The present invention relates to optical devices and systems, in particular optical devices and systems that include image projecting optical devices that project images produced by liquid-crystal-based electronic microdisplay devices, such as liquid crystal on silicon (LCoS) display devices and liquid crystal display (LCD) devices.
Compact optical devices are particularly needed in the field of head-mounted displays (HMDs) and near-eye displays (NEDs), wherein an optical module performs functions of image generation and collimation of the image to infinity, for delivery to the eye of the viewer. The image can be obtained from an electronic display device, either directly from a spatial light modulator (SLM), such as a cathode ray tube (CRT), a liquid crystal display (LCD), a liquid crystal on silicon (LCoS), a digital micro-mirror device (DMD), an OLED display, a scanning source or similar devices, or indirectly, by means of a relay lens or an optical fiber bundle. The image, made up of an array of pixels, is focused to infinity by a collimating arrangement and transmitted into the eye of the viewer, typically by a reflecting surface or a partially reflecting surface acting as a combiner, for non-see-through applications and see-through applications, respectively. Typically, a conventional, free-space optical module is used for these purposes.
A particularly advantageous family of solutions for HMDs and NEDs are commercially available from Lumus Ltd. (Israel), typically employing light-guide substrates (optical waveguides) with partially reflecting surfaces or other applicable optical elements for delivering an image to the eye of a user.
In optical architectures that rely on liquid-crystal-based devices as the display device, such as LCoS or LCD, the display device emits polarized light waves in response to illumination by illumination optics (which includes a source of polarized light). The polarized light waves emitted by the display device pass through imaging optics to produce collimated polarized image light waves, which in the case of the aforementioned family of solutions for HMDs and NEDs are then coupled into a light-guide substrate.
Birefringent elements are typically used in deployment between the display device and the illumination optics in order to suppress the transmission of unwanted light to the imaging optics. For reflective display devices, e.g., LCoS, the birefringent element is deployed between the output of the display device and the illumination optics. For backlit display devices, e.g., LCD, the birefringent element is deployed between the illumination optics and the input of the display device.
A source of polarized light, shown here as a combination of a light source 14, for example a light emitting diode (LED), with a linear polarizer 16, is associated with the light-wave entrance surface 28. The display device 12 is associated with the image display surface 30, and generates spatial modulation of reflected light corresponding to an image. Light from the source of polarized light, generally designated as incident beam 18, is reflected by the PBS 22 so as to illuminate the display device 12. The display device 12 is configured such that the reflected light corresponding to a bright region of a desired image has a polarization rotated relative to the source of polarized light. Thus, as shown in
In order to limit the propagation of slant and skew rays (having directional components coming out of the plane of the paper in
The present invention is directed to methods, system and devices that electronically compensate for the misalignment of an optical element, in particular a birefringent element, with a liquid-crystal-based electronic display device.
According to the teachings of an embodiment of the present invention, there is provided a method. The method comprises: obtaining an electronic display device and a birefringent element, the electronic display device having at least one layer of liquid crystal material deployed between two transparent electrodes, and the electronic display device and the birefringent element each having respective polarization axes; deploying the electronic display device and the birefringent element relative to each other such that the polarization axes of the electronic display device are rotationally offset from the polarization axes of the birefringent element by an offset amount in accordance with a predetermined direction of rotation; and determining a compensation voltage, proportional to the offset amount, that when applied across the transparent electrodes induces the liquid crystal material to assume an intermediate state, such that the electronic display device produces polarized image light waves having polarization in a polarization direction that is in accordance with the intermediate state assumed by the liquid crystal material and that compensates for the rotational offset between the polarization axes of the electronic display device and the birefringent element.
Optionally, the electronic display device comprises a liquid crystal on silicon display.
Optionally, the birefringent element includes a quarter wave plate.
Optionally, the birefringent element includes a full wave plate.
Optionally, the birefringent element includes a polarization compensator.
Optionally, the offset amount is within a predetermined range based on expected tolerances of the polarization axes of the electronic display device and the birefringent element.
Optionally, the determining the compensation voltage includes: applying a voltage across the transparent electrodes, and iteratively evaluating at least one image quality metric of the polarized image light waves produced in response to the applied voltage and adjusting the applied voltage until the at least one image quality metric satisfies a performance criterion.
Optionally, the method further comprises: passing the polarized image light waves emitted by the electronic display device through an optical arrangement prior to evaluating the at least one image quality metric.
