“Silicon Photonics”

Seminar Report
(21EC81)
Submitted in partial fulfillment of the requirements for the award of
Bachelor of Engineering
In
Electronics and Communication Engineering
Submitted to
VISVESVARAYA TECHNOLOGICAL UNIVERSITY
Belagavi, Karnataka, 590 014

Submitted by
Preeti C Ukli 2KE21EC069

Under the Guidance of

Mrs. Anusha A.M.
Department of Electronics and Communication Engineering
(NBA Accredited)
K. L. E. SOCIETY’S

K. L. E. INSTITUTE OF TECHNOLOGY
Department of Electronics and
Communication Engineering
 K. L. E. SOCIETY’S
K. L. E. INSTITUTE OF
TECHNOLOGY, HUBBALLI-
580027
2024-2025

(Affiliated to VTU, Approved by AICTE and ISO 21001:2018 Certified Institute)

ALL UG PROGRAMS ARE ACCREDITED BY NBA

CERTIFICATE

Certified that the seminar entitled “Silicon Photonics” is a bonafide work carried
out by Preeti C Ukli (2KE21EC069), in partial fulfilment for the award of degree
of Bachelor of Engineering in VIII Semester, Electronics and Communication
Engineering of Visvesvaraya Technological University, Belagavi, during the year
2024-25. It is certified that all corrections/suggestions indicated for internal
assessment have been incorporated in the report deposited in the department library.
The seminar report has been approved as it satisfies the academic requirements in
respect of seminar work prescribed for the said degree.

Mrs. Anusha A.M. Dr. Gopal Bidkar Dr. Manu T.M.

Guide HOD Principal

Name of the Examiners Signature with Date

1.
2.
 DECLARATION

I Preeti C Ukli (2KE21EC069), student of VIII Semester B.E., K.L.E. Institute of

Technology, Hubballi, hereby declare that the seminar has been carried out by me
and submitted in partial fulfillment of the requirements for the VIII Semester
degree of Bachelor of Engineering in Electronics and Communication
Engineering of Visvesvaraya Technological University, Belagavi during
academic year 2024-2025.

Date: 08-05-2025

Place: Hubballi Preeti C Ukli (2KE21EC069)

 ACKNOWLEDGEMENT

The Seminar on “Silicon Photonics” is the outcome of guidance, moral

support and devotion bestowed on us throughout our work. For this I
acknowledge and express my profound sense of gratitude and thanks to
everybody who has been a source of inspiration during the Seminar.

I would take this opportunity to acknowledge my Guide, Mrs. Anusha

A.M., who inspired me to take up this idea for the Seminar and equally
me technically. The result of her dedication towards perfection has
resulted in getting this project work done. I express my deep sense of
gratitude for being supportive in my curricular and co-curricular
activities throughout this course.

I wish to express our thanks to Seminar Coordinator, , Ms. Supriya

Puttappanavar for guiding me with presentation skills and for
conducting effective evaluations.

I am deeply indebted to our Head of Department, Dr. Gopal Bidkar

for the constant support and encouragement in all my endeavors. The
academic ambience has helped us to excel in our academics.

I would like to thank our Dean of SWO, Dr. Yerriswamy T. for their
constant encouragement for academic progress.

I would like to thank our Dean of R&D, Dr. Shridhar Mathad. for
their constant encouragement for academic progress.

It is indeed a great honor to express my sincere thanks to our Principal,

Dr. Manu T. M. who has always inspired us for academic excellence.

Finally, I would like to thank all the Technical and Non-Technical staff
of Electronics and Communication department for their valuable help
and support.
 ABSTRACT

Silicon photonics is a rapidly growing technology that integrates optical components

onto silicon chips,Enabling faster and more efficient data transmission. With the
increasing demand for high-speed internet, Cloud computing, and 5G networks,
traditional electronic communication systems face limitations in Speed, power
consumption, and scalability. Silicon photonics addresses these challenges by using
light.Instead of electrical signals for data transfer, significantly improving performance
while reducing energy Costs. This technology is based on the use of silicon waveguides,
modulators, and photodetectors to Transmit and process optical signals on a
microchip. It is widely used in data centers, telecommunications, And high-
performance computing, with potential applications in biomedical imaging and
quantum Computing. Despite its advantages, challenges such as optical signal loss and
integration of laser sources Remain, but ongoing research is making significant
progress. As industries continue to adopt silicon Photonics, it is expected to play a
crucial role in the future of communication technology.a structures, Paving the way for
faster, more efficient, and sustainable data transmission technologies.
 TABLE OF CONTENTS
Chapter Title Page No.

1. INTRODUCTION 1-11
1.1 MOORE’S LAW AND SILICON TECHNOLOGY 2
1.2 Optical Interconnects 3
1.3 Enter Optoelectronics 5
1.4 Components Of An Optical System 6
2. LITERATURE SURVEY 12-26
2.1 System Design 12
2.2 Methodology 13
2.3 Block Schematic 15
2.4 Description 17
2.5 System Workflow 24
3. CONCEPTS 29-
3.1 How Laser Occur 29
3.2 Raman Effect 30
3.3 Stimulated Raman Scattering & Raman Silicon Laser 31
3.4 Two Photon Absorption & Pin Diode Correction
3.5 Siliconize Photonics
3.5.1 Siliconize Photonics
3.5.2 Silicon Modulator
3.5.3 Encoding the Optical Data
3.5.4 Demodulation
3.5.5 Silicon Interfaces
3.5.6 Silicon Challenges
4. APPLICATIONS 33-36
4.1 Applications of Silicon Photonics 33
4.2 Data Centers and High Speed Communications
4.3 Sensing and Imaging
4.4 Biomedical Applications
4.5 Conclusion
REFERENCE
 LIST OF FIGURES

Figure No. Figure Name Page No.

1.1 Moore’s law 15
1.2 Technology vs delay 18
1.3 Arrayed Waveguide Grating (AWG) 18
structure
3.1 Six basic building blocks of Silicon 19
Photonics
3.2 Basic laser working 19
3.3 The indirect bandgap 20
3.4 Raman effect in optical fiber and silicon 20
waveguide
3.5 Raman silicon laser 21
3.6 Waveguide PIN structure 22
3.7 Creating multiple laser sources from 23
single pump
3.8 Direct and External Modulation 23
3.9 External modulation in silicon chip 26
3.10 The MachZender interferometric for data 27
encoding
3.1 Energy level transitions of an electron 29
during four-wave mixing
4.1 3D ICs (An artistic view) 30
4.2 Silicon photonics transceiver chip 30
Silicon Photonics 2024-2025
CHAPTER 1

INTRODUCTION

Fiber optic communication is well established today due to the great capacity and reliability it provides. .
Fiber-optic communication is the process of transporting data at high speeds on a glass fiber using light.
However, the technology has suffered from a reputation as an expensive solution. This view is based in large
part on the high cost of the hardware components. These components are typically fabricated using exotic
materials that are expensive to manufacture. In addition, these components tend to be specialized and require
complex steps to assemble and package. These limitations prompted Intel to research the construction of
fiber optic components from other materials, such as silicon. The vision of silicon photonics arose from the
research performed in this area. Its overarching goal is to develop high-volume, low cost optical components
using standard CMOS processing the same manufacturing process used for microprocessors and
semiconductor devices. Silicon presents a unique material for this research because the techniques for
processing it are well understood and it demonstrates certain desirable behaviors. For example, while silicon
is opaque in the visible spectrum, it is transparent at the infrared wavelengths used in optical transmission,
hence it can guide light. Moreover, manufacturing silicon components in high volume to the specifications
needed by optical communication is comparatively inexpensive.

