3-23
IM 735302-01E
Preparing for Measurement
Ripples in the 1350–1450 nm Area
Water (OH-) ions present in the monochromator absorb light in the 1350–1450 nm area,
resulting in ripples in the measurement waveform. Either set a coarser resolution or use
the monochromator in a lower-humidity environment to reduce the amount of ripples.
Waveforms with Resolutions of 0.020 nm
When the resolution is set to 0.020 nm for measurements of a light source such as a
DFB laser in which with the spectral width is narrower than the instrument’s resolution,
very small spikes may occur at the skirts of the waveform. This type of spike occurs due
to characteristics of the optical block and is not an indication of any problem. Even if such
spikes occur, satisfactory performance in terms of resolution, dynamic range, and the like
can be ensured. These spikes will disappear if the resolution is set to a coarser value.
Second-Order Diffracted Light
The monochromator in this instrument uses a diffraction grating, and when light in a
certain wavelength range is input, a “grating ghost” of second-order diffracted light
appears.
Therefore, it is important to understand this distinctive characteristic in order to correctly
analyze the measured results from the instrument.
The graph below shows the correlation between the wavelength displayed on screen and
the actual wavelength.
The displayed wavelength is on the horizontal axis, with the true wavelength on the
vertical axis. The solid lines in the graph indicate correspondences between displayed
and actual wavelengths. The thick solid line is the correlation with the correct light
spectrum (of course, the displayed wavelength and actual wavelength match), and
the thin solid line shows the correlation with the ghost spectrum of the second-order
diffracted light.
For example, if 633 nm light is input, a horizontal line is drawn at 633 nm on the vertical
axis, and the point of intersection on the graph of the line is the displayed wavelength.
From this, you can see that besides 633 nm, a grating ghost appears at 1266 nm.
3.8 Important Points During Measurement
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