CHAPTER 1 INTRODUCTION

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CHAPTER 1
INTRODUCTION
1.1
MOTIVATION
The fast and global spread of Internet and multimedia
communication are driving the need for more bandwidth in the next
generation networks. Internet traffic has rapidly increased by existing and
emerging high performance applications such as ultra high definition video on
demand streaming, video conferencing, and cloud computing resulting in an
increased bandwidth requirement from the network. As the bandwidth
requirement increases, the carriers increase the capacity by deploying optical
networks in which optics is merely used for transmission.
A significant amount of research and development effort has been
spent over the last decade to add more functionality at the optical level, which
leads us to the next generation of optical networks, which are being put in
place today. These networks make use of optical routing of signals, in
addition to optical transmission, to realize even more significant cost savings.
Today, these networks are commonly referred to as Intelligent Optical
Networks (Ceina 1999, David Benjamin et al 2001, Jones et al 2004, Joseph
Berthold and Adel Saleh 2008).
A major challenge for network operators to support the high speed
Internet applications is the efficient end-to-end delivery of networking
services in a cost effective manner. The network must be able to respond
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quickly and dynamically to the services required by end users. Emerging
Intelligent Optical Networks (ION) establishes optical light paths as on
bandwidth demand that enables the service provider to respond to the request
quickly and economically.
The key operational benefits of intelligent optical network are
faster provisioning, protection, efficient bandwidth utilization and automatic
reconfiguration of network. Intelligent optical network, as an advanced
network technology has become the research focus of many international
companies, such as CEINA, Sycamore and Nortel etc. (Ceina 1999, David
Benjamin et al 2001, Jones et al 2004, Joseph Berthold et al 2008).
Intelligent Optical Networking provides innovative and practical
solutions to network scaling and high-speed service delivery issues. This is
done by combining switching technology and network management software
to inter-connect access, metro, and long haul transport systems. Bringing
intelligence into the optical domain creates the opportunity to develop a
flexible, high capacity network that will deliver an abundance of usable
bandwidth and new bandwidth services (Hongsheng Song et al 2003, Cortez
2002, Otani et al 2005, Simeonidou et al 2011).
Various optical devices and components have been developed to
realize DWDM based intelligent optical networks. But still, there are several
researching problems connected with high speed switching, routing,
protection and survivability mechanisms, light path provisioning, efficient
wavelength assignment and routing algorithms needs to be addressed.
Since high speed networking devices are very much essential to the
network for faster routing and protection switching, there is a strong need for
high speed optical switching devices, which are the key components of ION.
As faster protection and provisioning of light paths are required, ultra fast
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optical switches and reconfigurable add drop multiplexer has become key
devices for intelligent optical network (Borella et al 1997, Elmirghani and
Mouftah 2000, Otani et al 2005).
Existing bandwidth allocation in optical network is static and is
time consuming. ION enabled by high capacity Optical Cross Connects
(OXCs), Reconfigurable Optical Add-Drop Multiplexers (ROADM) and
optical switches with software intelligence, grants new methods for managing
high capacity core optical networks. The reconfigurable optical add drop
multiplexer allows for adding and dropping data channels on a transport fiber
without converting all channels to electronic signals and again to optical
signals. It offers the benefit of flexible ligthpath provisioning and routing, and
better bandwidth utilization (Otani et al 2005).
The reconfigurable optical add drop multiplexers should be
capable of being configured to drop maximum number of channels. It should
maintain a low crosstalk between the adjacent channels. The channel
dropping pattern should not be fixed. It should allow for directionless
operation. It should have faster tuning capability. The existing ROADMs
considered so far is limited by fixed wavelength assignment and fixed
direction assignment.
Therefore, an effort is made in this thesis to design a multichannel
add/drop and directionless ROADM based on coupling mechanism between
parallely located periodic grating waveguide structures. The proposed design
is able to accommodate a maximum of 80 channels in the DWDM band of
1530nm – 1570nm with a channel spacing of 0.4nm. Also it has a wide range
of wavelength tuning capability which helps in improving the provisioning
and utilization of available bandwidth.
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An ION makes use of optical switches, which are of two types: the
Optical-Electrical-Optical (O-E-O) switches, and the Optical-Optical-Optical
(O-O-O) ones. They offer distinct advantages and they can be combined to
optimize network management. The Intelligent optical network relies
exclusively on optical transmission and O-O-O devices. Their main benefits
derive from the larger bandwidth available in the optical domain is avoiding
O-E-O conversions which allows, in theory, for one thousand times greater
data rates than with O-E-O switches. Further, high speed switching is an
important metrics which finds useful in the protection of the network.
