Fiber Optical Parametric Ampliﬁer Performance in a 1-Tbs DWDM Communication System

8/22/2019 Fiber Optical Parametric Amplifier Performance in a 1-Tbs DWDM Communication System

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950 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 18, NO. 2, MARCH/APRIL 2012

Fiber Optical Parametric Amplifier Performancein a 1-Tb/s DWDM Communication System

Nayla El Dahdah, Donald S. Govan, Mehdi Jamshidifar, Nick J. Doran, and Michel E. Marhic , Senior Member, IEEE

(Invited Paper)

AbstractWe have reduced signalsignal four-wave mixingcrosstalk in a fiber optical parametric amplifier (OPA) by usinga short nonlinear fiber for the gain medium and a high-powerpump. This allowed us to obtain less than 1 dB penalty for amplifi-cation of 26 dense wavelength-division multiplexed (WDM) chan-nels modulated at 43.7 Gb/s return to zero-differential phase-shiftkeying, with the OPA placed between transmitter and receiver.We then used the same OPA in several different roles for a long-haul transmission system. We did not insert the OPA within theloop, but investigated this role indirectly by using equivalent re-

sults for small numbers of loop recirculations. We found that stan-dard erbium-doped fiber amplifiers currently hold an advantageover this OPA, which becomes negligible for long distances. Thispaper shows that at this time OPAs can handle amplification ofWDM traffic in excess of 1 Tb/s with little degradation. It also indi-cates that with further improvements, fiber OPAs could be a con-tender for wideband amplification in future optical communicationnetworks.

Index TermsFiber optical parametric oscillators and ampli-fiers, fiber optic communication.

I. INTRODUCTION

HIGH spectral efficiency dense wavelength-division multi-

plexed (DWDM) systems are required to meet the rapidly

growing demand in Internet traffic due to emerging multimedia

applications [1]. Current systems are limited by the erbium-

doped fiber amplifier (EDFA) bands, i.e., about 32 nm. To use

larger bandwidths, it is, therefore, necessary to investigate other

amplifier types.

Fiber optical parametric amplifiers (OPAs) offer prospects for

amplification over large bandwidths [2] and outside the EDFA

bands, which could be useful for future communication sys-

tems. However, the nonlinearity of the amplifying medium,

Manuscript received December 1, 2010; revised May 5, 2011; accepted June9, 2011. Date of publication June 23, 2011; date of current version March 2,2012. This work was supported by the Engineering and Physical Sciences Re-search Council, U.K., under Grant EP/E033636/1.

N. El Dahdah was with Swansea University, Swansea, SA2 8PP, U.K. Sheis now with Gennum UK Ltd., Bishops Stanford, CM23 5DB, U.K. (e-mail:[email protected]).

D. S. Govan was with Swansea University, Swansea, SA2 8PP, U.K.He is now with Oclaro Inc., Paington, TQ4 7AU, U.K. (e-mail: [email protected]).

M. Jamshidifar, N. J. Doran, and M. E. Marhic are with the Col-lege of Engineering, Swansea University, Swansea, SA2 8PP, U.K. (e-mail:[email protected]; [email protected]; [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JSTQE.2011.2160155

coupled with the fact that good phase matching is necessary

for parametric amplification, may lead to detrimental nonlin-

ear crosstalk in wavelength-division multiplexing (WDM) sys-

tems [3]. This crosstalk can be greatly reduced by using highly

uniform fibers [4], low signal power [5], [6], polarization multi-

plexing [7], or short fibers [8]. Also, by using a one-pump OPA

(as opposed to a dual-pump one) it is easier to find spectral re-

gions that are free of pump-signal four-wave mixing (FWM) [9];

for that reason we used a one-pump OPA in this paper. To

date, the highest WDM capacity amplified with low penaltyby a fiber OPA is 120 Gb/s [5]. Simulations of a long fiber

OPA have shown its ability to work as a preamplifier for 64

10 Gb/s WDM signal, when receiving very low signal powers

(35 dBm) [10].

Here, we report a nearly tenfold capacity improvement for

low-penalty amplification of wideband WDM signals by means

of fiber OPAs. This was achieved by reducing signalsignal

FWM crosstalk, by using a short (114 m long) highly nonlinear

fiber (HNLF) in conjunction with a high-power (3 W) pump.

