a linearized optical single-sideband modulation analog microwave photonic link using dual parallel...

A Linearized Optical Single-SidebandModulation Analog Microwave PhotonicLink Using Dual Parallel InterferometersVolume 5, Number 5, October 2013

Zihang ZhuShanghong ZhaoQinggui TanWei JiangYongjun LiXuan Li

DOI: 10.1109/JPHOT.2013.22816131943-0655 � 2013 IEEE

A Linearized Optical Single-SidebandModulation Analog Microwave PhotonicLink Using Dual Parallel Interferometers

Zihang Zhu,1;2 Shanghong Zhao,1 Qinggui Tan,2 Wei Jiang,2Yongjun Li,1 and Xuan Li1

1School of Information and Navigation, Air Force Engineering University, Xi’an 710077, China2Key Laboratory of Science and Technology on Space Microwave Technology,

China Academy of Space Technology, Xi’an 710000, China

DOI: 10.1109/JPHOT.2013.22816131943-0655 � 2013 IEEE

Manuscript received August 18, 2013; revised September 5, 2013; accepted September 5, 2013. Date ofcurrent version September 18, 2013. This work was supported in part by the National High TechnologyResearch and Development Program of China (863 Program) under Grant 2007AA01Z263 and in part bythe National Natural Science Foundation of China under Grant 61205002. Corresponding author: Z. Zhu(e-mail: [email protected]).

Abstract: Dual parallel Mach–Zehnder interferometers (MZIs) are presented to linearize theoptical single-sideband (OSSB) modulation analog microwave photonic link. By using a dual-drive Mach–Zehnder modulator at the transmit side of the link, an OSSB modulation can beobtained. By exploiting different RF responses of two MZIs at the receive end, the third-orderintermodulation distortion (IMD3) is well suppressed and the spurious-free dynamic range(SFDR) is enhanced. More importantly, we demonstrate fundamental-to-IMD3 ratio of 49 dBfor an RF input signal power value of 10 dBm, which is 24 dBmore than a conventional OSSBmodulation link, and SFDR of 132 dB for a bandwidth of 1 Hz at the received optical power of8 dBm assuming shot noise is the dominant noise contribution, which is improvedapproximately 20 dB.

Index Terms: Microwave photonic link, optical single-sideband modulation, dual parallelinterferometers, linearized.

1. IntroductionAnalog microwave photonic links are used in various applications including broadband wirelessaccess networks, sensor networks, radar, satellite communications, instrumentation, and warfaresystems [1], due to the advantages of large bandwidth, reduced attenuation, size, weight, andimmunity to electromagnetic interference. Inmost of these links, the RF signal is externally modulatedwith a Mach–Zehnder modulator (MZM) based on different modulation schemes including opticaldouble-sideband (ODSB), optical carrier suppression (OCS), and optical single-sideband (OSSB)[2], [3]. Among them, OSSB modulation is more preferable in analog microwave photonic links sinceit can effectively eliminate the fading effect [4] and produce higher bandwidth efficiency [5].

In the conventional OSSB modulation scheme, nonlinear distortion such as harmonic distortionand intermodulation distortion will be generated due to the nonlinear transfer function of the MZM,which limits the overall link spurious-free dynamic range (SFDR). The third-order intermodulationdistortion (IMD3) is the most determining cause of distortion since it is in close proximity to thefundamental signal and difficult to filter out. In order to eliminate the IMD3 and enhance the SFDR ofthe link, many schemes have been presented. The general idea is to introduce certain predistortionto compensate for the existing ones using complex modulators, such as dual-drive MZM (DD-MZM)

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IEEE Photonics Journal OSSB Modulation Link Using Interferometers

with fiber Bragg grating (FBG) [6], integrated dual MZM [7], mixed polarization DD-MZM [8], dual-parallel MZM (DP-MZM) [9], and electro-optic polymeric DP-MZM [10]. However, those methodsare difficult to control at arbitrary operating points and increase the complexity of transmitter. Up tonow, a little attention has been paid on postcompensation for the nonlinearity of modulators directlyin the optical fields. However, these approaches are limited to ODSB modulation [11], [12], phasemodulation [13], [14], or frequency modulation [15].

