Single-polarization Single-mode Research Articles

Polarization filter of hollow-core anti-resonant fiber in the 1550 nm band based on SPR effect

Hollow-core anti-resonant fiber (HC-ARF) with unique light propagation through air present a promising avenue for advanced applications of polarization filters based on HC-ARF. This paper proposes a single-mode and single-polarization filters (SMSPF) around 1550 nm based on HC-ARF with tellurite glass as the substrate material. The polarization filtering characteristics of the HC-ARF with varying wall thickness and gold wire filling are simulated and analyzed using the finite element method. A single-mode single-polarization (SMSP) HC-ARF with a continuous bandwidth of 30 nm is obtained, and a polarization filter with low polarization loss and a high filtering bandwidth of 390 nm is achieved through the surface plasmon resonance (SPR) effect.

Modeling and analysis of single-mode widely tunable all-fiber Ho-doped CW master oscillator power amplifier system

We report the design of an all-fiber single-mode polarization maintaining widely tunable Ho-doped master oscillator power amplifier (MOPA) system operating in the wavelength range of 2005-2135 nm based on a pre-amplifier and two power amplification stages. The single clad Ho-doped active fibers in the ring cavity based master oscillator, pre-amplifier, and power amplifiers are pumped using 1950 nm semiconductor laser diode pump sources. The amplification of the MOPA system is investigated over the entire spectral range of 2005-2135 nm. The highest output power achieved by the continuous wave (CW) Ho-doped MOPA system is 43 W at a wavelength of 2028.6 nm using pump power of 20 W with power conversion efficiency (PCE) of 90% for second power amplifier while the total pump power of Ho-doped MOPA system is 45 W. Optical bandpass filters (OBPFs) are employed between different stages of MOPA system to enable amplification over the wider spectral range of 2005-2135 nm by suppressing the amplified spontaneous emission (ASE). Not using OBPFs results in amplification that is limited to the spectral range of 2045-2130 nm. Therefore, a penalty of 45 nm can be avoided at the expense of using the OBPFs between different stages of MOPA system. This flexible MOPA system can be used in multiple applications, especially for space-borne high power transmitters operating in atmospheric transmission windows.

Polymer-based three-waveguide polarization beam splitter with reduced crosstalk for optical circuitry

Polarization beam splitters are pivotal in manipulating polarized light within photonic integrated circuits for various optical applications. This study introduces a single-mode polarization beam splitter comprising three waveguides realized with polymer materials. The device optimization process employed the beam propagation method, explicitly using the RSoft CAD BeamProp solver. Our proposed beam splitter performs exceptionally well with 99% complete and null light transmission efficiency. In particular, it demonstrates minimal insertion loss (0.04 dB for complete transmission and 0.07 dB for null transmission) and low coupling loss (0.03 dB and 0.04 dB for complete transmission, 21.9 dB and 36.3 dB for null transmission from input to bridge and bridge to output waveguides, respectively). Additionally, the beam splitter showcases significantly reduced crosstalk: −27dB and −26.98dB for TE modes during complete light transfer, and −36.28dB and −33.61dB for TM modes during null light transfer. These results underscore its potential for advancing integrated optical systems.

A grating-modified broadband D-type photonic crystal fiber polarization filter

In this paper, a D-type grating-modified broadband photonic crystal fiber polarization filter based on surface plasmon resonance is proposed. The asymmetric design of D-type photonic crystal fiber is helpful to achieve single-mode polarization filtering, and grating can increase the coupling between the core mode and the SPP mode and thus increase the constraint loss. From our simulation results, it can be seen that the applicable bandwidth range can easily reach 1 μm. At the communication wavelength of 1750 nm, the calculated constraint losses of x-polarized and y-polarized core modes are 4.2526 dB cm−1 and 1491.8 dB cm−1, respectively, and the crosstalk is up to 1292 dB. The proposed grating-modified of photonic crystal fiber has achieved good filtering effect in the near-infrared band, and even extended to the mid-infrared band.

