Abstract
Coupling between free space components and slab waveguides is a common requirement for integrated optical devices, and is typically achieved by end-fire or grating coupling. Power splitting and distribution requires additional components. Usually grating couplers are used in combination with MMI/Y-splitters to do this task. In this paper, we present a photonic crystal device which performs both tasks simultaneously and is able to couple light at normal incidence and near normal incidence. Our approach is scalable to large channel counts with little impact on device footprint. We demonstrate in normal incidence coupling with multi-channel splitting for 785 nm light. Photonic crystals are etched into single mode low refractive index SiON film on both SiO2/Si and borosilicate glass substrate. Triangular lattices are shown to provide coupling to 6 beams with equal included angle (60°), while a quasi-crystal lattice with 12-fold rotational symmetry yields coupling to 12 beams with equal included angle (30°). We show how to optimize the lattice constant to achieve efficient phase matching between incident and coupled mode wave vectors, and how to adjust operating wavelength from visible to infrared wavelengths.
Highlights
Couplers and power splitters are key components for integrated optics and have been studied extensively for decades[1]
We have successfully demonstrated practical single photonic crystal/quasi-crystal devices, which serve the dual purpose of coupling incident light with large beam size to a planar slab waveguide and splitting the coupled light power to multiple guided beams simultaneously with benefit of small footprint
The number of split beams depends on the symmetry of the photonic crystal lattice
Summary
Couplers and power splitters are key components for integrated optics and have been studied extensively for decades[1]. Silicon Photonics applications generally only need single mode input coupling due to the nature of the applications Many applications such as Bio-sensing do not require fibre coupling, and can benefit from larger area free space coupling from light sources such as LEDs and Laser devices. There have been few attempts to perform free space light coupling and power splitting function in one single device in order to decrease the size, and cost, of the full chip Most of these approaches were based on high index contrast waveguides such as SOI working at IR wavelengths[18, 19]. We report the design and fabrication of couplers performing the dual functionality of coupling and splitting functions for 785 nm light These are based on two-dimensional photonic crystal (PC) and photonic quasi-crystal (PQC) lattices with the benefit of very small footprint (microns rather than mm for the combined system). A functional waveguide taper component is not needed in this configuration, and the coupling area can be scaled in size to match the input source dimensions
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