Presents by Roland Yuen

Coherent System in Remote Antenna Application

Overview Coherent system architecture Remote antenna: Radio over fiber link Design issues with coherent system Potential system Conclusion References

Coherent system architecture

Laser source:DFB, Nd:YAG

Direct Modulation

RF

ExternalModulation

RF

or

SMF at 1330 nm or 1550 nm

Local Oscillator Laser

3 dB directional coupler with balance detectorOptical combiner with signal detector

Polarization Control Receiver

Spurious Free Dynamic Range (SFDR)

The SNR in which its power due to non-linearity equals to the noise power.

[1] Cox et al.

Remote antenna: Radio over fiber link

ROF G Air

n_optical n_air

ROF G Air

n_optical n_air

G

Downlink

Uplink

Fiber loss: Converter loss, attenuationAir loss: fading (multipath) and shadowing

(surrounding object) SFDR requirement: 115 dB·Hz2/3 [3]

[4] Fernando et al.

Design issues with coherent system

External modulation or direct modulation? Power consideration – gain in external

modulation and loss in direct modulation

[1] Cox et al.

External modulation or direct modulation? Bandwidth and intermediate frequency External modulation and direct modulation

have 70 GHz and 20 GHz electrical bandwidth respectively. [2]

Linearization: Optical or electrical Increase SFDR Optical: Dual polarization, Multiple cascaded

modulator [3] Electrical: Predistortion circuit [3]

Amplitude modulation or angle modulation (PM, FM) Bandwidth and dynamic range (SFDR) Electronics – difficult to implement at

high intermediate frequency

[3] Kalman et al.

Relative Intensity Noise (RIN) Dominate when power are high for it is

proportional to the square of the mean optical power.

Balance receiver: Majority of the RIN noise can be cancelled

Balance receiver need to have very close matched photodiodes; 50:50 power split ratio from 3 dB directional coupler.

Phase noise (PM, FM) Phase noise only affects angle

modulation system Optical cancellation: Optical signal

sideband (SSB) [6] Electronics cancellation: Phase noise

cancellation circuit, AM-WIRNA [5],[7] Increase IF: IF limitation [3]

Potential systems Phase Modulation (PM) using phase

modulator Nd:YAG for transmitter and DFB laser

local oscillator Single receiver with optical combiner:

RIN does not affect the system IF amplifier (5-10 GHz) Phase noise cancellation circuit

Conclusion Coherent system enables angle modulation

that has more SFDR In remote antenna,losses in air channel lead

to high SFDR requirement (uplink) Phase noise cancellation circuit further

increase SFDR in angle modulation Potential system is to employ angle

modulation with external phase modulator

References[1] An analytic and experimental comparison of direct and external modulation in analog fiber-optic links

Cox, C.H., III; Betts, G.E.; Johnson, L.M.; Microwave Theory and Techniques, IEEE Transactions on , Volume: 38 Issue: 5 , May 1990 Page(s): 501 –509

[2] Direct-detection analog optical linksCox, C., III.; Ackerman, E.; Helkey, R.; Betts, G.E.; Microwave Theory and Techniques, IEEE Transactions on , Volume: 45 Issue: 8 , Aug. 1997Page(s): 1375 –1383

[3] Dynamic range of coherent analog fiber-optic links Kalman, R.F.; Fan, J.C.; Kazovsky, L.G.; Lightwave Technology, Journal of , Volume: 12 Issue: 7 , July 1994 Page(s): 1263 –1277

[4] On the design of optical fiber based wireless access systems..Fernando X. N.; Anpalagan A.;WINCORE laboratory, Ryerson University, Toronto

[5] Optically coherent direct modulated FM analog link with phase noise canceling circuit Taylor, R.; Forrest, S.; Lightwave Technology, Journal of , Volume: 17 Issue: 4 , April 1999 Page(s): 556 –563

[6] Technique for optical SSB generation to overcome dispersion penalties in fiber-radio systemsSmith, G. H.; Novak D.; Ahmed Z;

[7] Phase noise in coherent analog AM-WIRNA optical linkTayor R.; Poor H. V.; Forrest Stephen;