ANALYSIS OF ALL-OPTICALDEMULTIPLEXING FROM 160/320 Gbit/sTO 40 Gbit/s USING QUANTUM-DOTSEMICONDUCTOR OPTICAL AMPLIFIERSASSISTED MACH-ZEHNDERINTERFEROMETER

Wei Yang,1 Min Zhang,2 and Peida Ye21 Beijing Information Science and Technology University (BISTU),Beijing 100081, People’s Republic of China; Corresponding author:ywiaia006@gmail.com2Key Laboratory of Optical Communication and LightwaveTechnologies, Beijing University of Posts and Telecommunications,Ministry of Education, P.O. Box 201, Beijing 100876, People’sRepublic of China

Received 12 October 2009

ABSTRACT: The performance of ultrafast all-optical demultiplexer

using quantum-dot semiconductor optical amplifiers (QD-SOAs) assistedMach-Zehnder interferometer (MZI) is analyzed. Through numericalsimulations, a set of key parameters are optimized and all-optical

demultiplexing from 160/320 Gbit/s to 40 Gbit/s can be realized withfairly high performance. The results are useful for the system

performance studies and practical application. VC 2010 Wiley

Periodicals, Inc. Microwave Opt Technol Lett 52: 1629–1633, 2010;

Published online in Wiley InterScience (www.interscience.wiley.com).

DOI 10.1002/mop.25287

Key words: demultiplexing; quantum-dot semiconductor opticalamplifier; Mach-Zehnder interferometer

1. INTRODUCTION

In the optical time-division multiplexed (OTDM) systems, opti-

cal demultiplexing is an essential technique for extracting a sig-

nal channel at the base rate from a multiplexed high-bit-rate

data stream. A number of demultiplexers have been proposed

using effect of four-wave mixing (FWM) in semiconductor opti-

cal amplifier (SOA) [1], ultrafast chirp dynamics in a single

SOA [2–4], a ultrafast nonlinear interferometer (UNI) employing

an SOA [5], a fiber-loop with a LiNbO3 Mach-Zehnder modula-

tor (MZM) [6], cross-phase modulation in a dispersion-shifted

photonic crystal fiber and subsequent spectral filtering [7], a

variable optical delay [8], and electroabsorption modulators

(EAMs) under high-frequency sinusoidal modulation [9, 10].

And those schemes using SOAs are attractive, owing to the

SOAs’ characteristics of high gain, low switching power, and

wide gain bandwidth. The methods in Refs. 1 and 5 are success-

fully demonstrated for line rates of up to 160 Gbit/s, but for

much higher operation speed, the applications are limited due to

the slow gain recovery speed of the SOAs. In Refs. 2–4, the

ultrafast chirp dynamics in SOAs is utilized to achieve the 320/

640 Gbit/s optical demultiplexing. Recently, multi-section SOAs

have also been applied to extract 25 Gbit/s tributary channel

from a 100 Gbit/s RZ pattern [11–13]. On the other hand, the

switch performance using conventional SOAs may be improved

by using quantum-dot SOAs (QD-SOAs), due to their great

potential for high-speed optical communications and optical

processing [14–18], such as low noise figure and small degree

of patterning. Wavelength conversions at 160 Gbit/s using XGM

or XPM in QD SOAs have been simulated in Refs. [19–21].

In this article, we present a high-performance all-optical

demultiplexer employing QD-SOAs and MZI, which is capable

of demultiplexing 160/320 Gbit/s line-rate signals to 40 Gbit/s

base-rate channels. Such demultiplexer features simple structure,

high stability, low switching energy, and high integration ability.

Meanwhile, due to the use of symmetrical MZI architecture, the

operation condition is easy to adjust. We give detailed theoreti-

cal study and simulation analysis, and then advices on parame-

ters selection are drawn for the performance optimization.

