Polarization-dependent Transmission Research Articles

Highly birefringent and low loss anti-resonant hollow-core fiber with stadium-shaped nested structure

Abstract We propose a stadium-shaped nested anti-resonant hollow-core fiber (SSAF), designed to enable high birefringence and low loss in the near-infrared bands. Numerical investigation and simulation for variations in parameters of stadium-shaped nested structure are conducted, and confinement loss (CL) is reduced by parameters optimization while birefringence of 10−4 is maintained. With optimized SSAF structure, the birefringence and CL are improved to 1.39 × 10−4 and 26.5 dB km−1 at 1.38 µm, 1.28 × 10−4 and 2.64 dB km−1 at 1.55 µm, respectively. Meanwhile, it exhibits favorable single-mode characteristics and achieves a high high-order mode extinction ratio of up to 103, and the superior bending resistance characteristics are validated. Our work offers valuable guidance for designing and optimizing highly birefringent SSAF anti-resonant fiber, and the proposed SSAF has great application potential in polarization-dependent transmission and interferometric fiber gyroscope.

Microelectromechanical System-Based Reconfigurable Terahertz Metamaterial for Polarization Filter, Switch, and Logic Modulator Applications.

The terahertz (THz) metamaterials integrated with microelectromechanical systems (MEMS) have led to the realization of dynamic control in amplitude, phase, polarization, and spin angular momentum of the THz wave. In this study, we demonstrate an MEMS-based reconfigurable THz metamaterial (RTM) composed of a split ring resonator (SRR) for real-time modulation of THz wave. By gradually increasing the polarization angle of the incident THz wave, the resonant frequency of SRR switches from 0.74 to 1.16 THz, and the maximum modulation depth is more than 70%. When the MEMS-based RTM is actuated by different DC bias voltages, the polarization-dependent transmission intensity and resonant frequency of the device can be actively tuned. MEMS-based RTM shows logical function characteristics that can be used for logic modulators by performing the driving voltages and polarization states as 2-bit input signals and quantizing the transmission response as "on" and "off" states. The logic gates of "NAND" are at 0.439 THz and "AND" is at 0.732 THz. These results offer potential applications for the proposed MEMS-based RTM in tunable and reconfigurable polarization filters, optical switches, programmable logic modulators, and so on.

Optical functions of uniaxial rutile and anatase (TiO2) revisited

The optical functions of uniaxial rutile and anatase (TiO2) were determined from 200 to 850 nm (6.2 to 1.46 eV) using several of four optical techniques: (1) standard spectroscopic two-modulator generalized ellipsometry (2-MGE), (2) near-normal-incidence two-modulator generalized ellipsometry microscopy (2-MGEM), (3) Mueller matrix transmission of rutile, and (4) polarized transmission of rutile. The 2-MGE measurements yielded highly accurate values of the dielectric functions and error estimates from 1.46 to 6.2 eV, whereas the polarization-dependent transmission yielded more accurate values of the absorption coefficient below the band edge of rutile. The 2-MGEM also measured the diattenuation, which is related to the birefringence, and other parameters but at near-normal incidence at a single wavelength (577 nm).

Anisotropic Electron-Phonon Interactions in 2D Lead-Halide Perovskites.

Two-dimensional (2D) hybrid organic-inorganic metal halide perovskites offer enhanced stability for perovskite-based applications. Their crystal structure's soft and ionic nature gives rise to strong interaction between charge carriers and ionic rearrangements. Here, we investigate the interaction of photogenerated electrons and ionic polarizations in single-crystal 2D perovskite butylammonium lead iodide (BAPI), varying the inorganic lamellae thickness in the 2D single crystals. We determine the directionality of the transition dipole moments (TDMs) of the relevant phonon modes (in the 0.3-3 THz range) by the angle- and polarization-dependent THz transmission measurements. We find a clear anisotropy of the in-plane photoconductivity, with a ∼10% reduction along the axis parallel with the transition dipole moment of the most strongly coupled phonon. Detailed calculations, based on Feynman polaron theory, indicate that the anisotropy originates from directional electron-phonon interactions.

Highly birefringent anti-resonant hollow-core fiber with meniscoid nested structure.

