Fast Frequency Shift of Laser Diode by Optical Short Pulse Irradiation

Abstract

It is possible to modulate frequency of a laser diode (LD) applying an irradiation on its active layer.¹ There have been considered several causes for the modulation phenomena. We have already confirmed optical modulation of a LD up to 200 kHz applying sinusoidal power modulated optical beam on the active layer of the LD.^2,3 The frequency modulation depth depends on the power of the irradiated optical pulse although it is quite small (- 4.3 × 10^-4/ W). The reason of the modulation is reduced to the photo-thermal effect. The upper bound of the modulation frequency is expected, however, higher than 200 kHz due to certain causes other than the photo-thermal effect. In order to explore the upper bound, we carry out an experiment to modulate frequency of a LD, whose wavelength is 780 nm, by irradiating its active layer with a very short laser pulse. Oscillation frequency of the LD may shift due to the fast change of refractive index of the laser material.