Novel instrumentation for measurement of relative intensity noise

Laser diode relative intensity noise (RIN) metrology capabilities have been developed and demonstrated, providing significantly improved sensitivity and accuracy compared with existing methods. The novel use of the demonstrated reference noise source has shown significant advantages, achieving improved sensitivity, reducing measurement accuracy as low as ±1 dB and simplifying the system calibration methodology, thus improving flexibility. Laser RINs of between 10 and 14 dB below the shot RIN have been shown (typically −170 dBm/Hz), which is a direct result of the improved system sensitivity. A neodinium yag 1319-nm ring laser provided a ‘cold’ reference source, in a similar manner to that used in RF electrical metrology. Application of the ‘flat’ low noise optical RF noise source from 10 MHz to 20 GHz has been demonstrated for the first time in optical RF metrology, providing a calculable reference traceable via the incident optical power received. Because of the simplistic nature of this approach, system calibration can be performed for each RIN measurement that is carried out, reducing measurement uncertainty associated with RF mismatch, system linearity and loss. High specification components have been assessed individually and in the combined system indicating an overall system noise figure of 2–3 dB over the 10 MHz to 20 GHz frequency range (−171 to −172 dBm), some 4–5 dB better than previously reported.