AuNPs/GO Coated U-Shape Polished SMF Based Localized SPR Sensor for Musta’mal Water Identification

Potential of hybrid gold nanoparticles/graphene oxide (AuNPs/GO) coated single mode fiber (SMF) sensor by exploiting localized surface plasmon resonance (LSPR) effect for Musta’mal water identification was studied. Three structure shapes of fiber optics such as straight-shape, loop-shape and u-shape had been prepared. Three layers of AuNPs with 50 nm in diameter were drop-casted onto the partially unclad polished single mode fiber (SMF) to observe the maximum sensitivity of LSPR. To enhance the LSPR effect, one layer of GO was deposited on top of the AuNPs layer. Two optical light sources with least attenuation (1310 nm and 1550 nm) were employed to study the optical power output as the sensor immersed in different type of water samples. The u-shape SMF portrayed the maximum output power about 24.2 dBm at 1550 nm wavelength. According to the analysis, the deployment of 1550 nm laser wavelength resulted in better sensitivity with 23.2% improvement compared to 1310 nm wavelength. Apparently, the LSPR phenomenon created by AuNPs/GO able to enhance the plasmonic signal up to 51.9% than the uncoated SMF. The thinnest diameter of SMF’s cladding, d=0.1195 mm with U-shape structure exhibited the highest power different of 1.10 dBm, in which suggested the best sensing performance. In conclusion, the optimization of AuNPs/GO u-shape polished SMF resulted in the maximum sensitivity with value of S=72.7 dBm/RIU for Musta'mal water identification.

Polarization-stable single-mode multi-junction VCSELs with integrated anti-phase mode filter

In this paper, polarization-stable and spectrally single-mode operation of oxide-confined multi-junction vertical-cavity surface-emitting lasers (VCSELs) are achieved by using a non-circular integrated anti-phase transverse mode filter. A record-high single-mode output power is obtained by radially reducing effective mirror reflectivity at the surface areas where the higher order modes are expected to lase, leading to an increase in the threshold gain for these transverse modes, all the while minimal losses are introduced to the fundamental mode. The polarization control of such devices is achieved by using a non-circular mode filter in order to perturb the cylindrical symmetry of the cavity. An elliptically etched surface relief is shown to be effective in realizing a single-mode single-polarization device over a wide range of operating bias currents and temperatures. The continuous-wave light–current–voltage characteristics of 8-junction 940 nm VCSELs show single-mode output power >13 mW at room temperature, spectrally measured with a side-mode suppression ratio of >30 dB. This single-mode performance can be achieved depending on the ratio between the relief opening and the oxide aperture size. Additionally, the single-polarization behavior of such devices (with an extinction ratio of >15 dB) is shown to be dependent on the orientation of the elliptical mode filter, where the light is mainly polarized along the minor axis of the elliptical feature. Overall, combined with a multi-junction active region, the elliptical model filter is able to achieve highly efficient single-mode linearly polarized VCSELs.

Single-polarization single-mode broadband ultra-low loss hollow-core anti-resonant fiber with nested double C-type cladding tubes

A novel five-tube nested double C-type single-polarization hollow-core anti-resonant fiber (HC-ARF) is proposed for single-polarization single-mode, ultra-low loss, and broadband characteristics. Different tube thicknesses are introduced along the orthogonal direction to couple the x-polarized fundamental mode (FM) to the silica modes (SMs). At the same time, the y-polarized FM is tightly bound in the core, achieving a high polarization extinction ratio (PER). In order to achieve large bandwidth, a layer of high-refractive-index silicon material is coated on the inner surface of the cladding tube. To the best of our knowledge, the proposed single-polarization HC-ARF has the highest PER at 1.55μm with a remarkable value of 162486 so far, while the y-polarized FM loss is only 1.4 × 10-3 dB/km. However, the single-polarization bandwidth remains limited. By optimizing the structural parameters on single-polarization bandwidth, the HC-ARF at 1.55μm for single-polarization single-mode transmission is obtained with a high-order mode extinction ratio (HOMER) and PER of 2891, 9531, respectively. In addition, a remarkably high single-polarization bandwidth of up to 150 nm is achieved with ultra-low confinement loss (CL) as low as 2.8 × 10-3 dB/km. Furthermore, the proposed fiber exhibits good bending characteristics, with a bending loss of 6.7 dB/km at the bending radius of 5 cm in the x-direction.

Design of single-mode single-circularly polarized chiral anti-resonant fiber for the communication band

We propose a design of anti-resonant fiber (ARF) involving the introduction of chiral material into the inner regions of six germanium-doped silica glass cladding tubes, which can support the operation of single-mode single left-handed circular polarization in the communication band from 1.540 to 1.605 µm. In particular, the loss reaches a minimum value of 0.009 dB m−1 at 1.550 µm. The sign of the chiral parameter can control the handedness of polarization in the operation of single-mode single-circular polarization. In addition, the ARF possesses a good bending resistance performance. The minimum bending radius of the ARF is 10 to maintain the single-mode single left-handed circular polarization for 1.550 µm. We believe the novel ARF can find applications in optical communication, polarization imaging and chiral sensing.

