Ultra-broadband Polarization Research Articles

Tunable ultra-broadband polarization filter based on three-core resonance of the fluid-infiltrated and gold-coated photonic crystal fiber**Project supported by the National Natural Science Foundation of China (Grant Nos. 61505175 and 61475134) and the Natural Science Foundation of Hebei Province (Grant Nos. F2017203110 and F2017203193).

We propose a tunable ultra-broadband polarization filter based on three-core resonance of the fluid-infiltrated and gold-coated high birefringent photonic crystal fiber (HB-PCF). Gold film was applied to the inner walls of two cladding air holes and surface plasmon polaritons were generated on its surface. The two gold-coated cladding air holes acted as two defective cores. As the phase matching condition was satisfied, light transmitted in the fiber core and coupled to the two defective cores. The three-core PCF supported three super modes in two orthogonal polarization directions. The coupling characteristics among these modes were investigated using the finite-element method. We found that the coupling wavelengths and strength between these guided modes can be tuned by altering the structural parameters of the designed HB-PCF, such as the size of the voids, thickness of the gold-films and liquid infilling pattern. Under the optimized structural parameters, a tunable broadband polarization filter was realized. For one liquid infilling pattern, we obtained a broadband polarization filter which filtered out the light in y-polarization direction at the wavelength of 1550 nm. For another liquid infilling pattern, we filtered out light in the x-polarization direction at the wavelength of 1310 nm. Our studies on the designed HB-PCF made contributions to the further devising of tunable broadband polarization filters, which are extensively used in telecommunication and sensor systems.

Ultra-broadband polarization splitter based on graphene layer-filled dual-core photonic crystal fiber**Project supported by the National Natural Science Foundation of China (Grant Nos. 61405096 and 61504058), the Introduction of Talent Research and Research Fund of Nanjing University of Posts and Telecommunications, China (Grant No. NY214158), the Open Fund of Laboratory of Solid State Microstructures, Nanjing University, China (Grant No. M28035), and

An ultra-broadband polarization splitter based on graphene layer-filled dual-core photonic crystal fiber (GDC-PCF) that can work in a wavelength range from 1120 nm to 1730 nm is proposed in this paper. Through optimizing fiber configuration, the polarization splitter has an extinction ratio of at with a fiber length of 4.8 mm. Compared with the photonic crystal fiber reported splitters, to our knowledge, the GDC-PCF splitter with the extinction ratio below −20 dB has a super wide bandwidth of 610 nm. Due to the excellent splitting characteristics, the GDC-PCF will be used in coherent optical communication systems in a wavelength range from infrared to mid-infraed.

Ultra-broadband polarization filter covering O + E + S + C + L + U telecom wavebands based on Au-coated photonic crystal fiber

An ultra-broadband polarized filtering Au-coated photonic crystal fiber (PCF) is proposed by finite-element method with the software of Comsol Multiphysics. The pattern is further used to discuss the consequences on the operation of the PCF for the two polarized directions when the sizes of the cladding air holes d, the Au-coated enlarged air hole dl, and the thickness of the Au film t are varied. Numerical analyses have been simulated for the influence of the structural parameters on the performance of the designed polarization filter. A broadband of 1310nm (from 1190 to 2500nm) covering the two communication wavelengths of 1.31μm and 1.55μm for the crosstalk as high as 20dB is obtained, providing a wavelength coverage of six bands in the O+E+S+C+L+U telecom wavebands over a 500-μm-long PCF simultaneously. This report presents an extensive application in the development of high-capacity, ultra-broadband, and integrated optical communication systems.

Chalcogenide glass-on-graphene photonics

Two-dimensional (2-D) materials are of tremendous interest to integrated photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. In this paper, we present a new route for 2-D material integration with planar photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides claiming improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as graphene-based mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators.

Ultra-broadband silicon polarization splitter-rotator based on the multi-mode waveguide.

We propose and demonstrate an ultra-broadband polarization splitter-rotator (PSR) on the Silicon-On-Insulator (SOI) platform. The proposed PSR consists of a straight multi-mode waveguide, an asymmetrical directional coupler and a bent directional coupler. The multi-mode waveguide enables highly-efficient TM0-TE1 polarization rotation. The excited TE1 mode is then converted to be TE0 mode by the asymmetrical directional coupler. The remained TM0 mode is filtered out by the bent directional coupler. On the other hand, the incident light of TE0 mode goes through the PSR with negligible conversion and coupling. Only one-step etching is required for the proposed PSR. The fabricated PSR shows a high extinction ratio > 30.82 dB and a low loss < 0.57 dB at the central wavelength. The extinction ratio is > 20 dB over an ultra-broad wavelength band > 85 nm.

