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Mode-division multiplexing (MDM) technology is one of the suitable approaches to increase data transmission capacity in photonic integrated circuits. Multimode optical switches play an important role in MDM interconnection networks. In this article, we present a multimode on-off optical switch using G e 2 S b 2 S e 4 T e 1 phase-change material for the first two TE modes (TE0 and TE1) and the first two TM modes (TM0 and TM1) in a wide wavelength range between 100 nm to around 1550 nm. The 3D finite-difference time-domain simulations indicate that for each propagating mode across the bandwidth, the insertion loss and extinction ratio are less than 0.80 dB and more than 20.21 dB, respectively. The proposed switch has a compact footprint of 10.7µ m ×3µ m . The presented switch also tolerates a ±20 n m change in the waveguide width, a ±10 n m silicon waveguide height deflection, and a ±5 n m GSST thickness variation with an insertion loss lower than 0.91 dB and an extinction ratio higher than 19.04 dB.

In response to the increasing demands of the capacity enhancement of optical communication, a compact and high-performance silicon mode division multiplexer is proposed that multiplexes the fundamental and first-order transverse magnetic modes. The device structure is based on an asymmetric bent directional coupler with an ultrasmall coupling length of 3.67 µm. Utilizing single-layer silicon waveguides with the same heights allows the proposed device to be fabricated using a single-step CMOS-compatible fabrication process, which provides a cost-effective design in comparison with the previously reported structures. The three-dimensional finite-difference time-domain simulation results confirm that the device has a low loss of 0.87 dB, low crosstalk of ${-}{21.8}\;{\rm dB}$-21.8dB, and high mode conversion efficiency of 98.3% at the communication wavelength of 1.55 µm. Furthermore, the device shows a broad bandwidth of about 110 nm, completely covering the C and L bands with crosstalk less than ${-}{10}\;{\rm dB}$-10dB. Moreover, it is shown that the proposed mode (de)multiplexer is fabrication tolerant for the coupling gap variation of ${-}{40}\;{\rm nm} \lt \Delta {g} \lt {23}\;{\rm nm}$-40nm<Δg<23nm and the waveguide width variation of ${-}{25}\;{\rm nm} \lt \Delta {W} \lt {25}\;{\rm nm}$-25nm<ΔW<25nm for a low loss of ${ \lt }- {1.67}\;{\rm dB}$<-1.67dB and low crosstalk of ${ \lt }- {10}\;{\rm dB}$<-10dB.

An ultracompact and ultrabroadband two-mode (de)multiplexer based on an asymmetric directional coupler for mode division multiplexing is proposed. The device structure consists of a pair of silicon waveguides with an array of plasmonic Au nanocubes sandwiched in the coupling region. The coupling region length of the directional coupler is decreased to 1 µm for coupling of the fundamental transverse magnetic (TM) mode to the first order mode by excitation of the surface plasmon polaritons. This is the shortest length reported for multiplexing of the TM modes until now, to the best of our knowledge. The proposed mode (de)multiplexer has a low loss of 0.72 dB and low crosstalk of -28.3 d B at the communication wavelength of 1.55 µm. Also, the 3D finite-difference time-domain simulation results show that a broad bandwidth of 190 nm is realized with crosstalk less than -10 d B and the insertion loss lower than 1.29 dB. Furthermore, impact of the fabrication tolerances on the performance of the proposed (de)multiplexer is studied in detail.

Recently, mode-division multiplexing (MDM) technology has been used to enable high-bandwidth data transmission. Information swapping or data exchange is an essential function in such high-capacity networks. This paper presents a small, broadband on-chip optical data exchange between two multiplexed modes on the silicon-on-insulator platform. The device consists of a three-waveguide coupler in which the middle waveguide has a hybrid plasmonic structure and the two other ones are silicon waveguides. The total length and the width of the proposed structure are 15.25 μm and 1.0885 μm, respectively. The 3D finite-difference-time-domain simulation results show that the insertion loss is less than 2 dB for a broad bandwidth of 100 nm, over which the crosstalk is lower than -14.7  dB and -21.9  dB for TM0 to TM1 and TM1 to TM0 conversion, respectively.