volume116between the mold structures104aand104b.

For instance, in some implementations, the actuable stage102acan translate the mold structure104aalong one or more axes. As an example, the actuable stage102acan translate the mold structure104aalong an x-axis, a y-axis, and/or a z-axis in a Cartesian coordinate system (i.e., a coordinate system having three orthogonally arranged axes). In some implementations, the actuable stage102acan rotate, tip, or tilt the mold structure104aabout one or more axes. As an example, the actuable stage102acan rotate the mold structure104aalong an x-axis (e.g., to “roll” the mold structure104a), a y-axis (e.g., to “pitch” the mold structure104a), and/or a z-axis (e.g., to “yaw” the mold structure104a) in a Cartesian coordinate system. Translation and/or rotation with respect to one or more other axes are also possible, either in addition to or instead of those described above. Similarly, the actuable stage102bcan also translate the mold structure104balong one or more axes and/or rotate the mold structure104babout one or more axes.

In some implementations, the actuable stages102acan manipulate the mold structure104aaccording to one or more degrees of freedom (e.g., one, two, three, four, or more degrees of freedom). For instance, the actuable stage102acan manipulate the mold structure104aaccording to six degrees of freedom (e.g., translation along an x-axis, y-axis, and z-axis, and rotation about the x-axis, y-axis, and z-axis). Manipulation according to one or more other degrees of freedom is also possible, either in addition to or instead of those described above. Similarly, the actuable stage102bcan also manipulate the mold structure104baccording to one or more degrees of freedom

In some implementations, the actuable stages102aand102bcan include one or more motor assemblies configured to manipulate the mold structures104aand104band control the gap volume116. For example, the actuable stages102aand102bcan include a motor assembly118configured to manipulate the actuable stages102aand102b, thereby repositioning and/or reorienting the actuable stages102aand102b. The motor assembly118can include, for example, one or more motors or actuators coupled to the actuable stages102aand/or102b.

In the example shown inFIG.1, both the actuable stage102aand the actuable stage102bcan be moved relative to the support frame108to control the gap volume116. However, in some implementations, one of the actuable stages can be moved relative to the support frame108, whereas the other can remain static with respect to the support frame108. For example, in some implementations, the actuable stage102acan be configured to translate in one or more dimensions relative to the support frame108through the motor assembly118, whereas the actuable stage102bcan be held static with respect to the support frame108. In some implementations, one of the actuable stages can be moved according to a certain number of degrees of freedom (e.g., six degrees of freedom), whereas the other actuable stage can be moved according to a different number of degrees of freedom (e.g., three degrees of freedom).

The mold structures104aand104bcollectively define an enclosure for the photocurable material114. For example, the mold structures104aand104b, when aligned together, can define a hollow mold region (e.g., the gap volume116) within which the photocurable material114can be deposited and cured into a film. The mold structures104aand104bcan also define one or more structures in the resulting film. For example, the mold structures104aand104bcan include one or more protruding structures (e., gratings) from the surfaces120aand/or120bthat impart a corresponding channel in the resulting film. As another example, the mold structures104aand104bcan include one or more channels defined in the surfaces120aand/or120bthat impart a corresponding protruding structure in the resulting film. In some implementations, the mold structures104aand104bcan impart a particular pattern on one or both sides of the resulting film. In some implementations, the mold structures104aand104bneed not impart any pattern of protrusions and/or channels on the resulting film at all. In some implementations, the mold structures104aand104bcan define a particular shape and pattern, such that the resulting film is suitable for use as an eyepiece in an optical imaging system (e.g., such that the film has one or more light diffractive microstructures or nanostructures that impart particular optical characteristics to the film).

The physical characteristics of the polymer film (e.g., the thickness and shape of the polymer film) can be controlled, at least in part, by controlling the position of the mold structures104aand104brelative to one another during the curing process. To facilitate accurate positioning of the mold structures, the system100can use the position determination module150to measure the positions of at least three points on each of the mold structures104aand104b(e.g., three non-linear points that form a notional triangle on the surfaces120aand120b). Based on this information, the system100can determine the position of the mold structures104aand104bin space, and adjust the position of one or more of the mold structures104aand104bto reduce or eliminate misalignment between the opposing mold surfaces that contact the polymer film (e.g., such that the surfaces120aand120bare parallel or substantially parallel). For example, where surfaces of the mold structures are to be arranged parallel to one another, the system can reduce or eliminate any deviation of the surfaces from parallel. Accordingly, variations in thickness and/or distortions in the resulting polymer film may be reduced.

