Coupled Waveguide Polarization Splitter With Slightly Different Core Widths

Abstract

Abstract-A coupler-type transverse electric/transverse magnetic (TE/TM) polarization splitter, in which a metal-loaded core is slightly widened, is analyzed using the three-dimensional beam-propagation method. Before analyzing the splitter with the slightly different core widths, the performance of a splitter with two identical cores is evaluated. The use of the two identical cores results in a high crosstalk and a low extinction ratio due to the phase mismatch between the waveguides with and without the metal for the TE mode. Therefore, the core width in the metal-loaded waveguide is slightly widened so as to restore the phase-matching condition. In contrast to the conventional splitter with the two identical cores, the present splitter is found to offer a low crosstalk of less than 30 dB and a high extinction ratio of more than 30 dB with a coupling efficiency of more than 97% at a wavelength of 1.55 m. In addition, the wideband operation is demonstrated over a wavelength range of 1.50 to 1.61 m.Index Terms-Beam-propagation method (BPM), directional coupler, metal-clad layer, polarization splitter.

Passive technologies for future large-scale photonic integrated circuits on silicon: polarization handling, light non-reciprocity and loss reduction

“…Several kinds of waveguide type PBSs have been reported by using various structures, e.g., Mach-Zehnder interferometers (MZIs), 30,31 multimode interference (MMI) structure, [32][33][34][35] directional couplers (DCs) [36][37][38][39][40][41] and photonic crystal (PhC)/grating structures. 42,43 For the conventional MMI-based PBS, the MMI length is usually chosen as the common multiple of the beat lengths for transverse electric (TE) and transverse magnetic (TM) polarizations.…”

“…A DC-PBS usually consists of two identical coupling waveguides and the length for the coupling region is chosen to satisfy L5pL p_TE 5qL p_TM , where L p_TE and L p_TM are the coupling lengths for TE and TM polarizations, respectively, p, q are integers, and q5p1m (m561, 3, 5, …). This introduces some limits for the design flexibility and also makes the DC-PBS quite long (e.g., ,1600 mm), 40 especially when one uses low index-contrast (D) waveguides due to the weak birefringence. Furthermore, such a DC-PBS behaves like a series-cascaded DC filter, which definitely has a smaller wavelengthbandwidth than a single-stage DC.…”

Silicon-based on-chip multiplexing technologies and devices for Peta-bit optical interconnects

“…It has been realized that most photonic integrated devices are polarization dependent due to the birefringence of optical waveguides (as summarized in Table 2), which provides various ways to realize waveguide-type PBSs, including multimode interferometers (MMIs) [106][107][108][109][110], DCs [111][112][113][114][115][116][117][118], MZIs [119][120][121], photonic crystal (PhC) structures [122][123][124][125][126], AWGs [127], MRRs [128], etc. Among them, a DC structure is an attractive option for PBSs because of its structural simplicity.…”

“…The beat length L π MZI [119][120][121] The central wavelengths DC [111][112][113][114][115][116][117][118] The coupling length/the coupling ratio PhC/Grating [122][123][124][125][126] The bandgap (reflection/transmission) AWG [127] The central wavelengths (@ x = x o ) The imaging position (@λ = λ 0 ) MRR [128] The resonance wavelength Figure 16 The cross section of the two waveguides for an asymmetrical coupling system.…”

Characterization of Strongly Coupled Si-Wire Waveguides for High-Density Optical WDM and Sensing Applications

“…Several research groups have deployed ODCs as polarization beam splitters [1]- [5] due to their simplicity in design and fabrication. Directional couplers have been designed as optical power splitters or combiners as well [6], [7].…”