MGPA (CFA) Mini Fibre Amplifier System

System Overview

Fibre amplifier system block diagram description:

The fibre amplifier system comprises a central CFA (A132306xxx) unit. An external Device Under Test (DLC) unit, identified as (A2xxxx), connects to the main system via a DVI cable. This DVI signal is processed by a Mini Fibre Amplifier (MFP) module, model (A82201xxx), which is part of the overall CFA system. The MFP module also interfaces with a Control Electronics System (CES) module, model (A72402xxx), via a USB-C connection. The CES module contains an optical isolator and a waveguide doubler. The CES module outputs an armoured PMxxx FC/APC fibre, which connects to the CFA system. The MFP module has a PM980 fibre output that connects to an external Wavemeter or Power meter for monitoring. The CFA system itself also provides a PM980 fibre output for external measurement. The CES module receives power from the mains supply and is connected to an interlock system.

Turn ON Sequence

1. Connect the DLC to the DVI-DL input located in the rear of the CFA chassis. Note that, while this input appears to be embedded within the CFA chassis, it is actually connected to a headboard housed within the MFP; exiting this headboard is a USB-C cable which directly connects to, and hence operates, the CES seed laser.
2. Power on the DLC by flipping the switch on the rear of the DLC to its ON position.
3. On the front panel of the DLC, turn the keyswitch from the STANDBY position to the RUN position.
4. Turn the selector knob located immediately above the keyswitch on the front panel of the DLC to select the Temp set option, and verify that the temperature shown on the DLC display matches that of the Test Report (namely, 25.2°C).
5. Turn the selector knob to select the Temperature option and wait (for approximately 5-10 minutes) until the temperature shown on the DLC display both stabilises and matches the (25.2°C) temperature from the previous step.
6. Once the temperature has stabilised, ensure that the Current knob (located on the far left-hand side of the DLC front panel) is rotated fully counterclockwise, thus setting the current delivered to the seed laser to zero.
7. Flip the DLC power switch from the OFF position to the ON position.
8. Using the same selector knob from previous steps, select the Voltage option and verify that the voltage displayed on the DLC is approximately 1.1V.
9. Select the Curr max option using the selector knob and, using the appropriate trimpot located in the rear of the DLC, increase the maximum current to a value of 500mA.
10. From the pickoff port located above the DVI-DL input on the rear of the CFA chassis, remove the black fibre dust cap.
11. Retrieve a power meter, set to record 1064nm light, and place it at the just-uncovered pickoff output port.
12. Using the selector knob from previous steps, select the Current option. Then, slowly increase the current to the operational setpoint of 475mA. Verify that the power recorded by the power meter approximately matches that given in the Test Report (namely, 35uW). Note that the observed power here is dependent on the laboratory temperature (and in particular, the temperature of the fibres within the amplifier system). Should the power differ drastically from the expected value, refer to the Troubleshooting section below.
13. Inject the pickoff light into a wavemeter using a PM980 fibre, and verify that the wavelength of the seed laser is at 1064nm, or a given wavelength of interest. If this is not the case, refer to the Troubleshooting section below.
14. Once the seed laser wavelength has been verified, proceed to set up once more the power meter to record the pickoff output power.
15. With all seed-verification steps completed successfully, proceed to connect the CFA to the mains via an IEC cable; then, power on the CFA by flipping the switch on the rear of the CFA.
16. Turn the keyswitch on the front panel of the CFA to from the STANDBY position to the RUN position, ensuring that the AMP LED glows yellow. If the keyswitch was already in the RUN position, turn it into the STANDBY position and then back into the RUN position.
17. Using the selector knob and associated buttons on the front panel of the CFA, ensure that the Current Setpoint value for Stage 1 matches that of the Test Report (namely, 2A). Note that the setpoint can be set to 0A at this point and then changed later once the amplifier is powered on.
18. Press the AMP button on the front panel of the CFA and wait until the AMP LED glows green. At this point, the (MFP) amplifier will now amplify the seed light to produce approximately 450mW of 1064nm light at the output of the MFP (not directly measurable) and approximately 0.5mW at the pickoff output; the latter of these powers should now be verified using a power meter.
19. With the amplifier operating as expected, use the selection knob and associated buttons on the front panel of the CFA to verify that the Tset C value for the Oven matches that of the Test Report (namely, 44.6°C).
20. Insert the armoured PM480 FC/APC output fibre into a power meter, set to record 532nm light.
21. Press the OVEN button on the front panel of the CFA and wait until the OVEN LED glows green. At this point, the oven will begin the process of stabilising its temperature to that set via the front panel of the CFA.
22. Once the oven temperature has stabilised, observe the 532nm output power and verify that it matches that given in the Test Report (namely, approximately 115mW). Should the power differ from that given in the Test Report, refer to the Troubleshooting section below.