As an example, the position determination module can include at least three sensor modules152a-152cmounted to the mold structure104a. Each sensor module152a-152ccan be configured to measure the position of a point A1-A3, respectively, on the mold structure104a(e.g., a point on the surface120a) and a point B1-B3, respectively, on the mold structure104b(e.g., a point on the surface120b) along a measurement axis154a-154c, respectively. Further, the measurement axes154a-154ccan be parallel to one another (e.g., aligned along the z-axis).

The points A1-A3can form a notional triangle. For example, the points A1-A3can be arranged in a non-linear pattern, such as notional line segments extending between the points A1A2, the points A2-A3, and the points A3-A1form a equilateral, isosceles, or scalene triangle. This enables the position determination module110to determine the position of the mold structure104ain three-dimensional space, including the tilt angles of the mold structure104awith respect to the x-, y-, and z-axes.

Similarly, the points B1-B3also can form a notional triangle. For example, the points B1-B3can be arranged in a non-linear pattern, such as notional line segments extending between the points B1B2, the points B2-B3, and the points B3-B1form a equilateral, isosceles, or scalene triangle. This enables the position determination module150to determine the position of the mold structure104bin three-dimensional space, including the tilt angles of the mold structure104bwith respect to the x-, y-, and z-axes.

In some implementations, one or more of the sensor modules152a-152ccan include one or more low-coherence interferometry (LCI) sensor. An LCI sensor is a non-contact sensor that directs a beam of low-coherence light at a sample surface and sends reflected light signals to an interferometric detector (e.g., an interferometer) via an optical fiber for interpretation. When the measured sample includes of a stack of transparent or translucent material layers, light reflections are received by the detector from each interface where a reflection occurs, including the top and bottom of each layer. The interferometer interprets the reflected optical data from each interface and records it as a depth profile. In certain cases, the interferometer combines the reflected light with reference light from the same source. Where the optical path length of the reflected light matches, or approximately matches to within the coherence length of the source, the combined light interferences changing the intensity of the combined light (e.g., through constructive or destructive interference). By scanning the optical path length difference (e.g., by mechanically or optically scanning the reference light's optical path), the sensor can generate an interference signal where each interface causes a set of corresponding interference fringes. The distance between these fringes corresponds to the optical path difference between two interfaces. Multiple LCI sensors (e.g., three or more) can be used to determine the relative position of each layer in three-dimensions at multiple different scan points.

As a simplified example,FIG.2shows a sensor module152aincluding a light source156(e.g., a broadband light source) and an interferometer158. During operation, the light source156directs a beam of low-conference light160towards the mold structures104aand104b(e.g., along a measurement axis154aparallel to the z-axis). At least a portion of the light160reflects from each interface of the mold structures104aand104band the surrounding medium (e.g., air) back towards the interferometer158. For example, at least a portion of the light160can reflect from an upper surface of the mold structure104aas a light ray162a, at least a portion of the light160can reflect from a lower surface of the mold structure104aas a light ray162b, at least a portion of the light160can reflect from an upper surface of the mold structure104bas a light ray162c, and at least a portion of the light160can reflect from a lower surface of the mold structure104bas a light ray162d. For ease of illustration,FIG.2shows the beam of light160and the light rays162a-164din a row. However, it is understood that the beam of light160and the light rays162a-164dcan be superimposed over one another (e.g., along the measurement axis154a).

The sensor module152ameasures the reflected light rays162a-164dusing the interferometer158, and based on the measurements, determines of positions of the mold structure104aand104b(e.g., the relative depth of each of the interfaces along the measurement axis154a, and/or the relative distance between each interface). In some implementations, the sensor module152acan generate a plot that maps the optical path of reflected light to and from each interface (e.g., on the horizontal axis) against the intensity of the reflected light (e.g., on the vertical axis). The relative depths of the surfaces of the mold structure104aand104b(e.g., relative to the sensor module152a) can be determined by identifying the peaks in the plot, corresponding to the reflection of light at the interfaces.

