Broadband Polarization Beam Splitter Research Articles

Realization of a Compact Broadband Polarization Beam Splitter Using the Three-Waveguide Coupler

A compact broadband polarization beam splitter is designed and experimentally demonstrated based on a silicon-nitride-assisted three-waveguide coupler. With the help of coving a layer of silicon nitride on the center bridged silicon waveguide, the phase matching is met for the TM mode but not for the TE mode. The final optimized device length is only 7 μm, and the polarization beam splitter has the high extinction ratios of more than 30 dB for the TE mode and that of more than 20 dB for the TM mode in the wavelength ranging from 1.5 μm to 1.6 μm. And the corresponding insertion losses are less than 0.06 dB and 0.35 dB, respectively. The experimental measurement results also show the polarization beam splitter has good performances.

Broadband and compact polarization beam splitter based on an asymmetrical directional coupler with extra optimizing designs.

In this paper, a novel, to the best of our knowledge, polarization beam splitter (PBS) based on an asymmetrical directional coupler (DC) was proposed, which consists of a strip waveguide (WG) and a ${{\rm Si}_3}{{\rm N}_4}$Si3N4 loaded horizontal slot WG. By carefully adjusting the geometric parameters of the DC, the phase match condition between these two WGs can be satisfied for the transverse magnetic (TM) polarization, while the coupling efficiency of the transverse electric (TE) polarization is frustrated due to the large phase mismatch. The extra optimizing designs include adding filters to the output ports as well as introducing the tapered structure into the DC, which is settled by the particle swarm optimizing (PSO) algorithm so that the performance of the proposed PBS is improved over a broadband range. Numerical simulations show that the bandwidths for the extinction ratio (ER) $ \gt {20}\;{\rm dB}$>20dB, 30 dB, and 40 dB are 160 nm, 95 nm, and 50 nm, respectively, with insertion loss (IL) $ \lt {1}\;{\rm dB}$<1dB for the wavelength of 1.49-1.58 µm. The analysis of the deviations demonstrates that the proposed PBS allows high fabrication tolerances.

Broadband Polarization Beam Splitter by Using Cascaded Tapered Bent Directional Couplers

We propose and demonstrate a broadband silicon-based polarization beam splitter (PBS) by using cascaded tapered bent directional couplers (DCs). In our device, the TM-polarized light is efficiently cross coupled to the cross port due to the strong coupling in the DCs, while the TE-polarized light goes through the DC with weak coupling and outputs at the through port. This device can achieve a broad bandwidth performance and support O -, S -, C -, and L -band operations, with acceptable extinction ratios (ERs) and insertion losses (ILs). For both TE and TM polarizations, the simulation results show that ERs are ≥10.1 dB and ILs are ≤1.33 dB in 1280–1600 nm. In the measurement, for the TE polarization, an ER ≥10.94 dB and an IL ≤1.61 dB are obtained in 1280–1360 nm, while an ER ≥11.98 dB and an IL ≤1.39 dB are measured in 1510–1590 nm. For the TM polarization, an ER ≥12.25 dB and an IL ≤2.22 dB are obtained in 1280–1360 nm, while an ER ≥18.93 dB and an IL ≤1.22 dB are measured in 1510–1590 nm.

Omnidirectional polarization beam splitter for white light.

As a key element in optical systems, a broadband and omnidirectional polarization beam splitter has been long desired. Here, based on anisotropic metamaterials, a perfect polarizing beam splitter is theoretically designed for the extremely broad frequency and angle bands without energy loss. When an electromagnetic wave is incident on the beam splitter, the transverse magnetic-polarized component suffers total reflection, while the transverse electric-polarized component is completely transmitted within the incident angle range [-90°, 90°] for the white light. This study provides a new approach to design an efficient polarizing beam splitter and may promote the development and applications of anisotropic metamaterials.

