Refurbished  items are gaining a popularity more and more, and so does recently the refurbished equipment sales – people are trading all second hand refurbished equipment starting from expensive Cisco routers and ending with cheap switches – and optical equipment, what has a high risks to damage your business.

That’s the topic of our today’s conversation. Also, recently, as we get more and more feedback from our customers, there is a lot unfair suppliers on market, who artificially try to cost down the optical equipment price by using the second hand optical modules. Beware of them! That can cost you twice, and network breakdown can cause you claims from your customer.

First of all, you must know how the laser diode work, because it is one of the key elements in the any optical transmission system. There are two pairs of chipsets in laser diode, one pair (LD+/LD-) for creating and transmitting fiber signals, while the other (PD+/PD-) for receiving reflected signal.

The LD+ is connected to LD- by gold line at the size of 0.3 micrometer, the PD+ and PD- have the same connection. There is also a temperature-compensation device in the laser diode.

When power is on, the LD chipsets will transmit fiber signals with the help of a device to amplify it and the PD chipsets will receive reflection and transmit the signals to the temperature-compensation device ,stronger transmission means stronger reflection and stronger signals back to temperature-compensation device, then it will control the electrical current to ensure the whole device will work at suitable resistance, when the back signals is too strong /weak, that means the electrical current is also too strong/weak,then the temperature-compensation device will weaker/stronger the electrical current supply for LD chips.

Then you should know that to make the laser diode began to work, the electrical current in line must meet a fixed level, the normal value is from 8MA to 10MA, and the maximum value allowed is 13MA  according to standards, bigger value means bigger optical consumption. When the voltage is mixed (such as at 5v or 3.3v), the electrical current will become stronger/weaker as the resistance become stronger/weaker.

Now you can see why the old/second hand transceivers always stop working easily, and the life time is very short. No ebay sellers, or even more bad – unfair factories, who use second refurbished optical modules for example in media converters will tell you this. Yes, a product from such a factory looks nice, the casing and box is new – but do you see what can be inside?

The key reason is the gold lines connecting the chips have been broken in old/second hand transceivers, so these broken lines have less space to allow the electrical current through,and this will cause the resistance become bigger. And the electrical current will become stronger up to 25MA which is stronger than value allowed,then the signals transmission become stronger, the sinals reflected become stronger,and the PD chipsets may become too saturated to transmit any signals to temperature-compensation device or the PD chipsets will give temperature-compensation device too strong signals, and in these two situation the temperature-compensation device will cut the power supply and stop the whole system.

After reopening, the old/secondhand transceivers may work again, but they will stop working soon, that’s a maligant cycle, and the system will be not stable. You should use trustful suppliers first.

In AD-net we strive to provide customers with a new up to date optical transmission equipment, and educate them, how to avoid such unfair deals, as you can read above. E-mail to [email protected] for more questions on topic.

Our Fiber Media Converter range is using only brand new and high quality optical transceivers which are getting scrupulous pre-manufactury QC tests and QA.