There is also provided according to an embodiment of the teachings of the present invention a system. The system comprises: a power supply arrangement configured to output voltage over a range of voltages, and coupled to an electrical connection arrangement that provides an electrical coupling between the power supply arrangement and transparent electrodes of an electronic display device, the electronic display device having at least one layer of liquid crystal material deployed between the transparent electrodes; an analyzer configured to evaluate at least one image quality metric of polarized image light waves emitted by the electronic display device; and a polarization sensitive beamsplitter deployed in an optical path between the electronic display device and the analyzer. The polarization sensitive beamsplitter is configured to transmit the polarized image light waves produced by the electronic display device, and a birefringent is deployed relative to the electronic display device such that polarization axes of the electronic display device are rotationally offset from polarization axes of the birefringent element by an offset amount in accordance with a predetermined direction of rotation, and the power supply arrangement is configured to output a compensation voltage, proportional to the offset amount, that when applied across the transparent electrodes induces the liquid crystal material to assume an intermediate state, such that the electronic display device produces polarized image light waves having polarization in a polarization direction that is in accordance with the intermediate state assumed by the liquid crystal material and that compensates for the rotational offset between the polarization axes of the electronic display device and the birefringent element.
Optionally, the electronic display device comprises a liquid crystal on silicon display.
Optionally, the birefringent element includes a quarter wave plate.
Optionally, the birefringent element includes a polarization compensator.
Optionally, the offset amount is within a predetermined range based on expected tolerances of the polarization axes of the electronic display device and the birefringent element.
Optionally, the system further comprises: a control unit including at least one processor coupled to a storage medium, the control unit operatively coupled to the power supply arrangement and the analyzer and configured to: receive the image quality metric from the analyzer, and adjust the output voltage of the power supply arrangement until the image quality metric satisfies a performance criterion.
There is also provided according to an embodiment of the teachings of the present invention a method for compensating for misalignment between a birefringent element and an electronic display device having at least one layer of liquid crystal material deployed between two transparent electrodes, the electronic display device and the birefringent element each having respective polarization axes, the electronic display device configured to receive a range of applied voltages across the transparent electrodes between a minimum voltage and a maximum voltage and including a default voltage. The method comprises: deploying the electronic display device and the birefringent element relative to each other such that the polarization axes of the electronic display device are rotationally offset from the polarization axes of the birefringent element by an offset amount in accordance with a predetermined direction of rotation; and applying a change to voltage setting of a display driver associated with the electronic display device such that the default voltage is proportionally reduced in accordance with the offset amount to produce a proportionally reduced default voltage, and such that when the proportionally reduced default voltage is applied across the transparent electrodes the liquid crystal material assumes an intermediate state such that the electronic display device produces polarized image light waves having polarization in a polarization direction that is in accordance with the intermediate state assumed by the liquid crystal material and that compensates for the rotational offset between the polarization axes of the electronic display device and the birefringent element.
There is also provided according to an embodiment of the teachings of the present invention a display module. The display module comprises: an electronic display device including at least one layer of liquid crystal material deployed between two transparent electrodes, the liquid crystal material having polarization axes that define polarization axes of the electronic display device, the electronic display device associated with a display driver that controls voltage settings associated with the electronic display device, the voltage settings including a default voltage that can be applied across the transparent electrodes; and a birefringent element optically coupled to the electronic display device and having polarization axes. The electronic display device and the birefringent element are deployed relative to each other such that the polarization axes of the electronic display device are rotationally offset from the polarization axes of the birefringent element by an offset amount in accordance with a predetermined direction of rotation, and the voltage settings of the display driver are changed such that the default voltage is proportionally reduced in accordance with the offset amount to produce a proportionally reduced default voltage, and such that when the proportionally reduced default voltage is applied across the transparent electrodes the liquid crystal material assumes an intermediate state such that the electronic display device produces polarized image light waves having polarization in a polarization direction that is in accordance with the intermediate state assumed by the liquid crystal material and that compensates for the rotational offset between the polarization axes of the electronic display device and the birefringent element.
Optionally, the electronic display device is configured to operate in a normally white mode.
Optionally, the electronic display device is configured to operate in a normally dark mode.
Optionally, the electronic display device comprises a liquid crystal on silicon display, and one of the transparent electrodes is deployed between the at least one layer of liquid crystal and a reflecting surface.