Compact Broadband Polarization Beam Splitter Based on Multimode Interference Coupler With Internal Photonic Crystal for the SOI Platform

We experimentally demonstrate a compact broadband polarization beam splitter (PBS) based on a multimode interference (MMI) coupler with internal photonic crystal (PC) for the silicon-on-insulator platform. The internal PC structure is optimized to be reflective to the transverse electric polarization and transparent to the transverse magnetic polarization over a broad wavelength range. A detailed study of the device operation, including the photonic band gap and the influence of the internal PC structure on each mode of the MMI coupler, is presented. The designed PBS has been fabricated using electron beam lithography and the feature size used in our design is CMOS compatible. The fabricated device achieves measured extinction ratios higher than 20 dB and insertion losses lower than 2 dB for both polarizations over a 77 nm wavelength range from 1522 to 1599 nm that covers the entire C -band, with a device length of only 71.5 $\mu$ m.

Broadband Polarization Beam Splitter on a Silicon Nitride Platform for O-Band Operation

Wideband polarization beam splitters (PBS) are a key building block in polarization management circuits for wavelength division multiplexing applications. A broadband PBS on a 300-mm silicon nitride (SiN) photonic platform is reported based on phase-controlled directional coupler (DC). Unlike classical DC-based PBS made on silicon, the proposed configuration leverages the comparatively lower birefringence in SiN to yield wideband and efficient splitting. A semi-analytical approach, based on transfer matrix modeling and 3-D finite difference time domain, has been used to design and optimize the structure for O-band operation. The proposed PBS has been experimentally demonstrated showing insertion loss (IL) lower than 0.6 dB and extinction ratio (ER) as high as 10 dB over 95-nm bandwidth for both polarizations. Furthermore, this simplified architecture eases cascading, allowing the demonstration of IL below 1.1 dB and ER larger than 24 dB over 85-nm wavelength range in a dual-stage configuration.

Electromagnetic dipole resonant characteristics of all-dielectric one dimensional grating in terahertz region

Mie-type magnetic and electric resonances in an all-dielectric one-dimensional grating are theoretically demonstrated in terahertz region. It is found that strong polarization-sensitivity and frequency-selection behaviors of resonances can be excited in all dielectric subwavelength grating structure. This all dielectric grating with less absorption loss can be carefully designed as broadband reflectors and polarization beam splitters. The coupling effects of the array silicon pillar and the electromagnetic field distribution were numerically calculated by use of finite element method. The effective constitutive parameters of subwavelength grating, including in the effective refractive index, effective permittivity, effective permeability, and effective impedance, can be extracted by using the standard retrieval method of inversion algorithm. Magnetic and electric Mie resonances can be revealed by enhanced effective parameters at resonant frequencies.

Ultra-compact broadband polarization beam splitter with strong expansibility

Based on the traditional directional coupler, we proposed a scheme to design on-chip polarization beam splitters using an inverse design method. In our scheme, the coupling area of the designed devices are only 0.48 μm×6.4 μm. By manipulating the refractive index of the coupling region, the devices can work in C-band, L-band, O-band, or any other communication band. Different from conventional design methods, which need to adjust the design parameters artificially, if the initial conditions are determined, the proposed scheme can automatically adjust the design parameters of devices according to specific requirements. The simulation results show that the insertion losses of the designed polarization beam splitters can be less than 0.4 dB (0.35 dB) for TE (TM) mode at the wavelengths of 1310, 1550, and 1600 nm, and the extinction ratios are larger than 19.9 dB for the TE and TM modes at all three wavelengths. Besides, the extinction ratios of both polarization states are more than 14.5 dB within the wavelength range of 1286–1364 nm, 1497–1568 nm, and 1553–1634 nm. At the same time, the insertion losses are smaller than 0.46 dB.

