High Polarization Extinction Ratio Research Articles

Single-Layer Transmissive Chiral Plasma Metasurface with High Circular Polarization Extinction Ratio in Visible Wavelength.

Chiral metamaterials are extensively applied in the fields of photoelectric detection, biomedical diagnostics and micro-nano polarization imaging. Currently, single-layer chiral metamaterials are unfortunately limited by several issues, such as a weaker circular polarization extinction ratio and circular polarization transmittance difference. To tackle these issues, a single-layer transmissive chiral plasma metasurface (SCPMs) suitable for visible wavelength is proposed in this paper. Its basic unit is composed of double orthogonal rectangular slots and a spatial π/4 inclined arrangement of the rectangular slot to constitute a chiral structure. Each rectangular slot structure has characteristics that enable the SCPMs to easily achieve a high circular polarization extinction ratio and strong circular polarization transmittance difference. Both the circular polarization extinction ratio and circular polarization transmittance difference of the SCPMs reach over 1000 and 0.28 at a wavelength of 532 nm, respectively. In addition, the SCPMs is fabricated via the thermally evaporated deposition technique and focused ion beam system. This compact structure coupled with a simple process and excellent properties enhances its applicability for the control and detection of polarization, especially during integration with linear polarizers, to achieve the fabrication of a division-of-focal-plane full-Stokes polarimeter.

An Optimized Heading De-Noising Method of the Polarization Compass for Improving Orientation Accuracy

In recent years, the polarization compass (PC) has been extensively applied in the field of autonomous navigation due to its strong autonomy and anti-interference characteristics. Nevertheless, the existing research shows that the PC with high extinction ratio polarization sensor still offers poor orientation accuracy since there is a great quantity of noise in the heading data output from the compass. Here, we present a novel and promising scheme to denoise heading data to improve deficiency in heading data denoising of existing research. The purpose of this study aims to solve the problem that the orientation accuracy of PC caused by noise needs to be improved. Concretely, the major points of this research include an effective separation strategy of noise and useful signal based on the optimized variational mode decomposition (OVMD) and an effective heading data denoising method based on an adaptive singular spectrum analysis (AD-SSA). OVMD based on the center frequency is employed to decompose the original noisy heading data into a finite number of band-limited data intrinsic mode functions (DIMFs) so that the best number of decomposed layers for the noising data can be obtained. Subsequently, the above decomposed DIMFs are divided into low-frequency signal components, mixed components, and high-frequency noise components exploiting the maximum similar eigenvalue of the autocorrelation matrix corresponding to each DIMF as a classification method. An AD-SSA uses the correlation coefficient to further suppress the noise in classified DIMFs. These approaches are combined effectively to improve the orientation accuracy of the PC significantly and very contribute to the navigation application of unmanned mobile platforms such as unmanned aerial vehicles (UAVs). Compared to existing prior arts, the effectiveness of the proposed heading denoising scheme for the PC is demonstrated through the results obtained from the heading data sets on two representative sunny and dust days.

High extinction ratio and an ultra-broadband polarization beam splitter in silicon integrated photonics by employing an all-dielectric metamaterial cladding.

In silicon and other photonic integrated circuit platforms many devices exhibit a large polarization dependency, therefore a polarization beam splitter (PBS) is an essential building block to split optical signal to transversal electric (TE) and transversal magnetic (TM) modes. In this paper we propose a concept of integrated silicon-based PBS exploiting unique properties of all dielectric metamaterial cladding to achieve a high extinction ratio (ER) and wide bandwidth (BW) polarization splitting characteristics. We start from a structure (PBS-1) based on a directional coupler with metamaterial cladding combined with a bent waveguide with metamaterial cladding at the outer side in the role of a TE polarizer at the Thru port of the device. To increase BW we propose the improved concept (PBS-2) - a metamaterial compact dual Mach-Zehnder Interferometer structure in combination with the TE polarizer. Numerical simulations reveal that an exceptionally high ER over 35 dB can be achieved in a BW of 263 nm with insertion loss (IL) below 1 dB in case of PBS-2. The designed device has a footprint of 82 µm. Measurement results reveal that an ER > 30 dB is achievable in a BW of at least 140 nm (limited by the laser tuning range).

Polarization Control in Integrated Graphene-Silicon Quantum Photonics Waveguides.

We numerically investigated the use of graphene nanoribbons placed on top of silicon-on-insulator (SOI) strip waveguides for light polarization control in silicon photonic-integrated waveguides. We found that two factors mainly affected the polarization control: the graphene chemical potential and the geometrical parameters of the waveguide, such as the waveguide and nanoribbon widths and distance. We show that the graphene chemical potential influences both TE and TM polarizations almost in the same way, while the waveguide width tapering enables both TE-pass and TM-pass polarizing functionalities. Overall, by increasing the oxide spacer thickness between the silicon waveguide and the top graphene layer, the device insertion losses can be reduced, while preserving a high polarization extinction ratio.

