COMPACT OPTICAL MODULE

A compact optical package includes an RGB laser unit containing red, green, and blue laser diodes within a single package, with three lenses adjacent the RGB laser unit to collimate red, green, and blue laser light emitted by the red, green, and blue laser diodes. A beam combiner combines the red, green, and blue laser light into a single RGB laser beam and also outputs a lower power feedback beam. The compact optical package also includes a movable mirror apparatus, and a fixed folding mirror upon which the single RGB laser beam output by the beam splitter impinges and reflects the single RGB laser beam toward the movable mirror apparatus. The movable mirror apparatus directs the single RGB laser beam through an exit window and to scan the single RGB laser beam in a scan pattern to form at least one desired image on a target.

TECHNICAL FIELD

This disclosure is directed to the field of laser scanning projectors and, in particular, to a compact optical module for use in laser scanning projectors.

BACKGROUND

A laser scanning projector or “picoprojector” is a small, portable electronic device. Picoprojectors are typically paired to, or incorporated within, user devices such as smart glasses, smartphones, tablets, laptops, or digital cameras, and used to project virtual and augmented reality, documents, images, or video stored on those user devices onto a projection surface, such as a wall, light field, holographic surface, or inner display surface of virtual or augmented reality glasses.

Such picoprojectors typically include a projection subsystem and an optical module. The paired user device serves an image stream (e.g., a video stream) to the projection subsystem. The projection subsystem properly drives the optical module so as to project the image stream onto the projection surface for viewing.

In greater detail, typical optical modules are comprised of a laser source and one or more microelectromechanical (MEMS) mirrors to scan the laser beam produced by the laser source across the projection surface in a projection pattern. By modulating the laser beam according to its position on the projection surface, while the laser beam is scanned in the projection pattern, the image stream is displayed. Commonly, at least one lens focuses the beam after reflection by the one or more MEMS mirrors, and before the laser beam strikes the projection surface, although optical modules of other designs may be used.

The projection subsystem controls the driving of the laser source and the driving of the movement of the one or more MEMS mirrors. Typically, the driving of movement of one of MEMS mirrors is at, or close to, the resonance frequency of that MEMS mirror, and the driving of movement of another of the MEMS mirrors is performed linearly and not at resonance.

While existing picroprojector systems are usable within virtual reality headsets and augmented reality glasses, due to the fact such devices are carried by the user's head, it is desired for such devices to be as light as possible. Additionally, particularly in the case of augmented reality glasses, it is also for such devices to be as compact as possible, since a pair of augmented reality glasses that externally appears no different than a common pair of eyeglasses would be highly commercially desirable. Current optical modules are larger and heavier than desired for virtual reality and augmented reality applications, and as such, further development into ways to shrink and lighten such optical modules is necessary.

SUMMARY

Disclosed herein is an optical package, including a laser unit containing one or more laser diodes within a single package, one or more lenses adjacent the laser unit and configured to collimate laser light emitted by the one or more laser diodes of the laser unit, a beam combiner configured to combine the laser light from the one or more laser diodes into a single laser beam and to also output a lower power feedback beam, a movable mirror apparatus, and a fixed folding mirror upon which the single laser beam output by the beam combiner impinges and which is configured to reflect the single laser beam toward the movable mirror apparatus. The movable mirror apparatus is configured to direct the single laser beam through an exit window and to scan the single laser beam in a scan pattern to form at least one desired image on a target adjacent the optical package.

In some instances, the laser unit contains red, green, and blue laser diodes within a single package that lases to generate red, green, and blue laser light that is initially shone through a prism within the laser unit and which exit the prism to impinge upon the one or more lenses. In these instances, the one or more lenses are first, second, and third lenses upon which the red, green, and blue lasers impinge, and the single laser beam is a RGB laser beam. The red, green, and blue laser diodes may each be formed within respective dies contained within the single package of the laser unit, and the respective die into which the red, green, and blue laser diodes may be formed are separated from one another by free space within the laser unit. Also, the movable mirror apparatus may include a horizontal mirror upon which the RGB laser beam, as reflected by the folding mirror, impinges, and the horizontal mirror may reflect the RGB laser beam toward a vertical mirror that reflects the RGB laser beam out an exit window in the optical package.

