Once I needed to monitor the optical signal level on the Cisco Nexus C3064PQ-10GX to prevent cable sagging, stretching and signal loss, because in this case the signal deteriorates gradually, usually I monitor the signal on the end equipment, but I came across an old BDCOM 3310B model in which there was no support DDM.
You can also see my articles:
BDCOM OLT DDM SNMP OID
Juniper SNMP OIDs DDM for optical signal transceivers
You can use the following SNMP OID to determine the port index:
1.3.6.1.2.1.47.1.1.1.1.2
For example from Linux:
snmpwalk -v2c -c ixnfo.com 192.168.5.5 1.3.6.1.2.1.47.1.1.1.1.2
For example, I displayed the following indexes and their description:
SNMPv2-SMI::mib-2.47.1.1.1.1.2.300052803 = STRING: "Ethernet1/31 Lane 1 Transceiver Voltage Sensor"
SNMPv2-SMI::mib-2.47.1.1.1.1.2.300052804 = STRING: "Ethernet1/31 Lane 1 Transceiver Bias Current Sensor"
SNMPv2-SMI::mib-2.47.1.1.1.1.2.300052807 = STRING: "Ethernet1/31 Lane 1 Transceiver Temperature Sensor"
SNMPv2-SMI::mib-2.47.1.1.1.1.2.300052813 = STRING: "Ethernet1/31 Lane 1 Transceiver Receive Power Sensor"
SNMPv2-SMI::mib-2.47.1.1.1.1.2.300052814 = STRING: "Ethernet1/31 Lane 1 Transceiver Transmit Power Sensor"
Then you need to substitute the index into the following OID:
1.3.6.1.4.1.9.9.91.1.1.1.1.4
snmpwalk -v2c -c ixnfo.com 192.168.5.5 1.3.6.1.4.1.9.9.91.1.1.1.1.4.300052813
The result must be multiplied by 0.001 and the current level of the optical signal will be obtained.