Patent ID: 12196966

DETAILED DESCRIPTION

FIG.1shows a laser scanning projection system100of the present invention. A RGB laser source2is arranged directed to emit light in a first direction. In the arrangement shown inFIG.1the first direction is along the y-axis. A laser scanner4is spaced apart from the laser source2. The laser scanner4is separated from the laser source2along the x and y axis in the negative x and y direction. The laser scanner4is arranged to reflect light substantially in a second direction perpendicular to the first direction, i.e. substantially along the x-axis.

A first polarising beam splitter6is located between the laser source2and the laser scanner4. The first polarising beam splitter6has a first7a, second7b, third7c, and fourth face7d. The first7aand third7cfaces are in a parallel plane to each other. The second7band fourth7dfaces are in parallel plane to each other. The first7aand third7cfaces are in an orthogonal plane to the second7band fourth faces7d.

The laser source is arranged at the fourth face7dof the first polarising beam splitter6. The laser scanner is arranged at the third face7cof the first polarising beam splitter6.

Between the first polarising beam splitter6and the laser scanner4is located a first quarter waveplate8.

A second polarising beam splitter10is located adjacent to the first polarising beam splitter6at its first face7afurthest from the laser scanner4along the optical path. The second polarising beam splitter10is further along the positive x-axis than the first polarising beam splitter6.

The second polarising beam splitter10has a first14a, second14b, third14c, and fourth face14d. The first14aand third14cfaces are in a parallel plane to each other. The second14band fourth14dfaces are in parallel plane to each other. The first14aand third14cfaces are in an orthogonal plane to the second14band fourth faces14d.

Three mirrors12a,12b,12c, are arranged around the second polarising beam splitter10at three of its faces.

The first mirror12ais located at the first face14aof the second polarising beam splitter10. The first mirror12ais concave. The first face14ais the face furthest from the laser scanner4along the optical path. The principal axis of the first mirror12ais directed along the x axis.

The second mirror12bis located at the second face14bof the second polarising beam splitter10. The second mirror12bis convex. The principal axis of the second mirror12bis orthogonal to the principal axis of the first mirror12a. The principal axis of the second mirror12bis directed along the y-axis.

The third mirror12cis located at the fourth face14dof the second polarising beam splitter10. The third mirror12cis concave. The principal axis of the third mirror12cis parallel to the principal axis of the second mirror12b. The principal axis of the third mirror12cis directed along the y-axis.

Between each of the mirrors12a,12b,12cand the second polarising beam splitter10is a quarter waveplate16a,16b,16c.

A waveguide18is arranged having its largest axis parallel to the x-axis. The waveguide has an input grating20located at the input end22of the waveguide18. The input end22of the waveguide18is located at the second face7bof the first polarising beam splitter6.

The path of the light through the laser scanning projection system100will now be described with reference toFIGS.1to5.

FIG.1shows the complete light ray path through the laser scanning projection system100.FIGS.2to5show a portion of the light ray path showing a portion of the laser projection system100.

As can be seen inFIG.1the laser source2emits light along the y-axis. The light is incident on the first polarising beam splitter6at its fourth face7d. As the light is linearly polarised in the S polarisation state it is reflected by the first polarising beam splitter6. The first polarising beam splitter6causes the light to be reflected along the x-axis such that it exits the first polarising beam splitter6at its third face7c.

The light is then incident on the quarter wave plate8. The quarter waveplate8changes the linearly polarised light to circularly polarised light. The light is then incident on the laser scanner4.

The laser scanner4includes a mirror which is mounted on a pivot. The mirror scans along the y-axis across an angular field of view, creating an exit pupil. The light reflected by the laser scanner4is diverging. Upon reflection the handedness of the polarisation changes.

As can be seen fromFIG.2, the light from the laser scanner4then passes back through the quarter waveplate8. The quarter waveplate8changes the light from circularly polarised light to linearly polarised light in the P polarisation state. The light is then incident on the third7cface of the first polarising beam splitter6. As the light is in the P polarisation state the light passes straight through the first polarising beam splitter6exiting at its first7aface. The light then passes through the third face14cof the second polarising beam splitter10. As is the case with the first polarising beam splitter6as the light is in the P polarisation state the light passes straight through the second polarising beam splitter10exiting at its first14aface.

The light then passes through a quarter waveplate16a. The quarter waveplate16achanges the light from linearly polarised light to circularly polarised light.

The light is then incident on the first mirror12a. As can be seen inFIG.3the light is reflected by the first mirror12aback towards the second polarising beam splitter10. The reflected light is now converging. The light reflected by the first mirror12apasses again through the quarter waveplate16a. The quarter waveplate16achanges the circularly polarised light into linearly polarised light in the S polarisation state.

