Mode Control in Planar Waveguide Grating Couplers With Double Surface Corrugation

Abstract

Grating couplers with double surface corrugation are proposed to adjust the resonance behavior of both TE and TM modes simultaneously. Through proper selection of parameters, we designed a polarization-independent grating coupler operating at 1.55-µm telecommunication wavelength. Efficiency is achieved at around 55% for both TE and TM modes, and the polarization-dependent loss is <0.05 dB within the spectral window from 1544 to 1561 nm. Furthermore, a double-channel grating coupler is proposed to excite the TE and TM modes at 1.31 and 1.49 µm, respectively. The achievable efficiency is around 60% for both channels with good uniformity.

Polarization-independent nonuniform grating couplers on silicon-on-insulator

“…Therefore, 1D grating couplers are preferable for many applications. This approach has been proposed for the waveguide on SOI wafer such as using thick silicon waveguides [13][14][15][16][17][18], using double-etched gratings [17], or using double-surface corrugation [18]. The refractiveindex contrast (Δ) of a silicon waveguide, defined as n 2 core − n 2 clad ∕2n 2 core is ∼48%.…”

“…In the case of thick waveguides, a ridge waveguide design is required for single-mode operation, which also requires a larger bending radius than channel waveguides even though the small bending radius of the ridge waveguide has been achieved by special design with additional etch step [19]. Designs based on double-etched gratings [17] and double-surface corrugation [18] are undesirable due to the complicated fabrication process.In this Letter, 1D grating couplers for polarizationindependent fiber coupling are proposed using gratings with nonuniform periodicity. The nonuniform periods are formed by the mathematical intersection or union of a set of two different grating periods.…”

“…For single-mode operation with this Δ, the size of silicon channel waveguide is approximately 400 nm by 220 nm in width and thickness, respectively, when n core 3.5 and n clad 1.45. Waveguide thickness greater than 220 nm [13][14][15][16][17][18] may not provide single-mode operation even though the grating coupler formed with the thick waveguide can have better coupling efficiency and design flexibility. In the case of thick waveguides, a ridge waveguide design is required for single-mode operation, which also requires a larger bending radius than channel waveguides even though the small bending radius of the ridge waveguide has been achieved by special design with additional etch step [19].…”

High-performance and compact polarization-independent grating coupler

“…From the regions of interest, the grating parameters 800 , 300 xy nm nm     were chosen for the highest peak coupling efficiency. Usually there exists a small angle (5-15 degree) between the optical fiber and the normal of the grating surface in order to avoid the Bragg reflection [10]. Though the directionalities of TM and TE mode differ due to the difference of the effective refractive index, the coupling efficiencies of the two modes may be the same by adjusting the tilting angle of the optical fiber to control the power coupled into the fiber.…”

Design and optimisation of passive silicon photonic device for wideband communication system

“…As for the polarization insensitive grating coupler design, most of design methods are actually to realize two grating interfaces (or combined as one interface) using two-dimensional structures for mode excitation. In our study, a one-dimensional method using double surface corrugation gratings is proposed to control the coupling modes and achieve polarization insensitive excitation [89]. We theoretically investigate the property of the structure and describe the excitation condition with formulas.…”