Provided are a novel optical element that can be used as a sensor or the like and a sensor including the same optical element. The optical element includes a cholesteric liquid crystal layer, in which the cholesteric liquid crystal layer has a liquid crystal alignment pattern in which a direction of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction, and in a case where a cross-section taken in a thickness direction conforming the in-plane direction in which the direction of the optical axis rotates is observed using a scanning electron microscope, a portion where a bright line and a dark line derived from the cholesteric liquid crystalline phase are discontinuous is provided in the cholesteric liquid crystal layer in the in-plane direction in which the direction of the optical axis rotates.

Each of a mirror surface display device and a light reflecting member includes a support member having an optical thin film thereon, a broadband selective reflection film and a display in this order; the optical thin film being formed on a surface of the support member facing the broadband selective reflection film; and the broadband selective reflection film being a film selectively transmitting one of clockwise circularly polarized light and counterclockwise circularly polarized light, and selectively reflecting the other polarized light, and having cholesteric regularity.

A display medium comprising: a multilayered substrate including a polarized light separation layer and a phase difference layer; and a first reflective layer provided on a surface of the multilayered substrate on a side with the polarized light separation layer, wherein: the polarized light separation layer can reflect circularly polarized light which has one rotation direction D.sub.A, and can transmit circularly polarized light which has an opposite rotation direction to the rotation direction D.sub.A; the first reflective layer can reflect circularly polarized light which has one rotation direction D.sub.B1, and can transmit circularly polarized light which has an opposite rotation direction to the rotation direction D.sub.B1; and the rotation direction D.sub.A of the circularly polarized light that the polarized light separation layer can reflect and the rotation direction D.sub.B1 of the circularly polarized light that the first reflective layer can reflect are the same as each other.

A backlight unit includes a light guide plate; a light source provided on a side surface of the light guide plate, and configured to inject light into the light guide plate; a circular polarizing reflective layer provided on a front surface of the light guide plate, and configured to reflect a first polarizing component and transmit a second polarizing component among components of light emitted from the light guide plate; and a cholesteric liquid crystal layer provided on the front surface of the circular polarizing reflective layer and including a plurality of regions, and configured to reflect or transmit the second polarizing component that has passed through the circular polarizing reflective layer according to a voltage applied to each of the plurality of regions.

An object is to provide a projection image displaying member that enables display of a projection image using p-polarized light and can provide a head-up display system having high polarizing sunglasses suitability, a windshield, and a head-up display system. The object is achieved by a projection image displaying member having a transparent substrate having an in-plane retardation of 5000 nm or more and at least one selective reflection layer, wherein the selective reflection layer is located closer to the side on which projection light is incident than the transparent substrate is.

According to one embodiment, an illumination device includes a first liquid crystal element opposed to a light emitting region, a second liquid crystal element including a first main surface and a second main surface, a first phase difference layer disposed on the second main surface, a second phase difference layer disposed on the second main surface and adjacent to the first phase difference layer, and a diffusion layer opposed to the first phase difference layer and the second phase difference layer. Each of the first liquid crystal element and the second liquid crystal element has a plurality of liquid crystal molecules, and is cured in a state in which an alignment direction of the liquid crystal molecules has continuously changed in plane.

A device is provided. The device includes a first birefringent film including a calamitic liquid crystal (“LC”) material configured with a first helical structure. The device also includes a second birefringent film stacked with the first birefringent film and including a discotic LC material configured with a second helical structure.

According to one embodiment, a display device including a display panel emitting display light of linearly polarized light, a semi-transparent layer, a first retardation film, a reflective polarizer transmitting first linearly polarized light and reflecting second linearly polarized light orthogonal to the first linearly polarized light, a second retardation film, an element, and a third retardation film arranged between the reflective polarizer and the element, wherein the first retardation film, the second retardation film, and the third retardation film are quarter-wave plates, and the element has a lens action of condensing first circularly polarized light.

Provided is a sensor having a high SN ratio. The sensor includes a light source, a band pass filter, and a light-receiving element, in which the band pass filter includes two cholesteric liquid crystal layers and a discontinuous layer disposed between the two cholesteric liquid crystal layers, in the two cholesteric liquid crystal layers, helical twisted directions and helical pitches are the same, and in a case where the discontinuous layer is a layer other than a cholesteric liquid crystal layer and a wavelength having a lowest reflectivity in a selective reflection wavelength range of the band pass filter is represented by λm [nm], a thickness [nm] is in a range of “30×(λm/550) to 150×(λm/550)”.

Provided is a sensor having a high SN ratio. The sensor includes a light source, a band pass filter, and a light-receiving element, in which the band pass filter includes two cholesteric liquid crystal layers and a discontinuous layer disposed between the two cholesteric liquid crystal layers, in the two cholesteric liquid crystal layers, helical twisted directions and helical pitches are the same, and in a case where the discontinuous layer is a layer other than a cholesteric liquid crystal layer and a wavelength having a lowest reflectivity in a selective reflection wavelength range of the band pass filter is represented by λm [nm], a thickness [nm] is in a range of “30×(λm/550) to 150×(λm/550)”.