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Noise-equivalent power
 
 
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Noise-equivalent power (NEP) is a measure of the sensitivity of an optical detector or detector system. It is defined as the signal power which gives a signal to noise ratio of 1 for an integration time of half a second, or more technically the radiant power that produces a signal to noise ratio of unity at the output
Output

Output is the term denote either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the model ing, system design and system exploitation....
 of a given optical detector at a given data-signaling rate or modulation
Modulation

In telecommunications, modulation is the process of varying a Periodic function waveform, i.e. a tone, in order to use that signal to convey a message, in a similar fashion as a musician may modulate the tone from a musical instrument by varying its volume, timing and Pitch ....
 frequency
Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
, operating wavelength
Wavelength

In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek language letter lambda ....
, and effective noise
Noise

In common use, the word noise means unwanted sound or noise pollution. In electronics noise can refer to the electronic signal corresponding to acoustic noise or the electronic signal corresponding to the noise commonly seen as 'Noise ' on a degraded television or video image....
 bandwidth .






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Noise-equivalent power (NEP) is a measure of the sensitivity of an optical detector or detector system. It is defined as the signal power which gives a signal to noise ratio of 1 for an integration time of half a second, or more technically the radiant power that produces a signal to noise ratio of unity at the output
Output

Output is the term denote either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the model ing, system design and system exploitation....
 of a given optical detector at a given data-signaling rate or modulation
Modulation

In telecommunications, modulation is the process of varying a Periodic function waveform, i.e. a tone, in order to use that signal to convey a message, in a similar fashion as a musician may modulate the tone from a musical instrument by varying its volume, timing and Pitch ....
 frequency
Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
, operating wavelength
Wavelength

In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek language letter lambda ....
, and effective noise
Noise

In common use, the word noise means unwanted sound or noise pollution. In electronics noise can refer to the electronic signal corresponding to acoustic noise or the electronic signal corresponding to the noise commonly seen as 'Noise ' on a degraded television or video image....
 bandwidth . Therefore, it is desirable to have as low an NEP as possible, since a small NEP means a high signal to noise ratio (SNR).

The advantage of expressing a detector's sensitivity in NEP as opposed to a SNR is that the NEP remains constant for a given detector. For example, if a detector was placed 1 meter from the source it was observing, it would have a particular SNR. If the detector was then moved to 2 meters from the source, the amount of power from the source reaching it would be reduced but the noise could be assumed to stay the same, thus the SNR would have been reduced. However the NEP would remain the same for both of these measurements.

Note 1: Some manufacturers and authors define NEP as the minimum detectable power per square root bandwidth. When defined this way, NEP has the units of watts per (hertz
Hertz

The hertz is a measure of frequency per unit of time, or the number of list of cycles per second. It is the SI base unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts....
)1/2. Therefore, the term is a misnomer, because the units of power are watts.

Note 2: Some manufacturers define NEP as the radiant power that produces a signal-to-dark-current noise ratio of unity. The NEP measurement is valid only if the dark-current noise dominates the noise level
Noise level

In telecommunication, noise level is the noise power, usually relative to a reference.In atmospheric sound transmission, noise level is the noise power of the longitudinal sound wave relative to a point of reference....
.