100G CFP/CFP2 DCO Coherent optical module Q&A

Why does the module use DP-QPSK modulation?

Dual polarization quadrant-phase shift keying (DP-QPSK) modulation technology based on coherent reception is the first choice for 100G modulation format. On the one hand, DP-QPSK can maximize the spectral efficiency, and on the other hand, it takes advantage of the phase modulation technology to PMD, dispersion, nonlinear high tolerance characteristics. As shown in the figure below, DP-QPSK can double the amount of information by polarization multiplexing (that is, transmitting two different messages in two orthogonal polarization states), transmitting 4 bytes per symbol.

Why not use higher base modulation?

There is nothing wrong with using a higher base system in principle, but it increases the pressure for modulation, detection, and transmission. In order to achieve this, the associated costs will increase several times. The goal of 100G is to cost less than or equal to the cost of 8 10G, so rely on the multi-base system to improve the spectral efficiency, to the quaternary system can be stopped, and then the high is not worth the loss. But for 100G network, just doubling the spectral efficiency of base 4 is not enough, how to do? Compared with continuing to use octal, polarization multiplexing is found to be more cost-effective. That's why you add a DP in front of QPSK to make it DP-QPSK.

How do I switch between Module 100GE and OTU4?

Walsun's 100G CFP/CFP2 DCO provides two rates: 100GE and OTU4. Currently, the default rate is OTU4. If the rate is switched to 100GE, the operation method is as follows according to the requirements of CFP MSA protocol: To enter the low power state (software operation register 0xB010=0x400E or hardware low power pin), write 0xB011=0x0200, After the module is switched from low power to high power (0xB010=0x000E), the module is ready (0xB016=0x0020), that is, the 100GE switchover is successful. If you cut back to the OTU4 rate, the operation is similar, except that the value 0xB011 is rewritten to 0x0206.

How long does it take for the module to start?

After the module is powered on to high power, it takes 120 seconds to complete the configuration. After that, it takes about 60 seconds to turn on the TX to the ready state. That is, it takes about 180 seconds to power on the module to work properly.

Does the module require an external input reference clock?

The Walsun 100G CFP2/CFP DCO module does not require an external input reference clock.

How to configure module loopback?

According to the requirements of the CFP MSA protocol, Host lane loopback (register 0xB014[10], Figure 1, the customer side loopback to the electrical port in DSP) and Network lane loopback (register 0xB012[10], Figure 2) are supported. The DSP internal line is looped back to the optical port.