FC/APC optical interface. We opened equipment, see last 2 photos, 4x40 switch is made of one 1x40 switch module and one 1x4 switch module inside enclosure, cascaded together. Common port of 1x40 switch and common port of 1x4 switch are optically merged together. 01, 02, …, 40 ports on front panel are output channels of 1x40 switch. COM1, COM2, COM3, and COM4 ports on front panel are output channels of 1x4 switch.

User instruction example to switch on optical path between channel 40 and COM3 port:
At front panel,  insert the fiber end of optical source into port 40, insert the fiber end of optical receiver into COM3 port.
Choose channel 40 of 1x40 switch: Type in: “1” "A" on keypad. Adjust channel number gradually by pressing “B” (Up-Arrow key) or “C” (Down-Arrow) on keypad,  until LCD shows "1.40".
Choose channel 3 of 1x3 switch: Type in: “2” "A" on keypad. Adjust channel number gradually by pressing “B” (Up-Arrow key) or “C” (Down-Arrow)  on keypad,  until LCD shows "2.3".

Our test result of insertion loss of 4x40 switch from COM2 to
Ch1: 7.8dB.
Ch2: 6.6dB.
Ch3: 7.9dB.
Ch4: 7.9dB.
Ch5: 9.4dB.
Ch6: 10.0dB.
Ch6 – Ch39 loss: similar to Ch1 – Ch 6
Ch40: 10.1dB (connector needs cleaning by regular cleaner box for male connector).
Insertion loss of 4x40 switch from COM1, or COM3, or COM4 is almost same as COM2.
Test result includes 2 FC/APC connector loss.

Insertion loss is much higher at 1.3um, about 22dB.

On keypad:
“A” =”MRT”
“B”=UP“
C”=DOWN

GPIB commands are unknown.