Hello Giovanni
That sounds like a single strand full duplex connection which allows communication in both directions on a single fiber optic strand. This is achieved using a different wavelength for Tx and Rx transmissions (usually 1310nm and 1550 nm).
This bidirectional transmission is achieved via wavelength division multiplexing (WDM) couplers, also known as diplexers, that can combine and separate the data based on the wavelengths of the light. Generally, these WDM couplers are integrated into the optical transceiver module used to terminate the fiber on a device.
1000BASE-BX10 is an Ethernet standard that supports GigabitEthernet over a single strand of single mode fiber of up to 10 km. There are various other standards for single and multi mode, and at different speeds as well.
I hope this has been helpful!
Laz