Self-sustained Picosecond Pulse Generation in a GaAlAs Laser at an Electrically Tunable Repetition Rate

Abstract

Picosecond pulse generation from semiconductor lasers at high repetition rate is generally accomplished by two different means: mode-locking or direct electrical excitation. The shortest ever pulses of below lps was generated from a passively mode-locked GaAlAs laser [1], while active mode-locking produces somewhat longer optical pulses. The pulse repetion rate of the mode-locked laser is determined by the length of the external cavity and cannot be varied easily. The rather critical optical alignment necessary for operating the laser in an external cavity makes these mode-locked semiconductor lasers somewhat inconvenient in practical applications. A second means of picosecond pulse generation is by directly pumping the laser with intense, short electrical pulses [2,3] or by large amplitude sinusoidal current modulation [4,5]. Optical pulses generated by such means have pulse widths in the vicinity of 15-35 ps. This scheme requires an external RF source for exciting the laser. In this work, we will show that by using a state-of-the-art high speed laser in the optoelectronic feedback configuration shown in Fig. 1, highly stable optical pulses (with jitters of <10fs), with pulse widths between 10 and 20 ps can be generated, with a very high repetition rate from 1 5GHz which can be electrically tuned. This scheme has the advantage of eradicating the necessity of any external RF drive and/or sensitive optical alignment.