Researchers at Intel have announced advancement in silicon photonics by demonstrating the first continuous
silicon laser based on the Raman Effect. This research breakthrough paves the way for making optical
amplifiers, lasers and wavelength converters to act as light source and also switch a signal’s color in low-
cost silicon. It also brings Intel closer to realizing its vision of “siliconizing” photonics, which will enable
the creation of inexpensive, high-performance optical interconnects in and around PCs, servers and other
devices. There has also been developments which include the achievement of GHz range optical modulator
and detector devices in silicon.

Silicon Photonics Silicon’s key drawback is that it cannot emit laser light, and so the lasers that drive optical
communications have been made of more exotic materials such as indium phosphide and gallium arsenide.
However, silicon can be used to manipulate the light emitted by inexpensive lasers so as to provide light that
has characteristics similar to more-expensive devices. This is just one way in which silicon can lower the
cost of photonics. Intel’s silicon photonics research is an end-to end effort to build integrated photonic
devices in silicon for communication and other applications. To date, Intel has demonstrated laser
production from external light source, tunable filters, optical modulators, photo-detectors and optical
packaging techniques using silicon that can establish optical links with Gbps data rates. Even more is yet to
achieve.

Dept. of Electronics and Communication, KLEIT 1

Silicon Photonics 2024-2025

All sequential circuits have one property in common—a well-defined ordering of the switching events must
be imposed if the circuit is to operate correctly. If this were not the case, wrong data might be written into
the memory elements, resulting in a functional failure. The synchronous system approach, in which all
memory elements in the system are simultaneously updated using a globally distributed periodic
synchronization signal (that is, a global clock signal), represents an effective and popular way to enforce this
ordering. Functionality is ensured by imposing some strict constraints on the generation of the clock signals
and their distribution to the memory elements distributed over the chip; non-compliance often leads to
malfunction.

1.1 MOORE’S LAW AND SILICON TECHNOLOGY :

It is an understatement to remark that we live in a world made possible by silicon technology. Modern life
has been shaped and defined by innumerable products that rely on integrated electronic circuits fabricated in
mind-boggling number and precision on silicon wafers. The grand success of silicon technology is not only
the dramatic improvements that have been achieved in performance, but also the exponentially decreasing
per-component manufacturing costs that have kept that performance affordable. In fact, Gordon Moore’s
famous law(1962) describing progress in the semiconductor industry was originally stated in similar
economic terms:
“The complexity for minimum component costs has increased at a rate of roughly a factor of two per
year . . . , this rate can be expected to continue”
Complexity is usually equated to transistor count, and by that measure the exponential progress Department
of Electronics and Communication Engg. Page 2 Silicon Photonics predicted by Moore’s Law has been
maintained through the present day (figure1.1). It has become cheaper over time to pack more and more
transistors into integrated circuits because each individual transistor is continually being made smaller. This
scaling process allows more powerful chips with more transistors to be made for a reasonable price. Smaller
transistors also drive down the price of previous generation chips of any given complexity, because more
functionally identical copies can be simultaneously made on the surface of a silicon wafer for nearly the
same cost. Scaling is the engine of progress in silicon microelectronics. It is sustained only by intensive
research and development in the face of perpetual technology challenges always looming on the horizon.

Goals and benchmarks for scaling are established and monitored in the International Technology Roadmap
for Semiconductors (ITRS), a public document.

Dept. of Electronics and Communication, KLEIT 2

Silicon Photonics 2024-2025

Fig 1.1-moore’s law

In Figure 1.1, transistor counts for integrated circuits showing the historical accuracy of Gordon Moore’s
prediction of exponentially increasing integrated circuit complexity with year by a consortium representing
the global semiconductor industry. The roadmap is intended “to provide a reference of requirements,
potential solutions, and their timing for the semiconductor industry” over a fifteen -year horizon. For many
years, the ITRS has highlighted one threat to continued scaling in particular that must be addressed in the
short term future in order to avoid slowing down the pace of Moore’s Law.
The anticipated problem is often referred to as the “interconnect bottleneck.” As the number of transistors in
an integrated circuit increases, more and more interconnecting wires must be included in the chip to link
those transistors together. Today’s chips already contain well over one kilometer of wiring per square
centimeter of chip area. Sending information along these wires consumes significant power in various losses
and introduces the majority of speed-limiting circuit delay in a modern integrated circuit. Scaling
exacerbates both of these problems by decreasing the cross sectional area of each wire, proportionately
increasing its electrical resistance. With further scaling the RC capacitive charging delays in the wires will
increasingly dominate the overall performance of future integrated circuits. The interconnect bottleneck has
threatened Moore’s Law before. In the late 1990s, integrated circuits contained aluminum wires that were
surrounded by silicon oxide. As interconnect cross sections decreased, mounting circuit delay in capacitive
charging of these aluminum wires began to effect chip performance. A solution was found in a change of
materials. Copper was introduced in place of aluminum, which cut the resistance of the wires nearly in half.
Eventually low dielectric constant (“low-κ”) doped silica infill materials were also phased in to reduce the
capacitance.

Dept. of Electronics and Communication, KLEIT 3

Silicon Photonics 2024-2025

Fig 1.2-Technology vs delay

In Figure 1.2, according to the ITRS, there is no known manufacturable global or intermediate interconnect
solutions for the 45 nm technology node. In the roadmap, such challenges are highlighted on a spreadsheet in
red, forming the “red brick wall.”
Incorporating these new materials into existing fabrication processes posed Silicon Photonics significant
integration challenges. Copper can diffuse quickly through silicon and create short circuits in the transistors
of a chip unless care is taken to avoid contact between the copper wires and the silicon substrate.
Additionally, the nonexistence of any suitable gas phase etching process for copper requires additive
deposition techniques to be used. The silicon industry invested heavily in research and development to find
diffusion barriers and to perfect “Damascene” deposition processes relying on chemical-mechanical
planarization (CMP). These technologies made copper interconnects possible and have allowed scaling to
continue through the present day.

Further evolutionary progress through materials research in very low-κ dielectrics may postpone the return
of the interconnect bottleneck, but a new approach to information transfer within integrated circuits will
inevitably become necessary if transistors are to continue shrinking into the next decade. According to the
latest update of the ITRS chapter on interconnects, traditional interconnect scaling is not expected to satisfy
performance requirements after approximately 2010 (figure 1.2).

1.2 OPTICAL INTERCONNECTS

Dept. of Electronics and Communication, KLEIT 4

Silicon Photonics 2024-2025
Many expect photonics to provide the long term solution. In so-called optical interconnect schemes, the
copper wires between regions of an integrated circuit would be replaced by a system of lasers, modulators,
optical waveguides and photo-detectors. The metal interconnects at all levels starting from those within the
ICs to that between ICs on boards and that with peripheral devices are replaced with optical links. The

potential benefits of this approach include the virtual elimination of delay, cross talk, and power dissipation
in signal propagation, although significant new challenges will be introduced in signal generation and
detection.

