Method and system for patterning a liquid crystal layer
An optical master is created by using a nanoimprint alignment layer to pattern a liquid crystal layer. The nanoimprint alignment layer and the liquid crystal layer constitute the optical master. The optical master is positioned above a photo-alignment layer. The optical master is illuminated and light propagating through the nanoimprinted alignment layer and the liquid crystal layer is diffracted and subsequently strikes the photo-alignment layer. The incident diffracted light causes the pattern in the liquid crystal layer to be transferred to the photo-alignment layer. A second liquid crystal layer is deposited onto the patterned photo-alignment layer, which subsequently is used to align the molecules of the second liquid crystal layer. The second liquid crystal layer in the patterned photo-alignment layer may be utilized as a replica optical master or as a diffractive optical element for directing light in optical devices such as augmented reality display devices.
1 . A method of forming an optical master, the method comprising:
disposing a photo-alignment layer on a substrate;
propagating light through a first optical master to the photo-alignment layer, wherein the first optical master comprises:
an alignment layer including surface relief features, and
a first liquid crystal layer on the surface relief features,
wherein liquid crystal molecules of the first liquid crystal layer define a liquid crystal pattern, and
wherein propagating the light through the first optical master to the photo-alignment layer replicates the liquid crystal pattern in the photo-alignment layer; and
depositing a second liquid crystal layer on the photo-alignment layer to form the optical master, wherein the molecules of the second liquid crystal layer are aligned by the photo-alignment layer, and wherein the optical master comprises the second liquid crystal layer, the photo-alignment layer, and the substrate,
wherein the light comprises one of left and right circularly polarized light,
wherein the first liquid crystal layer diffracts the light into left circularly polarized light and right circularly polarized light,
wherein one of the left and the right circularly polarized light is +1 or −1 diffraction order light and the other of the left and the right circularly polarized light is zero diffraction order light, and
wherein the first liquid crystal layer diffracts about half the light into left circularly polarized light and about half the light into right circularly polarized light.
2 . The method of claim 1 , wherein the alignment layer comprises an imprint layer.
3 . The method of claim 1 , wherein the liquid crystal layer comprises a nematic liquid crystal layer.
4 . The method of claim 1 , wherein the surface relief features comprise nanostructures and the first liquid crystal layer is disposed on the alignment layer such that the liquid crystal molecules of the first liquid crystal layer align with the nanostructures.
5 . The method of claim 4 , wherein the nanostructures comprise imprinted nanostructures.
6 . The method of claim 4 , wherein the nanostructures comprise an optical phase and a grating period, and wherein the liquid crystal molecules of the first liquid crystal layer are aligned by the nanostructures to include substantially same optical phase and grating period.
7 . The method of claim 1 , wherein the first liquid crystal layer has a thickness of about d, wherein d=λ/(2Δn), where λ is the wavelength of light propagated through the first optical master to the photo-alignment layer, and where Δn is the birefringence of the first liquid crystal layer.
8 . The method of claim 7 , wherein the first liquid crystal layer has an optical phase and a grating period, wherein after replicating the liquid crystal pattern, the photo-alignment layer has an optical phase of about double the optical phase of the first liquid crystal layer and a grating period of about half the grating period of the first liquid crystal layer.
9 . The method of claim 7 , wherein the light comprises linearly polarized light.
10 . The method of claim 1 , wherein the first liquid crystal layer has a thickness of about d, wherein d=λ/(4Δn), where λ is the wavelength of light propagated through the first optical master, and Δn is the birefringence of the first liquid crystal layer.
11 . The method of claim 10 , wherein the first liquid crystal layer comprises an optical phase and a grating period, wherein after replicating the liquid crystal pattern, the photo-alignment layer has an optical phase and a grating period equal to that of the first liquid crystal layer.
12 . The method of claim 1 , wherein propagating light through the first optical master comprises positioning a collimated light source over the first optical master such that the collimated light source illuminates at least a portion of the first optical master.
13 . The method of claim 12 , wherein propagating light through the first optical master further comprises moving the collimated light source to a different portion of the first optical master.
14 . The method of claim 13 , wherein the collimated light source comprises a beam power (P) and beam width (W), and wherein the collimated light source is moved at a scanning speed(S), wherein a dose provided by the collimated light source equals P*W/S, and wherein the dose is between 0.5 Joules per cm 2 and 10 Joules per cm 2 .
15 . The method of claim 14 , wherein the scanning speed provides a total light exposure time of less than ⅙ second over any portion of the photoalignment layer.