Glimmerglass, one of the company dealing with ION uses MEMS based
optical switches in their network. The main drawback of MEMS based
architecture is its operating speed which is in terms of milliseconds and
reliability of the moving micromirrors in the switch configuration
(Glimmerglass, 2005).
There are many technologies used in the design of an optical
switch like thermo optic switch, acousto optic switch, reflection type switch,
bubble switch, photonic crystal switch and semiconductor optical amplifier
switch. The major drawback with those technologies is the limitation in
switching speed, insertion loss and crosstalk. Therefore, an effort is made in
this thesis to overcome these limitations by designing an electro optic
waveguide switch with polymer material which has high electro optic
coefficient, instead of their inorganic counterparts such as LiNbO3 in order to
get high switching response.
Thus the motivation of this thesis is to design and analyze
reconfigurable optical add drop multiplexer and high speed optical switches
which are the key components in ION to improve the provisioning,
protection, bandwidth utilization and scalability of the network.
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1.2
OBJECTIVE OF THE THESIS
This research work is carried out with the following objectives.
to provide flexible provisioning of lightpaths
The focus of this work is to analyze the performance of a
reconfigurable wavelength add drop multiplexer based on
different waveguide grating structures tuned to provision any
number of wavelength channels to a network node. So that the
reconfigurable wavelength add drop multiplexer provides
flexible provisioning of lightpaths.
to provide high speed protection switching
High speed switching of optical switch is an important metric
which finds useful in protection switching and packet
switching applications. The focus of this work is to design a
2X2 polymer electro optic waveguide (PEOW) switch and
analyze the characteristics of the device with varying device
parameters and different grating geometries, so as to provide
faster protection switching.
to achieve efficient bandwidth utilization
The number of channels that can be accommodated in
available bandwidth has to be increased to meet the
requirement of DWDM based ION. Therefore, the focus of
this work is to design a reconfigurable wavelength add drop
multiplexer which is able to accommodate nearly 80 channels
with
channel
spacing
of
0.4nm
in
1530nm-1570nm
wavelength grid, so that the available bandwidth is used
efficiently.
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Scalability of the network
The capacity of the existing network continues to grow rapidly
due to differentiated services and applications like Voice over
IP, high-definition video broadcasting and video conferencing.
The network must be scalable in order to accommodate new
customer services. This growth requires large capacity and
low power consumption, nodes with optical switches.
Therefore, the focus of this work is to design a polymer
electro optic waveguide switch with less insertion loss and
crosstalk, so that the scalability of the network is possible.
1.3
LITERATURE REVIEW
Intelligent optical network using DWDM as the multiplexing
technology is one of the important means of obtaining high speed and
reconfigurable network connectivity based on the type of services and
bandwidth requirement.
Reconfigurable add drop multiplexers and high speed optical
switches are the important functional devices of intelligent optical network.
Review of different technologies for designing a ROADM and optical
switches are presented in this section to achieve the objectives mentioned
above.
Several add drop multiplexing schemes have been reported in the
literature. They use both planar and fiber grating technology (Hill et al, 1978,
Takahashi et al 1990, Okamoto et al 1996, Doerr et al 1999, Kewitsch et al
1998, Kim et al 1997).
The first demonstration of a fiber bragg grating (FBG) devices was
reported by Hill et al in 1978. They found that the fundamental mode of a
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germanium-doped silica fiber launched with the wavelength in the range 488
nm to 514.5 nm exhibited gradually increasing reflection, which is due to the
interaction between the standing-wave induced refractive-index grating set by
reflection from the far end of the fiber and the incident wave. The grating
period of FBGs is on the order of sub-micrometer. It is the short grating
period that enables the coupling between a forward-propagating mode and a
backward-propagating mode, and an exchange of power between the modes
around a wavelength known as the Bragg wavelength. A FBG performs as a
narrow-band filter around the Bragg wavelength, which makes it particularly
promising in the application of dense wavelength-division multiplexing
(DWDM). Since then a lot of research has been done on FBG.
Ortega et al (1998) demonstrated a fiber add-drop multiplexer
based on a selective fused coupler consisting of a twin-core fiber and a
standard telecommunication fiber and a single fiber bragg grating. Isolation of
30 dB is achieved between the dropped and added channels. Loss of 1.1 dB
for the added and dropped channel is demonstrated.