All-silicon and ultra-compact transverse electric-pass polarizer with large bandwidth and high polarization extinction ratio based on subwavelength metamaterials

In this paper, we have proposed an all-silicon and compact transverse electric (TE)-pass polarizer with large bandwidth and high polarization extinction ratio (PER), where the polarizer uses a semi-arc waveguide to cause polarization-dependent bending loss (PDBL). The combination of the subwavelength grating (SWG) and double adiabatic tapers serve as an equivalent cladding to get strengthened PDBL. The parameters of SWG and double adiabatic tapers are analyzed in detail to improve the performance of the device. In the proposed TE-pass polarizer, the injected fundamental TE mode (i.e., TE0) gets protection and the injected fundamental transverse magnetic mode (i.e., TM0) lets out. The footprint is only about 6 μm × 10 μm, which is substantially reduced compared with the previous counterparts. From the results, its bandwidth is as high as 228 nm (from 1.482 to 1.710 μm) with PER > 39 dB and low excess loss (EL < 1 dB), and it has an ultra-high PER of 42.5 dB and a low EL of 0.1 dB at 1.55 μm. In addition, large fabrication tolerances of 20 nm ( ± 10 nm) to the key structural parameters are analyzed.

Bandgap-independent photoconductive detection in two-dimensional Sb2Te3

Broadening the spectral range of photodetectors is vital for photodetection. However, current photoelectric detectors are selective to wavelength, which depends on bandgap, and thermal detectors respond slowly at room temperature. It is challenging to achieve photoconductivity independent of the semiconductor bandgap, which is needed to broaden the spectral range of photodetectors. Here, we use 2D semiconductor Sb2Te3 to develop a photodetector with metal-semiconductor-metal structure for multiband response, covering visible, infrared, terahertz and millimeter wavelengths at room temperature. This is achieved by the synergy of the photoconductivity of photo-excited electron-hole pairs above the bandgap, and an electromagnetic-induced well effect below the bandgap. The photodetector achieves a responsivity of 0.6 A W−1 at 1550 nm, 515 A W−1 at 0.340 THz with a bias of 0.2 V, respectively. The response time is 900 ns, which is short compared to the reported detectors based on 2D materials. In addition, it also exhibits a high polarization extinction ratio of 90. These results suggest that our strategy achieves a photoconductivity independent of the semiconductor bandgap to broaden the spectral range of photodetectors, and could be a strong candidate for multiband photodetection systems.

An ultracompact optical polarizer based on the one-dimensional photonic crystals containing anisotropic layers

The linear birefringence effect of the uniaxial anisotropic materials is utilized to design an optical polarizer in this paper. We propose a one-dimensional photonic crystal structure with an anisotropic defect layer to break the degeneracy of the TE and TM mode resonances. The band structures of the TE and TM mode polarizations are calculated using the plane wave expansion method, which has been generalized for the structures containing anisotropic materials. By increasing the refractive index contrast ratio of the HL pair layers of the crystal, we present an ultracompact structure with significant performance of a very high polarization extinction ratio (PER) and a very low insertion loss (IL). The presented polarizer, which operates at the near-infrared region centered at the wavelength of 1550 nm, is 2.67 μm long. It is obvious that the structure is considerably compact for the long wavelength of the third communication window. The polarizer can be designed in such a way that only the fields with a specific polarization direction (TM, TE, or any other direction) are transmitted.

High Extinction Ratio and Large Bandwidth PCF Polarization Filter With Gold-Wires Coated by Monocrystalline Silicon

A kind of high extinction ratio (ER) and large bandwidth photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance is proposed. The SPP modes can be inspired by two gold-wires to improve the filter characteristics and the effect of surface plasmon resonance is further enhanced by cladding monocrystalline silicon surrounding gold-wires. An asymmetric structure of leakage channel is introduced in y-pol direction axis which intensifies the energy leakage to external cladding, high polarization extinction ratio is occurred. By using the finite element method (FEM), the structural parameters and optical properties are quantitatively analyzed. Numerical analysis shows that two main adjacent resonance peaks appear in y-pol direction, confinement losses of y-pol core mode at the resonance wavelength of 1519 and 1664 nm are 573.33 and 543.21 dB/cm, while the losses of x-pol core mode are 16.97 and 0.98 dB/cm. When the fiber length L=3 mm, the maximum ER reaches 1449 dB at the wavelength of 1519 nm, and the bandwidth with ER better than 20 dB reaches 405 nm. Hence the proposed PCF with gold-wires coated by monocrystalline silicon would have a widely application in optical fiber communication, optical information processing and other fields.