2. SCHEME AND OPERATION PRINCIPLE

Figure 1 shows the configuration of QD-SOAs assisted symmet-

rical MZI, with two QD-SOAs located in relatively the same

position of the two arms. For demultiplexing, the 160 Gbit/s

data signal at kS enters the upper arm of MZI via coupler C2,

acting as the control signal. A clock stream at kC, via coupler

C1, is divided into two parts, acting as the probe signal. We

assume that the clock and the data have been synchronized. In

the upper arm, the data signal modulates the QD-SOA1 gain,

and thus gain and phase of the copropagating probe signal via

cross-gain modulation (XGM) and cross-phase modulation

(XPM) effect. Hence, the gain and the phase difference are

introduced between the probe signals in the two arms. Both

probe signals interfere at coupler C3, causing a copy of the data

signal onto the probe wavelength kC at time slots where the

clock pulse is present. If the clock pulse is running at a sub-rate

of the data, one data channel at the sub-rate can be demulti-

plexed at the clock wavelength.

For simplicity, an ideal facet reflectivity is assumed, and the

effect of amplified spontaneous emission (ASE) on the gain sat-

uration is ignored since QD-SOA has lower noise figure com-

pared to bulk as well as QW amplifiers [22]. The theoretical

model for QD-SOA is based on the wave propagation equations

and the rate equations for wetting layer (WL), excited state

(ES), and ground state (GS). The propagation equations for the

photon density S and phase U can be written as [23].

@Sðz; tÞ@z

¼ gS� aintS (1)

@U@z

¼ � 1

2ag (2)

where S(z,t) ¼ P(z,t)/(AeffVghv), P(z,t) is the power, Aeff is the

QD-SOA’s effective cross section, z is the distance in longitudi-

nal direction, g is the modal gain, aint is the absorption coeffi-

cient of the material, and a is the linewidth enhancement factor.

By assuming uniform distributions of electrons and holes in

the QDs, the modal gain can be written as g ¼ gmax(2f�1),

where gmax is the maximum modal gain, f is the electron occu-

pation probability of the GS [18]. The rate equations for the

electron densities of WL, ES, and GS can be written, respec-

tively, as [15–17]

Figure 1 Schematic diagrams of the high speed demultiplexing using

QD-SOA assisted MZI

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 7, July 2010 1629

@Nw

@t¼ J

eLw� Nwð1� hÞ

sw2þ Nwh

s2w� Nw

swR(3)

@h

@t¼ NwLwð1� hÞ

NQsw2� NwLwh

NQs2w� ð1� f Þh

s21þ f ð1� hÞ

s12(4)

@f

@t¼ ð1� f Þh

s21� f ð1� hÞ

s12� f 2

s1R� gL

NQ

S � Vg (5)

where t is time, Nw is the electron density in the WL, h is the

electron occupation probability of the ES, sw2 is the electron

relaxation time from the WL to the ES, s2w is the electron

escape time from the ES to the WL, swR is the spontaneous

radiative lifetime in WL, and s1R is the spontaneous radiative

lifetime in the QDs. s21 is the electron relaxation time from the

ES to the GS and s12 is the electron escape time from the GS to

the ES. NQ is the surface density of QDs and Lw is the effective

thickness of the active layer.

Equationuations (1)–(5) describe the evolution of optical

wave in the active region of QD-SOA, and they are solved by

dividing the QD-SOA into sections, where the carrier densities

are considered constant at each time step. After calculation, the

QD-SOAs gains (Gi, i ¼ 1 and 2) and the pulse phase-shifts

(D/i, i ¼ 1 and 2) in both arms are expressed as:

GiðtÞ ¼ SiðL; tÞ=Sið0; tÞ (6)

D/iðtÞ ¼ � a2½lnðGiÞ þ aint � L� (7)

where Si(0,t) and Si(L,t) are the probe photon densities at input

and output of QD-SOAs. At the output of the MZI, the two

probe lights at kc interfere and the demultiplexed output inten-

sity is described as:

PoutðtÞ ¼ 1

4PprobeðtÞ

G1ðtÞ þ G2ðtÞ � 2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiG1ðtÞ � G2ðtÞ

pcos ½D/1ðtÞ � D/2ðtÞ�

n oð8Þ

3. SIMULATIONS AND RESULTS

To analyze and optimize the demultiplexer performance, we

conduct numerical simulations, where the OTDM signal is 160

Gbit/s RZ pseudorandom bit sequences (PRBS) with length of

27�1, and the clock signal is 40 GHz with a pulsewidth of 2 ps.

