Effects of fabrication deviations and fiber misalignments on a fork-shape edge coupler based on subwavelength gratings

A 60 μm-Long Fiber-to-Chip Edge Coupler Assisted by Subwavelength Grating Structure with Ultralow Loss and Large Bandwidth

“…As L 4 varies from 31.5 µm to 34 µm, the obtained IL is relatively stable and the lowest value is nearly 0.25 dB at the conversion length around L 4 = 33 µm. Therefore, the obtained ultralow-loss feature of the proposed edge coupler as well as quite short conversion length offers a good solution for the light coupling between optical fiber and on-chip silicon waveguide compared with previous reports [19][20][21][22][23][26][27][28].…”

“…Before we conduct the structural parameter analyses, the device performance index should be determined first. For the fiber-to-chip edge coupler, loss is a key indicator which includes coupling loss and transmission loss [26][27][28]. Here, we employ IL coming from input fiber mode to output silicon waveguide mode to characterize the device performance.…”

“…From results, we have obtained an ultralow insertion loss (IL) of 0.23 dB at 1550 nm and the working bandwidth can be extended to 390 nm (240 nm) by keeping IL < 1.5 dB (1 dB), which could well support the broadband operation of on-chip silicon devices. Note that the total conversion length of the proposed edge coupler is only 60 µm, which is quite short compared to some previous reports [20][21][22]26,28]. Therefore, we believe such a fiber-to-chip edge coupler will be very beneficial for low-loss, broadband, compact light connection between optical fiber and on-chip silicon waveguide, and will also push the development of silicon photonics.…”

“…Therefore, the total conversion length is a sum of L 1 , L 2 , and L 3 . Through these three key steps, the input fiber mode (lensed fiber, MFD: 3.2 µm [15,26]) can be efficiently converted to on-chip silicon waveguide mode with a typical waveguide size of 220 nm × 450 nm, which is a commonly used size for the on-chip single-mode silicon waveguide. In addition, the grating period and duty cycle of the employed SWG structure are set as Λ = 300 nm and a/Λ = 50%, respectively, which could alleviate the fabrication requirements.…”

“…However, the mechanical strength and stability of the suspended structure might pose challenges for on-chip applications. Recently, a subwavelength grating (SWG)-assisted edge coupler was proposed and the total conversion length was reduced to less than 100 µm, which is quite promising for on-chip compact integration [24][25][26][27][28]. However, the obtained fiber-to-chip coupling loss (e.g., 1~2.5 dB [26][27][28]) and working bandwidth (e.g., less than 150 nm [26][27][28]) still need to be reduced and increased, respectively, which could help generate the ideal on-chip fiber-to-chip edge coupler.…”