Tunable Birefringence Research Articles

Electrically tunable birefringence in nanophotonic waveguide with 2D electron gas in semiconductor heterojunction

An electrically tunable birefringence in a nanophotonic waveguide based on MgZnO-CdZnO semiconductor heterojunction is numerically proposed. Electrical control is realized with two-dimensional electron gas (2DEG) at the interface of ZnO based heterojunction and is used to control the polarization. The waveguide is engineered to enhance interaction of guided optical mode(s) with 2DEG providing us with a wide tuning in modal birefringence. We perform numerical analysis of phase and polarization characteristics of 2DEG based nanophotonic waveguide. Electrical tuning of 0.0112 in modal birefringence is reported by varying the applied voltage from 0 Vto −10 V. The proposed device also exhibits voltage variable optical phase modulation in both TE and TM polarizations. The proposed work can be utilized in applications where integrated photonic devices with variable polarization control are desirable.

Widely tunable dual-color waveguide-based optical parametric oscillator

Exploiting four-wave mixing in two orthogonally polarized fundamental modes of Si3N4 waveguides and a tunable birefringence in the cavity, an optical parametric oscillator generates two independently tunable output frequencies from 0 to 62 THz difference.

Passively Q-switched and broadly tunable continuous-wave operations of a 2-μm Tm3+:Lu2O3 ceramic laser upconversion pumped at 1.064 μm

We report passively Q-switched and broadly tunable continuous-wave operations of a trivalent thulium ion-doped Lu2O3 ceramic laser near 2 μm by employing upconversion pumping at 1 μm. Upconversion pumping was performed with a commercial 1064-nm Yb:fiber laser and nonlinear absorption of up to 41 % was obtained. In the continuous wave case, a four-mirror x-cavity generated as high as 257 mW of output power at 2.06 μm with a power slope efficiency of 12 % with respect to the incident pump power. Tuning performance was further investigated with a quartz birefringent tuning plate and broad, continuous tuning was obtained in the 1950–2090 nm wavelength range. In addition, passively Q-switched operation was demonstrated with a semiconductor saturable absorber, yielding stable, 4.15-μs-long pulses at the pulse repetition frequency of 28.8 kHz.

Tunable birefringence and elliptical polarization eigenmodes in a biplate of two quarter-wave plates.

Birefringence of elliptical polarization eigenmodes can be conceptualized as a composite system comprising two distinct media: one with linear polarization eigenmodes and the other with circular polarization eigenmodes. However, the practical realization of such a system often involves the combination of two birefringent quarter-wave plates (QWPs). In this study, our objective is to characterize the variable retardation and variable elliptical polarization eigenmodes exhibited by a biplate consisting of two quarter-wave plates. Additionally, we aim to analyze the geometric properties of the transformation of one state of polarization on the Poincaré sphere, employing the emerging state's curve. This curve corresponds to the intersection between the Poincaré sphere and a cone. The outcomes of our study are presented as a function of the angle between the fast axes of the two QWPs. The findings have the potential to contribute to the configuration of q-plates and facilitate the development of quantum communication protocols.

Manipulation of polarization topology using a Fabry–Pérot fiber cavity with a higher-order mode optical nanofiber

Optical nanofiber cavity research has mainly focused on the fundamental mode. Here, a Fabry–Pérot fiber cavity with an optical nanofiber supporting the higher-order modes (TE01, TM01, HE21 o , and HE21 e ) is demonstrated. Using cavity spectroscopy, with mode imaging and analysis, we observed cavity resonances that exhibited complex, inhomogeneous states of polarization with topological features containing Stokes singularities such as C-points, Poincaré vortices, and L-lines. In situ tuning of the intracavity birefringence enabled the desired profile and polarization of the cavity mode to be obtained. We believe these findings open new research possibilities for cold atom manipulation and multimode cavity quantum electrodynamics using the evanescent fields of higher-order mode optical nanofibers.