A Mid-Infrared Ultrawide-Bandwidth Single-Polarization Single-Mode Fiber Based on a Twin-Tube Structure

A novel chalcogenide As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fiber based on a twin-tube structure is proposed and numerically studied for mid-infrared (MIR) single-polarization single-mode (SPSM) operation. The proposed fiber consists of two identical thin-wall tubes, which are located symmetrically inside the cladding. The simulation results show that the y-polarization fundamental mode (YPFM) can be well confined between the two tube walls near the fiber center, while all of the unwanted modes, including the x-polarization fundamental mode (XPFM) and all of the higher order modes (HOMs), are effectively suppressed due to huge confinement loss (CL). The SPSM operation can be maintained in the wavelength range from 3 to 10 μm, covering almost the entire transparency region of an As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fiber, with the maximum YPFM CL of 8.63×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> dB/m at 10 μm. To the best of our knowledge, this is the first MIR fiber that can keep SPSM operation over such a wide wavelength region. Furthermore, the mode area of YPFM is quite small (e.g. 10.82 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the wavelength of 6 μm), which is beneficial to realize high nonlinearity. Besides, the bending induced CL increment of YPFM at 10 μm is only 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> dB/m even when the fiber bending radius is 1 cm. Owing to the simple structure and outstanding properties, the proposed fiber has practical applications in MIR photonics and nonlinear fiber optics.

Dual-core ultrawide-bandwidth and single-mode polarization beam splitter based on anti-resonant fiber

An ultra-bandwidth and single-mode polarization beam splitter (PBS) of dual hollow-core anti-resonant fiber (DHC-ARF) with circular outer tubes and inner tubes is proposed. Four outer tubes are introduced in the horizontal direction to obtain two hollow cores. The modal coupling is realized through the gap between the two hollow cores. The inner tubes also are inserted into two the outer tubes between the two hollow cores for realizing ultrawide bandwidth in DHC-ARF. To achieve single-mode performance, the high-order modes are coupled with the cladding modes by optimizing the diameter of outer tubes and the inner tubes. The calculation results show that an 11.0 cm long DHC-ARF can be used to develop a PBS with an operating bandwidth of 410 nm, where the polarization extinction ratio is lower than −20 dB. The high-order mode extinction ratio is 625.41, and the loss of fundamental mode is below 1.018 dB/m.

Highly birefringent polarization maintaining low-loss single-mode hollow-core antiresonant fiber

In this paper, a highly birefringent polarization maintaining low losses and a single mode antiresonant hollow core fiber is proposed and analyzed, that is able to exhibit better performances compared to the recent related structures. The usage of bi-thickness cladding tubes with additional high refractive index layers on our geometrically optimized structure improves birefringence nearly by one order: the highest birefringence is 4.7 × 10−4 at 1.51 µm and sustains &gt; 1 × 10−4 for a wide bandwidth of 100 nm with a larger core diameter of 26 µm. Elliptical nesting on our proposed structure lowers the confinement loss to 0.007 dB/m at 1.51 µm and maintains a loss of &lt; 1 dB/m for a wide range of 210 nm. A polarization extinction ratio of 300 and higher order mode extinction ratio of 63, for our fiber, ensure a single polarization and single mode operation at 1.51 µm. Moreover, the proposed fiber exhibits a bend robust performance with a very low bend loss of 0.009 dB/m at a small bend radius of 6 cm and sustains a bend loss of &lt; 0.01 dB/m from a bend radius of 4 cm and above. Hence, our presented fiber, containing the above excellent characteristics, may be fruitful for designing polarization-controlled devices (fiber optic sensors, fiber optic amplifiers, fiber optic gyroscope, etc.) in the field of optical communication.

Design and construction of passively pulse compressor using PM–Mach–Zehnder interferometers

Abstract In line fiber Mach–Zehnder inferometer (MZI) pulse compression was designed three different lengths of single mode-polarization maintaining fiber with (8, 16, 24) cm after splicing them between two single mode fibers (SMF-28e) with (23 and 13) cm and applying different weights on splicing region and the cross sectional area of SM-PM fiber, the designed performance of the in line fiber compressor system was studies in terms of compressor factor. Two minima pulse compression factor were obtained, one is 1.13 with FWHM 251.584 pm, centered wavelength 1547.394 nm, 52 cm interferometer length and 5 g was applied on the micro-cavity splicing region, and the second is equal 1.10 with FWHM 259.730 pm, centered wavelength 1547.120 pm and, 68 cm interferometer length and 10 g was applied on the cross sectional area of the second PMFs, in the case of single and cascaded interferometers, respectively. The input of the all interferometers was pulsed laser source with peak power 1.2297 mW, 286 pm spatial FWHM, 10 ns temporal FWHM, 3 kHz repetition rate and centered at 1546.7 nm.

