Achromatic Polarization Rotator Research Articles

Electrotunable 180° achromatic linear polarization rotator based on a dual-frequency liquid crystal.

Linear polarization rotators have been widely used in optical systems. Commonly used polarization rotators are still beset by strong dispersion and thus restricted spectral bandwidth of operation. This leads to the development of achromatic or broadband alternatives, but most of them incorporate multiple waveplates for retardation compensation, which comes at the cost of increased complexity and reduced flexibility in operation and system design. Here, we demonstrate a single-element achromatic polarization rotator based on a thin film of dual-frequency chiral liquid crystal. The angle of polarization rotation is electrically tunable from 0° to 180° with low dispersion (±3°) in the entire visible spectrum, and a high degree of linear polarization (>95%) at the output.

Polarization-controlled chirped guided-mode resonance filter incorporating a hybrid splay-twist liquid crystal.

This work develops a tunable chirped guided-mode resonant (GMR) filter that has a hybrid splay-twist (HST) liquid crystal as a cladding layer. The GMR filter is a color reflector that strongly reflects light at the resonance wavelength, and its chirped grating structure supports tuning of the resonance peak over a wavelength range of over 50 nm. The HST-LC configuration serves as an achromatic polarization rotator that can rotate the axis of polarization of linearly polarized light by providing effective twist angles in the LC layer under an applied voltage. The HST-LC is used to change the direction of the polarization axis of the light that is reflected by the GMR filter; continuous angles of rotation of ∼90∘ are achieved and the linear polarization is retained under applied voltages. The proposed filter enables an ultrabroadband polarization rotation and still maintains a high degree of linear polarization, which allows more degrees of freedom in spectral and polarization controls.

Electrotunable achromatic polarization rotator

Manipulating the polarization orientation of light is essential in modern optics, biology, and related fields, but the strong optical dispersion inherent in current polarization rotators severely restricts their use to single-frequency lasers and their flexibility in system design. Many attempts have been made to realize dispersionless polarization rotation, usually by designing a complex set of wave plates with mutually compensated dispersions. Here, enabled by a thin cell of hybrid splay–twist liquid crystal, we demonstrate a tunable achromatic polarization rotator that is free of dispersion engineering. The optic axis distribution in the liquid crystal cell can be dynamically controlled by an applied electric field and allows an input polarization vector to be continuously rotated up to 90° (or 180° in a tandem-cell geometry) in an adiabatic and nondispersive manner. The proposed mechanism can be further implemented to construct spatial light modulators for single-path ultrabroadband generation of complex vector fields from uniformly polarized light.

Achromatic polarization rotator imprinted by ultrafast laser nanostructuring in glass

We demonstrate achromatic polarization rotators implemented by femtosecond laser assisted nanostructuring of silica glass. The rotation of polarization plane results from the chiral arrangement of optical axis embedded in the multi-layered stack of birefringent layers. In our experiments, we achieved rotation of 46.0 ± 0.6° and 93 ± 6° in the broad spectral range of 600–1600 nm, which can be extended even further up to 5 μm. These silica birefringent optical components exhibit advantages over liquid crystal polarizing devices or broadband crystalline waveplates, including large acceptance angle, high thermal stability, and high damage threshold.

Achromatic linear polarization rotator using twisted nematic liquid crystals

In this letter, we propose a simple configuration that is capable of rotating a linear polarization state of light by a certain angle for a wide range of wavelengths. The device consists of three liquid-crystal cells: two homogeneous cells and one twisted nematic (TN) cell. It is well known that a thick TN cell can rotate the linear polarization state of light by following the twisted structure. However, for a thin TN cell, achromatic polarization rotation is not possible. By the use of the Poincaré sphere model of the TN structure, we demonstrate that if one thin homogeneous cell is placed before and another one is placed after a thin TN structure, then a linear polarization state can be transformed close to the eigenmodes of TN. Therefore, this structure can be used to achieve the achromatic polarization rotation. This letter provides a detailed discussion of the theoretical analysis and a demonstration of the achromatic linear polarization rotator by the use of a 1.9 μm TN cell for the wavelength range 450–700 nm.

Efficient polarization converter for projection displays

In the waveguiding limit, a twisted nematic liquid crystal cell behaves as an achromatic polarization rotator. We propose and demonstrate the application of such a polarization rotator to convert unpolarized light into linearly polarized light with almost 100% efficiency. This polarization converter has a 2:1 aspect ratio, which is close to the 16:9 ratio for modern televisions. It can be used therefore in a projection display with polarization-dependent light valves such as a liquid crystal light valve. Both transmittive and reflective light valves can be used. The temperature dependence of the achromatic polarization rotator is also studied.