User`s guide

Definition of Terms Specifications
Agilent 81618A/9A and Agilent 81623B/4B/6B/8B Optical Heads, Fourth Edition
27
Relative uncertainty due to speckle noise
This is the uncertainty of the power reading when using a coherent source.
This is due to a variation of the power meters responsivity caused by
optical interference
1
between different optical paths within the power
meters optical assembly.
Conditions: constant wavelength, constant power level, angled connector
as specified, linewidth of source as specified, temperature as specified.
1
Incoming light to the integrating sphere undergoes numerous internal
reflections (as many as several hundred) prior to hitting the detector. If the
source is sufficiently coherent, a complicated interference pattern (speckle
pattern) appears spread over the whole sphere volume. Slight changes of
the ambient conditions (temperature, vibration, shock) affect particular
optical paths which consequently changes the speckle pattern and results
in an instability of the head power reading (speckle noise).
Measurement: In contrast to the spectral ripple definition the source
wavelength isn’t stepped when measuring speckle noise.
Relative uncertainty due to polarization
Also termed polarization-dependent responsivity (PDR), the relative
uncertainty due to polarization is the uncertainty of the displayed power
level on the input polarization state, expressed as the difference between
the highest and the lowest displayed power. Uncertainty figures are based
upon a 95% confidence level.
Conditions: laser source with variable polarization state, generation of all
possible polarization states (covering the entire Poincaré sphere),
constant wavelength, constant power level, angled connector as specified,
temperature as specified.
Changes in the source wavelength have a similar effect on speckle noise
as environmental changes, because they cause fluctuations in the
interference pattern. If the source coherence length is small compared to
the effective path length, the interference pattern disappears and relative
uncertainty due to speckle noise becomes negligible.
NOTE