The current integration level of about 1.7 billion transistors is responsible for the high processing capability
of today’s processors. More transistors means more switching power. Since switching decides digital signal
processing power the very high integration of transistors is responsible for the processing power of today’s
processors. But the maximum performance power of systems with these processors is limited by the heat
loss in metal connections, inductive losses due to nearby conductors, proximity effect, i.e. expulsion of
current from inner conductor when conductors are in close proximity, skin effect i.e. concentration of current
flow to the surface of conductor due to its suppression at the interior due to the formation of eddy
currents(loop currents) at the interior whose flux linkage opposes the flux of the main current that caused
them. There are also losses due to metallic imperfections (impurities, lattice mismatch etc.). Due to all these
a speed greater than 10Gbps has never been possible with metal interconnections. Even the core series
processors from Intel has data bus speed around 5Gbps.

The integration density and data rate that can be achieved using conventional electrical interconnects set
very high performance requirements for any optical interconnect system to be viable. We can anticipate that
optical interconnects will make the chip-scale integration of the very best photonic technologies available
today. Stable laser sources, interferometry modulators, dense wavelength division multiplexing (WDM), and
low loss planar waveguides will all be necessary components of an optical interconnect system that can
reach an acceptable per-wire information bandwidth-per-watt figure of merit.

These photonic technologies are now applied primarily in the long-haul telecommuting actions industry,
where individual component cost and size do not drive the market. Data transfer rates and the cost per
transmitted bit through optical fiber networks have improved dramatically in performance over the last few
decades, following exponential progress curves that can compound even faster than Moore’s Law. These
advances underlie the infrastructure of the internet and are responsible for fundamental changes in our lives,
particularly in our experience of distance around the globe. However, while millions of miles of fiber optic
cable now stretch between cities and continents, the photonic components they connect are still typically
packaged separately. Obviously this must change if optical networks are to be replicated in microcosm
within millions of future chips.
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Silicon Photonics 2024-2025

Micro photonics refers to efforts to miniaturize the optical components used in long-distance
telecommunications networks so that integrated photonic circuits can become a reality. Work in this field
spans many subjects, including planar waveguides and photonic crystals, integrated diode detectors,

modulators, and lasers. In more recent years, research focused on the sub wavelength manipulation of light
via metal optics and dispersion engineered effective media has begun to explore the anticipated limits of
scaling in future photonic integrated circuits. Advances in the related and often overlapping field of “nan
photonics” suggest the possibility of eventually controlling optical properties through nano scale
engineering.

Between the long-haul telecommunications industry and research in micro photonics lies a small market that
will undoubtedly aid in driving the integration of on-chip optical networks: high performance
supercomputing. Modern supercomputer performance is typically dominated by the quality of the
interconnecting network that routes information between processor nodes. Consequently, a large body of
research exists on network topology and infrastructure designed to make the most of each photonic
component. This knowledge is ready to be applied to future optical interconnect networks that connect sub
processor cores within a single chip.

If optical interconnects become essential for continued scaling progress in silicon electronics, an enormous
market will open for integrated photonic circuit technology. Eventually, unimagined new products will be
made possible by the widespread availability of affordable, high-density optical systems. Considering the
historical development of computing hardware from the relays and vacuum tubes of early telephone
networks, it is possible that optical interconnects could someday lead to all-optical computers, perhaps
including systems capable of quantum computation.

Unfortunately, there is at present no clear path to practical on-chip optical data transfer and scalable all-
photonic integrated circuits. The obstacles that currently stand in the way of optical interconnects are
challenges for device physics and materials science. Break through are needed that either improve the set of
materials available for micro photonic devices or obviate the need for increased materials performance
through novel device designs.

1.3 ENTER OPTOELECTRONICS

Fiber optics use light to transmit data over a glass or plastic fiber(silica),and a seed of about 1.7Gbps was
achieved in 1980s itself. Though plastic fibers are also used silica (glass fiber), i.e. Silicon dioxide, that we
use as insulator in CMOS fabrication is most commonly used. The primary benefit of using light rather than
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Silicon Photonics 2024-2025
an electric signal over copper wiring is significantly greater capacity, since data transmission through fibers
is at light speed. But this alone cannot make high speed transmission possible, it also requires the end
devices like modulators, demodulators etc. where conversion between optical and electrical data takes place,
also to work at such high speeds. The Bell Labs in France currently holds the record of transmission with

mixing of about 155 different data streams each on its own light wave and each with a capacity of about
100Gbps that constitute in total a 14Tbps data link using a fiber pair with Dense WDM technology. In
addition, glass fiber has desirable physical properties: it is lighter and impervious to factors such as electrical
interference and crosstalk that degrade signal quality on copper wires. Hence optic fibers can be used even at
places of high lightning with all dielectric cables. The high electrical resistance of fibers makes them usable
even near high tension equipment. Hence repeaters are placed at ranges over 100Kms.

Photonics is the field of study that deals with light, especially the development of components for optical
communications. It is the hardware aspect of fiber optics; and due to commercial demand for bandwidth, it
has enjoyed considerable expansion and developments during the past decade. During the last few years,
researchers at Intel have been actively exploring the use of silicon as the primary basis of photonic
components. This research has established Intel’s reputation in a specialized field called silicon photonics,
which appears poised to provide solutions that break through longstanding limitations of silicon as a material
for fiber optics. In addition to this research, Intel’s expertise in fabricating processors from silicon could
enable it to create inexpensive, high-performance photonic devices that comprise numerous components
integrated on one silicon die.

1.4 COMPONENTS OF AN OPTICAL SYSTEM

To understand how optical data might one day travel through silicon in your computer, it helps to know how
it travels over optical fiber today. First, a computer sends regular electrical data to an optical transmitter,
where the signal is converted into pulses of light. The transmitter contains a laser and an electrical driver,
which uses the source data to modulate the laser beam, making beam on and off to generate 1s and 0s.
Imprinted with the data, the beam travels through the glass fiber, encountering switches at various junctures
that route the data to different destinations. If the data must travel more than about 100 kilometers, an optical
amplifier boosts the signal. At the destination, a photo detector reads and converts the data encoded in the
photons back into electrical data. Similar techniques could someday allow us to collapse the dozens of
copper conductors that currently carry data between processors and memory chips into a single photonic
link.

Dept. of Electronics and Communication, KLEIT 7

Silicon Photonics 2024-2025
The core of the internet and long-haul telecom links made the switch to fiber optics long ago. A single fiber
strand can now carry up to one trillion bits of data per second, enough to transmit a phone call from every
resident of New York City simultaneously. In theory, you could push fiber up to 150 trillion bits per second
—a rate that would deliver the text of all the books in the U.S. Library of Congress in about a second.

Today’s devices are specialized components made from indium phosphide, lithium notate, and other exotic

materials that can’t be integrated onto silicon chips. That makes their assembly much more complex than the
assembly of ordinary electronics, because the paths that the light travels must be painstakingly aligned to
micrometer precision. In a sense, the photonics industry is where the electronics industry was a half century
ago, before the breakthrough of the integrated circuit.

