High-performance Polarization Beam Splitter Research Articles

Ultra-compact, broadband polarization beam splitter based on x-cut lithium-niobate-on-insulator platform using hybrid plasmonic waveguide

We propose an ultra-compact, high-performance polarization beam splitter (PBS) on the x-cut lithium-niobate-on-insulator (LNOI) platform. The device based on asymmetrical directional coupler (ADC) consists of a single-mode waveguide (SMW) and a hybrid plasmonic waveguide (HPW). Whole length of the device is only 47 μm, which is the shortest PBS on the x-cut LNOI platform due to polarization-dependent characteristic of plasmonics. When choosing proper width of coupling waveguides (WGs), the phase-matching condition can be satisfied in TE polarization while phase-mismatching exists in TM polarization at the same time. Simulation result shows that bandwidth of the device can achieve at least 200 nm with −10 dB extinction for TE polarization and at least 200 nm with less than −20 dB extinction for TM polarization, which successfully covers entire C-band and L-band. Additionally, the device exhibits large fabrication tolerance and easily fabricated characteristic.

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.

Simulation of a High-Performance Polarization Beam Splitter Assisted by Two-Dimensional Metamaterials.

It is challenging to simultaneously consider device dimension, polarization extinction ratio (PER), insertion loss (IL), and operable bandwidth (BW) to design a polarization beam splitter (PBS) that is extensively used in photonic integrated circuits. The function of a PBS is to separate polarizations of light, doubling the transmission bandwidth in optical communication systems. In this work, we report a high-performance PBS comprising two-dimensional subwavelength grating metamaterials (2D SWGMs) between slot waveguides. The 2D SWGMs exhibited biaxial permittivity by tailoring the material anisotropy. The proposed PBS showed PERs of 26.8 and 26.4 dB for TE and TM modes, respectively, and ILs of ~0.25 dB for both modes, with an unprecedented small footprint of 1.35 μm × 2.75 μm working at the wavelength λ = 1550 nm. Moreover, the present structure attained satisfactory PERs of >20 dB and ILs of <0.5 dB within an ultrabroad BW of 200 nm.

Ultrawide bandwidth dual sakura hollow-core antiresonant fiber polarization beam splitter

A dual sakura hollow-core antiresonant fiber (DSHC-ARF) is proposed for developing an ultrawide-bandwidth polarization beam splitter (PBS). An air gap is introduced into the fiber between dual sakura hollow cores acting as a mode-coupling channel, which determines the implementation of a DSHC-ARF-based PBS. We demonstrate the wavelength dependence of coupling length can be reduced by introducing nested tubes and investigate their impact on single-mode operation further. Through optimizing the fiber, a high-performance PBS based on a 4.42 cm long DSHC-ARF can be obtained with an ultrawide bandwidth of 460 nm ranging from 1400 to 1860 nm, good single-mode operation with a higher-order mode extinction ratio above 100, and a low fundamental mode loss below 0.543 dB.

Broadband and compact polarization beam splitter in LNOI hetero-anisotropic metamaterials.

In this paper, theoretical modeling and numerical simulations of a high-performance polarization beam splitter (PBS) based on hetero-anisotropic metamaterials are proposed on the lithium-niobate-on-insulator (LNOI) platform. The hetero-anisotropic metamaterials constructed by sub-wavelength gratings (SWGs) can be regarded as effective anisotropy medium, which exhibits strong birefringence without breaking the geometrical symmetry, contributing to the formation of PBS. Rather than the principle of PBS based on beat-length difference of transverse electric (TE) polarization and transverse magnetic (TM) polarization, the device can realize polarization beam splitting in single beat length, and the footprint of the proposed PBS can be reduced to 8 µm × 160 µm (with S-bend). The simulation results show that the bandwidth is 185 nm (1450∼1634 nm) for TE polarization while the bandwidth is 85 nm (1490∼1575 nm) for TM polarization when the polarization extinction ratio is >20 dB. Furthermore, the insertion loss is less than 1 dB in the range of 1450 to 1650 nm, for both TE and TM polarization. Additionally, the proposed device proves strong robustness of the fabrication tolerance.

