Hello, everyone!
Today I will explain problems with optical modules.
There are several different optical modules for service cards. For GPON, B +, C +, and C ++ are the most widely used today. The main characteristics of these modules are given in the table below.
The strength of the optical power emitted by optical modules depends on the following factors:
Wavelength
Transmission distance
Rate
Mode
Type | Class B+ | Class C+ | Class C++ |
Min output power | 1.5 dBm | 3 dBm | 6 dBm |
Max output power | 5 dBm | 7 dBm | 10 dBm |
Optical receiver sensitivity | -28 dBm | -32 dBm | -35 dBm |
Receiver overload | -8 dBm | -12 dBm | -15dBm |
In the next figure, we can see an example of an optical module – GPON-OLT-CLASS C++.
Figure 1. The Optical module, GPON-OLT-CLASS C++
The command for checking the status of a PON port/optical module:
TEST(config-if-gpon-0/1)#display port state 0
{ <cr>||<K> }:
Command:
display port state all
----------------------------------------------------------------------------
F/S/P 0/1/0
Optical Module status Online
Port state Online
Laser state Normal
Available bandwidth(Kbps) 1150609
Temperature(C) 36
TX Bias current(mA) 9
Supply Voltage(V) 3.21
TX power(dBm) 3.89
Illegal rogue ONT Inexistent
Max Distance(Km) 40
Wave length(nm) 1490
Fiber type Single Mode
Length(9um)(km) 40.0
----------------------------------------------------------------------------
The most important parameters which we can see from this command are port state, laser state, temperature, Tx bias current, supply voltage, and Tx power. If we have a problem with optical modules, we can see it with these parameters.
Port state shows us the current state of the optical module/PON port. It can be online and offline. The regular situation is when there is no ONT device on that PON port that the status is offline. But, if these are active ONT devices on the PON port, but the state of the PON port is offline, it is problem. There are two main problems: LOS and optical module fault.
The laser state shows us the laser state of an optical module. It can be normal and failed. If there is a problem with the optical module, the laser state is failed.
Temperature indicates the current temperature of the optical module. The normal range of the temperature is from 0 to 70 C. If there is a problem with the optical module, the operating temperature of the optical module increases.
Tx bias current is the transmitted bias current by the optical module. The normal range of the Tx bias current is from 0 to 100 mA. If there is a problem with the optical module, the Tx bias current is out of the normal range.
Supply voltage shows us the supply voltage. The normal range is from 0 to 6.55 V. If there is a problem with the optical module, the supply voltage is out of the normal range.
Now, I will show you three examples of optical module failure.
1. The first example shows us the problem with the optical module, and we can see it on the port state and temperature.
TEST(config-if-gpon-0/4)#display port state 0
{ <cr>||<K> }:
Command:
display port state all
----------------------------------------------------------------------------
F/S/P 0/4/0
Optical Module status Online
Port state Offline
Laser state Normal
Available bandwidth(Kbps) 1239040
Temperature(C) 73
TX Bias current(mA) 31
Supply Voltage(V) 3.01
TX power(dBm) 4.26
Illegal rogue ONT Inexistent
Max Distance(Km) 20
Wave length(nm) 1490
Fiber type Single Mode
Length(9um)(km) 20.0
----------------------------------------------------------------------------
2. In this example we can see an abnormal value of Tx power, the data of temperature is blank, and post-state is offline.
TEST(config-if-gpon-0/4)#display port state 0
{ <cr>||<K> }:
Command:
display port state all
----------------------------------------------------------------------------
F/S/P 0/4/0
Optical Module status Online
Port state Offline
Laser state Normal
Available bandwidth(Kbps) 1239040
Temperature(C) -
TX Bias current(mA) 0
Supply Voltage(V) 0.5
TX power(dBm) 21474836.47
Illegal rogue ONT Inexistent
Max Distance(Km) 20
Wave length(nm) 1490
Fiber type Single Mode
Length(9um)(km) 20.0
----------------------------------------------------------------------------
3. In the last example, we can not see values of the next parameters: temperature, Tx bias current, supply voltage and Tx power.
TEST(config-if-gpon-0/4)#display port state 0
{ <cr>||<K> }:
Command:
display port state all
----------------------------------------------------------------------------
F/S/P 0/4/0
Optical Module status Online
Port state Offline
Laser state Normal
Available bandwidth(Kbps) 1239040
Temperature(C) -
TX Bias current(mA) -
Supply Voltage(V) -
TX power(dBm) -
Illegal rogue ONT -
Max Distance(Km) 20
Wave length(nm) 1490
Fiber type Single Mode
Length(9um)(km) 20.0
----------------------------------------------------------------------------
In this article, I just described how to find out that there is a problem with the optical module. When there is a problem that users do not have services and there is a proper optical power on ONTs, it already indicates a problem with optical modules/PON ports. The next step is to check the state of the ports, as I described.
Thank you!
