BACKGROUND OF THE INVENTION

Modern computing and display technologies have facilitated the development of systems for so-called “virtual reality” or “augmented reality” experiences, where digitally produced images are presented in a wearable device to a user in a manner where they seem to be, or may be perceived as, real. A virtual reality, or “VR,” scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or “AR,” scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user.

The wearable device may include augmented and/or virtual reality glasses. The image can be displayed using image frames or raster scanned images. In these display devices, optical combiners are often used to combine light beams from different light sources. For example, red, green, and blue light beams can be combined to form a collimated combined colored light beam for displaying an image. Conventional optical combiners made with glass lenses, mirrors, and prisms can be bulky and heavy. They are undesirable for wearable device in VR or AR applications.

Therefore, improved structures and methods for optical combiners are highly desirable.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide methods and systems for RGB (Red Green Blue) illuminators that are compact and light weight compared with conventional combiners. Some embodiments can also provide speckle reduction. In embodiments of the invention, the optical combiners can combine light beams from two or more light sources, such as laser diodes. In some embodiments, a mirror assembly reflects light beams from the light sources towards a combining element, which produces combined output beams along a common optical axis. The mirrors direct the beams to the combining element to achieve collinearity. The spatial arrangement of the mirror assembly and the combining element provides folded optical paths to reduce the dimension of the optical combiner. The mirror assembly can be a set of multiple mirrors or a single reflective element. Collimation and circularization can be achieved by a combination of refractive lens (for instance, toroidal) and mirrors (rotational symmetric/off-axis parabolic or freeform). These elements can be individual for each source or the same for each source. Therefore it can be a ‘segmented/separated’ solution or monolithic solution per element.

The combining element can be a stack of dichroic mirrors, prism configurations based on dichroic beam-combining, diffractive elements, or MEMS (Micro-electro-mechanical-system) mirrors. For example, the combining element can be a rotating MEMS mirror, which is tilted at a different angular displacement for each light source. For coherent sources, speckle reduction can be achieved in combination with an etendue generating element (for instance holographic diffusor) by wobbling the combining element to slightly shift the beam. Embodiments based on the rotating MEMS mirror can provide dithering of the light beams without requiring additional elements. In other embodiments, to provide beam dithering would need an additional actuator.

According to some embodiments of the invention, an optical combiner includes an input mirror assembly configured to receive multiple light beams and to provide a first reflected light beam, a second reflected light beam, and a third reflected light beam. The optical combiner also includes a rotating mirror configured to rotate through a range of angular displacement. During a first time period, the rotating mirror is disposed at a first angular displacement, and configured to receive the first reflected light beam from the input mirror assembly and provide a first output light beam along an output optical axis. During a second time period, the rotating mirror is disposed at a second angular displacement, and configured to receive the second reflected light beam from the input mirror assembly and provide a second output light beam along the output optical axis. During a third time period, the rotating mirror is disposed at a third angular displacement, and configured to receive the third reflected light beam from the input mirror assembly and provide a third output light beam along the output optical axis. The optical combiner is configured to provide a time-sequential collimated combined output light beam along the output optical axis, and is configured to dither the combined output light beam.

In some embodiments of the above optical combiner, the input mirror assembly includes a first input mirror disposed in a first light path between the rotating mirror and a first light source and configured to reflect a first input light beam emitted from the first light source and direct the first reflected light beam to the rotating mirror during the first time period when the rotating mirror is at the first angular displacement. The input mirror assembly also includes a second input mirror disposed in a second light path between the rotating mirror and a second light source and configured to reflect a second input light beam emitted from the second light source and direct the second reflected light beam to the rotating mirror during the second time period when the rotating mirror is at the second angular displacement. The input mirror assembly further includes a third input mirror disposed in a third light path between the rotating mirror and a third light source and configured to reflect a third input light beam emitted from the third light source and direct the third reflected light beam to the rotating mirror during the third time period when the rotating mirror is at the third angular displacement.

In some embodiments of the above optical combiner, the first light source is a red laser light source, the second light source is a green laser light source, and the third light source is a blue laser light source. Each of the first input mirror, the second input mirror, and the third input mirror is a collimating and circularizing mirror.

In some embodiments, the first light source, the second light source, the third light source, and the input mirror assembly are disposed in a two-dimensional planar configuration, and the rotating mirror is disposed offset in a third dimension to provide folded optical paths, thereby reducing a dimension of the optical combiner.

In alternative embodiments, the input mirror assembly can include a curved reflective element configured to reflect a first input light beam emitted from a first light source to the rotating mirror during the first time period when the rotating mirror is at the first angular displacement, reflect a second input light beam emitted from a second light source to the rotating mirror during the second time period when the rotating mirror is at the second angular displacement, and reflect a third input light beam emitted from a third light source to the rotating mirror during the third time period when the rotating mirror is at the second angular displacement.

