How to use QSFP28 transceiver with 100G datacenter？

The 100G QSFP28 transceiver can transmit 100G or 40G data and can be inserted into the switch with 40G QSFP+ port, but the 100G QSFP28 transceivers on either end of the fiber must be of the same type.

QSFP28 CWDM4 is compliant with the standard especially formulated for the deployment of 100G within 2 km of the data center. The interface of the QSFP28 CWDM4 optical module conforms to the duplex single-mode 2 km 100G optical interface specification, and the transmission distance can reach 2 km. It is the most widely used 100G QSFP28 series optical module in data centers.

By comparison, QSFP28 LR4 possesses all the features of QSFP28 CWDM and is a more cost effective and competitive in the application of 2 km transmission.

The two interface models are illustrated as follows:

In addition to QSFP28 CWDM4 transceiver, QSFP28 PSM4 is one of the alternative solutions in intermediate transmission distance.

QSFP28 PSM4 optical transceiver is a four-channel 100G interconnect solution over a parallel SMF and it is mainly used for 500m link application.

8-core SMF builds four independent channels(4 for transmitting and 4 for receiving)for 100Gbps optical interconnects, and the transmission rate of each channel is 25 Gbps.

Each signal direction uses four independent channels of the same wavelength. Therefore, the two transceivers usually communicate via 8-fiber MTP/MPO single-mode optical fiber cable. The maximum transmission distance of PSM4 is 500 m.

There's a wide (and growing) range of 100G PHYs. You need to get a transceiver that is compatible with the DC uplink, e.g. 100GBASE-SR4 or -LR4.

The transceiver you've linked to states "100GBASE-IR4" which seems to be a 1310 nm, single-mode variant of 100GBASE-SR4. It doesn't seem to be compatible with anything else.

Using a QSFP28 transceiver with 40 Gbit/s is possible but requires the port to support that mode with that transceiver. 40G normally uses QSFP+ transceivers which may or may not work in a QSFP28 slot, depending on the switch and transceiver's compatibility.

The usual way to connect is to get the DC's uplink options, look at the device(s) you've got and check out which kind of transceiver you need to connect. Then you go shopping.