Modern data centers rely on high-speed optical links, and 100G optical transceiver modules (especially the QSFP28 form factor) are now foundational for this connectivity. 100G transceivers convert electrical signals to laser light over fiber, enabling top-of-rack switches to connect. A 100G optical module is a high-speed optical transceiver that is capable of transmitting data at a rate of 100 gigabits per second. These modules are used in a variety of applications, including data centers, telecommunications networks, and high-performance computing environments. In this. QSFP28 is the main form factor for 100G optical modules. This article reviews QSFP28 module types and key WDM technologies like CWDM and DWDM. It also covers major modulation formats ( such as NRZ, PAM4, and. The Cisco 100GBASE Quad Small Form-Factor Pluggable (QSFP) portfolio offers customers a wide variety of high-density and low-power 100 Gigabit Ethernet connectivity options for data center, high-performance computing networks, enterprise core and distribution layers, and service provider. Industry pundits have recently speculated that demand for 100G/400G switches may take off in 2019, prompting optical transceiver module vendors to sample data center switches with high data transmission rates earlier than expected.