Add-drop ring resonator system is the fundamental building block of the optical transmission and communication systems. The microring resonator (MRR) made of semiconductor with a length of 750 μm, K1=k2= 0.02, is used to filter the input spectrum of Gaussian laser beam and generate the comb frequency of soliton pulses, where the transmission characteristics and group delay profile of the through and drop port output signals are presented. The semiconductor material (InGaAsP/InP) is used to generate the add-drop ring resonator. The operating wavelength is 1550 nm andthe iterative method is used to generate the results based on practical parameters of the system.

1. Soliton comb generation using add-drop ring resonators
IRJTIT
Soliton comb generation using add-drop ring
resonators
IS Amiri1*, MZ Zulkifli2, H Ahmad3
1*,2,3Photonics Research Centre, University of Malaya, Malaysia
*Corresponding author: Dr. IS Amiri, Photonics Research Centre, University of Malaya,50603 Kuala Lumpur, Malaysia. E-mail:
isafiz@yahoo.com, Tel.:+60127420567
Add-drop ring resonator system is the fundamental building block of the optical transmission and
communication systems. The microring resonator (MRR) made of semiconductor with a length of
750 μm, 0.02 1 2    , is used to filter the input spectrum of Gaussian laser beam and generate
the comb frequency of soliton pulses, where the transmission characteristics and group delay
profile of the through and drop port output signals are presented. The semiconductor material
(InGaAsP/InP) is used to generate the add-drop ring resonator. The operating wavelength is 1550
nm andthe iterative method is used to generate the results based on practical parameters of the
system.
Keywords: Microring resonator, Gaussian laser beam, soliton signal, add-drop system, comb generation
INTRODUCTION
Add-drop filters using Microring Resonators (MRRs) have shown great promise for practical applications (Cai et al.,
2000; Amiri I. S. et al., 2012a; I. S. Amiri et al., 2013a; I. S. Amiri et al., 2013b; I. S. Amiri and J. Ali, 2014a; I. S. Amiri et
al., 2014f). Microrings have been studied more thoroughly due to their ease of fabrication and on chip structure (Popovíc
et al., 2006; Xiao et al., 2008; Iraj Sadegh Amiri et al., 2014b; Sayed Ehsan Alavi et al., 2014).
Wavelength selective optical add-drop filter is required for adding and dropping a particular Wavelength Division
Multiplexing (WDM) channel at each subscriber node in the WDM based optical access networks. Add-drop filter used in
DWDM based optical networks should have a good reflection characteristic, a temperature stability, a narrow spectral
bandwidth, and a low implementation cost(Iraj Sadegh Amiri and Abdolkarim Afroozeh, 2014).For those reasons, many
researchers have been proposed various technologies to generate a comb frequency of soliton using the add-drop
filter(A Nikoukar et al., 2014; I. S. Amiri and J. Ali, 2014b; I. S. Amiri and J. Ali, 2014c; Y. S. Neo et al., 2014). Although
add-drop filters, including those devices have good operating performances, their cost is too expensive to apply for
DWDM based optical access network. The main contribution of this study is to generate multiple soliton wavelengths,
train of signals or a soliton comb which is widely applicable in optical communications. MRRs are made up of waveguide
by fabrication technology. Optical MRRs, filters, and switches have been successfully demonstrated in the two important
GaAs-AlGaAs and GaInAsP-InP material systems (Heebner and Boyd, 1999; Hryniewicz et al., 2000). The fabrication
process of the vertically coupled InP devices was developed by R. Grover (Grover et al., 2001). The III/V
semiconductors (InGaAsP/InP) on the basis of InP with a direct band gap is used to fabricate the ring resonator.
OPTICAL TRANSFER FUNCTION
The system of the add-drop ring resonator is shown in Figure 1. We propose the system when the stationary Gaussian
pulse is introduced into the system as shown in Figure 1.The material platform can be a waveguide or a semiconductor.
International Research Journal of Telecommunications and
Information Technology
Vol. 1(1), pp. 002-008, August, 2014. © www.premierpublishers.org, ISSN: XXXX-XXXX
Research Article

2. Soliton comb generation using add-drop ring resonators
Amiri et al 002
In this study the semiconductor material (InGaAsP/InP) is used. The practical parameters are used to simulate and
modelling the system.
Figure 1. Schematic Diagram of an add-drop System
The input optical field ( ) in E in the form of the Gaussian pulse can be expressed by Equation (1)






  