Binary solvent-exchange-induced self-assembly of silk fibroin birefringent fibers for optical applications

To generate birefringence in artificial materials has attracted increasing attention in terms of their potential for applications in sensor, tissue engineering and optical devices. Silk materials with patterned structures presented unique optical features, however, effectively fabricating of structural anisotropy in silk materials to directly tailor their birefringence is still challenging. Silk fibroin birefringent fibers (SBFs) with tunable birefringence were obtained in this study via a strategy that combined injection technique and binary solvent-exchange-induced self-assembly (BSEISA). The structural deformation of these SBFs that introduced by external stimulus such as tensile and solvent swelling was critical to their birefringence. As a result, pink, yellow, green, cyan, and purple were successfully achieved in the interference color of the SBFs with an exchanging solvent of 25, 55, 75, 90 wt% ethanol aqueous solution, and methanol respectively. Moreover, we respectively exchanged these SBFs against with Congo red (SBF-CR), methyl orange (SBF-MO), methylene blue (SBF-MB) and rhodamine B (SBF-RhB) solutions to produce fibers with diversity in their birefringent performance. Two types of patterns were designed and thereafter constructed by (1) SBF\\SBF-CR\\SBF-RhB, and (2) SBF\\SBF-MB\\SBF-CR. Interestingly, the patterns both displayed a letter of “A” in natural light, while displayed different letters of (1) “H” and (2) “U” in polarized light. This study demonstrated that these SBFs with unique optical and birefringent performances are anticipated to act as sensors and code labels for optical applications.

Dual wavelength generation and wavelength tunability in Yb-doped mode-locked laser using few-mode fiber as a saturable absorber

In this research, we demonstrate wavelength tunability and dual wavelength generation in all-fiber ytterbium (Yb)-doped mode-locked laser using a single mode–few-mode–single mode fiber (SMF–FMF–SMF) combination act as a saturable absorber (SA). The all-fiber SA exhibits high modulation depth of 34.53% and a saturation intensity of 9.17 MW/cm2. The SMF–FMF–SMF structure encompasses an inherent filtering along with SA property. By combining the tunable intra-cavity birefringence of the laser with the SA features result in dual-wavelength generation and wavelength tunability. Thus, the tuning of center wavelength of output spectrum from 1028.88 through 1076.18 nm, with the compressed pulse widths from 319 to 324 fs respectively, is achieved. Besides, the generated dual-wavelength is switched from 1033.32/1058.2 nm to 1049.7/1075.7 nm, respectively. These results indicate that an all-fiber SMF–FMF–SMF structure is a potential SA element for wavelength tunability and dual-wavelength mode-locking in Yb-doped fiber lasers, which can be used for nonlinear microscopy, bio-degradable material processing and terahertz spectroscopy.

Magnetically tunable and stable deep-ultraviolet birefringent optics using two-dimensional hexagonal boron nitride.

Birefringence is a fundamental optical property that can induce phase retardation of polarized light. Tuning the birefringence of liquid crystals is a core technology for light manipulation in current applications in the visible and infrared spectral regions. Due to the strong absorption or instability of conventional liquid crystals in deep-ultraviolet light, tunable birefringence remains elusive in this region, notwithstanding its significance in diverse applications. Here we show a stable and birefringence-tunable deep-ultraviolet modulator based on two-dimensional hexagonal boron nitride. It has an extremely large optical anisotropy factor of 6.5 × 10-12 C2 J-1 m-1 that gives rise to a specific magneto-optical Cotton-Mouton coefficient of 8.0 × 106 T-2 m-1, which is about five orders of magnitude higher than other potential deep-ultraviolet-transparent media. The large coefficient, high stability (retention rate of 99.7% after 270 cycles) and wide bandgap of boron nitride collectively enable the fabrication of stable deep-ultraviolet modulators with magnetically tunable birefringence.

Cation-anion synergetic interactions achieving tunable birefringence in quasi-one-dimensional antimony(III) fluoride oxalates

Birefringent materials with large optical anisotropy, which can be used to modulate the polarization of light, play a key role in laser techniques and science. However, the exploration studies of new, superior birefringent materials develop extremely slowly due to the lack of effective guidelines for rational design. Herein, three antimony(III) fluoride oxalates, namely, Na2Sb2(C2O4)F6, K2Sb2(C2O4)F6, and Cs2Sb2-(C2O4)2F4·H2O, were successfully synthesized through a rational combination of π-conjugated C2O42− anions and Sb3+ cations with stereochemically active lone pairs. These oxalates feature unique quasi-one-dimensional chain structures that induce large optical anisotropy. Remarkably, Cs2Sb2(C2O4)2-F4·H2O exhibits the largest birefringence (0.325@546 nm) among all reported antimony(III)-based oxysalts. Detailed structural analysis and theoretical calculations confirmed that the optical anisotropy of these oxalates could be tuned through the synergetic interactions of templated cations and anionic functional groups. This work may open the door to efficiently designing excellent birefringent materials and guide the further discovery of other novel structure-driven functional materials.

