Broadband Single-polarization Research Articles

Surface plasmon resonance based tunable D-shaped single polarization filter at the communication band

A surface plasmon resonance based D-shaped tunable and broadband single-polarization filter is proposed. The complex propagation constants and the guided modes’ corresponding field profiles are calculated using the full-vector finite element method based COMSOL Multiphysics v5.0 software. From the simulation study, it is found that the confinement losses of the desired x-polarized mode are 0.17 dB/cm, and 0.30 dB/cm at the resonance wavelength of 1.31 µm, and 1.55 µm, respectively, while the losses for y-polarized unwanted guided mode are 736.30 dB/cm, and 573.32 dB/cm at the mentioned wavelengths, respectively. It is also evident that the proposed fiber offers a crosstalk of 625.10 dB at the wavelength of 1.31 µm, and 495.31 dB at the wavelength of 1.55 µm with the corresponding bandwidth of 490 nm and 485 nm over which the crosstalk is more than 20 dB for a fiber length of 1.0 mm. The study also underpins that the resonant peak shifts linearly with the change of lattice constant, radius of the gold-coated channel in the polished surface, and the size and the distance between the tuning air holes of the proposed filter. Hence, this filter can be a potential fit for micro-integration in optical systems.

Design of broadband single-polarization filter based on simple structure photonic crystal fiber with gold-coated air holes

A polarization filter based on simple structure photonic crystal fiber (PCF) coated with gold air holes is designed in this work. The full vector finite element method (FEM) is used to calculate the characteristic parameters of PCF. In the final numerical simulation results, the loss peak in the [Formula: see text] polarization direction is 2305.72 dB/cm and the [Formula: see text]-polarized loss is as low as 75.86 dB/cm at 1.31 [Formula: see text]m. For the fiber length of 1000 [Formula: see text]m, the CT reaches 1936.83 dB and a wide bandwidth greater than 20 dB can provide above 800 nm. The content of this paper can provide a new idea for filter structure design.

Normal-dispersion CS2-filled silica fiber with broadband single-polarization property

The CS2-filled silica fiber with two air holes in the cladding can offer high nonlinearity, high birefringence and normal group velocity dispersion (GVD) profiles for both two orthogonally polarized fundamental modes (FMs) by an appropriate choice of the fiber parameters. Furthermore, the highly birefringent CS2-filled fiber assisted by two subwavelength-diameter gold wires can exhibit broadband single-polarization (SP) property because that, only the y-polarized FM guided in the CS2-core can couple to the fundamental surface plasmon polariton (SPP) modes with the field vectors along the radial direction, and then has a much larger losses than the x-polarized FM in the wavelength region beyond 1500 nm. The numerical results show that when the 25-kW 0.1-ps pulse at 1920 nm is coupled into the 0.035-m fiber and linearly polarized along the fast axis, the output pulse exhibits over one-octave supercontinuum (SC) spectrum linearly polarized in the fast axis, and can maintain a linear polarization state across the whole SC spectrum even though the input polarization angle increases to 15° from the fast axis.

Epsilon negative-based, broadband single-polarization single-mode hollow core anti-resonant photonic crystal fiber.

A broadband single-polarization single-mode (SPSM) hollow core anti-resonant photonic crystal fiber (HC-ARPCF) is proposed and analyzed by the finite element method in this paper. The HC-ARPCF design consisted of outer semicircular cladding tubes and inner circular cladding tubes. The SPSM behavior is achieved through controlling the effective material absorption loss (EML) by loading epsilon negative (ENG) material in the selected semicircular cladding tubes. Optimization of the configuration parameters is conducted to yield a large loss difference (LD) between one of the two orthogonally polarized fundamental modes and all the other unwanted modes. Therefore, only one desired mode will exist after a proper propagation distance, i.e., SPSM guidance. Specially, the optimal design provides a 288 nm (from 1408 nm to 1676 nm and from 1680 nm to 1700 nm) bandwidth in terms of 40 dB/m minimum LD (MLD) and 168 nm (from 1452 nm to 1620 nm) bandwidth in terms of 100 dB/m MLD. Furthermore, this fiber also exhibits a large effective mode area and near-zero dispersion properties over the entire operation bandwidth. The proposed HC-ARPCF may find its applications in polarization maintaining and high-power laser systems.

