Tunable Polarization Controller Research Articles

Tunable polarization control with self-assembled arrays of anisotropic plasmonic coaxial nanocavities

Polarization control with nanostructures having a tunable design and allowing inexpensive large-scale fabrication is important for many nanophotonic applications. For this purpose, we developed and experimentally demonstrated nanostructured plasmonic surfaces based on hexagonal arrays of anisotropic coaxial nanocavities, which can be fabricated by a low-cost self-assembled nanosphere lithography method. Their high polarization sensitivity is achieved by engineering anisotropy of the coaxial nanocavities, while the optical response is enhanced by the excitation of surface plasmon resonances. Particularly, varying the geometrical parameters of the coaxial nanocavities, namely the height and tilt angle of their central core nanoellipsoids, the plasmonic resonance wavelengths as well as the polarization-selective behavior can be individually tuned in the entire visible and near-infrared spectral regions, which makes such nanostructures good candidates for the implementation of polarization-controlled optical switches and polarization-tunable filters. Moreover, the developed nanostructures demonstrate sensitivity up to 1335 nm/RIU in refractive index sensing.

Tunable metasurface realizing dynamic chiroptical responses in infrared band

The chiral metasurfaces composed of chiral element structures have attracted much attention because of their interesting optical response. However, with the rapid development of chiral metasurface research, people gradually realize that the traditional chiral metasurfaces lacks tunability in practical application. Therefore, it is the latest research direction to design the tunable / reconfigurable chiral metasurfaces. In this work, a double split-ring metasurface consist of metal/phase change material (PCM) Ge2Sb2Se4Te1(GSS4T1)/metal/dielectric multilayer stack is designed, asymmetric transmission (AT) and circular dichroism (CD) dynamic control are achieved in the infrared band with a large tuning range of more than 50 THz by switching between the amorphous and crystalline states of the Ge2Sb2Se4Te1. The design in this work is of great significance for realizing the GSST-enabled tunable polarization control in the infrared band.

Polarization Division Multiplexing-Based Hybrid Microwave Photonic Links for Simultaneous mmW and Sub-6 GHz Wireless Transmissions

A new hybrid microwave photonic link based on a polarization division multiplexing Mach-Zehnder modulator (PDM-MZM) is proposed. The link enables co-transmission of millimeter-wave (mmW) and sub-6 GHz wireless signals over a seamless single-mode fiber (SMF) and free-space optics (FSO) channels. Optimization of the chromatic dispersion (CD)-induced power fading regardless of the power fading due to the non-deterministic atmospheric turbulence (AT) is simultaneously demonstrated. Extensive simulation analysis is first presented to examine (i) the impact of CD on mmW (25 GHz) and sub-6 GHz (2.6 GHz) signals, envisioned for the 5th generation networks, and (ii) optimization of CD-induced power fading by changing the phase relations between the optical carrier and optical sidebands in each polarization channel using single tunable polarization controller. A proof-of-concept experiment is finally performed to simultaneously deliver 25 GHz and 2.6 GHz signals with 4/16/64-quadrature amplitude modulation over (i) 20 km SMF and 2 m radio wireless link and (ii) 20 km SMF, 4.2 m FSO (with AT) and 2 m radio wireless links. The optimization of the CD-induced power fading is experimentally verified and link performance shows high tolerance to CD with no power penalties and the measured error vector magnitudes well below the required limits. The predicted bit error rates are also below the forward error correction threshold of $2 \times {10^{ - 4}}$.

Subwavelength polarization optics via individual and coupled helical traveling-wave nanoantennas

Light polarization control is a key factor in modern photonics. Recent advances in surface plasmon manipulation have introduced the prospect of more compact and more efficient devices for this purpose. However, the current plasmonic-based polarization optics remain much larger than the wavelength of light, which limits the design degrees of freedom. Here, we present a plasmonic traveling-wave nanoantenna using a gold-coated helical carbon nanowire end-fired with a dipolar aperture nanoantenna. Our nonresonant helical nanoantenna enables tunable polarization control by swirling surface plasmons on the subwavelength scale and taking advantage of the optical spin–orbit interaction. Four closely packed helical traveling-wave nanoantennas (HTNs) are demonstrated to locally convert an incoming light beam into four beams of tunable polarizations and intensities, with the ability to impart different polarization states to the output beams in a controllable way. Moreover, by near-field coupling four HTNs of opposite handedness, we demonstrate a subwavelength waveplate-like structure providing a degree of freedom in polarization control that is unachievable with ordinary polarization optics and current metamaterials.