Design and analysis of Micro-channelled Quasi D-shape optical Fiber plasmonic Sensor

This study reports on numerical investigation carried out over a newly designed open micro-channel incorporated, side polished single mode fiber (SMF) based plasmonic sensor. The proposed sensor operates on the principle of surface plasmon resonance (SPR) phenomenon to enhance the sensing performance. The commercially available COMSOL Multiphysics software tool is used to design sensor and finite element method (FEM) is used for numerical investigation. From the detail study, an average sensitivity of 1757 nm/RIU (refractive index unit) is obtained with a nanoscale gold strip for wide range of analyte RIs from 1.33 to 1.38. Result indicates that the fabricated sensor can be effectively used in RI measurement of the various fields involving chemical and biological sensing.

Research on novel single-mode polarization maintaining photonic crystal fiber

Abstract A PCF (photonic crystal fiber) with high birefringence and single-mode polarization retention over a wide wavelength range is designed and studied. The birefringence and polarization retention characteristics of the PCF base mode were studied using FVFEM (full vector finite element method) and APML (anisotropic perfect matching layer) as boundary conditions. The simulation results show that by rotating the elliptical air hole parallel to the horizontal axis by 45°, and then rotating the elliptical air hole parallel to the longitudinal axis by 45°, the birefringence of the PCF obtained is as high as 4.7 × 10−2, and it has good single model ability, which can be used for various optical devices.

Angled Flip-Chip Integration of VCSELs on Silicon Photonic Integrated Circuits

An investigation of angled flip-chip integration of a singlemode 850 nm vertical-cavity surface-emitting laser (VCSEL) on a silicon nitride photonic integrated circuit (PIC) is presented. Using numerical FDTD simulations, we consider the conditions under which the VCSEL can be integrated at an angle over a grating coupler with high coupling efficiency and low optical feedback. With both coupling efficiency and feedback decreasing with increasing angle, there is a trade-off. With co-directional coupling, first-order diffraction loss sets in at a critical angle, which further reduces the coupling efficiency. No such critical angle exists for contra-directional coupling. We also experimentally demonstrate angled flip-chip integration of GaAs-based 850 nm single transverse and polarization mode VCSELs over grating couplers on a silicon-nitride PIC. At the output grating coupler, light is either collected by an optical fiber or converted to a photocurrent using a flip-chip integrated GaAs-based photodetector. The latter forms an on-PIC optical link. We measured an insertion loss of 21.9, 17.6 and 20.1 dB with a singlemode fiber, multimode fiber and photodetector over the output grating coupler, respectively.

Underwater gradient metalens for broadband subwavelength focusing

Broadband effectiveness and impedance mismatching in fluid-structure coupling remain significant obstacles in the pursuit of broadband high-efficient high-symmetrical subwavelength underwater acoustic devices by using metamaterials. Here, we systematically propose a microstructure-macrostructure-functionality integrated design of underwater gradient metalens, which facilitates the realization of broadband, high-efficient, high-gain, and high-symmetry acoustic focusing. To improve the focusing capabilities of the metalens, an optimization approach of gradient index profile is presented. The square-latticed mode metamaterial is proven to support perfect single polarization characteristic and high customizability of the effective properties. The single polarization mode and optimized index contribute the metalens to presenting an excellent acoustic high-efficient subwavelength focus behavior. The sound pressure field shows that the meta-device can convert plane waves to subwavelength focusing with FWHM ≤ 0.5λ over an ultra-wide frequency range of 5∼33 kHz, even FWHM ≤ 0.4λ of 10∼24 kHz. The metalens can amplify sound intensity over 6 times at focal spots within 10∼22 kHz, when the efficiency is above 80% in 6∼20 kHz. Meanwhile, environmental adaptability evaluation reveals good hydrostatic pressure resistance (∼1.5 MPa) of lightweight porous underwater metalens. The present design strategy and the realized high-performance underwater metalens have application potential in the fields of acoustic transmission, harvesting, and communications.