Compact, Angled Polarization Splitter: Characterization of Broadband Performance and Fabrication Tolerance

We propose and experimentally demonstrate a broadband polarization beam splitter on the silicon-on-insulator platform using the concept of multimode interference. The angle between the input waveguide and the multimode interferometer (MMI) was optimized in order to extract the images corresponding to the fundamental transverse electric (TE) and transverse magnetic (TM) polarizations from a single, compact MMI. By changing the direction of propagation, the input angle enabled the addition of a parallelepiped to facilitate exclusively TM collection above the MMI, therefore eliminating the need to cascade successive MMIs. The MMI was tapered to improve coupling at the ports. The design allowed for a compact geometry with a length of 67.5 μm and width of 4 μm, while maintaining a feature size comparable to the waveguide width. The design was experimentally characterized over 72 parameter variations, including input angle, output TM and TE port positions, and bend radius of the output TE waveguide. The performance was consistent over the 100 nm wavelength range of 1500–1600 nm, with an average insertion loss of 2 dB. The device maintained an extinction ratio of at least 13.96 and 11.45 dB in the C-band for the TE and TM polarizations, respectively.

Broadband silicon polarization beam splitter with a high extinction ratio using a triple-bent-waveguide directional coupler.

We report on the design and experimental demonstration of a broadband silicon polarization beam splitter (PBS) with a high extinction ratio (ER)≥30 dB. This was achieved using triple-bent-waveguide directional coupling in a single PBS, and cascaded PBS topology. For the single PBS, the bandwidths for an ER≥30 dB are 20 nm for the quasi-TE mode, and 70 nm for the quasi-TM mode when a broadband light source (1520-1610 nm) was employed. The insertion loss (IL) varies from 0.2 to 1 dB for the quasi-TE mode and 0.2-2 dB for the quasi-TM mode. The cascaded PBS improved the bandwidth of the quasi-TE mode for an ER≥30 dB to 90 nm, with a low IL of 0.2-2 dB. To the best of our knowledge, our PBS system is one of the best broadband PBSs with an ER as high as ∼42 dB and a low IL below 1 dB around the central wavelength, and experimentally demonstrated using edge-coupling.

Ultracompact and Broadband Silicon-Based Polarization Beam Splitter Using an Asymmetrical Directional Coupler

An ultracompact and broadband polarization beam splitter (PBS) is proposed by using an asymmetrical directional coupler composed of a hybrid plasmonic waveguide (HPW) and a regular silicon wire (RSW). By properly choosing the structural parameters, transverse-magnetic (TM) mode is cutoff for the RSW and phase-matching condition is only satisfied for transverse-electric (TE) mode. As a result, the input TM-mode in HPW directly passes through, while the input TE-mode in the same HPW is coupled into the RSW. Consequently, the two polarized modes can be effectively separated. Moreover, the present PBS shows fabrication-friendly design and its length can be significantly reduced, since the gap between the HPW and RSW can be shortened to zero. From the results, a ~2.6- $\mu \text{m}$ -long PBS with a coupling length of $0.1~\mu \text{m}$ is achieved and its bandwidth is ~120 nm with a polarization extinction ratio over 14 dB, and an insertion loss below 1 dB for both polarizations. In addition, fabrication tolerances to the key structural parameters are analyzed in detail and field evolution through the designed PBS is also presented.

Broadband polarizing beam splitter based on two-layer metal grating with a high refractive index dielectric layer

A polarizing beam splitter (PBS) based on a two-layer metal grating operating in the near-infrared wavelength region is proposed. The PBS structure comprises a high refractive index dielectric layer and a subwavelength grating layer, which increases the transmittance and the extinction ratio of the grating. Using the rigorous coupled-wave analysis (RCWA) method, the parameters of the proposed polarizing beam splitter were simulated and optimized. The results show that transmission of more than 97% for the transverse-magnetic (TM) wave polarization and reflection of more than 98% for the transverse-electric (TE) wave polarization are achieved within the 1220–1690nm wavelength range. The corresponding maximum extinction ratios for the transmittance and reflectance are 33dB and 34dB, respectively. When compared with a single-layer PBS grating, the proposed two-layer structure shows greater design flexibility. The proposed PBS shows potential for application to devices such as routers and switches.

