HP Agilent Keysight fixed 10dB attenuator 81001FF.

Optical head attenuator. Based on metal mesh and wavelength insensitive. For wavelength range 450-1700nm. 

You can cascade multiple attenuators to achieve greater attentuation. Connector adapter can be screwed on it. 

For 815xxx and 816xxx HP Agilent Keysight Optical Heads