A swept wavelength meter provides a real-time wavelength calibration scheme for a swept laser. The calibration scheme generates an electrical signal from a swept optical output of the swept laser that is cyclical with respect to the wavelength of the swept optical output over a defined range of wavelengths. The point on the electrical signal at any given time provides an accurate phase for the swept optical output at that point. The electrical signal in turn is calibrated by generating calibration references from the swept optical output using known absorption lines within the defined range of interest. The wavelength of the swept laser is calibrated as a function of a reference wavelength from the known absorption lines and the phase at the given point. Simultaneously forward and reflective measurements may be taken, with the forward measurement being used as a normalizing measurement for determining insertion and return loss automatically for a device under test.