Cylinder and metal grating polarization beam splitter

We propose a novel and compact metal grating polarization beam splitter (PBS) based on its different reflected and transmitted orders. The metal grating exhibits a broadband high reflectivity and polarization dependence. The rigorous coupled wave analysis is used to calculate the reflectivity and the transmitting spectra and optimize the structure parameters to realize the broadband PBS. The finite-element method is used to calculate the field distribution. The characteristics of the broadband high reflectivity, transmitting and the polarization dependence are investigated including wavelength, period, refractive index and the radius of circle grating. When grating period d = 400 nm, incident wavelength λ = 441 nm, incident angle θ = 60° and radius of circle d/5, then the zeroth reflection order R0 = 0.35 and the transmission zeroth order T0 = 0.08 for TE polarization, however, T0 = 0.34 and R0 = 0.01 for TM mode. The simple fabrication method involves only single etch step and good compatibility with complementary metal oxide semiconductor technology. PBS designed here is particularly suited for optical communication and optical information processing.

Compact broadband polarization beam splitter using a symmetric directional coupler with sinusoidal bends.

We design and demonstrate a compact broadband polarization beam splitter (PBS) using a symmetric directional coupler with sinusoidal bends on a silicon-on-insulator platform. The sinusoidal bends in our PBS suppress the power exchange between two parallel symmetric strip waveguides for the transverse-electric (TE) mode, while allowing for the maximum power transfer to the adjacent waveguide for the transverse-magnetic (TM) mode. Our PBS has a nominal coupler length of 8.55 μm, and it has an average extinction ratio (ER) of 12.0 dB for the TE mode, an average ER of 20.1 dB for the TM mode, an average polarization isolation (PI) of 20.6 dB for the through port, and an average PI of 11.5 dB for the cross port, all over a bandwidth of 100 nm.

On-chip broadband ultra-compact optical couplers and polarization splitters based on off-centered and non-symmetric slotted Si-wire waveguides

In this work, we propose novel schemes to design on-chip ultra-compact optical directional couplers (DC) and broadband polarization beam splitters (PBS) based on off-centered and asymmetric dielectric slot waveguides, respectively. Slot dimensions and positions are optimized to achieve maximum coupling coefficients between two symmetric and non-symmetric slotted Si wire waveguides through overlap integral method. We observe >88% of enhancement in the coupling coefficients when the size-optimized slots are placed in optimal positions, with respect to the same waveguides with no slot. When the waveguides are parallel, in that case, a coupling length as short as 1.73 μm is accomplished for TM mode with the off-centered and optimized slots. This scheme enables us to design optical DC with very small footprint, Lc ∼ 0.9 μm in the presence of S-bends. We also report a compact (Lc ∼ 1.1 μm) on-chip broadband PBS with hybrid slots. Extinction ratios of 13 dB and 22.3 dB are realized with very low insertion loss (0.055 dB and 0.008 dB) for TM and TE modes at 1.55 μm, respectively. The designed PBS exhibits a bandwidth of 78 nm for the TM mode (C-and partial L-bands) and >100 nm for the TE mode (S + C + L wavelength bands). Such on-chip devices can be used to design compact photonic interconnects and quantum information processing units efficiently. We have also investigated the fabrication tolerances of the proposed devices and described the fabrication steps to realize such hybrid devices. Our results are in good agreement with 3D FDTD simulations.

Ultrashort broadband polarization beam splitter based on a combined hybrid plasmonic waveguide

We propose an ultracompact broadband polarization beam splitter (PBS) based on a combined hybrid plasmonic waveguide (HPW). The proposed PBS separates transverse-electric (TE) and transverse-magnetic (TM) modes using a bent lower HPW with vertical nanoscale gaps and a straight upper HPW with a horizontal nanoscale gap, respectively, without relying on an additional coupling region. This design considerably reduces the length of the PBS to the submicron scale (920 nm, the shortest PBS reported to date) while offering polarization extinction ratios (PERs) of ~19 dB (~18 dB) and insertion losses (ILs) of ~0.6 dB (~0.3 dB) for the TE (TM) mode over an extremely broad band of 400 nm (from λ = 1300 nm to 1700 nm, covering entirely second and third telecom windows). The length of the designed PBS can be reduced further to 620 nm while still offering PERs of 15 dB, realizing a densely photonic integrated circuit. Considering the fabrication tolerance, the designed PBS allows for large geometrical deviations of ±20 nm while restricting PER variations to within 1 dB, except for those in the nanoscale gaps smaller than 10nm. Additionally, we also address the input and ouput coupling efficiencies of the proposed PBS.