Each of the other sensor modules of the position determination module150(e.g., the sensors modules152band152c) can be configured in a similar manner as the sensor module152ashown inFIG.2. Further, althoughFIG.1shows a position determination module150having three sensor modules152a-152c, in practice, a position determination module150can include more than three sensors modules (e.g., to determine the positions of additional points on the surfaces of the mold structure).

In some implementations, each of the sensor modules152a-152ccan be positioned such that they emit beams of light160directly through the mold structures104aand/or104b. For example,FIG.3Ashows a perspective view of an example configuration of the position determination module150relative to the mold structure104aand the mold structure104b. In this example, the sensor module152a-152care directly mounted to the mold structure104ain such a way that the light sources of the sensor module152a-152bemit light along measurement axes154a-154c, respectively. The measurement axes154a-154ccan be parallel to one another (e.g., aligned along the z-axis).

In some implementations, each of the sensor modules152a-152ccan be positioned in such a way that they emit a beam of light in a direction that does not extend through the mold structures104aand/or104b. Further, the beams of light can be reflected (e.g., by one or more mirrors or other reflective surfaces) such that they pass through the mold structures104aand/or104b(e.g., through respective measurement axes154a-154c). Similarly, light reflecting from the mold structures104aand104bcan be reflected back to the sensor modules152a-152cvia the mirror or reflective surface for measurement. This can be useful, for example, as it enables the sensor modules152a-152cto be positioned more flexibly with respect to the other components of the system100. For example, the sensor modules152a-152ccan be positioned remote from the mold surfaces104aand/or104b, or positioned in such a way that they do not block the light emitted by the light sources106aor106bfrom reaching the gap volume116.

For example,FIG.3Bshows a perspective view of another example configuration of the position determination module150relative to the mold structure104aand the mold structure104b. In this example, the sensor modules152a-152care mounted remote from the mold structures104aand104b. Further, the sensor modules152a-152care positioned such that the light sources of the sensor module152a-152cemit light in a direction different from the measurement axes154a-154c, respectively (e.g., orthogonal to the measurement axes154a-154c). The light emitted by the sensor modules152a-152cis reflected by mirrors300a-300c, respectively, such that they propagate along the measurement axes154a-154c, respectively. Further, light that is reflected from the mold structures104aand104bis also re-directed by the mirrors300a-300cback towards the sensor modules152a-152cfor measurement.

The control module110is communicatively coupled to the actuable stages102aand102band the position determination module150, and is configured to control the positions of the mold structures104aand104brelative to one another based on the measurements obtained by the position determination module150. For instance, the control module110can receive measurements from the position determination module150, and continuously, periodically, or intermittently reposition and/or reorient one or both of the mold structures104aand104bin response (e.g., by transmitting commands to the actuable stages102aand102b). In some implementations, the control module110can reposition one or both of the mold structures104aand104bto reduce or eliminate an angle between the opposing mold surfaces that contact the polymer film (e.g., such that the surfaces120aand120bare parallel or substantially parallel). Accordingly, variations in thickness and/or distortions in the resulting polymer film may be reduced.

In some implementations, the position determination module150can determine the depths of the surfaces of the mold structures104aand104balong the measurements axes154a-154c, relative to the position of the sensor modules152a-152cand/or the other surfaces of the mold structures. For example, if the measurement axes154a-154care aligned with the z-axis, the sensor modules152a-152ccan determine the relative depths of the surfaces of the mold structures104aand104bwith respect to the z-axis.

Further, if the positions of the sensor modules152a-152cwith respect to the x-axis and y-axis are known, the control module110can ascertain the positions of the surfaces of the mold structures104aand104bwith respect to all three axes (e.g., x-, y-, and z-axes). The positions of the sensor modules152a-152cwith respect to the x-axis and y-axis can be determined, for example, based the known fixed positions of the sensor module152a-152crelative to the mold structure104aand/or mold structure104b, and known positions of the mold structures104aand/or mold structure104brelative to a reference coordinate system (e.g., a “wafer coordinate system” that is expressed relative to the one or more components of the system100, such as the surfaces120aand/or120b).

In some implementations, the positions of the surfaces of the mold structures104aand104bcan be expressed as a series of coordinates. For example, the point A1on the mold structure104acan be expressed as (x1, y1, z1) with respect to the wafer coordinate system, where z1is determined based on measurements obtained by the position determination module150, and x1and y1are determined based on the known position of the position determination module150relative to the mold structures104aand/or104b. Similarly, the point A2on the mold structure104acan be expressed as (x2, y2, z2) with respect to the wafer coordinate system, and the point A3on the mold structure104acan be expressed as (x3, y3, z3) with respect to the wafer coordinate system.

