Silicon Photonics Grating Coupler Array for Light Collection in Optical Wireless Communication

The receivers for Optical Wireless Communication (OWC) need to meet the challenging requirements for high-capacity data transmission. Photonic Integrated Circuits (PIC) allow separation of light collection and light detection. In this way, both functions can be optimized separately. Light can be coupled into a PIC from free space through a Surface Grating Coupler (SGC) and detected with a high-speed photodiode. This separation enables additional processing of light between the collection and detection, such as amplification or mixing with a local oscillator for coherent detection. In this paper, we focus on optimization of the light collection part of the receiver for OWC. We present a “windmill” array of SGC fabricated on a Silicon-on-Insulator (SOI) platform. The SOI SGC array consists of four focusing 85 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m-long SGCs with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$90^{\circ }$</tex-math></inline-formula> opening angle (240-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m array diameter) with measured vertical -3-dB field of view (FoV) of ><inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$6^{\circ }$</tex-math></inline-formula>, and -7-dB <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$360^{\circ }$</tex-math></inline-formula> horizontal FoV. We achieved error-free optical wireless data transmission of 8 Gbps NRZ OOK over a distance of 15 cm. The PIC structure presented here is a promising candidate for future advanced OWC receivers.