 


 i t
L
z
E z t E
D
in 0 0 2
( , ) exp  (1)
Here 0 E and z are the optical field amplitude and propagation distance, respectively(S. E. Alavi et al., 2014). The
dispersion length of the soliton pulse can be defined as 2
2
0 L T  D  , where the frequency carrier of the soliton is 0 
and 2  is the coefficients of the second order terms of the Taylor expansion of the propagation constant (Amiri I. S. et
al., 2012b). 0 T represents a soliton pulse propagation time(A. Afroozeh et al., 2015; I. S. Amiri et al., 2015).Here, the
soliton represents a pulse that keeps its width invariance as it propagates, known as a temporal or spatial soliton (I. S.
Amiri et al., 2014b). The intensity of soliton peak is | / | 2
2 0  T . When a temporal soliton pulse propagates inside the
microring device, a balance should be achieved between the dispersion length ( ) D L and the nonlinear length
( 1/ ) NL NL L   , where 2 0   n k , is the length scale over which disperse or nonlinear effects causes the beam becomes
wider or narrower. For a soliton pulse when the balance between dispersion and nonlinear lengths is achieved, hence
D NL L  L . The total refractive index (n) of the system is given by(Amiri I. S. et al., 2010)
( ) , 2
0 2 0 P
A
n
n n n I n
eff
    (2)
where 0 n and 2 n are the linear and nonlinear refractive indices, respectively(A. Afroozeh et al., 2014; I. S. Amiri et al.,
2014d). I and P are the optical intensity and optical power, respectively(IS Amiri et al., 2014). eff A represents the
effective mode core area of the device, where in the case of MRRs, the effective mode core areas range from 0.50 to
0.1 m2. When a Gaussian pulse is input and propagates within the MRR, the resonant output is formed for each round-

3. Soliton comb generation using add-drop ring resonators
Int. Res. J. Telecomm. Info. Technol. 003
trip. The normalized output of the light field is defined as the ratio between the output and input fields ( E (t) out and E (t) in )
in each round-trip. Thus, it can be expressed as(Amiri I. S. et al., 2012c; I. S. Amiri and A. Afroozeh, 2014;I. S. Amiri et
al., 2014e)
 




 




     
 
   
)
2
(1 1 1 ) 4 1 1 sin (
(1 (1 ) )
(1 ) 1
( )
( )
2
1
2
1
1
2

   
 

x x
x
E t
E t
in
out (3)
Here,  is the coupling coefficient, x  expL/ 2 represents a round-trip loss coefficient, 0 0   kLn and
2
NL 2 in   kLn E are the linear and nonlinear phase shifts and k  2 / is the wave propagation number(Amiri I. S. et
al., 2013). Here L and  are the waveguide length and linear absorption coefficient, respectively(Nikoukar et al., 2012;
Parisa Naraei et al., 2014). To retrieve the signals from the chaotic noise, we propose to use an add-drop system with
appropriate parameters (Afroozeh et al., 2011; Seyed Mohammad Reza Khalifeh Soltanian and Iraj Sadegh Amiri,
2014). The input powers expressed by Equations (1) and (2), insert into the input and add ports of the add-drop
interferometer system (Popović et al., 2006). Interior optical signals of the system can be expressed by Equations 4 and
5.
n ad
ad
ad
n
ad
jk L
L
L
jk
L
in add
a
e
E j E j e
E




    
     

2
1 2
2 2 2
1 2 1
1 (1 ) (1 )
(1 )


 
  
(4)
3
2
1 2
2
2 1 2
2
1 2
2 2 2
1 2
1 (1 ) (1 )
(1 ) (1 )
1 (1 ) (1 )
(1 )

 
  
 
 




E j
e
E j e
e
E j e
E
add
jk L
L
jk L
L
add
jk L
L
L
jk
L
in
b
n ad
ad
n ad
ad
n ad
ad
ad
n
ad
 
    
     

    
   









(5)
, where 1  and 2  are the coupling coefficients, ad ad L  2 R and ad R is the radius of the add-drop system. add E is the
input Gaussian pulse into the add port of the system. The through and drop ports output signals from the system are
given by(Amiri I.S. et al., 2011; Amiri I. S. and Ali, 2014):
1
2 2 2
1  1 

