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| '''End laser fiber setup''' *Find out the fiber mode *Designate space for the setup at end tables *Design telescopes for coupling light into the fiber *Layout the fiber along 40m arms in insulated tubes '''PSL fiber setup''' *Designate space on PSL table *Find the fiber beam splitter(FBS) mode *Design a telescope to couple light into the FBS mode '''Beat note setup''' *Couple fiber to fiber *Combine PSL and end laser with appropriate polarization (50/50 --> 90/10) *Detecting beatnote at the PD '''Frequency counter setup''' *Hook up frequency counter *Read beat frequency on StripTool '''End laser thermal actuator characterization''' '''Digital servo''' == MISC tasks == *Behavior of PM fiber to temperature fluctuations *Polarization controller characterization |
||'''Tasks'''||Who||Status||Last updated|| ||||||''General tasks''|| ||Make procurements list and purchase stuff||MT||Done||Oct 9|| ||Find an appropriate C-lens for telescope||EG|| || || ||Find out the fiber mode|| || || ||||||''End laser fiber setup''|| ||Designate space for the setup at end tables|| || || ||Design telescopes for coupling light into the fiber|| || || ||Layout the fiber along 40m arms in insulated tubes|| || || ||||||''PSL fiber setup''|| ||Designate space on PSL table|| || || ||Find the fiber beam splitter(FBS) mode|| || || ||Design a telescope to couple light into the FBS mode|| || || ||||||''Beat note setup''|| ||Couple fiber to fiber|| || || ||Combine PSL and end laser with appropriate polarization (50/50 --> 90/10)|| || || ||Detecting beatnote at the PD|| || || ||||||''Frequency counter setup''|| ||Hook up frequency counter|| || || ||Read beat frequency on StripTool|| || || ||||||''End laser thermal actuator characterization''|| ||||||''Digital servo''|| ||||||''MISC tasks''|| ||Behavior of PM fiber to temperature fluctuations|| || || ||Polarization controller characterization|| || || |
Frequency Offset Locking (FOL) for Dual Wavelength Laser Stabilisation
Overview
In order for the Arm Length Stabilization (ALS) system to be effective in its purpose, the beat frequency between the AUX lasers and the PSL must be within the efficient working range of ALS (< 50 MHz). Thus, our purpose in Frequency Offset Locking (FOL) is to design a feedback-control loop that will keep this beat frequency well within the working range of ALS, so that manual tuning of auxiliary (AUX) laser frequencies may be avoided.
Frequency offset locking works by sampling light from each laser source, PSL and AUX laser, and combining them to produce a beat note which corresponds to the difference between the frequencies of either laser.
The combined PSL and AUX light is sensed at an RF photodiode and an RF frequency counter is used to measure the beat frequency. A digital PID control loop compares the detected beat frequency with the desired beat frequency to produce an error signal. The error signal is then converted back to an analog signal, to actuate on the temperature of the crystal in the AUX laser to keep its frequency within the desired range.
Schematic
A schematic of the setup for FOL is shown below:
Project Tasks
Tasks |
Who |
Status |
Last updated |
General tasks |
|||
Make procurements list and purchase stuff |
MT |
Done |
Oct 9 |
Find an appropriate C-lens for telescope |
EG |
|
|
Find out the fiber mode |
|
|
|
End laser fiber setup |
|||
Designate space for the setup at end tables |
|
|
|
Design telescopes for coupling light into the fiber |
|
|
|
Layout the fiber along 40m arms in insulated tubes |
|
|
|
PSL fiber setup |
|||
Designate space on PSL table |
|
|
|
Find the fiber beam splitter(FBS) mode |
|
|
|
Design a telescope to couple light into the FBS mode |
|
|
|
Beat note setup |
|||
Couple fiber to fiber |
|
|
|
Combine PSL and end laser with appropriate polarization (50/50 --> 90/10) |
|
|
|
Detecting beatnote at the PD |
|
|
|
Frequency counter setup |
|||
Hook up frequency counter |
|
|
|
Read beat frequency on StripTool |
|
|
|
End laser thermal actuator characterization |
|||
Digital servo |
|||
MISC tasks |
|||
Behavior of PM fiber to temperature fluctuations |
|
|
|
Polarization controller characterization |
|
|
|
Procurements list
Component |
Quantity needed/procured |
Part number |
Order status |
As of |
70m PM fiber |
4/4 |
Corning PM98-U25A |
Procured |
Oct 7 |
6 axis fiber mount |
6/4 |
Thorlabs K6XS |
? |
Oct 7 |
Fiber mounting adapters |
6/4 |
Thorlabs SM1FCA |
Need to rder more |
Oct 7 |
Fiber collimators |
6/3 |
Thorlabs CFC-2X-C |
Need to order |
Oct 7 |
Fiber collimator mounts |
6/2 |
Thorlabs AD9.5F |
Need to order |
Oct 7 |
HR1064 mirrors |
?/plenty |
CVI Y1 mirrors |
Procured |
Oct 7 |
Lenses for telescopes |
?/1064nm lens kit available |
? |
? |
Oct 7 |
Fiber insulating tubes |
2/2 |
- |
Procured |
Oct 7 |
Fiber BS for splitting PSL light between the arms(PM = PM+PM in 50-50) |
1/1 |
Afw Tech POBC-64--C-(s)PM-7-2-25 dB |
Procured |
Oct 7 |
PM fiber mating sleeves (FC/APC) |
?/0 |
? |
? |
Oct 7 |
Fiber BC for beat note between arm and PSL (PM+PM=SM) |
2/2 |
Afw tech POBC-64-C-1-7-2-25 dB |
Procured |
Oct 7 |
Polarization controller |
?/1 |
Acrobat PCM4102-333 |
Procured |
Oct 7 |
Fiber BS for splitting combined light between PD and pick off (SM 10-90) |
2/2 |
Afw Tech FOSC-1-64-10-C-(s)3m-H64-2 |
Procured |
Oct 7 |
Fiber coupled PD |
2/1 |
Thorlabs FPD310 |
Procured |
Oct7 |
Frequency counter |
2/2 |
Minicircuits UFC6000 |
Procured |
Oct 7 |