1-4
IM AQ6376-01EN
1.2 Measurement
Averaging <<See section 4.10 for the operating procedure>>
This function performs multiple measurements and displays the average values.
The function is used in cases such as: when the light source’s level is fluctuating; when
measuring a modulated signal of several kHz or less; when the waveform is disrupted
and difficult to measure; when it is necessary to obtain even higher measurement
sensitivity.
Power spectral density Display <<See section 6.4 for the operating procedure>>
The power per 1 nm is called the power spectral density.
The level axis of the AQ6376 indicates the absolute power per wavelength resolution.
For example, if the resolution is set to 0.1 nm, the power per 0.1 nm will be displayed.
Since the optical spectrum of such devices as a gas laser or a laser diode is narrower
than the wavelength resolution of the instrument, the entire power is accommodated
within the band of a resolution. Therefore, the measured power (peak level) is equal
to the total power of the light source. This instrument has been calibrated to display
accurate power under such conditions.
On the other hand, natural light or lights such as fluorescent lamps or LEDs, have,
in many cases, optical spectrums wider than the wavelength resolution set for the
instrument. Therefore, if the instrument measures these lights, measured power will vary,
depending on the resolution setting.
In order to deal with this issue, the instrument is equipped with the dBm dBm/nm soft key
to allow the level axis displays to switch from the absolute power (dBm, mW, μW, nW,
pW) per resolution to power spectral density (dBm/nm, mW/nm, μW/nm, nW/nm, pW/
nm).
In the case of power spectral density displays, a measured value is converted to power
per 1 nm. Therefore, whatever resolution is used for measurement, certain measured
values will always be available.
Differences in usage between the absolute power display and the power spectral density
display are shown below:
Absolute power display: measurement of light sources with narrow spectrum widths,
such as gas lasers or laser diodes.
Power spectral density display: measurement of light sources with wide spectrum widths,
such as natural light or LEDs.
If the subtraction function between traces is used for such cases as A-B(A/B)→C or
B-A(B/A)→C, results will be the same whether the absolute power display or the power
spectral density display is used.
Since the power measurement function performs different calculations according to the
level axis display, correct results will be available whichever display is employed.
Note that, if the NF measurement function (ANALYSIS 2 EDFA-NF soft key) and the
WDM analysis function (ANALYSIS 2 WDM soft key) are executed, the level axis display
will be forcibly changed to the absolute power display.
Note
Specifications such as level accuracy, measurement level range, and level linearity of the
instrument are provided for the absolute power display.