Compact and low-loss TM-pass polarizer based on a hybrid plasmonic waveguide with a semiround arch Si core.

A compact and low loss TM-pass polarizer based on a hybrid plasmonic waveguide (HPW) has been demonstrated. By introducing the hollow HPW with a semiround arch (SRA) Si core, the unwanted TE mode can be effectively cut off and the TM mode can pass through by hybrid plasmonic mode with excellent transmission characteristics. The hollow structure realizes lower index with n=1 due to the air region, and the SRA construction effectively suppresses the energy loss of the TM mode caused by the corner effect. Thus, TM modes pass through with negligible loss and exhibit the characteristic of strong mode limitation. By optimizing the width of metal, the width of the HPW, and the length of the tapered mode converter, an optimum performance with a high polarization extinction ratio of 67.87 dB and a low insert loss of 0.029 dB at the work wavelength=1550nm is achieved. Detailed analysis also proves that the proposed polarizer has a compact size of only 7 µm and a great fabrication tolerance. This work offers a simple and effective scheme of polarization control on-chip.

High-performance silicon TE-pass polarizer assisted by anisotropic metamaterials.

The polarizer is a key component for integrated photonics to deal with the strong waveguide birefringence, especially for silicon photonics. A high-performance silicon TE-pass polarizer covering all optical communication bands with low insertion loss (IL) and high polarization extinction ratio (PER) is proposed here. This polarizer is based on anisotropic subwavelength grating (SWG) metamaterials, which maintain the fundamental TE mode as a guided mode but make the fundamental TM mode leaky. Furthermore, based on this working mechanism, the proposed polarizer can work well for any upper cladding material, including air and silicon dioxide (SiO2). The numerical results show that our proposed TE-pass polarizer has a remarkable performance with IL < 0.34 dB over 420 nm (PER > 23.5 dB) or 380 nm (PER > 30 dB) for the air cladding, and IL < 0.3 dB over 420 nm (PER > 25 dB) or 320 nm (PER > 30 dB) for the SiO2 cladding. The fabricated polarizer shows IL < 0.8 dB and PER > 23 dB for the bandwidths of 1.26-1.36 µm and 1.52-1.58 µm (other bandwidths were not measured due to the limited instrument in our research center, but it still covers the most important O-band and C-band).

High extinction ratio and low backreflection polarization maintaining hollow-core to solid-core fiber interconnection.

We develop a hybrid cold/heat two-step splicing approach for low loss, low backreflection, and high polarization extinction ratio (PER) hollow-core to solid-core fiber interconnection. The employed hollow-core fiber (HCF) is our recently developed high-birefringence polarization-maintaining hollow-core fiber (PM-HCF) with a PER value of ∼30 dB, and the solid-core fiber (SCF) is a commercial Panda polarization-maintaining fiber (Panda fiber). Simultaneous low backreflection (<-35 dB), low insertion loss (IL) (∼0.7 dB), and high PER (∼27 dB) are achieved, representing the first high-performance PM-HCF/SCF interconnections, to the best of our knowledge. This greatly facilitates the applications of PM-HCF in widespread fields such as precise metrologies, gyroscopes, and ultrafast/high-power laser deliveries.

Tunable Terahertz Perfect Absorber and Polarizer Based on one-Dimensional Anisotropic Graphene Photonic Crystal

In this article, a new tunable absorber and polarizer using one-dimensional anisotropic graphene photonic crystal (1D AGPC) is proposed for terahertz applications. The optical properties of the 1D AGPC structure is obtained through the transfer matrix method (TMM) calculations. In our design, a single defect layer is introduced in the 1D AGPC structure to increase its absorption. The absorption coefficient is further modified by optimizing the AGPC parameters such as the number of photonic crystal periods, the defect layer thickness, and the chemical potential of graphene. The modified structure can provide perfect absorption with a narrow bandwidth of 0.05 THz. On the other hand, considering the anisotropic optical properties of graphene, polarization dependence of the absorption coefficient is investigated. This feature of the structure can be employed to realize a tunable terahertz polarizer by adjusting incident angle at &#x0398;0 = 80&#x00B0;. In this way, high tunable polarization extinction ratio of 6.1 dB to 11.63 dB with respectively very narrow bandwidth of 0.031 THz to 0.023 THz are obtained. The maximum insertion losses within the tunable frequency range are as low as 0.023 dB and 0.031 dB. Hence, our design may have potential applications in narrow-band optoelectronic devices at the terahertz frequency range.

