FFC-100 Fiber Frequency Comb Quick Start Guide
Operating the FFC
This document provides instructions on how to operate the Vescent Photonics FFC-100 when controlled by the Vescent SLICE-FPGA.
FFC-100 rack-mountable Fiber Frequency Comb module
Power cord for your country (if known)
Instructions on how to download & install control software
Final Test Documentation
Other items depending on specific configuration
Absolute Maximum Ratings and Power Input
Note: All modules designed to be operated in a laboratory environment.
Tab. 1: Absolute Maximum Ratings
| Parameter || Rating
| Environmental Temperature || >15°C and <30°C
| Environmental Humidity || <60%
| Environmental Dew Points || <15°C
| Maximum AC Line Input Current || 2 A
The FFC-100 employs a proprietary design hybrid power supply that is both low noise and capable of accepting a range of AC input line voltages. It will accept input line voltages within the ranges shown in table 2.
Tab. 2: Input Voltage Specifications
| Parameter || Value || Units
| Input Line Voltage || 100-240 || VAC
| Frequency || 50-60 || Hz
| Phase || 1 phase
| User-serviceable fuse1) || T 2.0 A L 250V
| || If this instrument is used in a manner not specified by the manufacturer in this manual or other relevant literature, protection provided by the instrument may be impaired.
| Successful implementation of the FFC-100 depends critically on the design of the whole system: FFC-100, phase locking electronics, and any references to which the FFC is locked or vice versa.
Ensure all cables and fibers are connected according to the connection diagram figure 2
Turn on the power to the Fiber Frequency Comb (FFC) and the FPGA, as well as the reference laser.
Fig. 2: FFC-100 electrical and optical connection diagram (Click for larger image)
FFC Start Up GUI
Touch the “System Off” button at the top of the front panel screen (figure 3
) to bring up a drop-down menu. Select “Standby” (figure 4
) to turn on temperature control of the pump diodes and oscillator cavity.
Fig. 3: The FFC-100 GUI in off state
Fig. 4: Select Standby laser state
Once the temperature servos have stabilized and “Standby” has stopped blinking, touch the “Standby” drop-down menu (figure 5
) and select “Laser On” (figure 6
). The FFC should commence lasing and the Mode-locked indicator should turn green (figure 7
Fig. 5: The FFC-100 GUI: in Standby mode
Fig. 6: The FFC-100 GUI: Standby to System On
Fig. 7: System On
If necessary, adjust oscillator current by either holding down the “Osc” touch screen button and typing in a desired set-point (figure 8
), or briefly pressing the button and using the two control knobs (left changes digits, right adjusts values) to set a desired value.
Fig. 8: Adjust oscillator current via keypad
Cavity temperature can be adjusted in the same way.
Touch the “PZT” touch screen button (figure 9
) to bring up a drop-down menu and select “Full Range x20” to enable the PZT servo.
Fig. 9: Select PZT Gain
The SLICE-FPGA dual-channel Offset Phase Lock Servo can be used to phase lock ƒCEO to a reference (TBD) and ƒopt to a reference laser such as the Rio Planex.
If you have not already done so, install Python and the FPGA software for controlling the SLICE-FPGA dual Offset Phase Lock Servo.
Open a WinPython command window and navigate to the folder “GUI and Firmware”.
Start the SLICE-FPGA control GUI
by typing “python XEM_GUI3_VPv4.py”, figure 10
Fig. 10: Start FPGA GUI from Terminal
A start-up menu should appear (figure 11
). Make sure “superlaserland_v12.bit” is selected and select an appropriate clock option. Press OK.
Fig. 11: FPGA GUI Start Screen
Navigate to the “Filter Settings” tab and select “Narrowband (6MHz)” for both DDC0 and DDC1 (figure 12
Fig. 12: Set Loop Filter Bandwidth
Navigate to the “CEO Lock” tab and adjust the “Offset DAC 0” slider near the top left by clicking and dragging the slider until the the data in the Baseband IQ plot is circular (figure 13
). This centers the beat note near the reference frequency. It is also possible to adjust the FFC-100 oscillator current on its front panel to make this adjustment.
Fig. 13: Centering ƒ(CEO) on reference frequency (Baseband IQ optimization)
Press the “Lock” button (figure 14
, top middle). If the system doesn’t lock, change the VCO sign to the opposite polarity (top right) and try again. If the system still won't lock, try lowering the Kp
value (bottom left).
Fig. 14: Locking ƒ(CEO)
Navigate to the “Optical Lock” window. Center the beat note near the reference frequency: adjust the “Offset DAC 1” slider (or your reference laser frequency) until you see a circular Baseband IQ diagram (figure 15
Fig. 15: Centerig ƒ(opt) on reference frequency (Baseband IQ optimization)
Press the “Lock” button (figure 16
). If ƒopt
doesn’t lock, change the VCO sign to the opposite polarity and try again. If the system continues to not lock, lower the Kp
Fig. 16: Locking ƒ(opt)
Adjust PID settings (bottom middle of figure 16
) accordingly to lower the integrated phase noise of each parameter (fCEO
). The default settings provided in the software are a good place to start but tweaking the values can often improve performance.
Slow Loop Feedback
Slow loop functionality will be provided in a near-term software update.
Open your computer’s device manager from the control panel and find the COM port number for “STMicroelectronics”. Never assume that this number is the same as previous times. (If it doesn’t appear, make sure your computer is connected to the FFC.)
Navigate to the “Slow Loop” tab in the GUI
and enter the COM port number into “FFC COM Port”.
The PZT setpoint is set to an intermediate value (50V) to keep the servo from railing. This can be adjusted if desired.
Click “Activate Temperature Slow Loop”.