The WDM spectrum amplified in this paper consisted of

26 DWDM channels modulated at 43.7 Gb/s return to zero-

differential phase-shift keyed (RZ-DPSK), with a total data ratein excess of 1 Tb/s. This modulation format is known to yield

reduced crosstalk levels compared to OOK [7], [11]. Typical

communication system signal levels were used throughout.

The OPA performance was assessed at different locations in

a WDM transmission system. In Section II, we present the re-

sults obtained for the OPA placed between the WDM transmitter

and receiver: it exhibited less than 1 dB penalty compared to

a communication-grade EDFA. In Section III, we consider the

role of the OPA at the end of a long-haul transmission system.

In Section IV, we introduce the recirculating loop designed to

test WDM signal propagation over long distances, with the OPA

used as a booster amplifier before the loop; we also investigate

the performance of the OPA if it was placed in the transmission

line, by using results obtained for a smaller number of recircula-

tions. In Section V, the OPA is placed after an EDFA that loaded

noise to give the same optical signal-to-noise ratio (OSNR) as

was measured at the loop output for various distances. Finally,

we conclude in Section VI, and discuss developments required

for the evolution toward all-OPA communication networks.

II. OPA BETWEEN TRANSMITTER AND RECEIVER

In [8], we showed that by using a short HNLF, and cor-

respondingly increasing the pump power to maintain the de-

sired gain, signalsignal FWM crosstalk could be substantially

1077-260X/$26.00 2011 IEEE


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DAHDAH et al.: FIBER OPTICAL PARAMETRIC AMPLIFIER PERFORMANCE IN A 1-Tb/s DWDM COMMUNICATION SYSTEM 951

Fig. 1. Evaluated system configuration. Left: with OPA. Right: with EDFA(WDM: Wavelength Division Multiplexer, Tx: Transmitter, Rx: Receiver).(a)(d) Measurement points.

Fig. 2. Gain spectrum of the evaluated OPA. P = 1572.5 nm and 0 =1570nm.

reduced. As a result, bit-error rate performance was improved

for two 10 Gb/s signals simultaneously amplified by the OPA.

Here, we increased the data rate of each WDM signal being

amplified to over 40 Gb/s, and evaluated the OPA performance

as follows.

A. Experimental Setup

The performance of the OPA was evaluated using the back-

to-back configuration shown in Fig. 1. The OPA was placedbetween the transmitter and receiver of the DWDM testbed and

its performance was compared with a single-stage EDFA that

has 17 dB flat gain and 25-dBm maximum output power.

The testbed contained 26 channels on the ITU grid with

100-GHz channel spacing starting from 1531.11 nm, with the

channels at 1537.40 and 1538.19 nm missing. After multiplex-

ing, the channels were modulated at 43.7 Gb/s by two LiNbO3MachZehnder modulators. The first modulator was driven by a

2311 pseudo-random bit sequence to generate a DPSK signal.

The second was driven by a half-rate clock creating RZ-DPSK

modulation with 67% duty cycle. The channels were decorre-

lated through 1.5 km of standard fiber (SMF), and then launched

into the EDFA or OPA.The OPA used a single pump; the pump power was 35

dBm and its wavelength was 1572.5 nm; its relative intensity

noise (RIN) at the HNLF output, measured with a 3-MHz res-

olution bandwidth, was 63 dB. Pump phase modulation by

four RF tones was used for suppressing pump-induced stimu-

lated Brillouin scattering in the HNLF. The gain medium was

114 m of HNLF with 15 W1 km1 nonlinear coefficient and

0.023 ps/nm2-km dispersion slope. The gain curve of the OPA

was tailored by tuning pump wavelength and power in order

to obtain as flat a gain as possible in the transmission range.

Fig. 2 shows the gain spectrum of the OPA. Since the state of

the polarization (SOP) of the channels were slightly different

Fig. 3. Normalized optical spectra of the data at EDFA output (x) and OPAoutput (solid line) with some channels OFF (dotted line), measured with 0.5-nmresolution bandwidth.

after passing through the decorrelator fiber, it was possible to

further flatten the gain by polarization controlling so that all thechannels experienced almost the same gain of 20 dB. The OPA

was compared with an EDFA with a flat gain of 17 dB, a noise

figure of 5 dB, and a maximum output power of 25 dBm.

