5-6
IM AQ6373-01EN
LIN SCALE
This key is used to set the main scale to linear scale.
Settings per 1 DIV are set in the reference level.
LIN BASE LEVEL **.*mW
Value when the vertical axis is linear scale, you can set the level scale low-end. This is
not available when using a log scale.
The setting range is 0.0 to REF level x 0.9. Settings can be adjusted in steps of 0.1. The
value changes in steps of 1 if you press the COARSE key. Values can only be set in the
instrument set for the REF level.
When the setting is changed, the displayed waveform is redrawn according to the
changed scale.
The scale display in the upper left part of the waveform is 1/10 the value (*W/D) of the
reference (REF) level minus the low-end (BASE) level.
For information on the REF level setting, see section 5.4, "Setting the Reference Level."
LEVEL UNIT dBm dBm/nm
When the vertical axis is log scale, the display toggles between dBm and dBm/nm.
dBm: Power per resolution (absolute power)
dBm/nm: Power per 1 nm (power density)
For information on the use of dBm and dBm/nm, see “Power Density Display” in section
2.2, “Measurement.”
LEVEL UNIT mW mW/nm
When the level axis uses a linear scale, the display switches between nW, μW, mW, or
pW (absolute power), and nW/nm, μW/nm, mW/nm or pW/nm (power density).
Power Density Display
The power per 1 nm is called the power density.
The level axis of the AQ6373 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 density (dBm/nm, mW/nm, μW/nm, nW/nm, pW/nm).
In the case of power 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 density display
are shown below:
5.2 Horizontal/Vertical Axis Settings