22 Cooperative Molecular Alignment Process Enabled by Scanning …
381
has a square lattice with a lattice point distance of 27.4 μm and an irradiated region
width of 13.7 μm. POM observation of the resultant film showed an array pattern of
radial alignment. The size of a radial alignment was ~27.4 μm, reflecting the same
periodicity as a square lattice of irradiated pattern. It must be noted that the size
of each radial alignment in the film is much smaller (by a factor of 10
4 ) and highresolution than that obtained by means of conventional photoalignment methods [2,
33, 45]. Furthermore, the number of radial alignment patterns reached 500 × 300
throughout the film.
22.4 Single-Step Creation of Polarization Gratings
and Diffractive Q-Plates by Scanning Wave
Photopolymerization with Unpolarized Light
Diffractive waveplates (DWs) show the properties of a polarization diffraction grating
and have a molecular orientation pattern based on LCs that shows extremely high
diffraction efficiencies. Rational design of DWs is key for the development of some of
the greatest emerging technologies in the field of next-generation optics and photonics
[17, 45–61]. One of the greatest benefits is that massive optical systems for manipulation of light, which are typically composed of large and complex arrays of optical
elements such as lenses, prisms, and polarization converters, can be replaced with
several stacked DW films of a few micrometers in thickness. The orientation patterns
of LCs govern such optical properties of DWs because LCs with patterned birefringence (n) can spatially modulate the phase of light. As the simplest example of
such modulation, 1D aligned LCs act as a half-wave plate, which has the ability
to convert the phase of incident polarized light into 90° rotated. To exhibit such
property, the retardation (R = n d; d is a thickness of medium) must be matched
with λ/2 (λ: wavelength of incident light). In the same manner, more complexed
2D orientation patterns of LCs enables one to realize versatile geometrical phase
modulations, providing various optical functionalities (e.g., lenses, optical vortex
generators, beam steering, etc.) [17, 55, 58]. In particular, LC films with a cycloidal
molecular orientation pattern (Fig. 22.3., Pattern II) are known as “cycloidal diffractive waveplates (CDWs)”, having attracted a great deal of attention. Such films with
orientation patterns meeting the half-wave plate condition diffract the incident light
only into the +1st and −1st orders with the polarization state of left- and rightcircular polarization, respectively (Fig. 22.4) [46–56]. As a result, CDWs have the
potential to open windows for the application of next-generation projection displays.
The recent development of methods to control molecular orientation has readily
achieved abovementioned complex 2D alignment patterns of LCs. The most
advanced procedure is a “surface photoalignment control” technology [11–15, 29].
With this technology, LC orientation can be controlled through photoreactions of a
thin film coated over a substrate surface. Because the films contain photoresponsive
381
has a square lattice with a lattice point distance of 27.4 μm and an irradiated region
width of 13.7 μm. POM observation of the resultant film showed an array pattern of
radial alignment. The size of a radial alignment was ~27.4 μm, reflecting the same
periodicity as a square lattice of irradiated pattern. It must be noted that the size
of each radial alignment in the film is much smaller (by a factor of 10
4 ) and highresolution than that obtained by means of conventional photoalignment methods [2,
33, 45]. Furthermore, the number of radial alignment patterns reached 500 × 300
throughout the film.
22.4 Single-Step Creation of Polarization Gratings
and Diffractive Q-Plates by Scanning Wave
Photopolymerization with Unpolarized Light
Diffractive waveplates (DWs) show the properties of a polarization diffraction grating
and have a molecular orientation pattern based on LCs that shows extremely high
diffraction efficiencies. Rational design of DWs is key for the development of some of
the greatest emerging technologies in the field of next-generation optics and photonics
[17, 45–61]. One of the greatest benefits is that massive optical systems for manipulation of light, which are typically composed of large and complex arrays of optical
elements such as lenses, prisms, and polarization converters, can be replaced with
several stacked DW films of a few micrometers in thickness. The orientation patterns
of LCs govern such optical properties of DWs because LCs with patterned birefringence (n) can spatially modulate the phase of light. As the simplest example of
such modulation, 1D aligned LCs act as a half-wave plate, which has the ability
to convert the phase of incident polarized light into 90° rotated. To exhibit such
property, the retardation (R = n d; d is a thickness of medium) must be matched
with λ/2 (λ: wavelength of incident light). In the same manner, more complexed
2D orientation patterns of LCs enables one to realize versatile geometrical phase
modulations, providing various optical functionalities (e.g., lenses, optical vortex
generators, beam steering, etc.) [17, 55, 58]. In particular, LC films with a cycloidal
molecular orientation pattern (Fig. 22.3., Pattern II) are known as “cycloidal diffractive waveplates (CDWs)”, having attracted a great deal of attention. Such films with
orientation patterns meeting the half-wave plate condition diffract the incident light
only into the +1st and −1st orders with the polarization state of left- and rightcircular polarization, respectively (Fig. 22.4) [46–56]. As a result, CDWs have the
potential to open windows for the application of next-generation projection displays.
The recent development of methods to control molecular orientation has readily
achieved abovementioned complex 2D alignment patterns of LCs. The most
advanced procedure is a “surface photoalignment control” technology [11–15, 29].
With this technology, LC orientation can be controlled through photoreactions of a
thin film coated over a substrate surface. Because the films contain photoresponsive