Calculating Power in Decibels. In an optical communications system or electrical power transmission system, the power or signal often is transferred between several components. The decibel (dB) is a convenient unit to measure the relative power levels. If the input power to a device is P₁ and the output power is P₂, then P₂/P₁ is the ratio of power transmitted, thus representing efficiency. This ratio in decibels is written as

The power terms must be expressed in the same units. Write a computer program that will calculate the dB value for the transmission of power between two components of a fiber-optic system (e.g., light source to fiber). Then, extend this calculation to three components (e.g., light transmitted from source to fiber and then fiber to a detector).

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P₂ P₁ dB 10 log.