Louay Eldada et al (1999) has demonstrated a tunable optical
add/drop multiplexers by combining thermally tunable planar polymer bragg
gratings with optical circulators. The gratings exhibit a reflection of better
than -45dB. These OADM’s has bandwidth utilization (BWU) factor of 0.92,
with a minimum channel spacing of 75GHz.
Jungho Kim and Byoungho Lee (2000) has experimentally
demonstrated a bidirectional wavelength add drop multiplexer using multiport
optical circulators and fiber Bragg gratings.
Se-Kang Park et al (2000) proposed a structure which uses
polarization beam splitters (PBSs) and gratings for the construction of
bidirectional optical cross connect where the polarization state of the input
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signals needs to be controlled, and the position of gratings in each arm must
be precisely controlled to avoid induced polarization-mode dispersion (PMD)
due to the propagation time difference between two arms.
Trans et al (2001) has demonstrated a ROADM incorporating
optical circulators and fiber bragg grating.
The device length of these
circulator based devices were several centimeters which make the device
difficult to integrate.
ROADM based on MEMS technology has been developed by Pu et
al (2000). ROADM was demonstrated using a micromachined 8× 6 matrix
switch. The matrix switch was configured to add/drop any of the eight input
channels from/to any of the six add/drop ports. The insertion loss was around
3 dB for the dropped channels and around 9 dB for the added channels. The
OADM has an extinction ratio of over 40 dB and the crosstalk less than -40
dB. The problem with MEMS based OADM is high insertion loss and
aligning of micromirrors and packaging seems to be difficult.
In 1994, Ishida et al (1994) has demonstrated an ADM’s based on
discrete demultiplexers and optical switches. It reported a crosstalk of less
than -30 dB and drops single wavelength only.
Vreeburg et al (1997) has proposed an InP-Based Reconfigurable
Integrated Add–Drop Multiplexer. The device consists of a 5× 5 PHASAR
demultiplexer integrated with Mach–Zehnder interferometer electrooptical
switches. The OADM has a crosstalk of less than -21 dB and insertion loss of
1.6 dB.
Vu et al(1998) has proposed a four-channel OADMs using
cascaded fused WDM couplers with channel isolation of 25 dB and insertion
loss 0.5 dB achievable at a channel spacing of approximately 5 to 7 nm. The
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advantage of this device is that it is all-fiber and therefore potentially
inexpensive. The device is however a bulk, wide channel-spaced and nontunable OADM.
Klein et al (2005) has demonstrated a ROADM based on vertically
coupled micro ring resonator (MRR) with a tuning bandwidth of 4.18 nm and
tuning power efficiency of about 26.6mW/nm. However this type of ROADM
has a drawback of limited tuning range due to relatively larger radius of the
MRR.
Tang et al (2003) has demonstrated a tunable OADM using a staticstrain-induced grating in LiNbO3. However the integration of LiNbO3 on
semiconductor electronics is very difficult. Compared to LiNbO3 and InP
materials traditionally used, electro-optic polymers have the advantage of fast
electro-optic (EO) response time, high EO coefficient up to 300pm/V
compared with ~31pm/V of LiNbO3, low dielectric constant. It offers low
drive voltage electro optic devices compatible with conventional planar
lightwave circuits, enables integration of passive and active planar lightwave
devices.
Hai Yuan et al (2004) proposed a bidirectional optical cross
connect (BOXC) using ber Bragg gratings (FBGs) and optical circulators for
bidirectional wavelength-division-multiplexing ring networks. Dynamic and
independent wavelength routing is achieved by employing cascaded tunable
FBGs.
A wavelength-tunable OADM has been fabricated based on silicon
photonic wire waveguides with Bragg-grating-reflectors. The dropping
wavelength of the OADM was tuned through thermo optic effect by heating
the Bragg grating waveguides. A 6.6-nm dropping wavelength shift was
obtained at a heating power of 0.82 W, with a tuning power efficiency of
10
8.05 nm/W. The channel dropping bandwidth was about 0.4 nm while the
extinction ratio at Bragg wavelength for the through port was larger than 17
dB. The average tuning response time was about 200 s (Chu et al 2006).
Yamada et al (2007) has proposed a ROADM based on silicon (Si)
photonic wire waveguides (PWW). But it is designed to add/drop of single
channel only.
