Holographic VR display
A holographic display includes an illuminator, a spatial light modulator (SLM) coupled to the illuminator, and an ocular lens coupled to the SLM. The illuminator provides a wide-area illuminating light beam to illuminate the SLM with a spatially homogeneous beam of light. The illuminator may include a slab waveguide with an evanescent out-coupler, or a beam expander based on a diffraction grating with an oblique angle of incidence and a near-normal angle of diffraction of the illuminating light. A low-pass spatial filter may be provided to filter out higher diffraction orders of the illuminating light diffracted on the SLM.
1 . A holographic display comprising:
an illuminator comprising a substrate, a slab core layer on the substrate for guiding a light beam therein, a cladding layer on the slab core layer, and a light extractor on the cladding layer,
the light extractor having a refractive index higher than an effective refractive index of a mode of propagation of light in the slab core layer, for evanescent out-coupling of the light beam from the slab core layer into the light extractor, thereby forming an illuminating light beam, wherein the light extractor further comprises a prism having first and second faces at an acute angle to one another, wherein:
the first face is coupled to the cladding layer, and
the second face includes a reflector
with a curved outer surface defined by a radius of curvature having an optical power for at least one of focusing or defocusing; and
a spatial light modulator (SLM) operably coupled to the illuminator for receiving and spatially modulating the illuminating light beam in amplitude and phase to provide an image light beam.
2 . The holographic display of claim 1 , wherein a thickness of the cladding layer decreases in a direction of propagation of the light beam to improve a spatial uniformity of light extraction by the light extractor.
3 . The holographic display of claim 1 , wherein the cladding layer and the slab core layer are configured for singlemode propagation of the light beam in the slab core layer.
4 . The holographic display of claim 1 , further comprising an ocular lens operably coupled to the SLM for receiving the image light beam and forming an image at an eyebox of the holographic display for observation by a user's eye.
5 . The holographic display of claim 4 , further comprising a beam redirector in an optical path of the image light between the SLM and the ocular lens, for controllably redirecting the image light beam.
6 . The holographic display of claim 5 , wherein the beam redirector comprises a tunable liquid crystal redirector of the image light beam.
7 . The holographic display of claim 5 , wherein the beam redirector comprises a stack of active Pancharatnam-Berry phase (PBP) layers configured for switching a direction of propagation of the image light beam.
8 . The holographic display of claim 5 , further comprising:
an eye tracking system for determining a position of a pupil of the user's eye in the eyebox; and
a controller operably coupled to the eye tracking system and the beam redirector for causing the beam redirector to controllably redirect the image light beam towards the eye pupil position determined by the eye tracking system.
9 . A holographic display comprising:
a beam expander comprising a diffractive layer for diffracting a collimated light beam at an angle of incidence exceeding an angle of diffraction, whereby a lateral size of the collimated light beam increases upon diffraction on the diffractive layer;
a spatial light modulator (SLM) operably coupled to the beam expander for receiving the light beam diffracted by the diffractive layer and spatially modulating the light beam in amplitude and phase to provide an image light beam, wherein in operation, the image light beam propagates through the diffractive layer; and
a light extractor including a prism having first and second faces at an acute angle to one another, wherein
the first face is coupled to a cladding layer, and
the second face includes a reflector with a curved outer surface defined by a radius of curvature with an optical power for at least one of focusing or defocusing.
10 . The holographic display of claim 9 , wherein the angle of incidence is at least 75 degrees, and the angle of diffraction is no greater than 15 degrees.
11 . The holographic display of claim 9 , the diffractive layer comprises a polarization volume hologram.
12 . The holographic display of claim 9 , wherein the diffractive layer comprises a volume Bragg grating.
13 . The holographic display of claim 9 , wherein the beam expander further comprises first and second prismatic elements each comprising a diagonal face, the first prismatic element further comprising a side face joining the diagonal face of the first prismatic element; and
wherein the diffractive layer is sandwiched between the diagonal faces of the first and second prismatic elements, and wherein in operation, the collimated light beam is received at the side face of the first prismatic element.
14 . The holographic display of claim 9 , further comprises an ocular lens operably coupled to the SLM for receiving the image light beam and forming an image at an eyebox of the holographic display for observation by a user's eye.
15 . The holographic display of claim 14 , further comprising a beam redirector in an optical path of the image light between the SLM and the ocular lens, for controllably redirecting the image light beam.
16 . The holographic display of claim 15 , wherein the beam redirector comprises a tunable liquid crystal beam redirector.
17 . The holographic display of claim 15 , wherein the beam redirector comprises a stack of active Pancharatnam-Berry phase (PBP) layers configured for switching a direction of propagation of the image light beam.
18 . The holographic display of claim 15 , further comprising:
an eye tracking system for determining a position of a pupil of the user's eye in the eyebox; and
a controller operably coupled to the eye tracking system and the beam redirector for causing the beam redirector to controllably redirect the image light beam towards the eye pupil position determined by the eye tracking system.
19 . A holographic display comprising:
a frontlight illuminator for providing an illuminating light beam;
a spatial light modulator (SLM) operably coupled to the frontlight illuminator for receiving and spatially modulating the illuminating light beam in amplitude and phase to provide an image light beam propagating through the frontlight illuminator;
a light extractor including a prism having first and second faces at an acute angle to one another, wherein
the first face is coupled to a cladding layer, and
the second face includes a reflector with a curved outer surface defined by a radius of curvature with an optical power for at least one of focusing or defocusing;
an ocular lens operably coupled to the SLM for receiving the image light beam and forming an image at an eyebox of the holographic display for observation by a user's eye; and
a low-pass spatial filter in an optical path of the image light beam between the SLM and the ocular lens, for blocking higher orders of diffraction of the illuminating light beam on the SLM while propagating a zeroth order of diffraction of the illuminating light beam.