The horizontal mirror may be driven at resonance and the vertical mirror may be driven linearly. The vertical mirror may be arranged such that the RGB laser beam exits the exit window at a desired keystone angle.

A photodiode may receive the low power feedback beam.

The beam combiner may include a single beam splitter unit arranged such that the laser light emitted by the one or more laser diodes enters into outputs of the beam splitter, such that the low power feedback beam exits from another output of the beam splitter, and such that the single laser beam exists from the input of the beam splitter.

The beam combiner may instead include first, second, and third discrete dichroic beam combiners spaced apart from one another.

Also disclosed herein is an augmented reality package, including a printed circuit board containing laser driver circuitry and mirror driver circuitry, and a compact optical package mechanically connected to the printed circuit board and electrically connected to the laser driver circuitry and mirror driver circuitry. The compact optical package includes an RGB laser unit containing red, green, and blue laser diodes within a single package, the RGB laser unit being electrically connected to the laser driver circuitry. The compact optical package also includes three lenses adjacent the RGB laser unit and configured to collimate red, green, and blue laser light emitted by the red, green, and blue laser diodes of the RGB laser unit. A beam combiner within the compact optical package is configured to combine the red, green, and blue laser light into a single RGB laser beam and to also output a lower power feedback beam. A movable mirror apparatus within the compact optical package is electrically connected to the mirror driver circuitry, and there is a fixed folding mirror upon which the single RGB laser beam output by the beam splitter impinges and which is configured to reflect the single RGB laser beam toward the movable mirror apparatus. The movable mirror apparatus is configured to, under control of the mirror driver circuitry, direct the single RGB laser beam through an exit window and to scan the single RGB laser beam in a scan pattern to form at least one desired image on a target of the augmented reality package.

The red, green, and blue laser diodes may each be formed within respective dies contained within the single package of the RGB laser unit. The respective die into which the red, green, and blue laser diodes are formed may be separated from one another by free space within the RGB laser unit.

The movable mirror apparatus may include a horizontal mirror upon which the RGB laser beam, as reflected by the folding mirror, impinges. The horizontal mirror may reflect the RGB laser beam toward a vertical mirror that reflects the RGB laser beam out an exit window in the compact optical package toward the target.

The horizontal mirror may be driven at resonance and the vertical mirror may be driven linearly. The vertical mirror may be arranged such that the RGB laser beam exits the exit window at a desired keystone angle.

A photodiode may receive the low power feedback beam.

The beam combiner may include a single beam splitter unit arranged such that the red, green, and blue laser light enters into outputs of the beam splitter, such that the low power feedback beam exits from another output of the beam splitter, and such that the single RGB laser beam exists from the input of the beam splitter.

As an alternative, the beam combiner may include first, second, and third discrete dichroic beam combiners spaced apart from one another.

DETAILED DESCRIPTION

The following disclosure enables a person skilled in the art to make and use the subject matter disclosed herein. The general principles described herein may be applied to embodiments and applications other than those detailed above without departing from the spirit and scope of this disclosure. This disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed or suggested herein.

A compact optical module10is now described with reference toFIG. 1. The compact optical module10includes a housing11carrying a compact RGB laser package12that includes a red laser diode12a, green laser diode12b, and blue laser diode12ctherein.

Details of the compact RGB laser package12are shown inFIG. 2. The compact RGB laser package12includes an aluminum nitride body39, on a front face of which are aluminum nitride sub-mounts41,42, and43. The red laser diode12ais mounted to the first aluminum nitride sub-mount41, green laser diode12bis mounted to the second aluminum nitride sub-mount42, and the blue laser diode12cis mounted to the third aluminum nitride sub-mount43. The laser diodes12a,12b, and12cthemselves are each formed in their own die. A single glass prism40is mounted to the front side of the aluminum nitride body39, and serves to help focus the red, green, and blue laser beams respectively emitted by the red laser diode12a, green laser diode12b, and blue laser diode12c, although it should be appreciated that in some instances, the element40may instead be three glass prisms, one for each laser diode12a,12b, and13c. On the back face of the aluminum nitride body39, electrical pads45are mounted, which provide connections to the red laser diode12a, green laser diode12b, and blue laser diode12c. A thermal pad46is mounted on the back face of the aluminum nitride body39and makes contact with the housing11at the location therein where the compact RGB laser package12is carried. The physical dimensions of the housing11may be, for example, 5.3 mm in width, 4 mm in depth, and 1.25 mm in height. Prior art systems utilize individually packaged laser diodes, each of which is nearly the size of the RGB laser package12used herein; thus the RGB laser package12provides a large amount of savings in terms of space and weight. Naturally, the RGB laser package12and housing11may have other dimensions, and the given dimensions are just examples.