We propose a meniscoid nested anti-resonant hollow-core fiber (MAF), wherein the fourfold rotational symmetry structure enables high birefringence and low loss in dual-wavelength range. Numerical investigation and simulation for variations in wall thickness along orthogonal directions are conducted, through which a formulated optimization criterion revealing the relationship between minimum difference in wall thickness and birefringence of 10-5 is obtained. A parameter of beat length to loss ratio η is defined to evaluate MAF performance with respect to birefringence and confinement loss (CL). With optimized MAF structure, the birefringence and CL are improved to 3.62 × 10-5 and 8.5 dB/km at 1.06 µm, 9.83 × 10-5 and 204.1 dB/km at 1.55 µm, respectively. Meanwhile, the bandwidths extend to 172 nm at 1.06 µm and 216 nm at 1.55 µm, and the superior bending resistance characteristics are validated. Our work offers valuable guidance for designing and optimizing highly birefringent anti-resonant hollow-core fiber (ARF), and the proposed MAF has great potential in polarization-dependent transmission and interferometric fiber gyroscopes.

Broadband silicon nitride integrated polarization rotators at 780 nm

Polarization management, and in particular polarization rotation, is becoming increasingly important for photonic integrated circuits (PICs). While fiber-optic networks are generally polarization insensitive, the large aspect ratio of high-index-contrast PIC waveguides leads to a large polarization-dependent response of integrated components such as waveguides, optical cavities, couplers, etc. Although foundry-processed polarization rotators operating at telecom and datacom wavelengths (C- and O-band) have been demonstrated, to date, there have been few reports of devices operating at shorter wavelengths. This work demonstrates silicon nitride (SiN) polarization rotators operating from λ=700-1000 nm (the I/Z-band) that take advantage of optical coupling between two waveguiding layers in a standard foundry process. We demonstrate a broadband white-light polarization measurement setup that enables precise characterization of the polarization-dependent transmission of photonic waveguide devices. Measurements on foundry-processed devices confirm full TE-to-TM rotation exhibiting a maximum polarization extinction ratio (PER) approaching 20 dB (limited by our measurement setup), and an exceptionally large bandwidth of up to 160 nm with an insertion loss less than 0.2 dB. Beam propagation method (3D-BPM) simulations show good agreement with experimental data and enable the device parameters to be adjusted to accommodate different operating wavelengths and geometries with no changes to the existing foundry process. This work opens up opportunities for applications in quantum information and bio-sensing where operation at λ<1000nm is needed.

Chiroptical Switching of Electrochromic Polymer Thin Films.

The interaction between light and chiroptical polymers plays a crucial role in chiroptics, spintronics, and chiral-spin selectivity. Despite considerable successes in creating dissymmetric polymer films, the elucidation of chiroptical activities under electrochemical switching remains unexplored. Here homogeneous chiral electrochromics is reported using chiral assembly of conjugated polymers through a transient solidification process with molecular chiral templates. In their neutral state, the chiral electrochromic polymers directly produce a remarkably dissymmetric polarization-dependent transmittance. The circular dichroism (CD) and dissymmetric transmission can be tuned by adjusting the doping level of the electrochemically active polymer films. Under high levels of oxidation, the chiroptical activities are reversed with strong bleaching in the visible, leading to formation of monosignate CD spectra over the infrared region. The matching between circular polarization handedness and chirality of chiroptical polymers makes a distinct impact on optical contrast and color switching dynamics due to the flipped chiroptical activities through polymer redox reactions. The differential circularly polarized transmission in the chiral see-through display can make a well-resolved color change in human eyes, demonstrating proof-of-concept devices for 3D imaging and information encryption. This work serves as a foundation to develop advanced on-chip fabrication of circular polarization-multiplexed display in flexible and highly integrated platforms.

Polarization-dependent multichannel transmission of 5G signals based on Zn0.91(Li0.5Bi0.5)0.09MoO4 low-temperature co-fired ceramics

Polarization-dependent multichannel transmission of 5G signals based on Zn0.91(Li0.5Bi0.5)0.09MoO4 low-temperature co-fired ceramics

The impact of light polarization and the nature of modes in the formation of quasi-bound states in the continuum at near-normal incidence