The channel powers were leveled at the output of the ampli-

fiers by adjusting the input channel powers. The total power at

the OPA (EDFA) input was 1.5 dBm (4.8 dBm).

The signals were received using a tunable flat-top filter with

a bandwidth of 0.6 nm to demultiplex the selected channel, fol-

lowed by a MachZehnder delay interferometer and balanced

photodiodes.

B. Results and Discussion

The performance of the OPA was evaluated by measuring bit

error rate (BER) versus power and OSNR at the receiver input

(points (b) and (d)). We used throughout a 0.5-nm resolution

bandwidth for measuring OSNR, to ensure that the entire signal

spectrum was included in the resolution bandwidth. We first

measured the back-to-back performance of the OPA. Next we

substituted the OPA with the EDFA ensuring that the input and

output OSNRs measured at points (c) and (d) were equal to those

measured at points (a) and (b), which required a reduction of

the total input power using a variable optical attenuator (VOA).

The normalized optical spectra of the transmitted channels at

the output of the OPA and EDFA are shown in Fig. 3. It is seenin this figure that the noise level is different on either sides of

the spectrum. This tilt in noise is the same for OPA and EDFA

and increases for increased total power or number of channels

for the OPA. The tilt in the noise level for the EDFA is caused

by the nonflat gain when it is used outside its optimum gain

level. Moreover, by turning OFF channels in pairs across the

band, e.g., 4 and 5, 16 and 17, we measure different levels of

noise. Indeed, the OPA-induced noise is generated by nonlinear

crosstalk due to FWM which is greater at short wavelengths

because of stronger phase matching. This is in agreement with

simulation results obtained using the split-step Fourier method.

Fig. 4 shows the simulated output spectrum obtained with the


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Fig. 4. Simulated OPA output spectrum for four equal power input signals,with wavelengths 1540, 1540.8, 1545, and 1545.8 nm.

Fig. 5. BER measurements versus received power of the data amplified by theEDFA (solid line) and OPA (dotted line) at channels 1 (diamond), 4 (square), 9(triangle), 12 (x), 16 (star), 20 (circle), and 26 (+).

parameters used in our experiments, and four equal-power input

signals. The results clearly verified that crosstalk level is higher

for shorter wavelengths.

With 34-dB input OSNR (0.5-nm resolution bandwidth) at

points (a) and (c), the BER variations of channels 1, 4, 9, 12, 16,

20, and 26, measured at points (b) and (d), respectively, versus

the received power, measured at points (b) and (d), respectively,

are shown in Fig. 5. The accuracy on the received power levelwas 0.3 dB; therefore, both cases exhibit similar performance

variation with channel wavelength. The penalty on the received

powerwas plotted against wavelengthin Fig. 6. We found 0.7-dB

average penalty across the channels. The origin of the measured

penalty at the OPA output is partly due to the coherent nature

(FWM crosstalk) of the induced noise. Indeed, we verified that

the channels amplified by the OPA contain additional intrinsic

noise, i.e., they have higher RIN. It originates from the pump

and is independent of the signals characteristics [12][14].

These results show that OPAs can be suitable amplifiers for

DWDM systems. In the following section, we assess the OPA

as a receiver amplifier.

Fig. 6. Received power penalty versus wavelength of the channels 1, 4, 9,12, 16, 20, and 26 amplified by OPA compared with EDFA.

Fig. 7. System configuration (WDM: Wavelength Division Multiplexer, Tx:Transmitter, Rx: Receiver). (a)(c) Measurement points.

III. OPA AS A RECEIVER AMPLIFIER

The assessment of the OPA at the receiver, e.g., destination

node, was achieved by decreasing the OSNR at its input and

measuring the BER, and assuming that the residual chromatic

dispersion-induced penalty is negligible.


The performance of the OPA was evaluated using the con-

figuration shown in Fig. 7. The OPA was placed at the receiver

input of the DWDM testbed. Its performance was comparedwith a single-stage EDFA that has 30-dB flat gain and 24-dBm

maximum output power.

