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