The Tektronix 11F10 is an optical-input plug-in introduced in 1989 for 11000-series scopes.
The 11F10 has DC to 1 GHz bandwidth and appeared only in the 1989 catalog, without price indication. Like the 7F10A, which was advertised in the 1989 catalog too, it was not released to the market.
The 11F10 is specified for the 700 nm to 1550 nm range of optical wavelengths. It uses a germanium avalanche photodiode as the O/E transducer.