Stabilized director buckling patterns in nematic elastomers and their dynamic optical effects

AbstractPearlescence and iridescence, which are a class of light diffusion effects that exhibit sharp viewing-angle-dependent brightness and colors, are important material properties for notification purposes and lighting devices. Here we report elastomeric materials with self-organized periodic birefringent patterns that exhibit these optical effects, with additional dynamic and reversible tunability. A stack of micron-thick layers, each of which has a nematic director tilted from the layer normal in a different direction, assembles a birefringence-pattern-based anisotropic diffuser in a nematic liquid-crystal elastomer. The periodic pattern is formed after buckling induced by the uniaxial thermal shrinkage, and the associated rotation of an initially uniform director state. The patterns can be stabilized by secondary crosslinking. Upon deformation or increasing the temperature, the light diffusion with viewing-angle-dependent colors reversibly fades owing to the diminishing of optical effects via strain-induced alignment or thermal randomization of birefringence, respectively. Such elastomers with tunable self-organized birefringence patterns can be used for reconfigurable optical elements and strain/temperature detection in the form of films, tapes, rods, and fibers.

Full-range birefringence control with piezoelectric MEMS-based metasurfaces

Dynamic polarization control is crucial for emerging highly integrated photonic systems with diverse metasurfaces being explored for its realization, but efficient, fast, and broadband operation remains a cumbersome challenge. While efficient optical metasurfaces (OMSs) involving liquid crystals suffer from inherently slow responses, other OMS realizations are limited either in the operating wavelength range (due to resonances involved) or in the range of birefringence tuning. Capitalizing on our development of piezoelectric micro-electro-mechanical system (MEMS) based dynamic OMSs, we demonstrate reflective MEMS-OMS dynamic wave plates (DWPs) with high polarization conversion efficiencies (∼75%), broadband operation (∼100 nm near the operating wavelength of 800 nm), fast responses (<0.4 milliseconds) and full-range birefringence control that enables completely encircling the Poincaré sphere along trajectories determined by the incident light polarization and DWP orientation. Demonstrated complete electrical control over light polarization opens new avenues in further integration and miniaturization of optical networks and systems.

Group Birefringence Regulation and Measurement With Twin Zeros in a Selectively Infiltrated Microstructured Optical Fiber Based on OFDR

We propose and demonstrate a selectively microfluidic-infiltrated method for the group birefringence regulation in a microstructured optical fiber. Meanwhile, an Optical Frequency Domain Reflectometry (OFDR) with an equivalent resolution of 0.6 Hz or 10-6 RIU is utilized to characterize its polarization separation and group birefringence change. By selectively infiltrating a fluid with a high thermal-optic coefficient into twin air holes nearby the silica fiber core, tunable group birefringence is observed and measured by polarization separation in beat frequency domain. Moreover, due to the co-effects of the filled and unfilled fiber segments, the twin critical zeros of the overall group birefringence are observed at 16.5 and 43.0, respectively. The unique position exchange of LP01x and LP01y presents at the twin critical zeros, which is investigated via the OFDR technique as well. Therefore, by combining the unfilled fiber segment with negative group birefringence and filled fiber segment with positive group birefringence, dual zeros in group birefringence are achieved with position exchange of the LP01x and LP01y peaks in beat frequency domain. Our demonstration provides potentials in flexible regulation and real-time observation of the group birefringence in microstructured optical fiber.

Unusual ferroelectric-dependent birefringence in 2D trilayered perovskite-type ferroelectric exploited by dimensional tailoring

<h2>Summary</h2> Ferroelectrics with switchable spontaneous polarization have taken a dominant position as the nonlinear optical candidates, of which birefringence is an essential merit to optical devices. Despite the increasing advance of hybrid perovskite ferroelectrics, it remains a great challenge to control and tune their birefringence, thus hindering their practical optical applications. Here, we present a 2D trilayered hybrid perovskite-type ferroelectric obtained by 3D-to-2D dimensional tailoring, [(CH₃)₂CH(CH₂)₂NH₃]₂(CH₃NH₃)₂Pb₃Cl₁₀, showing biaxial polarizations of ∼5 μC/cm² and a relatively wide optical band gap. The intrinsic 2D architecture results in highly anisotropic principal refractive indices, namely, the optical birefringence. Interestingly, its birefringence can be reversibly switched through ferroelectric-to-paraelectric symmetry breaking. The birefringence tuning is further established by virtue of pretransitional modulation of ferroelectricity, exhibiting unusual polarization-dependent behaviors. In our judgment, this study on the polarization-dependent birefringence of hybrid perovskite ferroelectrics will provide a new pathway toward modulating nonlinear optical properties for smart devices.