Narrow-linewidth high-efficiency single-frequency ytterbium-doped fiber laser with highly linear polarization at 1064 nm.

We present a linearly polarized single-longitudinal-mode (SLM) ytterbium-doped fiber laser with a polarization extinction ratio (PER) of over 35 dB and a narrow linewidth of less than 4.5 kHz. The very high PER is obtained by utilizing the polarization evolution effect at the optical fiber and the high-performance polarizing beam splitter. The SLM is achieved by using a segment of polarization-maintaining ytterbium-doped fiber as a narrowband filter. In addition, a high optical signal-to-noise ratio of 50 dB and a good slope efficiency of 60.5% are achieved. Using an ytterbium-doped fiber amplifier, a linearly polarized SLM laser system with a high power of over 2.5 W is demonstrated at 1064 nm.

Femtosecond Laser Inscribed Novel Polarization Beam Splitters Based on Tailored Waveguide Configurations

We report on a novel waveguide-based polarization beam splitter (PBS) fabricated by femtosecond (fs) laser in lithium niobate (LiNbO3) crystals. This monolithic PBS is composed of tailored waveguide configurations with different guiding properties in which linearly polarized light along extraordinary refractive index ( ne ) and ordinary index ( no ) can be well separated. At the wavelength of 1064 nm, polarization extinction ratio (PER) can reach to 16.60 dB and 16.18 dB for ne and no polarizations, with insertion loss (IL) of 3.86 dB and 4.15 dB respectively. Our work may pave a new way for designing high-performance PBS and creating compact polarization conversion systems in integrated photonics and quantum photonics.

Compact high-performance polarization beam splitter based on a silicon photonic crystal heterojunction

A novel polarization beam splitter based on a silicon photonic crystal (PC) heterostructure operating in the optical-telecommunications band is envisaged and is configured for planar integration with other PC or waveguide structures. The small 9μm×9.4μm footprint polarization beam splitter is investigated by the plane-wave expansion and finite-difference time-domain methods. Due to the combined effects of self-collimation and the photonic band gap, self-collimation transmission and 90° beam splitting for the two orthogonal polarizations are achieved. The transmissivity exceeds 60% (78%) for TE (TM) polarization covering a 115-nm bandwidth, and it is also observed that the polarization extinction ratios of the device are higher than 13 and 31 dB, respectively. Moreover, at the wavelength of 1550 nm, TE (TM) polarization has high transmissivity 94.9% (88%) with high polarization extinction ratio of 17 dB (41 dB). A compact and efficient polarization beam splitter is successfully designed for applications in optical communications.

Ultra-compact and high-performance polarization beam splitter assisted by slotted waveguide subwavelength gratings

We propose an ultra-short polarization beam splitter (PBS) consisting of two slot waveguides assisted by slotted waveguide subwavelength gratings (SWSWGs), located between the two slotted waveguides. By controlling the optical momentum of evanescent waves with the anisotropic characteristics of the SWSWGs, we considerably suppress and enhance the couplings of transverse-electric (TE) and transverse-magnetic (TM) modes, respectively, concurrently improving performances and reducing length of the proposed PBS, compared with conventional slotted waveguide couplers (CSWCs). Exceptionally, a transition point is found to show almost zero crosstalk between waveguides for the TE mode, i.e., infinite coupling length. Differing from conventional single-material SWGs, the SWSWGs not only simplify the fabrication process but improve polarization extinction ratio (PER). Numerical results demonstrate the improvement in PERTM (PERTE) from approximately 13 (23) dB for the CSWCs to 26 (24) dB for the present structure, with a > 70% reduction in device length, operating at the wavelength of λ = 1,550 nm. Our design achieves performance of PERTM > 25 dB and PERTE > 20 dB, and insertion loss (IL) < 0.05 dB for TE and < 0.3 dB for TM modes within a bandwidth width (BW) of ~ 50 nm from λ = 1,530 to 1,580 nm. Additionally, geometry deviation is also investigated to assess experimental tolerance. The present idea provides an approach for improving PER, device length, and operating BW of PBSs composed of various waveguide couplers.

