Relative intensity noise of DFB LD's with near and far end reflections

The relative intensity noise (RIN) spectra of DC driven 1.3 mu m distributed feedback laser diodes under the influence of external reflections are measured for various currents and reflection lengths. The effective power reflectivities are 3 x 10(-4)-3 x 10(-3). The enhanced noise is observed when the relaxation oscillation frequency coincides with the external cavity frequency. It is also observed that the RIN spectra with the near end reflections differ from those with the far end reflections. The degradation of the RIN spectra is analyzed with the rate equations numerically. A new reflection noise model, which includes the carrier density change induced by the reflections, is introduced. The near and far end reflections are characterized well by this model. Furthermore, it is found that the reflection induced noise effect can be described well by the far end reflection noise model even when the reflection length is as short as 1 m.