Patent Description:
As used herein, VR and AR systems are described and referenced interchangeably. Unless stated otherwise, the descriptions herein apply equally to all types of mixed-reality systems, which (as detailed above) include AR systems, VR systems, and/or any other similar system capable of displaying holograms.

Some of the disclosed mixed-reality systems use one or more on-body devices (e.g., the HMD, a handheld device, etc.). The HMD provides a display that enables a user to view overlapping and/or integrated visual information (e.g., holograms) in whatever environment the user is in, be it a VR environment, an AR environment, or any other type of environment. Continued advances in hardware capabilities and rendering technologies have greatly improved how mixed-reality systems render holograms. Notwithstanding these advances, the process of immersing a user into a mixed-reality environment creates many challenges, difficulties, and costs, particularly with regard to providing a high-quality hologram or holographic image to the user.

For instance, methodologies are in place to use a red, green, blue (RGB) laser assembly to visually project an image for the user to view in a mixed-reality environment/scene. As will be described in more detail later on, however, certain imperfections due to laser coherence effects, such as "artifacts," can appear in the images as a result of using a RGB laser. Such imperfections can negatively impact the user experience.

In view of the foregoing, there is currently a need to improve the manner in which images are projected into mixed-reality environments with RGB lasers.

<CIT> discloses a technique capable of, in an image display apparatus and a laser projection apparatus that reduce speckle noise by means of high-frequency superimposition, reducing a deterioration in the light emission intensity of a semiconductor laser while suppressing EMI. To achieve the object, the image display apparatus includes a plurality of semiconductor lasers for emitting laser beams of different wavelengths in accordance with drive currents supplied thereto, a laser-drive circuit for generating the drive currents by superimposing a plurality of high-frequency signals on image signals of a plurality of color components, respectively, and deflection means for deflecting each of the laser beams, wherein the plurality of high-frequency signals have different fundamental frequencies.

<CIT> discloses a diagram showing a wavelength spectrum during optical pulse drive oscillation as an example of a spectrum of a semiconductor laser in a multimode oscillation state A multimode oscillation spectrum and an individual oscillation mode spectrum having a wide spectrum width are observed. The light beams emitted from the semiconductor laser during the relaxation oscillation operation are composed of superposed light beams from a large number of laser modes having no phase correlation with each other. As a result, its coherence is greatly reduced. By using such a low-coherence light beam as a light source of a projection display, it becomes possible to eliminate speckle noise due to the coherence of laser light.

<CIT> discloses an image display device including a light source and a scanner. The scanner includes (a) a first mirror on which a light beam emitted from the light source is incident, (b) a first light deflector on which the light beam output from the first mirror is incident and that outputs collimated light forming a first output angle depending on a first incident angle of the light beam in association with the pivoting of the first mirror, (c) a second mirror on which the collimated light output from the first light deflector is incident, and (d) a second light deflector on which the collimated light output from the second mirror is incident and that outputs collimated light forming a second output angle depending on a second incident angle of the collimated light in association with the pivoting of the second mirror.

It is the object of the present invention to provide an improved method for operation of a laser assembly.

Disclosed embodiments are directed to systems and methods for controlling and/or modifying operation of a red, green, blue (RGB) laser assembly used for creating images in mixed-reality environments.

The invention is directed to methods that initially identify a set of pixels that are to be irradiated by the RGB laser assembly. Subsequently, these pixels are irradiated with pulsed laser light in the following manner. Initially, the RGB laser assembly is configured to operate below a particular laser threshold such that it refrains from irradiating any pixels. Then, the RGB laser assembly is energized so that it operates above the laser threshold and so that it irradiates at least one pixel with laser light. This irradiation occurs only for a selected period of time lasting no longer than <NUM> nanoseconds. Furthermore, the intensity of the laser light is set to not exceed a pre-determined optical power level. Thereafter, the RGB laser assembly is again caused to operate below the laser threshold so that it again refrains from irradiating any pixels.

In some embodiments, a certain set of pixels are selected to be irradiated with RGB laser light. As such, a RGB laser assembly is selectively pulsed by energizing the RGB laser assembly with electrical current for a pre-selected period of time lasting no longer than <NUM> nanoseconds. As a result of this operation, the RGB laser assembly emits laser light having a spectral linewidth that satisfies a pre-selected spectral linewidth threshold. Subsequently, the pixels are irradiated with this specially structured laser light.

According to the invention, a RGB laser assembly is selectively pulsed for a pre-selected period of time lasting no longer than <NUM> nanoseconds. Additionally, the RGB laser assembly emits structured laser light having a number of Fabry-Perot modes that is greater in number than laser light that is emitted for longer than <NUM> nanoseconds. Consequently, the spectral linewidth of the structured laser light exceeds a pre-selected width threshold. Then, a set of pixels are irradiated with this structured laser light.

In some instances, the disclosed embodiments can be used to help omit or reduce the occurrence of visual artifacts.

Disclosed embodiments are directed to systems and methods for controlling and/or modifying operation of a red, green, blue (RGB) laser assembly used for creating images in a mixed-reality environment. In some embodiments, the disclosed embodiments can be used to help improve image quality of rendered images over corresponding images created by conventional systems and that omit or reduce the occurrence of coherence artifacts.

The disclosed embodiments include operating any one or combination of the red laser, the green laser, and/or the blue laser in the RGB laser assembly in a burst or pulsed mode when illuminating a set of one or more pixels for the image. In other words, the RGB lasers initially start out in a non-emitting state. Then, the RGB lasers emit laser light to illuminate a pixel. This illumination occurs for a period of time spanning (according to the disclosed embodiments) less than <NUM> nanoseconds (ns). By causing the RGB lasers to chirp for this short period of time, the resulting laser light is structured with a reduced spatial coherence level. Once the time period elapses, then the RGB lasers again return to the non-emitting state. By operating the RGB lasers in this manner (i.e. with a reduced spatial coherence), the emitted laser light is structured to have an increased spectral linewidth, which beneficially eliminates the presence of undesired visual artifacts, as will be described in more detail later.

