Agilent Technologies 5517B Operation And Service Manual page 73

8-40. When the state machine places the liquid crystal in its passive state, the liquid crystal rotates the polarization
of both components by 90'. In this state, the polarizer blocks the vertical component and passes the horizontal
component. The voltage out of the photodiode amplifier is proportional to the horizontal component and is held by
the negative input of the subtracting sample and hold circuit. The error signal output of the subtracting sample and
hold circuit is proportional to any difference in power between the two components.
NOTE
A TILDE ("-") PRECEDING ALL SIGNALS INDICATES NEGATIVE-TRUE
LOGIC.
8-41. After the optical mode tuning has stabilized, LOCKED TUNED OPTICAL (LTO) signal is held true enabling
the reference frequency output. Proper laser tuning and reference receiver operation is indicated by -REF ON true. -
REF ON false will cause the state machine to reset to the warmup mode.
8-42. Laser Assembly Optics
8-43. The laser assembly optics ensure correct laser frequency polarizations and also collimate the laser beam. When
the laser beam leaves the laser assembly, the horizontal component is polarized parallel to the base of the HP
5517B. The vertical component is polarized perpendicular to the horizontal component. The laser beam is collimated
to minimize variations in beam diameter as it travels away from the laser head.
Figure 8-8. Liquid Crystal Timing Diagram (Optical Mode)