Low-twist chiral liquid crystal polarization gratings and related fabrication methods

A method of forming a polarization grating, the method comprising:

• providing a first polarization grating layer comprising a molecular structure that is twisted according to a first twist sense over a first thickness defined between opposing faces of the first polarization grating layer such that respective orientations of molecules of the first polarization grating layer are rotated by a first twist angle over the first thickness throughout the first polarization grating layer;
• and
• providing a second polarization grating layer on the first polarization grating layer, the second polarization grating layer comprising a molecular structure that is twisted according to a second twist sense opposite the first twist sense over a second thickness defined between opposing faces of the second polarization grating layer such that respective orientations of molecules of the second polarization grating layer are rotated by a second twist angle over the second thickness throughout the second polarization grating layer,
• wherein the second twist angle is about +70 degrees, and wherein the first twist angle is about −70 degrees.

A switchable polarization grating, comprising:

• a first substrate including a first periodic alignment condition;
• a second substrate including a second periodic alignment condition;
• and
• a nematic liquid crystal layer between the first and second substrates, the nematic liquid crystal layer including a chiral dopant therein configured to twist a molecular structure of the nematic liquid crystal layer over a thickness defined between opposing faces thereof by a twist angle that is different from a relative phase angle between the first and second periodic alignment conditions,
• wherein the first and second periodic alignment conditions provide a same periodicity along respective interfaces with the nematic liquid crystal layer.

A method of fabricating a switchable polarization grating, the method comprising:

• providing a first substrate including a first periodic alignment condition;
• providing a second substrate including a second periodic alignment condition;
• doping a nematic liquid crystal layer with a chiral molecule configured to twist a molecular structure of the nematic liquid crystal layer;
• and
• forming the nematic liquid crystal layer on the first and second substrates, the nematic liquid crystal layer including the chiral molecule therein configured to twist the molecular structure of the nematic liquid crystal layer over a thickness defined between opposing faces thereof by a twist angle that is different from a relative phase angle between the first and second periodic alignment conditions,
• wherein the first and second periodic alignment conditions provide a same periodicity along respective interfaces with the nematic liquid crystal layer.