There is also provided according to an embodiment of the teachings of the present invention an image projector for projecting image light waves. The image projector comprises: the display module; a prism including: a plurality of external surfaces including a light-wave entrance surface, an image display surface associated with the electronic display device, and a light-wave exit surface, and a polarization sensitive beamsplitter configuration deployed within the prism on a plane oblique to the light-wave entrance surface; and a source of polarized light associated with the light-wave entrance surface configured to produce linearly polarized light, such that polarized light produced by the source of polarized light enters the prism through the light-wave entrance surface, is reflected by the polarization sensitive beamsplitter configuration, impinges on the electronic display device via the image display surface such that the electronic display device generates spatial modulation of the polarized light corresponding to an image and such that the polarized light is reflected by the reflecting surface and has a polarization rotated relative to the source of polarized light, and such that the reflected light re-enters the prism via the image display surface and is transmitted by the polarization sensitive beamsplitter configuration, and exits the prism through the light-wave exit surface.
There is also provided according to an embodiment of the teachings of the present invention an optical device. The optical device comprises: the image projector and a light-guiding substrate having at least two major surfaces parallel to each other, the projected image light waves produced by the image projector are coupled into the light-guiding substrate.
As used herein, the term “light-guide” refers to any light-waves transmitting body, preferably light-waves transmitting solid bodies, which may also be referred to as “optical substrates”.
Unless otherwise defined herein, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein may be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.
Some embodiments of the present invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.
Attention is now directed to the drawings, where like reference numerals or characters indicate corresponding or like components. In the drawings:
The present invention is directed to methods, system and devices that electronically compensate for the misalignment of an optical element, in particular a birefringent element, with a liquid-crystal-based electronic display device.
The principles and operation of the optical devices and systems according to present invention may be better understood with reference to the drawings accompanying the description.
Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Initially, throughout this document, references are made to directions such as, for example, top and bottom, clockwise and counter clockwise, and the like. These directional references are exemplary only to illustrate the invention and embodiments thereof.
By way of introduction, liquid-crystal-based electronic display devices, such as LCoS and LCD, harness the optical properties of liquid crystals, in particular birefringent (polarization) properties, to enable control of the brightness of the image pixels displayed by the electronic display device. The liquid crystal material has properties that enable the material to assume a continuum of states that are intermediate between liquid and solid, and that can be used to alter the polarization (i.e., phase) of incident light passing through the liquid crystals. The liquid crystal material regulates the amount of polarized light passing through the liquid crystal in accordance with the state of the liquid crystal material, which can be electronically controlled to change the state assumed by liquid crystals by varying the electric field applied to the liquid crystal material. In this way, the liquid crystal material behaves as a gate or valve that controls the amount light emitted by the display device.
Many liquid-crystal-based display devices take advantage of the twisted nematic (TN) effect, which is based on the precisely controlled realignment of liquid crystal molecules between different ordered molecular configurations under the action of an applied electric field. When little or no electric field is applied, a twisted configuration (resembling a helical structure or a helix) of nematic liquid crystal molecules is formed. As the magnitude of the electric field that is applied to the liquid crystal is increased, the liquid crystal molecules depart from the twisted configuration and move toward an aligned structure. When a maximum electric field is applied, the twisted configuration is broken, and the liquid crystal molecules form the aligned structure.
Liquid-crystal-based electronic display devices can operate in various operational modes, two exemplary modes being referred to in the literature as “normally dark mode” and “normally white mode”. In normally dark mode, when little or no voltage (electric field) is applied across the transparent electrodes 42, 44, the display device is considered to be in the “off state”, whereby the liquid crystal material assumes a state (twisted configuration) that, optionally in combination with one or more polarizers, suppresses the light that is emitted by the display device 12 such that any image appears as black. To switch the display device to the “on state” to produce a bright image, an appropriate voltage (Vwhite) is applied across the transparent electrodes 42, 44, whereby the liquid crystal material assumes a different state (aligned configuration) that allows light to pass and birefringence effects of the birefringent element 34 are suppressed, i.e., reduced or minimized, and preferably eliminated. The operation of normally white mode is generally opposite to that of normally dark mode. In other words, the display device is in the “on state” when little to no voltage is applied across the transparent electrodes, and the display device is in the “off state” when an appropriate voltage (Vblack) is applied across the transparent electrodes (and birefringence effects of the birefringent element 34 are suppressed, i.e., reduced or minimized, and preferably eliminated). The advantage of operating in normally white mode is that little or no voltage is required to produce bright images, thereby significantly reducing the power consumption of the display device 12. In general terms, display devices, particularly microdisplays implemented as LCoS displays configured to operate in “normally white mode”, are preferably used in combination with the family of solutions for HMDs and NEDs commercially available from Lumus Ltd.
