A compact and high extinction ratio polarization beam splitter using subwavelength grating (SWG) couplers is proposed and characterized, where the SWG couplers are located between the two input/output strip waveguides, including SWG-based transitions combined at both ends. The TM mode can be confined well in the strip waveguide and transmits along it with nearly neglected coupling, while the TE mode undergoes a strong coupling and is transferred to the adjacent waveguide with the help of SWG couplers due to dissimilar modal characteristics and cutoff conditions between these two polarizations. To further enhance the performance, an additional tapered waveguide is added in the lateral end of the input SWG-based transition. Results show that a total length of 6.8 μm with an insertion loss of 0.08 (0.36) dB, extinction ratio (ER) of 32.19 (20.93) dB, and reflection loss of $-34.76$ ($-32.59$) dB for TE (TM) mode is obtained at 1.55 μm; its bandwidth can be enlarged to $\sim 81\mathrm{nm}$ for an $\mathrm{ER}>18\mathrm{dB}$. In addition, fabrication tolerances and mode-field evolution are also presented.

On-chip polarization manipulation is pivotal for silicon-on-insulator material platform to realize polarization-transparent circuits and polarization-division-multiplexing transmissions, where polarization splitters and rotators are fundamental components. In this work, we propose an ultracompact and high efficient silicon-based polarization splitter-rotator (PSR) using a partially-etched subwavelength grating (SWG) coupler. The proposed PSR consists of a taper-integrated SWG coupler combined with a partially-etched waveguide between the input and output strip waveguides to make the input transverse-electric (TE) mode couple and convert to the output transverse-magnetic (TM) mode at the cross port while the input TM mode confine well in the strip waveguide during propagation and directly output from the bar port with nearly neglected coupling. Moreover, to better separate input polarizations, an additional tapered waveguide extended from the partially-etched waveguide is also added. From results, an ultracompact PSR of only 8.2 μm in length is achieved, which is so far the reported shortest one. The polarization conversion loss and efficiency are 0.12 dB and 98.52%, respectively, together with the crosstalk and reflection loss of −31.41/−22.43 dB and −34.74/−33.13 dB for input TE/TM mode at wavelength of 1.55 μm. These attributes make the present device suitable for constructing on-chip compact photonic integrated circuits with polarization-independence.

A compact polarization beam splitter (PBS) for silicon-based slot waveguides is proposed, where an asymmetrical multimode waveguide (AMW), cut by a right angle at one corner, is employed to efficiently separate the TE and TM modes. With the unique modal properties of the slot waveguides, the input TE mode almost passes through the AMW and enters into the bar port, while the input TM mode forms a mirror image at the cross port due to the self-imaging effect. Tapered waveguide structures and S-bend are incorporated into the PBS for enhancing the performance. Results show that a PBS with an AMW of 2.3 μm in length is achieved, where the extinction ratios are 16.6 and 20.9 dB, respectively, for TE and TM modes, and the insertion losses are 1.37 and 0.81 dB, respectively, at the wavelength of 1.55 μm, and the bandwidths can cover the entire C-band for both polarizations. In addition, fabrication tolerances to the structural parameters are investigated and field evolution along the propagation distance through the designed PBS is also demonstrated.

A compact polarization rotator (PR) for silicon-based slot waveguides is proposed, where a metal strip of aluminum (Al) is embedded in its upper-claddings. With the features of asymmetric hybrid plasmonic waveguide induced by the metal strip, an optimal optical axis rotation angle of 45° is realized, leading to high polarization conversion efficiency (PCE). The numerical results show that a PR of 11.6 μm in length at the wavelength of 1.55 μm is achieved with the PCE and insertion loss of 97.6% and 0.86 dB for TM-to-TE conversion, respectively. In addition, fabrication tolerances to the structural parameters are investigated and field evolution along the propagation distance through the PR is demonstrated.

A compact TE-pass polarizer for silicon-based slot waveguides is proposed by utilizing a strip waveguide right above the slot waveguide and two identical metal strips symmetrically located on its outer sides. With the unique modal features of the slot waveguide and optimal designs for the vertical structure, only the input TE mode can directly output, while the input TM mode will be coupled to the upper waveguides, and thus, an efficient TE-pass polarizer can be realized. Moreover, the added metal strips can help to enhance the device performance significantly using their hybrid plasmonic effects. Results show that a polarizer of 3.2 μm in coupling length is achieved with the extinction ratio (ER) of 19.61 dB, insertion loss of 0.39 dB, and reflection losses of -24.15 dB (TM mode) and -34.41 dB (TE mode) at 1.55 μm, respectively. The optical bandwidth is ~110 nm for an ER >18 dB. In addition, fabrication tolerances and field evolution are presented.