Based on this information, the control module110can determine the rotation (or “tip” and “tilt”) of the surfaces of the mold about the x- and y-axes. For example, this can be determined using the relationship:

[y⁢1-x⁢11y⁢2-x⁢21y⁢3-x⁢31][R⁢xR⁢yZ]=[z⁢1z⁢2z⁢3],Eq.1
where Rx corresponds to the rotation of the surface of the mold structure about the x-axis, Ry corresponds to the rotation of the surface of the mold structure about the y-axis, and Z corresponds to the translation of the surface of the mold structure along the z-axis (e.g., relative to a reference point). The values Rx, Ry, and Z can be determined, for example, by performing an matrix inversion operation with respect to the relationship above.

The control module110can perform a similar calculation with respect to the other mold surface, such that it also determines the rotation of the surface of the other mold structure about the x-axis, the rotation of the surface of the other mold structure about the y-axis, and the translation of the surface of the mold structure along the z-axis relative to the reference point.

Further, the control module110can adjust the position of the mold structure104and/or the mold structure104bto reduce or eliminate misalignment between the surfaces of the mold structures104aand104bthat contact the polymer film (e.g., the surfaces120aand120b). For example, the control module110can adjust the position of the mold structure104aand/or the mold structure104bsuch that Rx for the surface120aof the mold structure104ais equal to or substantially equal to Rx for the surface120bof the mold structure104b, and Ry for the surface120aof the mold structure104ais equal to or substantially equal to Ry for the surface120bof the mold structure104b. Further, the control module110can adjust the position of the mold structure104aand/or the mold structure104bsuch that the difference between Z for the surface120aof the mold structure104aand Z for the surface120bof the mold structure104bis a particular distance (e.g., corresponding to a desired thickness of the resulting polymer film).

In some implementations, the position determination module150can determine the position of the mold structures104aand/or104ba single time (e.g., prior to the curing of a polymer film). In some implementations, the position determination module150can determine the position of the mold structures104aand/or104bmultiple times before, during, and/or after the curing of the polymer film (e.g., continuously, periodically, or intermittently). In some implementations, the position determination module150can store measurements for later retrieval and processing (e.g., using one or more storage devices). In some implementations, the measurements can be provided by to the control module110for storage (e.g., using one or more storage devices).

Further, the control module110can adjust the position of the mold structures104aand/or104ba single time, or multiple times before, during, and/or after the curing of the polymer film (e.g., continuously, periodically, or intermittently). In some implementations, the control module110can adjust the position of the mold structures104aand/or104baccording to a feedback loop (e.g., a closed loop), with the measurements from the position determination system150used as control inputs.

In at least some of the examples described above, a position determination module150can include at least three sensor modules152a-152c, each having a respective light source and a respective an interferometer. However, in some implementations, a position determination module can include a single light source and/or interferometer. Light emitted by the light source can be distributed along three or more measurement axes (e.g., using one or more beam splitters, mirrors, and/or reflective surfaces). Further, light reflecting from the mold structures can be directed to the interferometer (e.g., using one or more beam combiners, mirrors, and/or reflective surfaces). In some implementations, a position determination module150can include one or more autocollimators to measure reflections with respect to multiple different measurement axes concurrently.

FIGS.4A-4Dshow an upper portion of a system400for producing polymer film (e.g., the portion of the system configured to manipulate an upper actuable stage and mold structure). For ease of illustration, the lower portion of the system400(e.g., the portion of the system configured to manipulate a lower actuable stage and mold structure) is not shown.FIGS.4A and4Bshows the system400according to perspective views,FIG.4Cshows the system according to an upper view, andFIG.4Dshows the system according to a bottom view.

In general, the system400can be similar to the system100shown inFIG.1. For example, the system400can include two actuable stages102aand102b, two mold structures104aand104b, a support frame108, a control module110, a motor assembly118, light sources106aand106b, a position determination system150. For ease of illustration, the control module110, the light sources106aand106b, the actuable stages102b, and mold structure104bare not shown.