As seen in
As seen in
The above description of the behavior of light propagation through the layers of liquid crystal material 40, with reference to
Parenthetically, it is noted that as used within the context of this document, the term “perfectly aligned”, with reference to the birefringent element 34 and/or the display device 12, refers to the ideal case in which the respective Eigen axes of the birefringent element 34 and the display device 12 are aligned with each other.
As is known in the art, one of the foremost properties of liquid crystal materials for the phase manipulation of incident light is the birefringence, denoted Δη, which is defined as:
where ηo is the ordinary refractive index for incident light having electric field polarization in a direction that is perpendicular to the director of the layers of liquid crystal material 40, and ηe is the extraordinary refractive index for incident light having electric field polarization in a direction that is parallel to the director. The director is generally defined to be the average direction of the long molecular axes of all of the liquid crystal molecules in the layers of liquid crystal material 40.
The accumulated phase retardation between two linear polarizations for incident light passing through the liquid crystal material is expressed as:
where λ is the wavelength of the incident light, and d is the thickness of the liquid crystal material (referred to as the cell gap). In LCoS displays the incident light passes through the liquid crystal layer twice (due to reflection from the reflective surface 50), and therefore the effective cell gap is 2d, resulting in an effective doubling of the accumulated phase retardation.
As the magnitude of the electric field applied across the transparent electrodes 42, 44 changes, so does the orientation of the liquid crystal molecules. For an LCoS operating in normally white mode, as the magnitude of the electric field is increased, the liquid crystal material departs from the nominally twisted state (
where Vmax is the maximum voltage (electric field) that can be applied across the transparent electrodes 42, 44. In general, the voltage ν applied across the transparent electrodes 42, 44 can vary continuously between a default minimum voltage Vmin (most typically 0 volts), and a default maximum voltage Vmax (for example 3.3 volts). Accordingly, when voltages of Vmin and Vmax are applied, the liquid crystal material assumes the first state (i.e., twisted state as in
By combining equations (1)-(3), the accumulated phase difference, δ, between the two Eigen polarizations for light propagating back and forth through the layers of liquid crystal material 40, can be expressed as:
The importance of the birefringent element 34, and the alignment of its Eigen axes with the Eigen axes of the display device 12, is illustrated in
Referring again to
Referring again to
Embodiments of the present disclosure describe steps for compensating for misalignment between the respective Eigen axes (referred to interchangeably as polarization axes) of the display device 12 and the birefringent element 34. The proposed method relies on deliberately misaligning the aforementioned Eigen axes and electronically compensating for the misalignment by exploiting the underlying link between the rotation in polarization caused by the misalignment and the accumulated phase difference δ of light propagating through the layers of liquid crystal material 40, as outlined above with reference to equations (1)-(4).
Initially, the birefringent element 34 and the display device 12 are deliberately misaligned in a prescribed direction, in order to ensure that the alignment error is positive, and within a prescribed amount based on the tolerances of the Eigen axes of the birefringent element 34 and the display device 12. The deliberate misalignment is preferably performed mechanically using a mechanical alignment methodology generally known to those of skill in the art. Subsequent to the deliberate misalignment, steps are executed to determine a compensation voltage Vc (between Vmin and Vmax), that when applied across the transparent electrodes 42, 44, causes the layers of liquid crystal material 40 to assume an intermediate state such that the accumulated phase difference δ of polarized light passing through the layers of liquid crystal material 40 results in the image produced by the electronic display source 12 having sufficient image quality (as determined by an image quality metric or metrics). In particular, the layers of liquid crystal material 40 assume the intermediate state at the compensation voltage Vc such that the electronic display device 12 produces polarized image light waves having polarization in a polarization direction that is in accordance with the intermediate state and that compensates for the deliberate misalignment (i.e., rotational offset) between the Eigen axes of the electronic display device 12 and the birefringent element 34.
Parenthetically, it is noted herein that the term “intermediate state” generally refers to any state in a continuum of states, that can be assumed by the layers of liquid crystal material 40, that is between the two extreme states assumed in response to application of voltages Vmin and Vmax, exemplified, for example, as the twisted state and aligned state illustrated in
The following paragraphs describe steps for the deliberate misalignment of the birefringent element 34 and the display device 12. Referring to
Referring now to
In certain implementations, the expected tolerances θ and ϕ may be the same. In other implementations, the expected tolerances θ and ϕ are different.
