Optical Module Maintenance Methods and Installation Tips
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Optical Module Maintenance Methods and Installation Tips

Posted on by FS.COM

As we all know, basically, a fiber optical transceiver consists of a transmitter and a receiver. When a transmitter connect with a receiver through a fiber but the system doesn’t achieve your desired bit-error-ratio (BER), is the transmitter at fault? Or, is it the receiver? Perhaps both are faulty. The fault might come from either internally in the optical module itself or externally by improper usage. Anyway, we have to diagnose where’s the fault and take measure to maintain the fiber optics so as to continue our normal transmission. Some issues are easy to be noticed and solved while some others are more difficult to deal with.

Common-Badness Types of an Optical Module and Judging Methods

For any optical module, there are some common-badness types that we may meet. They are:

 Optical power badness
 Eye diagram badness
 Receiving end badness
 Working current badness
 Program programming failed

In order to figure out where’s the fault, we can adopt several measures to judge an optical transceiver module. The first is visual method, which is the simplest. Check the faulty fiber optic module appearance. Whether there is obvious damage, component burned black, crack, leakage, even tin or not. The second method is by comparing the fiber module with another good module. Use certain tools and a good fiber transceiver module. Test the good module and the target module. Mainly analyze circuit parts or components’ resistance, voltage, waveform, etc. Then make a comparison. The third one is substitution method. To replace the components of the module, then to analyze the change of operating parameters.

Maintenance Methods for Internal Problems of Optical Modules

The five common problems listed in the last part might be faults internally. Take the 1G SFP transceiver as example, we are going to present the phenomenons belonging to each type. Also the possible reasons and maintenance methods will be given.

Fiber transceiver module optical power badness performance:

Phenomenon Reason Method
BIAS optical bias current within the normal range, the optical power exceeds out of the control range. Emission component TOSA is bad. Replace the TOSA.
The TOSA PINs PD+ is welded badly so that the power is so large. But when debug the software, the power won’t be changed. Weld the pin better.
Power and resistance don’t match with the BIAS optical bias current. Improve the power and resistance.
BIAS optical bias current within the normal range, the optical power is less than the control range. Emission component TOSA is bad. Replace the TOSA.
Paste is bad or poor performance of driver chip. Re-paste driver chip or replace the chip.
Power and resistance don’t match with the BIAS optical bias current. Reduce the power and resistance.
There is no light, BIAS value is displayed as 0. The TOSA PINs PD+ is welded badly. Weld the pin better.
Paste is bad or poor performance of storage chip. Re-paste storage chip or to replace the chip.
There is no light. BIAS short circuit, value is very great, displayed as 90mA ~ 150mA; and data can be saved. The TOSA PINs LD+ is welded badly. Weld the pin better.
Magnetic bead on LD- or LD+ line is bad, drain stickers or mislabeled. Reattach the same type of magnetic beads.
Paste is bad or poor performance of driver chip. Re-paste driver chip or to replace the chip.
Components of the storage chip pin is bad, drain stickers or mislabeled. Reattach the same type of the component.
There is light during the debug process, but the optical power doesn’t change. Emission component TOSA is bad. Replace the TOSA.
The TOSA PINs LD- is welded badly. Weld the pin better.

Fiber optic module eye diagram badness:

Phenomenon Reason Method
Extinction ratio of non-performing. Small extinction ratio. Replace the TOSA or reduce the optical power resistance.
Large extinction ratio. Replace the TOSA or improve the optical power resistance.
Eye diagram scatter. TOSA is bad. Replace the TOSA.
Driver chip performance is bad. Change the driver chip.
Signal impedance mismatch. Change the head-end matching resistance.
Graphics irregular. / Modify the value of pull-up resistor, pull-down resistor and the matching resistor.
Diagram without eye. TOSA is bad. Replace the TOSA.
Head-end matching resistor is weld badly or missing stickers. Re-paste the same size resistor.