In some instances, technical advantages and improvements over conventional systems are realized by operating the red lasers, green lasers, and/or blue lasers in the RGB laser assembly according to the disclosed embodiments. In particular, conventional systems that utilize lasers to render virtual or holographic content experience many undesired visual artifacts. These artifacts occur (as will be described in more detail later) as a result of the typically high coherence of the laser light. Indeed, in most conventional systems, it is desirable to have high coherence when using a laser because the high coherence results in a more spectrally pure/intense waveform. In contrast to these conventional systems, however, the disclosed embodiments purposely reduce the coherence of laser light (specifically the spatial coherence) to address other problems that can be caused by the highly coherent laser light. Such an operation is counterintuitive, as described above, because most systems try to achieve very high coherence levels for laser light. Nevertheless, such an operation produces unanticipated and highly beneficial results. In particular, implementations of the current embodiments can reduce the occurrence of undesired visual artifacts.

Having just disclosed some of the features and benefits of the embodiments at a high level, the disclosure will now focus on <FIG> and <FIG> which provide a description of how laser light is structured. Following that discussion, the disclosure will turn to <FIG> which illustrate how laser light can be used to project images. Next, the disclosure will focus on <FIG> which illustrate various architectures, supporting illustrations, and operations for controlling the spatial coherence and spectral linewidth of laser light. Finally, the disclosure will turn to <FIG> which illustrate example methods as well as a computer system capable of performing those methods.

"Coherence" is a central topic in the field of optics, and the concept of "coherence" generally relates to the capability of light to interfere with itself. To be perfectly "coherent," light from a light source is structured to have a definite phase relationship both in terms of electrical field values at different times and electrical field values at different positions. As such, the term coherency is used to describe the range between incoherent light (i.e. there is little or no degree of phase relationship) and coherent light (i.e. there is a high degree of phase relationship). The topic of coherence is typically broken down into two sub-topics, namely, spatial coherence and temporal coherence.

The term "spatial coherence" is used to describe the correlation between the light's electrical field values at different locations. In other words, spatial coherence relates to how well light waves align with each other at different points along a traversal path. In contrast, the term "temporal coherence" is used to describe the correlation between the light's electrical field values at different points in time. In other words, temporal coherence relates to how well light waves align with each other at a specific location when measured at different points in time.

With that understanding, attention will now be directed to <FIG> which illustrates the differences in coherence between light emitted from one light source (e.g., a lightbulb) and light emitted from another light source (e.g., a laser). Specifically, <FIG> shows a first type of light source <NUM>. Light source <NUM> is any type of light source that is not a laser. For instance, light source <NUM> may be a traditional light emitting diode (LED), a fluorescent lightbulb, the sun, or any other non-laser-type light source. As shown by the light fields <NUM>, light source <NUM> does not emit coherent light because the light fields <NUM> are not aligned spatially or temporally.

In contrast, laser <NUM> is shown as emitting light <NUM> which does have high coherence characteristics. For example, the vertical dashed line <NUM> shows that the phase of the light waves correspond with each other and the horizontal dashed line <NUM> shows that the amplitudes also correspond with one another. Accordingly, emitted light <NUM> has high spatial coherence and high temporal coherence. In this manner, laser light is structured quite differently than light emitted from other light sources.

The purity of a laser is sometimes referred to as its "linewidth. " Generally, the laser's linewidth corresponds to a measurement of the wavelengths that are included in the emitted laser light. As the laser light's linewidth gets narrower (i.e. as the laser light's coherence becomes higher), the emitted light will correspond more closely to only a single wavelength (i.e. a single color). In this regard, a laser is sometimes said to be "monochromatic. " In actual practice, however, laser light typically includes a small range of wavelengths and thus is not truly or perfectly monochromatic or coherent. Regardless, as the wavelength range of the laser light gets smaller (i.e. the coherency increases), so too does the linewidth (i.e. it gets more narrow), and it may be suggested that the quality/purity/coherency of the laser improves.

<FIG> shows an example of laser light <NUM>, including a symbolic envelope <NUM> and the linewidth <NUM>. The symbolic envelope <NUM> is simply a contoured representation of how the laser light <NUM> generally appears. <FIG> also shows the various different Fabry-Perot (FP) modes (or simply "modes") in the form of modes 215A, 215B, 215C, 215D, 215E, 215F, <NUM>, and <NUM>. Although only eight modes are labeled, it will be appreciated that the number of modes may be any number (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or more than <NUM>). Furthermore, the depiction shown in <FIG> is just a simplified illustration, and it will be appreciated that real laser light may actually have a different appearance.

Some lasers are formed from an assembly that includes at least two parallel mirrors and an active region located between those mirrors. Together, this assembly is often referred to as a "resonator. " When multiple wavelengths operate/propagate within the resonator, they can form a standing wave. As such, the attributes of the resonator (e.g., the length of the mirrors, the distance between the mirrors, etc.) influence which wavelengths can successfully propagate in the resonator and thereby form a standing wave. The wavelengths that are supportable by the resonator are often referred to as "longitudinal modes.

Although an innumerable number of wavelengths may exist in the resonator (i.e. the longitudinal modes), the active region of the laser will provide a gain only for a selected wavelength range, which are often referred to the "resonant" wavelengths. Furthermore, laser light is formed only from an even smaller or limited number of those resonant wavelengths. Specifically, only resonant wavelengths whose gains exceed their losses will contribute to the light output of the laser. Resonant wavelengths whose gains exceed their losses (and thus contribute to the laser's output) are referred to as the Fabry-Perot ("FP") modes (e.g., modes 215A, 215B, 215C, 215D, 215E, 215F, <NUM>, and <NUM>). These FP modes are shown as being distributed across the "optical frequency" x-axis in <FIG>. The collective combination of these modes forms the envelope <NUM>. Furthermore, linewidth <NUM> is typically measured or determined by the full width of the laser light <NUM> at the laser light <NUM>'s half maximum (i.e. "full-width-half-maximum" or simply "FWHM") of the laser light <NUM>'s power spectrum, as shown by the "intensity" y-axis in <FIG>. In this manner, laser light may be created. Furthermore, different colors of laser light (e.g., red, green, blue, etc.) may be formed based on the type or attributes of the laser assembly.

