Ultra-compact, low-loss,TE0- and TE1-compatible mode waveguide bends.

Waveguide bends have become an interesting research direction because they allow highly curved light transmission in a limited space. Here, we propose waveguide bends supporting two TE modes by etching slots and adding germanium arcs in the inner side of a waveguide bend. Simulations show that the bending radius of our proposed base-mode T E 0 waveguide bend drops to 500 nm and its insertion loss (IL) is reduced to 0.13 dB with footprints as small as 0.75µm×0.75µm. For the higher-order T E 1 mode waveguide bend, we adjust the introduced structure in combination with the light field distribution. The IL of the waveguide bend is also reduced to 0.18 dB with footprints as small as 1.85µm×1.85µm. T E 0 mode has 410 nm bandwidth in the optical communication band while T E 1 mode has 330 nm bandwidth by keeping I L<0.5d B. Through the analysis of these structural characteristics, we believe that this method still has great potential in higher-order mode transmission.

On-chip multifunctional polarizer based on phase change material.

Polarizers are used to eliminate the undesired polarization state and maintain the other one. The phase change material Ge2Sb2Se4Te1 (GSST) has been widely studied for providing reconfigurable function in optical systems. In this paper, based on a silicon waveguide embedded with a GSST, which is able to absorb light by taking advantage of the relatively large imaginary part of its refractive index in the crystalline state, a multifunctional polarizer with transverse electric (TE) and transverse magnetic (TM) passages has been designed. The interconversion between the two types of polarizers relies only on the state switching of GSST. The size of the device is 7.5µm∗4.3µm, and the simulation results showed that the extinction ratio of the TE-pass polarizer is 45.37 dB and the insertion loss is 1.10 dB at the wavelength of 1550 nm, while the extinction ratio (ER) of the TM-pass polarizer is 20.09 dB and the insertion loss (IL) is 1.35 dB. For the TE-pass polarizer, a bandwidth broader than 200 nm is achieved with ER>20dB and IL<2.0dB over the wavelength region from 1450 to 1650 nm  and for the TM-pass polarizer, ER>15dB and IL<1.5dB in the wavelength region from 1525 to 1600 nm, with a bandwidth of approximately 75 nm.

Reconfigurable TE-pass polarizer based on lithium niobate waveguide assisted by Ge2Sb2Te5 and silicon nitride.

On-chip polarization management components play a critical role in tackling polarization dependence in the lithium-niobate-on-insulator (LNOI) platform. In this work, we proposed a reconfigurable TE-pass polarizer based on optical phase change material (GST) and the LNOI wafer. The key region is formed by a hybrid GST-S i 3 N 4 layer symmetrically deposited atop the centerline of the LNOI waveguide along the propagation direction where the GST is sandwiched in the middle of the S i 3 N 4 layer. Whether the polarizer will take effect depends on the phase states of the GST layer and the graphene and aluminum oxide layers are coated atop the G S T-S i 3 N 4 layer as the microheater to control the conversion of phase states. The proposed device length is 7.5 µm with an insertion loss (IL)=0.22 dB and extinction ratio (ER)=32.8 dB at the wavelength of 1550 nm. Moreover, it also has a high ER (>25d B) and a low IL (<0.5d B) in the operating bandwidth of 200 nm. Such a high-performance TE-pass polarizer paves a new way for applications of photonics integrated circuits.

On-Chip Reconfigurable and Ultracompact Silicon Waveguide Mode Converters Based on Nonvolatile Optical Phase Change Materials.

Reconfigurable mode converters are essential components in efficient higher-order mode sources for on-chip multimode applications. We propose an on-chip reconfigurable silicon waveguide mode conversion scheme based on the nonvolatile and low-loss optical phase change material antimony triselenide (Sb2Se3). The key mode conversion region is formed by embedding a tapered Sb2Se3 layer into the silicon waveguide along the propagation direction and further cladding with graphene and aluminum oxide layers as the microheater. The proposed device can achieve the TE0-to-TE1 mode conversion and reconfigurable conversion (no mode conversion) depending on the phase state of embedded Sb2Se3 layer, whereas such function could not be realized according to previous reports. The proposed device length is only 2.3 µm with conversion efficiency (CE) = 97.5%, insertion loss (IL) = 0.2 dB, and mode crosstalk (CT) = -20.5 dB. Furthermore, the proposed device scheme can be extended to achieve other reconfigurable higher-order mode conversions. We believe the proposed reconfigurable mode conversion scheme and related devices could serve as the fundamental building blocks to provide higher-order mode sources for on-chip multimode photonics.