In practice, the birefringent element 34 is coupled to the display device 12, for example via a mechanical body, to form a unitary display module. The mechanical body maintains the position of the birefringent element 34 and the display device 12, and as such maintains the orientation of the Eigen axes of the birefringent element 34 and the display device 12. Prior to coupling the birefringent element 34 and the display device 12 together, the birefringent element 34 and the display device 12 are relatively deployed such that Eigen axes of the birefringent element 34 and the display device 12 are deliberately rotationally offset from each other in a prescribed direction such that the angle between the respective Eigen axes of the birefringent element 34 and the display device 12 is positive and is within a maximum tolerance of τ=θ+ϕ (where τ=2θ in the case of θ=ϕ).
Note that since the ordinary and extraordinary axes are orthogonal axes, the rotational offset between the ordinary axes of the birefringent element 34 and the display device 12 is the same as the rotational offset between the extraordinary axes of the birefringent element 34 and the display device 12. Therefore, the aforementioned rotation results in an angle of ϕ between the boundary extraordinary axis of the birefringent element 34 (EBE1) and the boundary extraordinary axis of the display device 12 (ED1).
Once the birefringent element 34 and the display device 12 are rotationally offset from each other within the prescribed offset amount in the prescribed offset direction, the birefringent element 34 is coupled (i.e., attached) to the display device 12 to form the unitary display module.
Generally speaking, the birefringent element 34 and the display device 12 may be substantially rectangular in the XY plane (with reference to the arbitrary coordinate system of
As mentioned above, subsequent to the deliberate misalignment of the birefringent element 34 and the display device 12, steps are executed to determine the compensation voltage Vc (between Vmin and Vmax) at which the image generated by the unitary display module (with the deliberately misaligned birefringent element 34) has the same or similar image quality (determined by contrast ratio or other relevant image quality metric or metrics) as an image generated at Vblack with a perfectly aligned birefringent element 34. The following paragraphs describe the steps for determining the compensation voltage Vc.
The power supply arrangement 110 is electrically coupled to the display device 12 via an electrical connection arrangement 112. The power supply arrangement 110 can be implemented as a voltage source configured to output a voltage (that can be selected from a range of voltages between Vmin and Vmax and set by a human operator of the system 100 or by a hardware controller) that is to be applied across the transparent electrodes 42, 44. In such an implementation, the electrical connection arrangement 112 can be implemented, for example, as a set of leads, with one lead extending from a positive terminal of the voltage source to one of the transparent electrodes 42, 44 and another lead extending from a negative terminal of the voltage source to the other of the transparent electrodes 42, 44. Such an implementation is schematically illustrated in
The image analyzer 130 is deployed to receive image light waves emitted by the display module 60 in response to illumination by the source of polarized light. Specifically, the image analyzer is 130 is configured to receive the spatial modulation of (reflected) light (from the source of polarized light), corresponding to an image, generated by the display device 12 of the display module 60. Light from the source of polarized light follows a similar path of traversal as that described with reference to
The image analyzer 130 may include at least one computerized processor coupled to a storage medium (such as a memory or the like). The image analyzer 130 is further configured to evaluate one or more image quality metric of the image produced by the display module 60, and in certain preferred but non-limiting implementations is configured to evaluate the contrast ratio of the images produced by the display module 60. The image analyzer 130 can be implemented as part of a computer system that includes a display for displaying the aforesaid image quality metric(s), such that when the system 100 is operated by a human operator in an optical test environment, the human operator may visually perceive the image quality metric(s) displayed by the computer system.
As the voltage output by the power supply arrangement 110 is varied between Vmin and Vmax, the state assumed by the layers of liquid crystal material 40 also changes. The change in state of the layers of liquid crystal material 40 effects the accumulated phase difference δ of light propagating through the layers of liquid crystal material 40, and as a result, directly effects the brightness of the reflected beam 19. At some point, the voltage output reaches a compensation voltage Vc that causes the layers of liquid crystal material 40 to assume an intermediate state which effects the polarization of light passing therethrough in a way that results in an output image having contrast ratio that is the same or similar to that of an output image that is the result of the layers of liquid crystal material 40 assuming a state at voltage Vblack when the birefringent element 34 is perfectly aligned.
