the grid constructed as we observe- TOSLINK (Wikipedia)
TOSLINK (from Toshiba Link) is a standardized optical fiber connector system. Also known generically as optical audio, its most common use is in consumer audio equipment (via a “digital optical” socket), where it carries a digital audio stream from components such as CD and DVD players, Digital Audio Tape recorders, computers, and modern video game consoles, to an AV receiver that can decode two channels of uncompressed pulse-code modulated (PCM) audio or compressed 5.1/7.1 surround sound such as Dolby Digital or DTS Surround System. Unlike HDMI, TOSLINK does not have the bandwidth to carry the uncompressed versions of Dolby TrueHD, DTS-HD Master Audio, or more than two channels of PCM audio.