Returning toFIG. 1, alignment lenses14a,14b, and14care carried within the housing11adjacent the RGB laser package12, and serve to collimate the laser beams30,31, and32respectively generated by the red laser diode12a, green laser diode12b, and blue laser diode12cin operation. The alignment lenses14a,14b, and14care set such that the laser spots would overlap at a certain distance, for example, at a 450 mm focal distance. In addition, the maximum angular deviation between any two laser spots should helpfully be no more than 0.2°, and the maximum deviation between all laser spots should helpfully be no more than 0.5°. The spot size produced by the red laser diode12a, after focusing by the alignment lens14a, is to be around 830×650 microns; the spot size produced by the blue laser diode12b, after focusing by the alignment lens14b, is to be around 800×600 microns; and the spot size produced by the green laser diode12c, after focusing by the alignment lens14c, is to be around 780×550 microns. If the focal distance is changed from this example for a particular application, the spot size changes accordingly. The alignment lenses14a,14b, and14cmay have a numerical aperture of 0.38, with an effective focal length of 2 mm, and a 1 mm diameter, and may be coated with anti-reflective coating that allows light in the range of 400 nm-700 nm to pass but rejects other light. The alignment lenses14a,14b, and14cmay have a generally cylindrical cross section, with a flat rear surface and a convex front surface, or, in some cases, may have an aspherical shape. The effective focal length and diameter of the alignment lenses14a,14b, and14ccan be altered as desired for specific applications. For example, the alignment lenses14a,14b, and14cmay be 1.5 mm in diameter. Also appreciate that in some cases, the alignment lenses14a,14b, and14cmay have different diameters from one another, or one of the alignment lenses may have a different diameter than the other two alignment lenses.

A 4:1 beam splitter16is carried within the housing11adjacent the alignment lenses14a,14b, and14c. This beam splitter16is a single rectangularly shaped unit formed of three square units, each square unit being comprised of two triangular prisms having their bases affixed to one another. The overall dimensions of the beam splitter may be, for example, 6 mm in length, 2 mm in depth, and 2.5 mm in height. Naturally, these dimensions are just examples, and the beam splitter16may instead of other dimensions.

The prisms of the beam splitter16that serve to reflect the laser beams30and31are arranged so as to reflect as close to 100% of those beams as possible along a trajectory out the right side of the beam splitter36to help form the combined RGB laser beam33, while the prisms of the beam splitter16that serve to reflect the laser beam32is arranged so as to reflect about 98% of the laser beam32out the right side of the beam splitter36to form the combined RGB laser beam33, while passing about 2% of the laser beam32through to reach a photodiode18used to provide feedback for the system driving the laser diodes12a,12b, and12cof the RGB laser package12.

Note that while the beam splitter16here is used to combine the laser beams30,31, and32to form the RGB laser beam33, the beam splitter16is still technically a 4:1 beam splitter, as if a beam33were to be input into the right side (the output) of the beam splitter16, the beam splitter would split it to produce the beams32(exiting toward the lens14cand toward the photodiode18),31, and30. Thus, despite its use as a beam combiner, the component16is indeed a beam splitter16.

A vertical mirror20, horizontal mirror24, and folding mirror22are adjacent the beam splitter16, and collectively are used to reflect the RGB laser beam33out an exit window26on a housing11and onto a display surface. Note that the position of the folding mirror22is fixed during operation, while the horizontal mirror24is driven to oscillate at its resonance frequency and the vertical mirror22is driven linearly. Therefore, the purpose of the folding mirror22is simply to “fold” the path of the RGB laser beam33to strike the horizontal mirror24, while the purpose of the horizontal mirror24and vertical mirror22is to scan the RGB laser beam33across the display surface in a scan pattern designed to reproduce the desired still or moving images. The overall dimensions of the vertical mirror22may be, for example, 7.94 mm in length, 2.34 mm in depth, and 0.67 mm in height; the overall dimensions of the horizontal mirror24may be, for example, 4.44 mm in length, 2.94 mm in depth, and 0.67 mm in height. Naturally, the vertical mirror22and horizontal mirror24may have other dimensions, and the given dimensions are just examples.