A novel ultra-broadband single polarization single mode photonic crystal fiber

The concept of employing a central hole infiltrated with nematic liquid crystal (NLC) and two additional air holes in the core region is exploited to obtain an ultra-broadband single polarization single mode photonic crystal fiber (SPSM-PCF). The effects of structural parameters on the SPSM operation are studied using the full-vectorial finite element method. Numerical results show that the proposed structure can attain the SPSM operation bandwidth of 1610nm (from 1.51 to 3.12µm) with confinement loss lower than 0.01dB/km. The SPSM operation range can also be widely tuned to shorter wavelengths by adjusting the structure parameters. And meanwhile, a broad dispersion-flattened SPSM PCF is also obtained around the communication wavelength. Moreover, the dual-core SPSM PCF has also been investigated, enabling potential applications in the wavelength splitter of 1.31 and 1.55µm bands at a short fiber length of 1.629mm with SPSM operation.

Ultra-broadband and high-efficiency reflective linear polarization convertor based on planar anisotropic metamaterial in microwave region

A simple design of an ultra-broadband and high-efficiency reflective linear polarization convertor with 90° rotation is presented in the microwave region. This convertor is formed from the planar anisotropic metamaterial (MM) using cut-wire (CW) structure. Three resonance modes are generated by electric and magnetic fields of incident wave, which lead to bandwidth expansion extremely of cross-polarization reflection. The simulation result shows that a linearly polarized wave can be converted into its orthogonal polarization after reflection, the polarization conversion ratio is above 90% in the frequency range of 5.1–12.1GHz and the relative bandwidth is up to 78.6%, which agree well with the experimental results. Both simulation and experiment results demonstrate the capability of linear polarization conversion by 90° with high polarization purity after reflection in the above frequency range, which can be confirmed by ellipticity η and the polarization rotation azimuth angle θ. The designed structure that utilized to build the thin MM slab is about λ0/8.72 evaluated at operating center frequency. It has application values in polarization control with high performances.

Ultra-Broadband Polarization Splitter-Rotator Based on the Mode Evolution in a Dual-Core Adiabatic Taper

A polarization splitter-rotator (PSR) based on the supermode evolution in a dual-core adiabatic taper with multiple segments is designed. For this dual-core adiabatic taper, one core becomes narrow and the other one becomes wide. The gap between them is kept constant except the input/output parts where these dual cores are separated gradually. When choosing some specific widths for the dual cores, mode hybridization between the TM0 supermode and the TE 1 supermode happens. As a result, when light propagates along the dual-core adiabatic taper, the TM0 supermode launched from the input port can be efficiently converted to the TE1 supermode, which is mainly confined in the core connected to the cross port, and finally one has the TE0 mode output from the cross port. On the other hand, the TE0 mode launched from the input port is confined tightly in the core connected to the through port and finally outputs from the through port with a very low loss. For the structural design of the adiabatic taper, three operation wavelengths of 1450, 1550, and 1650 nm are considered simultaneously so that the PSR works well in a very broad band from 1450 to 1650 nm. Here, the widths of the multiple segments in the taper section are chosen optimally according to the mode hybridization regions of the dual-core waveguide when operating at the wavelengths of 1450, 1550, and 1650 nm. With this design method, the designed PSR based on silicon-on-insulator nanowires is about 240 μm long. The bandwidth is even as large as 300 nm (1450–1750 nm) for an extinction ratio of >16 dB and an excess loss of <0.1 dB in theory.

Design of an Ultrabroadband and High-efficiency Reflective Linear Polarization Convertor at Optical Frequency

A simple design of an ultrabroadband and high-efficiency reflective linear polarization convertor is presented in the optical frequency region. This ultrabroadband convertor is formed from the planar anisotropic metasurface using a meander wire structure. The numerical simulation demonstrates that the polarization conversion ratio over 90% is achieved from 181 to 506 THz, which is equivalent to 94.6% relative bandwidth for y -polarized incident lights under normal incidence. Further simulation results show that the high polarization conversion efficiency can be sustained well when the incident angle increases to 45 ${}^{\circ}$ for both transverse electric (TE) and transverse magnetic (TM) modes. By taking advantage of surface current distribution, the physical mechanisms are elucidated in detail. The further theoretical calculation results based on the interference theory are good agreement with the simualtion. Our design provides a unique approach in realizing the polarization manipulation with high performances in the optical frequency region.

