Jose Luis Sirvent
Jonathan Emery
Student Meeting 08– May -2012

1.2 Coupling Efficiency VS D2 Variation

2.1 Main problems (SMF): Signal Modulation
◦ Disk imperfections? NO!
◦ SMF Vibrations sensibility? NO!
◦ Fabry-Perot Interferometer? YES!

2.2 Fabry-Perot Interferometer: Principle
◦ Optical waves interference due to:
 path difference




Phase diference & Coherence lengh
R= Mirror reflectivity
R1= Fresnel reflectivity (Interface Silica/air)
Xo= Path Difefence
◦ Detection of movements in the order of ½ lamda
http://physics-animations.com

Let’s simulate to verify!
◦ Real values: Fibre-disk= 200um
 Fresnel Reflection (end of fiber): -17dB
 Borofloat Reflectivity: 5%
 Chrome Reflectivity: 60%
 Displacement 2.5um
 Solution: Avoid Fresnel
reflections.
Use APC Fiber ending

Is the APC ending a solution?
◦ Let’s simulate: Real values again




Fresnel Reflection (end of fiber): -40dB
Borofloat Reflectivity: 5%
Chrome Reflectivity: 60%
Displacement 2.5um
 It seems to work!
 Practical verification?

Practical verification:
◦ Results:
 1. Fresnel Reflections reduced (not avoided)
 2. Less light is collected back
 3. Necessity of tilting the fiber a bit
 4. Lens verification needed (Components ordered)
PC Ending
APC Ending
Proto glass disk pattern v3 [mm]
Chrome(brillant)
Gap= 6 * Alpha
30 °
750
1000
1000
Track
1
30 °
485
30
485
16.450[mm]
140 mm
40 mm
2
3
4
5
450
100
450
6
Glass disk line 1:
Alpha = 0.004 deg
Edges (360 / Alpha)= 90000 (-2 * 6)  Gaps
Glass disk line 2:
Alpha = 0.009 deg
Edges (360 / Alpha)= 40000 (-2 * 6)  Gaps
………….
(See table attached)
7
8
500
100
100
Proto glass disk pattern v3 [mm]
Duty cycle= 50%
Track shape 