The only way for photonics to move into the mass market is to introduce integration, high-volume
manufacturing, and low- cost assembly—that is, to “siliconize” photonics. By that we mean integrating
several different optical devices onto one silicon chip, rather than separately assembling each from exotic
materials. In our lab, we have been developing all the photonic devices needed for optical communications,
using the same complementary metal oxide semiconductor (CMOS) manufacturing techniques that the
world’s chip makers now use to fabricate tens of millions of microprocessors and memory chips each year.

A source that can produce narrow coherent beam of light is the prime necessity in optical communication.
Hence lasers are the first choice. However LEDs are also used for some low cost applications. Also for
lasers a 1000 times more power output may be obtained compared to LEDs, based on how we set the gain
medium. However optical communication has limitations due to scattering effects at discontinuities or
imperfections in fiber and also very slight variations in refractive index along the fiber that can affect the
wavelength of signal transmitted. When such limiting factors persist a coherent narrow beam from source,
i.e. a beam of light with each photon at equal lengths along the fiber as well that at a single cross section
showing the same wave properties (frequency, phase, polarization etc.), is a must otherwise the dispersion
and diffraction phenomenon may occur in a different way to each photon in the beam and this can severely
distort or destroy the light signal.

Optical communication operates on the short wave or IR region of EM spectrum (i.e. from 1260-1675nm).
The operating range of wavelength is divided into 6 bands. Among them the C-band (Conventional band),
i.e. from 1530-1565nm is most commonly used, since it has showed the least scattering. Most optical
devices have been developed to work in this range. For communication single mode fibers are preferred,
where mode represents the angles of incidence at the core-cladding interface for which transmission is
possible. Multimode fibers (cross-section diameter>50um) are avoided due to intermodal dispersion, and
Dept. of Electronics and Communication, KLEIT 8
Silicon Photonics 2024-2025
even LEDs can be used. However single mode fibers require high stability for the light source used.

WDM started with mixing of 2 channels and now you can pack dozens of channels of high-speed data onto a
single mode fiber with cross-section as low as 9um,separating the channels by wavelength, a technique
called wavelength-division multiplexing, similar to frequency division multiplexing in radio communication.
Arrayed waveguide grating structures that can perform both mixing and DE multiplexing are used to
implement WDM (Figure 1.3).

In AWG shown in Figure1.3, from 1 to 5, it acts as mux and demux the other way. Regions 2 and 4 are free
space segments and section 3 forms the array of waveguides with a constant length increment. Wherever
light comes out of waveguide to free space, it diffracts, i.e. spreads. A multi wavelength beam coming from
section 1 after diffraction at section 2 passes to each of the waveguides of the array. The phase shift between
the waves coming to section 4 will be such that the waves after diffraction constructive interference of the
composed waves occur where they are received by different waveguides as shown in Figure 1.3. It has the
advantage of integrated planar structure, low cost, low insertion loss and ease of network up gradation, since
with increasing demand for bandwidth instead of laying new fibers, it only requires this device replaced with
a higher capacity structure. As in any optical devices, changes in refractive index with temperature that can
affect wavelength is a problem, and hence precision temperature control within +/-2 degree Celsius is
required.

Fig 1.3-Arrayed Waveguide Grating (AWG) structure

Dept. of Electronics and Communication, KLEIT 9

Silicon Photonics 2024-2025

CHAPTER 2

LITERATURE SURVEY

This section reviews key research and technological advancements related to Silicon Photonics. It highlights
various studies that have contributed to the development of photonic devices using silicon as a core material,
identifies existing gaps, and sets the foundation for the current seminar discussion.

[1] “Silicon Photonics for High-Speed Optical Interconnects”

Thomson, D., Zilkie, A., Bowers, J. E., et al. (2016)
Published in the Journal of Optical Communications, this study explores the design and fabrication of
silicon-based photonic devices for high-speed data transmission. The authors emphasize the benefits of
integrating photonic interconnects on silicon chips to meet the demands of data centers and high-
performance computing. Their research demonstrated the feasibility of achieving low-loss, high-bandwidth
optical links using CMOS-compatible processes.

[2] “CMOS-Compatible Silicon Photonics: Progress and Prospects”

Soref, R. (2018)
Soref’s review, featured in the IEEE Journal of Selected Topics in Quantum Electronics, outlines the
evolution of silicon photonics and the growing interest in its compatibility with CMOS manufacturing. The
paper details the challenges in optical modulation and detection on silicon and discusses successful
implementations of silicon photonic waveguides, modulators, and photodetectors.

This study, published in Optics Express, focuses on packaging challenges in silicon photonic systems. The
authors address thermal management, optical coupling losses, and mechanical stability as key factors in
commercial deployment. Their work contributed significantly to the development of low-cost, scalable
packaging solutions essential for widespread silicon photonics adoption.

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Silicon Photonics 2024-2025

[4] “Silicon Photonics in Telecommunication Networks”

Sun, C., Wade, M. T., Lee, Y., et al. (2020)
Published in Nature, this paper analyzes the use of silicon photonics in next-generation telecommunication
systems. The researchers demonstrate the integration of modulators, multiplexers, and detectors on a single
chip, enabling ultra-fast data transmission over optical fiber. The study’s findings showcase the role of
silicon photonics in enabling 5G networks and beyond.

[5] “Thermo-Optic Effects in Silicon Photonic Devices”

Xu, Q., Schmidt, B., Pradhan, S., Lipson, M. (2021)
Featured in the Journal of Applied Physics, this research investigates the impact of thermal effects on silicon
photonic device performance. The authors model the thermo-optic effect in ring resonators and waveguides,
proposing temperature compensation techniques to maintain stability. This study is crucial for developing
robust photonic circuits in variable environmental conditions.

[6] “Silicon Photonics for High-Capacity Data Communications”

Sun, C., Wade, M. T., Lee, Y., et al. (2020)
In this article from IEEE Journal of Lightwave Technology, the authors explore silicon photonics as a
solution for high-capacity data communications. They present advancements in modulators, detectors, and
integration techniques that enable scalable and energy-efficient optical interconnects for data centers.

[7] “Silicon Photonic Phase Shifters and Their Applications: A Review”

Zhang, Y., Wang, X., Li, J., et al. (2022)
Published in Micromachines, this review focuses on silicon photonic phase shifters, essential components for
reconfigurable photonic circuits. The authors discuss various phase shifter designs, their operating
principles, and applications in modulators, filters, and optical computing systems. 

[8] “Development of CMOS-Compatible Integrated Silicon Photonics Devices”

Paniccia, M., et al. (2005)
This early work, presented at the IEEE International Electron Devices Meeting, discusses the development
of CMOS-compatible silicon photonic devices. The authors highlight the integration of photonic components
with electronic circuits, paving the way for mass production of silicon photonics using existing
semiconductor fabrication infrastructure.

Dept. of Electronics and Communication, KLEIT 11

Silicon Photonics 2024-2025

CHAPTER 3

CONCEPTS

3.1 Fundamentals of Silicon Photonics

 Silicon photonics (SiPh) is a material platform from which photonic integrated circuits (PICs) can be
made. Silicon on insulator (SOI) wafers are used as the semiconductor substrate material, and most
of the standard CMOS foundry manufacturing processes can be applied. This compatibility allows
for the cost-effective mass production of silicon photonic devices, making the technology more
accessible and scalable.