Hole-Assisted Solid Core Bragg Fibers With a High-Index-Contrast Cladding for Broadband Single-Polarization Operation

We propose a hole-assisted solid core Bragg fiber (SCBF) with a high-index-contrast cladding for near-infrared broadband single-polarization transmission in this article. The circular symmetry of a common SCBF is broken by the introduced air holes in the solid core for increasing the modal birefringence and polarization-dependent loss (PDL). In the proposed single-polarization SCBF, the confinement of guided modes predominantly depends on the photonic bandgap effect from the high-index-contrast cladding, and simultaneously rests with the total internal reflection from the interface between the solid core and air holes. The numerical results show that both the enhanced modal birefringence and PDL are strongly related to the refractive index, size and locations of air holes. We demonstrate that the modal birefringence for the fundamental mode can be up to the order of 10−3, and the difference in confinement losses between both polarized fundamental modes is no less than an order of magnitude, which is sufficiently large to support single-polarization operation. Moreover, the single-polarization bandwidth with the transmission loss lower than 0.1 dB/m is as high as 277 nm and the critical bend radius is as low as 1 cm, indicating the excellent performances of high bandwidth and bending resistance in the hole-assisted single-polarization SCBF.

Single-polarization single-mode hollow-core negative-curvature fiber with silicon-coated cladding

We propose a hollow-core negative-curvature fiber with a silicon-coated double-ring cladding structure. Simulation results show that three broadband single-polarization single-mode regions of 1514–1529 nm, 1536–1546 nm, and 1549–1579 nm are achieved in this fiber. The polarization extinction ratio is up to 4803 and higher order mode extinction ratio reaches 308 at the wavelength of 1550 nm with an x-polarization loss of 0.11 dB/m. The highest polarization extinction ratio is up to 14,232 at the wavelength of 1520 nm. Furthermore, the minimum bend radius that can maintain single-polarization single-mode guidance at the wavelength of 1550 nm is as low as 3 cm.

A Broadband Single Polarization Photonic Crystal Fiber Filter Around 1.55 μm Based on Gold-Coated and Pentagonal Structure

In this paper, a broadband single polarization photonic crystal fiber (PCF) filter around 1.55 μm is presented on account of surface plasmon resonance. The finite element method is used to investigate the performance of the filter, and the structure parameters’ influences on the performances of the filter are studied. Due to asymmetry which is caused by the pentagonal arranged cladding air holes, the confinement loss of the Y polarization core mode reaches to as high as 1751.05 dB/cm around 1.55 μm, while the loss for the X polarization mode is only 0.22 dB/cm. This indicates that a loss ratio of 7959.32 is achieved and the crosstalk value is up to 304.15 dB with 200 μm PCF around 1.55 μm. Moreover, the bandwidth of 20 dB crosstalk value is 1010 nm with a wavelength coverage from 1.39 to 2.40 μm. Numerical simulations also show that the designed filter has good tolerance to structural deformation. Therefore, the proposed pentagonal filter has great potentials in the application of broadband communication system.

Surface plasmon induced broadband single-polarization filter based on high birefringence photonic crystal fiber

A broadband and single-polarization filter based on high birefringence photonic crystal fiber (HB-PCF) with selectively infiltrated gold wires and liquid crystal is proposed, and its filtering characteristics are studied by the full-vector finite element method (FV-FEM). Two gold wires are selectively filled on both sides of the liquid crystal core to act as two defect cores. The results show that the confinement loss of x-polarized core mode is much larger than that of y-polarized core mode in the wavelength range of 0.85–1.75 μm. The confinement losses of x- and y-polarized core modes are 99.87 dB/cm and 0.001 dB/cm at 0.88 um, 726.50 dB/cm and 0.004 dB/cm at 1.02 um, and 474.60 dB/cm and 0.046 dB/cm at 1.30 um, respectively. The bandwidth with extinction ratio less than 20 dB is 900 nm. Moreover, compared with the traditional structures, we find that our structure has higher birefringence. High birefringence helps to separate the resonant wavelengths of x- and y-polarized core modes. Therefore, the excellent properties of the proposed filter can make it widely used in sensing systems and broadband optical communication systems.

Broadband single-polarization optical fiber based on surface plasmon resonance.