Attention will now be directed to <FIG> which shows a holographic display <NUM> that uses a laser assembly <NUM> with lasers 305A (e.g., a red laser), 305B (e.g., a green laser), and 305C (e.g., a blue laser). The lasers 305A-C may be configured in the manner described with respect to <FIG> and <FIG>. Furthermore, although only three lasers are shown, it will be appreciated that the laser assembly <NUM> may include any number of lasers. For example, the laser assembly <NUM> may include <NUM>, <NUM>, <NUM>, <NUM>, or more than <NUM> red lasers, <NUM>, <NUM>, <NUM>, <NUM>, or more than <NUM> green lasers, and <NUM>, <NUM>, <NUM>, <NUM>, or more than <NUM> blue lasers. Any combination or modification in the number of lasers may also be available (e.g., <NUM> red, <NUM> green, <NUM> blue, or <NUM> red, <NUM> green, <NUM> blue, etc.). Accordingly, any number of lasers may be used to irradiate/illuminate pixels for generating virtual or holographic image content.

In some instances (though not all), the laser assembly <NUM> also includes one (or more) collimating lens <NUM> (or other diffractive optical element) that is structured to direct light to another location or otherwise operate on the light in some manner. In this example, each of the lasers 305A, 305B, and 305C has a corresponding collimating lens. In some embodiments, however, a single collimating lens may be used for more than one laser. In this example scenario, the holographic display <NUM> also includes a microelectromechanical mirror (MEMs) system <NUM>, though the principles disclosed herein are applicable to any type of laser-based display unit and not only to architectures with the MEMs system <NUM>. In the example shown in <FIG>, the MEMs system <NUM> is collecting laser light from three different sources (i.e. the lasers 305A, 305B, and 305C). Additionally, the MEMs <NUM> is combing these three different laser lights into a single laser beam, such as is shown by laser light 315A. The MEMs system <NUM> then directs the combined laser light 315A (which, in this example is a combination of red laser light, green laser light, and blue laser light) to a waveguide <NUM>. Furthermore, the MEMs system <NUM> is able to redirect its mirrors/mirror array so that the laser light 315A is aimed at different locations at the waveguide <NUM>. For instance, the laser light 315B and 315C are also combined laser beams (i.e. a combined beam comprising red laser light, green laser light, and blue laser light). As shown, laser lights 315B and 315C are aimed at different locations on the waveguide <NUM>. In this manner, the MEMs system <NUM> is able to route light to different locations by adjusting the aim of its corresponding mirror array.

As shown, laser light 315A, 315B, and 315C, which is produced by the lasers 305A, 305B, and 305C, respectively, (e.g., by combing the red laser light from laser 305A, the green laser light from laser 305B, and the blue laser light from laser 305C) is re-projected or re-routed by the MEMs system <NUM> to the waveguide <NUM>. In these example scenarios, the laser 305A is a red laser, laser 305B is a green laser, and laser 305C is a blue laser. Consequently, the laser light 315A-C is a combined laser beam comprising a combination of red laser light, green laser light, and blue laser light. Of course, it will be appreciated that the laser lights 315A-C may consist of varying degrees or intensities (or even an absence of any one or more) of red, green, and blue laser light.

The MEMs system <NUM> then redirects the laser light 315A-C (which is a combined laser beam comprising any combination of red laser light, green laser light, and blue laser light) to a waveguide <NUM>. This waveguide <NUM> is useful for redirecting or propagating the laser light 315A-C to a desired location which is viewable by a user's eye. It will be appreciated that waveguide <NUM> may be any type of waveguide display (e.g., a surface relief grating waveguide).

By directing the laser light 315A-C in this manner, the MEMs system <NUM> is able to generate an entire holographic image by scanning (e.g., by adjusting the mirror array so that the combined RGB laser beam or light is aimed at different locations) individual pixels of that image in such a rapid manner that the entirety of the hologram/holographic image appears before the user's eye without the user realizing that the image was progressively scanned pixel by pixel and line by line. In this regard, the MEMs system <NUM> is able to scan an image (i.e. pixels of that image) at any image resolution or range of image resolutions (e.g., in cases where foveated rendering is used). For example, in some embodiments, the MEMs system <NUM> is configured to scan RGB light from the laser assembly <NUM> with a resolution of <NUM>,<NUM> pixels by <NUM>,<NUM> pixels, or any other resolution.

<FIG> also shows laser light 315A-C entering the waveguide <NUM> via an entry grating <NUM>. Once laser light 315A-C enters waveguide <NUM>, then it propagates (e.g., reflects back and forth off of the walls of waveguide <NUM>) through waveguide <NUM> until it reaches an exit grating <NUM>. By configurating the entry grating <NUM> and the exit grating <NUM> to meet certain design parameters, MEMs system <NUM> is able to use waveguide <NUM> to progressively scan a set of pixels <NUM> to a target display area for a user's eye <NUM> to view. In this manner, the MEMs system <NUM>, in conjunction with the laser assembly <NUM> and the waveguide <NUM>, is able to project or render holographic image content for a user to view and interact with. It will be appreciated that the angles with which the laser light enters the waveguide <NUM> are preserved as the laser light 315A-315C propagates through the waveguide <NUM>. This condition is shown by the different angles that each of the respective laser lights 315A-C is propagating through the waveguide <NUM>.

<FIG> shows a blown-up view of a portion of a holographic display <NUM>, which is representative of the holographic display <NUM> of <FIG>. In particular, <FIG> more fully emphasizes the angular relationships of the reflecting/propagating laser light.