The system400can manipulate the actuable stages102band102busing the motor assembly118according to different respective degrees of freedom. For example, the system400can be configured to translate the actuable stage102a(e.g., the upper actuable stage) along the z-direction, and to rotate the actuable stage102aabout the x-axis and the y-axis (e.g., to “tip” or “tilt” the actuable stage102a). However, the system400can be configured to constrain translation of the actuable stage102aalong the y-direction and the x-direction, and to constrain rotation of the actuable stage102about the z-axis.

As another example, the system400can be configured to translate the actuable stage102b(e.g., the lower actuable stage) along the x-direction, the y-direction, and the z-direction, and to rotate the actuable stage102aabout the z-axis. However, the system400can be configured to constrain rotation of the actuable stage102babout the x-axis and the y-axis.

This configuration enables the system400to align the actuable stage102aand102brelative to one another (e.g., to facilitate performance of the molding and casting process). Further, this can reduce the complexity of operating and maintaining the system (e.g., by reducing the degrees of freedom of the system to a limited subset). Nevertheless, in some implementations, the system400can be configured to manipulate the actuable stage102aand/or the actuable stage102baccording to six digress of freedom (e.g., translation along the x-direction, the y-direction, and the z-direction, and rotation about the x-direction, the y-direction, and the z-direction), or according to any subset of thereof.

As shown inFIGS.4A-4C, the motor assembly118includes several motors402a-402cto manipulate the actuable stage102a. One or more of the motors402a-402ccan be linear motors. For example, a motor402a-402ccan include a voice coil and an optical linear encoder that tracks the vertical position (e.g., z-position) of opposing mounting surfaces of the motor (e.g., a mounting surface secured to the support frame, and another mounting surface secured to the actuable stage102a). The control module110(e.g., as shown inFIG.1) is configured to apply an electrical current to the voice coil. This electric current induces a magnetic force through the voice coil, which provides a motive force (e.g., pushing or pulling the mounting structures of the motor away or towards each other).

The control module110can be configured to apply varying amount of electrical current to the voice coil to control actuation of the motor. Further, the optical linear encoders of each of the motors402a-402cand the control module can operate in conjunction to manipulate the actuable stage102ain different ways. For instance, the control module110can determine the position of each of the motors402a-402cusing the optical linear encoders, and can apply different patterns of electrical current to each of the voice coils to translate and/or rotate the actuable stage102ain different ways. As an example, the motors402a-402ccan be operated in unison to raise or lower the actuable stage102ain the z-direction. As another example, the motors402a-402ccan be operated to selectively raise the actuable102astage at one or more points and/or to lower the actuable stage102bat one or more other points selectively (e.g., to tip or tilt the actuable stage102a). One or more of the actuable motors402a-402ccan remain stationary during a position adjustment.

As described herein, the position determination module150can measure the positions of at least three points on each of the mold structures104aand104b(e.g., three non-linear points that form a notional triangle on the surfaces120aand120b). Based on this information, the system100can determine the position of the mold structures104aand104bin space, and adjust the position of one or more of the mold structures104aand104bto reduce or eliminate misalignment between the opposing mold surfaces that contact the polymer film (e.g., such that the surfaces120aand120bare parallel or substantially parallel).

In the example shown inFIGS.4A-4D, the position determination module includes three sensor modules152a-124c(e.g., LCI sensors), each configured to measure points on the mold structures104aand104balong a respective measurement axis154a-154c. Further, in this example, each of the sensor modules124a-124cis mounted to the actuable stage102aand/or mold structure104ain such a way that it emits a beam of low-coherence light in a direction orthogonal to the z-axis (e.g., along the x-y plane). Further, each of the sensor modules152a-152cinclude a respective mirror300a-300c. The mirrors300a-300care positioned such that the beams of light emitted by the sensor modules152a-152care reflected by the mirrors300a-300c, respectively, and propagate along the measurement axes154a-154c, respectively. Further, light that is reflected form the mold structures104aand104bare also re-directed by the mirrors300a-300cback towards the sensor modules152a-152cfor measurement. As shown inFIG.4C, the sensor modules152a-152ccan be positioned beyond the periphery of the portion of the surface120athat contacts the photocurable material, such they do not block the light emitted by the light sources106aor106bfrom reaching the gap volume between the mold structures104aand104band curing the photocurable material. Further, due to the inclusion of the mirrors300a-300c, the sensor modules152a-152ccan be positioned with their longer edges flush against the actuable stage102aand/or mold structure104a, thereby reducing the vertical profile of the position determination module150. This can be useful, for example, as it enables the system400to be implemented in a more compact form factor.

