Abstract
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.
Highlights
Over the last decade, silicon photonics based on silicon-on-insulator (SOI) has attracted more and more interests due to the advantages of high index contrast, compact footprint and compatibility to the complementary metal oxide semiconductor (CMOS)
The sub-wavelength grating (SWG) structures act as effectively anisotropic cladding to enhance the separation of the two fundamental polarizations
Various polarization beam splitter (PBS) on silicon chip have been reported by using different structures, such as Mach-Zehnder interferometers (MZIs) [1], [2], multi-mode interference (MMI) couplers [3]–[5], and directional couplers (DCs) [6]–[12]
Summary
Silicon photonics based on silicon-on-insulator (SOI) has attracted more and more interests due to the advantages of high index contrast, compact footprint and compatibility to the complementary metal oxide semiconductor (CMOS). Various PBSs on silicon chip have been reported by using different structures, such as Mach-Zehnder interferometers (MZIs) [1], [2], multi-mode interference (MMI) couplers [3]–[5], and directional couplers (DCs) [6]–[12]. Among these structures, DC is often used. By taking advantage of polarization-dependent evanescent wave control via the SWG as effectively anisotropic structures in the cascaded DCs, we have designed theoretically a PBS with ER > 20 dB and IL < 0.4 dB over a bandwidth of 250 nm [19]. By using the cascaded MZIs assisted by SWG structures and two filters at the two outputs, we further improve the bandwidth and reduce the footprint of the PBS than before
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