Broadband polarization beam splitter based on a negative refractive lithium niobate photonic crystal slab

Using a lithium niobate (LN) material, we propose a broadband polarization beam splitter (PBS) with high efficiency by employing a negative refractive photonic crystal (PhC) wedge slab with an angle of 60°. It can split the incident light into two parts at about 90° with TE and TM polarizations. The transmissions of polarized light for an LN-based PBS are more than 80% with a broad angle and wavelength bandwidth of 8° and 70 nm at 1.55 μm, while with a Si-based PhC, no PBS with high efficiency can be realized for the relatively lower transmission of TM output light.

Compact and broadband polarization beam splitter based on a silicon nitride augmented low-index guiding structure.

We propose a compact polarization beam splitter (PBS) based on a silicon nitride enhanced silicon-on-insulator platform using an augmented low-index guiding (ALIG) waveguide structure. In the ALIG structure, the TM mode is mostly confined in the low-index silicon nitride, while the TE mode is confined in the high-index silicon. Since the two modes are confined in two separate layers, their properties can be controlled independently. The PBS is formed using an asymmetric multimode interference (MMI) section. The TM mode is directed to an output port by the ALIG waveguide, while the TE mode is coupled to the other output port via the multimode interferometer. Such a PBS has a very small footprint, low insertion loss, high polarization extinction ratio, and broadband response.

Ultracompact and broadband polarization beam splitter based on polarization-dependent critical guiding condition.

An ultracompact and broadband polarization beam splitter (PBS) based on the polarization-dependent critical guiding condition of an asymmetrical directional coupler is proposed. The device consists of a pair of silicon waveguides with different height and width. Due to the different cutoff conditions for the TE and TM polarization modes, it is possible to have the TM mode guided in one waveguide while the TE mode is supported in both. Therefore, only the phase-matching condition for the cross-coupling of the TE mode needs to be considered. This approach not only simplifies the design procedures but also significantly improves device performance with smaller total length and larger bandwidth. Finally, regardless of the contribution of S-bend waveguides, our proposed PBS has a coupling region as short as 0.2μm, which is the shortest reported until now. The simulation result shows that the extinction ratios for the TE and TM polarization are 13.5 and 16.6dB at their respective output ports, and their insertion losses are 0.29 and 0.13dB, respectively. Numerical simulations also show that the device offers a very large bandwidth (∼140 nm) with large extinction ratio (>10 dB) and low insertion loss (<1 dB).

Design and optimization of broadband polarization beam splitter made from a wave-structured multilayer film

Based on the 2D-PC wave multilayer film structure, a method to broaden the bandwidth of polarization beam splitter is proposed, which is composed of two different thickness periodic film stacks. Combined with the evaluation function of polarization splitting characteristic, the particle swarm optimization method is employed to design the optimal structural parameters. A broadband and compact polarization beam splitter is acquired, in which the center wavelength is 565 nm and its working range has achieved 220 nm with the average extinction ratio over 30 dB. In addition, by using the finite difference time domain method, the band structure and transmission spectrum of the wave-structure multilayer film are calculated, the angle sensitivity of the structure is investigated in detail. And we also study the electromagnetic field in the wavy-structure. Simulation results prove that the structure composed of the two different thickness periodic film stacks can avoid the discontinuity of bandgap, and PSO method can accelerate the convergence of the optimization algorithm and extend the bandwidth effectively.