As shown, MEMs system <NUM> directs laser light (e.g., RGB laser light) to a waveguide <NUM> which includes an input or entry grating <NUM>. MEMs system <NUM> is able to direct the laser light so that it enters the entry grating <NUM> at any desired angle, such as angles θi<NUM> and θi<NUM>. As MEMs system <NUM> performs its scanning operations, these angles will change based on how MEMs system <NUM> aims the laser light at entry grating <NUM>. Once inside waveguide <NUM>, the laser light propagates through waveguide <NUM> until it reaches the exit grating <NUM>.

Worthwhile to note, the angles at which the laser light leaves the exit grating <NUM> are the same as the angles at which the laser light entered the entry grating <NUM>. In other words, angles θi<NUM> and θi<NUM> are the same as angles θi<NUM> and θi<NUM>, respectively. In this regard, MEMs system <NUM> is able to progressively scan individual pixels of a hologram.

<FIG> more fully illustrates this scanning operation. In particular, there is provided a waveguide <NUM>, which is representative of the waveguides <NUM> and <NUM> from <FIG> and <FIG>, respectively. The laser light exits waveguide <NUM> via the exit grating <NUM> (and in the same angular relationship the laser light had when it entered the waveguide <NUM>). By aiming the laser light (which may include any combination of red laser light, green laser light, and/or blue laser light), the MEMs system is able to progressively scan an area <NUM> which represents or corresponds to a holographic/virtual image. Because area <NUM> is viewable by a user's eye <NUM>, the user is able to view and interact with the holographic image. In this regard, holographic images are projected to a user's eye via the waveguide <NUM>.

Having just described the properties of a laser and of a holographic display, attention will now be directed to <FIG> which shows some further characteristics and properties of how laser light propagates through a waveguide. Here, waveguide <NUM> is shown and is representative of the waveguides discussed earlier. Waveguide <NUM> also includes an exit grating <NUM>, similar to the earlier exit gratings.

As discussed earlier, laser light has some wavelike characteristics. These wavelike characteristics are shown by waves <NUM>, <NUM>, and <NUM>. As laser light propagates or reflects back and forth through waveguide <NUM> (e.g., wave <NUM> reflects off of a wall to form wave <NUM>), the laser light will eventually reach and pass through exit grating <NUM>, as shown by wave <NUM>.

In some instances, due to the nature of laser light (e.g., the waveform or wavelength properties) as well as the attributes of the waveguide (e.g., its length, reflective properties, and other attributes), certain transformations may occur to the laser light. For example, <FIG> shows a waveguide <NUM> with an exit grating <NUM>. As laser light <NUM> propagates through waveguide <NUM>, some portions of that laser light <NUM> will exit waveguide <NUM> via exit grating <NUM>. Other portions of laser light <NUM>, however, will persist in waveguide <NUM> beyond the exit grating <NUM>, as shown by laser light <NUM>.

In some circumstances, laser light <NUM> will be reflected and may eventually return to exit grating <NUM>. At that time, some of laser light <NUM> and some of laser light <NUM> may interfere with each other. In some scenarios, this interference results in a constructive combination of laser light <NUM> and laser light <NUM>, resulting in the constructive laser light <NUM>. As shown, constructive laser light <NUM> is the added combination or collection of laser light <NUM> and laser light <NUM>. Such constructive combination periodically occurs and is a result of (<NUM>) the angles at which the laser light enters waveguide <NUM>, (<NUM>) the attributes of the waveguide <NUM>, (<NUM>) the attributes of the laser light (e.g., waveform/wavelength), and other factors.

When such a constructive or destructive interference condition occurs, it produces an optical phenomenon or visual imaging artifact. As used herein, an artifact is an undesired interference fringe that appears in the user's field of view. These interference fringes are caused, as described above, by a match in the optical path length of the waveguide (to the target display area, such as the user's eye) and to the physical distance where the laser is spatially coherent. This coherence distance is referred to as the "coherence function of the laser" and is related to the Fourier Transform of the laser's spectral characteristics.

<FIG> and <FIG> provide a description relating to artifacts. Turning first to <FIG>, there is provided a similar architecture as that which was shown in <FIG>. In particular, there is illustrated laser light <NUM>, which is representative of constructive laser light <NUM> from <FIG>. As shown, there are various instances in which, due to the wavelike properties of laser light, certain interferences occur. For instance, laser light <NUM>, which is propagating out of the waveguide, is actually generated from the construction of multiple waveforms <NUM> (e.g., waveform 805A, waveform 805B, and waveform 805C). In this manner, multiple waveforms <NUM> and laser light <NUM> are actually the same waveform, but the multiple waveforms <NUM> are provided to illustrate how the end result (i.e. laser light <NUM>) is actually a combination of multiple separate waveforms. Furthermore, waveform <NUM> is a composite of the multiple waveforms <NUM>. In other words, laser light <NUM> is the same as the combination of the multiple waveforms <NUM>, which combination is illustrated as waveform <NUM> (thus, laser light <NUM> is actually in the form of waveform <NUM>). These multiple illustrations were provided to better describe the properties of the laser light exiting the waveguide. As shown, waveform <NUM> is not a sinusoidal wave. Instead, it has multiple peaks as valleys as a result of the interference from the combination of each of the multiple waveforms <NUM>. These interferences are a result of back scattering and/or back reflections combining with the outgoing laser light exiting the waveguide. As a result of these interferences, various different bright and dark rings/spots are created, as shown by the illumination <NUM>, where the peaks correspond to lighter areas and the valleys correspond to darker areas.

<FIG> shows an actual depiction of an artifact <NUM>. To clarify, <FIG> shows an actual rendition of the appearance of artifact <NUM>, which can affect the image being rendered by the laser light that is causing the artifact <NUM>. Although the rendered image is not presently shown, the artifact <NUM> includes circular irregularities in terms of brightness that will correspondingly modify the image being rendered and which can negatively affect the user experience.