Note that, instead of the beam splitter16, as shown inFIG. 3, three separate dichroic beam combiners16a′,16b′, and16c′ may be used to reproduce the RGB laser beam33and its illustrated path. Understand that, as compared to the beam splitter16which is a single component formed from sub-components bonded together, the dichroic beam combiners16a′,16b′, and16c′ are separate, discrete components. The overall dimension of each dichroic beam combiner16a′,16b′, and16c′ may be 2.6 mm in length, 0.5 mm in depth, and 3.2 mm in height, for example. Naturally, dichroic beam combiners16a′,16b′, and16c′ may have other dimensions, and the given dimensions are just examples. The dichroic beam combiners16a′,16b′, and16c′ have the same functional operation as the beam splitter16described above.

Turning now toFIG. 4, the geometry of the vertical mirror20, horizontal mirror24, and folding mirror22is now described. The RGB laser beam33is aimed by the beam splitter16to pass over the top of the vertical mirror20to strike the folding mirror22, which reflects the RGB laser beam33onto the horizontal mirror24, which then reflects the RGB laser beam33onto the vertical mirror20, which reflects the RGB laser beam33out the exit window26on the housing11and onto the display surface.

Sample angles for this path taken by the RGB laser beam33may be seen inFIG. 5, where the folding mirror32reflects the RGB laser beam33at an angle of 54° toward the horizontal mirror24, and the horizontal mirror24reflects the RGB laser beam33at an angle of 54° toward the vertical mirror. The vertical mirror20is arranged to reflect the RGB laser beam33in a direction parallel to the plane in which the horizontal mirror24lies, and therefore directly out the exit window26without any keystone. In this arrangement, it may be observed that the path traveled by the RGB laser beam33between the centers of the horizontal mirror24and vertical mirror20is about 0.9 mm. The mechanical opening angle of the vertical mirror20is ±5°, and the mechanical opening angle of the horizontal mirror24is ±12°.

In some instances, it may be desired for the RGB laser beam33to exit the exit window with keystone. For example, inFIG. 6, the folding mirror32reflects the RGB laser beam33at an angle of 54° toward the horizontal mirror24, and the horizontal mirror24reflects the RGB laser beam33at an angle of 56.5° toward the vertical mirror, and the vertical mirror20reflects the RGB laser beam33out the exit window26at a keystone angle of 5°, which permits ±10° in mechanical opening angle of the vertical mirror20. In this arrangement, it may be observed that the path traveled by the RGB laser beam33between the centers of the horizontal mirror24and vertical mirror20is about 1.02 mm.

As another example, inFIG. 7, the folding mirror32reflects the RGB laser beam33at an angle of 54° toward the horizontal mirror24, and the horizontal mirror24reflects the RGB laser beam33at an angle of 61° toward the vertical mirror, and the vertical mirror20reflects the RGB laser beam33out the exit window26at a keystone angle of 14°, which permits ±7° in mechanical opening angle of the vertical mirror20. In this arrangement, it may be observed that the path traveled by the RGB laser beam33between the horizontal mirror24and vertical mirror20is about 1.28 mm.

From the above, it is to be noticed that the distance between the centers of the horizontal mirror24and vertical mirror20changes as the keystone angle changes. The larger the keystone, the larger the distance between the centers of the horizontal mirror24and vertical mirror20, and vice versa.

A perspective view of the compact optical module10may be seen inFIG. 8, where it can be seen that the housing11has dimensions of 10.2 mm in width, 11 mm in depth, and 5.5 mm in height.

A potential augmented reality unit40is shown inFIG. 9, where it can be observed that the compact optical module10is installed and electrically connected to the end of a printed circuit board51that includes drivers for the mirrors and RGB laser package within the compact optical module10. A target surface52is adjacent the exit window of the compact optical module10, and therefore in operation, images are formed on the target surface52by the compact optical module10.

This augmented reality unit40may be installed into a pair of augmented reality glasses60, as shown inFIG. 10, where it can be observed that the compact optical module10is sufficiently small such that the augmented reality glasses60appear to be a normal pair of eyeglasses.