The testbed transmitter was as previously. The OSNR at point

(a) was set by a VOA followed by a dual-stage EDFA (used in

fixed output power mode, 19 dBm) with a VOA at the mid stage.

The channel powers were leveled at the output of the dual-stage

EDFA, by adjusting the input channel powers. The total power

at the OPA/EDFA input (point (a)) was set to 1 dBm using a

VOA.


We first assessed the performance of the OPA by measur-ing BER versus OSNR at the input and the output of the re-

ceiver amplifiers (points (a) and (b)), with 1-dBm constant input

power (point (a)). This was carried out using the mid channels 4

and 16.

The OSNR at the receiver input was decreased by attenuat-

ing input power of the dual-stage EDFA and was measured by

turning the channel OFF. The OSNR values chosen correspond

to those recorded at the output of the recirculating loop detailed

in the next section. Hence, the input OSNR was varied between

14.2 and 7 dB (0.5-nm resolution bandwidth).

The BER measured at point (c) against the input OSNR (point

(a)) at a constant receivedpower (0.5 dBm) for channels 4 and 16


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Fig. 8. BER versus OSNR of channels 4 (left) and 16 (right) at the input ofthe EDFA (close diamond) and OPA (open diamond).

Fig. 9. Normalized noise power versus wavelength at the output of the OPA.

are shown in Fig. 8 for both amplifiers. The estimated accuracyon the OSNR and BER measurements was 5%, represented by

error bars. We note different performance variations with chan-

nel wavelength and input OSNR for both amplifiers. Indeed,

at channel 16, both amplifiers perform similarly. At channel 4,

there is a large difference in performance for high OSNRs (BER

108) giving a 3-dB OSNR penalty. However, this penalty de-

creases and the results converge as the input OSNR is reduced.

The difference in performance at the start is due to the tilt in

the OPA-induced noise across the band (see Fig. 9) resulting

in different OSNRs. This was measured by turning the chan-

nels OFF in pairs with a 16-dB input OSNR. As expected, the

OPA-induced noise, mainly generated by FWM, is greater at

short wavelengths because of stronger phase matching. How-ever, by degrading the input OSNR, the generated amplified

spontaneous emission (ASE) noise dominates the OPA noise

and is responsible for the results converging.

In Fig. 10, we display the results for channel 4 by plotting

the BER against the corresponding OSNR at the receiver input

(point (b)). It illustrates clearly how the relationship between

the OSNR and BER is altered by the nature of the OPA-induced

noise, predominantly coherent. We verified that it is not affected

by the increase of the input power leading to the growth of the

OPA-induced noise (see Fig. 10, open dots). In addition, the

relationship between the input and output OSNRs is different

with each amplifier.

Fig. 10. BER versus received OSNR of the data amplified by EDFA (closeddiamond) and OPA (open diamond) at channel 4 after input OSNR degradation(dots + line) and input power increase (scatter dots).

Fig. 11. Evaluated system configuration (WDM: Wavelength Division Mul-tiplexer, Tx: Transmitter, T-DCM: Tunable DCM, Rx: Receiver). (a)(d) Mea-surement points.

In the next section, the OPA is assessed as a transmitter am-

plifier and as an intermediate amplifier in a WDM transmission

line.

IV. OPA USED WITH RECIRCULATING LOOP

We then inserted the OPA in a WDM system containing a

recirculating loop. We first performed tests to evaluate the OPAs

performance when placed before the loop. We then used the

results of measurements obtained with different loop lengths

to estimate the OPAs performance if it was placed at different

locations, i.e., between two transmission lines. The OPA was

not placed in the loop as it had highly polarization-dependent

gain.

A. Experimental SetupThe performance of the OPA was evaluated using the config-

uration shown in Fig. 11. It is similar to that of Fig. 1, except

for the insertion of a recirculating loop DWDM testbed in the

middle. The OPA was placed between the transmitter and the

recirculating loop. Its performance was compared with a single-

stage EDFA that has 17-dB flat gain and 25-dBm maximum

output power.

The channels were decorrelated (by 6 bits per channel) and

precompensated through a dispersion compensating fiber (DCF)

with dispersion of166.5 ps/nm before being amplified in the

OPA or EDFA. The channel powers were leveled at the output

of the OPA/EDFA by adjusting the input channel powers. The


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total powerat the OPA/EDFA input (point (a)) was 1 dBm(137

13 dBm per wavelength).

