Silicon photonics
#1

Silicon photonics can be defined as the utilization of silicon-based materials for the generation (electrical-to-optical conversion), guidance, control, and detection (optical-to-electrical conversion) of light to communicate information over distance.The most advanced extension of this concept is to have a comprehensive set of optical and electronic functions available to the designer as monolithically integrated building blocks upon a single silicon substrate.Within the range of fibre optic telecommunication wavelength (1.3 µm to 1.6 µm), silicon is nearly transparent and generally does not interact with the light, making it an exceptional medium for guiding optical data streams between active components
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#2
send full report on silicon photonics
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#3
hey
please read http://studentbank.in/report-silicon-in-...ull-report and http://studentbank.in/report-silicon-photonics--1315 for getting more information of Silicon photonics


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and come again for helping other students issues in this forum
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#4
PRESENTED BY-
VAIBHAV DESHWAL

[attachment=11717]
“PHOTONICS”
INTRODUCTION

The science of photonics includes –
 Generation
 Emission
 Transmission
 Modulation
 Signal processing
 Switching
 Amplification
 Detection
 Sensing
• Its goal was to use light to perform functions that traditionally fell within the typical domain of electronics, such as telecommunications, information processing, etc.
• Photonics is related to quantum optics, optomechanics, electrooptics, optoelectronics and quantum electronics
History
• Photonics as a field began with the invention of the laser in 1960.
• Photonics goal waswas to use light to perform functions that traditionally fell within the typical domain of electronics, such as telecommunications, information processing, etc.
• Developments followed optical fiber and erbium -doped fiber ampifier, which formed the basis of telecom. revolution and gave the infrastucture of internet.
Principle
Components

• Generator-. Photonics commonly uses semiconductor light sources like LEDs, superluminescent diodes, and lasers
• Other light sources include fluorescent lamps,CRTs, and plasma screens .
2.Transmission media-
Light can be transmitted throug any transparent medium. Glass fiber or plastic optical fiber can be used to guide the light along a desired path. In optical communications optical fibers allow fortransmission distances of more than 100 km.
3. Amplifier-
• Optical amplifiers are used to amplify an optical signal. Optical amplifiers used in optical communications are erbium-doped fiber amplifiers, semiconductor optical amplifiers, Raman amplifiers andoptical parametric amplifiers
4.Detector-
• Photodetectors detect light. Photodetectors range from very fast photodiodes for communications applications over medium speed charge coupled devices (CCDs) for digital cameras to very slow solar cells that are used for energy harvesting from sunlight.
5. Modulation-
• Modulation of a light source is used to encode information on a light source. Modulation can be achieved by the light source directly. One of the easiest examples is to use a flashlight to send Morse code. Another method is to take the light from a light source and modulate it in an external optical modulator.
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#5