Bound states in the continuum (BIC) is a peculiar resonant mode with an infinite radiative lifetime and quality factor (Q-factor) embedded within the radiation continuum, which find applications in sensing, lasing, and quantum photonics. While an ideal BIC with an infinite Q-factor can only occur in theory, observing quasi-BIC in realistic samples with finite sizes is possible. However, the robustness of quasi-BIC depends primarily on the trapped electromagnetic modes. Here, we discuss the polarization dependence and the nature of quasi-BIC mode in a two-dimensional array of gallium arsenide (GaAs) scatterers through finite difference time domain simulations and analytical calculations. The calculated angle- and polarization-dependent transmission spectra show quasi-BIC evolution with high Q-factor at near-normal incidence only for transverse magnetic polarization. The calculated total scattering cross-section implies the dominant contribution from electric dipole moments in generating the quasi-BIC. The evolution of quasi-BIC mode is discussed in terms of Mie or Fabry–Perot modes using geometry-dependent transmission and field intensity calculations. The proposed GaAs metasurfaces with quasi-BIC at 638 nm, corresponding to the zero phonon line of nitrogen-vacancy centers in diamond are useful for applications in photonic quantum technologies.

Measurement of azo dye film with large photo-induced birefringence and complex refractive index

Azo dyes are valuable functional materials due to their sensitive response to and effective modulation of polarized light. It is essential to find out not only the optical anisotropy but also the complex refractive index of azo dye materials for photonics applications. We report here such measurements of highly ordered photoaligned azo dye films. The film has an apparent dichroic ratio of about 60. We model the photoaligned azo dye film systems using the Berreman transfer matrix. By means of regression fitting of the polarization dependent transmittance and reflectance data, we were able to determine the complex refractive indices of the aligned film at the wavelength range of 400–1000 nm. This material is found to have exceptionally large optical birefringence (Δn ∼ 0.75 at 632.5 nm and Δn ∼ 0.48 at 850.6 nm). The aligned azo dye film is valuable to applications such as coatable polarizers and optical modulation devices.

Polarization-Dependent Absorption and Transmission Metasurfaces for Linearly and Circularly Polarized Light in Terahertz Band

Polarization detection is an important part of many polarization applications such as polarization imaging, wireless communication, and circular dichroism spectroscopy. In this paper, two polarization-dependent terahertz wave absorption and transmission metasurface for linearly and circularly polarized light are proposed and proved by numerical simulations. Polarization filtering and polarization absorption are integrated on a single cell, and the orthogonal polarization component is transmitted and absorbed, respectively. The linearly polarization-dependent transmission and absorption structure can obtain a transmission extinction ratio of 11.5 dB and an absorption extinction ratio of over 270 dB at 3 THz. Moreover, the circularly polarization-dependent structure can obtain a transmission extinction ratio of 8.1 dB and an absorption extinction ratio of 4.66 dB at 2.8 THz. Our design facilitates the acquisition of full Stokes parameters and the high-resolution imaging.

Ultra-Broadband and Compact TM-Pass Polarizer Based on Graphene-Buried Polymer Waveguide.

We report an ultra-broadband and compact TM-pass polarizer based on graphene-buried polymer waveguides. The characteristic parameters of the polarizer were carefully designed and optimized. The standard microfabrication processes were employed to fabricate the device. The presented polarizers exhibit high polarization-dependent transmission imposing a TE mode cutoff while leaving the TM mode almost unaffected. We experimentally demonstrated the polarizer that has an ultra-high extinction ratio of more than 22.9 dB and 41.9 dB for the monolayer graphene film placed on the surface of core layer and buried in the center of core layer, respectively, and as low insertion loss as ~4.0 dB for the TM mode with the bandwidth over 110 nm. The presented polarizer has the advantages of high extinction ratio, ultra-broadband, low cost, and easy integration with other polymer-based planar lightwave devices.

Silver-Coated 45° Radiated Tilted Fiber Grating Based Interferometer and Its Sensing Applications

We proposed a silver-coated 45° radiated tilted fiber grating (45° RTFG) based interferometer, in which the 45° RTFG is working as a beam splitter and a coupler, and the light transmitting in the fiber core is radiated out and resonant in the cladding radial cavity formed by the fully coated silver film, which forms multiple beam interference. We have theoretically and experimentally investigated the proposed fiber interferometer in terms of polarization-dependent transmission spectra, the free spectral range (FSR), spectral visibility and sensing characteristics. Due to the single polarization radiation feature of 45° RTFG, only S-polarized light could form the multiple beam interference and P-polarized light would pass through the grating with low loss. And the FSR of the proposed fiber interferometer is around 6.8 nm, which is determined by the 125 μm cladding diameter. The theoretical results show that the spectral visibility of interference is proportional to the coupling efficient of 45° RTFG and when the coupling efficient reaches 0.92, the spectral visibility is the maximum. In the experiment, the fiber interferometer formed by the 45° RTFG with 11 dB polarization extinction ratio has the spectral visibility of 26 dB. Moreover, we have also investigated the temperature, strain and twist characteristics of the proposed interferometer. The experimental results show that the transmission peak has a red shift with increasing temperature, with a sensitivity of 10 ± 0.1 pm/°C; The strain causes a blue shift for the transmission peak with −0.42 ± 0.01 pm/μϵ sensitivity, and the twist sensitivity reaches 22.408 ± 0.2 dB/rad. The proposed silver-coated 45° RTFG based interferometer has an in-fiber and compact structure, which can be potentially used for optical fiber sensing.

