Raman Tuning Algorithm calculates and sets the different pump power values across five Raman pumps to obtain the target Raman Gain on a span. Raman tuning runs in both directions of the span independently at the node level. Raman tuning requires communication between peer nodes. Hence, OSC communication between the two nodes is a prerequisite for Raman Tuning.

Raman tuning algorithm uses the following parameters to calculate the pump powers necessary to achieve the target Raman gain.

• Fiber type

• Fiber length

• Loss on the fiber at each pump wavelength

• Loss on the fiber at the signal wavelength

If you configure a span length value, Raman tuning uses this value.

Raman tuning is disabled by default. Raman tuning is enabled if automatic link bring up is enabled. You can manually trigger Raman tuning if necessary. initiates the tuning process under the following circumstances:

• During the initial link bring up

• After a fiber cut

• After a power cycle event

• After a line card cold reload event

• After a DFB shut or unshut event

• After an OTS controller shut or unshut event on near end or far end node

• After modification of span length configuration

Raman tuning is traffic impacting. When Raman tuning is in progress, the amplifier on the far end of the span is turned off to block traffic. The Optical Safety Remote Interlock (OSRI) feature allows turning off the amplifier on the peer node for Raman tuning. Only the OSC is active on the link while Raman tuning is in progress.

At the LINE-TX port on the far end of the span, the dedicated Raman probe (DFB) is combined with the transmitted optical channels. The DFB laser at 191.1 THz is used to perform a link continuity check on the Raman span for optical safety. The DFB laser is used during Raman tuning.

At the LINE-RX port, five wavelengths between 1424 nm and 1495 nm are inserted in the counter propagating direction of the signal to provide amplification using the Raman effect for both C and L band optical channels.

The system triggers Raman tuning when a link goes down and comes back up. After completing Raman tuning successfully, soft reloads, RP reloads, Raman OSRI change, and Raman Force APR change do not retrigger Raman tuning.

The following table lists and describes the different Raman Tuning Status.

Raman tuning works in the following three modes:

• Auto mode: Raman tuning defines the target gain and sets the pump powers and DFB VOA attenuation to achieve the target gain overwriting user configuration.

• Gain mode: User defines the gain target and Raman tuning sets the pump powers and DFB VOA attenuation to achieve the target gain.

• Manual mode: User disables Raman tuning and manually configures the Raman pumps and DFB VOA attenuation.

Note

If Raman back reflection (BR) is high, Raman tuning turns the Raman pumps off and goes into blocked state. High BR can damage the optics. When you clear the high BR and BR is at acceptable levels, the system triggers Raman tuning and turns the Raman pumps on. If a Raman span has a span loss value less than 14 dB, Raman tuning goes into the BLOCKED state. performs a span loss check at system startup to verify if you can use Raman amplification effectively on the span.

View Raman Tuning Status

You can view the Raman tuning status using show olc raman-tuning command. The following sample is an output of the show olc raman-tuning command.

RP/0/RP0/CPU0:ios#sh olc raman-tuning 
Tue Mar 21 06:11:36.944 UTC

Controller : Ots0/0/0/0
Raman-Tuning Status : TUNED
Tuning Complete Timestamp : 2023-03-20 07:54:00
Estimated Max Possible Gain : 19.8 dB
Raman Gain Target : 16.0 dB
Gain Achieved on Tuning Complete : 15.7 dB

You can view the Raman tuning status for individual controllers using show olc raman-tuning controller ots r/s/i/p command. The following sample is an output of the show olc raman-tuning controller ots r/s/i/p command.

RP/0/RP0/CPU0:ios#sh olc raman-tuning controller ots 0/0/0/0
Tue Mar 21 06:13:26.535 UTC

Controller : Ots0/0/0/0
Raman-Tuning Status : TUNED
Tuning Complete Timestamp : 2023-03-20 07:54:00
Estimated Max Possible Gain : 19.8 dB
Raman Gain Target : 16.0 dB
Gain Achieved on Tuning Complete : 15.7 dB

To view the individual Raman pump information and other parameters, use the show controllers ots r/s/i/p raman-info command.

RP/0/RP0/CPU0:ios#show controllers ots 0/0/0/0 raman-info 
Fri Apr  1 06:40:33.849 UTC

         Alarm Status:
         -------------
         Detected Alarms: None


         Alarm Statistics:
         -----------------
         RAMAN-AUTO-POW-RED = 0          
         RAMAN-1-LOW-POW = 0          
         RAMAN-2-LOW-POW = 0          
         RAMAN-3-LOW-POW = 0          
         RAMAN-4-LOW-POW = 0          
         RAMAN-5-LOW-POW = 0          
         RAMAN-1-HIGH-POW = 1          
         RAMAN-2-HIGH-POW = 0          
         RAMAN-3-HIGH-POW = 0          
         RAMAN-4-HIGH-POW = 0          
         RAMAN-5-HIGH-POW = 0          

         Parameter Statistics:
         ---------------------
         Raman Safety Control mode = auto 
         Raman Osri = OFF 
         Raman Force Apr = OFF 
         Composite Raman Power = 886.60 mW

         RAMAN Pump Info:
         ---------------------
         Instance        Wavelength(nm)  Power(mW)
          1               1424.00                 257.60
          2               1438.00                 255.10
          3               1457.00                 71.60
          4               1470.00                 127.50
          5               1495.00                 170.10



         Configured Parameters:
         -------------
         Raman Safety Control mode = auto 
         Raman Osri = OFF 
         Raman Force Apr = OFF 

         RAMAN Pump Info:
         ---------------------
         Instance        Power(mW)
          1               45.00
          2               40.00
          3               40.00
          4               40.00
          5               35.00

Note

In the previous output, there are two sections for Raman Pump Info that show different values. The first Raman Pump Info section displays operational data (current pumps power values). The second Raman Pump Info section displays Raman Pump Power configuration. In this case, the default pump powers are displayed. Use the raman-tx-power pumpvaluevalue command to configure individual Raman pump powers.