3-22
IM AQ6373-01EN
Waveforms when set to high resolution
When the resolution is set high (to 0.01 nm or 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.
Switching the diffraction order or high order optical cut filter during a sweep
There are times when the diffraction order or high order optical cut filter is switched from
the sweep interval. All switching is performed automatically. When sweeping a range
including a switching point, the sweep pauses after reaching (measuring) the switching
point, then the filter/order is switched, the sweep parameter (grating speed, etc.) is
calculated, and sweeping resumes.
Switching of the Diffraction Order
The instrument can measure wider bandwidths by changing the diffraction order
according to the wavelength to be measured. The instrument switches between second
and first order diffracted light for its measurements. The division of orders is shown in the
figure below.
Order switching point
First order light
Division of diffraction orders
A: 450nm
B: 470nm
Second order light
350nm
1200nm
A: Switches at 450 nm when the center wavelength is set to 460 nm or higher
B: Switches at 470 nm when the center wavelength is set to less than 460 nm
or
A: Switches at 480 nm when the center wavelength is set to 490 nm or higher
B: Switches at 500 nm when the center wavelength is set to less than 490 nm
When the order is switched, the effective resolution changes. Thus, when measuring a
light source having an optical spectrum with a wide wavelength range, the measurement
level becomes discontinuous at the point where the order is switched, and steps can
occur. To keep these steps as far as possible from the center of the screen, the switching
point changes according to the center wavelength setting as shown in the figure above.
3.7 Important Points During Measurement