Optical module receiving end badness performance:

Phenomenon Reason Method
Low sensitivity. ROSA is bad. Replace the ROSA.
ROSA pin OUT+ and OUT- are poorly contacted. Re-weld the pin.
Extinction ratio of light source is too small. Adjust the extinction ratio to 10 or more.
Burn of program is not complete. Burn again.
Limiting amplifier chip is bad or poor performance. Re-posted or replace limiting amplifier.
If the avalanche diode ADP causes the sensitivity low. Adjust to ADP voltage to the best.
No sensitivity. ROSA is bad. Replace the TOSA.
ROSA pin OUT+ and OUT- are poor welded. Re-weld the pin.
The coupling capacitor of OUT+ and OUT- line is even tin. Separate the even tin between the capacitances.
The magnetic beads is welded badly or leakage stickers. Re-paste the same type of magnetic beads.
Limiting amplifier chip is bad or poor performance. Re-posted or replace limiting amplifier.
Alarm dysfunction. The ROSA is bad or the alarm resistor is mismatch. Replace the ROSA or change the value of the alarm resistor.

Fiber optic module working current badness performance:

Phenomenon Reason Method
Open circuit-operating current is less than 70mA. MOS is bad. Replace the MOS tube.
The program hasn’t been burnt. Re-burn the program.
Operating current is greater than 300mA. / Replace components one by one; then observe whether the working current is smaller than before. If it is smaller, the components cause this problem.
/ Observe whether there is even tin or patch bad among the components.
Short-circuit-operating current is greater than 500mA. TOSA or ROSA is short circuit internally. Replace the TOSA or ROSA.
Chip is short circuit internally. Replace the chip.
Even tin among various components of PCBA. Separate the even tin.
VCC and GND of PCBA are short circuit. Scrap the PCBA because it can’t be repaired.

Fiber optic transceiver program programming failed:

Phenomenon Reason Method
Program can’t be burnt. MOS tube performance or patch is bad. Replace or re-paste MOS.
The save chip performance or patch is bad. Replace or re-paste the save chip.
Program can be burnt but without ID Components of the save chip is bad or leakage stickers. Re-paste same type of the component.
Module or shell is short circuit. The module includes TOSA, ROSA and PCBA, in which only TOSA is metal and is connected to the shell. Replace the TOSA; then to observe whether it is short circuit. If it is short circuit, the PCBA is bad, or the TOSA is bad. In this case, we should replace the TOSA or scrap the PCBA.

Maintenance Methods for External Problems of Optical Modules

Apart from the faults of the components in the optical module, the problems might also be caused by improper operations during the use of fiber optic transceivers. They are mainly categorized into four types here.

Power light does not light:

Power supply fault. Check the power line or replace the power supply.

Link lights are not lit:

 Check whether the fiber lines are intact: loose connection between device interfaces and fiber jumpers, fiber jumpers and couplers, broken fiber.
 Check whether the fiber line loss is too large and exceed the loss budget of the transmitter/receiver pair used.
 Check whether the optical interfaces are connected properly, local TX and RX connection from afar, local RX and TX connection in the distance.
 Check whether the optical fiber patch cable is correct. Ensure that the connector type matches the device interface (APC/UPC/PC), the fiber type (MMF/SMF) matches the device type, and the supported transfer length matches the link distance.

The circuit link light does not light:

 Check whether network cable is the circuit breaker.
 Check whether the connection matches the type: devices such as computers use crossover cable. Switches, hubs and other equipment use straight line.
 Check whether the equipment transfer rate matches.

Serious network packet:

 The transceiver’s power port and the network device interface don’t match or device interface’s transmission mode (half-duplex/full-duplex) doesn’t match on both ends.
 RJ-45 head twisted issues.
 The fiber connectivity issues. Fiber jumper are not in alignment; couplers and jumpers don’t match.