High extinction ratio and broadband polarization beam splitter based on bricked subwavelength gratings on SOI platform

A compact asymmetrical directional coupler (ADC) based on coupling between a conventional subwavelength grating (SWG) and a bricked subwavelength grating (BSWG) is proposed to realize broadband polarization beam splitter (PBS) with high extinction ratio (ER) on silicon-on-insulator (SOI) platform. Apart from conventional SWG structural parameters (duty cycle and period), the BSWG is utilized to provide a new design space to control TE and TM modal effective index for accurate phase match. Accordingly, as to the TM mode, it is possible to satisfy phase-matching condition and then can be coupled more efficiently with higher ER by introducing the BSWG. Meanwhile, there is a significant phase mismatch for the TE mode. In this way, the proposed PBS that separates TE and TM mode to the through and cross ports can be realized. Simulation results show that the proposed PBS with a compact coupling length of 8.4 μm can achieve a high ER of 35.06 dB and an insertion loss of 0.25 dB for the TM mode at 1.55 μm, while the ER is 18.92 dB and insertion loss is 0.01 dB for the TE mode. Moreover, the operating bandwidth is up to 300 nm (1400∼1700 nm) for the TE mode and 155 nm (1487∼1642 nm) for the TM mode when the ER is >15 dB.

Sensing Characteristics of Polarization-Dependent Helical Long-Period Grating-Based Interferometer

We demonstrate an all-fiber Mach-Zehnder interferometer (MZI) by cascading a pair of helical long-period gratings (HLPGs) inscribed in a Panda-type polarization-maintaining fiber (PMF) using a CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -laser. By cascading two grating with different lengths, a serial of polarization-dependent MZIs with different free spectral ranges have been demonstrated. The maximum polarization-dependence loss of the MZI was measured to be more than 35 dB. Two orthogonal interference spectra corresponding to fast axis mode and slow axis mode can be observed. The sensing characteristics of the polarization-dependent MZI we investigated experimentally. For liquid level sensing, the maximum wavelength shifts of the fast and slow axis interference dips were measured to be 11.03 and 3.25 nm when the surrounding refractive index is 1.424 and the interference length is 12.0 cm, respectively. The fast and slow axis interference dips have good linearity and opposite response with the temperature and strain change, the measured temperature and strain sensitivities of the fast and slow axis interference dips were 103.43 pm/°C, −31.26 pm/°C and −2.13 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , 1.68 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , respectively. Based on the high polarization extinction ratio, narrow resonant bandwidth, and low insertion loss, the demonstrated MZI has potential application in polarization-dependent multi-parameter sensing or multi-channel polarization filter.

Fabrication of biaxial polarization-maintaining optical fiber with ultra-low bending-dependent polarization extinction ratio deterioration

Different applications, including interferometers, gyroscopes, and frequency combs, require a single polarized light transmission by maintaining this property against the environmental perturbation. As a new type of polarization-maintaining (PM) fiber, a biaxial PM fiber was fabricated over 30 dB of high polarization extinction ratio (PER) values among two orthogonal axes over a fiber length of 110 m. The PM fiber was manufactured with a combination of an elliptical core and Panda-type geometries. The PER values were demonstrated to be preserved at harsh temperature conditions from −55 °C to +85 °C. The bending loss measurements indicate the biaxial PM fiber has ultra-low bending dependent PER deterioration (<0.5 %) at various bending diameters from 12 mm to 5 mm. The biaxial PM property was also confirmed by the group beat length measurements and found to be less than 1.5 mm at 1550 nm. The optical time-domain reflectometer (OTDR) measurements show that the optical loss of the biaxial PM fiber was below 1.5 dB/km over 3kmlength. The mode-field diameter (MFD) and the numerical aperture (NA) values were also reported along two polarized axes. This novel PM fiber offers a single solution for the elliptical and Panda-type PM fibers utilized for integrated fiber-based sensors and instruments.

Ultrabroadband and -compact chip-integrated polarization beam splitters based on intelligent inverse design method

In chip-integrated optical circuits, the polarization beam splitter (PBS) is one of the core elements that separates TE/TM modes and transmits them to different ports. We designed an ultracompact Si-based PBS with a footprint of 2 μm × 2 μm by an intelligent inverse design method. This method combines the method of moving asymptotes algorithm and the finite element method, and it has a high polarization extinction ratio (PER) and large splitting bandwidth from 850 to 1450 nm. The transmission of the TE and TM modes reaches 93% and 73%, respectively, and the average PER is 21 and 20 dB, respectively. Moreover, we developed other PBSs with different materials and different directional output ports that have wonderful splitting performance in different wavebands.

