wdm optical interfaces for future fiber radio systems phần 6 potx

Chapter 4: Characterisation and Enhancement of Links Performance

Incorporating WDM Optical Interface

Fig. 4.10 shows the transmission and reflection responses for the double-notch

FBGs used in the demonstration. The characteristic curves at Fig. 4.10(a) show that

the nominal Bragg wavelengths for the notches are 1556.207 nm and 1556.509 nm

with a separation of 0.302 nm between the notches. The Bragg wavelengths can be

tuned to the desired experimental wavelengths by employing suitable mechanical

stretchers. The transmission spectrum shows that the notches have leakages of

approximately -26 and -27 dB at the Bragg wavelengths from which the reflectivity

can be calculated as 99.7% and 99.8% respectively. The characteristic curves at Fig.

-45

-65

-55

1556.0 1556.2 1556.4 1556.6

Wavelength (nm)

(dB)

Transmission

Reflection

(b)

-45

-65

-55

1556.0 1556.2 1556.4 1556.6

Wavelength (nm)

(dB)

Transmission

Reflection

(a)

Insertion Loss 0.3 dB

Insertion Loss 0.3 dB

-26 dB

-27 dB

-22 dB

-22.5 dB

-45

-65

-55

1556.0 1556.2 1556.4 1556.6

Wavelength (nm)

(dB)

Transmission

Reflection

-45

-65

-55

1556.0 1556.2 1556.4 1556.6

Wavelength (nm)

(dB)

Transmission

Reflection

(b)

-45

-65

-55

1556.0 1556.2 1556.4 1556.6

Wavelength (nm)

(dB)

Transmission

Reflection

(a)

Insertion Loss 0.3 dB

Insertion Loss 0.3 dB

-26 dB

-27 dB

-22 dB

-22.5 dB

Fig. 4.10: Measured transmission and reflection spectra for the double-notch FBGs to be used in

the experimental characterisation of single and cascaded WDM optical interfaces.

135

Chapter 4: Characterisation and Enhancement of Links Performance

Incorporating WDM Optical Interface

4.10(b) show that the nominal Bragg wavelengths for the notches are 1556.157 nm

and 1556.459 nm with a separation of 0.302 nm between the notches. The

transmission spectrum shows that the notches have leakages of approximately -22

and -22.5 dB at the Bragg wavelengths from which the reflectivity can be calculated

as 99.3% and 99.4% respectively. Also, the reflection spectra demonstrate its sharp

roll-off profiles with minimum side-lobe ripples. The measured insertion losses of

the gratings were approximately 0.3 dB each.

(a)

-41

-43

-42

-44

1555.8 1556.1 1556.4 1555.8 1556.1 1556.4

-46

-54

-58

-50

-41

-43

-42

-44

1555.8 1556.1 1556.4 1555.8 1556.1 1556.4

-46

-54

-58

-50

(b)

(a)

-41

-43

-42

-44

1555.8 1556.1 1556.4 1555.8 1556.1 1556.4

-46

-54

-58

-50

(a)

-41

-43

-42

-44

1555.8 1556.1 1556.4

-41

-43

-42

-44

1555.8 1556.1 1556.4 1555.8 1556.1 1556.4

-46

-54

-58

-50

1555.8 1556.1 1556.4

-46

-54

-58

-50

-41

-43

-42

-44

1555.8 1556.1 1556.4 1555.8 1556.1 1556.4

-46

-54

-58

-50

(b)

-41

-43

-42

-44

1555.8 1556.1 1556.4

-41

-43

-42

-44

1555.8 1556.1 1556.4 1555.8 1556.1 1556.4

-46

-54

-58

-50

1555.8 1556.1 1556.4

-46

-54

-58

-50

(b)

Fig. 4.11: Measured transmission and reflection spectra for the 50% reflective FBGs to be used in

the experimental characterisation of single and cascaded WDM optical interfaces.

The characteristic curves for 50% reflective FBGs with nominal Bragg

wavelengths of 1556.109 nm and 1556.129 nm are shown in Fig. 4.11. Like before,

these Bragg wavelengths also can be tuned to the desired experimental wavelengths

136

Chapter 4: Characterisation and Enhancement of Links Performance

Incorporating WDM Optical Interface

by employing suitable mechanical stretchers. The transmission spectra show that

46% and 47% of the optical power entering to these FBGs will be transmitted, while

the respective remaining 54% and 53% will be reflected and recovered by the

proposed interface, and eventually, will be reused as optical carriers in the uplink

path. These reflection spectra also indicate its sharp roll-off profiles with minimum

side-lobe ripples. The measured insertion losses of these grating were approximately

0.3 dB each.

4.4.1.2 8-Port Optical Circulators

Two 8-port OCs are required for this experiment. The 8-port OC described in the

previous chapter (Chapter 3) will also be used here. However, due to aging and

multiple uses, the characteristics of the OC have been changed slightly, especially in

port to port insertion losses. The new measurements for the port-to-port insertion

losses are shown in the 2nd column of Table 4.1. Due to the unavailability of another

8-port OC, a combination of one 4-port and one 3-port OCs will be used. The port to

port insertion losses of the cascaded OCs are also shown in the 3rd column of Table

4.1. The other characteristics of the cascaded OCs (e.g. isolation, directivity etc.) are

very similar to that of the 8-port OC, illustrated in the previous chapter.

Port to Port Insertion Losses of

8-port OC (dB)

Insertion Losses of Cascaded

7-port OCs (dB)

1 to 2 0.7 0.9

2 to 3 1.21 1.21

3 to 4 0.94 1.4

4 to 5 2.56 n/a

5 to 6 3.25 1.35

6 to 7 1.14 1.55

7 to 8 1.13 n/a

Table 4.1: Port-to- port insertion losses of the optical circulators

137