The light then passes into the second polarising beam splitter10through the first face14a. As the light is in the S polarisation state it is reflected along the y axis to exit the second face14bof the second polarising beam splitter10.

The light then passes through the quarter waveplate16b. The quarter waveplate16bchanges the light from linearly polarised light to circularly polarised light.

The light is then incident on the second mirror12b. As can be seen inFIG.4, the light is reflected by the second mirror12bback towards the second polarising beam splitter10. The reflected light is now diverging. The light reflected by the second mirror12bpasses again through the quarter waveplate16b. The quarter waveplate16bchanges the circularly polarised light into linearly polarised light in the P polarisation state.

The light then passes into the second polarising beam splitter10through the second face14b. As the light is in the P polarisation state it travels through the second polarising beam splitter10along the y axis to exit the fourth face14dof the second polarising beam splitter10.

The light then passes through a quarter waveplate16c. The quarter waveplate16cchanges the light from linearly polarised light to circularly polarised light.

The light is then incident on the third mirror12c. As can be seen inFIG.5, the light is reflected by the third mirror12cback towards the second polarising beam splitter10. The reflected light is now converging. The light reflected by the third mirror12cpasses again through the quarter waveplate16c. The quarter waveplate16cchanges the circularly polarised light into linearly polarised light in the S polarisation state.

The light then passes into the second polarising beam splitter10through the fourth face14d. As the light is in the S polarisation state it is reflected along the x axis to exit the third face14cof the second polarising beam splitter10.

The light then passes into the first polarising beam splitter6through its first face7a. As the light is in the S polarisation state it is reflected along the y-axis to exit the second face7bof the first polarising beam splitter6.

The light is then incident on the input grating20of the waveguide18. As can be seen fromFIG.5all of the light is coupled into the input grating20. This causes the exit pupil of the laser scanner to be relayed onto the input grating20.

The laser scanning projection system100described above provides a compact way of coupling the light from the laser scanner4into the waveguide18. This enables its use for headmounted augmented reality displays (HMD). In addition, as the mirrors12a,12b, and12care on-axis with the light that is incident on them they are less prone to aberrations that can occur when the mirrors are arranged with off-axis illumination.

FIG.6shows a further arrangement of the laser scanning projection system. The components are given the same reference number as to those shown inFIGS.1to5. This arrangement differs in that the first polarising beam splitter6is arranged such that its central reflective axis is oriented in a different orientation to that of the second polarising beam splitter. The first polarising beam splitter is orientated at 180° compared to the first polarising beam splitter shown inFIGS.1to5. This causes the path that the light takes through the system to differ to that of the light path inFIGS.1to5. The path that the light takes is the same as inFIGS.1to5until the final reflection out of the first polarising beam splitter6. InFIG.6the light, after being reflected by each of the mirrors12a12b12cas described above, is then reflected such that it exits the first polarising beam splitter through side7d, before being incident on the waveguide (not shown). Of course, although not shown, the laser source2inFIG.6would instead be located at a different side of the first polarising beam splitter to that shown inFIG.1, such as at side7b.

In other arrangements, the first polarising beam splitter6may instead be orientated at any angle with respect to the first polarising beam splitter shown inFIGS.1to5. In one arrangement the first polarising beam splitter6may be originated at 90° with respect to the first polarising beam splitter6shown inFIGS.1to5. In this arrangement a half waveplate would be required between the first polarising beam splitter and the second polarising beam splitter.

With the laser scanning projection system100of the present invention it is possible to control the size of the exit pupil relayed into waveguide18. This may be achieved by varying the focal length the mirrors12a12b12c, e.g. by varying their curvature.

For instance, the size of the relayed pupil can be increased, such that it is larger than the pupil formed at the laser scanner. This has a benefit of reducing waveguide artefacts, such as banding in thicker substrates.

In addition, it is possible to alter the resolution achieved when using the laser scanning projection system100of the present invention by having a larger exit pupil. Laser scanning projectors typically are limited by their narrow beam width. When directly viewed by an eye of the viewer the laser under fills the lens of the eye. This can be seen by looking at the standard Rayleigh criterion in the equation below

θ=1.2⁢2⁢λD

Where θ is the angular resolution in radians, λ is the wavelength of light in meters, and D is the diameter of the lens aperture in meters. With, the laser underfilling the lens of the eye this reduces D in the above equation. This limits the resolution achieved.

Example 1: Focal Length of the First Mirror12aand the Third Mirror12cthe Same, Resulting in No Pupil Magnification

The field of view achieved at the scanner is 35.4°The field of view achieved at the waveguide is 35.4°The size of the relayed exit pupil is 1 mmDiffraction limited resolution at 550 nm=2.3 arc minutes.