We present, to the best of our knowledge, a new scheme of broadband single-polarization optical fiber with high extinction ratio based on surface plasmon resonance (SPR). The double-hole optical fiber with a Ge-doped core is modified by integrating the stacks of conductive and dielectric layers to support SPR. The strong couplings between the guided modes and surface plasmon mode can bring about serious polarization loss of TM mode, while supporting the efficient transmission of TE polarization in broadband. The achievable extinction ratio can be more than 25 dB covering a wide telecom band of 1.17-1.42 µm in short fiber lengths=2.5mm. Meanwhile, the insertion loss of the fiber is less than 0.25 dB. The modified SPR fiber shows promising application in high-quality fiber-integrated polarizers.

A Double-Cladding Single Polarization Photonic Crystal Fiber and Its Structure Deviation Tolerance

We propose a novel broadband single-polarization single-mode (SPSM) photonic crystal fiber with hexagonally latticed circular airholes. Combined with our fabricated polarization maintaining fiber, it has demonstrated that the enlarged air holes in the outmost layer are superior for the confinement loss reduction. At the optimized parameters, the wavelength of SPSM region ranges from 1.52 to 2.13 $\mu$ m, where only y-polarized fundamental mode exists and the confinement loss is 0.051 dB/km at 1.55 $\mu$ m. The influence of realistic fabrication errors involving structure deviation on SPSM operation has also been systematically investigated.

Broadband single-polarization filter of D-shaped photonic crystal fiber with a micro-opening based on surface plasmon resonance.

In this paper, a D-shaped photonic crystal fiber is designed to achieve a single-polarization filter that has a broadband filtering property. The D-shaped structure is a triangular array of air holes, forming a micro-opening on the side-polished surface and plating a gold layer thereon. The investigation of the polarization filter is based on the finite element method; its principle is surface plasmon resonance. The single-polarization filter in the y direction is realized by adjusting parameters such as the apertures of the fiber, the thickness of the gold layer, and the polishing depth. The confinement loss of the core mode in y polarization reaches to a high value of 376.31dB/cm at 1.55μm, and that of the x polarization is 0.17dB/cm; the former is 2225.35 times the latter. When the fiber length L is 1mm, the crosstalk reaches a peak value of 326.7dB at 1.55μm, and the bandwidth of crosstalk higher than 20dB is 480nm. In addition, the external gold coating operation is more conducive to application in the manufacturing process. This filter will be an effective application of the optical communication window near 1.55μm.

Broadband Single-Polarization Single-Mode Operation in Photonic Crystal Fibers With Hexagonally Latticed Circular Airholes

A photonic crystal fiber with hexagonally latticed circular airholes is designed to deliver single-polarization single-mode (SPSM) operation over a broad wavelength band. Base on a W profile and a triple-defect arrangement, such a design can provide an SPSM spectrum of ∼1600 nm (from 0.406 to 2.304 μm) with confinement loss lower than 0.01 dB/km. To the best of our knowledge, this is the broadest to date for a hexagonal lattice with all circular airholes, which can be realized by the simple “stack and draw” process. In favor of the broadband operation, the adjustment of structural parameters allow the dispersion engineering for a flattened behavior within a certain SPSM window, which is highly desired in communication systems, as both the chromatic and polarization-mode dispersions can be radically eliminated.

Broadband single-polarization single-mode photonic crystal fibers with three different background materials.

A modified structure of single-polarization single-mode (SPSM) photonic crystal fiber (PCF) with different background materials is presented and analyzed by using the full-vector finite-element method. Simulation results confirmed that the proposed PCF can realize low-loss SPSM on three wavebands with the same structure and different background materials. The wavebands are 1.46-1.60 μm for silica-based fiber, 1.97-2.3 μm for lead silicate glass fiber, and 3.16-3.58 μm for chalcogenide glass fiber. For three PCFs with different background materials, only the slow-axis mode exists and the confinement loss is less than 100 dB/m in the SPSM wavebands.

