A few days ago we posted our Going 800Gbps at up to 1000km with the Marvell COLORZ 800 piece and in that we briefly showed inside two other modules. One we already featured in Inside a 100G QSFP28 DAC. The other, the 100G SR4 QSFP28 module is certainly more complex than the 100G QSFP28 DAC, so we wanted to show that as well. Usually it is not the best idea to take apart optical modules if you want to ensure they keep working, so we decided to sacrifice one for STH.
Inside a 100G SR4 QSFP28 Housing
This is an AMC Optics module that is coded for Juniper as a JNP part number. We can see this is a MTP/MPO-12 optic so it is for 12 fiber multimode cables. It is also a QSFP28 connector on the other end so it fits into the same slot as the 100G QSFP28 DAC we showed previously.
Taking apart the casing was easy since it just used screws. Be warned, these often have springs for their retention latches and those springs sense the freedom of being liberated from the enclosure and like to jump beyond workbenches and onto the floor. Pulling off the metal casing, here is one side of the PCB.
That looks like a lower-cost DSP / CDR on this side but the chip information was rubbed off.
On the other end, we can see the PIC with the photonic components, both the laser and modulators as well as the photodetector and likely a TIA. You can see that the send and receive optical components that convert electrical and light are glued onto the PCB.
Out of that is a very short color-coded 12x fiber run that then goes to the rear connector.
That rear connector is what is exposed to the outside of the QSFP28 module and where you would connect a MTP/MPO-12 cable into.
Just as a point of comparison, here is what is going on inside a 100G DAC that we showed.
As one can see, there is a lot more going on in the optical module than the DAC.
Final Words
A 100G SR4 optical module is designed to be low-cost so it can be deployed widely. It does not need the more complex setups of longer-range optics since it only needs to span 100m. Still, it is a really good contrast to the DAC and also that 800G OSFP 1000km module that we looked at. Hopefully, this quick look means that you do not need to open up a module to satisfy your curiosity.
100G has replaced DSP with CDR.