Compact Polarization Beam Splitter Research Articles

3D Printing of Glass Micro-Optics with Subwavelength Features on Optical Fiber Tips.

Integration of functional materials and structures on the tips of optical fibers has enabled various applications in micro-optics, such as sensing, imaging, and optical trapping. Direct laser writing is a 3D printing technology that holds promise for fabricating advanced micro-optical structures on fiber tips. To date, material selection has been limited to organic polymer-based photoresists because existing methods for 3D direct laser writing of inorganic materials involve high-temperature processing that is not compatible with optical fibers. However, organic polymers do not feature stability and transparency comparable to those of inorganic glasses. Herein, we demonstrate 3D direct laser writing of inorganic glass with a subwavelength resolution on optical fiber tips. We show two distinct printing modes that enable the printing of solid silica glass structures ("Uniform Mode") and self-organized subwavelength gratings ("Nanograting Mode"), respectively. We illustrate the utility of our approach by printing two functional devices: (1) a refractive index sensor that can measure the indices of binary mixtures of acetone and methanol at near-infrared wavelengths and (2) a compact polarization beam splitter for polarization control and beam steering in an all-in-fiber system. By combining the superior material properties of glass with the plug-and-play nature of optical fibers, this approach enables promising applications in fields such as fiber sensing, optical microelectromechanical systems (MEMS), and quantum photonics.

Compact polarization beam splitter based on metal-capped thin-film LiNbO3-on-insulator plasmonic waveguide

A compact polarization beam splitter based on a triple-waveguide plasmonic directional coupler is proposed and modeled. The directional coupler consists of two usual lithium-niobate-on-insulator (LNOI) ridge waveguides and a metal-capped plasmonic LNOI waveguide located between them. It utilizes stronger polarization dependence of modal birefringence of a plasmonic waveguide. By appropriately designing the plasmonic waveguide geometry, the TM component wave meets the resonant coupling condition and outputs at cross port. Instead, the TE component wave does not meet the resonant coupling condition, cannot be resonant in the triple-waveguide directional coupler and outputs at through port directly. Excellent performance is expected for an optimal device. First, the device shows an ultra-high polarization extinction ratio(PER) of 28.3 dB and an ultra-low insertion loss(IL) of 0.06 dB for the TE-polarized wave, and of 31.7 dB and of 0.31 dB in order for the TM-polarized wave. Second, the working bandwidth with PER > 25 dB and IL < 0.08 dB is 100 nm (1500–1600 nm) for the TE-polarized wave, and that with PER > 20 dB and IL < 0.4 dB is 30 nm (1534–1564 nm) for the TM-polarized wave. Third, the device has a compact structure of 33 μm in length and exhibits definite fabrication tolerance. Overall, the proposed device exhibits ultra-high PER and ultra-low IL, and has a compact size suitable for on-chip use. A comparison shows that present device exhibits advantage in IL and/or size over that based on other LNOI structures or the SOI platform.

Design and analysis of a compact and broadband polarization beam splitter on silicon nitride on silicon-on-insulator multilayer platform using a partially overlapped vertical asymmetrical directional coupler

Design and analysis of a compact and broadband polarization beam splitter on silicon nitride on silicon-on-insulator multilayer platform using a partially overlapped vertical asymmetrical directional coupler

Numerical analysis of a compact all-fiber polarization beam splitter based on dual-core photonic crystal fiber with As2S3 thin layer

Modern-day optical systems are evolving towards miniaturization and integration, leading to higher performance demands for polarizing beam splitters (PBSs). A simple-structure and high-performance PBS based on dual-core photonic crystal fiber (DC-PCF) with As2S3 layer is proposed. The finite element method (FEM) and classical coupled-mode theory (CMT) are utilized to investigate the performance of this PBS. Simulation results demonstrate that the proposed PBS can achieve a minimum length of 2.65 mm, a minimum extinction ratio of −64 dB, an operating bandwidth of 420 nm, and a minimum insertion loss of 0.03 dB when the optimal parameters include cladding hole diameter of 1.0 μm, central hole diameter of 2.0 μm, lattice spacing of 2.0 μm, and As2S3 ring layer thickness of 50 nm. Moreover, it also possesses a high birefringence of 3.58 × 10−3 and a negative dispersion of −30 ps/km/nm at 1.55 μm. It is believed that the proposed PBS holds great potential to become a critical device in optical multiplexing technologies.