As described, conventional laser imaging techniques used for rendering holographic content in a mixed-reality environments can experience negative effects, such as artifacts, because of the high purity and/or high coherency of the lasers that are used. Consequently, there is a need to improve how holographic content is rendered from the lasers to help mitigate these negative effects.

The disclosed embodiments can be used to help solve these problems by dynamically controlling the spectral properties of a laser when it is used to render holographic content. In particular, the disclosed systems and methods operate to reduce the spatial coherence of a laser by operating in a chirped, or rather fast-pulsed mode, where every pixel is illuminated by a separate red, green, and/or blue laser pulse for only a very brief period of time. By operating the lasers in a fast-pulsed mode, the spatial coherence of the resulting laser light emission is reduced and the spectral linewidth of that emission is increased. As a direct result of these operations, the disclosed embodiments are able to reduce and/or entirely eliminate interference fringes (e.g., artifacts) from the display, thereby improving the display quality as well as the user's experience, as will be described in further detail later.

Specifically, by modulating a laser with short (e.g., less than <NUM> nanoseconds (ns)) optical pulses, it is possible to increase the spectral envelope (i.e. the linewidth) of the laser light, thereby reducing spatial coherence. In this regard, the laser light's spectral linewidth can be increased by operating the device with extremely short electrical pulses.

Increasing a laser's spectral envelope or linewidth is considered undesirable for conventional systems. However, when done properly, this modification can actually result in an unanticipated benefit of reducing the creation of undesired laser artifacts. For example, most fiber-based communications desire to use as high of a coherence as possible. In contrast, the disclosed embodiments actually operate to reduce coherence to bring about highly beneficial results (i.e. the elimination of the visual artifacts). As a result, the disclosed embodiments actually bring about unanticipated and counter-intuitive (but highly beneficial) results.

<FIG> shows an illustration of how laser light can be pulsed. In this illustration, a laser pulses graph <NUM> includes a plurality of laser pulses that are graphed by "time" (x-axis) and "pulse intensity" (y-axis). In particular, the laser pulses graph <NUM> includes a number of different pulses (e.g., pulses <NUM>, <NUM>, <NUM>, and <NUM>) separated by a plurality of corresponding non-emission periods (e.g., non-emissions <NUM>, <NUM>, and <NUM>). As described above, the pulses <NUM>, <NUM>, <NUM>, and <NUM> are configured to last less than <NUM> ns. In some embodiments, the pulses are reduced in duration even further such that they last anywhere between (and including) <NUM> ns to <NUM> ns. In this manner, a pre-selected period of time (e.g., <NUM> ns) may be used to selectively pulse a laser or a combination of multiple lasers. For example, an RGB laser assembly may include a red laser, a green laser, and a blue laser. Each of these lasers may be used to illuminate a particular pixel when rendering holographic content. By selectively pulsing any one or combination of the red, green, and blue lasers for the pre-selected period of time, then the embodiments are able to improve image quality by removing undesired artifacts.

In this regard, it can be said that the embodiments cause an RGB laser assembly to emit laser light periodically based on a pre-selected schedule or frequency. As such, during periods when the RGB laser assembly is energized with electrical current, these periods constitute "lasing" periods. Furthermore, and as suggested by the term "pulse," the process of selectively pulsing the RGB laser assembly includes causing the RGB laser assembly to refrain from generating a stimulated emission (i.e. RGB laser light) in between the lasing periods (as shown by the non-emissions <NUM>, <NUM>, and <NUM>). This may include turning the laser off (e.g., by cutting off all power to the laser) and/or by reducing the power provided to the laser to the point that light is not emitted from the laser and without turning the laser completely off.

<FIG> provides an illustration showing how the embodiments are able to broaden the laser's spectral linewidth. Specifically, <FIG> shows a graph, where the x-axis represents energy and the y-axis represents the amount of current or laser gain for a laser.

As the laser device is pumped with small amounts of current (e.g., pumps <NUM>, <NUM>, and <NUM>), a lasing "gain" is produced, as was described earlier in connection with <FIG>. As also described in connection with <FIG>, there is some threshold level <NUM> that is required to enable the laser to lase. Normally, the laser's gain is clamped at the threshold level <NUM>, as shown in <FIG>, such that the pumps <NUM> and <NUM> are restricted near the threshold level <NUM>.

When the laser is pulsed, it is advantageous to pulse the laser in a manner so that the resulting gain is above the threshold level <NUM>. By operating above this threshold level <NUM>, the number of supported FP modes (e.g., modes <NUM>) increases, and thus the spectral linewidth of the laser also increases.

Additionally, for very short pulses, (e.g., ≤ <NUM> ns), the optical gain can temporarily exceed the threshold level <NUM>, further increasing the spectral linewidth of the emitted pulses. This phenomenon is known as "relaxation oscillations.

In some embodiments, selectively pulsing any one or combination of the RGB lasers is performed by initially biasing those lasers to operate below a threshold current or laser threshold (e.g., the threshold level <NUM>) between each of the laser pulses. For example, after the RGB laser assembly is energized with electrical current for the pre-selected period of time, the embodiments will refrain from biasing the RGB lasers above each of their respective RGB laser thresholds so that those lasers do not emit laser light. Subsequently, the RGB lasers may again be energized above their respective threshold levels so that they do emit laser light. In this manner, the RGB lasers will generate pulsed laser light emissions, in the manner described earlier.

