Novel Low-Loss Fiber-Chip Edge Coupler for Coupling Standard Single Mode Fibers to Silicon Photonic Wire Waveguides

Abstract

Fiber-to-chip optical interconnects is a big challenge in silicon photonics application scenarios such as data centers and optical transmission systems. An edge coupler, compared to optical grating, is appealing to in the application of silicon photonics due to the high coupling efficiency between standard optical fibers (SMF-28) and the sub-micron silicon wire waveguides. In this work, we proposed a novel fiber–chip edge coupler approach with a large mode size for silicon photonic wire waveguides. The edge coupler consists of a multiple structure which was fulfilled by multiple silicon nitride layers embedded in SiO2 upper cladding, curved waveguides and two adiabatic spot size converter (SSC) sections. The multiple structure can allow light directly coupling from large mode size fiber-to-chip coupler, and then the curved waveguides and SSCs transmit the evanescent field to a 220 nm-thick silicon wire waveguide based on the silicon-on-insulator (SOI) platform. The edge coupler, designed for a standard SMF-28 fiber with 8.2 μm mode field diameter (MFD) at a wavelength of 1550 nm, exhibits a mode overlap efficiency exceeding 95% at the chip facet and the overall coupling exceeding 90%. The proposed edge coupler is fully compatible with standard microfabrication processes.

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].…”

“…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.…”

“…Meanwhile, the key silicon inverse taper length was already 300 µm and the total conversion length would be even longer. To enhance the mode field match between optical fiber and coupler facet, multiple silicon nitride waveguides at different layers have been suggested, but the required multi-stage waveguide tapers make the total device length quite long (e.g., 895 µm [21], 300 µm [22]). Furthermore, the fabrication steps and complexities of such a scheme were obviously increased.…”

“…These reported multi-layer taper schemes are mainly using silicon nitride waveguides located in the upper cladding region of the silicon waveguide as bridges to efficiently connect optical fiber mode and silicon waveguide mode at different thick levels. If we want to make the light coupling between optical fiber and on-chip silicon waveguide directly without assistance of other intermediate waveguides (e.g., silicon nitride waveguides [20][21][22]), the mode field mismatch between optical fiber and silicon inverse taper should be reduced as far as possible. Under such conditions, Jia et al removed the buried oxide (BOX) layer below the silicon inverse taper and formed a suspended silicon inverse taper for the fiber mode coupling, where the measured coupling loss was lower than 1.3 dB for both polarizations [23].…”

Integrated Polarization-Splitting Grating Coupler for Chip-Scale Atomic Magnetometer

“…As for mode converter, multi-stage [ 74 ] or adiabatic taper [ 75 , 76 ] are beneficial to improvement of conversion efficiency. Multi-tip [ 77 , 78 ] or multi-layer [ 79 ] structures are capable of enhancing coupling efficiency from photonic chip to lensed fibers whilst making the device ultra-compact. We will implement on-chip integration of traditional optical components widely utilized in conventional miniaturized AM while achieving comparable performance in future work.…”