The investigated device is a typical QD-SOA with values of the

material parameters: Lw ¼ 0.2 lm, W ¼ 3 lm, NQ ¼5 � 1010cm�2, gmax¼ 12 cm�1, aint ¼ 2 cm�1, sw2 ¼ 3 ps, s2w ¼1 ns, s21 ¼ 0.16 ps, s21 ¼ 1.2 ps, swR ¼ 1 ns, and s1R ¼ 0.4 ns.

To start, we study the QD-SOA parameters (e.g., the length

L, the linewidth-enhancement factor a, and so on) and the bias

current density (J) for the demultiplexing operation, with the op-

tical signal parameters fixed. The calculated 3 dB input satura-

tion power as a function of the current density in case of various

SOA lengths is plotted in Figure 2. The saturation power

increases with the current density, for that larger current density

can supply more carriers to compensate the carrier consumption.

Meanwhile, under the same current density, the saturation power

decreases with the increase of the SOA length, which means

that the QD-SOA can be saturated easily (with lower input

power) in case of longer device length. With the input data

energy (E1) and clock energy (E2) fixed at 200 fJ and 3 fJ,

respectively, we plot the contrast ratio (CR) of the demulti-

plexed signal against J with L as a parameter under different

linewidth-enhancement factor, as shown in Figure 3. No wonder,

larger J and shorter L may yield better switching performance.

It is also found that under the same J and L, smaller a may be

beneficial to obtain larger CR, and the effect of a becomes

stronger on the conditions of larger L. Since in our simulations,

the input CR is 20 dB, the maximum output CR is lower than

20 dB. When a ¼ 0.1, to get a CR over 10 dB, J should be

larger than 0.8, 1.7, and 5 kA/cm2 for L ¼ 2 mm, 4 mm, and 6

mm, respectively. In practical use of QD-SOA, too large current

density may be unfeasible, which limits the use of longer QD-

SOA. On the other hand, longer L corresponds to larger unsatu-

rated gain. Therefore, a moderate QD-SOA length should be

selected to achieve a good demultiplexer performance while

maintaining an efficient gain.

Then, setting L ¼ 4 mm and a ¼ 0.1, we go on to study the

output ‘‘pseudo-eye-diagrams’’ (PED) under different current

density, as shown in Figure 4. Obviously, when J � 2 kA/cm2,

a clearly-opened eye diagram can be obtained and the output Q-factor is larger than 10, which indicates the good quality of the

demultiplexed signal.

Figure 2 3 dB input saturation power as a function of the current den-

sity J for different SOA length L

Figure 3 Output CR against J at different SOA length L and a, withE1 ¼ 200 fJ, E2 ¼ 3 fJ, where open marks, � center marks and solid

marks correspond to a ¼ 0.1, a ¼ 1.0, and a ¼ 2, respectively

1630 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 7, July 2010 DOI 10.1002/mop

According to the analysis above, we select moderate values

of L, J, and a here and simulate the 160-to-40 Gbit/s demulti-

plexing operation. The corresponding input and output signals

are plotted in Figure 5, which conveys the demultiplexing is real-

ized desirably. Obviously, the data channel that is synchronized

with the clock is obtained after demultiplexing, while the other

channels are restrained. Different data channel can be obtained

by introducing some delay (nT, n ¼1, 2, 3) into the clock signal.