The amplified channels were launched into the recirculating

loop. The loop was controlled by two acousto-optic switches

that were synchronized by a digital delay generator (DDG). The

loop consisted of four spans, with a total transmission distance

of 360 km per recirculation. The first span comprised 60 km

of SMF followed by a dual-stage EDFA including DCF. The

second and third spans were 100 km of SMF alsowithdual-stage

EDFAs containing DCF. The fourth span also contained 100 km

of SMF; however, the dual-stage EDFA had a leveler in the mid

stage. The average dispersion range per recirculation across

the channels is between 0.057 and 0.071 ps/nm/km leading to

[20.5, 25.6]-ps/nm residual dispersion range per recirculation.

The power level at the loop input (point (b)) was equalized with

the transmission power level using a VOA.

After transmission, the signals were dispersion compensated

with a tunable DCM. Following an EDFA, they were received

using a tunable flat-top filter with a bandwidth of 0.6 nm to de-

multiplex the selected channel, a MachZehnder delay interfer-ometer, and balanced photodiodes. The receiver amplifier was a

single-stage EDFA with 30-dB flat gain and 24-dBm maximum

output power. The receiver was operated in its optimal power

range [1, 1] dBm, giving the best BER. The test equipment

was triggered by the DDG.


The performance of the OPA was evaluated in two scenarios,

source node amplifier and intermediate node amplifier. It was

assessed by measuring BER versus recirculation number and

OSNR at the input of the recirculating loop and the receiver

(points (b) and (c)). The maximum transmission distance wasdetermined by the forward error correction (FEC) limit, i.e., 2

103 BER.

We first measured the performance of the OPA before replac-

ing it by the EDFA, ensuring that the input power and OSNR

(0.5-nm resolution bandwidth optical spectrum analyzer) mea-

sured at point (a) remained constant.

C. Source Node Amplifier

With 17.6-dB input OSNR at point (a), the BER variations

after 2, 4, 6, and 8 recirculations measured at point (d) with a

constant received power (0.5 dBm) for channels 1, 4, 9, 12, 16,

20, and 26, are shown in Fig. 12 for both amplifiers. We notesimilar performance variations with channel wavelength and

transmission distance for both amplifiers. Despite a difference in

BER for short distances, the results for both amplifiers converge

with increasing number of recirculations.

In Figs. 13 and 14, we display the results for channel 4 by

plotting the BER against number of recirculations and the cor-

responding OSNR at the receiver input (point (c)), respectively.

The estimated accuracy on the OSNR and BER measurements

was 5%, represented by error bars. Fig. 13 illustrates that for

short-haul transmission, the OPA performance as source node

amplifier is equivalent to the EDFA performance on the sub-

sequent recirculation due to the OPAs back-to-back perfor-

Fig. 12. BER versus channel number for the OPA (left) and EDFA (right)after 2 (square), 4 (diamond), 6 (triangle), and 8 (star) recirculations.

Fig. 13. BER versus recirculation of the data amplified by OPA (open dia-mond) and EDFA (closed diamond) at channel 4.

Fig. 14. BER versus received OSNR of the data amplified by OPA (opendiamond) and EDFA (closed diamond) at channel 4.

mance [15]. However, the gap decreases with distance as theloop EDFAs noise dominates.

In order to assess the difference in performance between the

amplifiers in terms of OSNR penalty, we plotted the BER against

OSNR at therecirculating loop output(see Fig. 14). As expected,

we found that for the same BER we measured different OSNR

values with theEDFA andOPA. This difference canbe explained

by the different nature of the noise generated by the OPA which

is predominately coherent resulting from pump-noise transfer,

creating an altered relationship between the OSNR and BER as

illustrated in previous section. Therefore, to be able to measure a

meaningful OSNR penalty we must first extrapolate the required

EDFA OSNR for each BER measured with the OPA.


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Fig. 15. OSNR average penalty versus recirculation of the data amplified byOPA compared with EDFA.

