The TLS-101 is a compact tunable laser source for daily test and measurement applications. The laser can be step-tuned across the C-band communication channels with a tuning resolution of 50 GHz in less than 20 ms. The internal wavelength locker assures that the wavelengths or frequencies of the output light are exactly on the ITU grid of the DWDM channels. The light source has three operation modes: fixed wavelength output at any of the 89 grid wavelengths (or frequencies), single-trip wavelength (frequency) scan with a user-set range, step, and speed, and round-trip frequency scan. Finally, the TLS-101 comes with USB, RS-232, Ethernet, and GPIB communication ports for easy, flexible interface with computers and other instruments. In particular, the Ethernet port allows the instrument to be controlled remotely, from home, office or a hotel room when on travel. The TLS-101 is an ideal source for WDM component testing, sensor interrogation, optical coherence tomography (OCT), PMD and PDL characterization, and for use in general purpose test and measurement applications.