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What Is Optical Transceiver Simulation?

Number of visits: Date:2018-7-3 14:12


At present, the global telecommunications industry is developing steadily, and broadband users are also in steady growth. With the increasing demand of global bandwidth, and the expansion of the applications of the optical communications industry, such as data center and security monitoring, fiber broadband access has become the mainstream communication mode, and the investment scale of optical communication equipment has been further expanded, and it has become an important force to promote the growth of optical communication industry.

With the rapid development of optical communication and the Internet, the demand for network bandwidth has also increased rapidly, which leads to the rapid growth of the traffic of the backbone network by 50% to 80% a year. The transmission data rates of optical transceivers are upgrading from 10G/25G/40G to 100G/200G or even 400G. The improvement of data rates has optimized user experience, but it also poses more challenges for optical transceiver developers and designers. In order to ensure that the signal can be effectively transmitted from the transmitting end to the receiving end, we need to make a special simulation of the discontinuous points on the high speed links, that is, the optical transceiver simulation.

So, what is the optical transceiver simulation in the end?

There are three cases here.

First, the road between A and B is relatively flat, and there is no source of interference on the road.

Case 1

Secondly, there is a bulge (e.g. stone) between the road between A and B.

Case 1

Third, there are sunken sections between A and B.

Case 1

So, if you want to transport eggs safely from A to B, which way will you choose?

Obviously, you will choose the first situation. Because the road in the first case is relatively smooth, it can ensure the minimum vibration of eggs during transportation.

And for the signal, the truth is similar. We hope in the transmission process, the path of light would be always smooth, and there are no high or low ups and downs, so that the maximum transmission can be guaranteed.

But what is the actual situation?

For example, let's take a look at the signal line marked yellow. The signal comes out from the foot of the chip pin, reaches the inner layer through a via, and goes to the outer layer through another via, then connects to the capacitance pad, and finally reaches the connector end.

Case 1

As you can see, this road is not perfect, so it takes a lot of effort to get the signal to pass through with high quality.

Let's analyze that how many impedance discontinuities there are.

First, from pin pad to the line, there will be impedance discontinuity, because the impedance varies with the pad width and the trace line width.

The second is the Via, from top layer to inner layer, then from inner layer to top layer. Because there will be residual piles and parasitic capacitive effects across the hole, resulting in low impedance across the hole.

The fourth is at the connector pad. Because the pad width is not consistent with the trace line width, the impedance changes are caused.

As you can see, in the link, as long as the trace line width changes, or the equivalent line width changes, the impedance discontinuities will be generated, which will affect the impedance discontinuity of the transmission path, and then cause various problems of the signal.

Here is a simple example to illustrate the discontinuity of impedance. In the optical module, there are, of course, the discontinuity of connector welding, or line location.

Since there are so many problems, what shall we do? At this point, the simulation engineer is in use.

Now that the signal needs a smooth road, let's try to make the road smooth. But how can we guarantee it? This requires a datum. In optical transceiver modules, the usual definition is the characteristic impedance of a single 50ohm and differential 100ohm. What is the characteristic impedance? In simple terms, the characteristic impedance is the impedance determined by the characteristics of the line itself. Basically, the characteristic impedance is determined as long as the line width, the line distance, the copper thickness and the thickness of the medium are determined.

Of course, this is only a theoretical value. In practice, due to the influence of the fabrication process, the variation in line width, the change of copper thickness, and the control of the thickness of the dielectric layer will result in the change of the impedance.

Now that the benchmark is clear, what we need to do is to keep all factors as close as possible to benchmarks. Next, take via as an example to illustrate the simulation process.

First, after determining the discontinuity point, we need to model it according to the actual situation. The simulation software used here is HFSS, and the simulation is the line of differential 100ohm. There are many tutorials in the process of modeling.

Case 1

Once the modeling is completed, check the error and start the simulation. The simulation results will be obtained after the completion of the simulation.

Case 1

Case 1

As you can see, the impedance is low. The usual method is to use the hollowing process to keep the reference point away from the ground to increase the impedance.

The model after the hollowing is as follows:

Case 1

The simulation results are as follows. It can be seen that after the hollowing process, the impedance increases a lot. And the signal return loss and Insertion loss have also improved a lot.

Case 1

Case 1

Through the above examples, we can see that the use of simulation means can quickly avoid possible risks in the design phase, thus improving the development efficiency, reducing the development cycle and cost.

Aa a global optical interconnection design innovator, Gigalight has also been using optical transceiver simulation technology to save the design and manufacturing costs to ensure a lower cost of optical interconnection solutions for customers.

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