The average OSNR penalty across the channels was calcu-

lated after each recirculation (see Fig. 15). This decreases from

0.9 dB to zero. After five recirculations, the penalty is negligi-

ble and the OPA performance converges with that of the EDFA

across the channels.Therefore, despite differences at short distances, an equal

maximum distance, 2880 km, was obtained with either amplifier

at the source node. This distance was taken to be the distance

where all channels were within the FEC limit.

D. Intermediate Node Amplifier

The assessment of the OPA at an intermediate node was

achieved by decreasing the OSNR at its input (point (a)), and

measuring as previously the maximum number of recirculations,

referred to as postrecirculation. This approximation is only valid

for short distances with relatively low nonlinear penalties andnegligible residual chromatic dispersion.The OSNR values cho-

sen correspond to those recorded with the EDFA after the first

three recirculations in the previous section. The effective dis-

tance equivalent to each OSNR used, referred to as pretransmis-

sion distance, was found using numerical models based on the

split-step Fourier method to assess the nonlinear penalties.

The OSNR was set by a VOA followed by a dual-stage EDFA

with a VOA at the mid stage. The decrease in OSNR induced

a tilt in the spectrum at the loop input (point (b)), with either

amplifier, to the extent that the channel powers could no longer

be perfectly leveled. This increased the power level at short

wavelengths. The tilt is larger with the EDFA as it is used in

fixed output power mode.Theevaluation wascarried out with channels 4 and16. There-

sulting maximum number of postrecirculations is plotted against

the equivalent pretransmission distance in Fig. 16. In this sce-

nario, the OPA exhibits a better performance than the EDFA

as a result of the flatter channel power profile at the OPA out-

put. Indeed, when the OPA had an increased tilt, a penalty was

observed.

The minimal decrease of postrecirculation with pretransmis-

sion distance demonstrates that the level of ASE noise before the

OPA does not limit its performance, particularly where phase

modulated signals are used in reducing the penalties associated

with cross-gain modulation.

Fig. 16. Maximum number of postrecirculation versus equivalent pretrans-mission distance of the data amplified by OPA (open diamond) and EDFA(closed diamond).

In the next section, we attempt to evaluate the impact of

multiple OPAs in a WDM system.

V. OPA CASCADING

The assessment of using multiple OPAs (i.e., cascading) was

achieved by increasing the power at the OPA input to induce an

increasein the noise and, therefore, a decrease of the OSNRat its

output. We then measured the maximum transmission distance

(determined by the FEC limit) with the recirculating loop.


The performance of the OPA was evaluated using the con-

figuration shown in Fig. 11. The OPA was placed between the

transmitter and recirculating loop of the DWDM testbed.

The average OSNR at the OPA input (point (a)) was 16.5 dB.


The assessment of OPA cascading was achieved by increas-

ing the OPA input power (point (a)) and, hence, the OSNR at

its output (point (b)), and measuring the maximum number of

recirculations referred to as postrecirculation.

Indeed, in the case of two OPAs separated by a transmission

fiber, the channels at the input to the second OPA will be differ-

ently aligned following transmission through a fiber span. As

a result, the amplifier-induced noise will be different at each

amplifier, i.e., random, acting as incoherent noise. Therefore,

simply reducing the OSNR by 3 dB with the same OPA induces

a greater penalty than doubling the number of OPAs.In Fig. 17, we show the variation of the output OSNR with the

input power for a constant input OSNR (16 dB) and channels

4 and 16. The relationship between the OPA output OSNR and

input power is different with wavelength. Indeed, the OSNR

at short wavelength is lower as expected as the OPA-induced

noise at short wavelength is higher. However, a 3-dB OSNR

decrease is obtained at both channels 4 and 16 for same input

power, 7 dBm. In addition, the relationship between OPA output

OSNR and BER is not altered by the increase of the input power

as mentioned in the previous section (see Fig. 16).

In Fig. 18, we plot the resulting maximum number of postre-

circulations against the input power. Again, as anticipated,


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Fig. 17. Received OSNR versus total powerat OPA input forchannels4 (opendiamond) and 16 (open square).

Fig. 18. Maximum number of recirculation versus total power at OPA inputfor channels 4 (open diamond) and 16 (open square).

channel 16 exhibits a better performance than channel 4 as a

result of a better OSNR at the OPA output. However, channel4 performance is worse than expected for 7-dBm input power.

