The CLT2A0CRTX-L TOSA is a cooled, 4x25Gb/s, 1310nm transmit optical sub-assembly, for 100G applications, consisting of four high reliability, high performance DFB lasers ,internal driver and an optical multiplexer to combine the outputs from the four lasers. These elements are packaged in a hermetic, planar package with an LC receptacle. The electrical interface is through two flex connects. The TOSA is intended for use in QSFP28 modules, serving the 100G BASE-LR4 application for links up to 10km, per IEEE 802.3ba standard