Simultaneous Measurement of pH and Temperature with Phase-Shifted Long-Period Fiber Grating Inscribed on High-Birefringence Fiber by CO₂ Laser Pulses.

We propose an optical fiber grating sensor capable of simultaneously measuring pH and temperature based on a phase-shifted long-period fiber grating (PS-LPFG) inscribed on high-birefringence fiber (HBF). The PS-LPFG was fabricated on HBF with CO₂ laser pulses, and a phase shift π was induced by inserting a grating-free fiber region (GFFR) between two identical LPFGs with a grating period of ˜510 μm. The length of the GFFR was set as half of the grating period to induce a π phase shift. With the spectral characteristics of a π-PS-LPFG exhibiting two split attenuation bands, the PS-LPFG written on HBF, which is referred to as the HB-PS-LPFG, can create two polarization-dependent transmission spectra with dual-resonance dips at different wavelengths according to two orthogonal input polarization states, e.g., linear horizontal polarization (LHP) and linear vertical polarization (LVP). For simultaneous measurement of pH and temperature with the fabricated HB-PS-LPFG as a sensor head, the inter-resonance wavelength separation of the dual-resonance dips in each transmission spectrum obtained for an LHP or LVP input signal was exploited as a sensor indicator. By investigating the wavelength changes of the two sensor indicators, which were induced by pH and temperature variations, linear and independent spectral responses to both pH and temperature variations were experimentally confirmed in a pH range from 1 to 11 and a temperature range from 25 to 65 °C. Owing to the unique pH and temperature responses of the fabricated HB-PS-LPFG, ambient variations in pH and temperature could be simultaneously estimated from the measured wavelength changes and sensitivities of the two sensor indicators.

The nonlinear optical loop mirror: soliton and noise-like pulse emission in a figure-eight fiber laser

In this article, a symmetrical nonlinear optical loop mirror (NOLM) exhibiting a polarization-dependent transmission is evaluated to generate optical pulse emission in a figure-eight fiber laser in the soliton and noise-like pulse (NLP) regimes. The NOLM structure relies on a 50:50 fiber coupler, a loop with highly twisted single-mode optical fiber and a quarter-wave retarder (QWR) to break the polarization asymmetry. The pulse operation regime is determined by properly adjusting the NOLM low-power transmission, which is easily realized by the rotation of the QWR angle. Soliton pulses of 1.48 ps pulse duration and peak power of 18 W were observed with a peak to peak separation of 1.25 µs, corresponding to a fundamental cavity repetition rate of 0.8 MHz. Moreover, by incrementing the NOLM low-power transmission, NLP emission is generated exhibiting a wide and smooth spectrum of 8.5 nm bandwidth.

Spectral polarization-encoding of broadband laser pulses by optical rotatory dispersion and its applications in spectral manipulation* *Project supported by the National Natural Science Foundation of China (Grant Nos. 92050203, 62075138, 61827815, and 61775142) and Shenzhen Fundamental Research Project (Grant Nos. JCYJ20190808164007485, JCYJ20190808121817100, JSGG20191231144201722, and JCYJ20190808115601653).

We propose a kind of spectral polarization-encoding (SPE) for broadband light pulses, which is realized by inducing optical rotatory dispersion (ORD), and decoded by compensating ORD. Combining with polarization-sensitive devices, SPE can not only work to control polarization-dependent transmission for central wavelength or bandwidth-tunable filtering, but also can be used for broadband regenerative or multi-pass amplification with a polarization-dependent gain medium to improve output bandwidth. SPE is entirely passive thus very simple to be designed and aligned. By using an ORD crystal with a good transmission beyond 3-μm mid-infrared region, e.g., AgGaS2, SPE promises to be applied for the wavelength tuning lasers in mid-infrared region, where the tunning devices are rather under developed compared with those in visible and near-infrared region.