Silicon-Based Integrated Terahertz Polarization Beam Splitters

Terahertz (THz) technology offers multifaceted capabilities and disruptive applications in line-of-sight wireless communication, highly sensitive (bio)sensing, imaging and so on. However, the severe lack of polarization devices comparable to those for other electromagnetic frequencies is impeding moving towards practical applications. Here we demonstrate, for the first time, silicon-based integrated, high polarization extinction ratio, low insertion loss, and compact THz polarization beam splitters (PBSs) fabricated by CMOS-compatible technologies based on dielectric environment variation induced evanescent wave coupling effect. Through comprehensively analyzing working principles of conventional two-waveguide-based PBS, a high-performance three-waveguide PBS is successfully realized. Further optimizing the device parameters and working bandwidth, we achieve an integrated broadband PBS based on cascaded asymmetric directional couplers, whose polarization extinction ratios reach up to 20 dB and 32 dB for transverse electric and transverse magnetic modes, respectively, and their 10-dB bandwidth is 32 GHz for a device length of 15.5 mm. These numbers are the highest in silicon-based integrated THz PBSs so far. We believe our observations provide an effective way for exploring on-chip high-performance THz-PBSs for polarization-diverse systems, accelerating the development and application of on-chip THz photonics.

Metrological Traceability of High Polarization Extinction Ratio (PER) Based on Precision Coaxial Rotating Polarization-Maintaining Fiber

This article proposes a metrological traceability method for polarization extinction ratio (PER) ranging from 0 up to 70 dB, while the common method is limited to 50 dB. A precision alignment coupling point is designed and manufactured using two polarization-maintaining fibers (PMFs). By rotating one of the PMFs to change the axis-alignment angle and to control the distribution of light energy in the fast and slow axis, a traceability chain from the PER to the rotation angle is established. With extremely low-stress clamping of the PMF, 5-D precision adjustment of the fiber position, and precision coaxial rotation in the order of arc seconds, accurate and controllable generation of any PER in the range of 0–70 dB can be achieved. A high PER traceability system is designed and built, which is successfully used in the traceability of PER to the angle of circumference. The expanded uncertainty ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k = 2$ </tex-math></inline-formula> ) in the ranges of 0–30 dB, 30–50 dB, and 50–70 dB is 0.01, 0.06, and 1.20 dB, respectively. Controlled generation of high PER (50–70 dB) with metrological traceability is realized for the first time as far as we know.

Ultra-compact, efficient and high-polarization-extinction-ratio polarization beam splitters based on photonic anisotropic metamaterials.

Anisotropic metameterials (AM) provide a new avenue for a next-generation silicon platform to design ultra-compact, densely integrated optical components, thus functional devices based on AM are drawing increasing attention recently. Here, we propose a novel efficient polarization beam splitter (PBS) with high polarization extinction ratio based on AM. An ultra-compact coupling region of 2.5 × 14 µm2 is achieved by tailoring the AM structures, which can efficiently suppress the TE mode coupling, and enhance the TM mode coupling in the directional couplers simultaneously. The insertion loss is simulated to be as low as <0.2 dB within a bandwidth of 70 nm for both modes, and the polarization extinction ratio is as high as 46 dB and 33 dB for TE and TM modes, respectively. We also experimentally demonstrate the proposed PBS, with low insertion loss of 1 dB , high extinction ratio of >20 dB and wide operational bandwidth of >80 nm.

Broadband graphene-based optical power coupler and polarization beam splitter using a directional coupler

The utilization of directional couplers (DCs) as power splitters and combiners is ubiquitous for the realization of integrated silicon photonic devices in the silicon-on-insulator (SOI) platform. Benefiting from the excellent modal modulation performance of graphene in silicon waveguides, we present its high flexibility to engineer and reduce the wavelength dependence of devices based on the DC. In this regard, a wavelength-insensitive 3-dB optical power coupler (3-dB OPC) is firstly proposed, in which various power splitting ratios are realized for the TE mode. Next, we design a broadband polarization beam splitter (PBS) consisting of a silicon waveguide (SW) and a graphene-silicon vertical slot waveguide (GSVSW). The simulation results show that the proposed PBS has high polarization extinction ratios (PERs) of 20.93 and 20.4 dB and low insertion losses (ILs) of 0.12 and 0.21 dB at 1550 nm for the thru and cross ports, respectively. In addition, the designed PBS demonstrates the ability to work over a wide range of wavelengths by changing the chemical potential of graphene.