Systems, devices, and methods for holographic optical elements
Systems, devices, and methods for holographic optical elements are described. A holographic optical element includes a first layer of holographic material and a second layer of holographic material. The first layer of holographic material includes a first hologram responsive to light in a first waveband and a second hologram responsive to light in a second waveband. The second layer of holographic material includes a third hologram responsive to light in a third waveband and may include a fourth hologram responsive to light in a fourth waveband. The first, second, third, and fourth wavebands are distinct and may comprise light of red, blue, green, and infrared wavelengths, respectively. Distribution of the three or four holograms on two layers of holographic material allows each hologram to have an index modulation of greater than 0.016, a diffraction efficiency of greater than 15%, and an angular bandwidth of greater than 12°.
1. A wearable heads-up display (WHUD) comprising:
a support structure that in use is worn on a head of a user, the support structure having the general shape and appearance of an eyeglass frame;
at least one eyeglass lens carried by the support structure;
a holographic optical element physically coupled to the at least one eyeglass lens and positioned in a field of view of the user when the support structure is worn on the head of the user, the holographic optical element (HOE) comprising:
a first layer of holographic material that includes a first hologram and a second hologram; and
a second layer of holographic material that includes at least a third hologram, wherein each of the first hologram, the second hologram, and the third hologram has a respective index modulation of at least 0.016, and wherein:
the first hologram is responsive to light in a first waveband and unresponsive to light outside of the first waveband;
the second hologram is responsive to light in a second waveband and unresponsive to light outside of the second waveband;
the third hologram is responsive to light in a third waveband and unresponsive to light outside of the third waveband, wherein the first waveband, the second waveband, and the third waveband are distinct and non-overlapping
and
a laser projector carried by the support structure, the laser projector comprising:
a first laser diode to output laser light in the first waveband;
a second laser diode to output laser light in the second waveband;
a third laser diode to output laser light in the third waveband;
a beam combiner to combine the laser light from the laser diodes into an aggregate beam; and
at least one controllable mirror to scan the aggregate beam over the holographic optical element.
2. The WHUD of claim 1 wherein:
the first waveband, the second waveband, and the third waveband include: a red waveband comprising light of red wavelengths, a green waveband comprising light of green wavelengths, and a blue waveband comprising light of blue wavelengths.
3. The WHUD of claim 1 , wherein:
the at least a third hologram includes a fourth hologram that is responsive to light in a fourth waveband and unresponsive to light outside of the third waveband, wherein the fourth waveband is distinct from the first waveband, the second waveband, and the third waveband with no overlap therebetween; and
the laser projector further includes a fourth laser diode to output laser light in a fourth waveband.
4. The WHUD of claim 3 wherein:
the first waveband, the second waveband, the third waveband, and the fourth waveband include: a red waveband comprising light of red wavelengths, a green waveband comprising light of green wavelengths, a blue waveband comprising light of blue wavelengths, and an infrared waveband comprising light of infrared wavelengths.
5. The WHUD of claim 1 wherein the at least one eyeglass lens and the HOE are curved.
6. The WHUD of claim 1 wherein a respective diffraction efficiency of each of the first hologram, the second hologram, and the third hologram is at least 15%.
7. The WHUD of claim 1 wherein a respective angular bandwidth of each of the first hologram, the second hologram, and the third hologram is at least 12°.
8. The WHUD of claim 1 wherein the first layer of holographic material and the second layer of holographic material have a thickness not greater than 8 μm.
9. The WHUD of claim 1 wherein the holographic material is a photopolymer.