Turn OFF Sequence

1. Press the AMP button on the front panel of the CFA and wait until the AMP LED glows yellow. It is important to turn off the amplifier before powering off both the seed laser and oven.
2. Press the OVEN button on the front panel of the CFA and wait until the OVEN LED glows yellow. Note that this will, naturally, turn the oven off, and hence the observed oven temperature in the OVEN menu of the CFA will fall away from the oven setpoint temperature.
3. Turn the keyswitch on the front panel of the CFA to the STANDBY position. The LEDs should now glow red.
4. Power off the CFA.
5. Flip the switch on the front panel of the DLC from ON to OFF. This will cease the delivery of current to the seed laser, hence powering it off.
6. Turn the keyswitch on the front panel of the DLC from RUN to STANDBY. Note that, while no current is being delivered to the seed laser at this point, the temperature stabilisation of the seed laser is still active at this point.
7. Power off the DLC using the switch on its rear panel. This step will now cease the temperature stabilisation of the seed laser.

Troubleshooting

Low Non-Amplified Pickoff Power

1. Using a 2mm hex driver, remove the four M3x6 FHCS screws securing the CFA lid to the body of the chassis; then, remove the lid.
2. Using a 3mm hex driver, loosen the four M4x20 SHCS screws securing the CES lid to the body of the CES chassis, but do not remove the screws. Use extreme care whilst loosening the screws so as to avoid damaging the bare fibres that have been spooled within the CFA chassis.
3. Gently remove the CES lid from its chassis, again taking care to not damage any spooled fibres.
4. At the rear of the (now-visible) CES barrel is a hexagonally-shaped threaded end cap from which a red and black wire exit. Carefully and slowly proceed to rotate this end cap whilst observing the power recorded at the amplifier pickoff until the maximum power is observed.
5. Replace all lids to seal up the amplifier.

Incorrect Wavelength

1. Follow the steps outlined in the Low Non-Amplified Pickoff Power section above to reveal the CES barrel.
2. Insert a 1.5mm right-angled Allen key into the head of the high TPI screw. Slowly and carefully tighten or loosen the screw whilst observing the wavelength recorded on a wavemeter until a single lasing mode at the desired target wavelength is obtained.
3. Disconnect the end of the PM980 fibre inserted into the pickoff butt-coupler and verify that the pickoff power observed is correct and appropriate, using the steps outlined in the Low Non-Amplified Pickoff Power section above to improve the power if necessary.
4. Replace all lids to seal up the amplifier.

Low Amplified (and Doubled) Power

1. Ensure that the seed is lasing at the correct desired wavelength and that the amplified pickoff power is correct and appropriate, using the steps in the Low Non-Amplified Pickoff Power and the Incorrect Wavelength sections above to remedy if necessary.
2. Replace all lids to seal up the amplifier.
3. Whilst observing the 532nm output power, proceed to change the temperature setpoint of the oven in "coarse” 0.1°C increments, waiting 15-20 seconds after each new temperature setpoint for the output power to stabilise, until the maximum power is observed.
4. With the temperature setpoint of the oven set to its maximum “coarse” value, proceed to scan the temperature about this setpoint by changing the temperature setpoint of the oven in “fine” 0.01°C increments until the maximum power is observed.