FC/APC optical interface. We opened equipment, see last 3 photos below, 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” "MRT" on keypad. Type in “40” "ENT" on keypad,  then LCD will show "Switch No.: 001, Channel No.: 040".
Choose channel 3 of 1x3 switch: Type in: “2” "MRT" on keypad. Type in “3”, then "ENT" on keypad,  then LCD will show "Switch No.: 002, Channel No.: 003".
You can also adjust channel number gradually by pressing Up-Arrow key or Down-Arrow key on keypad.

GPIB commands:
To select channel 40 of 1x40 switch: SWITCH:1:40. Then LCD will show "Switch No.: 001, Channel No.: 040".
To select channel 3 of 1x4 switch: SWITCH:2:3. Then LCD will show "Switch No.: 002, Channel No.: 003".

Our test result of insertion loss of 4x40 switch from COM1 to
Ch10: 3.9dB.
Ch11: 3.7dB.
Ch15: 3.5dB.
Ch19: 3.1dB.
Ch21: 3.7dB.
Ch23: 3.6dB.
Ch25: 3.3dB.
Ch29: 4.8dB.
Other channels: less than 2.9dB.
Insertion loss of 4x40 switch from COM2, or COM3, or COM4 is lower than COM1.
Test result includes 2 FC/APC connector loss, at 1550nm.