SILICONIZE PHOTONICS
To siliconize photonics, we need six basic building blocks:
• An inexpensive light source.
• Devices that route, split, and direct light on the silicon chip.
• A modulator to encode or modulate data into the optical signal.
• A photo detector to convert the optical signal back into electrical bits.
• Low-cost, high-volume assembly methods.
• Supporting electronics for intelligence and photonics contro

Dept. of Electronics and Communication, KLEIT 12

Silicon Photonics 2024-2025

Figure 3.1- Six basic building blocks of Silicon Photonics

3.2 HOW LASER OCCUR

Lasers generate a beam of a single wavelength by amplifying light. As shown in (Figure 3.4) electrical or
optical energy is pumped into a gain medium which is surrounded by mirrors to form a “cavity.” Initial
photons are either electrically generated within the cavity or injected into the cavity by an optical pumpm
may be a Light Emitting Diode. As the photons stream through the gain medium, they trigger the release of
duplicate photons from an electron in high energy orbital by disturbing it .The emitted photon will have the
same optical properties (wavelength, phase and polarization), and travelling in the same direction as the
incident photon. This same direction of motion and wave characteristics of every phton that constitute the
laser beam is responsible for the directional narrow beam and coherent properties of the light emitted. As the
photons move back and forth between the mirrors, they gather additional photons. This College of
Engineering, Chengannur Silicon Photonics gain has the effect of amplifying the light. An external chemical,
electrical or optical pump source will be provided to maintain population invertion, i.e the state of electrons
in the gain medium such that more number of electrons will be present in higher energy levels than at low
levels. This is necessary to facilitate continous laser emission to occur. Ultimately, the light is sufficiently
strong to form a “coherent” laser beam in which all the photons stream in parallel at the same wavelength.
This laser beam is shown exiting the cavity by the red beam at the right of the figure below.

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Figure 3.2-Basic laser working

3.3 RAMAN EFFECT

The term “laser” is an acronym for Light Amplification through Stimulated Emission of Radiation. The
stimulated emission is created by changing the state of electrons the subatomic particles that make up
electricity. Electrons in conduction band may fall to valence band with the emission of a photon, a process
stimulated by another photon. This generation of photons can be stimulated in many materials, but not in
silicon due to its material properties. Silicon and Germanium are indirect bang gap materials where a
recombination of electron in conduction band with a hole in valence band is least probable or does not occur
at all. It has some momentum consideration as shown in Figure3.3. However there are recombinations that
result in phonon emission(heat) as is seen in ordinary silicon diodes. In case if photonic recombination occur
they are associated with phonon emissions and such large transitions of electron energy that cause this may

cause lattice instability.

Figure 3.3-The indirect bandgap

Using an external laser source coupled with waveguide has significant problems due to sub-micron
misalignments of laser and fibre and also reflections of laser back to source that result in source instability of
operation and variations in emitted wavelength that will distort the data being transmitted. However, an
alternate process called the Raman effect can be used to amplify light in silicon and other materials, such as

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glass fiber, where laser formation occurs within waveguide. Named for the Indian physicist Chandrasekhara
Venkata Raman, who first described it in 1928, this effect causes light to scatter in certain materials to
produce longer or shorter wavelengths. These scattering is associated with energy transitions i.e during
scattering of light the incident photon is absorbed which cause an electron excitation, which is immediately
followed by the fall of the excited electron to lower energy state (a process stimulated by an immediately
following photon), with the emission of a second photon. The energy and characteristics of the emitted
photon depends on the atomic or molecular vibrational energy state of the atom or molecule that caused the
scattering. The Raman effect is widely used today to make amplifiers and lasers in glass fiber. These devices
are built by directing a laser beam known as the pump beam – into a fiber. As the light enters, the photons
collide with vibrating atoms in the material and, through the Raman effect, energy is transferred to photons
of longer wavelengths. If a data beam is applied at the appropriate wavelength, it will pick up additional
photons. After traveling several kilometers in the fiber, the beam acquires enough energy to cause a
significant amplification of the data signal. By reflecting light back and forth through the fiber, the repeated
action of the Raman effect can produce a pure laser beam (figure 3.2). However, fiber-based devices using
the Raman effect are limited because they require kilometers of fiber to provide sufficient amplification. The
Raman effect is more than 10,000 times stronger in silicon than in glass optical fiber, making silicon an
advantageous material. Instead of kilometers of fiber, only centimeters of silicon are required. By using the
Raman effect and an optical pump beam, silicon can now be used to make useful amplifiers and lasers.

Raman scattering is used today, for example, to boost signals traveling through long stretches of glass fiber.
It allows light energy to be transferred from a strong pump beam into a weaker data beam. Most long-
distance telephone calls today benefit from Raman amplification. Typically, a Raman amplifier requires
kilometers of fiber to produce a useful amount of amplification, because glass exhibits very weak scattering.

Figure 3.4-Raman effect in optical fiber and silicon waveguide

2.4 STIMULATED RAMAN SCATTERING & RAMAN SILICON LASER

Dept. of Electronics and Communication, KLEIT 15

Silicon Photonics 2024-2025
College of Engineering, Chengannur Silicon Photonics Unlike in ordinary scattering, in stimulated raman
scattering the energy of weak data beam to be amplified is coupled to light from pump source(Figure 3.4),
where, as the pump laser power travels across the fibre, along with amplification through stimulated
emission a wavelength shift also occurs. Here the energy of data beam being weak is passed to molecular
vibrational energy. The light from pump photons with sufficient energy to excite electron undergoes
scattering and Stimulated Raman Scattering (SRS) occurs without the need of a state of population invertion
as in ordinary lasers. Since the energy of weak data beam passed to molecular vibrational energy, which
decides the wave characteristics of the emitted photon. This finally result the production of a final laser
beam with characteristics of the weak data beam, or it can be said that energy is passed from amplified form
of pump beam to weak data beam. This is similar to technique in microwave amplifier-The Travelling Wave
Tube(TWT). The final wavelength will be in the usable range(i.e least scattering region: 1260-1675 nm).
Further amplification limited by scattering outside this range. To build a Raman laser in silicon, we first
need to create a conduit, also known as a waveguide, for the light beam. This can be done using standard
CMOS techniques to etch a ridge or channel into a silicon wafer. In any waveguide, some light is lost
through imperfections, surface roughness, and absorption by the material. The trick, of course, is to ensure
that the amplification provided by the Raman effect exceeds the loss in the waveguide. The back and forth
reflections within a small waveguide section creates laser within silicon, a process initiated by light from a
superior material like GaAs or InP (the direct bandgap materials that are used to create LEDs). With the

Raman amplifier between the two dielectric mirrors, we had the basic configuration needed for a laser. After
all, laser stands for “light amplification by stimulated emission of radiation,” and that’s what was going on in
our device. Photons that entered were multiplied in number by the Raman amplifier. Meanwhile, as the light
waves bounced back and forth between the two mirrors, they stimulated the emission of yet more photons
through Raman scattering. The photons stimulated in this way were in phase with the others in the amplifier,
so the beam generated will be coherent.

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Figure 3.5-Raman silicon laser

In mid-2004, intel discovered that increasing the pump power beyond a certain point failed to increase the
Raman amplification and eventually even reduced it. The culprit was a process called two-photon
absorption, which caused the silicon to absorb a fraction of the pump beam’s photons and release free
electrons. Almost immediately after we turned on the pump laser, a cloud of free electrons built up in the
waveguide, absorbing some of the pump and signal beams and killing the amplification. The stronger the
pump beam, the more electrons created and the more photons lost.

