Optical Position Sensor for the VWS.
Losses, First Calculus
Jose Luis SirventSupervisor: Jonathan Emery
Student Meeting19 September 2011
1.Introduction & Objectives 2.Schema proposed 3.Components to use. 4.Optical path 5.Sources of losses 6.Next Steps
Index
A) Objective:
◦ Accurate Position Measures
◦ Absolute position measurement (Motor control) Solid rotor resolver Rotasyn® (Mohamed)
◦ Relative position measurement (Optical system) Based in disk encoder, should be more precise (Me)
1. Introduction & Objectives
B) Introduction:
◦ Technical Student, I’ll do here my master thesis
◦ I’ll contribute in the work of Julien, Mohamed, Jonathan & Juan in the OPS for the VWS.
◦ Optical system based on encoder disk in transmission or reflection (In order to obtain the relative position of the folk).
◦ First approach to study: Transmission
◦ The optical system must work under the next conditions:
Position measurement every: 500 µrad Accuracy: 25 µrad Ultra High Vacuum Operation Temperature: 200 ºC Service life: 20 years Cumulated ionizing radiation: 20KGy (1KGy/year) Cables length: 250m
1. Introduction & Objectives
Schema Proposed for the transmission approach
2. Schema Proposed
1. Laser Diodes (850nm)
◦ A) KLD085VC (VCSEL) 2.5mW to 4mW Max If 12 mA Op Temp: 0 to 85 deg
◦ B) PL85B002ST83-T-0 (ST) 2mW to 5mW Max If 45mA
◦ C) OPF372A (ST) 30µW (may not work) Max If 100mA Op Temp: -40 to 85 deg
3. Components
2. Optical Fiber
◦ FPC-22010-10 - FIBRE OPTIQUE ST-ST 1M ◦ Multimode fiber with ST Connectors◦ Duplex◦ Bandwidh 850-1300nm◦ Working in the first transmission window◦ Diamètre, faisceau:0.0625mm◦ Attenuation ≤ 3.5 dB/Km (850nm) ◦ Insertion Loss ≤ *0.35 dB
◦ Final model: 500m ◦ Simulator model: 2m
◦ Pz=Pi*e-αz
◦ α=A(dB/Km) /4.34*103
3. Components
*Typical for St Connectors, verified with Sabritec
3. Hybrid ST-SMA 905 adapter
◦ Interface between fiber and Feedthrough
◦ Typical Insertion Loss: 0.35 dB (ST Connector) >1dB (SMA 905) *according to Newport
3. Components
4. FeedThrought
◦ Materials: SS, Polyimide, Fused Silica RoHS ◦ Gender: Male / Bare Polished◦ Max. Bake Temperature: 250ºC◦ Max. Operating Temperature: 250ºC◦ Max. Vacuum Level: 1x10-10 Torr◦ Contact Material: 62.5 Micron◦ Operating Wavelength: Optimized for 850nm and 1300nm◦ Numerical Aperture: 0.27 ± 0.02Fiber (AN) or (0.22)◦ Profile: Graded-Index, Multimode
◦ Alpha= Asin(0.27) 15.6 deg◦ Laser Diameter= (0.27*D*2)+62.5
3. Components
0 500 1000 1500 2000 2500 3000 3500 4000 45000
500
1000
1500
2000
2500
3000
Laser Diameter Vs Distance (µm)
5. Optical Disk
◦ Material: Borofloat◦ nBorofloat= 1.46 (850nm)◦ Pattern in Chrome (brilliant)
◦ Possible Problems: Light area much bigger than
certain holes Light Duality Interference Pattern in
receiver? Could this be good or bad?
6. Optical disk
6. Optical Receivers A) KPGX1G (GaAs)
◦ TIA: Transimpedance amplifier
◦ Input power monitoring
◦ Optical sensitivity: -24dB
◦ Photo-electric conversion efficency: 3.9 mV/µW
B) OPF562 (SI)◦ TIA: Transimpedance amplifier
◦ SMA or ST connector (Better with SMA, directly to the feedthrough)
◦ Optical sensitivity: ?
◦ Photo-electric conversion efficency: 7 mV/µW
C) KPIX150-H333 (SI)◦ TIA: Transimpedance amplifier
◦ Optical sensitivity: -31dB
◦ Photo-electric conversion efficency: 40 mV/µW
D) KPIXA1G-H33 (SI-APD)◦ TIA: Transimpedance amplifier
◦ Optical sensitivity: -33dB
◦ APD Responsivity: 0.45 A/W
E) PDSIU500-ST-83 (SI)◦ Perfect couple for the PL85B002ST83-T-0
◦ Responsivity: 0.45 A/W
3. Components
1. Study of Light: This study can be done in two ways
◦ A. Laser as a constant light distribution * Traditional optics principle
◦ B. Laser as a Gausian light distribution ** Gausian optics: More realistic and accurate… but more
difficult
4. Optical path
*The literature consider this approach suitable for light coupling in multimode fiber.
** Gausian optics are applied when coupling lignt in monomode fibers
4. Optical path 2. The optical path through the Disk
◦ The radius of the light is bigger with the distance
3. The Fresnel Reflexion Effect:
Effect produced in the intersection of two environments with different refraction index.
This happens 4 times:• Fiber - Vacuum • Vacuum - Disk Disk - Vacuum• Vacuum – Fiber
• Loses in disk:• nvac= 1 , nfloat= 1.46• LossFres = 0.315 dB
• Loses in Fiber-vacuum… nfiber ?
4.Optical path
nvacuum ndisk
WIRE SCANER OPTICAL POSITION SENSOR n(vacuum) 1 FEEDTHROUGH DISK LASER BEAM nf Thickness (D2) 500microns Alpha1 0.27radians Core Diameter 62.5microns nd (float) 1.4655 d1 332.50microns Numerical Aperture (A.N.) 0.27 Distance to disk (D1) 500microns FIBER Alpha2 0.19radians Length 2meters d2 516.74microns Att 3.5dB/Km LOSSES (Lc) Alpha3 0.27radians Fresnell Disk-Vacuum 0.315284dB d3 786.74microns Fresnell Fiber-Vacuum dB Insertion Losses ST 0.35*4 1.4dB Intersection with Pattern Insertion Losses SMC 1*2 2dB Pattern (um) 50 70 100 150 Optical Fiber 0.007dB Gaps 3.325 2.375 1.6625 1.108333 Free Space 10.9995dB Total Losses 14.72178dB Pr 3.37%Ps Power Balance Ps 5mW 6.9897dBm Pr 0.168574mW -7.732082dBm
5. Sources of losses
A) Check these calculus in the test bench and verify the existence of other possible sources of losses.
◦ Is the dispersion of the fiber applicable for our signals (850nm)? (exists pulse enlargement in 500 meters?)
◦ Apply possible optical penalizations and effects (if rise times are significant there would be a delay).
6. Next Steps
B) Is this scheme optimal for detection?◦ Check other possible approaches
1. Check the possibilities and losses in reflection
2. Usage of collimator in reflection or/and transmission.
6. Next Steps
That’s all for now, thanks.
Jose Luis Sirvent
Student Meeting19 September 2011
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