OSNR is the ratio of the signal power to the noise power of an optical channel after passing through an optical network. It provides an estimate of how badly the noise power has affected the signal power. The higher the OSNR, the better it is for the overall system.

The general formula for calculating OSNR is:

OSNR=10*log(S/N)

where S is the signal power and N is the noise power, both expressed in watts or milliwatts.

OSNR values are most important at the receiver because a low OSNR value means that the signal will not be detected by the receiver. Typically, OSNR should be greater than 15 dB to 18 dB at the receiver, but this value will depend on many factors like the data rate, required BER etc. OSNR measurement methods are defined in IEC 61282-12 / b-IEC 61280-2-9 standards.

1. OSNR [dB] is the measure of the ratio of signal power to noise power in an optical channel . ​

2. It is key parameter to estimate performance of Optical Networks. It helps in BER calculation of Optical System.

3. OSNR is important because it suggests a degree of impairment when the optical signal is carried by an optical transmission system that includes optical amplifiers.

4. If we know the OSNR and the bandwidths, we can find Q and the BER It can be seen as the QoS at the physical layer of optical networks. OSNR is directly related to bit-error rate, which will lead to packet losses seen by higher layers.

5. OSNR indirectly reflects BER and can provide a warning of potential BER deterioration.

6. OSNR has long been recognised as a key performance indicator for amplified high-speed transmission networks to ensure network performance and reliability and it is related to many design parameter such as number or repeater/amplifiers ,reach ,available modulation formats etc.

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