Third harmonic-induced external second harmonic modulation distortion in injection-locked Fabry-Perot semiconductor laser

This paper unravels some novel observations on the effect of third harmonic input distortion on the second harmonic modulation at the output of a low-level injection-locked (IL) Fabry-Perot laser diode (FPLD) operating at a central wavelength of 1557.1 nm and directly modulated by a distorted sinusoidal fundamental signal. The important observation is that both the fundamental and second harmonic modulation components are suppressed upon illumination. The second harmonic suppression (2H) upon light injection is modified by the additional 2H generated through nonlinear mixing of fundamental and third harmonic (3H) components. At modulation frequencies where the fundamental suppression is less pronounced than the resultant 2H suppression, an overall suppression of second harmonic distortion (2HD) is observed. On the other hand, when the fundamental suppression dominates over the resultant 2H suppression upon light injection, an overall 2HD enhancement is noticed.