What is excess RIN?

Relative intensity noise (RIN) is defined as the total quantity of photon noise within a given bandwidth.  Total noise from a laser typically includes shot noise, thermal/system noise, and light power (total photon energy per second) fluctuation.  The term RIN and excess photon noise have been often used interchangeably although it is critical to differentiate the excess photon noise from other sources of noise in applications where excess photon noise is limiting the performance. Excess RIN is informally termed to differentiate such without contribution from shot noise and thermal noise.