3.5 TWO PHOTON ABSORPTION & PIN DIODE CORRECTION

The realization of continous wave all-silicon laser was a challenge due to the existence of two photon
absoption. Intel has achieved a research breakthrough by creating an optical device based on the Raman
effect, enabling silicon to be used for the first time to amplify signals and create continuous beams of laser
light. This breakthrough opens up new possibilities for making optical devices in silicon.Usually, silicon is
transparent to infrared light, meaning atoms do not absorb photons as they pass through the silicon because
the infrared light does not have enough energy to excite an electron. Occasionally, however, two photons
arrive at the atom at the same time in such a way that the combined energy is enough to free an electron
from an atom. Usually, this is a very rare occurrence. However, the higher the pump power, the more
College of

Engineering, Chengannur Silicon Photonics likely it is to happen. Eventually, these free electrons recombine
with the crystal lattice and pose no further problem. However, at high power densities, the rate at which the
free electrons are created exceeds the rate of recombination and they build up in the waveguide.
Unfortunately, these free electrons begin absorbing the light passing through the silicon waveguide and
diminish the power of these signals. The end result is a loss significant enough to cancel out the benefit of
Raman amplification. In 2005, Intel disclosed the development of a way to flush out the extra electrons by
sandwiching the waveguide within a device called a PIN diode; PIN stands for p-type–intrinsic n-type,
where the waveguide forms a part of the intrinsic region of the waveguide. When a reverse voltage is applied
to the PIN structure, the free electrons move toward the diode’s positively charged side; the diode effectively
acts like a vacuum and sweeps the free electrons from the path of the light. This is due to the initial high
electric field that setup across the PIN structure. Using the PIN waveguide, we demonstrated continuous
amplification of a stream of optical bits, more than doubling its original power. Once we had the
amplification, we created the silicon laser by coating the ends of the PIN waveguide with specially designed
mirrors. We make these dielectric mirrors by carefully stacking alternating layers of no conducting
materials, so that the reflected light waves combine and intensify. They can also reflect light at certain

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wavelengths while allowing other wavelengths to pass through. With the implementation of this2024-2025
technique
intel built the first continuous silicon laser(Figure 3.6).

Figure 3.6-Waveguide PIN structure

3.6 APPLICATIONS OF RAMAN EFFECT

Fundamentally, Intel researchers have demonstrated silicon’s potential as an optical gain material. This
could lead to many applications including optical amplifiers, wavelength converters, and various types of
lasers in silicon.

An example of a silicon optical amplifier (SiOA) using the Raman effect is shown in Figure 1b. Two beams

are coupled into the silicon waveguide. The first is an optical pump, the source of the photons whose energy
will cause the Raman effect. The spectral properties of this pump determine the wavelengths that can be
amplified. As the second beam, which contains the data to be amplified, passes through the waveguide,
energy is transferred from the pump into the signal beam via the Raman effect. The optical data exits the
chip brighter than when it entered; that is, amplified.

Optical amplifiers such as this are most commonly used to strengthen signals that have become weak after
traveling a great distance. Because silicon Raman amplifiers are so compact, they could be integrated
directly alongside other silicon photonic components, with a pump laser attached directly to silicon through
passive alignment. Since any optical device (such as a modulator) introduces losses, an integrated amplifier
could be used to negate these losses. The result could be lossless silicon photonic devices.

The Raman effect could also be used to generate lasers of different wavelengths from a single pump
beam(Figure 3.7). As the pump beam enters the material, the light splits off into different laser cavities with
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mirrors made from integrated silicon filters. Here the resonant wavelength of each cavity exist 2024-2025
and others
cancel by destructive interference during multiple back and forth reflections. The length of the cavity must
be an integral multiple of the wavelength that sustains. The use of lasers at multiple wavelengths is a
common way of sending multiple data streams on a single glass fiber. In such a scenario, Intel’s silicon
components could be used to generate the lasers and to encode the data on each wavelength. The encoding
could be performed by a silicon modulator un veiled by Intel in early 2004. This approach would create an
inexpensive solution for fiber networking that could scale with the data loads of large enterprises.

Figure 3.7-Creating multiple laser sources from single pump

Optical amplifiers such as this are most commonly used to strengthen signals that have become weak after
traveling a great distance. Because silicon Raman amplifiers are so compact, they could be integrated
directly alongside other silicon photonic components, with a pump laser attached directly to silicon through
passive alignment. Since any optical device (such as amodulator) introduces losses, an integrated amplifier

could be used to negate these losses. The result could be lossless silicon photonic devices.

3.7 SILICON MODULATOR

Beyond building the light source and moving light through the chip, you need a way to modulate the light
beam with data. The simplest option is switching the laser on and off, a technique called direct modulation.
An alternative, called external modulation, is analogous to waving your hand in front of a flashlight beam
blocking the beam of light represents a logical 0; letting it pass represents a 1, without disturbing the source.
The only difference is that in external modulation the beam is always on.(figure 3.8)

Silicon Photonics For data rates of 10 Gbps or higher and traveling distances greater than tens of kilometers,
this difference is critical. Each time a semiconductor laser is turned on, it “chirps” i.e a pulse broadening
occurs due to device heating that result in variation in refractive index. The initial surge of current through
the laser changes its optical properties, causing an undesired shift in wavelength. A similar phenomenon

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Silicon Photonics
occurs when you turn on a flashlight: the light changes quickly from orange to yellow to white 2024-2025
as the bulb
filament heats up. If the chirped beam is sent through an optical fiber, the different wavelengths will travel at
slightly different speeds, which warps data patterns. When there’s a lot of data traveling quickly, this
distortion causes, errors in the data. Also, the phenomenon of chirp worsen as sorce power increase. Hence a
high source power cannot be used, so range is limited to 10 kms.

With an external modulator, by contrast, the laser beam remains stable, continuous, and chirp-free, hence
comparatively a high power source can be used. The light enters the modulator, which shutters the beam
rapidly to produce a data stream; even 10 Gbps data can be sent up to about 100 km with no significant
distortion. Fast modulators are typically made from lithium niobate, which has a strong electro-optic effect
—that is, when an electric field is applied to it, it changes the speed at which light travels through the
material, as a result of variations in refractive index of the material which varies inearly with modulating
voltage applied (Figure 3.9).

A silicon-base modulator, as mentioned before, has the disadvantage of lacking this electro-optic effect. To
get around this drawback, we devised a way to selectively inject charge carriers (electrons or holes) into the
silicon waveguide as the light beam passes through. This used a PIN diode type structure where waveguide
forms the intrinsic region. Because of a phenomenon known as the free carrier plasma dispersion effect, the
accumulated charges change the silicon’s refractive index and thus the speed at which light travels through
it. The silicon modulator splits the beam in two, just like the lithium niobate modulator. However, instead of
the electro-optic effect, it’s the presence or absence of electrons and holes that determines the phases of the
beams and whether they combine to produce a 1 or a 0.The trick is to get those electrons and holes into and

out of the beam’s path fast enough to reach gigahertz data rates. Previous schemes injected the electrons and
holes into the same region of the waveguide. When the power was turned off, the free electrons and holes
faded away very slowly (by lattice recombinations etc.). Hence the maximum speed was limited to about 20
megahertz.