Looking again at equation (4), it is clear that the accumulated phase difference δ is a function of the voltage ν applied across the transparent electrodes 42, 44, and in particular is proportional to the voltage ν applied across the transparent electrodes 42, 44. Therefore, by adjusting the voltage ν applied across the transparent electrodes 42, 44 in proportion to the deliberate misalignment angle, the layers of liquid crystal material 40 assume an intermediate state such that the display device 12 compensates for the change in polarization of light passing through the liquid crystal material induced by the misalignment of the birefringent element 34. In effect, if the deliberate misalignment angle is measured as ϕ degrees, the compensation voltage Vc that is required to compensate for the deliberate misalignment of the birefringent element 34 can be expressed as:
Since the exact misalignment angle ϕ is unknown (due to the variability of the true Eigen axes of the birefringent element 34 and the display device 12), the compensation voltage Vc is also unknown. However, the compensation voltage Vc can be determined by adjusting the voltage applied across the transparent electrodes 42, 44 (via the power supply arrangement 110), while simultaneously evaluating the image quality metric(s), until the image quality metric(s) satisfy corresponding performance criteria (e.g., until the contrast ratio is deemed to be high enough). At that point, the voltage output by the power supply arrangement 110 is determined to be the compensation voltage Vc. Furthermore, once the compensation voltage Vc is determined, the misalignment angle ϕ can be estimated as
As see from equation (5), the compensation voltage Vc is a proportionally reduced version of Vblack, in particular Vblack is reduced by an amount of
in order to achieve Vc.
Continuing with the numerical example of a deliberate misalignment of 5 degrees described with reference to
Accordingly, the compensation voltage Vc is achieved by reducing Vblack by
is applied across the transparent electrodes 42, 44 so as to compensate for the deliberate misalignment. As can be seen in
According to certain embodiments of the present disclosure, the voltage output by the power supply arrangement 110 is electronically adjusted in response to actuation/operation of the power supply arrangement 110 by a human operator of the system 100. In such embodiments, the human operator of the system 100 may manually actuate/operate the power supply arrangement 110 to output a desired voltage while visually inspecting the image quality metric(s) until the image quality metric(s) satisfy corresponding performance criteria. In other embodiments, the optical test system is implemented as part of a closed loop system with feedback, so as to enable the automated adjustment of the output voltage of the power supply arrangement 110 until the requisite performance criterion (or criteria) are satisfied.
Refer now to
The mass storage device 148 is a non-limiting example of a non-transitory computer-readable (storage) medium bearing computer-readable code for implementing the compensation methodology functionality described herein. Other examples of such computer-readable (storage) media include read-only memories such as, for example, compact disks (CDs) bearing such code. The control unit 140 may have an operating system stored on the memory devices, the boot ROM 146 may include boot code for the operating system, and the processor 142 may be configured for executing the boot code to the load the operating system to the RAM 144, executing the operating system to copy computer-readable code to the RAM 144 and execute the copied computer-readable code. The operating system may include any conventional computer operating systems, such as iOS available from Apple of Cupertino, Calif., and Android available from Google of Mountain View, Calif., or may be implemented as a real-time operating system (RTOS).
The control unit 140 may include a network connection 156 that provides communication (e.g., data communication) to and from the control unit 140. Typically, a single network connection provides one or more links, including virtual connections, to other devices on local and/or remote networks. Alternatively, the control unit 140 can include more than one network connection (not shown), each network connection providing one or more links to other devices and/or networks. Alternatively, the control unit 140 can include an additional data bus to provide communication and data exchange functionality between the control unit 140 and external devices.
Returning to
In certain embodiments, the image analyzer 130 may be implemented together with the control unit 140 as part of a single control and processing system executed on a single computer system. In such embodiments, the computer system may include a display that displays various outputs to a human operator of the system 100′. The displayed outputs may include, for example, the determined compensation voltage Vc, the various intermediate voltages applied across the transparent electrodes 42, 44, and the corresponding determined contrast ratios (or other image quality metric values). In embodiments in which the image analyzer 130 is not used with the closed loop system 100′, but rather is used as described with reference to
Attention is now directed to
The process begins at block 1602, by obtaining the birefringent element 34 and the display device 12. At block 1604, the birefringent element 34 and the display device 12 are deployed relative to each other. The deployment includes the sub-step of deliberately misaligning the birefringent element 34 relative to the display device 12 such that the respective polarization axes (i.e., Eigen exes, i.e., ordinary and extraordinary axes) of the birefringent element 34 and the display device 12 are rotationally offset from each other in a prescribed direction and within a prescribed amount in accordance with the tolerances of the Eigen axes of the birefringent element 34 and the display device 12. The misalignment sub-step may be performed using a mechanical alignment mechanism, for example, an optical alignment mechanism that can be used for passively aligning optical components. The deployment preferably further includes the sub-step of mechanically attaching the misaligned birefringent element 34 to the display device 12, using, for example a mechanical body, to form the unitary display module 60.
