An on-chip polarization splitter based on the radiation loss in the bending hybrid plasmonic waveguide structure

Abstract

Polarization beam splitters (PBSs) are one of the key components in the integrated photonic circuits. To increase the integration density, various complex hybrid plasmonic structures have been numerically designed to shrink the footprints of the PBSs. Here, to decrease the complexity of the small hybrid structures and the difficulty of the hybrid micro-nano fabrications, the radiation losses are utilized to experimentally demonstrate an ultra-small, broadband, and efficient PBS in a simple bending hybrid plasmonic waveguide structure. The hybrid plasmonic waveguide comprising a dielectric strip on the metal surface supports both the transverse-magnetic (TM) and transverse-electric (TE) waveguide modes. Because of the different field confinements, the TE waveguide mode has larger radiation loss than the TM waveguide mode in the bending hybrid strip waveguide. Based on the different radiation losses, the two incident waveguide modes of orthogonal polarization states are efficiently split in the proposed structure with a footprint of only about 2.2 × 2.2 μm2 on chips. Since there is no resonance or interference in the splitting process, the operation bandwidth is as broad as Δλ = 70 nm. Moreover, the utilization of the strongly confined waveguide modes instead of the bulk free-space light (with the spot size of at least a few wavelengths) as the incident source considerably increases the coupling efficiency, resulting in a low insertion loss of <3 dB.

On-chip polarization splitter based on a multimode plasmonic waveguide

“…4(a). This footprint is comparable to that in the previous experimental reports [5,35]. To excite two SPP modes, a grating with a period of about 740 nm is etched on the input waveguide, as shown in Fig.…”

“…The reason is that the propagation length of the antisymmetric mode (L spp 6.0 μm) is much smaller than that of the symmetric mode (L spp 32.8 μm). At λ 960 nm, the extinction ratios are calculated to be about 6.3 and 12.5 dB for the symmetric and antisymmetric waveguide modes, respectively, and the corresponding insertion losses are as low as about 0.7 and 0.9 dB, respectively, which are much smaller than that in the previous experimental works [23,25,26,32,35].…”

“…5(a) and 5(b). This insertion loss is smaller than that in the previous experimental works [23,25,26,32,35]. Hence, there is a broad 3 dB bandwidth of about 120 nm in the proposed PBS [3,38], in which the extinction ratios are greater than 5.0 dB.…”

“…For the fixed bending radius, the transmittances of the two SPP modes increase with the decrease of the bending angle. It should be pointed out that the transmittances of the antisymmetric waveguide mode at small bending radii are a little greater than 1.0 because of the mode conversion from the antisymmetric SPP waveguide mode (with a small propagation length of L spp ≈ 6.0 μm ) to the corner waveguide mode (with a large propagation length of L spp ≈ 29.0 μm) [34,35]. To get a large transmittance for the antisymmetric waveguide mode and a small transmittance for the symmetric waveguide mode, the bending angle is chosen to be α 30°.…”

“…3(e) and 3(f ). In the calculation, the corresponding straight waveguides with the same lengths are used as the reference waveguides for the symmetric and antisymmetric waveguide modes [35,36]. From Fig.…”