Recently ROADM based on micro ring resonators has been
proposed. Jocelyn Takayesu et al (2009) has reported a electrooptic microring
resonator-based ROADM which provides up to 0.36 GHz/V of electrooptic
voltage tuning for each channel and 2.7-nm free spectral range.
In 1996, a long-period fiber grating (LPFG) filter was reported
(Vengsarkar et al 1996). An LPFG can be formed by introduction of a
periodic index change to the fiber core with a pitch of the order of 100nm or
by a physical deformation of the fiber. The transmission spectrum of a LPFG
consists of a number of rejection bands at specific resonance wavelengths
each of which corresponds to the coupling between the guided mode and a
particular cladding mode. However, the resonance wavelengths of LPFGs
written in standard communications fibers can be tuned only by about 10 nm
with a temperature change of 100 °C, which is too low for many applications.
Long period fiber gratings also find application in add drop
multiplexing. An add/drop multiplexer in the form of two parallel coupled
LPFGs has been demonstrated, where the outputs from the two gratings
show complementary band rejection and band pass characteristics (Grubsky et
al 2000, Chiang et al 2004). However, maintaining two fibers in strict parallel
is very much a challenge in device packaging. It is also difficult to increase
the number of the output ports by scaling up the number of fibers.
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Bai et al (2005) has reported the characteristics of a two parallel
coupled long period waveguide grating, where the outputs from the two
gratings show complementary band-rejection and band pass characteristics.
This structure uses rectangular grating geometry and shows single wavelength
pass or reject.
Bernardo et al 2009 has demonstrated a compact silicon-oninsulator wavelength division multiplexer using etched diffraction grating.
The device supports 21 channels, with 1 nm channel spacing and less than -10
dB crosstalk.
Miyata et al has demonstrated a Reconfigurable Optical Add Drop
Multiplexer using acousto-optic tunable filter (AOTF) and compact
wavelength-tunable LD module. It has a channel spacing of 0.8nm. However,
when an AOTF is operated under multichannel selection, coherent crosstalk
increases as the number of selection channels increases and channel spacing
narrows.
Xinyong et al (2005) has realized a strain-tuned LPG pair-based
Mach–Zehnder interferometer WDM filter with 0.8-nm channel spacing.
Among the different configurations reported, planar devices had a
drawback of high insertion loss as high as 7dB, and their polarization
dependence. All fiber devices are although an attractive technology due to
their low insertion losses, polarization insensitivity; due to their larger
dimensions these devices are sensitive to environmental variations and
difficult to integrate in OIC.
Even though, FBG based devices found wide applications, there is
a need of inexpensive and compact fiber-optic filters with both low insertion
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loss and low back-reflection in optical fiber communication systems deployed
with optical amplifiers.
In order to overcome these drawbacks, this thesis discusses about
the design and analysis of wavelength add drop multiplexer based on the
coupling mechanism of long period waveguide grating structure with different
geometries like rectangular, triangular and trapezoidal gratings. The proposed
structure is able to add or drop multiple wavelengths, so that provisioning of
services to different end users can be easily accommodated. This component
finds applications in provisioning of lightpaths to different variety of services,
rerouting and reconfiguration of the existing network.
In order to achieve the objective of high speed protection in ION,
an exhaustive literature review on optical switching technologies has been
presented.
Optical switches are one of the key components in an intelligent
optical network which finds application in protection switching, provisioning
of lightpaths, packet switching applications requiring ultra high speed
switching. As for optical switches, several performances are required
depending on the applied systems, such as low insertion loss, low polarization
dependent loss (PDL), low cross talk, , high extinction ratio, non-blocking,
scalability, short device length in order to get compact module size and to
implement system on chip, low power consumption and higher switching
speed. Different technologies has been proposed and demonstrated to realize
optical switches, such as Micro-Electro-MechanicalSystem (MEMS) based
switches, acousto-optic switches, liquid crystal switches, thermal-optical
switches, electro-optic switches and photonic crystal switches
Diemeer et al (1989) has demonstrated an all-polymeric optical
waveguide switch which uses total internal reflection from a thermally
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induced index barrier. Very large effective index changes
n=2×10-2 were
found in the polymeric waveguide. The temperature under the evaporated
stripe heater was measured from the change in its resistance. Switching times
of about 10 ms were measured.
Lee and Shin (1997) demonstrated an EO polymer 1X2 DOS
operating at 1300 nm and 1550 nm. It is composed of
linear Y-branch
waveguide and a switching electrode. The switch exhibits a crosstalk value of
less than -16 dB, but the switching voltage was as high as 110 V.