Plasma-based polarization modulator for high-intensity lasers

Manipulation of laser pulses at high intensities is an important yet challenging issue. New types of plasma-based optical devices are promising alternatives to achieve this goal. Here we propose to modulate the polarization state of intense lasers based on oblique reflection from solid-plasma surfaces. A new analytical description is presented considering the plasma as an uniaxial medium that causes birefringence effect. Particle-in-cell simulation results numerically demonstrate that such a scheme can provide a tunable polarization control of the laser pulses even in the relativistic regime. The results are thus relevant for the design of compact, easy to use, and versatile polarization modulators for high-intensity laser pulses.

Piezoelectric tuning of narrowband perfect plasmonic absorbers via an optomechanic cavity.

Optical antennas enable the control of light-matter interaction on the nanometer scale. Efficient on-chip electrical switching of plasmonic resonances is a crucial step toward the integration of optical antennas into practical optoelectronic circuits. We propose and numerically investigate the on-chip low-voltage linear electrical tuning of a narrowband optical antenna perfect absorber via a piezoelectric optomechanic cavity. Near unity absorption is realized by an array of gold nanostrip antennas separated from a membrane-based deformable backreflector by a small gap. A narrow linewidth of 33nm at 2.58μm is realized through the coupling between the plasmonic mode and photonic mode in the cavity-enhanced antenna structure. An aluminum nitride piezoelectric layer enabled efficient actuation of the backreflector and therefore changed the gap size, allowing for the tuning of the spectral absorption. The peak wavelength can be shifted linearly by 250nm with 10V of tuning voltage, and the tuning range is not limited by the pull-in effect. The polarization dependence of the nanostrip antenna coupled with the optomechanic cavity allows the use of our device as a voltage tunable polarization control device.

Polarization control in an X-ray free-electron laser

X-ray free-electron lasers are unique sources of high-brightness coherent radiation. However, existing devices supply only linearly polarized light, precluding studies of chiral dynamics. A device called the Delta undulator has been installed at the Linac Coherent Light Source (LCLS) to provide tunable polarization. With a reverse tapered planar undulator line to pre-microbunch the beam and the novel technique of beam diverting, hundreds of microjoules of circularly polarized X-ray pulses are produced at 500–1,200 eV. These X-ray pulses are tens of femtoseconds long, have a degree of circular polarization of 0.98–0.04+0.02 at 707 eV and may be scanned in energy. We also present a new two-colour X-ray pump–X-ray probe operating mode for the LCLS. Energy differences of ΔE/E = 2.4% are supported, and the second pulse can be adjusted to any elliptical polarization. In this mode, the pointing, timing, intensity and wavelength of the two pulses can be modified. Tunable polarization control and a two-colour X-ray pump–X-ray probe operating mode are demonstrated at the Linac Coherent Light Source (LCLS).

Terahertz switch and polarization controller based on photonic crystal fiber

Theoretical studies on liquid crystal filled photonic crystal fiber (LC-PCF) are presented. The effects of electric birefringence of liquid crystal (LC) in the LC-PCF and the transmitting properties of photonic crystal fiber (PCF) are investigated by using the full vector plane wave expansion and beam propagation method. The simulation results show that the electrically controlled LC-PCF can act as not only a terahertz (THz) switch with about 0.55 THz bandwidth, but also a tunable polarization controller for changing the polarization state of the fundamental mode.

All-fiber narrowband polarization controller based on coherent acousto-optic mode coupling in single-mode fiber

An all-fiber, narrowband, tunable polarization controller is proposed and demonstrated. The device is based on coherent acousto-optic mode coupling induced by two orthogonal acoustic waves on a dispersion-compensating fiber. The cooperative coupling between the two polarizations of the core mode and the TE01 cladding mode through the two gratings permits indirect coupling between the two polarizations of the core mode with nearly 100% efficiency, which makes the polarization-controlling function possible. Experimental results verify the operation of the polarization controller with an insertion loss of <1 dB.