Then, fixing the values of the other parameters, we study the

output CR, Q-factor, and the average output power (Pout) with

respect to the input data energy (E1). Here, the linewidth-

enhancement factor is also selected as a parameter. As shown in

Figure 6, with the increase of the control pulse energy, CR

decreases quickly and then the decrease slows down. The influ-

ence of a on CR is the same as described in Figure 3, i.e.,

smaller a is beneficial to obtain larger CR, and when 0.1 � a �1, such effect can be neglected in the whole range of the signal

energy studied here. Regarding Figure 7, when 0.1 � a � 1, Q-factor is not greatly affected by the changes of the control pulse

energy, and at moderate pulse energy (e.g. E1 < 0.4 pJ), larger

a is beneficial to get a higher Q-factor. When a ¼ 2, however,

the influence of the pulse energy on Q-factor is apparent, and

the rapid increase and decrease in Q-factor are observed, with

the boundary point of E1 ¼ 0.25 pJ. Thus for larger pulse

energy (e.g., E1 > 0.4 pJ), increasing a (a � 2) may degrade

the Q-factor. Such evident differences between a ¼ 0.1,1 and a¼ 2 may be explained partly by Figure 8, where the average

output power increases with the pulse energy for a ¼ 0.1,1, and

when E1 > 0.4 pJ, the increase slows down and Pout tends to

become a constant. While for a ¼ 2, Pout increases first and

then decreases when E1 > 0.25 pJ. The insets in Figure 7 are

the output eye-diagrams at different operation points (A, B, C,

D, and E). Based on the analysis above, the trade-off among the

output CR, Q-factor and Pout can be obtained by choosing

proper values of a and data energy. Here, we set a ¼ 1 to

achieve a large effective range of the data energy.

In the following context, we give an overall analysis of the

demultiplexer performance by optimizing the input date energy

to achieve an output CR of 10 dB. The optimal data energy as a

function of the current density for different device lengths of 4

mm and 6 mm are plotted in Figure 9(a). Since that CR

decreases with the data energy as described in Figure 6, to get a

CR larger than 10 dB the input data energy should be lower

than the optimal energy. Thus, the larger the optimal data

energy is, the larger the effective range of the input data energy.

It can be found in Figure 9(a) that the effective energy range

Figure 5 Input logic signals and simulated output signals for L ¼ 4

mm, a ¼ 0.1, J ¼ 2 kA/cm2, E1 ¼ 200 fJ, E2 ¼ 3 fJ

Figure 6 Output CR for the demultiplexing operation, with a as a

parameter for L ¼ 4 mm, J ¼ 2 kA/cm2 and E2 ¼ 3 fJ

Figure 4 Output eye-diagrams at different current density: (a) J ¼ 1.5

kA/cm2, (b) J ¼ 2 kA/cm2, (c) J ¼ 2.5 kA/cm2, (d) J ¼ 3 kA/cm2, for

L ¼ 4 mm, a ¼ 0.1, E1 ¼ 200 fJ, E2 ¼ 3 fJ

Figure 7 Output Q-factor for the demultiplexing operation, with a as

a parameter for L ¼ 4 mm, J ¼ 2 kA/cm2 and E2 ¼ 3 fJ

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 7, July 2010 1631

can be extended by increasing the current density or reducing

the device length. When L ¼ 6 mm, to achieve the effective

demultiplexing operation, the current density should be larger

than 3.5 kA/cm2. Then, we study the output Q-factor within the

effective energy range, where the CR is larger than 10 dB. The

corresponding Q-factor for L ¼ 4 mm at J ¼ 2 kA/cm2, J ¼ 2.5

kA/cm2, and J ¼ 3 kA/cm2 is shown in Figure 9(b), and that for

L ¼ 6 mm is given in the inset. When L ¼ 4 mm and J � 2

kA/cm2, the output Q-factor is larger than 8 in the effective

energy range, and when L ¼ 6 mm and J � 3.5 kA/cm2, the Q-factor >8 is also obtained.

