The excess noise characteristics of InGaAs/InP APD in consideration of nonlinearity effect

In general, the excess noise of avalanche photodiodes (APDs) will increase with incident mean optical power (P-in). However, it is found that the excess noise of InGaAs/InP APD decreases rather than increases with P-in in the case of high gain. The experimental and simulated results reveal that this phenomenon can be attributed to the nonlinearity effects, which results in the degradation of gain of APDs. And the nonlinearity effect is more significant with larger gain. Consequently, the excess noise will decrease due to the decreases of gain. For free space optical (FSO) communication systems which commonly operates the APDs at high gain, this discovery can be used to determine the optimum threshold of receivers to achieve the minimum bit error rate (BER).