Microwave modulation of a quantum-well laser with and without external optical injection

We compare three microwave modulation methods experimentally and theoretically using a semiconductor quantum-well (QW) Fabry-Perot test laser: (1) direct microwave current modulation of the test laser (electrical modulation); (2) optical modulation by an external single-wavelength pump laser with a modulated optical injection power; and (3) electrical modulation of the test laser that is injection locked by an external single-wavelength pump laser with a constant injection power. This is the first direct comparison of the three modulation methods on the same QW laser, to the best of our knowledge. The bandwidth of optical absorption modulation is 7.7 GHz, which is 1.45 times the direct electrical modulation bandwidth (5.3 GHz) at a bias current of 30 mA in the test laser. On the other hand, the electrical modulation of the test laser under injection-locking condition has a significantly higher modulation bandwidth (10.5 GHz) than both the electrical and optical modulation methods.