Using the same methods, we conduct the 320-to-40 Gbit/s

demultiplexing and the demultiplexer performance is described

in Figure 10. It is obvious that under the same current density

and the device length, the effective range of the input data

energy is smaller than that of the 160-to-40 Gbit/s demultiplex-

ing, and when L ¼ 6 mm, to achieve the effective demultiplex-

ing operation, the current density should be larger than 4.5 kA/

cm2. Also, in the effective energy range, the corresponding Q-factor is �3 lower than that of the 160-to-40 Gbit/s demultiplex-

ing. According to Figures 9 and 10, we can select proper device

length, current density, and input data energy to meet specific

performance requirements.

Based on the analysis above, advices on parameter design

and performance optimization for the ultrafast OTDM demulti-

plexer are drawn as follows:

(1) Shorter L and larger current density may lead to larger

input saturation power and consequently higher CR can

be obtained; however, with other parameters fixed, reduc-

ing the device length may reduce the unsaturated gain of

the QD-SOA. Thus, to maintain an efficient gain, a mod-

erate device length should be selected.

(2) Smaller a is beneficial to get a larger CR, and its influ-

ence on CR may become apparent with the increase of

the device length and the input data energy.

(3) The effect of a on Q-factor is related with the data

energy; under moderate current density (J ¼ 2 kA/cm2)

and relatively small probe energy (E2 ¼ 3 fJ), increasing

a (0.1 � a � 2) may enhance the Q-factor when E1 <0.4 pJ, but for E1 > 0.4 pJ, larger a (a ¼ 2) may degrade

the demultiplexer performance in terms of the Q-factorand the average output power. To meet certain perform-

ance requirement, the input data energy may be opti-

mized according to the QD-SOA parameter (a).(4) Shorter L and larger current density may result in a

larger effective range of the input data energy for CR

>8. When L ¼ 4 mm, the effective energy range is E1 <0.275 pJ, E1 < 0.425 pJ, E1 < 0.57 pJ for J ¼ 2 kA/

cm2, J ¼ 2.5 kA/cm2, and J ¼ 3 kA/cm2, respectively;

moreover, the corresponding Q-factor is larger than eight.

For a longer device (L ¼ 6 mm), to get a CR larger

than 10 dB, the current density should be larger than

3.5 kA/cm2.

(5) Under the same conditions, the calculated energy range

of the 320-to-40 Gbit/s demultiplexing is smaller than

that of the 160-to-40 Gbit/s operation; meanwhile, the

corresponding Q-factor is �3 lower than that of the 160-

to-40 Gbit/s demultiplexing. For a longer device (L ¼ 6

mm), to get a CR larger than 10 dB, the current density

should be larger than 4.5 kA/2.

4. CONCLUSIONS

In this article, the all-optical demultiplexing from 160/320 Gbit/

s to 40 Gbit/s is achieved using quantum-dot semiconductor op-

tical amplifiers (QD-SOAs) assisted Mach-Zehnder interferome-

ter (MZI). The performance of the demultiplexer is analyzed

through numerical simulations, and the QD-SOAs parameters

(e.g., the length L, the linewidth-enhancement factor a, and so

Figure 8 Average output power against E1, with a as a parameter for

L ¼ 4 mm, J ¼ 2 kA/cm2 and E2 ¼ 3 fJ

Figure 9 Demultiplexing performance of 160-to-40 Gbit/s (a) the

input data energy for CR ¼ 10 dB and (b) the corresponding output

Q-factor, with E2 ¼ 3 fJ and a ¼ 1

Figure 10 Demultiplexing performance of 320-to-40 Gbit/s (a) the

input data energy for CR ¼ 10 dB and (b) the corresponding output

Q-factor, with E2 ¼ 3 fJ and a ¼ 1

1632 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 7, July 2010 DOI 10.1002/mop

on), the current density (J) and the optical signal energy are

studied for the demultiplexing operation. According to the

analysis, good performance of the 160/320-to-40 Gbit/s demulti-

plexing can be achieved, and the effective energy range for

CR � 10 dB at different device length and current density is

determined. Then, we study the corresponding Q-factor in the

effective energy range. The conclusions in the article can be

applied for parameter selection to optimize the demultplexer

performance.

