5.9 Fiber Based Measurements
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5.9 Fiber Based Measurements
Laser light emits from an optical fiber in a conical shape, with an angle twice the
acceptance angle of the fiber. The acceptance angle is calculated by the numerical
aperture of the fiber and is defined as the inverse sine of the numerical aperture.
Fore typical single mode fibers the total angle of the emitted light is between 15° and
25°, for an angled connector (APC) the cone shifts by approximately 4° from the fiber
axis.
This expansion of the beam has to be considered to avoid overfilling the detector
and getting wrong results. On the other hand for measurements with high power fiber
lasers a certain gap between fiber tip and detector surface has to be kept to
decrease the power density.
Thorlabs offers fiber adapters with the most common connectors that are verified
with the S12xC series optical sensors and with most thermal sensors.
For large divergence angles or fiber measurements that are critical to back-
reflections it is recommended to use an integrating sphere based sensor from the
S14xC series.
Another good choice for fiber based measurements are the new „Fiber-Heads‟ of the
S15xC series. They plug directly to the meter and go without a disturbing cable
between sensor and console.
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