Thomas Berenz, MPIfR Bonn 1RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

RF fiber opticsRF fiber optics

Analog RF transmission with mechanically stressed fibers

Thomas Berenz, MPIfR Bonn 2RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

IntroductionIntroduction

• Advantages of fiber links:– Bandwidth depends mainly on the electrical components

– Very long distances can be achieved

• Current installation in the Effelsberg telescope:– 400m from primary focus cabin to faraday room

– Transmission of RF signals through coaxial cables (25 dB/100m @ 1GHz)

– Max. useable bandwidth < 1 GHz

• Analog transmission is able to avoid the bandwidth bottleneck

Thomas Berenz, MPIfR Bonn 3RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

Analog fiber linksAnalog fiber links

• Miteq SCM Series 0.1 – 18 GHz

• Miteq MDD Series 0.1 – 11 GHz

• 9/125 single mode fiber with FC/APC connectors

• Laser is modulated directly

Thomas Berenz, MPIfR Bonn 4RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

Broadband measurementBroadband measurement

LWL-TX1 LWL-RX1

Gwhite noise

1-2GHz

S

1 2

3dB

LWL2a

360m 9/125 SM Fiber

LWL2b

360m 9/125 SM Fiber

faraday - room primary focus cabin

- fulcrum pin -

LAN RS232

azimuthelevation

V V

F FCh A Ch B

Gegentakt-pulse

Thomas Berenz, MPIfR Bonn 5RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

Results of broadband measResults of broadband meas

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0

0,1

0,2

0,3

12:53:17 13:00:29 13:07:41 13:14:53 13:22:05

IRIG-B Time

TP

/Ari

th.

me

an

(T

P)

in d

B

0

50

100

150

200

250

300

350

400

450

Azi

mu

th-

& e

lev

ati

on

an

gle

TP_HF_in

TP_HF_out

Azimuth

Elevation

20070618_Messung_Effelsberg_ohne_PI_Regler_07_Gesamt.pdf

•TP_in: nearly constant

•TP_out: -0,47 – 0,25 dB

Thomas Berenz, MPIfR Bonn 6RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

VNA MeasurementsVNA Measurements

• Build up at the lab bench

• No loop

• Miteq SCM Transmitter (18 GHz BW)

• Miteq SCM Receiver (18 GHz BW)

• Miteq MDD Transmitter (11 GHz BW)

• Miteq MDD Receiver (11 GHz BW)

• 100m 9/125 SM fiber

• 2m 9/125 SM fiber

Thomas Berenz, MPIfR Bonn 7RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

Measurement setupMeasurement setup

Thomas Berenz, MPIfR Bonn 8RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

18 GHz Tx + 18 GHz Rx18 GHz Tx + 18 GHz RxSCM_Tx (18 GHz) - SCM_Rx (11 GHz)

-0,9

-0,8

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0,

0,1

0 5 10 15 20 25

frequency in GHz

Me

as

ure

d v

alu

e(d

B)

- re

f(d

B)

(fre

qu

nc

y r

es

po

ns

e is

ca

libra

ted

ou

t)

S21_Ref-S21_1

S21_Ref-S21_2

20070823_Zusammenfassung_SCM_MDD.xls

~ -0.77 dB~ -0.69 dB

Thomas Berenz, MPIfR Bonn 9RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

11 GHz Tx + 11 GHz Rx11 GHz Tx + 11 GHz RxMDD_Tx (11 GHz) - MDD_Rx (11 GHz)

-0,9

-0,8

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0,

0,1

0 2 4 6 8 10 12 14 16 18

frequency in GHz

Me

as

ure

d v

alu

e(d

B)

- re

f(d

B)

(fre

qu

nc

y r

es

po

ns

e is

ca

libra

ted

ou

t)

S21_Ref-S21_1

S21_Ref-S21_2

20070823_Zusammenfassung_SCM_MDD.xls

~ -0.22 dB

Thomas Berenz, MPIfR Bonn 10RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

11 GHz Tx + 18 GHz Rx11 GHz Tx + 18 GHz RxMDD_Tx (11 GHz) - SCM_Rx (18 GHz)

-0,9

-0,8

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0,

0,1

0 2 4 6 8 10 12 14 16 18

frequency in GHz

Me

as

ure

d v

alu

e(d

B)

- re

f(d

B)

(fre

qu

nc

y r

es

po

ns

e is

ca

libra

ted

ou

t)

S21_Ref-S21_1

S21_Ref-S21_2

20070823_Zusammenfassung_SCM_MDD.xls

~ -0.78 dB~ -0.7 dB

Thomas Berenz, MPIfR Bonn 11RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

18 GHz Tx + 11 GHz Rx18 GHz Tx + 11 GHz RxSCM_Tx (18 GHz) - MDD_Rx (11 GHz)

-0,9

-0,8

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0,

0,1

0 5 10 15 20 25

frequency in GHz

Me

as

ure

d v

alu

e(d

B)

- re

f(d

B)

(fre

qu

nc

y r

es

po

ns

e is

ca

libra

ted

ou

t)

S21_Ref-S21_1

S21_Ref-S21_2

20070823_Zusammenfassung_SCM_MDD.xls

~ -0.22 dB~ -0.2 dB

Thomas Berenz, MPIfR Bonn 12RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

SummarySummary

• MDD (11 GHz) Receiver: ∆A = 0.22 dB

• SCC (18 GHz) Receiver: ∆A = 0.78 dB

• Transmitter has no influence

• Same measurements with 2m fiber instead of 100m:no change Fiber length has no influence

• Measurments with the fiber installed in the telescope are compareable with those in the lab although the fiber is different Fiber type has no influence

Thomas Berenz, MPIfR Bonn 13RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

ConclusionConclusion

• Changes in insertion loss:Effect seems to depend on birefrigence caused by mechanical force applied to the fiber. Together with a polarization sensitivity of the photodiode this can cause the difference in insertion loss.

• Changes in frequency response:Still an open question; Has to be investigated further

Thomas Berenz, MPIfR Bonn 14RF fiber optics4th SKADS Workshop, Lisbon, 2-3 October 2008

QuestionsQuestions