Compact polarizing beam splitter based on a metal-insulator-metal inserted into multimode interference coupler

Abstract

We propose and analyze a compact polarizing beam splitter (PBS) based on a metal-insulator-metal (MIM) structure inserted into a multimode interference coupler (MMI). Owing to the MIM structure, the TE polarized state is reflected by the cut-off condition while the TM polarized state is transmitted by the surface plasmon polariton, and the two polarized states can thus be separated. In this paper, the dependence of the reflected TE and transmitted TM field intensities on the MIM length and the gap thickness has been studied systematically. The proposed PBS structure, with a total size of 4 × 0.7 × 44 µm(3) is designed with MIM length, gap thickness, and metal thickness of 0.6 µm, 0.5 µm, and 0.05 µm, respectively. In the designed PBS, the transmittance for the TM polarized light, reflectance for the TE polarized light, extinction ratio, and insertion losses of the TE and TM modes are obtained using a 3D finite-difference time-domain method to be 0.9, 0.88, 12.55 dB, and 1.1 dB and 0.9 dB, respectively. The designed PBS has a much shorter length, 44 µm, compared to previous PBS devices.

Design of a Broadband Polarization Splitter Based on Anisotropy-Engineered Tilted Subwavelength Gratings

“…For broadband polarization splitting, multimode interference couplers (MMIs) are particularly promising candidates. PBSs based on conventional MMIs have comparatively large footprints [19], [20], which can be reduced by using quasi-imaging [21], photonic crystals [22], slot waveguides [23], metalinsulator-metal structures [24] and augmented-low-index-guiding waveguides [25]. In particular, the inherent anisotropy of SWG enables MMIs with virtually wavelength independent beat lengths for TE polarization, thereby enabling ultra-broad bandwidths.…”

Compact polarization beam splitter for silicon-based slot waveguides based on an asymmetrical multimode interference coupler

“…To overcome this issue, polarization diversity scheme is often used, 2 where polarization beam splitter (PBS), efficiently separating the TE and TM modes, is a fundamental component. So far, there have been many kinds of approaches reported for designing and/or fabricating a compact PBS with various structures, e.g., directional couplers (DCs), 3,4 multimode interference (MMI) couplers, 5,6 Mach-Zehnder interferometers, 7 photonic crystal structures. 8 Moreover, hybrid plasmonic waveguide (HPW), which confines mode within the low index gap between a metal cap and a high index dielectric layer, and long-range surface plasmon polariton (LR-SPP) waveguide, have also been introduced into the design of PBS.…”

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

“…Over the years, many types of PBSs 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 have been reported that have utilized various designs and have included adiabatic mode evolution (AME) devices 6 7 , directional couplers (DC) 8 9 10 11 12 13 14 15 16 17 18 19 20 , multimode interference (MMI) devices 21 22 23 24 25 , Mach–Zehnder interferometers (MZI) 26 27 28 , photonic crystals (PhC) 29 30 31 , and grating 31 32 33 structures. Most PBSs 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 28 32 33 …”

“…Although the device lengths of DC-based PBSs 8 9 10 11 12 13 14 15 16 17 18 19 20 can be reduced to several to tens of micrometers with reasonable PERs (10–20 dB), operating bandwidths are narrower than those of AME-based PBSs because of the requirement of utilizing phase-matched modes with a precisely tuned coupling. MMI-based PBSs 21 22 23 24 25 have a simpler fabrication process and larger fabrication tolerance than those of AME-based PBSs; however, dimensions of conventional MMI devices 35 36 are determined by the common multiple of the self-imaging lengths 37 of TE and TM modes, resulting in very long devices (>1000 μm). To shorten the lengths of MMI-based PBSs, some innovative designs have recently been reported, including two-mode interference 21 (~8.8 μm), 2 × 2 two-mode interference 22 (~0.94 μm for the length of MMI section only other than the whole PBS, the lengths for the input/output part should be included), metal–insulator–metal (MIM)-embedded 22 (~44 μm), hybrid plasmonic waveguide (HPW) 24 (~2.5 μm), and cascaded 25 (<950 μm) MMIs.…”

“…Among the aforementioned PBSs 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 , DC-based PBSs 8 9 10 11 12 13 14 15 16 17 18 19 20 have become the most popular, due to their structural simplicity, satisfactory performance, and diverse designs. In a DC-based PBS, one selected mode is separated using evanescent field coupling to the cross bar, while the remaining mode propagates straight along the through bar.…”