This spectral linewidth response is shown in <FIG>, <FIG>, and <FIG>. <FIG> shows a graph 1200A with a number of different plots representing the spectral linewidth of a laser when that laser is pulsed for different durations. Specifically, graph 1200A shows a plot when the pulsed emissions last a duration of <NUM> ns, <NUM> ns, <NUM> ns, <NUM> ns, <NUM> ns, <NUM> ns, <NUM> ns, and <NUM> ns. When the pulse duration is longer (e.g., <NUM> ns), the spectral linewidth is more narrow than when the pulse duration is smaller (e.g., <NUM> ns). Therefore, by chirping or pulsing the laser, the spectral linewidth of the emitted laser light is broadened and the coherence decreased. The process of pulsing the laser can be specially engineered, calibrated, or otherwise determined so that the spectral linewidth of the emitted laser light satisfies a pre-selected width and/or wavelength threshold.

For instance, in some embodiments, the pre-selected width threshold ranges between <NUM> in wavelength up to <NUM> in wavelength (e.g., <NUM>, <NUM>, <NUM>, <NUM>, etc.) such that the spectral linewidth is anywhere between <NUM> and <NUM> (e.g., <NUM>, <NUM>, <NUM>, <NUM>, etc.) as measured by the full-width-half-maximum intensity.

<FIG> shows another comparison of different spectral linewidths that occur as a result of decreasing the duration of a laser pulse. Specifically, <FIG> shows a graph 1200B with four different laser emissions. As shown, each of these emissions has a different spectral linewidth (e.g., spectral linewidths <NUM>, <NUM>, <NUM>, and <NUM>). While conventional systems typically operate using a very tight or narrow spectral linewidth (e.g., spectral linewidth <NUM>), the disclosed embodiments operate using broader spectral linewidths (e.g., spectral linewidth <NUM>).

<FIG> provides another descriptive representation of broader spectral linewidths. As shown, there are three different plots, namely, plots 1200C, 1200D, and 1200E. Each of these plots shows an increased spectral linewidth due to the short pulse operation and a corresponding reduction in the coherence of the laser light.

<FIG> is similar to <FIG>, but now shows a reduction in the coherence of a laser <NUM>. Here, there is a laser assembly <NUM> with at least one laser 1305B. The laser 1305B is emitting laser light <NUM>. In this example scenario, the spatial coherence of the laser light <NUM> has been reduced, in contrast with the high spatial coherence of the emitted light <NUM> in <FIG>.

Attention is now directed to <FIG> and <FIG>, which illustrate views of a waveguide. These embodiments will be used to further demonstrate how the disclosed techniques for pulsing lasers having relatively low coherence and increased spectral linewidth can be beneficial, particularly for systems that render holographic content through surface relief gratings.

<FIG> shows a waveguide <NUM> with an exit grating <NUM>. Waveguide <NUM> and exit grating <NUM> are representative of the waveguides and exit gratings that were discussed earlier. Also shown is laser light <NUM> that has wavelike characteristics and that is propagating through waveguide <NUM>. Similar to the disclosure presented earlier, some portions of laser light <NUM> will leave waveguide <NUM> via exit grating <NUM>. Additionally, some portions of laser light <NUM> will back-scatter or continue to reflect in waveguide <NUM>, as shown by laser light <NUM>. In some instances, laser light <NUM> will eventually leave waveguide <NUM> via exit grating <NUM>.

Because the spectral linewidth of the laser light <NUM> and <NUM> has been broadened, the resulting laser light <NUM> interferes with itself much more than the laser light <NUM> or <NUM> from <FIG> and <FIG>, respectively. As a result of this increased interference, the combination of the laser light <NUM> and <NUM> will not constructively and destructively add to create the bright and dark artifacts. Instead, the resulting laser light <NUM> is less coherent, thereby preventing the generation of the visual artifacts.

<FIG> shows an example of why this occurs. Here, there is resulting laser light <NUM> which is representative of the resulting laser light <NUM> from <FIG>. Although different laser light reflections are merged together or otherwise interfere with each other (e.g., interference <NUM> and interference <NUM>), the combination of these interferences does not result in a constructive wave. Instead, the combination of the laser light results in a smooth illumination <NUM> that does not include the dark and bright spots discussed in connection with <FIG>. As such, it is highly beneficial to broaden the spectral linewidth of a laser when the laser is being used to render holographic content. By performing a broadening operation, the embodiments eliminate the occurrence of artifacts and thereby significantly improve the user's experience.

In some embodiments, the holographic display supports foveated rendering such that some areas of the display will have a higher resolution (or resolution requirement) than other areas of the display. Accordingly, in the present invention, selected pixels (but not all pixels in the display) may be illuminated or irradiated by the RGB lasers for different pre-selected periods of pulse time. As such, the pre-selected periods of time may be based, at least in part, on a location of a pixel in the display's field of view. Additionally, some embodiments support eye tracking to determine which selected portions of the display (which pixels) are to be rendered by pulsed lasers having the decreased coherence and increased spectral linewidth and for which periods of time during the image rendering. Therefore, the pre-selected periods of time may be based on where the user's eye is directed as opposed to a location on the display's field of view. Even further, some embodiments cause the pre-selected period of time to be based on a desired image resolution for the holographic image (i.e. an AR or VR image). Combinations of the above features are also possible.

Attention will now be directed to <FIG>, <FIG> which refer to a number of method acts that may be performed. Although the method acts may be discussed in a certain order or illustrated in a flowchart as occurring in a particular order, no particular ordering is required unless specifically stated, or required because an act is dependent on another act being completed prior to the act being performed.

<FIG> illustrates a flowchart <NUM> of a method for improving image quality when a red, green, blue (RGB) laser assembly is used to display an image in a mixed-reality environment. This method may be performed by any kind of computing system (e.g., the computer system described later in <FIG>) that includes the RGB laser assembly.

Initially, a set of one or more pixels are identified (act <NUM>). These pixels are to be irradiated by any one or a combination of a red laser, a green laser, or a blue laser that are included in the RGB laser assembly. In some embodiments, the pixels will be irradiated by multiple red lasers, and/or multiple green lasers, and/or multiple blue lasers. In other embodiments some pixels are illuminated by one of the red, green, or blue lasers, while other pixels are illuminated by other red, green, or blue lasers. Furthermore, the pixels may be irradiated simultaneously by these multiple red, green, and blue lasers.

