Search

A TM polarizer working for whole optical communication bands with high performance is proposed on a 220-nm-thick silicon-on-insulator (SOI) platform. The device is based on polarization-dependent band engineering in a subwavelength grating waveguide (SWGW). By utilizing an SWGW with a relatively larger lateral width, an ultra-broad bandgap of ∼476 nm (1238 nm-1714nm) is obtained for the TE mode, while the TM mode is well supported in this range. Then, a novel tapered and chirped grating design is adopted for efficient mode conversion, which results in a polarizer with a compact footprint (3.0 µm × 18 µm), low insertion loss (IL < 1.15 dB) and high polarization extinction ratio (PER > 21 dB) covering O-U bands (1260 nm-1675 nm). Experimental results show that the fabricated device has an IL < 1.0 dB and PER > 22 dB over a 300- nm bandwidth, which is limited by our measurement setup. To the best of our knowledge, no TM polarizer on the 220-nm SOI platform with comparable performance covering O-U bands has ever been reported.

An ultracompact polarization beam splitter based on silicon nitride-on-silicon platform is proposed and analyzed, where the two polarized modes are guided in two separated layers independently, almost no affecting each other. By using subwavelength grating structure in bottom silicon layer, the injected TE mode undergoes a strong coupling from input port to adjacent waveguide and then outputs from a bending waveguide. As to the injected TM mode, it is directly transmitted along the above silicon nitride layer. Moreover, the adjacent waveguide in bottom layer is cut by a right angle at one corner to further enhance the device performance. Results show that a coupling length of only 2.7~\mu \textm is achieved with an insertion loss of 0.22 dB (0.2 dB), an extinction ratio of 27.05 dB (25.73 dB), and a reflection loss of −26.94 dB (−37.79 dB) for TE (TM) mode at 1.55~\mu \textm . In addition, fabrication tolerances and field evolution are also presented. [ABSTRACT FROM PUBLISHER]

An ultracompact and broadband polarization beam splitter (PBS) is proposed by using an asymmetrical directional coupler composed of a hybrid plasmonic waveguide (HPW) and a regular silicon wire (RSW). By properly choosing the structural parameters, transverse-magnetic (TM) mode is cutoff for the RSW and phase-matching condition is only satisfied for transverse-electric (TE) mode. As a result, the input TM-mode in HPW directly passes through, while the input TE-mode in the same HPW is coupled into the RSW. Consequently, the two polarized modes can be effectively separated. Moreover, the present PBS shows fabrication-friendly design and its length can be significantly reduced, since the gap between the HPW and RSW can be shortened to zero. From the results, a ~2.6- \mu \textm -long PBS with a coupling length of 0.1~\mu \textm is achieved and its bandwidth is ~120 nm with a polarization extinction ratio over 14 dB, and an insertion loss below 1 dB for both polarizations. In addition, fabrication tolerances to the key structural parameters are analyzed in detail and field evolution through the designed PBS is also presented. [ABSTRACT FROM AUTHOR]

A compact silicon-based polarization splitter (PS) is proposed using a three-guide directional coupler composed of a silicon nanowire in the center and two horizontal/vertical hybrid-plasmonic waveguides (HPWs) at outer sides. Utilizing the evanescent coupling, the injected TE/TM modes in the central silicon nanowire can be only coupled to the horizontal/vertical HPWs, leading to the separation of input polarizations. Moreover, to improve the extinction ratio (ER), an S-bend connecting with the vertical HPW is employed. Results show that a coupling length of 6.5 (4.5) \mu \textm is achieved at the wavelength of 1.55~\mu \textm with ER and insertion loss of $\sim 18.9$ (15.2) dB and $\sim 0.44$ (0.89) dB for TE (TM) mode, and the bandwidths can cover the entire C-band for both polarizations. In addition, fabrication tolerances to the structural parameters are presented and field evolution through the designed PS is also demonstrated. [ABSTRACT FROM PUBLISHER]

A compact crossing scheme for a silicon-based slot-to-strip (or vice versa) waveguide is proposed and analyzed by using a finite-difference time-domain method, where a strip–multimode waveguide (SMW) crossing is used at the center and two logarithmically tapered slot-to-strip mode converters are incorporated into the ports with slot waveguides. For the input ports with slot waveguides and output ports with strip waveguides, the guided modes are efficiently transformed through the mode converter, and then enter into the SMW, where the fields converge at the center of the intersection due to the self-imaging effect. Hence, the size of the input beam is much smaller than the width of the SMW at the crossing center, leading to significant reductions of both crosstalk and radiation loss. The numerical results show that a slot-to-strip waveguide crossing operating at a wavelength of 1.55??m can be achieved with insertion loss, crosstalk, and reflection of 0.134/0.182, ?36.18/?38.6, and ?35.8/?42.02?dB for input ports with slot/strip waveguides, respectively. [ABSTRACT FROM PUBLISHER]

A compact silicon-based slot-waveguide crossing composed of a slot-to-strip mode converter (at each port) and an orthogonal strip multimode waveguide (SMW) is proposed and designed using a finite difference time domain method. With the mode converter based on logarithmically transitional tapers, the guided modes of the input slot waveguide are efficiently transformed to those of a strip one, and then enter into the SMW, where the fields converge at the centre of the intersection due to the self-imaging effect. As a result, the size of the input beam is much smaller than the width of the SMW at the crossing centre, leading to significant reductions in the crosstalk and radiation loss. The numerical results show that a slot-waveguide crossing operating at a wavelength of 1.55 µm with insertion loss, crosstalk and reflection of 0.131 dB, −37.44 dB and −35.47 dB, respectively, is achieved. Moreover, the fabrication tolerances to the structural parameters are investigated in detail. And the evolution of the injected field along the propagation distance through the slot-waveguide crossing is also demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: A silicon-based horizontal multiple-slotted waveguide with slanted sidewalls is analyzed by using a full-vectorial mode solver based on the finite element method. The results show that the mode classification of the present waveguide structures is different from that of the conventional ones (e.g., typical rib waveguides, optical fibers), both symmetric and anti-symmetric fundamental (and higher-order) quasi-TE and quasi-TM modes exist due to the strong coupling of high-index silicon layers. The field distributions, effective indexes, and optical field confinement factors, both in quasi-TE and quasi-TM modes, as functions of the top width and sidewalls angle of the waveguides, and the refractive index and thickness of the slots are investigated in detail, where the single-mode regime, non-birefringence condition, and maximum optical confinement factor are obtained. From the numerical results, a single-mode waveguide structure for fundamental symmetric quasi-TM modes with the power confinement factor of 80% and the normalized power density of 120μm−2 is achieved. [Copyright &y& Elsevier]

The article presents a reply on the research on the design of a compact silicon-based slot-waveguide through orthogonal strip multimode waveguide.