Broadband low loss single-polarization single-mode hollow-core antiresonant fiber with hybrid cladding

A hollow-core antiresonant fiber (HC-ARF) using nested hybrid silica/silicon cladding is proposed for single-polarization single-mode (SPSM) and broadband. The HC-ARF design consists of four cladding tubes with nested tubes, and a cladding tube with an inner surface coated with silicon. Single-polarization guidance is realized by adjusting the thickness of the silicon layer to control the coupling between the y-polarization and cladding mode, and by optimizing the diameter of the nested tube, the high-order modes (HOMs) can be significantly suppressed. The simulation results show that the performance of SPSM can be improved by selecting appropriate structural parameters. The polarization extinction ratio (PER) is up to 139,804 and the y-polarization loss is 133 dB / m, the x-polarization loss is as low as 0.00095 dB / m at 1550 nm. Moreover, high-order mode extinction ratio (HOMER) between the HOMs and x-polarization, as high as 40,360, is obtained in proposed fiber with HOMs loss of 32.38 dB / m. Particularly, the proposed fiber also has a bandwidth of 230 nm (1450 to 1680 nm) with x-polarization mode loss <1 and 0.08 dB / m bending loss when the fiber is bent in the y-direction at a bending radius of 5 cm. The proposed fiber has potential applications in short-distance, polarization-sensitive fiber systems.

Operation of a fiber-coupled laser-cooler down to cryogenic temperatures.

We report on the optical cooling of a 7.5%Yb:LiYF4 crystal down to 125 K in a multi-pass Herriott absorption cell, coupled via a single mode polarization maintaining optical fiber to the laser source. This configuration, never exploited before, is more practical for potential applications, in particular for spaceborne cryogenics setups. Moreover, the temperature reached is exactly the one needed in many setup embarked in small and medium satellites. We evaluate the heat load on the crystal at the minimum attainable temperature, which is comparable to state of the art systems.

Design, fabrication, and characterization of a single-polarization single-mode flexible hollow waveguide for low loss millimeter wave propagation.

A flexible metallic waveguide with elliptical core that achieves single-polarization single-mode (SPSM) propagation at millimeter wave was designed, fabricated, and characterized. In order to achieve SPSM propagation, optimization of the lengths of major/minor axes of elliptical core was conducted to cut off one of the two orthogonally polarized fundamental modes and all high-order modes. A one-meter long hollow elliptical waveguide (HEW) with major/minor axis length of 1.5/2.7 mm was fabricated. The substrate tube was a flexible elliptical polycarbonate (PC) tube, which was fabricated through glass-draw technique. Silver film was then coated on the inner surface of the tube. Simulation results show that the 1.5/2.7 mm HEW maintains SPSM propagation in the frequency band from 66.5 to 114 GHz. The SPSM operation was experimentally discussed in detail at 100 GHz. The measured loss of 2.58 dB/m and the output polarization ratio of 99.9% was obtained after propagating one meter. Furthermore, the waveguide was robust to bending and twisting. The additional loss was as small as 0.2 dB/m even when the waveguide was coiled into a circle. The potential application of HEWs as polarizers was demonstrated by using a 10 cm long waveguide for polarization detection and extinction ratio of 22.3 dB was achieved at 100 GHz.

Simulation of Single-Mode Waveguides of Gallium Nitride/ Aluminum Nitride (GaN/AlN) on Sapphire by using Finite Difference Mode (FDM) solver

This paper presents a model of the optical waveguide of GaN/ AlN on a sapphire based on the different refractive index (n) between the wave's guideline regions and surrounding medium (cladding). The model analysis is done by using finite-difference mode (FDM) solver simulation is performed by FDTD (finite-difference-time-domain). In the infrared area, this study reveals a fully unique and rigorous modal analysis waveguide. The investigation includes both primary and single-mode polarization; the waveguide is reliant on the refractive index of the layers, thickness, and substrate type. The primary novelty here for the micro-waveguide single-mode is to realize optical characteristics such as attenuation, amplitude, and full width half maximum (FWHM),which has not been done previously for specific thickness (given thickness) and for that geometrical design. Despite we investigated how Optical waveguides are structures that confine and direct optical signals in a region of a higher effective index than its surrounding media. Our experiment (simulation) aims to investigate the single-mode waveguide of Gallium Nitride/ Aluminum Nitride GaN/ AlN on sapphire of a specified thickness in order to obtain infrared waveguide mode with minimum attenuation. Attenuation refers to any decrease in the propagated signal power that does not affect its waveform while the input wavelength is1.55μm. Additionally describe the characterization of the mode, in keeping with our modal analysis. The waveguides have many applications in various fields such as Optical fiber communication and Photonic integrated circuits.