     


in
L
jk
L
th b E E j e E
ad
n
ad
(6)
2
2 2 2
2  1 

     


add
L
jk
L
drop a E E j e E
ad
n
ad
(7)
, where th E and drop E represent the optical electric fields of the through and drop ports, respectively. Therefore (Amiri I.S.
and Ali, 2013; Abdolkarim Afroozeh et al., 2014; I.S. Amiri et al., 2014c),
1
4 2
1 2
2
1 2
2
3
4
3
1 2 1 2
2
1 2
2
1 2
1
1 (1 ) (1 )
( ) (1 ) (1 )
1 (1 ) (1 )
1
  
 
   
 
 





     

    
       

    
    











in
L
jk
L
add
jk L
L
L
jk
L
add
jk L
L
jk L
L
in
th
E e E
e
E e
e
E e
E
ad
n
ad
n ad
ad
ad
n
ad
n ad
ad
n ad
ad
(8)

4. Soliton comb generation using add-drop ring resonators
Amiri et al 004
2
2
1 2
2
2 1
2
1 2
2 2 2
1 2
1
1 (1 ) (1 )
1
1 (1 ) (1 )

 
 
 
 




  
    
   

    
   









add
jk L
L
L jk L
add
jk L
L
L
jk
L
in
drop
E
e
E e
e
E e
E
n ad
ad
ad n ad
n ad
ad
ad
n
ad
(9)
The waveguide (ring resonator) loss is   0.5 dBmm−1(A.Zeinalinezhad et al., 2014; I. S. Amiri et al., 2014a; Iraj
Sadegh Amiri et al., 2014a), where the fractional coupler intensity loss is  0.1(Iraj Sadegh Amiri et al., 2014c).
RESULTS AND DISCUSSION
The Gaussian pulse is input into the input and add ports of the system. The operating wavelength is 1550 nm. The
iterative method is used to generate the results based on practical parameters of the system. The throughput output
signals of the add-drop filter system with two waveguide and coupling factor of 1  = 2  =0.02 in both symmetrical
couplers is shown in Figure 2. The 3dB band width and the free spectral range of the pulses can be adjusted respect to
different configuration and the designs of the ring resonator systems. In this study single ring resonator add-drop filter
system is analysed.
Figure 2. Throughput output signals of the add-drop ring resonator with
L=750μm, 1  = 2  =0.02, α=0
In the following new parameter will be used for simplifying:
2
1
D  (1 ) )
2
x Dexp( L

  , 1 1 y  1 and 2 2 y  1
The maximum and minimum transmissions are calculated as follows. For the throughput port:

5. Soliton comb generation using add-drop ring resonators
Int. Res. J. Telecomm. Info. Technol. 005
(10)
(11)
and for the drop port:
(12)
(13)
The on-off ratio of an add-drop filter system is given by:
(14)
The output intensity at the drop port will is shown in Figure 3, which indicates that the resonance wavelength is
fully extracted by the resonator when 1  = 2  and α=0.
Figure 3. Drop port output of an add-drop ring resonator with
R=750μm, 1  = 2  =0.02, α=0
The group delay profile of the drop port output referenced to the input port is shown in Figure 4. This group delay is
simulated from drop port respect to the input port. Resonance in this case occurs when θ = (2N+1) π, where N is the
mode number and the required equations to obtain the group delay are given in reference (Schwelb, 2004).
2
1 2
2
1 2
max (1 )
( )
y y x
y y x
T



2
1 2
2
1 2
min (1 )
( )
y y x
y y x
T



2
1 2
2
2
2
1
max (1 )
(1 ).(1 ).
y y x
y y x
T

 

2
1 2
2
2
2
1
min (1 )
(1 ).(1 ).
y y x
y y x
T

 

y y x
y y x
T drop port
T throughput port
(1 ).(1 ).
( )
( )
( )
2
2
2
1
2
1 2
min
max
 



6. Soliton comb generation using add-drop ring resonators
Amiri et al 006
Figure 4. Group delay of the add-drop ring resonator with R=750μm, 1  = 2  =0.02, α=0
CONCLUSION
The add-drop system is used to show constructive interference of the inputs optical Gaussian laser beam. Its
transmission characteristics are theoretically derived and confirmed by the results. Here the transmission characteristics
of the optical through and drop ports output powers and the group delay are presented.
ACKNOWLEDGEMENTS
I. S. Amiri would like to thank the, Photonics Research Centre, Department of Physics, Faculty of Science, University of
Malaya, 50603 Kuala Lumpur, Malaysia for providing the research facilities. The authors acknowledge the financial
support from University Malaya/MOHE under grant number UM.C/625/1/HIR/MOHE/SCI/29.
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