Simultaneous reduction of IMD3 and IMD5 in bisection laser diode by feedback second harmonic injection

Abstract

This paper reports a scheme for reducing third and fifth order intermodulation distortion in 1.3µm gain lever laser diode. Third and fifth order intermodulation components are reduced in the laser diode output by second harmonic frequency signals which are extracted from the laser diode itself. The number of RF components required in the linearization circuit for distortion reduction is significantly reduced in this scheme. The active region of the laser diode is split into two sections at a ratio of 0.97:0.03 for realizing gain lever effect. The longer and shorter section currents are fixed as 20mA and 5mA, respectively, corresponding to maximum gain lever. The rate equation approach is used for the analysis. In this scheme, third and fifth order intermodulation components are simultaneously reduced, by injecting second harmonic of two tone signals with appropriate amplitude and phase. A 14.7dB and 9.4dB improvement in third order and fifth order intermodulation respectively, are predicted at 2.4GHz. The magnitudes of third and fifth order intermodulation products are calculated from analytical expressions and the results are found to agree with simulation. Further the effect of RF carrier frequency and channel spacing on distortion reduction is also investigated.