Highly efficient vertical fiber interfacing grating coupler with bilayer anti-reflection cladding and backside metal mirror

Abstract

A highly efficient bidirectional grating coupler for perfectly vertical coupling is designed. With a Si 3 N 4 /SiO 2 bilayer structure and a backside metal mirror acting as anti-reflection cladding (ARC) and substrate reflector respectively, the coupling efficiency can be greatly enhanced for a cost-effective uniform grating coupler. To maximize the grating coupling, all the grating parameters including the bilayer thicknesses are fully optimized using numerical simulation method. As a design trade-off between coupling efficiency (CE) and optical bandwidth (OB), CE of 88.3% (-0.54dB) and 1-dB bandwidth of 61nm can be obtained. In addition, this grating coupler shows strong fiber misalignment tolerance. With a 2μm fiber misalignment, the coupling loss increases by less than 0.5dB and the upreflection loss increases by less than 2dB. Also it is found that the splitting behavior of the grating is quite stable near the grating resonant wavelength. Such characteristics make this device very attractive for low-cost photonic packaging and Mach-Zehnder type device applications. In addition, two optimal designs are presented based on the Particle Swarm Optimization (PSO) method and genetic algorithm (GA). Numerical calculated results show that the coupling efficiency at center wavelength can be further improved compared to that of the balanced design. However, the optical bandwidth suffer at a expense. At last, Fourier analysis of the grating is carried out to analyze the optical field profile and frequency spectrum of the grating region. It is believed such a grating structure can provide flexible designs for different coupler requirements and applications.

Efficiency Enhanced Grating Coupler for Perfectly Vertical Fiber-to-Chip Coupling

“…The reflection back into the fiber is reduced and total in-plane CE is increased. Compared with our previous work [23], both Si 3 N 4 /SiO 2 structures are above the grating to reduce the back-reflection in both designs, but in a different manner. In our previous work, the Si 3 N 4 layer was sandwiched by the grating and silicon oxide, while in this new design, the Si 3 N 4 layer is above the silicon oxide.…”

“…In order to avoid complicated design or extra fabrication steps, a grating coupler that enables vertical to in-plane bidirectional transmission with bi-layer anti-reflection cladding was proposed in our previous work [23]. The bidirectional grating coupler functions as both a fiber coupler and optical power splitter, so that it cannot only act as a highly efficient vertical coupler but also work in Mach-Zehnder type optical modulators [24][25][26].…”

S-matrix absolute optimization method for a perfect vertical waveguide grating coupler

“…It is based on scattering matrix model which was previously applied to design a grating-coupled laser resonator [9]. In our case it assumes a 3-port vertical grating coupler, meaning it was designed to allow only negligible light transmission into the substrate [2,6,10,11]. A schematic drawing of the device is presented in Fig.1.…”

100 Gb/s Silicon Photonic WDM Transmitter with Misalignment-Tolerant Surface-Normal Optical Interfaces

“…The upreflection power is suppressed to 16% around the center coupling wavelength, corresponding to an optical return loss of 8 dB. Although such a result is not as superior as that of a conventional GC, further improvement of the reflection loss can be achieved by utilizing an apodized grating design [21] or introducing a bilayer antireflection cladding [22].…”