ACKNOWLEDGMENTS

This study is supported by Programs NCET-06-0094, 863 No.

2007AA01Z243, 863 No. 2009AA01z255, PCSIRT No.IRT0609,

111 Project (NO. B07005), and Beijing New Star Programme of

Science and Technologies (2007A048).

REFERENCES

1. S.L. Jansen, M. Heid, S. Spdlter, E. Meissner, C.-J. Weiske, A.

Sch6pflin, D. Khoe, and H. de Waardt, Demultiplexing 160 Gbit/s

OTDM signal to 40 Gb/s by FWM in SOA, Electron Lett 38

(2002), 978–980.

2. E. Tangdiongga, Y. Liu, H. de Waardt, D. Khoe, and H. Dorren,

Demultiplexing 160/320 Gb/s to 40 Gb/s using a single SOA

assisted by an optical filter, Presented at the Optical Fiber Commu-

nication Conference and Exposition and The National Fiber Optic

Engineers Conference, Technical Digest (CD) (Optical Society of

America, 2006), paper OTuB5, 2006.

3. E. Tangdiongga, Y. Liu, H. de Waardt, G.D. Khoe, A.M.J. Koo-

nen, H.J.S. Dorren, X. Shu, and I. Bennion, All-optical demulti-

plexing of 640 to 40 Gbits/s using filtered chirp of a

semiconductor optical amplifier, Opt Lett 32 (2007), 835–837.

4. H.J.S. Dorren, E. Tangdiongga, Y. Liu, Z. Li, H. de Waardt, A.M.

Koonen, G.D. Khoe, and X. Shu, Semiconductor-based optical

demultiplexing and wavelength conversion at 320 Gbit/s, Presented

at the Optical Fiber Communication Conference and Exposition

and The National Fiber Optic Engineers Conference, OSA Techni-

cal Digest Series (CD) (Optical Society of America, 2007), paper

OThT3, 2007.

5. C. Schubert, C. Schmidt, S. Ferber, R. Ludwig, and H.G. Weber,

Error-free all-optical add-drop multiplexing at 160 Gbit/s, Pre-

sented at the Optical Fiber Communication Conference (OFC ’03),

postdeadline paper PD17-1.

6. M.D. Pelusi, Fiber-looped LiNbO3 Mach-Zehnder modulator for

160 Gb/s optical time division demultiplexing and its comparison

to an electro-absorption modulator, Presented at the Optical Fiber

Communication Conference and Exposition and The National Fiber

Optic Engineers Conference, OSA Technical Digest (CD) (Optical

Society of America, 2008), paper OMN4, 2008.

7. K. Igarashi, K. Katoh, K. Kikuchi, T. Nagashima, T. Hasegawa, S.

Ohara, and N. Sugimoto, 160-Gbit/s optical time-division demulti-

plexing based on cross-phase modulation in a 2-m-long dispersion-

shifted Bi2O3 photonic crystal fiber, Presented at the Conference

on Lasers and Electro-Optics/Quantum Electronics and Laser Sci-

ence Conference and Photonic Applications Systems Technologies,

OSA Technical Digest (CD) (Optical Society of America, 2007),

paper JTuC3, 2007.

8. A. Cheng, M.P. Fok, and C. Shu, All-optical tunable delay line for

channel selection in OTDM demultiplexing, Presented at the Asia

Optical Fiber Communication and Optoelectronic Exposition and

Conference, OSA Technical Digest (CD) (Optical Society of Amer-

ica, 2008), paper SuA3, 2008.