In this paper, a postcompensation scheme for nonlinearity of OSSBmodulation analog microwavephotonic link is proposed and demonstrated. At the transmit side of the link, OSSB modulation isrealized by using a DD-MZM [16]. At the receive end, IMD3 is suppressed by utilizing two parallelinterferometers. This architecture greatly simplifies the transmitter. The theoretical derivation ofSFDR for our linearized link is presented and the comparison between our scheme and conventionalOSSB modulation is carried out. Finally, the bandwidth over which our linearized link still out-performs a conventional OSSB modulation link is discussed.

2. Link Geometry and Theory of OperationFig. 1 shows the proposed architecture for linearization of an OSSB modulation microwave photoniclink. Two RF signals are optically modulated by a DFB laser with a DD-MZM, but they are 90- phaseshift from each other and the MZM is biased at quadrature. Thus, an OSSB modulation signal isgenerated. Postmodulator the OSSB signal is equally divided into two parts by a 3 dB opticalsplitter, and drives two parallel interferometers with different differential delays. The differencingoperation is performed with a balanced detector to suppress the IMD3. In order to make phasematching of IMD3 between two paths, a variable fiber delay line is used before each photodiode(PD) on the two demodulation paths.

2.1. OSSB Modulation Generation and LinearizationAccording to the transfer function of DD-MZM, the optical field at the output of modulator can be

quantified by

Eout ðtÞ ¼Ecejwc t

2ej’ðtÞ þ jej’0ðtÞh i

(1)

where

’ðtÞ ¼ffiffiffi2p

2m cosðw1tÞ þ cosðw2tÞ½ � (2)

’0ðtÞ ¼ffiffiffi2p

2m sinðw1tÞ þ sinðw2tÞ½ � (3)

Fig. 1. Linearized microwave photonic link architecture for OSSB modulation.


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are the optical phase shift applied to each arms of modulator for a two-tone measurement, Ec andwc are the lightwave amplitude and angular frequency, respectively, m ¼ �V=V� is the modulationindex of MZM, V ¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffi2PrfRip

is the amplitude of RF input signal, Prf is the RF input power, Ri is theinput resistance of the modulator, V� is the half-wave voltage of modulator, w1 and w2 are theangular frequencies of RF input signals.

By using the Jacobi-Auger expansions ejmcosðwtÞ ¼P1

n¼�1 j nJnðmÞejnwt and ejmsinðwtÞ ¼P1n¼�1 JnðmÞejnwt , (1) can be further expanded as

Eout ðtÞ ¼Ecejwc t

2

X1n¼�1

j nJn

ffiffiffi2p

2m

!ejnw1t

X1k¼�1

j k Jk

ffiffiffi2p

2m

!ejkw2t

"

þ jX1

n¼�1Jn

ffiffiffi2p

2m

!ejnw1t

X1k¼�1

Jk

ffiffiffi2p

2m

!ejkw2t

#

¼ Ecejwc t

2

X1n¼�1

X1k¼�1

ðj nþk þ jÞJnffiffiffi2p

2m

!Jk

ffiffiffi2p

2m

!ejðnw1þkw2Þt : (4)

It is shown from (4) that only the upper first-order sideband exists. Thus, an OSSB modulationsignal is generated.

After interferometric demodulation, the output photocurrent from the up-path can be obtained as

I1ðtÞ ¼R

ffiffiffi2p

8Ecejwc t e�jwc�1 ej’ðt��1Þ þ jej’0ðt��1Þ

� �� ðej’ðtÞ þ jej’0ðtÞÞ

h i�

ffiffiffi2p

8Ece�jwc t ejwc�1 e�j’ðt��1Þ � je�j’

