High sensitivity precision relativeintensity noise calibration standardusing low noise reference laser source

The intensity noise of laser diodes is an increasingly important parameter for broadband analogue and high data rate telecommunication systems. The authors describe a new primary calibration standard for measuring the relative intensity noise (RIN) as a function of frequency (up to 20 GHz) with high sensitivities (< –171 dBm/Hz). In addition a new optical technique has been developed based on a low noise optical source which provides an adjustable shot noise level. By comparing this flat noise spectrum with the test spectrum the main traceable path is provided by the measured DC photocurrent. Errors due to responsivity, gain, mismatch etc., as a function of frequency are significantly reduced and precisions of < 0.4 dB have been achieved.