Indeed, we were anticipating the maximum number of recircu-

lation to decrease by 1 as measured with EDFA with a similar

change in the OSNR. This can be explained by the coherent

nature of the noise instead of incoherent. Besides, the minimal

decrease of postrecirculation with power increase of channel

16 indicates that with a shorter HNLF a similar degradation of

performance is expected at channel 4.

These results show that using multiple OPAs in an optical

transmission system with phase-shift keying modulation format

will not introduce any significant additional penalties.

VI. CONCLUSION

We have demonstrated, for the first time to our knowledge,

the amplification with a fiber OPA of 26 RZ-DPSK DWDM

channels with a net capacity of 1.04 Tb/s.

We have also demonstrated that using this fiber OPA at either

the transmitter or an intermediate node in a recirculating loop

induces no further limitation on the maximum transmission dis-

tance of this WDM spectrum. We have also shown that OPA

performance at the receiver is not altered when predegraded

signals are used.

These experiments indicate that fiber OPAs exhibit sufficient

performance to be used at several locations in long-haul WDM

systems. At this time these OPAs are still not equivalent to ED-

FAs, and so cannot replace them entirely in long-haul systems.

To arrive at this stage, it will be necessary to improve the OPAs,

particularly by further reducing the nonlinear crosstalk between

WDM channels.

ACKNOWLEDGMENT

The authors thank Sumitomo Electric Industries, Japan, for

supplying the HNLFs.

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[8] M. Jamshidifar, A. Vedadi, and M. E. Marhic, Reduction of four-wave-mixing crosstalk in a short fiber-optical parametric amplifier, IEEEPhoton. Technol. Lett., vol. 21, no. 17, pp. 12441246, Sep. 2009.

[9] M. E. Marhic, Fiber Optical Amplifiers, Oscillators and Related Devices.Cambridge, U.K.: Cambridge Univ. Press, 2007.

[10] J. M. Chavez Boggio, P. Dainese, and H. L. Fragnito, Performance ofa two-pump fiber optical parametric amplifier in a 10 Gb/s 64 channeldense wavelength divisionmultiplexing system, Opt.Commun., vol. 218,pp. 303310, 2003.

[11] B. P.-P. Kuo, P. C. Chui, and K. K.-Y. Wong, A comprehensive studyon crosstalk suppression techniques in fiber optical parametric amplifierby modulation format, IEEE J. Sel. Topics Quantum Electron., vol. 14,no. 3, pp. 659665, May/Jun. 2008.

[12] P. Kylemark, P. O. Hedekvist, H. Sunnerud, M. Karlsson, and P. A.Andrekson, Noise characteristics of fiber optical parametric amplifiers,J. Lightw. Technol., vol. 22, no. 2, pp. 409416, Feb. 2004.

[13] P. Kylemark, P. O. Hedekvist, H. Sunnerud, M. Karlsson, and P. A.Andrekson, Correction to noise characteristics of fiber optical parametricamplifiers, J. Lightw. Technol., vol. 23, no. 6, p. 2192, Jun. 2005.

[14] M. E. Marhic, Fiber Optical Amplifiers, Oscillators and Related Devices.Cambridge, U.K.: Cambridge Univ. Press, 2007, ch. 10.[15] M. Jamshidifar,N. El Dahdah, D. S. Govan,N. J. Doran,and M.E. Marhic,

1-Tb/s DWDM amplification in a fiber optical parametric amplifier, inProc. IEEE Opt. Fiber Commun. Nat. Fiber. Opt. Eng. Conf., San Diego,CA, Mar. 2125, 2010, Paper OWT1, pp. 12.

Nayla El Dahdah received the M.Sc. degree in physics and the Ph.D. degreein optics from the University of Paris XI, Orsay, France, in 1999 and 2003,respectively.

She wasa Research Engineerat Laboratoire de Photonique et Nanostructures,CNRS, Marcoussis, France, where she stayed until 2004. She was a ResearchEngineer at France Telecom R&D, Lannion, France, before joining the Instituteof Advanced Telecommunications, Swansea University, Swansea, U.K., as aResearch Assistant. She is currently at Gennum UK, Bishops Stanford, U.K.Her research interests include transmission systems, optical signal processing,

and optical components.