Compact reconfigurable on-chip polarization beam splitters enabled by phase change material.

In this paper, we present the design of a compact reconfigurable polarization beam splitter (PBS) enabled by ultralow-loss phase-changing Sb2Se3. By harnessing the phase-change-mediated mode coupling in a directional coupler (DC), guided light with different polarizations could be routed into different paths and this routing could be dynamically switched upon the phase change of Sb2Se3. With an optimized DC region, the proposed PBS demonstrates efficient polarization splitting with crosstalk less than -21.3 dB and insertion loss less than 0.16 dB at 1550 nm for both phase states of Sb2Se3, and features energy efficient property benefitting from the nonvolatile phase change of Sb2Se3, which holds great potentials for on-chip applications involving polarization control, including polarization-division multiplexing system, quantum photonics, microwave photonics, etc.

Compact topological polarization beam splitter based on all-dielectric fishnet photonic crystals.

Conventional polarization beam splitters (PBSs) suffer energy loss and signal distortion due to backscattering caused by disturbances. Topological photonic crystals provide backscattering immunity and anti-disturbance robustness transmission owing to the topological edge states. Here, we put forward a kind of dual-polarization air hole-type fishnet valley photonic crystal with a common bandgap (CBG). The Dirac points at the K point formed by different neighboring bands for transverse magnetic and transverse electric polarizations are drawn closer via changing the filling ratio of the scatterer. Then the CBG is constructed by lifting the Dirac cones for dual polarizations within a same frequency range. We further design a topological PBS using the proposed CBG via changing the effective refractive index at the interfaces which guide polarization-dependent edge modes. Based on these tunable edge states, the designed topological PBS (TPBS) achieves efficient polarization separation and is robust against sharp bends and defects, verified by simulation results. The TPBS's footprint is approximately 22.4 × 15.2 μ m 2, allowing high-density on-chip integration. Our work has potential application in photonic integrated circuits and optical communication systems.

Compact and broadband polarization beam splitter on lithium-niobate-on-insulator using a hybrid plasmonic waveguide

A compact and broadband polarization beam splitter (PBS) is proposed based on an asymmetric directional coupler consisting of a hybrid plasmonic waveguide and a ridge waveguide on lithium-niobate-on-insulator. Due to the surface plasma polariton (SPP) effect, the phase-matching condition is satisfied for transverse electric polarization, whereas the transverse magnetic polarization has a significant phase mismatch by choosing reasonable widths of both waveguides. A short ( ∼ 28 μm long) PBS is designed while the gap width is chosen to be 200 nm to make it easy to fabricate. Numerical simulations show that the designed PBS has a broad bandwidth (>130 nm) for an extinction ratio of >15 dB and a large fabrication tolerance for the variation of the waveguide width (over ± 50 nm).

Compact and high-performance polarization beam splitter based on triple-waveguide coupler

Polarization beam splitter (PBS) is a fundamental component of integrated photonics to manipulate wave polarization state, and most PBS devices were designed on the popular SOI. As an alternative, a PBS may be implemented on the basis of thin-film LiNbO3-on-insulator (LNOI), a promising platform for developing various compact or ultra-compact photonic active and passive devices. However, smaller modal birefringence of the LNOI waveguide makes it not easy to implement a PBS of high-performance. Here, we propose a compact, high-performance PBS on the basis of a triple-waveguide coupler consisted of two LNOI ridge waveguides and an amorphous silicon (α-Si) nanostrip assisted waveguide. By making use of the α-Si nanostrip, the PBS works in the case that the TM polarization mode meets the phase matching condition while the TE polarization mode does not. Numerical results show that the PBS is compact with a length of only 31 μm. The device can achieve an ultra-high polarization extinction ratio (>29.4 dB) and an ultra-low insertion loss (<0.066 dB) in the operating wavelength range of 1500–1600 nm for the TE polarization mode, and a polarization extinction ratio of > 20 dB and an insertion loss of < 0.16 dB over a ∼ 60 nm bandwidth from 1527 nm to 1587 nm for the TM polarization mode. Moreover, the device has a larger feature size that facilitates fabrication. Overall, this device has the advantages of compact size, higher polarization extinction ratio, lower insertion loss, and larger feature size, which is suitable for on-chip applications.

