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IM AQ6376-01EN
Preparing for Measurement
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App
Index
Explanation
Types of Optical Fibers
The instrument can use single mode optical fibers with core diameters of 5 to 9.5 μm,
and multimode (GI) optical fibers with core diameters of 50 and 62.5 μm. Functions may
be limited or restricted depending on which type of optical fiber is used. The table below
shows which of the typical types of fiber may be used and the limitations on their use.
When measuring wavelengths of 2000 nm or greater, use an optical fiber (e.g., fluoride
fiber) with small infrared absorption.
Limitations on Wavelength Resolution
The maximum wavelength resolution for the instrument is 0.1 nm, which is only
obtainable when using a single-mode optical fiber with a core diameter of 9.5
μ
m or less.
As shown in Table, the maximum wavelength resolution decreases when optical fibers
with thicker core diameters are used.
Setting a resolution value finer than those shown in the table below will simply result in
an inaccurate measurement level without improving resolution.
Optical fibers with a thick core diameter are especially useful for inputting spatial light for
measurement, but they have poor resolution.
Choose the best type of optical fiber for your particular application.
Note that the instrument is designed for input through optical fiber only. It will not work
with inputs that do not pass through optical fiber, such as direct input of a gas laser
beam to the optical input connector, or bonding an LED to the optical input connector. It
is important to note that optical spectrum measurements taken through such inputs are
completely unreliable.
For spatial light measurements, input the spatial light to the optical fiber and from the
optical fiber to the instrument. A variety of adapters are available for this purpose.
Summary of usable optical fiber types and usage limitations
Optical Fiber Type
Obtained Wavelength
Absolute Level
Resolution (in nm)
Accuracy
Type Core Diameter
SM 5
0.10
NG
SM 9.5
0.10
OK
GI
50
0.10
NG
GI
62.5
0.10
NG
SI
50
0.10
NG
SI
80
0.20
NG
SI
100
0.50
NG
SI
200
1.00
NG
SI
400
2.00
NG
SI
800
2.00
NG
Level Accuracy below the Cutoff Wavelength (Short Wavelength) of a
Connected Optical Fiber
With wavelengths at or below the cutoff level of the connected fiber, light propagates
through the optical fiber in multiple modes. When high-coherent light from a light source
such as a gas laser or DFB-LD light source propagates in multiple modes, speckle noise
contained in the optical fiber output light may become unstable by the optical fiber’s form,
resulting in an inaccurate measurement level.
In such cases, improving the coupling between the light source and the optical fiber will
lessen the level inaccuracy.
2.1 Alignment Adjustment