In some embodiments, the curved reflective element can have discrete prescriptions for each individual incidence location on the curved reflective element. In some embodiments, the curved reflective element can have a parabolic surface contour. In some embodiments, the curved reflective element can have an elliptical surface contour. In some embodiments, the curved reflective element can have a hyperbolic surface contour.

Depending on the embodiments, the rotating mirror can be a one-axis MEMS mirror or a two-axis MEMS mirror.

In some embodiments, an RGB illuminator includes red, green, and blue laser light sources and an optical combiner as described above.

According to some embodiments, an optical combiner can include a rotating mirror configured to rotate through a range of angular displacement. During a first time period, the rotating mirror is disposed at a first angular displacement, and configured to receive a first incident light beam and provide a first output light beam along an output optical axis. During a second time period, the rotating mirror is disposed at a second angular displacement, and configured to receive a second incident light beam and provide a second output light beam along the output optical axis. The optical combiner is configured to provide a time sequential collimated combined light beam.

In some embodiments of the above optical combiner, the rotating mirror is configured to dither the first output light beam and the second output light beam.

In some embodiments, the optical combiner also includes an input mirror assembly configured to receive a first input light beam and a second input light beam from a first light source and a second light source, respectively, reflect the first input light beam to form a first reflected light beam to provide the first incident light beam to the rotating mirror, and reflect the second input light beam to form a second reflected light beam to provide the second incident light beam to the rotating mirror.

In some embodiments, the input mirror assembly includes a first input mirror disposed in a first light path between the rotating mirror and the first light source and configured to reflect the first input light beam emitted from the first light source and direct the first reflected light beam to the rotating mirror during the first time period when the rotating mirror is at the first angular displacement. The first reflected light beam forms the first incident light beam to the rotating mirror. The input mirror assembly also includes a second input mirror disposed in a second light path of the rotating mirror and the second light source and configured to reflect the second input light beam emitted from the second light source and direct the second reflected light beam to the rotating mirror during the second time period when the rotating mirror is at the second angular displacement. The second reflected light beam forms the second incident light beam to the rotating mirror.

In some embodiments, the first input mirror and the second input mirror are collimating and circularizing mirrors.

In some embodiments, the input mirror assembly can include a curved reflective element configured to reflect the first input light beam emitted from the first light source to the rotating mirror during the first time period when the rotating mirror is at the first angular displacement, and reflect the second input light beam emitted from the second light source to the rotating mirror during the second time period when the rotating mirror is at the second angular displacement.

According to some embodiments, a method for combining light beams from multiple light sources includes, during a first time period, disposing a rotating mirror at a first angular displacement, and receiving a first incident light beam to provide a first output light beam along an output optical axis. The method includes, during a second time period, disposing the rotating mirror at a second angular displacement, and receiving a second incident light beam to provide a second output light beam along the output optical axis. The method further includes repeating the above operation to provide a time-sequential collimated combined output light beam along the output optical axis.

In some embodiments, the above method can also include, during a third time period, disposing the rotating mirror at a third angular displacement, and receiving a third incident light beam to provide a third output light beam along the output optical axis.

In some embodiments, the method can also include dithering the combined output light beam using the rotating mirror.

In some embodiments, the method can also include receiving a first input light beam and a second input light beam from a first light source and a second light source, respectively, using an input mirror assembly. The method can further include reflecting the first input light beam to form a first reflected light beam to provide the first incident light beam to the rotating mirror, using the input mirror assembly, and reflecting the second input light beam to form a second reflected light beam to provide the first incident light beam to the rotating mirror, using the input mirror assembly.

In some embodiments, the method also includes collimating and circularizing the first output light beam and the second output light beam using the input mirror assembly.

In some embodiments, the curved reflective element comprises a parabolic surface contour.

In some embodiments, the curved reflective element comprises an elliptical surface contour.

In some embodiments, the curved reflective element comprises a hyperbolic surface contour.

In some embodiments, the method includes forming an RGB (Red Green Blue) illuminator with the optical combiner described above, a red laser light source, a green laser light source, and a blue laser light source.