Then, for each of these pixels, the red, green, and/or blue lasers in the RGB laser assembly are caused to pulsedly irradiate each of the pixels (act <NUM>). <FIG> provides further description on how this act may be performed. For instance, <FIG> continues the flowchart <NUM> by showing a number of additional acts that may be performed to irradiate the pixels.

Initially, the RGB laser assembly is operated below a laser threshold (act <NUM>). As a result of this operation, the RGB laser assembly is refrained from irradiating any pixels.

Subsequently, the RGB laser assembly is energized above the laser threshold (act <NUM>). This action causes the RGB laser assembly to begin to irradiate at least one pixel with laser light.

In connection with the above acts, there is also an act (act <NUM>) of causing the irradiated pixel to be irradiated with the laser light for a selected period of time lasting no longer than <NUM> nanoseconds (ns). Additionally, while the pixel is being irradiated with the laser light, an intensity of the laser light is set to not exceed a pre-determined optical power level based on the resolution requirement associated with the pixel and/or other attributes for that particular pixel.

After the selected period of time elapses, the RGB laser assembly is caused to again operate below the laser threshold (act <NUM>). Consequently, the RGB laser assembly is again refrained from irradiating any pixels with laser light.

<FIG> shows a flowchart <NUM> of an example method for improving virtual content when a RGB laser assembly is used to project holograms/holographic content. First, the RGB laser is selectively pulsed to irradiate some pixels (act <NUM>). Here, this pulsing operation is performed by energizing the RGB laser assembly with electrical current for a pre-selected period of time lasting no longer than <NUM> ns. In this manner, the red laser, green laser, and/or blue laser is biased so that they emit structured laser light.

As a result of pulsing the RGB laser assembly, the RGB laser assembly is caused to emit laser light (act <NUM>). Here, this laser light is specially structured to have a spectral linewidth that satisfies a pre-selected spectral linewidth threshold, as described earlier.

As a result of performing the above method acts, each pixel is then irradiated using the emitted laser light (act <NUM>). Consequently, the pixels are illuminated with laser light having a spectral linewidth that satisfies the pre-selected linewidth threshold.

<FIG> shows another flowchart <NUM> of an example method for improving holographic image quality when a RGB laser assembly is used to display AR or VR image content. Initially, the RGB laser assembly is selectively pulsed (act <NUM>). This pulsing operation is performed for each of at least some pixels that are selected to be irradiated with laser light. Furthermore, the operation of selectively pulsing the RGB laser assembly is performed by energizing the RGB laser assembly with electrical current for a pre-selected period of time. In some embodiments, this period of time lasts no longer than <NUM> ns.

For those pixels that are to be irradiated, the RGB laser assembly is caused to emit structured laser light (act <NUM>). This structured laser light is configured to have a number of Fabry-Perot modes that is greater in number than laser light that is emitted for longer than <NUM> ns. As a result of using laser light with a larger number of modes, the spectral linewidth of the structured laser light exceeds a pre-selected width threshold (e.g., <NUM> in wavelength as measured by the full-width-half-maximum intensity).

Additionally, each of the pixels are irradiated with the structured laser light for the pre-selected period of time (act <NUM>). In other words, the pixels are irradiated for no longer than <NUM> ns.

It will be appreciated that the foregoing methods will also be implemented, in some embodiments, in coordination with the scanning of the MEMs during the rendering of holograms and other images to selectively affect the desired pixels of the rendered images and to negate the creation of undesired artifacts.

Accordingly, the disclosed embodiments provide an unanticipated solution to problems related to using RGB lasers to render virtual content. In particular, the disclosed embodiments cause the RGB lasers to operate in a short, pulsed mode when illuminating an individual pixel or a group of pixels. While operating in this pulsed mode or state, the RGB lasers emit laser light for a period of time spanning less than <NUM> ns (hence the use of the term "pulsed"). Once the emission time period elapses, then the RGB lasers no longer emit laser light such that they operate in a non-emitting mode or state for a different period of time. Subsequently, the RGB lasers will be used to emit another pixel(s) in a pulsed manner. As a result, a hologram is progressively scanned or rendered by chirping/pulsing the RGB lasers. In this manner, the disclosed embodiments are able to reduce/eliminate the presence or occurrence of visual artifacts by operating the RGB lasers in a pulsed mode, which causes the resulting laser light to have a relatively larger/broader spectral linewidth than what would conventionally be used in a hologram-creation scenario.

Having just described the various features and functionalities of some of the disclosed embodiments, the focus will now be directed to <FIG> which illustrates an example computer system <NUM> that may be used to facilitate the operations described herein. In particular, this computer system <NUM> may be in the form of the HMDs that were described earlier. When in the form of a HMD, then the computer system may be an augmented-reality system or a virtual-reality system.

The computer system <NUM> may take various different forms. For example, in <FIG>, the computer system <NUM> may be embodied as a tablet 1900A, a desktop 1900B, or a HMD 1900C. The ellipsis 1900D demonstrates that the computer system <NUM> may be embodied in any form. For example, the computer system <NUM> may also be a distributed system that includes one or more connected computing components/devices that are in communication with the computer system <NUM>, a laptop computer, a mobile phone, a server, a data center, and/or any other computer system.

In its most basic configuration, computer system <NUM> includes various different components. For example, <FIG> shows that computer system <NUM> includes at least one processor <NUM> (e.g., a "hardware processing unit"), sensors <NUM>, a laser assembly <NUM> (such as described throughout this disclosure), and storage <NUM>. The storage <NUM> is shown as including code <NUM> (which is code that is executable by the processors to implement the disclosed functionality).

As discussed earlier, the computer system <NUM> may also include a MEMs system, or any other type of laser-based hologram projection unit. When a MEMs system is present, then the MEMs system operates in conjunction with the RGB laser assembly along with a waveguide (e.g., a surface relief grating waveguide) to display virtual or holographic images and may be part of the illustrated laser assembly <NUM>.