Numerical design of a high-performance polarization beam splitter assisted by composite subwavelength gratings.

We report a compact polarization beam splitter (PBS) consisting of slotted waveguides assisted by composite subwavelength gratings (CSWGs) on a silicon-on-insulator platform. By tailoring the material anisotropy of the CSWGs, coupling strengths of transverse-electric (TE) and transverse-magnetic (TM) polarization coupling strengths are respectively suppressed and enhanced significantly, achieving concurrent improvements in polarization extinction ratio (PER), device footprint, and working bandwidth (BW) compared with purely slotted waveguides. Differing in construction from mono-material SWGs, the CSWGs comprise silicon strips covered with a silicon dioxide (SiO2) layer of the same thickness as the slot layer of the slotted waveguides, simplifying the fabrication process and further reducing device length. Numerical simulations show significant improvement in PERTM from about 15 dB for the purely slotted waveguides to 28 dB for the proposed design, with a 40% reduction in device length at a wavelength of λ = 1550 nm. Within a BW of ∼60 nm, the proposed PBS achieves PERTM ∼25 dB, PERTE >15 dB, and insertion loss (ILs) <0.1 dB for TE and TM modes. Fabrication tolerance investigations are also described and discussed. The proposed idea paves the way for simultaneous improvements in PER, footprint, and working BW for PBSs comprising a variety of coupled-waveguide systems.

High Performance Polarization Beam Splitter Based on Cascaded Directional Couplers Assisted by Effectively Anisotropic Structures

A high performance polarization beam splitter (PBS) based on cascaded directional couplers (DCs) assisted by effectively anisotropic structures is proposed. The sub-wavelength grating (SWG) structures between the two coupled waveguides act as anisotropic metamaterial cladding to block/enhance light coupling for transverse electric (TE)/magnetic (TM) polarization. Cascading the DCs designed at different central wavelengths can improve the extinction ratio (ER) within the desired bandwidth or broaden the working wavelength bandwidth for TM polarization. Three design examples show the excellent performance of PBS with ER of >35 dB, 20 dB or 14 dB and loss of 20dB of the PBS based on the cascaded DCs increases by ∼11 times when compared with a single DC.

An ultra-broadband polarizing beam splitter/coupler using asymmetric-waveguides

A high-performance polarizing beam splitter (PBS) is demonstrated by using asymmetrical directional couplers on a 220nm-thick silicon-on-insulator (SOI) photonics platform. The extinction ratio of the PBS with cascaded directional couplers is > 35 dB for both TE and TM polarizations around the central wavelength of 1550 nm. The bandwidths for an extinction ratio of 20 dB and 30 dB are 275 nm and 230 nm, respectively, for TE polarization, as well as > 300 nm and 225 nm, respectively, for TM polarization. The insertion losses for TE polarization are < 0.5 dB with a bandwidth of > 300 nm. The insertion losses for TM polarization are < 1 dB and < 0.5 dB with a bandwidth of 218 nm and 174 nm, respectively.

Compact polarization beam splitter with a high extinction ratio over S + C + L band.

In this paper, we experimentally demonstrate an ultra-broadband high-performance polarization beam splitter (PBS) based on silicon-on-insulator (SOI) platform. The proposed device is based on a directional coupler consisting of a 70-nm taper-etched waveguide and a slot waveguide with a compact coupling length of 11 microns, the structure of which is suitable for a commercial two-step fabrication process. Benefiting from the preferences of coupling TM mode to slot waveguide and restricting TE mode in taper-etched waveguide, the polarization extinction ratios (PER) for TE and TM polarizations can reach as high as 30 dB and 40 dB at 1550 nm based on experimental results, respectively; besides, an ultra-wide operation bandwidth with PER >20 dB is achieved as ~175 nm from 1450 nm to 1625 nm (covering S, C and L bands), or the bandwidth with PER >25 dB is over ~120 nm from 1462 nm to 1582 nm, which is the largest operation bandwidth to the best of our knowledge. At last, the insertion losses (IL) are -0.17 dB and -0.22 dB for TE and TM polarizations at 1550 nm, respectively.