Example 2: Focal Length of the First Mirror12aand the Third Mirror12cNOT the Same, Results in a 1.4× Pupil Magnification

The field of view achieved at the scanner is 35.4°The field of view achieved at the waveguide is 25°The size of the relayed exit pupil is 1.4 mmDiffraction limited resolution at 550 nm=1.65 arc minutes

As can be seen above in example 1, the focal lengths of the first mirror12aand the third mirror12care the same such that the relayed exit pupil has a diameter of 1 mm and the magnification of the relay is 1×. Whereas a larger relayed exit pupil of 1.4 mm is achieved in example 2 by varying the focal length of the first mirror12aand the third mirror12csuch that they are not the same so the magnification of the relay is 1.4×.

As can be seen from the above examples, the system can be designed such that the relayed exit pupil is magnified, and necessarily the field of view is reduced. Therefore, the resolution enhancement that is achieved is at the expense of the field of view. However, for certain applications this improvement in resolution outweighs the loss of field of view.

Varying the focal length of mirror12aand the third mirror12cmay be achieved by having a radius of curvature of the first mirror12athat is different to the radius of curvature of the third mirror12b. For instance, in a typical illustrative example the radius of curvature of each of the mirrors may be: first mirror12aR=12.25 mm, second mirror12bR=6.47 mm, third mirror12cR=15.46 mm. With this arrangement for an input pupil diameter of 1 mm an exit pupil of diameter 1.55 mm is achieved. These values are merely illustrative and could be increased by one or more orders of magnitude.

Alternatively, varying the focal length may be achieved by other means, such as by having mirrors with different refractive index glasses to one another.

In other arrangements, there may be a plurality of waveguides18in the form of a waveguide stack, the waveguides stacked along the y-direction. The laser scanning projection system enables the exit pupil to be relayed at an optimum position with respect to the waveguides in the waveguide stack. This may not necessarily be at the input grating of one of the waveguides, as outlined above. Instead it may be beneficial to relay the exit pupil in-between the waveguides in the stack. For two waveguides this might be exactly half way between the respective input gratings on each guide. Alternatively the exit pupil may be relayed to form at a particular one of the waveguides of the stack. This might be to target the less efficient waveguide, which may provide an improved performance of the system.

The waveguide stack may include a red waveguide, a green waveguide and a blue waveguide. If it is desirable to control the efficiency of one of the waveguides of a particular colour, the exit pupil may be relayed such that it forms within that particular waveguide. Alternatively, the exit pupil may be relayed onto the input grating of the first waveguide in the waveguide stack in a similar way as shown inFIGS.1to6.

The polarising beam splitters shown inFIGS.1to6are polarising beam splitter cubes. The diagrams above describe four faces of the polarising beam splitters. However, it would be understood to the skilled person that the polarising beam splitter may have further faces. The described arrangement is the arrangement when viewed in the 2D plane, with the polarising beam splitter cubes arranged such that they direct the light in the manner described above.

The invention also includes numerous modifications and variations to the above-described methods and apparatus.

The laser scanning projection system may be used for augmented reality or virtual reality head mounted displays. Alternatively they may be used for any type of augmented reality or virtual reality displays.

The laser source described in the above arrangement is an RGB laser. However the laser scanning projection system may be used with any type of lasers depending on the use required. This may be any type of visible wavelength source. For instance, in other arrangements the laser may be a monochromatic laser source.

The input grating may not necessarily be an input grating of the waveguide. It may alternatively be any input that couples the light into the waveguide. For instance, it may be a lens, or reflector that is suitable for coupling the light into the waveguide.

The waveguide may be any type of waveguide that is configured to receive light. In some arrangements the waveguide may be a diffractive waveguide. In other arrangements the waveguide may be a reflective waveguide.

The arrangement of the optics of the laser scanning projection system may be modified according to the requirements of its use. For instance, the first, second and third mirrors may be positioned at alternative faces of the second polarising beam splitter to the arrangement described. Alternatively, the polarisation of the light may be altered such that it takes a different path through the laser scanning projection system. For instance, the light may first be incident on the third mirror rather than the first mirror by having a different initial polarisation state.

In addition, additional optical components may be inserted into the laser scanning projection system described above. For instance, a further mirror, polarising beam splitter, quarter waveplate or other optical component may be inserted. This may cause a directional change in the light path. In other arrangements the optical components may be substituted with other optical components that achieve the same or a similar effect. For instance, the quarter waveplates may be removed, replaced or repositioned. In addition, or alternatively, additional lenses may be included before or after the relay. These lenses may aid to correct for aberrations.

Where it is described above a component has received light from another component it is not necessarily that the light is received directly from that component. In some alternative arrangements the light may interact with an additional intermediate component before it is incident on the final component.