Example Processes

FIG.5shows an example process500for forming an optical film for an eyepiece of a display device. The process500can be performed, for example, using the systems100or400. In some implementations, the process500can be used to produce polymer films suitable for use in optical applications (e.g., as a part of waveguides or eyepieces in an optical imaging system). In some implementations, the process can be particularly useful for producing waveguides or eyepieces suitable for use in a head mounted display device, such as one used for presenting virtual reality content and/or augmented reality content).

In the process500, a curable material is dispensed into a space between a first mold surface and a second mold surface opposite the first mold surface (step502). As an example, referring toFIG.1, a curable material can be dispensed into the gap volume116between the surface120aof the mold structure104aand the surface120bof the mold structure104b.

A position of the first mold surface relative to the second mold surface is determined using a plurality of sensors (step504). This includes determining a first relative distance along a first measurement axis between a first point on a planar portion of the first mold surface and a first point on a planar portion of the second mold surface using a first of the sensors. This also includes determining a second relative distance along a second measurement axis between a second point on the planar portion of the first mold surface and a second point on the planar portion of the second mold surface using a second of the sensors. This also includes determining a third relative distance along a third measurement axis between a third point on the planar portion of the first mold surface and a third point on the planar portion of the second mold surface using a third of the sensors. The first, second, and third measurement axes are parallel to each other. Further, the first, second, and third points define corresponding triangles on the first and second mold surfaces, respectively. The space between the first and second mold surfaces is located within the triangles.

As an example, referring toFIGS.1,3A, and3B, a first relative distance can be determined along a measurement axis154abetween points A1and B1using a first sensor module152a, a second relative distance can be determined along a measurement axis154bbetween points A2and B2using a second sensor module152b, and a third relative distance can be determined along a measurement axis154cbetween points A3and B3using a third sensor module152c.

In implementations, the position of the first mold surface relative to the second mold surface can be determined prior to curing the curable material. In some implementations, the position of the first mold surface relative to the second mold surface can be determined concurrently with curing the curable material. In some implementations, the position of the first mold surface relative to the second mold surface can be determined continuously over time.

In some implementations, adjusting the position of the first mold surface relative to the second mold surface can include determining, based on the position of the first mold surface relative to the second mold surface, one or more adjustments to at least one of a position of the first mold surface or a position of the second mold surface can be made to reduce an angle between the planar portion of the first mold surface and the planar portion of the second mold surface (e.g., such that the surfaces120aand120bare parallel or substantially parallel). Further, one or more actuators can be activated to move the at least one of the first mold surface or the second mold surface according to the one or more determined adjustments. Example actuators are shown and described, for example, with respect toFIGS.4A-4D.

In some implementations, the one or more adjustments can include a translation of at least one of the first mold surface or the second mold surface along an axis of translation, and/or a rotation of at least one of the first mold surface or the second mold surface about an axis of rotation. In some implementations, the axis of translation can be substantially parallel to the first, second, and third measurement axes. In some implementations, the axis of rotation can be substantially orthogonal to the first, second, and third measurement axes. In some implementations, the term “substantially” can refer to a deviation of no more than 5%.

In some implementations, adjusting the position of the first mold surface relative to the second mold surface can include determining—based on the first relative distance along a first measurement axis, the second relative distance along a second measurement axis, and the third relative distance along a third measurement axis—coordinates (x1, y1, z1), coordinates (x2, y2, z2), and coordinates (x3, y3, z3). The coordinates (x1, y1, z1) can refer to the first point on the planar portion of the first mold surface or the first point on the planar portion of the second mold surface with respect to a Cartesian coordinate system. The coordinates (x2, y2, z2) can refer to the second point on the planar portion of the first mold surface or the second point on the planar portion of the second mold surface with respect to the Cartesian coordinate system. The coordinates (x3, y3, z3) can refer to the third point on the planar portion of the first mold surface or the third point on the planar portion of the second mold surface with respect to the Cartesian coordinate system.

