wdm optical interfaces for future fiber radio systems phần 5 pot

Chapter 3: WDM Optical Interface for Simplified Antenna Base Stations

signal at DL Drop port and the uplink signal at ADD port, generated by reusing the

recovered optical carrier, were also quantified, which are shown in Fig. 3.20. The

error-free (at a BER of 10-9) data recovery and the recovered optical spectra verified

-50

Wavelength relative to 1552.22 (nm)

-30

-10

-0.8 -0.4 0 0.4 0.8

Optical Power (dB)

DL Drop

-50

Wavelength relative to 1552.22 (nm)

-30

-10

-0.8 -0.4 0 0.4 0.8

Optical Power (dB)

IN to Interface

(a) (b)

-50

Wavelength relative to 1552.22 (nm)

-30

-10

-0.8 -0.4 0 0.4 0.8

Optical Power (dB)

DL Drop

-50

Wavelength relative to 1552.22 (nm)

-30

-10

-0.8 -0.4 0 0.4 0.8

Optical Power (dB)

DL Drop

-50

Wavelength relative to 1552.22 (nm)

-30

-10

-0.8 -0.4 0 0.4 0.8

Optical Power (dB)

IN to Interface

-50

Wavelength relative to 1552.22 (nm)

-30

-10

-0.8 -0.4 0 0.4 0.8

Optical Power (dB)

IN to Interface

(a) (b)

-50

Wavelength relative to 1552.22 (nm)

-30

-20

-0.6 -0.4 0 0.4 0.8

Optical Power (dB)

ADD to Interface

-40

-50

Wavelength relative to 1552.22 (nm)

-30

-10

-0.8 -0.4 0 0.4 0.8

Optical Power (d

B)

λ-Re-Use Carrier

(c) (d)

-50

Wavelength relative to 1552.22 (nm)

-30

-20

-0.6 -0.4 0 0.4 0.8

Optical Power (dB)

ADD to Interface

-40

-50

Wavelength relative to 1552.22 (nm)

-30

-20

-0.6 -0.4 0 0.4 0.8

Optical Power (dB)

ADD to Interface

-40

-50

Wavelength relative to 1552.22 (nm)

-30

-10

-0.8 -0.4 0 0.4 0.8

Optical Power (d

B)

λ-Re-Use Carrier

-50

Wavelength relative to 1552.22 (nm)

-30

-10

-0.8 -0.4 0 0.4 0.8

Optical Power (d

B)

λ-Re-Use Carrier

(c) (d)

Fig. 3.19: Optical spectra of the proposed WDM optical interface while modelled by VPI

simulator using three WI-DWDM channels: (a): the input signal at port IN, (b): the downlink

signal at port DL Drop, (c): the recovered optical carrier at λ-Re-Use port, and (d): the uplink

optical mm-wave signal to be added to the interface, generated by reusing the recovered optical

carrier.

105

Chapter 3: WDM Optical Interface for Simplified Antenna Base Stations

the functionality of the proposed interface, which was later demonstrated in

experiment, as described in Section 3.5.3

-8 -7 -6 -5 -4

-5

-3

-11

-9

l

-7 og l 10 (BER)

Received Optical Power (dBm)

Uplink at ADD Port

-5

-3

-11

-9

-7

-9 -8 -7 -6

ol g10 (BER)

Received Optical Power (dBm)

Downlink at DL Drop Port

(a) (b)

-8 -7 -6 -5 -4

-5

-3

-11

-9

l

-7 og l 10 (BER)

Received Optical Power (dBm)

Uplink at ADD Port

-8 -7 -6 -5 -4

-5

-3

-11

-9

l

-7 og l 10 (BER)

Received Optical Power (dBm)

Uplink at ADD Port

-5

-3

-11

-9

-7

-9 -8 -7 -6

ol g10 (BER)

Received Optical Power (dBm)

Downlink at DL Drop Port

-5

-3

-11

-9

-7

-9 -8 -7 -6

ol g10 (BER)

Received Optical Power (dBm)

Downlink at DL Drop Port

(a) (b)

Fig. 3.20: Simulation BER curves that quantify the degradation of the signals due to traversing the

proposed interface: (a): the recovered downlink signal at DL Drop port, and (b): the uplink signal,

generated by reusing the recovered optical carrier, at ADD port.

3.7 Effects of the Performance of O/E Devices

The overall receiver sensitivity of the experimentally demonstrated system

incorporating the proposed interface, irrespective of direction of communication, is

less than or equal to -7.7 dBm at a BER of 10-9, which is very poor and needs to be

improved through further investigation. The performance of the optoelectronic and

electrooptic devices such as DE-MZMs and the PD play a very important role in

limiting the overall performance of the link. The DE-MZMs used in the experiment

exhibit a CSR from 22 to 28 dB. Also, the PD used in the experiment had a

responsitivity of less than 0.4. If the performance of O/E devices can be improved

either by replacing it with better performing devices or by applying some external

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Chapter 3: WDM Optical Interface for Simplified Antenna Base Stations

performance enhancing techniques (such as CSR reduction by external means), the

sensitivity limitation can be resolved quite easily.

Fig. 3.21 shows a simulation model developed by using VPI platform, which

quantifies the performance enhancement of the system at different values of CSR at

the output of the DE-MZMs and the responsitivity of the PD. To make the results

comparable, the properties of the modules in the model follow the experimental

parameters very closely. To enable variable CSRs in the generated WI-DWDM

signals, the sidebands of the OSSB+C signal are separated from the optical carriers

using a Fabry Perot filter in conjunction with a 3 port optical circulator, where the

intensities of the sidebands were varied by another EDFA (keeping the noise figure

unchanged) before combining them back with the separated optical carriers. Fig.

3.22(a) shows the sensitivity at BER = 10-9 vs. reduction in CSR curve obtained from

simulation model, which clearly indicates that, the sensitivity of the system increases

almost linearly with reduction in CSR.

1. IN

3. DL Drop

4. λ-Re-Use

5. ADD

7. OUT

10 km

SMF

WDM Optical

Interface 7

3 4 5

1

Uplink

OSSB+C2

Data Recovery

4x1

OSSB+C1

OSSB+C2

OSSB+C3

FP

2x1

EDFA

BPF: band pass filter

SMF: single-mode fiber

PD: photo detector

FP: Febry Perot Filter

SB: Sideband

PD PD

SB

EDFA

BPF

1. IN

3. DL Drop

4. λ-Re-Use

5. ADD

7. OUT

10 km

SMF

WDM Optical

Interface 7

3 4 5

1

Uplink

OSSB+C2

Data Recovery

4x1

OSSB+C1

OSSB+C2

OSSB+C3

FP

2x1

EDFA

BPF: band pass filter

SMF: single-mode fiber

PD: photo detector

FP: Febry Perot Filter

SB: Sideband

PD PD

SB

EDFA

BPF

Fig. 3.21: Simulation model that quantifies the performance enhancement of the system at

different values of the CSR of the DE-MZMs as well as the responsitivity of the photodetector.

107