0ðt��1Þ� �

� e�j’ðtÞ � je�j’0ðtÞ

� �h i

¼ RE2c

162þ J0ðmÞ

X1n¼1�1þ ð�1Þn� �

j nþ1JnðmÞcos nw1ðt � �1Þ þn�4

h i(

þ J0ðmÞX1k¼1�1þ ð�1Þkh i

j kþ1Jk ðmÞcos kw2ðt � �1Þ þk�4

� �

þ 2X1n¼1

X1k¼1�1þ ð�1Þnþkh i

j nþkþ1JnðmÞJk ðmÞ

� cos nw1ðt � �1Þ þn�4

h icos kw2ðt � �1Þ þ

k�4

� �

�X1

n¼�1

X1k¼�1

Jnffiffiffi2p

msinw1�12

� �� Jk

ffiffiffi2p

msinw2�12

� ��

� cos n w1t �w1�12

� �þ k w2t �

w2�12

� �� wc�1

h i�X1

n¼�1

X1n¼�1

Jnffiffiffi2p

msin �w1�12þ �4

� �� Jk

ffiffiffi2p


� ��

� sin n w1t �w1�12þ 3�

4

� k w2t �

w2�12� �

4

� �� wc�1

� �

þX1

n¼�1

X1n¼�1

Jnffiffiffi2p

mcos �w1�12þ �4

� �� Jk

ffiffiffi2p


� ��

� sin n w1t �w1�12� �

4

� �þ k w2t �

w2�12� �

4

� �� wc�1

h i� J0

ffiffiffi2p

msinw1�12

� �� J0

ffiffiffi2p

msinw2�12

� �� coswc�1

� 2J0ffiffiffi2p

msinw1�12

� �� X1k¼1

Jkffiffiffi2p

msinw2�12

� ��


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� cos k w2t �w2�12

� �h icos wc�1 þ

k�2

� 2J0ffiffiffi2p

msinw2�12

� �� X1n¼1

Jnffiffiffi2p

msinw1�12

� ��

� cos n w1t �w1�12


n�2

� �

� 4X1n¼1

X1k¼1ð�jÞnþkJn

ffiffiffi2p

msinw1�12

� �� Jk

ffiffiffi2p

msinw2�12

� ��

� cos n w1t �w1�12

� �h icos k w2t �

w2�12


ðk þ nÞ�2

� �

þ J0ðmÞX1k¼1�1þ ð�1Þkh i

j kþ1Jk ðmÞcos kw2t þk�4

� �

þ J0ðmÞX1n¼1�1þ ð�1Þn� �

jnþ1JnðmÞcos nw1t þn�4

h i

þ 2X1n¼1

X1k¼1�1þ ð�1Þnþkh i

j nþkþ1JnðmÞJk ðmÞcos nw1t þn�4

h icos kw2t þ

k�4

� �)(5)

where R is the responsivity of photodiode, �1 is the differential delay of the MZI1, Jn and Jk are

Bessel functions of the first kind. From (5), the amplitude of the fundamental response for up-path

can be obtained as

I1;w1 ¼R8E2c 2J0ðmÞJ1ðmÞcos

w1�12

� �þ

ffiffiffi2p

J0ffiffiffi2p

msinw2�12

� �J1

ffiffiffi2p

msinw1�12

� �sinðwc�1Þ

n� J0

ffiffiffi2p


� �h iJ1

ffiffiffi2p


� �h icosðwc�1Þ

� J0ffiffiffi2p

mcos �w2�12þ �

4

� �h iJ1

ffiffiffi2p


4


o� cos w1t �

w1�12þ �

4

� �: (6)

The in-band third-order intermodulation products are the limiting distortion components, theamplitude of this distortion term can be obtained as

I1;2w1�w2 ¼R8E2c �2J1ðmÞJ2ðmÞcos �w1�1 þ

w2�12

� �n�

ffiffiffi2p

J1ffiffiffi2p

msinw2�12

� �h iJ2

ffiffiffi2p

msinw1�12

� �h isinðwc�1Þ

þ J1ffiffiffi2p

msin �w2�12þ �

4

� �h iJ2

ffiffiffi2p

msin �w1�12þ �

4


þ J1ffiffiffi2p


� �h iJ2

ffiffiffi2p


4


o� cos 2w1t � w2t � w1�1 þ

w2�12þ �4

� �: (7)

In order to better understand the principle of our linearization scheme, a small-signal approximation

m � 1 is considered. Thus, equation (6) can be further simplified as

I1;w1 ¼R8E2c cos

w1�12

� �1� cosðwc�1Þ½ � þ sin

w1�12


n omcos w1t �

w1�12þ �4

� �¼A1;1mcos w1t �

w1�12þ �4

� �: (8)


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Following the same method, equation (7) can be further simplified as:

I1;2w1�w2 ¼R8E2c �

cos �w1�1 þ w2�12

� �8

�sin w2�1

2

� �sin2 w1�1

2

� �4

sinðwc�1Þ"(

þffiffiffi2p

sin � w2�12 þ �

4

� �sin2 � w1�1

2 þ �4

� �8

cosðwc�1Þ

þffiffiffi2p

cos � w2�12 þ �

4

� �cos2 � w1�1

2 þ �4

� �8

cosðwc�1Þ#m3

þ 5192

cos �w1�1 þw2�12

� �þsin w2�1

2

� �sin4 w1�1

2

� �24

sinðwc�1Þ"