Design and performance of a hyperspectral camera for full-face in vivo imaging.

Red, green, blue color photography is a mature technology and a powerful tool for the evaluation and understanding of the way an object reflects light and its related optical properties, but color photography fails to give a complete picture of these effects due to its inherent lack of spectral resolution. In this work, we update the L'OREAL reference device for skin color measurement, the Chromasphere, by replacing its current color camera system with an imaging spectrometer. This imaging spectrometer must provide a spatial resolution on par with the previous color cameras and a spectral resolution commensurate with a spectroradiometer while also achieving a time resolution suitable for in vivo studies of the human face. Due to these requirements, common spatial scanning techniques are not suitable for this application, and so we utilized a spectral-scanning approach based on a tunable liquid-crystal birefringent filter. We present the design and performance tests of a working prototype that is capable of measuring the spectrum in each of 4 MP with a nominal spectral resolution of 10nm across the wavelength range from 420 to 730nm in a total imaging time of less than 10s. We cross-compared the spectral and color measurements obtained with this prototype, an industry-standard spectroradiometer, and a charge-coupled device color camera in order to assess the prototype's performance, and the results of this comparison show that our prototype is capable of taking spectral measurements near enough in quality to those of a spectroradiometer to successfully bridge the divide between such devices and conventional color cameras. Doing so, this instrument opens new possibilities for studies of complex in vivo phenomena that neither non-imaging spectrometers nor conventional cameras can pursue.

Tunable Q-switched mode-locked Cr:LiSAF laser

We have achieved stable passively Q-switched mode-locked (QML) operation in a Cr: LiSAF laser. In the experiments, a 10 mm long, %1.5 Cr-doped LiSAF crystal was pumped by two 150 mW single-mode diodes at 660 nm. An AlGaAs based saturable Bragg reflector (SBR) with a central wavelength of 850 nm and a modulation depth of 0.8% was used for initiating and sustaining QML operation. The QML laser was self-starting and robust against environmental fluctuations. In QML operation, the system produced sub-5-ps long mode-locked pulses at 150–200 MHz, inside 2–2.5 μs long Q-switched envelopes with 30–70 kHz repetition rate. The modulation depth of mode-locking stayed around 50%. We have also observed variation of mode-locked pulse parameters within the Q-switched envelope and also from Q-switched pulse to pulse. At an absorbed pump power level of around 280 mW, the QML pulses had an average power of 50 mW, whereas the estimated peak power of the mode-locked pulses were around 0.5 kW. Simple rotation of an intracavity birefringent tuning plate (BRF) enabled tuning of the central wavelength of the pulses between 835 and 865 nm. To our knowledge, this study is the first work focusing on QML operation in Cr: LiSAF lasers. The findings in this initial study is an initial attempt to understand the dynamics of QML operation in Cr:LiSAF. Further work will focus on reducing the mode-locked pulsewidths to sub-1-ps level and also on increasing the modulation depth of mode-locking for further peak power scaling.

Photoinduced tunable birefringence and dichroism in silver nanogratings

Silver nanogratings are anisotropic plasmonic nanostructures with potential application in optical components due to their large birefringence and dichroism. We induced linear birefringence and linear dichroism in subwavelength Ag-AgCl films by irradiating with a single low-power linearly polarized laser beam. The laser beam aligns silver nanoparticles in the direction of laser polarization and forms nanograting. We used Stokes parameters to determine linear birefringence and linear dichroism in silver aligned nanostructures. The values of linear dichroism and linear birefringence in silver nanogratings are controllable through manipulating the spatial period of nanogratings. The dispersion characteristic of dichroism and birefringence is also investigated.

