Abstract:In the past decade there has been tremendous progress in using subwavelength-scale nanostructures with elaborately designed periodic and disordered photonic materials for applications in integrated photonics. In this paper, we review the advances in subwavelength engineering used in silicon photonic devices, with an emphasis on our own contributions on the use of subwavelength gratings and hyperuniform disordered photonic structures to attain state-of-the-art performances for near-and mid-infrared applications… Show more
“…If the index variation has a period larger than the wavelength of light inside the grating material, diffraction effect prevails. Otherwise, the light propagation in grating will exhibit similar feature as uniform medium, which becomes more significant as its period decreases [ 15 , 16 , 17 ]. GCs, as depicted in Figure 1 , work in the diffraction regime.…”
Section: Fundamentals Of Grating Couplermentioning
confidence: 99%
“…Subwavelength grating (SWG) refers to grating with period small enough to suppress diffraction effects [ 16 , 17 ]. Under certain conditions, it behaves as a homogeneous medium and has found wide range of applications in silicon photonics in the last decade.…”
Section: Fundamentals Of Grating Couplermentioning
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.
“…If the index variation has a period larger than the wavelength of light inside the grating material, diffraction effect prevails. Otherwise, the light propagation in grating will exhibit similar feature as uniform medium, which becomes more significant as its period decreases [ 15 , 16 , 17 ]. GCs, as depicted in Figure 1 , work in the diffraction regime.…”
Section: Fundamentals Of Grating Couplermentioning
confidence: 99%
“…Subwavelength grating (SWG) refers to grating with period small enough to suppress diffraction effects [ 16 , 17 ]. Under certain conditions, it behaves as a homogeneous medium and has found wide range of applications in silicon photonics in the last decade.…”
Section: Fundamentals Of Grating Couplermentioning
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.
“…Several SOI TM-pass polarizers have been proposed and experimentally demonstrated in the literature. They are based on one-dimensional or two-dimensional photonic crystal waveguides [13][14][15], a silicon strip waveguide embedding a graphene/Si3N4/graphene multilayer [16], photonic/plasmonic hybrid grating waveguides [17][18][19], a silicon wire coupled to a highly doped silicon waveguide [20], a silicon wire with a VO2 film on the vertical sidewalls [21], subwavelength grating waveguides [22][23][24][25], a waveguiding structure with two tapered waveguides sandwiching a narrow waveguide only supporting TM mode propagation [25], plasmonic bends [26], and hyperuniform disordered structures [27][28][29][30]. The features of these components, in terms of length, insertion loss (IL) and extinction ratio (ER), are summarized in Table I.…”
TM-pass polarizers are pivotal components of photonic integrated circuits (PICs), especially those intended for biosensing applications. In the literature, several silicon TM-pass polarizers have been proposed, designed and experimentally demonstrated, but their insertion loss is not compatible with the current trend of silicon photonics aimed at exponentially increasing the component density within PICs. Herein, we propose and design a TM-pass polarizer whose insertion loss is carefully minimized to 0.05 dB at wavelength 1.55 µm by utilizing a combination of an asymmetric directional coupler and a mode evolution section. The adoption of appropriate technical solutions makes this record insertion loss value compatible with a high extinction ratio equal to 38 dB. With a device footprint of only 2.5 × 20 µm 2 , the design exhibits an insertion loss less than 1.7 dB and extinction ratio better than 30 dB over a large bandwidth of 200 nm. The design assumes the constraints of a typical silicon photonics open-access technological process and a standard 220 nm silicon-on-insulator (SOI) wafer. A very low sensitivity of the achieved performance to reasonable fabrication inaccuracies is demonstrated, with a worst-case insertion loss of only 0.32 dB at wavelength 1.55 µm.
“…Sub‐wavelength features that have been incorporated in different devices exhibit similar geometries [25–28]. These similarities allude to a set of guidelines for sub‐wavelength engineering in SiP.…”
Rapid advances in high‐resolution chip lithography have accelerated nanophotonic device development on the silicon‐on‐insulator (SOI) platform. The ability to create sub‐wavelength features in silicon has attracted research in photonic band and dispersion engineering and consequently made available a wide array of device functionalities. By drawing on recent demonstrations, the authors review how periodic, sub‐wavelength structures are used for passive wave manipulation in SOI device design. The optical response is evaluated for both orthogonal polarisations at the telecom wavelengths of 1310 and 1550 nm. The results offer a versatile toolkit for the integration of these features in conventional nanophotonic device geometries. Notable benefits include a fine control of dispersion, wavelength and polarisation selectivity, and broadband performance.
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