þsin3 w2�1

2

� �sin2 w1�1

2

� �16

sinðwc�1Þ

�ffiffiffi2p

sin � w2�12 þ �

4

� �sin4 � w1�1

2 þ �4

� �48

cosðwc�1Þ

�ffiffiffi2p

sin3 � w2�12 þ �

4

� �sin2 � w1�1

2 þ �4

� �32

cosðwc�1Þ

�ffiffiffi2p

cos � w2�12 þ �

4

� �cos4 � w1�1

2 þ �4

� �48

cosðwc�1Þ

�ffiffiffi2p

cos3 � w2�12 þ �

4

� �cos2 � w1�1

2 þ �4

� �32

cosðwc�1Þ#m5

)

� cos 2w1t � w2t � w1�1 þw2�12þ �

4

� �¼ðB1;3m3 þ B1;5m5Þ � cos 2w1t � w2t � w1�1 þ

w2�12þ �

4

� �: (9)

In this paper, the third-order term in equation (9) will be suppressed, which is the dominantdistortion.

The output photocurrents from the two arms of MZI are � out of phase. Thus, following the samemethod, the small-signal fundamental photocurrent for bottom-path can be obtained as:

I2;w1 ¼R8E2c cos

w1�22

� �1þ cosðwc�2Þ½ � � sin

w1�22


n omcos w1t �

w1�22þ �4

� �¼A2;1mcos w1t �

w1�22þ �

4

� �(10)

where �2 is the differential delay of the MZI2.The small-signal third-order intermodulation distortion (IMD3) photocurrent for bottom-path can

be obtained as

I2;2w1�w2 ¼R8E2c �

cos �w1�2 þ w2�22

� �8

þsin w2�2

2

� �sin2 w1�2

2

� �4

sinðwc�2Þ"(

�ffiffiffi2p

sin � w2�22 þ �

4

� �sin2 � w1�2

2 þ �4

� �8

cos wc�2ð Þ

�ffiffiffi2p

cos � w2�22 þ �

4

� �cos2 � w1�2

2 þ �4

� �8

cosðwc�2Þ#m3


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þ 5192

cos �w1�2 þw2�22

� ��sin w2�2

2

� �sin4 w1�2

2

� �24

sinðwc�2Þ"

�sin3 w2�2

2

� �sin2 w1�2

2

� �16

sinðwc�2Þ

þffiffiffi2p

sin � w2�22 þ �

4

� �sin4 � w1�2

2 þ �4

� �48

cosðwc�2Þ

þffiffiffi2p

sin3 � w2�22 þ �

4

� �sin2 � w1�2

2 þ �4

� �32

cosðwc�2Þ

þffiffiffi2p

cos � w2�22 þ �

4

� �cos4 � w1�2

2 þ �4

� �48

cosðwc�2Þ

þffiffiffi2p

cos3 � w2�22 þ �

4

� �cos2 � w1�2

2 þ �4

� �32

cosðwc�2Þ#m5

)

� cos 2w1t � w2t � w1�2 þw2�22þ �

4

� �¼ðB2;3m3 þ B2;5m5Þcos 2w1t � w2t � w1�2 þ

w2�22þ �

4

� �: (11)

From (9) and (11), in order to make phase matching of IMD3 between two paths, the time delay offiber delay line on the bottom-path should satisfy the condition

� ¼ 12ð�1 � �2Þ: (12)

Furthermore, the third-order terms have equal amplitude when the coefficients B1;3 and B2;3

satisfy the condition

10��10B1;3 ¼ B2;3 (13)

where � is the power attenuation for up-path.Thus, the third-order terms of IMD3 have equal intensity and phase. After the differencing operation

is performed, these two kinds of IMD3 terms will cancel each other out while the fundamental term stillexists. In the circumstances, the fifth-order terms at frequencies 2w1 � w2 and 2w2 � w1 are thedominant distortion components.

2.2. Spur-Free Dynamic RangeThe spurious-free dynamic range of link is first determined by the output Nth order intercept point,

which can be written as

OIPN ¼PN1

PN

1=ðN�1Þ

(14)

where P1 and PN are the fundamental and N th order distortion output power, respectively.Then, theN th order limited SFDR can be expressed as

SFDRN ¼OIPN

No

ðN�1Þ=N(15)

where No is the output noise power spectral density per unit bandwidth (W/Hz).Taking expressions of output fundamental and distortion power into equation (14), the fifth-order

intercept point of our linearization link can be written as

OIPð2w1�w2Þ5 ¼

10��10A1;1 � A2;1

� �5=22 10�

�10B1;5 � B2;5

� �1=2 Ro (16)

where Ro is the photodiode output resistance.


