In-line SOA amplification

due to the reduction of the maximum input power, corresponding to the inserted non-linear distortions of the optical fiber.

Conclusion

Again the APD allows to recover the UMTS carrier for optical budgets of 28, 30, and 32dB yielding EVM figures compliant with the 3GPP standard, albeit the RF input range values 25dB (transmitted as well as received) and is 10dB lower than the fiber free case, because of the added non-linear distortion of the optical fiber.

For equivalent over optical losses of 49dB, it is the combination with the lowestTransport section budget which yields the highest maximum RF power (-25.5dBm) for the given EVM threshold. These differentiations are confirmed in Fig. 10.5d.

6 8 10 12 14 16 18 20

-55 -50 -45 -40 -35 -30 -25 -20

RX channel power [dBm] (5MHz)

EVM %

19dB Transp. + SOA + 28dB Access 19dB Transp. + SOA + 30dB Access 21dB Transp. + SOA + 28dB Access 21dB Transp. + SOA + 30dB Access

(a)

6 8 10 12 14 16 18 20

-15 -10 -5 0 5 10 15 20 25

TX channel power [dBm] (5MHz)

EVM %

19dB Transp. + SOA + 28dB Access 19dB Transp. + SOA + 30dB Access 21dB Transp. + SOA + 28dB Access 21dB Transp. + SOA + 30dB Access

(b)

6 8 10 12 14 16 18 20

1 10 100

OMI RMS [%]

EVM %

19dB Transp. + SOA + 28dB Access 19dB Transp. + SOA + 30dB Access 21dB Transp. + SOA + 28dB Access 21dB Transp. + SOA + 30dB Access

(c)

-70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20

-20 -15 -10 -5 0 5 10 15 20 25 30 35

TX channel power [dBm] (5MHz)

RX channel power [dBm] (5MHz)

19dB Transp. + SOA + 28dB Access 19dB Transp. + SOA + 30dB Access 21dB Transp. + SOA + 28dB Access 21dB Transp. + SOA + 30dB Access

(d)

Figure 10.5.: Measurements for an APD receiver after 20km S-SMF containing link and an in-line SOA

Fig. 10.5b (and 10.5c) show that from an RF input power perspective (and OMI point of view), the combination of the highest Transport and Access budgets (21 and 30dB respectively) requires the highest minimum RF input power (-5.5dBm) for yielding 3GPP compliant EVM performances, while the combinations of the lowest Transport and Access budgets requires a minimum RF input power of only -11dBm. The other combinations of Transport and Access budgets require minimum RF input powers ranging in between the previous ones. The RF input power is nearly 5dB higher than in the case of Fig. 10.2.

Fig. 10.5b shows the maximum RF input power, for yielding 3GPP compliant EVM results, to be almost common: for RF input powers beyond +15.5dBm the EVM curves leave the plateau² and increase sharply.

This inflexion points corresponds to an over-modulation of the LD: since the sine peak

RF over-driving power values +25dBm (10 log ((95𝑚𝐴−15𝑚𝐴)²·50Ω·10³) = +25𝑑𝐵𝑚), by subtracting the crest factor of the UMTS carrier of 9 to 10dB, than a correspondence ranging between +15 and +16dBm can be found. The input power range value corresponds to the one measured in the case Fig. 10.2.

Conclusion

These measurements have demonstrated the possibility of using a SOA for realizing the reach extension of UMTS carrier distribution through PON architectures with an additional Transport Section. The overall optical budgets range from 47 to 51dB.

Here the benefit of the in-line SOA acting as an optical repeater is to make RoF to become able to take advantage of the reach-extension concept initially developed for cascading several PONs. Indeed if RoF is to be used in RE-PONs, it is suitable that it can be adapted to the latter.

10.2.2. Dual UMTS carrier with 20km of S-SMF

Given the previous sections’ results, the transmission of two UMTS carriers is envisaged.

Therefore a second UMTS carrier equal power is emulated by a second Vector Signal Generator (VSG) which outputs a 3.84Mchips/s signal which is pulse-shaped by a Root- Raised Cosine (RRC) filter with a roll-off factor of 0.22, at frequency offsets of 5, 10, or 15MHz. This signal is not a UMTS signal compliant to TestModel 4 of [59], yet it plays the role of a dummy carrier. Thus only the Composite EVM of the compliant signal is measured.

For different couples of optical budgets of theTransport Section (19 and 21dB) and of the Access Section (28 and 30dB) the EVM of the carrier of interest, in presence of the dummy carrier, is measured. The place-holding carrier is successively spaced by 5, 10, and 15MHz.

Measured results

6 8 10 12 14 16 18 20

-20 -15 -10 -5 0 5 10 15 20

TX power for one channel [dBm] (5MHz)

Composite EVM [%]

EVM limit Dual 5MHz Dual 10MHz Dual 15MHz

(a)

6 8 10 12 14 16 18 20

-55 -50 -45 -40 -35 -30 -25 -20

RX carrier power [dBm] (5MHz)

Composite EVM [%]

EVM limit Dual 5MHz Dual 10MHz Dual 15MHz

(b)

6 8 10 12 14 16 18 20

-20 -15 -10 -5 0 5 10 15 20

TX power for one channel [dBm] (5MHz)

Composite EVM [%]

EVM limit Dual 5MHz Dual 10MHz Dual 15MHz

(c)

6 8 10 12 14 16 18 20

-55 -50 -45 -40 -35 -30 -25 -20

RX carrier power [dBm] (5MHz)

Composite EVM [%] EVM limit

Dual 5MHz Dual 10MHz Dual 15MHz

(d)

Figure 10.6.: EVM performances for a dual carrier transmission over an ER-PON architecture:

(a)-(b): 19dB Transport budget + 28dB Access budget (best case);

(c)-(d): 21dB Transport budget + 30dB Access budget (worst case)

The reported measurements concern the overall optical budgets of 47 and 51dB. Fig. 10.6 shows the corresponding EVM curves against the transmitted and received carrier power.

From the minimum required RF input power for yielding compliant EVM figures, the 47dB overall optical budget variant requires -16dBm per carrier while the 51dB variant requires 6dB more: -10dBm per carrier.

As a consequence of this the minimum required received RF power for yielding compliant EVM figures is 6dB lower for the 47dB overall optical budget variant than for the 51dB variant. Thus the RF dynamic for which the EVM is compliant with the specifications is 6dB wider for the 47dB overall optical budget variant than for the 51dB variant, since Fig. 10.6b and 10.6d show that maximum received RF power yielding compliant EVM results is common to both optical budgets variants (except for the 5MHz spacing).

Conclusion

These performances were obtained for a single propagating wavelength carrying two UMTS carriers centered at 2140MHz, and demonstrate their possible distribution over ER-PON architectures. Furthermore whether the place-holding carrier was spaced by 5, 10, or 15MHz, the results remain unchanged.

Finally similar performances are obtained when transmitting two UMTS carriers centered at 1940MHz in the uplink direction and when the positions of the Transport and Access Sections are swapped.