Abstract

The intrinsic wavelength stability of current free-running DFB lasers implies that wavelengths in a DWDM network could be periodically measured and corrected to keep them within tolerances. The main element of the wavelength controller is based on the measurement of the surface emission angle of a sum-frequency (SF) signal generated by the interaction of two counterpropagating near-infrared waves in a semiconductor multilayer waveguide.¹ This angle is related to the optical frequency-difference between the two input signals. We have shown that a frequency-difference of less than 2 GHz around 1.3 µm can be resolved with a simple optoelectronic setup using a photodiode sensing array.² In this paper we incorporate into the setup a reference wavelength as one of the two inputs. This reference is obtained by locking a DFB laser to an atomic transition of Krypton at 1.318102 µm using the optogalvanic effect. We describe a calibration procedure for measuring the frequency-difference between the reference and another laser. We then show absolute control, within a few GHz, of a slave laser at 1.304 µm by adjusting its current to obtain a prescribed SF emission angle, i.e. a prescribed wavelength. This technique could also be used to control laser frequency in the 1.55 µm communication band. The frequency resolution demonstrated in our work is already compatible with the projected requirements of next-generation high bit rate DWDM networks.

© 1993 Optical Society of America