Common Faults Caused by Incorrect Optical Module Installation

Among the external faults, some are generally caused by incorrect installation of the optical module.

Contamination

The most common source of contaminants in the optical bores is debris picked up on the ferrules of the optical connectors. So using cleaning tools, like an alcohol swab, pen cleaner or lint-free absorbent wipes, to clean the optical connector (both of the patch cable and the fiber transceiver receptacle) before is very necessary. Also if the optical connector is not inserted or pulled out horizontally, it might cause the ferrule in the ends of fiber patch cord to break in the transceiver’s port and make the module fault.

Using pen cleaner to clean transceiver optical port

Figure 1: Using pen cleaner to clean transceiver optical port.

In addition, using shoddy or non-standard fiber optic patch cables will also damage the transceiver module. For example, using unpolished ferrule or damaged fiber optic connectors easily leads the transceiver to be contaminated.

Absence of Conductive Metal

In general, the conductive metal are of a normal and good quality optical module is glossy. But for transceivers that are frequently plugged in and out, or incorrectly used in non-standard device slots, the conductive pins will be worn out. For transceivers that is lack of conductive metal or whose pins are of serious aging, the transmission performance will be affected.

https://community.fs.com/blog/wp-content/uploads/2016/01/Lack-of-conductive-metal-left-and-good-conductive-metal.jpg

Figure 2: Bad transceiver conductive pins (left two) and good transceiver conductive pins(right).

The Fiber Transceiver Module Is Not Plugged Tightly

When plugged into devices, fiber optic transceiver module must be tightly plugged and the bale clasp must be in place. Otherwise it will easily be interrupted or loosed when there are vibration and impact on the device.

Tips for Optical Module Installation

It might not be easy to avoid the internal faults of the optical module, but by following some tips, we can reduce the unnecessary faults that may be caused externally during the installation.

Careful Check Before Installation

 Check the conductive metal. A good transceiver module should look bright and neat.
 Check whether the bale clasp is intact.
 Check the transceiver port interface. Ensure there’s no obvious matters in it.
 Check whether the ferrule of the patch cord is damaged.

How to Install and Remove the Fiber Optic Transceiver & Patch Cord?

Here are the general steps for installing fiber optic transceivers and fiber patch cords.

A good example of installing the optical transceiver into the switch

Figure 3: A good example of installing the optical transceiver into the switch.

Steps Note
Remove the dust cover from the device slot chosen for the transceiver. Do not remove the dust plug from the transceiver slot if you are not installing the transceiver at this time. The dust plug protects the line card from dust contamination. The dust plug protects the fiber optic port on the transceiver from dust contamination. It should not be removed until you are ready to connect the fiber optic cable.
Slide the transceiver in the slot horizontally until it clicks into place. Make sure you hear the click.
Remove the dust cap of the fiber patch cord, and clean the ferrules. The dust cap protects the ferrules on the patch cord from dust contamination. It should not be removed until you are ready to connect it.
Remove the dust cap from the transceiver. The dust cap protects the fiber optic port on the transceiver from dust contamination. It should not be removed until you are ready to connect the fiber optic cable.
Plug in the patch cord to the transceiver receptacle. If the transceiver has bale clasp, make sure the bale clasp in is the right place before plugging in.
Repeat the above steps for the transceiver at the other side of the link.
Check the port status LED.

For detailed procedure of installing or removing transceiver module, you can read: How to Install or Remove SFP, SFP+, QSFP, XFP Transceiver Modules.

Conclusion

When plugging a fiber optic module in but it can’t work normally, it might be the faults of the optical components within it or the improper operation during installation. We should take different methods to solve these problems. In order to avoid the possible faults existing in the optical components of a module, every optical transceiver in FS.COM will be fully tested in a wide range of networking devices to ensure its good quality and compatibility before it is sent to customers. At the same time, FS.COM provides all types of compatible and generic optical modules. Any specific needs for fiber optic transceiver can be customized for your applications.

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