According to some embodiments, an optical combiner has a dichroic mirror assembly including a first dichroic mirror, a second dichroic mirror, and a third dichroic mirror arranged in a stack along an output optical axis. The first dichroic mirror is configured to reflect light beams of a first color. The second dichroic mirror is configured to reflect light beams of a second color and to transmit light beams of the first color. The third dichroic mirror is configured to reflect light beams of a third color and to transmit light beams of the first color and light beams of the second color. The first dichroic mirror is disposed at a first angular displacement and configured to receive a first incident light beam of a first color and provide a first output light beam along an output optical axis. The second dichroic mirror is disposed at a second angular displacement and configured to receive a second incident light beam of a second color and provide a second output light beam along the output optical axis. The third dichroic mirror is disposed at a third angular displacement and configured to receive a third incident light beam of a third color and provide a third output light beam along the output optical axis. The optical combiner is configured to provide a collimated combined output light beam along the output optical axis. In an alternative embodiment, the first dichroic mirror can be replaced with a reflective mirror.

In some embodiments, a portion of the first incident light beam passes through the third dichroic mirror and the second dichroic mirror before reaching the first dichroic mirror, and a portion of the second incident light beam passes through the third dichroic mirror before reaching the second dichroic mirror.

In some embodiments, a portion of the first output light beam passes through the second dichroic mirror and the third dichroic mirror before reaching the first dichroic mirror; and

a portion of the second output light beam passes through the third dichroic mirror before reaching the second dichroic mirror.

In some embodiments, the optical combiner also includes an input mirror assembly configured to receive a first input light beam, a second input light beam, and a third input light beam from a first light source, a second light source, and a third light source, respectively. The input mirror assembly is also configured to reflect the first input light beam to form a first reflected light beam to provide the first incident light beam to the dichroic mirror assembly, reflect the second input light beam to form a second reflected light beam to provide the second incident light beam to the dichroic mirror assembly, and reflect the third input light beam to form a third reflected light beam to provide the third incident light beam to the dichroic mirror assembly.

In some embodiments, the input mirror assembly includes a first input mirror, a second input mirror, and a third input mirror. The first input mirror is disposed in a first light path between the dichroic mirror assembly and the first light source and configured to reflect the first input light beam emitted from the first light source and direct the first reflected light beam to the dichroic mirror assembly, wherein the first reflected light beam forms the first incident light beam to the dichroic mirror assembly. The second input mirror is disposed in a second light path between the dichroic mirror assembly and the second light source and configured to reflect the second input light beam emitted from the second light source and direct the second reflected light beam to the dichroic mirror assembly, wherein the second reflected light beam forms the second incident light beam to the dichroic mirror assembly. The third input mirror disposed in a third light path between the dichroic mirror assembly and the third light source and configured to reflect the second input light beam emitted from the third light source and direct the third reflected light beam to the dichroic mirror assembly, wherein the second reflected light beam forms the second incident light beam to the dichroic mirror assembly.

In some embodiments, the first input mirror, the second input mirror, and the third input mirror in the input mirror assembly are collimating and circularizing mirrors.

In some embodiments, the input mirror assembly includes a curved reflective element configured to reflect the first input light beam emitted from the first light source to the dichroic mirror assembly, reflect the second input light beam emitted from the second light source to the dichroic mirror assembly, and reflect the third input light beam emitted from the third light source to the dichroic mirror assembly.

In some embodiments, the curved reflective element comprises discrete prescriptions for each individual incidence location on the curved reflective element.

In some embodiments, the curved reflective element comprises a parabolic surface contour.

In some embodiments, the curved reflective element comprises an elliptical surface contour.

In some embodiments, the curved reflective element comprises a hyperbolic surface contour.

In some embodiments, an RGB (Red Green Blue) illuminator includes the optical combiner having the dichroic mirror assembly described above, a red laser light source, a green laser light source, and a blue laser light source.

According to some embodiments, a method for combining light beams from multiple light sources includes providing a dichroic mirror assembly including a first dichroic mirror, a second dichroic mirror, and a third dichroic mirror arranged in a stack along an output optical axis. The first dichroic mirror is configured to reflect light beams of a first color. The second dichroic mirror is configured to reflect light beams of a second color and to transmit light beams of the first color. The third dichroic mirror is configured to reflect light beams of a third color and to transmit light beams of the first color and light beams of the second color. The method includes disposing the first dichroic mirror at a first angular displacement to receive a first incident light beam of a first color and provide a first output light beam along an output optical axis. The method also includes disposing the second dichroic mirror at a second angular displacement to receive a second incident light beam of a second color and provide a second output light beam along the output optical axis. The method further includes disposing the third dichroic mirror at a third angular displacement to receive a third incident light beam of a third color and provide a third output light beam along the output optical axis. The method configures the optical combiner to provide a collimated combined output light beam along the output optical axis. In an alternative embodiment, the first dichroic mirror can be replaced with a reflective mirror.

In some embodiments, the method can also include dithering the combined output light beam using the rotating mirror.

Additional features, benefits, and embodiments are described below in the detailed description, figures, and claims.