Scattering Fields Control by Metamaterial Device Based on Ultra-Broadband Polarization Converters

Scattering Fields Control by Metamaterial Device Based on Ultra-Broadband Polarization Converters

Ultrabroadband polarization splitter based on three-core photonic crystal fiber with a modulation core.

We design an ultrabroadband polarization splitter based on three-core photonic crystal fiber (PCF). A modulation core and two fluorine-doped cores are introduced to achieve an ultrawide bandwidth. The properties of three-core PCF are modeled by using the full-vector finite element method along with the full-vector beam propagation method. Numerical results demonstrate that an ultrabroadband splitter with 320 nm bandwidth with an extinction ratio as low as -20 dB can be achieved by using 52.8 mm long three-core PCF. This splitter also has high compatibility with standard single-mode fibers as the input and output ports due to low splicing loss of 0.02 dB. All the air holes in the proposed structure are circular holes and arranged in a triangular lattice that makes it easy to fabricate.

An Ultra-broadband Single Polarization Filter Based on Plasmonic Photonic Crystal Fiber with a Liquid Crystal Core

An ultra-broadband single polarization filter based on plasmonic photonic crystal fiber with a liquid crystal core is investigated using the full-vectorial finite element method. Numerical simulations show that the loss of x-polarized core mode is better than 248.95 dB/cm in a 1.25–2.1 μm wavelength range, while the corresponding loss of y-polarized core mode is lower than 0.21 dB/cm. The high polarization extinction ratio is obtained at the communication wavelength of 1.3 μm, where the losses of x- and y-polarized core modes are 433.25 and 0.0064 dB/cm, respectively. When the fiber length is 1 mm, a broad bandwidth of 850 nm with an extinction ratio lower than −20 dB is obtained. Moreover, the proposed single polarization filter exhibits a better tolerance of realistic fabrication.

Ultra-broadband and high-efficiency polarization conversion metasurface with multiple plasmon resonance modes**Project supported by the National Natural Science Foundation of China (Grant Nos. 61471292, 61331005, 61471388, 51277012, 41404095, and 61501365), the 111 Project, China (Grant No. B14040), the National Basic Research Program of China (Grant No. 2015CB654602), and the China Postdoctoral Science Foundation ( Grant No. 2015M580849).

In this paper, we present a novel metasurface design that achieves a high-efficiency ultra-broadband cross polarization conversion. The metasurface is composed of an array of unit resonators, each of which combines an H-shaped structure and two rectangular metallic patches. Different plasmon resonance modes are excited in unit resonators and allow the polarization states to be manipulated. The bandwidth of the cross polarization converter is 82% of the central frequency, covering the range from 15.7 GHz to 37.5 GHz. The conversion efficiency of the innovative new design is higher than 90%. At 14.43 GHz and 40.95 GHz, the linearly polarized incident wave is converted into a circularly polarized wave.

Polarization rotator-splitter covering full optical communication bands based on L-shaped cross-section waveguide

We propose an ultra-broadband and fabrication-tolerant polarization rotator-splitter (PRS) based on a waveguide with an L-shaped cross section and a Y-junction. The proposed PRS is based on the 220 nm silicon-on-insulator platform, and it shows less than 0.27 dB insertion losses and larger than 14 dB polarization extinction ratios over a wavelength range from 1200 to 1700 nm. To the best of our knowledge, the PRS working in the whole optical communication band is proposed for the first time.

Design of an ultra-broadband and fabrication-tolerant silicon polarization rotator splitter with SiO2 top cladding

An ultra-broadband and fabrication-tolerant silicon polarization rotator splitter is proposed in this Letter. Benefitting from the broadband and low-loss characteristics of the bi-level taper and counter-tapered coupler, the designed device has a simulated insertion loss and crosstalk of less than 0.2 and −15 dB in the waveband from 1290 to 1610 nm. These characteristics make it valuable in applications with large bandwidth requirements, such as full-grid Coarse wavelength division multiplexer (CWDM) and diplexer/triplexer fiber-to-the-home systems. The fabrication tolerance of the design is also analyzed, showing that the device performance is quite stable with normal manufacturing errors in silicon photonics foundries.