In 2005, Intel disclosed the development of a silicon modulator that uses a transistor like device rather than a
diode both to inject and to remove the charges. Electrons and holes are inserted on opposite sides of an oxide
layer at the heart of the waveguide, where the light is most intense. Unlike ordinary transistors which is a
combination of PN junction diodes connected back to back, here the structure has PIN diodes connected
back to back, where the waveguide on either side of the oxide layer forms the intrinsic regions. Rather than
waiting for the charges to fade away, the transistor structure pulls them out as rapidly as they go in. To date,
this silicon modulator has encoded data at speeds of up to 10 Gbps fast enough to rival conventional optical
communications systems in use today.

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Silicon Photonics
A speed of 18 Gbps was demonstrated with an optical ring modulator that uses a circular 2024-2025
waveguide
structure with multiple inputs, in which the resonant wavelength of the ring will sustain and is modulated
using a PIN diode structure. A 40 Gbps silicon modulator demonstrated in 2007 and an 8-channel integrated
200 Gbps detector demonstrated in 2008 are the recent achievements.

Figure 3.8-Direct and external modulation

Figure 3.9-External modulation in silicon chip

3.8 ENCODING THE OPTICAL DATA

Dept. of Electronics and Communication, KLEIT 21

Silicon Photonics 2024-2025
By splitting the laser beam into two using semitransparent surface within the waveguide and then applying
phase shifts to either waves using electro-optic modulator incorporated within the waveguides (Figure 3.10).
If the phase (speed) change is such that beams will be out of phase resulting in a destructive interference at
where they recombine. If, on the other hand, no voltage is applied to modulators, then beams remain in
phase, and they will add constructively when recombined, encoding the beam with 1s and 0s (Figure 3.11).

Figure 3.10-The MachZender interferometric structure for data encoding

Figure 3.11-Encoding the optical data

3.9 DEMODULATION

Once the beam is flowing through the waveguide, photo detectors are used to collect the photons and
convert them into electrical signals. They can also be used to monitor the optical beam’s properties—power,
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Silicon Photonics
wavelength, and so on—and feed this information back to the transmitter, so that it can optimize2024-2025
the beam.
Silicon absorbs visible light well, which is why it appears opaque to the naked eye.

Infrared Rays, however, passes through silicon without being absorbed, so photons at those wavelengths can
be neither collected nor detected. This problem can be overcome by adding germanium to the silicon
waveguides. Germanium absorbs infrared radiation at longer wavelengths than does silicon, germanium
being a lwer bandgap material than silicon. So using an alloy of silicon and germanium in part of the
waveguide creates a region where infrared photons can be absorbed. Our research shows that silicon
germanium can achieve fast and Silicon Photonics efficient infrared photo detection at 850 nanometers and
1310 nm, the communications wavelengths most commonly used in enterprise networks today.(figure 3.12).

A PIN diode structure in which waveguide forming intrinsic region is used with reverse bias for improved
depletion region width into the intrinsic region. This will enhance the detection since the electron-hole pairs
created at intrinsic region is swept by the electric field in depletion region and forms diode current, and also
the depletion capacitance decreases. However, increased depletion region increases transit time delay and
hence an optimization is necessary.

Figure 3.12-Demodulation of optical data

The detector devices commonly used are the above said PIN diode detector and Avalanche photodiode
detector. InGaAs and germanium are the preferred materials to be used with silicon. In Avalanche
detectors(Figure 3.13) a strong built in electric field exist at the pn junction due to heavy dopping on either
side. This will give an additional advantage of built in amplification.

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Silicon Photonics 2024-2025
These devices however suffer from noise problems due to low bandgap and output current fluctuations due
to variations in the occurrence of photons at the detector. Another problem is the dark current- the reverse
leakage current in the absence of photon. However typical response time is found to be 0.5ns (a switching
speed of about 2GHz). A 40Gbps PIN Silicon Photonics detector demonstrated in 2007 and Avalanche
photodetector with 340GHz Gain*BW demonstrated in 2008 are the recent achievements.

Figure 3.13-Avalanche Photodiode detector

3.10 SILICON INTERFACES

One step that’s often overlooked in discussions of optical devices is assembly. But this step can account for
as much as a third of the cost of the finished product. Integrating all the devices onto a single chip will help
reduce costs significantly; the fewer discrete devices, the fewer assembly steps required. We’re not yet at the

point of full integration, however, and in the mean time, we still need a way to assemble and connect the
silicon optical devices to external light emitters and optical fibers.

Optical assembly has long been much more challenging than electronics assembly. First, the surfaces where
light enters and exits each component must be polished to near perfection. Each of these mirror like facets
must then be coated to prevent reflections, just as sunglasses are coated to reduce glare. With silicon, some
of these extra assembly steps can be greatly simplified by making them part of the wafer fabrication process.
For example, the ends of the chips can be etched away to a mirror-smooth finish using a procedure known as
deep silicon etching, first developed for making micro electro mechanical systems. This smooth facet can
then be coated with a dielectric layer to produce an antireflective coating. Silicon Photonics Because a fiber
and a waveguide are different sizes, a third device—typically a taper—is needed to connect the two. The
taper acts like a funnel, taking light from a larger optical fiber or laser and feeding it into a smaller silicon
waveguide; it works in the opposite direction as well. Obviously, you don’t want to lose light in the process,
which can be tricky when hooking up a waveguide 1 micrometer across to a 10-µm-diameter optical fiber.

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Silicon Photonics 2024-2025
Connecting optical fibers to optical devices on a chip requires attaching the fiber directly to the chip
somehow. One approach we are pursuing is micromachining precise grooves in the chip that are
lithographically aligned with the waveguide. Fibers placed in these grooves fall naturally into the proper
position. Our research indicates that such passive alignments could lose less than 1 decibel of light as the
beam passes from the fiber through the taper and into the waveguide. An index-matching gel material may
be used sometimes.

To passively couple a laser to a silicon photonic chip, you start by bonding the laser onto the silicon. Silicon
etching can be used to produce mirrors, to help align the laser beam to the waveguides. You can also etch
posts and stops into the silicon surface, to control the vertical alignment of the laser to the waveguide, and
add lithographic marks, to help with horizontal alignment.

When we lay silicon optic links on silicon chip, it must be optically independent from the rest of the
substrate. For this an interleaving material is used, commonly silica, i.e silicon dioxide which has a
refractive index 1.44 which is less than 3.4 of silicon and hence facilitates light transmission by total internal
reflection.

3.11 SILICON CHALLENGES

The various challenges at each stage in the development of silicon photonics, include the difficulty to
develop a continous wave all-silicon laser, GHz range modulator and detector devices etc. However there are
also some other effects seen in silicon that has adverse effect at lower micrometer scale fibre transmissions.

These include Kerr nonlinearity effect and Four wave mixing phenomenon. These are significant, since we
deal with micrometer or nanometer range fibres in silicon photonics. Kerr nonlinearity variation in refractive
index proportional to the square of electric field intensity. When multiplexed waves of different intensities
are transmitted, this will lead to separation of waves and destroy the transmission.