Plasmonic Demultiplexer With Tunable Output Power Ratio Based on Metal-Dielectric-Metal Structure and E7 Liquid Crystal Arrays

A novel tunable plasmonic demultiplexer is proposed and numerically investigated by finite element method (FEM). It consists of two half-nanodisk cavities and two sets of E7 liquid crystal arrays which are side-coupled to three metal-dielectric-metal (MDM) waveguides. The demultiplexer can split the input lights into two parts corresponding to port1 (1310 nm) and port2 (1550 nm). The Q-factors of port1 and port2 are 54.6 and 36, and the crosstalk values are −20.7 dB and −29.9 dB, respectively. Obviously, both channels have high Q-factors and low crosstalk value. Moreover, the E7 liquid crystal arrays play a key role in the whole structure, which makes the output power adjustable proportionally by adjusting the applied voltage. This novel feature greatly enriches the function of our demultiplexer. Using the electronical tunable birefringence characteristic of liquid crystal and its arrays structure paves a new way to realize practical on-chip plasmonic system, which can be widely used not only in demultiplexers but also in nanosensors, optical splitters, filters, optical switches, nonlinear photonic and slow-light devices.

Bias current and temperature dependence of polarization dynamics in spin-lasers with electrically tunable birefringence

We investigate and compare the intensity and polarization dynamics in a vertical-cavity surface-emitting laser (VCSEL) with a monolithically integrated, electrically controlled birefringence tuning mechanism. The influence of the bias current on the polarization dynamics is investigated over a large range of birefringence values. Bias current tuning toward low values and simultaneous maximization of the resonance frequency is an important strategy to optimize the spin-VCSEL toward energy-efficient operation. A polarization dynamics resonance tuning range from a few GHz up to the maximum frequency of 36 GHz was achieved, and polarization dynamics at maximum frequency are demonstrated at minimum bias current and at high temperatures of approximately 70 °C. We propose a strategy for data communication with low energy consumption and low cooling effort.

Active Terahertz Anisotropy and Dispersion Engineering Based on Dual-frequency Liquid Crystal and Dielectric Metasurface

Active broadband terahertz (THz) phase difference and its dispersion engineering based on the combination of dielectric metasurface and dual-frequency liquid crystal (DFLC) has been demonstrated, which can realize broadband achromatic wave plates and active manipulation by tuning the alternating ( AC ) frequency of electric field from 1 to 90 kHz. The artificial anisotropy of the dielectric metasurface is introduced to offset the tunable natural birefringence of the DFLC, so that the effective tuning range of the composite metadevice has been significantly improved, across from 0 to 1.0π, thus realizing the conversion from linear polarization (LP) light to arbitrarily polarized light. Moreover, a negative-dispersion phase difference of the dielectric metasurface can be achieved in the range of 0.69–1.4 THz by designing proper geometric parameters, which can be compensated with the positive-dispersion phase difference of DFLC to realize an achromatic device with broadband zero dispersion. The results show that the device can be tuned from OFF state without polarization conversion to a half-wave plate in 0.97–1.3 THz with the polarization conversion ratio (PCR) of over 97%, or to a quarter-wave plate in 0.67–1.3 THz with the PCR of over 96% by changing the AC frequency of the electric field. The active AC frequency tuning characteristics, anisotropic enhancement and broadband dispersion compensation show its great potential in THz application systems.

Tunable birefringence in silica mediated magnetic fluid

The present study reports magnetic and optical properties of silica mediated lauric acid stabilized magnetic fluids. The tunable birefringence (Δn) and other properties are investigated as a function of (i) concentrations of silica suspension, and (ii) saturation magnetization (MS) 0.5099 kA m−1 (FN30) and 1.2855 kA m−1 (F30) of magnetite magnetic fluid (MF). The study reveals that Δn suppresses on addition of silica in FN30, whereas enhances (up to critical concentrations of silica) in F30. The magnetic field induced chain observed in the FN30 based fluids are long, thick and scattered, while short, thin and dense chains emerges in F30 based fluid. The magnetic field induced assembly and the magnetic parameters correlates with the results of Δn. The particle size analysis indicates increment of particle size on addition of silica nanoparticles. The thermogravimetry analysis confirms the direct interaction of silica nanoparticles and the lauric acid coated magnetite particles. This is the first report of direct interaction of silica—magnetite magnetic fluids, and its subsequent effect on tunable birefringence and other properties.