9. H.-F. Chou, J. E. Bowers, and D.J. Blumenthal, Compact 160Gb/s

add-drop multiplexing with 40Gb/s base-rate, Presented at the

Optical Fiber Communication Conference (OFC ’04), February

2004.

10. A.D. Gallant and J.C. Cartledge, Characterization of the dynamic

absorption of electroabsorption modulators with application to

OTDM demultiplexing, J Lightwave Technol 26 (2008),

1835–1839.

11. C. Crognale and A. Di Giansante, Ultrafast all-optical demultiplex-

ing by using multi-section semiconductor optical amplifiers in a

M-Z interferometer, Presented at the Laser Science XXIV, OSA

Technical Digest (CD) (Optical Society of America, 2008), paper

JSuA25, 2008.

12. C. Crognale, V. Ricchiuti, and A. Di Giansante, Signal integrity in an

all-optical demultiplexer for OTDM interconnections by using cross-

gain modulation in a multi-section SOA, Presented at the 12th IEEE

Workshop on SPI 2008, PS13, Avignon, France, 2008, pp.12–15.

13. C. Crognale, V. Ricchiuti, S. Caputo, and S. Saracino, All-optical

de-multiplexing by cross-phase modulation in pattern independent

semiconductor optical amplifiers, In: Nonlinear Optics 2007,WE20,

Kona, Hawaii, 2007.

14. A.V. Uskov, T.W. Berg, and J. Mørk, Theory of pule-train amplifi-

cation without patterning effects in quantum-dot semiconductor op-

tical amplifiers, IEEE J Quantum Electron 40 (2004), 306–320.

15. O. Qasaimeh, Characteristics of cross-gain (XG) wavelength con-

version in quantum dot semiconductor optical amplifiers, IEEE

Photon Technol Lett 16 (2004), 542–544.

16. O. Qasaimeh, Optical gain and saturation characteristics of quan-

tum-dot semiconductor optical amplifiers, IEEE J Quantum Elec-

tron 39 (2003), 793–798.

17. T.W. Berg, S. Bischoff, I. Magnusdottir, and J. Mørk, Ultrafast

gain recovery and modulation limitations in self-assembled quan-

tum-dot devices, IEEE Photon Technol Lett 13 (2001), 541–543.

18. A.V. Uskov, J. Mork, B. Tromborg, T.W. Berg, et al.,On high-

speed cross-gain modulation without pattern effects in quantum dot

semiconductor optical amplifiers, Opt Commun 227 (2003),

363–369.

19. H. Sun, Q. Wang, H. Dong, and N. Dutta, XOR performance of a

quantum dot semiconductor optical amplifier based Mach-Zehnder

interferometer, Opt Express 13 (2005), 1892–1899.

20. J.F. Pina, H.J.A. Silva, P.N. Monteiro, J. Wang, W. Freude, and J.

Leuthold, Performance evaluation of wavelength conversion at 160

Gbit/s using XGM in quantum-dot semiconductor optical amplifiers

in MZI configuration, Photon Switch 2007, 77–78.

21. J.F. Pina, H.J.A. da Silva, P.N. Monteiro, J. Wang, W. Freude, and

J. Leuthold, Cross-gain modulation-based 2R regenerator using

quantum-dot semiconductor optical amplifiers at 160 Gbit/s, Pre-

sented at the 9th International Conference on Transparent Optical

Networks, ICTON ’07, 2007, pp.106–109.

22. T.W. Berg and J. Mork, Saturation and noise properties of quan-

tum-dot optical amplifiers, IEEE J Quantum Electron 40 (2004),

1527–1539.

23. Y. Ben-Ezra, M. Haridim, and B.I. Lembrikov, Theoretical analysis

of gain-recovery time and chirp in QD-SOA, IEEE Photon Technol

Lett 17 (2005), 1803–1805.

VC 2010 Wiley Periodicals, Inc.

SHIELDING BOX ANTENNA FORAPPLICATION IN WUSB FLASH DISK

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DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 7, July 2010 1633