Transcript FSS

FSS
Frequency Stabilisation System
Overview
Why we need FSS:
 Stabilise the optical frequency of fibre laser to
+3 kHz
 Use Rb frequency standard at 780 nm
access from 1560 nm SHG
Tuning control





0-200 V
Tuning over 10 GHz
+70 µV ≡ +3 kHz
Stabilise to 3 kHz
Stabilise circuit temperature
All voltage variations due to lock-in
signals
 Peltier Cooler
Peltier Cooler
 Heat pump uses Peltier-Seebeck effect
 Array of p and n type semiconductors
 Transfers heat from one face to the other
 depending on current flow
Experiments
 Evaluation board which controlled Peltier test setup
 Experiments done by adjusting set-point voltage
and looking at how the Peltier temperature
changed
 Measured the voltage across the module; THERM
voltage, and convergence
Results
 0.7 V-4 A power
supply to get 25 °C
 Gradient of linear
region agreed with
specification
 Convergence
between THERM and
set-point deviated
further from 100 µV at
higher temperatures
Hall Probe
 Magnetic field
 Single turn inductive loop in lines of
magnetic flux
 5²S1/2 → 5²P3/2
 Magnetic field affect the energy of
transition
 Ambient fields
 4-layer cylindrical shield lined with mumetal
Results
 Opto-isolator:
 Top 4 frequency bits set by DIP switch
 FPGA controls bits 8-26
Plans
 Test tuning part of system
 Spectrum analyser
112
Frequency/ MHz
111
110
109
108
-1.5
-1
-0.5
0
Control voltage/ V
0.5
1
1.5