Abstract
We report that polymerization makes a robust, practically applicable multifunctional optical device with a continuous wavelength tunable over 500 nm spectral range using UV-polymerizable cholesteric liquid crystals (CLCs). It can be used as a circular polarizer generating an extremely high degree of circularly polarized light with |g| = 1.85~2.00. It can also be used for optical notch filters, bandwidth-variable (from ~28 nm to ~93 nm) bandpass filters, mirrors, and intensity-variable beam splitters. Furthermore, this CLC device shows excellent stability owing to the polymerization of CLC cells. Its performance remains constant for a long time (~2 years) after a high-temperature exposure (170 °C for 1 h) and an extremely high laser beam intensity exposure (~143 W/cm2 of CW 532 nm diode laser and ~2.98 MW/cm2 of Nd: YAG pulse laser operation for two hours, respectively). The optical properties of polymerized CLC were theoretically analyzed by Berreman’s 4 × 4 matrix method. The characteristics of this device were significantly improved by introducing an anti-reflection layer on the device. This wavelength-tunable and multifunctional device could dramatically increase optical research efficiency in various spectroscopic works. It could be applied to many instruments using visible and near-infrared wavelengths.
Highlights
Basic optics such as mirrors, circular polarizers, filters, and beam splitters are essential elements in optics and photonics
Due to general Cholesteric liquid crystals (CLCs), a well-developed pitch gradient of the wedge CLC cell, which is an essential condition for a wide range of continuous wavelength tunings of the photonic bandgap (PBG), does not have long-term stability
We developed a polymerized CLC (PCLC) device system with optical multifunction of a left- or right-circular polarizer generating an extremely high degree of circularly polarized light with a dissymmetry factor |g| = 1.98, notch or bandpass filter, mirror, and beam splitter that could be utilized in practical devices
Summary
Basic optics such as mirrors, circular polarizers, filters, and beam splitters are essential elements in optics and photonics. Due to general CLCs, a well-developed pitch gradient of the wedge CLC cell, which is an essential condition for a wide range of continuous wavelength tunings of the photonic bandgap (PBG), does not have long-term stability. Polymerized CLC cells showed excellent stability performance after a long time (about two years), a high-temperature exposure (170 ◦C for 1 h), and an extremely high laser beam intensity exposure (~143 W/cm CW 532 nm CW diode laser and 2.98 MW/cm Nd: YAG pulse for 2 h each) Their optical properties were studied theoretically, including the refractive index, pitch, and FWHM of the photonic bandgap and the thickness of the polymerized CLC cell by Berreman’s 4 × 4 matrix method. It could be applied to many devices using visible (VIS) and near-infrared (NIR) wavelengths
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