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Substituting (16) into (15) and assuming shot noise is the dominant noise contributions, the fifthorder limited SFDR is obtained as

SFDRð2w1�w2Þ5 ¼

10��10A1;1 � A2;1

� �5=24qR 10�

�10B1;5 � B2;5

� �1=2Pr

" #4=5(17)

where

Pr ¼E2c

810�

�10 1� cosðwc�1Þ½ � þ 1þ cosðwc�2Þ

�(18)

is the total optical power at the photodiode, q ¼ 1:6� 10�19 C is the electron charge.If the link does not operate at the desired frequency, the coefficients ratio given by (13) will not be

satisfied. In this case, the third order contribution to the IMD3 becomes dominant. Following theapproach presented before, the third-order intercept point and SFDR can be expressed as

OIPð2w1�w2Þ3 ¼

10��10A1;1 � A2;1

� �32 10�

�10B1;3 � B2;3

� �Ro (19)


10��10A1;1 � A2;1

� �34qR 10�

�10B1;3 � B2;3

� �Pr

" #2=3: (20)

Since our linearized architecture requires phase matching to achieve the desired IMD3 sup-pression, any slight relative delay introduced between the two parallel interferometers or smallchanges in the time delays of the MZIs will make SFDR converted from fifth-order-limited to third-order-limited. In this case, the third-order intercept point and third-order-limited SFDR can bewritten as

OIPð2w1�w2Þ3 ¼

10��10A1;1

� �2þA22;1

h i34 10�

�10B1;3

� �2þB22;3

h i8><>:

9>=>;

12

Ro (21)


10��10A1;1

� �2þA22;1

ð4qRPr Þ2 10��10B1;3

� �2þB22;3

h in o13

: (22)

3. Simulation Results and AnalysisTo demonstrate the operation for linearization of an OSSB modulation microwave photonic link, aproof-of-concept simulation is constructed with the commercial software OptiSystem, for a two-toneinvestigation [see Fig. 1]. The simulation parameters for the setup are given in Table 1.

In order to explain the principle of our linearized scheme, the fundamental and IMD3 responsesfor both up and bottom paths are simulated independently, as shown in Fig. 2. Here, the simulatedresponses of the link employing �1 ¼ 100 ps MZI1 are shown by the squares and those of the linkconstructed with the �2 ¼ 75 ps MZI2 are shown by the circles. It can be seen that the IMD3 powerof up and bottom paths are identical, while the fundamental power of bottom path is higher than thatof the up path. When the third-order terms of IMD3 have identical phase, they will be eliminated andthe fundamental power of bottom path will become dominant after differenced with a balanceddetector.

In order to show the suppression of IMD3 by using our proposed scheme over the conventionalOSSB modulation scheme, a microwave photonic link using the conventional OSSB modulation isalso built for comparison, and the main simulation parameters are the same as mentioned inTable 1. Fig. 3 shows the RF output spectrum for conventional OSSB modulation link and our highlylinearized link. It can be seen from Fig. 3(a) that the fundamental-to-IMD3 ratio (FIR) is only 25 dB


Vol. 5, No. 5, October 2013 5501712

Fig. 2. Fundamental and IMD3 responses for both up and bottom pathsVoperating at the linearizationconditionVwhen simulated independently. Squares and solid lines represent the simulated responsesand linear fits of up path. Circles and dashed lines represent the simulated responses and linear fits ofbottom path.

TABLE 1

Simulation Parameters


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using the conventional OSSB modulation scheme. However, it is obviously seen from Fig. 3(b) thatthe FIR is about 49 dB and other distortion components are greatly suppressed.

To further demonstrate the superiority of our linearized link, we compare its SFDR to that oftraditional OSSB link for the identical received optical power, as shown in Fig. 4. It can be seen thatour linearized link is obviously limited by the fifth-order term of IMD3. The simulated fifth-orderintercept of approximately OIPð2w1�w2Þ

5 ¼ 3:9 dBm and shot noise level per unit bandwidth of No ¼�161:1 dBm/Hz yield a fifth-order-limited spurious-free dynamic range of SFDRð2w1�w2Þ

5 ¼ 132 dB(extrapolated to 1 Hz bandwidth). Both the intercept point and SFDR match very well with thetheoretical results shown in (16) and (17) which are OIPð2w1�w2Þ

5 ¼ 3:4 dBm and SFDRð2w1�w2Þ5 ¼

131:5 dB, respectively. For comparison, the simulated third-order intercept and spurious-freedynamic range of the conventional OSSB link operating at the same total received optical power areOIPð2w1�w2Þ

3 ¼ 7:2 dBm and SFDRð2w1�w2Þ3 ¼ 112:1 dB for a bandwidth of 1 Hz. Thus, the SFDR of

our linearized link is approximately 20 dB higher than that of the traditional OSSB link at theidentical received optical power.

