The wavelength of light emitted by a laser and modulated by a frequency response modulator is determined from the power of the emitted light and the current drawn by the modulator. From the temperature and current applied to the modulator and the optical power of the emitted light; the wavelength of the beam of light is determined as a function of a ratio of the current and power for each temperature of operation. As the wavelength of the emitted light shifts, for example as the laser ages or the laser temperature shifts, the inventive methods and devices then detect the wavelength shift and implement any necessary adjustments in the operating conditions of the laser diode. For example, a thermoelectric cooler can be used to heat or cool the laser diode as necessary to thereby adjust the wavelength of the emitted light.