The process 1600 then moves to block 1606, where the display module 60 is deployed in the optical test system 100. Block 1606 includes the sub-step of positioning the display module 60 relative to the optical arrangement 120 (e.g., illumination prism 20 and source of polarized light in the configuration of the optical test system in which the display device 12 is implemented as an LCoS) such that image light waves emitted by the display module 60 traverse the optical arrangement 120 and are received at the image analyzer 130. Block 1606 further includes the sub-step of connecting the power supply arrangement 110 to the display module 60.
After the display module 60 is deployed in the optical test system 100, the process 1600 moves to block 1608, where the compensation voltage Vc, output by the power supply arrangement 110 and applied across the transparent electrodes 42, 44, is determined. The compensation voltage Vc is the voltage that, when applied across the transparent electrodes 42, 44, induces the layers of liquid crystal material 40 to assume an intermediate state that causes the display device 12 to generate spatial modulation of polarized light that passes through the liquid crystal material (the polarized light corresponding to an image), so as to produce polarized image light waves having polarization in a specific polarization direction that is in accordance with the state of the liquid crystal material and that compensates for the rotational offset. In particular, the layers of liquid crystal material 40 assume the intermediate state at the compensation voltage Vc such that the electronic display device 12 produces polarized image light waves having polarization in a polarization direction that is in accordance with the intermediate state and that compensates for the deliberate misalignment (i.e., rotational offset) between the Eigen axes of the electronic display device 12 and the birefringent element 34.
As discussed above, when the compensation voltage Vc is applied across the transparent electrodes 42, 44 the layers of liquid crystal material 40 assume an intermediate state which effects the polarization of light passing therethrough in a way that results in the output polarized image light waves having contrast ratio that is the same or similar to that of output polarized image light waves that is the result of the layers of liquid crystal material 40 assuming a state at voltage Vblack when the birefringent element 34 is perfectly aligned
The process 1600 then moves to block 1610, where the voltage settings of a display driver 64 associated with the display device 12 are programmed in accordance with the compensation voltage Vc determined in block 1608. The display driver 64 is shown as being part of the display module 60 in
With continued reference to
The sub-process 1700 then moves to block 1708, where the evaluated image quality metric is compared with a desired image quality metric value (i.e., the evaluated image quality metric is compared with a threshold value to determine whether the evaluated image quality metric satisfies a performance criterion), for example, an evaluated contrast ratio is compared with a desired contrast ratio. If the evaluated image quality metric satisfies the performance criterion, the process 1700 moves from block 1708 to block 1710, where the compensation voltage Vc is determined to be the output voltage. If the evaluated image quality metric does not satisfy the performance criterion (e.g., if the evaluated contrast ratio is below the desired contrast ratio), the process 1700 moves from block 1708 to block 1712, where the set output voltage (i.e., the voltage that is output by the power supply arrangement 110) is adjusted (increased or decreased) and set as a new output voltage. The process 1700 then returns to block 1704, and iterates on blocks 1704-1708 until the performance criterion is satisfied.
Some of the sub-processes of the process 1700 may be performed using computerized components (e.g., electronic control units, computer processors, etc.), and may be performed automatically or manually. For example, when employing the closed loop system discussed above, the control unit 140 is configured to: set the output voltage of the power supply arrangement 110 and actuate the power supply arrangement 110 to output the set voltage (as in block 1702), determine whether the evaluated image quality metric satisfies the performance criterion (as in block 1708), and adjust the output voltage of the power supply arrangement 110 and actuate the power supply arrangement 110 to output the adjusted voltage (as in block 1712).
In practice, after completion of the execution of the process 1600 (and the process 1700), the display module 60—having a display device 12 a birefringent element 34 with deliberately misaligned Eigen axes but having the deliberate misaligned electronically compensated with a compensation voltage programmed via the display driver 64—may be deployed as part of an image projector.
The image projector 160 can be used in a wide range of applications for which a microdisplay is needed. Examples of suitable applications include, but are not limited to, various imaging applications, such as near eye displays (NEDs), head mounted displays (HMDs), and head-up displays (HUDs) that utilize image projectors that project images into components of the NED, HMD, and HUD, cellular phones, compact displays, 3-D displays, compact beam expanders, as well as non-imaging applications, such as flat-panel indicators and scanners.