A compact ultrabroadband polarization beam splitter utilizing a hybrid plasmonic Y-branch

A compact and ultrabroadband polarization beam splitter (PBS) utilizing a hybrid plasmonic Y-branch (HPYB) on a silicon-on-insulator (SOI) platform is proposed and numerically demonstrated. The HPYB consists of a vertical hybrid plasmonic waveguide (HPW) and a horizontal HPW formed by silicon (Si) and silver (Ag) strip waveguides sandwiched with a silicon dioxide (SiO2) layer, in which the vertical and horizontal hybrid plasmonic modes (HPMs) are excited by the input transverse electric (TE) and transverse magnetic (TM) modes, respectively. The HPMs are split into different ports and coupled back to TE and TM modes to implement the polarization splitting function. A simplified and compact HPYB is robust for the HPMs' generation. The structure is wavelength insensitive since the HPMs' excitation is weakly correlated to the optical wavelengths. The simulation results show that the HPYB-based PBS has a compact footprint of $5 \times 1.8 \mu\text{m}^2$ and an ultralarge working bandwidth of 285 nm, with the polarization crosstalk < −10 dB and the worst-case TE (TM) mode insertion loss of −1.53 (−2.35) dB. The device also exhibits a large fabrication tolerance of 210-nm variation (from −100 to 110 nm) to the waveguide width for both polarizations.

Ultra-broadband perfect cross polarization conversion metasurface

We propose a metasurface with multiple plasmon resonances that achieves an ultra-broadband perfect cross polarization conversion. The metasurface is composed of an array of unit resonators, three plasmon resonances are excited in the unit resonator, which leads to an ultra-broadband perfect cross polarization conversion. The cross polarization conversion efficiency is higher than 99%, and the bandwidth of the converter is 53.7% of the central wavelength. Both numerical and experimental results were used to validate the ultra-broadband perfect cross polarization converter presented here.

Ultra-broadband and compact polarization splitter based on gold filled dual-core photonic crystal fiber

A polarization splitter based on gold filled dual-core photonic crystal fiber (DC-PCF) that can work from 1420 nm to 1980 nm (560 nm bandwidth) is proposed in this work. The splitter has an extinction ratio lower than −20 dB over a large bandwidth with a total length of 254.6 μm. The key principle of operation of the splitter is the induced change in the refractive index of the y-odd mode when it is coupled to the second order plasmonic mode, while other supermodes are weakly affected by the plasmonic mode. The proposed broadband and compact polarization splitter may find applications in communications and sensing, being capable of working in the infrared and mid-infrared wavelength ranges.

Achromatic polarization manipulation by dispersion management of anisotropic meta-mirror with dual-metasurface.

A dual-metasurface-based reflective device ("meta-mirror") has been proposed for broadband polarization manipulation, which is composed of orthogonal metallic cut-wire arrays separated from a grounded plane with different distances. The reflective phases of orthogonally linearly-polarized components can be independently adjusted by changing the dimensions of the cut-wire pairs. Benefiting from the fully released dispersion management ability in both dimensions, achromatic (i.e., ultra-broadband) polarization manipulation can be achieved. The suggested approach has been numerically verified in both microwave and optical band. Moreover, experimental characterization in microwave regime has demonstrated the broadband polarization manipulation ability within 5 - 30 GHz. The underlying physical mechanism of dispersion engineering was explained in general equivalent circuit theory and transmission line model.

Broadband and ultra-broadband polarization rotators with adiabatic modular design

We experimentally demonstrate broadband and ultra-broadband spectral bandwidth polarization rotators with modular design. The presented polarization rotators comprise arrays of half-wave plates rotated at different angles. We give the general recipe to determine the exact values of the rotation angles as follows: align the fast polarization axis of the first half-wave plate with the incoming polarized light, and then rotate each subsequent half-wave plate at a gradually increasing angle until the fast polarization axis of the last half-wave plate is parallel with the desired polarization rotation angle. We show that the broadband and ultra-broadband performance of the polarization rotators is due to the adiabatic nature of the evolution of the light polarization. In this paper we experimentally investigate the performance of broadband and ultra-broadband polarization rotators comprising ten multi-order half-wave plates and ten commercial achromatic half-wave plates, respectively.