Broadband Single-Polarization Photonic Crystal Fiber Based on Surface Plasmon Resonance for Polarization Filter

A broadband single-polarization photonic crystal fiber polarized filter based on surface plasmon resonance is proposed based on finite element method. Numerical simulations show the confinement loss of y-PCM (y-polarized core mode) is much higher than that of x-PCM (x-polarized core mode) in the wavelength range 1.20–1.63 μm. The confinement loss of y-polarized mode is 45,240 and 10,200 dB/m at the communication wavelength 1.31 and 1.55 um, respectively, and the corresponding loss of x-polarized mode is just 90 and 80 dB/m. When the fiber length is 3 mm, the bandwidth of extinction ratio better than -20 dB is greater than 430 nm covering almost all the communication wavelength. To our best knowledge, the bandwidth is the widest. The impacts of structural parameters on the resonance characteristics are also discussed. The structure could be further optimized for better result.

Design of Broadband Single-Polarization Single-Mode Photonic Crystal Fiber Based on Index-Matching Coupling

A new type broadband single-polarization single-mode photonic crystal fiber based on index-matching coupling is proposed by using the full vector finite-element method. Polarization-dependent loss of the proposed fiber is larger than 24.08 dB/m within a wavelength range from 1.25 to 1.65 , and the single-polarization single-mode operation bandwidth reaches 400 nm.

Broadband single-polarization guidance in hybrid photonic crystal fibers

We present hybrid photonic crystal fibers that provide broadband single-polarization guidance based on two different propagation mechanisms, namely, total internal reflection and the photonic bandgap effect. Experimental results demonstrate polarization dependent loss as high as 26.7 dB and the bandwidth of single-polarization behavior over 225 nm.

Broadband Single-Polarization Single-Mode Operation in Highly Birefringent Photonic Crystal Fiber with a Depressed-Index Core

A novel design for a broadband single-polarization single-mode photonic crystal fibers is proposed and numerically analyzed by using a finite-element method. It is shown that the single-polarization single-mode operation spectral region of a highly birefringent photonic crystal fiber can be strongly enhanced by introducing a suitably down-doped silica rod inside the fiber core. In the proposed design, the single-polarization single-mode guidance can be realized in the wavelength range from 1.0 to 1.8 µm with the confinement loss less than 0.12 dB/km.

Broadband Single-Polarization Operation in Square-Lattice Photonic Crystal Fibers

A broadband single-polarization single-mode optical fiber is proposed. One of the polarized states of the highly birefringent square-lattice photonic crystal fiber is eliminated by index-matched coupling with the modes of two cladding defects. Numerical results show that single-polarization operation with the transmission losses of one polarized state larger than 2 dB/m and the losses of another state lower than 2 dB/km can be realized in a spectral region ranged from 1477 to 1776 nm. In addition, by modifying the air holes surrounding the cladding defects, the losses of the unwanted polarized state can be enhanced to be larger than 10 dB/m, with the losses of the transmission state lower than 0.1 dB/m in a 560-nm-broad spectral region.

Tunable Broadband In-Fiber Polarizer Based on Photonic Liquid Crystal Fiber

In this paper a tunable broad-band polarizer based on the photonic crystal fiber (PCF) filled with liquid crystal (LC) is presented. Host PCF is made of glass with 1.518 refractive index and ordinary refractive index of the LCs is lower than glass index. Numerical simulations have proven that by changing LC orientation from planar to transverse a broad-band single-polarization guidance is possible: for planar orientation of LC molecules both polarizations are index-guided, whereas for transverse orientation only one polarization is index-guided. Also some initial experimental results are included showing that polarization dependent losses and phase birefringence can be tuned with transverse electric field.

An Ultra-Broadband Single-Polarization Single-Mode PhotonicCrystal Fibre

An ultra broadband single-polarization single-mode (SPSM) photoniccrystal fibre (PCF) is proposed and analysed by using the plane-waveexpansion method and the beam propagation method. Numerical resultsdemonstrate that the SPSM wavelength region nearly at 580 nm in widthfrom 1.46 μm to 2.04 μm is obtained in this PCF. The startwavelength of the SPSM region is close to the hole pitch, and the widthof the SPSM region increases with the increasing hole pitch. Effects ofdopant concentration on SPSM properties are investigated. Theconfinement loss decreases and the width of SPSM region widens slightlywith the increasing dopant concentration. These results offer a newpossibility of fabricating active doped SPSM PCFs with high performancethat is crucial for improving the performance of linearly polarizedfibre lasers.