Ultra-broadband Polarization Beam Splitter Research Articles

High extinction ratio and an ultra-broadband polarization beam splitter in silicon integrated photonics by employing an all-dielectric metamaterial cladding.

In silicon and other photonic integrated circuit platforms many devices exhibit a large polarization dependency, therefore a polarization beam splitter (PBS) is an essential building block to split optical signal to transversal electric (TE) and transversal magnetic (TM) modes. In this paper we propose a concept of integrated silicon-based PBS exploiting unique properties of all dielectric metamaterial cladding to achieve a high extinction ratio (ER) and wide bandwidth (BW) polarization splitting characteristics. We start from a structure (PBS-1) based on a directional coupler with metamaterial cladding combined with a bent waveguide with metamaterial cladding at the outer side in the role of a TE polarizer at the Thru port of the device. To increase BW we propose the improved concept (PBS-2) - a metamaterial compact dual Mach-Zehnder Interferometer structure in combination with the TE polarizer. Numerical simulations reveal that an exceptionally high ER over 35 dB can be achieved in a BW of 263 nm with insertion loss (IL) below 1 dB in case of PBS-2. The designed device has a footprint of 82 µm. Measurement results reveal that an ER > 30 dB is achievable in a BW of at least 140 nm (limited by the laser tuning range).

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.

2-[formula omitted] Ultra-broadband polarization beam splitter with tunable transmissions based on silicon-Ge[formula omitted]Sb[formula omitted]Se[formula omitted]Te[formula omitted] hybrid subwavelength gratings

Recently, integrated optical devices working at 2-μm wavelengths have attracted considerable attention. Among such devices, a polarization beam splitter is an essential building block for constructing the on-chip circuit. Here, we have proposed an ultra-broadband polarization beam splitter with tunable transmissions working at 2-μm waveband. Coupled-mode based directional coupler is utilized for the device design. Subwavelength grating structures provide efficient dispersion control, which endows broad optical bandwidths. In addition, a rear-bent coupler is cascaded at the output of the device to furtherly suppress the crosstalk. The silicon-Ge2Sb2Se4Te1 hybrid materials provide tunable transmissions. When the Ge2Sb2Se4Te1 is in the amorphous state, with high extinction ratios more than 20 dB, the bandwidths exceed 200 nm (1900∼2100 nm) and 130 nm (1925∼2055 nm) for TE0 and TM0, respectively. Furthermore, the insertion losses are less than 0.24 dB (1900∼2100 nm) and 0.56 dB (1925∼2055 nm) for TE0 and TM0, respectively. When being in the crystalline state, the device works as an absorber that fully attenuates the input energy. In different intermediate amorphous–crystalline​ hybrid states, it is also possible to achieve tunable transmissions.

An Ultra-Broadband Polarization Beam Splitter Based on the Digital Meta-Structure at the 2 µm Waveband

The 2 μm waveband is considered to have great potential in optical communications. Driven by the demands on high-performance functional devices in this spectral band, various integrated photonic components have been demonstrated. In this work, an analog and digital topology optimization method is proposed to design an ultra-broadband polarization beam splitter at the 2 μm waveband. Within an optical bandwidth of 213 nm, the excess losses of TE and TM modes are <0.53 dB and 0.3 dB, respectively. The corresponding polarization extinction ratios are >16.5 dB and 18.1 dB. The device has a very compact footprint of only 2.52 µm × 5.4 µm. According to our best knowledge, this is a benchmark demonstration of an ultra-broadband and ultra-compact polarization beam splitter enabled by the proposed optimization method.

Ultra-Broadband Polarization Beam Splitter Based on Cascaded Mach-Zehnder Interferometers Assisted by Effectively Anisotropic Structures

An ultra-broadband polarization beam splitter (PBS) consisting of cascaded Mach-Zehnder interferometers (MZIs) is proposed on 220 nm-thick silicon-on-insulator (SOI) platform. The configuration of the cascaded MZIs has a point symmetry in order to broaden the bandwidth of the cross-coupling for the TM polarization. The sub-wavelength grating (SWG) structures act as effectively anisotropic cladding to enhance the separation of the two fundamental polarizations. Two filters with cascaded bends and a Bragg reflection structure at the two outputs, respectively, are used to further improve the extinction ratio (ER). The proposed PBS has a remarkable performance with ER > 20 dB over a record broad bandwidth of 310 nm (IL <; 0.5 dB) or 350nm (IL <; 1 dB) for both TE and TM polarization inputs.