Another phenomenon is the four wave mixing. In case when three photons of different wavelength meet at
an atom or molecule in the fibre, such that one photon will cause an electron excitation, a second photon
brings stimulated transition of excited electron to a lower energy state, again a third photon cause excitation
of the same electron to a much heigher energy state, from where a spontaneous transition to initial actual
energy state of electron occur, with the release of a photon of a fourth different wavelength (Figure 3.14).

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Silicon Photonics 2024-2025

Figure 3.14-Energy level transitions of an electron during four-wave mixing

CHAPTER 4

4.1 APPLICATIONS OF SILICON PHTONICS

The high modulation-demodulation rates along with Dense Wavelength Division Multiplexing with which
Tbps data transmission has been achieved in optical communication, that has never been achieved in any
other forms of communication, is expected to come on computer systems, corporate datacenters and in high
end servers. With the developments in silicon photonics where the electronic and optical components comes
on a single integrated platform, this can be achieved at reduced cost and with the elimination of wired
connections. Routers, signal processors etc. that forms the internet backbone will become more simple and
powerful at low cost. College of Engineering, Chengannur Silicon Photonics Another achievement with
Dept. of Electronics and Communication, KLEIT 26
Silicon Photonics 2024-2025
developments in silicon photonics will be the faster and more compact medical equipments like imaging
machines, lasik surgical instruments etc. There will also be reduction in cost, the same thing that we seen in
electronics industry with the developments in integrated circuits. 3D ICs (Figure 4.1) an emerging
technology. With the developments in silicon photonics there will be developments 3D IC technology which
consist of various layers of electronic and photonic components or circuits. In figure 4.1, a 100-core
processor layer is at the bottom. The communication between cores of the processor and that of the chip with
external devices (off-chip traffic) is handled by a superfast photonic or optical link layer at the top. The
research in this area is going on at the IBM’s research centre.

Figure 4.1-3D ICs (An artistic view)

Data Centers and High-Speed Communications

One of the primary applications of silicon photonics is in data centers and high-speed communications. The
rapid growth of data traffic, driven by the increasing use of cloud services, streaming media, and the Internet
of Things (IoT), has created a need for faster and more efficient data transmission solutions.

Silicon photonic devices, such as transceivers and optical switches, can significantly improve the
performance of data center interconnects by enabling higher data rates, lower latency, and reduced power
consumption compared to traditional electronic devices. For example, silicon photonic transceivers can
support data rates of up to 400 gigabits per second (Gbps) and beyond while consuming less power than
their electronic counterparts.

In high-speed communications, silicon photonics can also be crucial in long-haul telecommunications and
high-performance computing. Its ability to transmit data at high speeds over long distances with minimal
signal loss makes it an attractive option for upgrading existing optical networks and enabling next-
generation communication systems.
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Silicon Photonics 2024-2025
Sensing and Imaging

The technology's ability to manipulate light at the nanoscale opens up new possibilities for creating highly
sensitive and compact sensors for various applications, including environmental monitoring, industrial
process control, and biomedical diagnostics.

In environmental monitoring, these sensors can detect and measure various ecological parameters, such as
temperature, humidity, and gas concentrations. These sensors operate by detecting alterations in these factors
through light interactions. For instance, lidar,which stands for light detection and ranging, is a remote
sensing method that uses light as a pulsed laser to measure variable distances to the Earth. These light
pulses, combined with other data recorded by the airborne system, generate precise, three-dimensional
information about the shape of the Earth and its surface characteristics.

Photonics sensors can monitor industrial process parameters in real-time, such as pressure, flow rate, and
chemical composition. These sensors can offer high sensitivity, fast response times, and resistance to harsh
industrial environments, making them ideal for ensuring process efficiency and safety.

Regarding biomedical diagnostics, silicon photonics can enable the development of lab-on-a-chip devices
that can perform complex biochemical analyses on a single chip. These devices use light interactions with
biological samples to detect and measure various biomarkers, such as proteins, DNA, and cells. For
example, a biosensor might use the change in refractive index caused by the binding of a target biomolecule
to a sensor surface to detect the presence of that biomolecule.

This technology can enable the development of high-resolution, compact, and cost-effective imaging
systems. These systems can leverage these devices' waveguiding and interference properties to manipulate
light in ways that enhance imaging capabilities. For instance, an imaging system might use an array of

optical waveguides to focus light onto a sample, enabling high-resolution imaging.

Biomedical Applications

Biomedical studies, in general, can get valuable insights by analyzing nanoscale interactions with silicon
photonics. Silicon photonics can be used to develop lab-on-a-chip systems, allowing complex biochemical
analyses on a single chip.

These systems can detect and measure various biomarkers, such as proteins, DNA, and cells, enabling the
rapid and accurate diagnosis of diseases. For instance, a biosensor might use the change in refractive index

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Silicon Photonics 2024-2025
caused by the binding of a target biomolecule to a sensor surface to detect the presence of that biomolecule.
This could enable the early detection of diseases such as cancer, improving patient outcomes.

In therapeutics, such devices can be used to develop targeted drug delivery systems and photothermal
therapies. For example, nanoparticles can be designed to absorb light at specific wavelengths, generating
heat that can kill cancer cells or trigger the release of drugs. This could enable more effective and less
invasive treatments for cancer-related diseases.

CONCLUSION

Silicon photonics is a transformative technology with great promise for the future of optical communications
and various other applications. By leveraging silicon's unique properties and photonics principles, this
technology can deliver high-speed, energy-efficient, and integrated solutions that can revolutionize
industries such as data centers, artificial intelligence, telecommunications, sensing and imaging, and
biomedical applications. Despite the challenges associated with integration and device fabrication, ongoing
research and development efforts push the boundaries of what is possible, paving the way for a more
connected and data-driven future.

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Silicon Photonics 2024-2025
Silicon photonics is emerging as a key technology that bridges the gap between the growing demand for
high-speed data transfer and the limitations of traditional electronic systems. With the continuous progress of
Moore’s Law and the rise in data traffic, optical communication offers a scalable, high-bandwidth, and
energy-efficient solution. The integration of optical components such as modulators, detectors, and
waveguides on a silicon substrate using CMOS fabrication techniques presents a cost-effective approach,
leveraging existing semiconductor manufacturing infrastructure.

Intel and other industry leaders are working towards creating hybrid platforms by combining silicon with
non-silicon materials, with the future goal of achieving full silicon-based integration. This would not only
reduce production costs but also enable the convergence of photonic and electronic systems on a single chip.
As a result, devices such as servers, high-end PCs, and even everyday gadgets could benefit from ultra-fast
optical communication, making high-speed data transfer more accessible.

With increased research activity, government support, and industrial investment, silicon photonics is steadily
advancing toward commercial viability. The technology promises to transform data centers, cloud
computing, and advanced computing systems, eventually enabling new architectures that were not possible
with traditional electronic components alone. Therefore, silicon photonics is not just an improvement in
communication systems—it is a foundation for the next generation of computing.

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Allow”, Electron. Lett. 25 (22), 1500 (1989)

[3] M. Bruel, “Silicon on insulator material technology”, Electron. Lett. 31 (14), 1201

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Silicon Photonics 2024-2025
(1995)

[4] B. Jalali et al., “Advances in silicon-on-insulator optoelectronics”, IEEE J. Sel. Top. Quantum Electron.
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Dept. of Electronics and Communication, KLEIT 31