The linearized scheme relies upon differencing two properly adjusted third-order terms of IMD3resulting from two frequency-dependent MZIs. In order to explain the frequency-dependence of ourscheme, the power attenuation for up-path is fixed so that the link is linearized at w=2� ¼ 1:01 GHz

Fig. 3. (a) The RF output spectrum for conventional OSSB modulation scheme. (b) The RF outputspectrum for our highly linearized scheme.


Vol. 5, No. 5, October 2013 5501712

and alter the frequencies of two RF input signals between 200 MHz and 2 GHz (maintain the powerand frequency spacing of RF input signals). Circles in Fig. 5 represent the simulated SFDR as afunction of the offset frequency from w=2� ¼ 1:01 GHz. Solid line and dashed line represent thecalculated third-order [see (20)] and fifth-order [see (17)] limited SFDR of our linearized scheme,respectively. While dotted line represents the third-order limited SFDR of a conventional OSSB link.It can be seen obviously that the SFDR is third-order limited for almost all frequencies, except for

Fig. 4. RF output power as a function of RF input power for linearized and traditional OSSB schemes.Circles and solid lines represent the simulated and linear fits to the fundamental and limiting IMD3 of thelinearized scheme. Squares and dashed lines represent the simulated and linear fits to the fundamentaland limiting IMD3 of the traditional OSSB scheme.

Fig. 5. Simulated SFDR as a function of frequency offset from w=2� ¼ 1:01 GHz.


Vol. 5, No. 5, October 2013 5501712

the desired RF input signal frequency where it arrives at maximal value of SFDRð2w1�w2Þ5 ¼ 132 dB.

However, the SFDR is greater than the SFDRð2w1�w2Þ3 ¼ 112:1 dB of a traditional OSSB scheme in

a frequency range of �8.8 GHz.In real systems, the time delays of MZI1 and MZI2 may deviate from 100 ps and 75 ps,

respectively. These conditions will result in the degradation of SFDR. Fig. 6 shows the simulatedSFDR versus time delay deviation and theoretical calculation results using equation (22), thesimulation results match well with the theoretical ones. It can be seen that the SFDR peaks at both��1 ¼ 0 and ��2 ¼ 0. The proposed highly linear scheme improves the SFDR if the time delayvariation for MZI1 or MZI2 is within �4 ps G ��1 G 42 ps or �2 ps G ��2 G 34 ps, respectively.This indicates that ��1 has larger operation ranges, in which the SFDRs are still higher than that ofthe conventional OSSB link.

Finally, the advantages of our approach relative to the state of the art are discussed. First, ourlinearization approach could be readily realized by integrating the interferometers into a singleplanar lightwave circuit and easily scaled to achieve even higher linearity. Second, compared to thetransmitter-based linearization OSSB links [6], [8], our link greatly reduces the complexity on thetransmit side since linearization is achieved at the receiver end. Third, compared to the transmitter-based linearization OSSB scheme in [8], where a 13 dB improvement in SFDR is obtained, anapproximately 20 dB improvement in SFDR is achieved using our OSSB linearization approach.

4. ConclusionWe have proposed and investigated a linearized analog microwave photonic link that utilizes aDD-MZM to obtain OSSB modulation signal and two parallel interferometers to suppress IMD3. It isshown by theoretical derivation and simulation that fundamental-to-IMD3 ratio (FIR) is 49 dB for a RFinput signal power of 10 dBm using our proposed linearized link, which is 24 dB more than aconventional OSSB modulation link, and SFDR is 132 dB for a bandwidth of 1 Hz at the receivedoptical power of 8 dBm assuming shot noise is the dominant noise contributions, which is improvedapproximately 20 dB. Simulation results show that even if the time delays of MZIs deviate from theideal values to a certain degree, the performance is still acceptable. Our scheme extremely simplifiesthe transmit end of link since the linearization is realized on the receive end.

Fig. 6. Simulated SFDR as a function of time delay deviation.


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