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The state machine always starts in the Init StateINIT state.  In this state, all temperature controllers are enabled, while all phase controllers are disabled.  

In the Startup StateSTARTUP state, the power supply voltages, ethernet connection between the Tx and Rx units and environmental conditions are checked. All units are equipped with external humidity, pressure and temperature sensors.  

After the thermal stabilization of all internal modules (Warming Up StateWARMING UP state), the Tuning State TUNING state is reached. This state consists of 30 sub-states.  See attached manual for details on this.  The basic tasks that are performed in these sub-states are: starting the laser, identification of MZM and VOA best working points, checking if the optical power levels are sufficient, stabilizing the optical power at different photodiodes and closing the phase and amplitude control loops for the optical and RF signals in the Tx and Rx units.

When all phase control loops are closed and the RF output power at Rx is stabilized, the state machine enters the Ready StateREADY state.  The latter has two basic sub-states: Locked LOCKED and UnlockedUNLOCKED.  Sub-State Locked consists of two additional sub-states. As before, see the manual for more details on these states and sub-states.  In  

In summary however, in Sub-State LockedLOCKED, all phase loops are locked and some other actuators are in their nominal working regions (laser and fiber spool temperatures in Tx module, RF phase shifters, RF attenuators, MZM bias voltage, VOA voltage). The Locked LOCKED state is indicated as an illuminated green LED diode on the front panel of the Tx and Rx units and with the LOCKD caption on the LCD display.

If any of these actuators approaches its working region boundary and all the phase control loops are still closed and the output RF power at Rx unit is sufficient, then the system goes in Sub-State Semi-Locked.  This state is indicated as to the SEMI-LOCKED state.  The latter is indicated by a blinking green LED on the front panel of Tx and Rx units and as with the blinking LOCKD* caption on the LCD display.

In the case that any of the phase control loops is unlocked or the output RF power is too low, then the system goes in to the SubUNLOCKED sub-State Unlockedstate.  If the timer exceeds the 15 minutes limit, then the state machine enters the Shutdown SHUTDOWN state and procedure and state.

Also, the Tx unit receives data from Rx via the ethernet connection at all time. In  In the case of a broken ethernet connection, the system goes from Locked LOCKED to UnlockedUNLOCKED. This may eventually cause the system to go to the Shutdown State if SHUTDOWN, unless the connection is not reestablished within 10 minutes.

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