The Keysight Technologies 81950A compact tunable laser source is step-tunable for setting channel frequencies within any grid in the C- or L-band. With high output power up to +15 dBm, narrow linewidth of 100 kHz, and offset grid fine-tuning capability, the 81950A is a universal source for realistic loading of the latest transmission systems. It is available with C-band or L-band wavelength coverage. The 81950A can reach any wavelength point within its specified wavelength range just like all other Keysight tunable lasers. In this mode, code compatibility with existing test setups based on Keysight's range of full-size and compact tunable lasers is a great asset. In system loading applications, it may be preferable to grid-tune the laser like system transmitters, simply by changing the channel index. The channel grid is adjustable to standard ITU-T grid spacing like 50 GHz, and to arbitrary grids. Likewise, the zero frequency (base channel) of the chosen grid is adjustable. A 12 GHz fine-tuning range allows de-tuning the frequency.