Multichannel tunable polarizing filter properties of one-dimensional ternary photonic crystal containing single-negative materials

Angle and polarization-dependent tunable transmission properties of a one-dimensional (1D) ternary photonic crystal (TPC) whose period consists of three alternate layers of two different kinds of single-negative [Epsilon-negative (ENG) and mu-negative (MNG)] media are theoretically investigated by using the transfer matrix method (TMM). It has been shown that the proposed polarizing filter is capable of transmitting multiple polarized transmission peaks (called as channels) by adjusting the incident angle from 21° to 89° as per need. The resonant frequencies of these respective transmission channels are completely different for the case of TE and TM polarizations. The proposed structure contains only twelve SNG material layers corresponding to the period number N = 4. This structure filters 18 separate transmission channels for TE and TM waves each at incident angle $$ \theta_{0} = 21^{\circ} $$ . The number of polarization dependent channels can be further increased to 35 and 37 for TE and TM polarizations, respectively, when the period number of 1D TPC increases from 4 to 8 at $$ \theta_{0} = 89^{\circ} $$ . This eight-period 1D TPC structure requires only 24 SNG material layers. The effect of lossy SNG materials on the performance of the filter is also investigated. This study may find its application in the field of optical communication for accommodating a large number of optical channels in the same bandwidth. Such types of filters may have their applications in integrated optics for dense wavelength division multiplexing systems and ultrafast light information processing.

A miniaturized and high-bandwidth polarization filter based on a plasmonic and liquid crystal offset core photonic crystal fiber

Miniaturized and broadband polarization-dependent filters with high crosstalk values are extremely desirable for practical applications in the fields of optical communications and sensing. A miniaturized photonic crystal fiber (PCF) with highly broadband polarization filtering properties is proposed in this paper. Two relatively large air holes coated with a gold film on opposite sides of the liquid crystal-filled offset core are introduced in this PCF structure to produce highly broadband polarization-dependent filtering transmissions. The impacts of the filtering properties with variable structural parameters have been studied based on the finite element method. By altering the gold film thickness (t) to be 18.7 nm and 13.8 nm, the proposed broadband polarization filter offers high resonance peaks of 2041.79 dB/cm and 2342.88 dB/cm for y-polarized mode at the wavelengths of 1.31 μm and 1.55 μm, while the corresponding loss for x-polarized one is 0.10 dB/cm and 0.83 dB/cm, respectively. Moreover, the crosstalk of the 100-μm-long PCF polarization filter with t = 18.7 nm and t = 13.8 nm is up to 177.34 dB and 203.43 dB at 1.31 μm and 1.55 μm, respectively. As the fiber length is 100 μm, the bandwidth with the crosstalk less than − 20 dB can be up to 1200 nm, from 1.2 to 2.4 μm. In addition, the proposed broadband and miniaturized PCF filter is not sensitive to the temperature variation and exhibits stable filtering characteristics with the ± 1% fabrication tolerances.

Light–Matter Interactions in Films of Randomly Distributed Unidirectionally Scattering Dielectric Nanoparticles

We theoretically investigate the light scattering characteristics of monolayer films composed of randomly positioned unidirectionally scattering dielectric nanoparticles that support overlapping electric and magnetic dipole modes. We show using generalized Mie theory that the optical response of both sparse and dense nanoparticle films can be understood from the scattering properties of the individual dielectric nanoparticles, despite random particle-particle coupling effects, and validate these results with full wave electromagnetic simulations. The spectral, angular, and polarization dependent reflection and transmission scattering characteristics of these random particle films are also shown to be strikingly different from those of homogeneous dense solid thin films of equivalent dielectric permittivity.

Diffraction-induced enhancement of optical spin Hall effect in a dielectric grating

The enhancement of the optical spin Hall effect (OSHE) of a transmitted beam has been achieved in a small incident angle of a sub-degree scale. The OSHE at a large incident angle can be beneficial in optical applications, such as polarization-dependent sensors and filters, but studies to increase the OSHE at a large incident angle have been elusive in transmission mode. We propose a dielectric grating on a metal layer to achieve the grating-induced increase of the OSHE. The polarization-dependent transmission and OSHE that reaches several wavelengths are numerically demonstrated. We also show the tunability of the operating wavelength and incident angle of the OSHE by changing materials and geometrical parameters.