Patel et al (1995) demonstrated a liquid-crystal and grating based
optical cross-connect add-drop switch that operates simultaneously on several
wavelengths channels.
Riza et al (1999) has proposed a liquid crystal optical switch based
on the change of polarization state of incident light by a liquid crystal by the
application of an electric field over the liquid crystal. The change of
polarization in combination with polarization selective beam splitters allows
optical space switching. In order to make the devices polarization insensitive,
polarization diversity scheme must be implemented, which makes the
technology more complex.
Toshiyoshi and Fujita (1996) reported a micromechanical optical
fiber switch to regulate light beams in a free space using electro statically
driven micromirrors. The device has torsion mirror substrate and counter
electrode substrate. When a bias voltage is applied to the mirror and
electrodes, the mirror is attracted inward by 90 degree to reflect the incident
light. Micro mechanical switches generally have low insertion loss (around
0.6 dB), low channel crosstalk (around -60dB) and good extinction ratio.
However, the fundamental drawback is the durability of the moving parts.
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Nagaoka and Suzuki (1997) has demonstrated a 1×2 opto
mechanical switch that exhibit a low insertion loss of 0.31 dB and high return
loss of 51 dB which finds application in optical testing and sensing systems.
Chen et al (1999) has reported a micromachined 2×2 optical
switch. The optical switch consists of an elevated vertical micromirrors that
can be lowered to re ect the optical beams. When a voltage is applied
between the cantilever and the substrate, electrostatic force lowers the mirror
from the cross state to bar state. It requires a operating voltage of 20 V. The
switching time is found to be 600 s.
An all-optical switch based on digital mirror arrays has been
analyzed by Sundaram et al (2003). It works on the principle of switching
mechanism of digital micro mirror device. It shows an insertion loss of -5.5
dB and crosstalk of -36.8 dB.
Pruessner et al (2005) has presented an optical waveguide MEMS
switch fabricated on an indium phosphide (InP) substrate for operation at
1550 nm wavelength. Compared to other MEMS optical switches, which
typically use relatively large mirrors or long end-coupled waveguides, this
device uses a parallel switching mechanism. The device utilizes evanescent
coupling between two closely-spaced waveguides fabricated side by side. The
switching voltage was found to be below 10 V. Channel isolation was around
47 dB and coupling efficiencies about 66%. The switching time was found to
be 4 s.
Even though MEMS switches are in micro scale size, they have
moving parts controlled by electronics. Hence reliability of MEMS optical
switches is serious issue. Further, large amount of electrical connections for
the micromirrors are required which leads to more crosstalk. Also, the
switching time is in the order microseconds only.
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Goh et al (2001) has demonstrated a silica-based 16×16 strictly
nonblocking thermooptic switch. The switch consists of two asymmetrical
MZIs with a path difference of a half-wavelength and thermooptic phase
shifters. An insertion loss of 6.6 dB, extinction ratio of 53 dB and crosstalk of
-40dB were observed.
Kasahara et al (2002) has demonstrated an optical switch made
with silica-based planar lightwave circuit (PLC) technology. It is based on the
principle of thermally induced changes of the refractive index in silica-based
waveguides. This technology has disadvantage of limited integration density
and high power dissipation. The switching time of the switch was about 4.9
ms, which is lesser for protection application.
Sakata et al (2001) has demonstrated a thermo capillary optical
switch. It consists of a crossing waveguide substrate that has a groove which
is partially filled with the refractive-index-matching liquid at each crossing
point and a pair of microheaters. The liquid in the groove is driven due to
heating, to move away from the crossing point, thus switching the input
signal. The switching time was found to be 6ms. It shows a reflection loss of
1.3 dB and crosstalk around -60dB.
Baojun Li and Soo-Jin (2002) has proposed a reflection type
optical waveguide switch. The switching time for this switch was about 180ns
with 21.8 db crosstalk at a 1550nm wavelength. These switches require
precise reflection interfaces in the switch structure.
Wei Yuan et al (2003) demonstrated polymeric digital optical
switch based on electro-optic effects in polymeric materials. It has a Ybranch waveguide driven by electrodes on the top of each of two arms in
the mode evolution region. When electrical field is applied on the two
arms, the refractive index of each arm is changed so that the signal
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switches its state. The length of the switching region is 0.95 cm and
switching voltage is 7V.
