The Tektronix SD-42 is an optical-to-electrical converter.
From Tektronix' site:
The SD42 Optical-to-electrical Converter head can be used to analyze optical signals in the 1000 nm to 1700 nm wavelength range. The pulse response of the measurement system is less than 55 ps FWHM (Full-width, Half-maximum), which is equivalent to a calculated bandwidth of DC to 6.4 GHz. The electrical output on the front panel is coupled to the adjacent sampling head via the semi-rigid coaxial link provided.
The SD42 is also equipped with an optical power meter for average power monitoring through a pair of voltage outputs on the front panel. Power from 5 nW to 5 mW can be measured.
|Pulse response||55 ps FWHM|
|Bandwidth||DC to 6.4 GHz|
|Conversion factor||25 mW/V (40 mV/mW)|
|Optical wavelength||1000 to 1700 nm (calibrated for use with a single-mode fiber input at 1300 nm)|
|Linear Response Range||<25 mW peak power / <5 mW mean power|
|Maximum Nondestructive Input||75 mW peak power / 10 mW mean power|
|Equivalent Display Noise||10 μWRMS typ. with SD-22, 33 μWRMS typ. with SD-24/SD-26 (<10 μWRMS typ. with smoothing)|