High-performance polarization beam splitter based on anisotropic plasmonic nanostructures

We propose an alternative design of efficient and compact polarization beam splitters for wide-angle and polarization-sensitive incidence of electromagnetic waves at near-infrared frequencies. The designed system is constructed by depositing periodic metallic strips on top and bottom of a continuous metal film. Based on the optimization of structure parameters, the whole system can suppress transmission (~ 0%) for one polarization and enhance transmission for another polarization (~ 95%). This phenomenon of anisotropic transmission can be attributed to different performances of impedance along different polarization directions. This device may find applications in optical components and polarization filter.

Ultra-broadband high-performance polarizing beam splitter on silicon.

A high-performance silicon-based polarizing beam splitter (PBS) is proposed and demonstrated experimentally by using an improved structure with cascaded bent directional couplers. The measured extinction ratio (ER) is >35dB and the excess losses (EL) is <0.35dB around the central wavelength for both polarizations. The present PBS has a compact footprint of ~6.9 × 20μm2. The measured bandwidths for an ER of >20dB, >25dB and >30dB are ~135nm, ~95nm and ~70nm, respectively, while the measured EL is <1dB and <0.5dB in a bandwidth of ~140nm and ~85nm, respectively. The fabrication tolerance of the core-width variation is as large as ± 40nm, which makes the fabrication very easy.

High-Performance Polarizing Beam Splitters Based on Cascaded Bent Directional Couplers

A fabrication-tolerant high-performance polarizing beam splitter (PBS) is proposed and demonstrated with silicon-on-insulator nanowire waveguides. This PBS is realized with cascaded bent direction couplers, which is designed to make the phase-matching condition satisfied for the transverse-magnetic (TM) polarization mode. There is significant phase-mismatch for the transverse-electric (TE) polarization mode. As a result, TM-polarization mode is cross coupled efficiently to the cross port, while TE-polarization mode outputs from the through port with a low loss. The present PBS has a footprint of as small as $\sim 4\times 15\,\,\mu \text{m}^{2}$ . The extinction ratio at the center wavelength is 32.6 and 36.8 dB for TE and TM polarizations, respectively. The bandwidth for achieving a >25-dB extinction ratio is ~32nm, and the excess loss is <0.9 dB for both polarizations. The fabrication tolerance is as large as ±50 nm for the waveguide core width.

Design of ultra-short polarization beam splitter based on liquid-filled photonic crystal fiber

A high performance polarization beam splitter is designed. It is based on a liquid-filled dual-core photonic crystal fiber (DC-PCF), and possesses ultra-short-length and simple structure. We have researched the effects of DC-PCF structure parameters on performances of the splitter by finite element method. The results show that the extinction ratio of the \(92\,\upmu \hbox {m}\)-long splitter can reach \(-53.2\) dB at the communication wavelength of \(1.55\,\upmu \hbox {m}\). Furthermore, the extinction ratio of the \(139\,\upmu \hbox {m}\)-long splitter can reach \(-57.1\) dB at the communication wavelength of \(1.31\,\upmu \hbox {m}\). The bandwidths of extinction ratio better than \(-20\) dB are about 30 and 20 nm at wavelength of 1.55 and \(1.31\,\upmu \hbox {m}\), respectively.

Comparative Research on Different Solutions of a High-Performance Thin-Film Polarizing Beam Splitter

In the process of fabricating an ultra-high precision thin-film polarizing beam splitter (PBS), which is the key element in a new kind of Y-shaped cavity dual-frequency laser, low production yield is a serious problem. Based on the robust design method by controlling sensitivity of optical films to production errors, response characteristics to production errors of different kinds of PBSs are comparatively studied. By experimental study of robust design, essential determinant of sensitivity of PBSs to production errors is found to be the physical requirement that the propagation angle should be larger than the critical angle of total reflection of the interface between the substrate and outer space. By fulfilling the physical requirement, optimum incidence angle has been found by repeated robust design on different incidence angles, and a high-performance thin-film PBS with low sensitivity to production errors has been designed. The coating structure of the obtained PBS is simple and it is easy to be batch manufactured, which will make a positive impact on fabrication, engineering and application of the new Y-shaped cavity dual-frequency laser.