Quantum noise in superluminescent diodes

Intensity noise in a superluminescent diode (SLD) has been studied over the frequency range from 100 Hz to 2 MHz. The"1/f"noise which dominates at low frequencies (< 50 kHz) is superceded by a flat "white noise" spectrum at higher frequencies (> 500 kHz). A more extensive investigation has been carried out in this higher frequency regime, where the intensity noise is assumed to result from quantum fluctuation effects. For a given SLD driving current, the excess noise power is found to be a linear function of photodetector current to the maximum observed level of 12 dB. These results agree well with the behavior predicted by a quantum amplifier model for the SLD.