By way of illustration of one particularly preferred but non-limiting subset of applications,
The collimated image light waves (i.e., beam 19, also referred to as output light-waves 19) produced by the image projector 160 enter the light-guiding substrate 202. The light-guiding substrate 202 typically includes at least two major surfaces 204, 206 that are parallel to each other, one or more preferably mutually parallel partially reflecting surfaces 210 that are non-parallel to the major surfaces 204, 206, and an optical wedge element 208 for coupling light into the light-guiding substrate 202. The output light-waves 19 from the image projector 160 enter the light-guiding substrate 202 through the optical wedge element 208. The incoming light-waves (vis-a-vis the light-guiding substrate 202) are trapped in the light-guiding substrate 202 between the major surfaces 204, 206 by total internal reflection (TIR), as illustrated in
Although the embodiments of the present disclosure have been described thus far within the context of a display device implemented as a liquid crystal on silicon microdisplay (in particular an LCoS configured to operate in normally white mode), the particular implementation of a normally white mode LCoS is merely illustrative of one non-limiting implementation of a liquid-crystal-based electronic display device for which the described methods and systems are applicable. It is emphasized that the methodologies of the embodiments of the present disclosure are equally applicable to other LCoS modal configurations, including, for example, LCoS that operates in normally dark mode, and other display devices that harness the polarization properties of liquid crystals, for example LCD devices.
It is noted that although the embodiments of the present disclosure have been described within the context of using contrast ratio as the image quality metric of interest, contrast ratio is merely illustrative of one non-limiting image quality metric, and other image quality metrics, including, but not limited to, modulation transfer function (MTF), can be used in addition to, or in place of, contrast ratio, as should be apparent to those of ordinary skill in the art.
Implementation of the method and/or system and/or device of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of embodiments of the method and/or system and/or device of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system.
For example, hardware for performing selected tasks according to embodiments of the invention could be implemented as a chip or a circuit. As software, selected tasks according to embodiments of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In an exemplary embodiment of the invention, one or more tasks according to exemplary embodiments of method and/or system and/or device as described herein are performed by a data processor, such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and/or data and/or a non-volatile storage, for example, non-transitory storage media such as a magnetic hard-disk and/or removable media, for storing instructions and/or data. Optionally, a network connection is provided as well. A display and/or a user input device such as a keyboard or mouse are optionally provided as well.
For example, any combination of one or more non-transitory computer readable (storage) medium(s) may be utilized in accordance with the above-listed embodiments of the present invention. The non-transitory computer readable (storage) medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a RAM, a ROM, an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.
As will be understood with reference to the paragraphs and the referenced drawings, provided above, various embodiments of computer-implemented methods are provided herein, some of which can be performed by various embodiments of apparatuses and systems described herein and some of which can be performed according to instructions stored in non-transitory computer-readable storage media described herein. Still, some embodiments of computer-implemented methods provided herein can be performed by other apparatuses or systems and can be performed according to instructions stored in computer-readable storage media other than that described herein, as will become apparent to those having skill in the art with reference to the embodiments described herein. Any reference to systems and computer-readable storage media with respect to the following computer-implemented methods is provided for explanatory purposes, and is not intended to limit any of such systems and any of such non-transitory computer-readable storage media with regard to embodiments of computer-implemented methods described above. Likewise, any reference to the following computer-implemented methods with respect to systems and computer-readable storage media is provided for explanatory purposes, and is not intended to limit any of such computer-implemented methods disclosed herein.
The flowcharts and block diagrams in the drawings illustrate the architecture, functionality, and operation of possible implementations of methods, systems and computer program products according to various embodiments of the present invention. In this regard, some of the blocks in the flowcharts, and blocks in the block diagrams, may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the blocks of the flowcharts may occur out of the order noted in the drawings. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or some of the blocks in the flowchart illustrations, and combinations of blocks in the block diagrams and/or some of the blocks in the flowchart illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
As used herein, the singular form, “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.
The word “exemplary” is used herein to mean “serving as an example, instance or illustration”. Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.
It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.
To the extent that the appended claims have been drafted without multiple dependencies, this has been done only to accommodate formal requirements in jurisdictions which do not allow such multiple dependencies. It should be noted that all possible combinations of features which would be implied by rendering the claims multiply dependent are explicitly envisaged and should be considered part of the invention.
Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.
This application claims priority from U.S. Provisional Patent Application No. 62/797,973, filed Jan. 29, 2019, whose disclosure is incorporated by reference in its entirety herein.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2020/050649 | 1/28/2020 | WO | 00 |
Number | Date | Country | |
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62797973 | Jan 2019 | US |