Compact and broadband on-chip silicon polarization beam splitter based on tilted subwavelength grating

Efficient polarization management is a key issue for on-chip silicon photonic integrated circuits. Here, we propose a compact and broadband on-chip silicon polarization beam splitter (PBS) using tilted subwavelength grating (SWG) structure. The key polarization separation region consists of an input tapered SWG, a titled SWG, and two output tapered SWGs at both output ports. The tilted SWG has a strong polarization dependence for the mode coupling, and we have introduced different grating duty cycles, positional offset, and a new, to the best of our knowledge, output mode transition structure to enhance the device performance. Based on these techniques, the key coupling length of the proposed PBS is only 5 µm (total length, 12 µm), together with polarization extinction ratio (ER) 21.2 dB (19.7 dB) and insertion loss 0.21 dB (0.39 dB) for the TE (TM) mode. Moreover, the device working bandwidth can be extended to 311 nm (154 nm) by keeping E R &gt; --> 15 d B ( E R &gt; --> 18 d B ), satisfying the on-chip broadband applications. We believe the proposed device could become a good candidate to boost the on-chip polarization management toward compact and broadband directions.

Design and Optimization of a Compact Ultra-Broadband Polarization Beam Splitter for the SCL-Band Based on a Thick Silicon Nitride Platform

The polarization beam splitter is an essential photonic integrated circuit in applications where a high-performing on-chip polarization diversity scheme is required. The lower refractive index contrast of the silicon nitride material platform compared to silicon-on-insulator constitutes the separation of polarized light states a challenging task since for this purpose a large difference between the effective refractive indices of the fundamental TE and TM modes is highly desirable. In this paper, we present the design and optimization analysis of an ultra-broadband polarization beam splitter based on a thick silicon nitride platform through extensive 3D-FDTD simulations. The proposed device exploits two different Si3N4 thicknesses that enable the discrimination of the two polarizations at the proximity of an 800 nm thick slot and a 470 nm thick strip waveguide via directional coupling. The proposed two-stage PBS achieves higher than 30.6 dB polarization extinction ratio (PER) for both TE and TM polarizations across a 130 nm span at the SCL-band. The dimensions of the PBS are 94 × 14 μm2 and the insertion losses are calculated to be lower than 0.8 dB for both polarizations. The fabrication tolerance of the device is also discussed.

Design of broadband and compact mid-infrared polarization beam splitter based on all-circular air holes with low loss

A mid-infrared (mid-IR) broadband polarization beam splitter (PBS) based on a gallium sulfide dual core highly birefringent photonic crystal fiber is proposed. The high birefringence and dual core are achieved by introducing two kinds of circular air holes with different diameters into the fiber core. The mode coupling characteristics of the even and odd modes in the proposed dual core PBS are investigated using the finite-difference time-domain method and coupled-mode theory. The numerical simulation results indicate that, when the incident light frequency is 4.5 μm and the PBS length is 277.1 μm, a wide bandwidth of 170 nm (from 4.472 to 6.642 μm) with a polarization extinction ratio (ER) >20 dB is obtained in the mid-IR waveband. The highest ER of 112.8 dB is realized. The designed PBS will find potential applications in mid-IR optical sensing, communication, and imaging systems because of its wide bandwidth and ultrashort length.