Ultra-broadband polarization beam splitter with silicon subwavelength-grating waveguides.

An ultra-broadband polarization beam splitter (PBS) with low excess loss (EL) and a high extinction ratio (ER) is proposed and demonstrated for the case with 340 nm thick silicon-on-insulator waveguides. Here the PBS is realized by using cascaded adiabatic dual-core tapers, which consist of a strip core and a subwavelength-grating core. For the designed PBS, which has a 33.6 µm long mode-evolution region, the ELs are ${ \lt }{0.3}\;{\rm dB}$<0.3dB, and the ERs are ${ \gt }{20}\;{\rm dB}$>20dB for both TE and TM polarizations in an ultra-broad bandwidth of ${ \gt }{270}\;{\rm nm}$>270nm (1400-1670 nm) in theory. For the fabricated PBS, the measured bandwidths for achieving ERs of ${\sim}{20}$∼20 and ${\sim}{25}\;{\rm dB}$∼25dB are 240 and 220 nm, while the 1 dB bandwidth is as large as 230 nm, which are the largest bandwidths reported to date, to the best of our knowledge.

A compact ultrabroadband polarization beam splitter utilizing a hybrid plasmonic Y-branch

A compact and ultrabroadband polarization beam splitter (PBS) utilizing a hybrid plasmonic Y-branch (HPYB) on a silicon-on-insulator (SOI) platform is proposed and numerically demonstrated. The HPYB consists of a vertical hybrid plasmonic waveguide (HPW) and a horizontal HPW formed by silicon (Si) and silver (Ag) strip waveguides sandwiched with a silicon dioxide (SiO2) layer, in which the vertical and horizontal hybrid plasmonic modes (HPMs) are excited by the input transverse electric (TE) and transverse magnetic (TM) modes, respectively. The HPMs are split into different ports and coupled back to TE and TM modes to implement the polarization splitting function. A simplified and compact HPYB is robust for the HPMs' generation. The structure is wavelength insensitive since the HPMs' excitation is weakly correlated to the optical wavelengths. The simulation results show that the HPYB-based PBS has a compact footprint of $5 \times 1.8 \mu\text{m}^2$ and an ultralarge working bandwidth of 285 nm, with the polarization crosstalk < −10 dB and the worst-case TE (TM) mode insertion loss of −1.53 (−2.35) dB. The device also exhibits a large fabrication tolerance of 210-nm variation (from −100 to 110 nm) to the waveguide width for both polarizations.

Novel ultra-broadband polarization beam splitter based on dual-core photonic crystal fiber

A novel broadband polarization beam splitter (PBS) based on dual-core photonic crystal fiber is proposed. With a full-vector finite element method, the effects of structural parameters of fiber on the bandwidth and length of PBS are systematically investigated in detail. Numerical results indicate that an increase in the index of fluorine-doped region can not only broaden the bandwidth but also shorten the length of PBS. An increase in the diameters of air hole and hole pitch in an optical fiber can broaden the bandwidth of PBS, however, lengthen the length of PBS at the same time. Thus, it is necessary to balance the bandwidth and length of PBS when selecting the fiber structure parameters. Through optimizing the fiber structure parameters mentioned above, a kind of ultra-broadband PBS is achieved. When the extinction ratio is greater than 20 dB, the length of PBS is as short as 7.362 mm and its bandwidth is more than 600 nm.

Novel ultra-short and ultra-broadband polarization beam splitter based on a bent directional coupler

A novel ultra-short polarization beam splitter (PBS) based on a bent directional coupler is proposed by utilizing the evanescent coupling between two bent optical waveguides with different core widths. For the bent directional coupler, there is a significant phase-mismatch for TE polarization while the phase-matching condition is satisfied for TM polarization. Therefore, the TM polarized light can be coupled from the narrow input waveguide to the adjacent wide waveguide while the TE polarization goes through the coupling region without significant coupling. An ultra-short (<10 μm-long) PBS is designed based on silicon-on-insulator nanowires and the length of the bent coupling region is as small as 4.5 μm while the gap width is chosen as 200 nm (large enough to simplify the fabrication). Numerical simulations show that the present PBS has a good fabrication tolerance for the variation of the waveguide width (more than ± 60 nm) and a very broad band (~200 nm) for an extinction ratio of >10 dB.