The 100G QSFP28 CWDM4 optical transceiver (TQS-CG02-31DCR) is designed for use in 100 Gigabit Ethernet links on up to 2 km over single mode fiber (SMF).  They are compliant with the QSFP28 MSA, CWDM4 MSA, and relevant portions of IEEE P802.3bm standard.

The QSFP28 CWDM4 module uses Mux/Demux technologies, which converts 4 input channels of 25Gb/s electrical data to 4 channels of CWDM optical signals and then multiplexes them into a single channel for 100Gb/s optical transmission. Reversely on the receiver side, the module de-multiplexes a 100Gb/s optical input into 4 channels of CWDM optical signals and then converts them to 4 output channels of electrical data.
 
It is centered around the 1310nm band with 20nm channel spacing as defined by the ITU standard. With a reach of 2km, QSFP28 CWDM4 transmits 100G optical signals via a duplex LC interface.
Digital diagnostics functions are available via the I2C interface as specified by the QSFP28 MSA. The optical transceiver is compliant per the RoHS Directive 2011/65/EU.