The storage <NUM> may be physical system memory, which may be volatile, non-volatile, or some combination of the two. The term "memory" may also be used herein to refer to non-volatile mass storage such as physical storage media. If the computer system <NUM> is distributed, the processing, memory, and/or storage capability may be distributed as well. As used herein, the term "executable module," "executable component," or even "component" can refer to software objects, routines, or methods that may be executed on the computer system <NUM>. The different components, modules, engines, and services described herein may be implemented as objects or processors that execute on the computer system <NUM> (e.g. as separate threads).

The disclosed embodiments may comprise or utilize a special-purpose or general-purpose computer including computer hardware, such as, for example, one or more processors (such as processor <NUM>) and system memory (such as storage <NUM>), as discussed in greater detail below. Embodiments also include physical and other computer-readable media for carrying or storing computer-executable instructions and/or data structures. Such computer-readable media can be any available media that can be accessed by a general-purpose or special-purpose computer system. Computer-readable media that store computer-executable instructions in the form of data are physical computer storage media. Thus, by way of example and not limitation, the current embodiments can comprise at least two distinctly different kinds of computer-readable media: computer storage media and transmission media.

Computer storage media are hardware storage devices, such as RAM, ROM, EEPROM, CD-ROM, solid state drives (SSDs) that are based on RAM, Flash memory, phase-change memory (PCM), or other types of memory, or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code means in the form of computer-executable instructions, data, or data structures and that can be accessed by a general-purpose or special-purpose computer.

The computer system <NUM> may also be connected (via a wired or wireless connection) to external sensors (e.g., one or more remote cameras, accelerometers, gyroscopes, acoustic sensors, magnetometers, etc.). Further, the computer system <NUM> may also be connected through one or more wired or wireless networks <NUM> to remote systems(s) that are configured to perform any of the processing described with regard to computer system <NUM>.

During use, a user of the computer system <NUM> is able to perceive information (e.g., a mixed-reality environment) through a display screen that is included among any I/O interface(s) and that is visible to the user. The I/O interface(s) and sensors <NUM> also include gesture detection devices, eye trackers, and/or other movement detecting components (e.g., cameras, gyroscopes, accelerometers, magnetometers, acoustic sensors, global positioning systems ("GPS"), etc.) that are able to detect positioning and movement of one or more real-world objects, such as a user's hand, a stylus, and/or any other object(s) that the user may interact with while being immersed in the scene.

A graphics rendering engine may also be configured, with the processor <NUM>, to render one or more virtual objects within a mixed-reality scene/environment. As a result, the virtual objects accurately move in response to a movement of the user and/or in response to user input as the user interacts within the virtual scene.

A "network," like the network <NUM> shown in <FIG>, is defined as one or more data links and/or data switches that enable the transport of electronic data between computer systems, modules, and/or other electronic devices. When information is transferred, or provided, over a network (either hardwired, wireless, or a combination of hardwired and wireless) to a computer, the computer properly views the connection as a transmission medium. The computer system <NUM> will include one or more communication channels that are used to communicate with the network <NUM>. Transmissions media include a network that can be used to carry data or desired program code means in the form of computer-executable instructions or in the form of data structures. Further, these computer-executable instructions can be accessed by a general-purpose or special-purpose computer.

Computer-executable (or computer-interpretable) instructions comprise, for example, instructions that cause a general-purpose computer, special-purpose computer, or special-purpose processing device to perform a certain function or group of functions.

Additionally, or alternatively, the functionality described herein can be performed, at least in part, by one or more hardware logic components (e.g., the processor <NUM>). For example, and without limitation, illustrative types of hardware logic components that can be used include Field-Programmable Gate Arrays (FPGAs), Program-Specific or Application-Specific Integrated Circuits (ASICs), Program-Specific Standard Products (ASSPs), System-On-A-Chip Systems (SOCs), Complex Programmable Logic Devices (CPLDs), Central Processing Units (CPUs), and other types of programmable hardware.

Claim 1:
A method for operation of a red, green, blue, RGB, laser assembly (<NUM>) used for creating an image in a mixed-reality environment in order to increase a spectral linewidth (<NUM>-<NUM>) of laser light that is emitted by the RGB laser assembly, the method being performed by a computer system that includes the RGB laser assembly, wherein the laser light is directed via a waveguide (<NUM>) to an eye (<NUM>) of a user of the computer system, the method comprising:
identifying (<NUM>) a set of one or more pixels (<NUM>) that are to be irradiated by any one or a combination of one or more red lasers, one or more green lasers, or one or more blue lasers that are included within the RGB laser assembly;
for each pixel in the set of one or more pixels, cause (<NUM>) the any one or the combination of the one or more red lasers, the one or more green lasers, or the one or more blue lasers in the RGB laser assembly to pulsedly irradiate each pixel by performing at least the following:
initially operating (<NUM>) the RGB laser assembly below a laser threshold such that the RGB laser assembly is refrained from irradiating any pixels in the set of one or more pixels;
energizing (<NUM>) the RGB laser assembly above the laser threshold to cause the RGB laser assembly to begin to irradiate at least one pixel in the set of one or more pixels with laser light;
causing (<NUM>) the at least one pixel to be irradiated with the laser light for a selected period of time lasting no longer than <NUM> nanoseconds (ns), wherein, while the at least one pixel is irradiated with the laser light, an intensity of the laser light is set to not exceed a pre-determined optical power level, wherein the pre-determined power level is based on a resolution requirement associated with the pixel and/or other attributes for that particular pixel, wherein different pixels are associated with different selected periods of time, wherein the different selected periods of time are based, at least in part, on a location of each corresponding pixel in a field of view of a display for the computer system; and
after the selected period of time elapses, operating (<NUM>) the RGB laser assembly below the laser threshold such that the RGB laser assembly is again refrained from irradiating any pixels.