Grating Couplers on Silicon Photonics: Design Principles, Emerging Trends and Practical Issues

Abstract

<jats:p>Silicon photonics is an enabling technology that provides integrated photonic devices and systems with low-cost mass manufacturing capability. It has attracted increasing attention in both academia and industry in recent years, not only for its applications in communications, but also in sensing. One important issue of silicon photonics that comes with its high integration density is an interface between its high-performance integrated waveguide devices and optical fibers or free-space optics. Surface grating coupler is a preferred candidate that provides flexibility for circuit design and reduces effort for both fabrication and alignment. In the past decades, considerable research efforts have been made on in-plane grating couplers to address their insufficiency in coupling efficiency, wavelength sensitivity and polarization sensitivity compared with out-of-plane edge-coupling. Apart from improved performances, new functionalities are also on the horizon for grating couplers. In this paper, we review the current research progresses made on grating couplers, starting from their fundamental theories and concepts. Then, we conclude various methods to improve their performance, including coupling efficiency, polarization and wavelength sensitivity. Finally, we discuss some emerging research topics on grating couplers, as well as practical issues such as testing, packaging and promising applications.</jats:p>

Design and Fabrication of Grating Couplers for the Optical Addressing of Trapped Ions

“…where A is a constant describing the laser beam characteristics, 0 is the beam width coupled to grating coupler, and is the distance parallel to the waveguide axis, is the separation between the input fibre and the top of the input grating, which is fixed at 0 [30]. Despite expressing the coupling efficiency of grating coupler, Equation (2) does not include characteristics of the grating coupler such as pitch, duty cycle, etch depth, etc [31].…”

Experimental Characterization of Particle Swarm Optimized Focusing Non-Uniform Grating Coupler for Multiple SOI Thicknesses

“…1 panel (b), can be a valid alternative. In fact, its planarity allows to reduce the vertical dimension of the final package resulting in a less bulky photonic device typical of an almost 2D structure [6].…”

“…Grating couplers (GCs) represent a promising solution due to the possibility of placing these structures almost anywhere on the PIC, while providing relatively relaxed alignment tolerances compared to competing edge-coupling geometries [6][7]. A wide variety of GCs structures have been optimized for the 220nm and 340nm-thick SOIs standard platforms [8][9][10]; in particular, on a "pure" SOI platform, non-uniform GCs (characterized by a non-constant pitch) have been demonstrated as the highest performers displaying theoretical and experimental CE values up to 89% and 81% respectively [11][12][13][14][15][16][17].…”

Optical Technology for NFV Converged Networks

“…However, since the polarization state of the input light is unknown in many applications, a dual polarization design for the photonic circuitry is often necessary, enabled by a polarization splitter and rotator [19]. In a Grating Coupler (GC), a diffraction grating is realized by periodically notching a silicon waveguide, so that light within a certain wavelength range is diffracted off in the direction of the connected optical fiber [20,21]. This mitigates the need for accurate alignment between silicon chip and fiber, facilitating the testing of the circuit and, consequently, its fabrication process.…”

“…Several GC designs exist, some of them able to deal with an arbitrary input polarization state. An example is the Polarization Splitting Grating Couplers [21], where input light in two orthogonal linear polarization states is directed into two different orthogonal waveguides in the silicon photonic circuit. These may commonly have insertion losses in a range of 3-5 dB but state of the art components may reach values close to 2 dB [23,24].…”