Further, adjusting the position of the first mold surface relative to the second mold surface can include determine the one or more adjustments are determined according to a relationship:

[y⁢1-x⁢11y⁢2-x⁢21y⁢3-x⁢31][R⁢xR⁢yZ]=[z⁢1z⁢2z⁢3],
where Z corresponds to the translation of at least one of the first mold surface or the second mold surface along an axis of translation, Rx corresponds to the rotation of at least one of the first mold surface or the second mold surface about a first axis of rotation, and Ry corresponds to the rotation of at least one of the first mold surface or the second mold surface about a second axis of rotation.

The position of the first mold surface is adjusted relative to the second mold surface based on the measured position (step506). In some implementations, the position of the first mold surface relative to the second mold surface can be adjusted prior to curing the curable material. In some implementations, the position of the first mold surface relative to the second mold surface can be adjusted concurrently with curing the curable material. In some implementations, the position of the first mold surface relative to the second mold surface can be adjusted continuously over time.

The curable material is cured in the space to form the optical film (step508). In some implementations, the curable material can include a photocurable material. Curing the curable material to form the optical film can include irradiating the photocurable material with radiation suitable for photocuring the photocurable material. For example, referring toFIG.1, the photocurable material can be irradiated with radiation produced by one or more of the light sources106aand106b.

In some implementations, the curable material can be confined entirety within the space between the first mold surface and the second mold surface during the curing of the curable material.

In some implementations, the plurality of sensors can include one or more low-coherence interferometry (LCI) sensors. The one or more LCI sensors can be mounted on a first mold portion that includes the first mold surface or a second mold portion that includes the second mold surface. As an example, referring toFIG.3A, one or more LCI sensors can be mounted on the mold structure104aand/or the mold structure104b.

In some implementations, measuring the position of the first mold surface relative to the second mold surface can include directing an optical beam from each of the one or more LCI sensors along a corresponding measurement axis so that, for each LCI sensor, a first portion of the optical beam reflects from the first mold surface and a second portion of the optical beam reflects from the second mold surface. The reflected portions of the optical beam are detected by the LCI sensor. Examples of this technique are show and described, for example, with respect toFIG.2.

In some implementations, the one or more LCI sensors can be mounted remote from the first mold surface or the second mold portion. Directing the optical beam from at least one of the LCI sensors can include reflecting the optical beam with a mirror toward the first and second mold surfaces. As an example, referring toFIG.3B, one or more LCI sensors can be mounted remove from the mold structure104aand/or the mold structure104b, and optical beams emitted from the LCI sensors can be reflected towards the molds structures using mirrors300a-300c.

In some implementations, the process500can further include separating the optical film from the first mold portion and the second mold portion.

In some implementations, the process500can further include assembling a head mounted display including the optical film.

Example Computer System

Some implementations of subject matter and operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. For example, in some implementations, the control module110and/or the position determination module150can be implemented using digital electronic circuitry, or in computer software, firmware, or hardware, or in combinations of one or more of them. In another example, the process500shown inFIG.5can be implemented, at least in part, using digital electronic circuitry, or in computer software, firmware, or hardware, or in combinations of one or more of them.

Some implementations described in this specification can be implemented as one or more groups or modules of digital electronic circuitry, computer software, firmware, or hardware, or in combinations of one or more of them. Although different modules can be used, each module need not be distinct, and multiple modules can be implemented on the same digital electronic circuitry, computer software, firmware, or hardware, or combination thereof.

Some implementations described in this specification can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. A computer storage medium can be, or can be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

FIG.6shows an example computer system600that includes a processor610, a memory620, a storage device630and an input/output device640. Each of the components610,620,630and640can be interconnected, for example, by a system bus650. The processor610is capable of processing instructions for execution within the system600. In some implementations, the processor610is a single-threaded processor, a multi-threaded processor, or another type of processor. The processor610is capable of processing instructions stored in the memory620or on the storage device630. The memory620and the storage device630can store information within the system600.

The input/output device640provides input/output operations for the system600. In some implementations, the input/output device640can include one or more of a network interface device, e.g., an Ethernet card, a serial communication device, e.g., an RS-232 port, and/or a wireless interface device, e.g., an 802.11 card, a 3G wireless modem, a 4G wireless modem, etc. In some implementations, the input/output device can include driver devices configured to receive input data and send output data to other input/output devices, e.g., keyboard, printer and display devices660. In some implementations, mobile computing devices, mobile communication devices, and other devices can be used.