Mode-hopping noise reduction by rf modulation of the pump current of an injection semiconductor laser with an external cavity

An experimental investigation was made of the influence of rf modulation of the pump current on the mode-hopping noise of a semiconductor injection laser coupled to an external nonselective mirror. The modulation frequencies were of the order of the intermode interval of the system. When two or more modes were generated, the imposition of rf modulation on the laser pump current reduced the intensity of the mode-hopping noise in a separate spectral mode. The maximum reduction (by an order of magnitude) occurred at a modulation frequency equal to the frequency interval between the modes of the laser with the external cavity or to harmonics of this frequency. When one mode was generated, the imposition of rf modulation at the same frequency as the intermode interval increased the mode-hopping noise.