Xiaolong et al (2005) has demonstrated a thermo-optic switch
using total internal reflection waveguide for optical true time delay. The
device shows a bar state crosstalk as low as -42dB and the total insertion loss
of -4dB at the wavelength of 1.55 m. A power consumption of 130mWand
switching speeds of 2ms are obtained.
Qing Wang et al (2007) demonstrated a 2×2 electro-optic switch
using a polarization Modulator (PolM).
Two linearly polarized input
lightwaves with orthogonal polarization directions are sent to the PolM which
is connected to a polarization beam splitter (PBS). When a switching signal is
applied to the PolM, the polarization directions of the two lightwaves at the
output of PolM will exchange. Thus, a 2×2 switch is realized by switching
the, lightwaves at the two output ports of the PBS. An optical switch with a
crosstalk lower than -35 dB and a switching time less than 25 ps is
experimentally demonstrated.
Recently, a number of photonic crystal (PhC) based devices has
been proposed as a solution to the need of compact, low power switches
Beggs et al (2009) has proposed an optical switch based on a PhC directional
coupler in the silicon-on-insulator. The switch was actuated thermo-optically
using an integrated micro-heater. The device shows an insertion loss around
2dB. The switching response was found to be 20 s.
However these devices are susceptible to damage and difficult to
integrate with other components, as they rely on membrane geometry. Also
this geometry presents a switching response time in the order of
(Yamamoto et al 2006, Beggs et al 2008, Beggs et al 2009).
s only
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Nan Xie et al (2009) has demonstrated a very low-power
consuming, polarization-independent, and high-speed polymer Mach-Zehnder
2 × 2 photonic switch. This thermo optic switch is operated with less than 4
mW of power consumption via a small-area heater and shows a crosstalk of
less than -25 dB. However the problem with thermo optic switch is its low
switching speed and high crosstalk.
Among these switches, waveguide based electro optic switches are
of major concern because of its speed, stability and reliability as compared
with other switching technologies. The ability of waveguide grating based
switch architecture to achieve large input and output-port is the primary driver
of the large-scale optical cross connects (OXC) and in expanding the network.
In particular, this switch provide high application flexibility in network design
because of faster switching speed, low and uniform insertion loss under
various operating conditions.
1.4
ORGANISATION OF THE THESIS
This thesis is about designing and analysing high speed,
reconfigurable optical components which are the key elements in an
intelligent optical network which improves the provisioning, protection,
bandwidth utilization and scalability of the network.
The thesis consists of seven chapters including the present chapter
which discusses about the motivation and objectives of the thesis. A Detailed
review on reconfigurable add-drop multiplexers and high speed optical
switches which have been developed and published by other researchers are
discussed (chapter 1).
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Chapter 2, gives a brief introduction about the evolution of
intelligent optical networks and wavelength division multiplexing techniques.
This chapter gives a detailed study on different optical switching technologies
and reconfigurable add-drop multiplexing technologies.
In Chapter 3, the role of ROADM in provisioning of lighpaths is
discussed. The design of 2×2 reconfigurable wavelength add-drop multiplexer
based on different waveguide grating structures are given. The analysis of the
proposed structure by coupled mode theory and derivation of coupled mode
equations are presented. The transmission characteristics of the proposed
design with different device parameters and grating structures are simulated.
The role of electro optic effect in reconfiguration and flexible provisioning of
lightpaths is discussed with the simulated results.
In Chapter 4, the requirement of high speed optical switches in
protection of lightpaths is discussed. The design of 2×2 polymer electro optic
waveguide switch is presented. The analysis of the switch is done with
coupled mode theory. The coupled mode equations are derived. The
characteristics of the PEOW switch with different device parameters and
grating structures are simulated. Its application in protection switching is
presented.
In Chapter 5, the bandwidth utilization of the network is studied
with the design and analysis of a multiport reconfigurable wavelength add
drop multiplexer. The variation in the channel spacing with change in
refractive index due to electro optic effect is discussed with the simulated
results.
`
In Chapter 6, the scalability issue of the network is discussed with
the design of a 3×3 polymer electro optic waveguide switch. The analysis of
the switch is done with coupled mode theory. The coupled mode equations
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are derived. The characteristics of the switch with different device parameters
and grating structures are simulated. The performance metrics like switching
time, crosstalk and insertion loss are analysed which helps in enhancing the
scalability of the network.
Finally in Chapter 7, concluding remarks and recommendations for
future prospects for this work are given.

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