Abstract
Dielectric gratings that couple optical fibers and planar waveguide circuits are key for optical-to-electronic (electronic-to-optical) signal conversion, but their applicability to platforms that require broader bandwidths and higher capacity is limited by their single-wavelength response. Herein, we present the design of a quasi-periodic grating coupler with multiband fiber-to-waveguide (waveguide-to-fiber) coupling response, where the grating consists of a periodic repetition of unit cells made of alternating silicon and air grooves according to the Fibonacci sequence. Through finite-difference time-domain (FDTD) calculations, we show that this new device could be used for coupling multi-wavelength fiber modes in a single grating structure. The results were obtained for fibers operating in the wavelength range from 1000 nm to 2000 nm, but the concept can be readily extended to other frequency ranges. Moreover, the allowed modes in the grating are almost insensitive to fiber misalignments and small fabrication errors for high Fibonacci steps, which is useful when alignment of optical components is impractical. It is hoped that properly designed gratings overlapping multiple modes may lead to ultra-broadband fiber-waveguide couplers that can cope with the growing demand for higher capacity and bandwidth in optical communications.
Highlights
The seamless integration of fibre-optics networks with photonic integrated circuits (PIC) and microelectronic devices may fulfill the ever growing demand for higher data rates in optical communications [1], [2]
We present the design of a quasi-periodic grating coupler with multiband fiber-to-waveguide coupling response, where the grating consists of a periodic repetition of unit cells made of alternating silicon and air grooves according to the Fibonacci sequence
Through finite-difference time-domain (FDTD) calculations, we show that this new device could be used for coupling multi-wavelength fiber modes in a single grating structure
Summary
The seamless integration of fibre-optics networks with photonic integrated circuits (PIC) and microelectronic devices may fulfill the ever growing demand for higher data rates in optical communications [1], [2] This convergence of optical and electronics, mediated by photonic technologies, has stimulated research into various directions, as in the coupling of optical-to-electronic or electronic-to-optical signals (optoelectronics) through dielectric semiconducting periodic grating couplers [2]–[9]. Multiple coupling-efficiency peaks in quasiperiodic structures (in contrast to periodic ones) result from the loss of long-range spatial coherence of the electromagnetic field along the patterning direction [28]. The aim in this work is to demonstrate the possible use of quasiperiodic gratings for multiple high efficiency peaks within a desired frequency range, i.e., geometrical parameters and the number of periods can be optimized for improved efficiencies [14], [32]. For the case of F5 in Figure 4(d) does one note that the coupling efficiency remains around 10%, which may be due to the dominant reflective behavior at the fiber-grating interface
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