You don't have a manual but you have the model number and an internet connection. That's one fact more than you gave us. I don't mean to be a deek, but why are you asking instead of looking for the manual online?
Sony manuals can be found at sonystyle.com, and every item I've ever seen for sale at crutchfield.com has a manual download. I got the manual from crutchfield.
On page 11 of the manual, the jack is identified thus:
Connects to the optical audio input of your digital audio
equipment that is PCM/Dolby* Digital compatible.
Page 15's label of that jack is
Digital audio equipment (A/V Receiver/Home Theater
Page 56,
When using HDMI input with Super Audio CD or DVD-Audio,
DIGITAL AUDIO OUT (Optical) may not provide an audio signal.
Page 58 has
PCM/Dolby Digital optical signal
If this information is not correct for your model number,....
