Teledyne Lecroy IQS25, Руководство оператора

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Optical Modulation Analyzer
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Appendix 3: OMA Measurement Definitions
I and Q Bias Offset
The bias offset is a measure of how far the center of the constellation is with respect to the ideal center
point. For QPSK and QAM modulation formats, the ideal center point is [0, 0] (I, Q). It is more convenient to
represent the bias errors in percentages since this makes it independent of the average optical power.
Additionally, the bias error can be separated into orthogonal components (I and Q) as shown in Equation
1 to help identify the origin of the bias error. Since the electrical to optical transfer function of optical
modulators is typically non-linear, a 5% bias offset as measured in the optical domain may not
necessarily correspond to a 5% error in bias voltage.
Equation 1 - I and Q Bias offset calculations
I and Q Bias offset for QPSK