Design of Compact Polarization Beam Splitter Based on Triple-waveguide Directional Coupler

Design of Compact Polarization Beam Splitter Based on Triple-waveguide Directional Coupler

Compact low-birefringence polarization beam splitter using vertical-dual-slot waveguides in silicon carbide integrated platforms

The polarization beam splitter is a key component for polarization manipulation in photonic integrated circuits, but it is challenging to design for low-refractive-index optical materials, due to the low birefringence of the waveguides. We propose what we believe is a novel compact vertical-dual-slot waveguide-based coupling scheme for silicon carbide, enabling efficient low-birefringence polarization splitting by extensively modulating the transverse-magnetic mode distribution. We numerically and experimentally demonstrate the device in the 4H-silicon-carbide-on-insulator integrated platform, with a small footprint of 2 . 2 μm × 15 μm . The device, easy to fabricate via a single lithography process as other components on the chip, exhibits low insertion loss of &lt; 0.71 dB and &lt; 0.51 dB for the transverse-electric and transverse-magnetic polarized light, respectively, and polarization extinction ratio of &gt; 13 dB , over 80 nm wavelength range.

Compact and broadband silicon-based polarization beam splitter using asymmetric directional couplers embedded with subwavelength gratings and slots.

A compact and broadband silicon-based polarization beam splitter (PBS) is proposed and investigated in detail, where the two arms of the directional coupler (DC) are, respectively, embedded with subwavelength gratings (SWGs) and vertical slots so that field distributions for the TE mode are significantly changed, effectively weakening coupling strength, whereas those for the TM mode are almost unaffected, nearly analogous to the DC with strip waveguides. By carefully optimizing structural parameters, efficient coupling will emerge between the two waveguides for the TM mode, while TE mode will be confined in the SWG-assisted strip waveguide. Consequently, the two modes can be effectively separated, and thus the realization of a PBS is accomplished. Results show that a compact PBS with a coupling length of 6.45 µm is achieved, together with the extinction ratio (ER) of 27.54/31.88 dB, the insertion loss of 0.12/0.14 dB, and the reflection loss of -43.67/-30.50dB, respectively, for TE/TM mode at the wavelength of 1.55 µm. The bandwidth, for both modes, is up to 230/100 nm when ER is larger than 15/20 dB. In addition, fabrication tolerances to the critical structural parameters and field evolution through the proposed device are analyzed.

Compact Photonic Crystal Polarization Beam Splitter Based on the Self-Collimation Effect

We propose a new compact polarization beam splitter based on the self-collimation effect of two-dimensional photonic crystals and photonic bandgap characteristics. The device is composed of a rectangular air holes-based polarization beam splitting structure and circular air holes-based self-collimating structure. By inserting the polarization beam splitting structure into the self-collimating structure, the TE and TM polarized lights are orthogonally separated at their junction. When the number of rows in the hypotenuse of the inserted rectangular holes is 5, the transmittance of TE polarized light at 1550 nm is 95.4% and the corresponding polarization extinction ratio is 23 dB; on the other hand, the transmittance of TM polarized light is 88.5% and the corresponding polarization extinction ratio is 37 dB. For TE and TM polarized lights covering a 100 nm bandwidth, the TE and TM polarization extinction ratios are higher than 18 dB and 30 dB, respectively. Compared with the previous polarization beam splitters, our structure is simple, the size is small, and the extinction ratio is high, which meets the needs of modern optical communications, optical interconnection, and optical integrated systems.

Ultra-high extinction ratio polarization beam splitter with extreme skin-depth waveguide.

In this Letter, we present a high extinction ratio and compact on-chip polarization beam splitter (PBS), based on an extreme skin-depth (eskid) waveguide. Subwavelength-scale gratings form an effectively anisotropic metamaterial cladding and introduce a large birefringence. The anisotropic dielectric perturbation of the metamaterial cladding suppresses the TE polarization extinction via exceptional coupling, while the large birefringence efficiently cross-couples the TM mode, thus reducing the coupling length. We demonstrated the eskid-PBS on a silicon-on-insulator platform and achieved an ultra-high extinction ratio PBS (${\approx} 60\;{\rm dB} $ for TE and ${\approx} 48\;{\rm dB} $ for TM) with a compact coupling length (${\approx} 14.5\,\,\unicode{x00B5}{\rm m}$). The insertion loss is also negligible (${\lt}{0.6}\;{\rm dB}$). The bandwidth is ${\gt}{80}$ (30) nm for the TE (TM) extinction ratio ${\gt}{20}\;{\rm dB}$. Our ultra-high extinction ratio PBS is crucial in implementing efficient polarization diversity circuits, especially where a high degree of polarization distinguishability is necessary, such as photonic quantum information processing.

