Compact, high-performance, and fabrication friendly two-mode division multiplexer based on a silicon bent directional coupler

• Published in: Applied optics (2004) 2020-04, Vol.59 (12), p.3645
• Main Authors: Mehrabi, Kolsoom, Zarifkar, Abbas, Babaei, Mahsa
• Format: Article
• Language: English
• Subjects: Bandwidths; CMOS; Coupling; Crosstalk; Demultiplexers; Directional couplers; Finite difference time domain method; Multiplexing; Optical communication; Silicon; Transverse magnetic modes; Waveguides
• ISSN: 1559-128X; 2155-3165
• DOI: 10.1364/AO.385585

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