HP 86037B, Instruction Manual

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7-3
Reference
Theory of Operation
cal modulator which modulates the lightwave signal from a tunable laser at a
frequency of up to 2.5 GHz. A polarization-maintaining fiber connects the tun-
able laser to the modulator to maintain a stable modulation index. This modu-
lated lightwave signal passes through the device under test, is detected and
converted back into a RF signal by an optical-to-electrical converter.
Figure 7-2. HP 86037B Block Diagram (standard and Options 111, 112, 113, 114)
The HP 8753 RF network analyzer measures the shift in phase of the RF signal
by comparing it to a reference derived from the signal driving the modulator.
The measured phase is numerically converted into a value for group delay. By
tuning the wavelength of the laser, we obtain group delay as a function of
wavelength and, after data processing, the dispersion of the device under test.
Increased wavelength accuracy is made possible by an external wavelength
meter which automatically measures and provides feedback on the wave-
length as the laser tunes. The wavelength meter may be supplied by the user.
The HP 83427A chromatic dispersion test set contains an instrument grade
receiver and modulator to ensure a stable and accurate recovery of the optical
signal. This test set was designed to be part of the HP 86037B.