Direct-binary-search-optimized compact silicon-based polarization beam splitter using a pixelated directional coupler

In this paper, a polarization beam splitter using a pixelated directional coupler is proposed, designed, and experimentally demonstrated on silicon-on-insulator platform. According to the phase matching, structural parameters for the coupling region consisting of a straight waveguide and a pixelated waveguide are carefully selected by using direct-binary-search optimization algorithm and the finite difference time domain method, and thus the input fundamental transverse-magnetic and transverse-electric modes can be effectively separated from each other in an ultra-compact coupling length. The coupling length of our designed device is only 6 μm. Experimental results reveal that, the measured polarization extinction ratio is greater than 14.22 dB and the corresponding insertion loss is smaller than 1.36 dB within a bandwidth from 1527 to 1580 nm for the fabricated device operating in transverse-electric polarization, while the measured polarization extinction ratio and insertion loss are respectively larger than 14.47 dB and lower than 1.53 dB from 1527 to 1580 nm for the fabricated device operating in transverse-magnetic polarization.

Compact, Broadband and Low-Loss Polarization Beam Splitter on Lithium-Niobate-On-Insulator Using a Silicon Nanowire Assisted Waveguide

We propose a compact, broadband, and low-loss polarization beam splitter (PBS) based on an asymmetrical directional coupler on the lithium-niobate-on-insulator platform, consisting of an amorphous silicon (a-Si) assisted waveguide, and a normal waveguide. With proper design of the a-Si nanowire, and lithium niobate waveguides, the phase-matching condition is satisfied for TE polarization, while significant mismatching exists for TM polarization. A 16- $\mu$ m-long PBS (including the s-bend region) with a 200 nm gap is achieved. Numerical simulations show that the PBS exhibits a 140-nm bandwidth for extinction ratios lager than 10 dB. Moreover, the device has an ultra-low insertion loss (IL $\sim$ 0.05 dB), and maintaining ILs $ 0.5 dB over a 170 nm wavelength range.

Silicon-based dual-mode polarization beam splitter for hybrid mode/polarization-division-multiplexed systems

This paper presents a compact dual-mode polarization beam splitter (PBS) based on silicon on insulator platform. The proposed PBS separates two lowest-order transverse magnetic (TM) modes from two lowest-order transverse electric (TE) ones by employing an optimized tapered directional coupler. To the best of our knowledge, this is the first PBS with the ability of separating two sets of modes with different polarizations, simultaneously. Such a component is an essential block in the hybrid mode/polarization-multiplexing systems. The three-dimensional finite-difference time-domain (FDTD) simulation results confirm that the designed PBS has a low loss of 1.6 dB and high extinction ratio of more than 10 dB over a broad wavelength range of 90 nm. Also, the presented PBS tolerates ±15 nm change in the coupling gap, ±30 nm waveguide width deflection, and more than ±100 nm coupling length variation with an insertion loss lower than 1 dB and extinction ratio higher than 10 dB.

High Extinction Ratio Polarization Beam Splitter Realized by Separately Coupling

A novel compact polarization beam splitter (PBS) based on a triple-waveguide directional coupler is presented. Among these three waveguides, the middle one is regarded as an input where the contrast of effective refractive index between fundamental modes is enhanced with dielectric-loaded waveguide. Confined into the waveguides with coupling lengths of $8.3~\mu \text{m}$ (TM) and $9.9~\mu $ m (TE) on both sides, the two fundamental modes are separately coupled. In virtue of the separated coupling structure, a high polarization extinction ratio (PER) of 45.6 dB together with a low insertion loss ( $1.55~\mu \text{m}$ . Furthermore, the operation bandwidth of this PBS, during which the PER is higher than 40 dB, is up to 80 nm for TE mode.