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Donald S. Govan received the B.Sc.(Hons.) degree in laser physics and opto-electronics from the University of Strathclyde, Glasgow, U.K., in 1995, and thePh.D. degree from the Photonics Research Group at Aston University, Birming-ham, U.K., in 1999, where he was a Contact Research Fellow until 2000.

He joined Marconi Company as a Senior Development Engineer in May2000, where he was part of the team that developed the UPLx160 product,Marconis ultralong haul (>3000 km) dense wavelength-division multiplexedphotonic line system. From June 2004 to May 2006, he was at the George GreenInstitute for Electromagnetics Research, Nottingham University, Nottingham,U.K. In May 2006, he joined the Institute of Advanced Telecommunications,Swansea University, Swansea, U.K., as a Research Assistant. He is currently atOclaro Inc., Paington, U.K. His research interests include numerical modelingof optical networks, subsystems, and components.

Mehdi Jamshidifar was born in Oroumieh, Iran,in August 1981. He received the B.Sc. degree inelectrical and electronic engineering from the Insti-tute of Electro-technique, Tehran University, Tehran,Iran, in 2005, and the M.Sc. degree (with Distinc-tion) in photonics and telecommunication systemsfrom Swansea University, Swansea, U.K., in 2007.He received the Ph.D. degree from the College ofEngineering, Swansea University, Swansea, U.K., in2010, where he was involved in research on fiber op-tical parametric amplifiers and nonlinear fiber optics.

He is currently a Postdoctoral Researcher at Swansea University, Swansea,where he has been conducting research on next-generation optical systems, incollaboration with Oclaro Inc. His research interests include nonlinear fiberoptics, coherent systems, and optical parametric amplifiers.

Dr. Jamshidifar is a member of the Optical Society of America.

Nick J. Doran received the B Sc. and Ph.D. degreesin physicsfrom Reading Universityin 1970and 1974,respectively.

He is currentlya Professorof photonics at SwanseaUniversity, Swansea, U.K., where he headed the In-stitute of Advanced Telecommunications, SwanseaUniversity, which is nowmergedin the Collegeof En-gineering, Swansea University. He was the CTO andFounder of Marconi-Solstis, which developed andinstalled the worlds longest land-based ultrahigh-capacity optical communications system in 2003.

From 1991 to 2000, he was a Professor of photonics at Aston University,cofounding the Photonics Research Group there and, prior to that, he was theLeader of the Ultrafast Communications Group at BT Laboratories, MartleshamHeath. He has more than 200 publications and numerous patents on nonlinearand ultrafast transmission and optical devices.

Michel E. Marhic (M78SM87) received theDiplome DIngenieur from Ecole SuperieureDElectricite, Metz, France, the M.S. degree fromCase Western Reserve University, Cleveland, OH,and the Ph.D. degree from the University of

California, Los Angeles, all in electricalengineering.

He was on the Faculty of the Department ofElectrical Engineering, Northwestern University(19741998), and on sabbatical leaves at USC(197980) and Stanford University (19841985

and 19931994). From 1998 to 2006, he was a Consulting Professor in theDepartment of Electrical Engineering, Stanford University. He is currentlya Chair Professor at the Institute of Advanced Telecommunications, Schoolof Engineering, Swansea University, Swansea, U.K. He cofounded Holicon,Holographic Industries, and OPAL Laboratories. Over the past 15 years, hisemphasis has been on optical communication systems and on nonlinear opticalinteractions in fibers. He has written the first book on Fiber Optical ParametricAmplifiers, Oscillators and Related Devices (Cambridge, U.K.: CambridgeUniv. Press, 2007). He is the author or coauthor of more than 300 journals andconference papers, and his 9 patents are awarded. His research spans areasof applied optics, including nonlinear interactions in plasmas, optical fibermeasurements, hollow infrared waveguides, holography, phase conjugation,and fiber networks.

Dr. Marhic is a Fellow of the Optical Society of America and an EminentMember of Tau Beta Pi. He was the recipient of the Ameritech ResearchProfessorship (19901991) from the Institute for Modern Communications.

Fiber Optical Parametric Ampliﬁer Performance in a 1-Tbs DWDM Communication System

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