Presented By,
Supreetha S R

[attachment=12979]
SILICON PHOTONICS
INTRODUCTION
Silicon photonics can be defined as the utilization of silicon-based materials for the generation, guidance, control, and detection of light to communicate information over distance.
It is an evolving technology in which data is transferred among computer chips by optical rays. Optical rays can carry far more data in less time than electrical conductors.
It aims to determine how to use silicon and standard silicon processing techniques to build optical devices. The concept is based on developing optical building blocks that give active functionality, rather than simple, passive optical wave-guiding. These tiny silicon building blocks can be selectively placed into optical modules, reducing cost and size.
Why silicon photonics?
The presence of a single material, silicon, which is widely available, can be purified to an unprecedented level, is easy to handle and to manufacture and shows very good thermal and mechanical properties which render the processing of devices based on it easy.
The presence of a single dominating processing technology, CMOS, with integration of more and more devices on larger wafers.
Limitations of operating speed due to interconnects.
The success and capacity of optical communication.
Properties of silicon
Transparent in 1.3 – 1.6 µm region
CMOS compatibility
Low cost
It has a very high refractive index
It exhibits stronger Raman effect
Very good thermal and mechanical properties
Hybrid integration is considered to achieve electrically pumped light emission, known as Electro Luminescence (EL), from silicon.
In this approach, a simple gain element is coupled to a silicon based bragg filter and used to form an ECL.
Silicon wave guide based Bragg grating can be used in an external cavity to alter the lasing properties of a III-V gain chip to produce a useful source for optical communications. The strong thermo-optic effect in silicon can be used to tune the lasing wavelength by heating the silicon grating.
The ECL is formed by butt coupling a Single Angled Facet (SAF) gain chip to a waveguide containing the polycrystalline/crystalline silicon Bragg grating.
The laser cavity is formed between the Bragg grating as one end mirror, and a 90% high-reflection coating of the gain chip as the other mirror. The 8º angled facet between the two chips decreased the effective reflectivity of that facet to ~10-3.Combining an angled facet with a 1% antireflection coating resulted in an effective facet reflectivity of ~10-5.
The output of the laser was taken from the 90% high-reflectivity coated side of the laser diode with a conical polished (140º) lensed single-mode fiber.
CONTINUOUS SILICON LASER
RAMAN EFFECT
:
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 (Figure 1a).
By reflecting light back and forth through the fiber, the repeated action of the Raman Effect can produce a pure laser beam. However, fiber-based devices using the Raman Effect are limited because they require kilometers of fiber to provide sufficient amplification.
The process of building a Raman amplifier or laser in silicon begins with the creation of a waveguide – a conduit for light in silicon. This can be done using standard CMOS techniques to etch a ridge or channel into a silicon wafer (Figure 1b).
Light directed into this waveguide will be contained and channeled across the chip. In any waveguide, some light is lost through absorption by the material, imperfections in the physical structure, roughness of the surfaces and other optical effects.
The amplification provided by the Raman effect exceeds the loss in silicon waveguide.
The reason was a physical process called two-photon absorption which absorbs a fraction of the pump beam and creates free electrons. These electrons build up over time and collect in the waveguide.
The problem is that the free electrons absorb some of the pump and signal beams, reducing the net amplification. The higher the power density in the waveguide, the higher the loss incurred.
Intel’s Breakthrough Laser
Change the design of the waveguide so that it contains a semiconductor structure, technically called a PIN (P-type – Intrinsic – N-type) device. When a voltage is applied to this device, it acts like a vacuum and removes the electrons from the path of the light.
Figure 3 is a schematic of the PIN device. The PIN is represented by the p- and n- doped regions as well as the intrinsic (undoped) silicon in between. This silicon device can direct the flow of current in much the same way as diodes and other semiconductor devices.
To create the breakthrough laser, the ends of the PIN waveguide were coated with mirrors to form a laser cavity (Figure 4). After applying a voltage and a pump beam to the silicon, a steady beam of laser light of a different wavelength exiting the cavity was observed – the first continuous silicon laser.
SILICON MODULATOR
Silicon optical intensity modulator with a modulation bandwidth of 2.5 GHz at optical wavelengths of around 1.55 μm.
The high-speed modulation is achieved by using a novel phase shifter design based on a metal-oxide-semiconductor (MOS) capacitor embedded in a passive silicon waveguide Mach- Zehnder Interferometer (MZI).
Light wave coupled into the MZI is split equally into the two arms, each of which may contain an active section which converts an applied voltage into a small modification in the propagation velocity of light in the waveguide. Over the length of the active section(s), the velocity differences result in a phase diff. in 2 waves. Depending on the relative phase of 2 waves after passing through the arms, the recombined wave will experience an intensity modulation.
A ~1.4 μm n-type doped crystalline silicon slab and a p-type doped poly-silicon rib with a 120 Å gate oxide .
The poly-silicon rib and the gate oxide widths are ~2.5 μm and total polysilicon thickness is ~0.9 μm.
To minimize metal contact loss- a wide (~10.5 μm) top polysilicon layer on top of the oxide layers. Aluminum contacts on top of polysilicon layer.
The oxide regions maintain horizontal optical confinement and prevent the optical field from penetrating into the metal contact areas.Vertical optical confinement is provided by buried oxide (~0.375 μm) and an oxide cover.
The n-type silicon in the MOS capacitor phase shifter is grounded and a positive drive voltage, VD, is applied to the p-type poly-silicon causing a thin charge layer to accumulate on both sides of the gate oxide. The voltage-induced charge density change ΔNe (for electrons) and ΔNh (for holes) is related to the drive voltage by
where ε 0 and ε r are the vacuum permittivity and low frequency relative permittivity of the oxide, e is the electron charge, tox is the gate oxide thickness, t is the effective charge layer thickness, and VFB is the flat band voltage of the MOS capacitor.
Due to the free carrier plasma dispersion effect, the accumulated charges induce a refractive index change in the silicon. The index changes obtained through Kramers-Kronig analysis, are given by
Δne=−8.8×10−22ΔNe
Δnh=−8.5×10−18(ΔNh)0.8
The change in refractive index results in a phase shift Δφ in the optical mode given by
where L is the length of the phase shifter, λ is the wavelength of light in free space, and Δneff is the effective index change in the waveguide, which is the difference between the effective indices of the waveguide phase shifter before and after charge accumulation.
SI-BASED PHOTODETECTORS
Silicon is a poor detector in infrared region. So it is combined with germanium to reduce the bandgap and extend the maximum detectable wavelength. The two main factors to be considered in photodetectors are absorption coefficient or penetration depth of the light; responsivity and bandwidth.
The responsivity is the ratio of collected photocurrent to the optical power incident on the detector. The bandwidth of a photodetector can be limited by the transit time required for the photocarriers to travel to the contacts.
Maximizing the light absorption by making the layers thicker results in a reduction of bandwidth due to transit time issues. The way around this problem is to illuminate the device from the side. By doing this, the transit time can be kept low while the effective length of the detector is increased from a few micrometers to as long as a few millimeters. This is the approach used for waveguide-based photodetectors.
ADVANTAGES
Low cost/high volume production
Faster data transmission
Silicon Photonics interfaces and medium remain constant
Low power consumption
High thermal conductivity
Robustness of device
APPLICATIONS
Fiber to the home
High speed interconnects
Multi-core processors and Supercomputers
Microwave systems and Biometrics
Optical sensors
CONCLUSION
Silicon photonics is a generic technology with a wide range of high volume applications for which the industrial technology base largely exists today. The development of silicon photonics has seen enormous progress over the last decade.
Silicon photonics is being used to make commercially competitive devices that provide the modulation and detection functions needed in data communications, telecommunications systems and optical interconnects. Exciting new applications are emerging in sensing, mid-infrared optics and optomechanical systems.
Silicon photonics will likely eventually make a revolutionary impact in the high-volume data communication and computing industries.
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#6

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ABSTRACT
Silicon photonics can be defined as the utilization of silicon-based materials for the generation (electrical-to-optical conversion), guidance, control, and detection (optical-to-electrical conversion) of light to communicate information over distance. The most advanced extension of this concept is to have a comprehensive set of optical and electronic functions available to the designer as monolithically integrated building blocks upon a single silicon substrate.
Within the range of fiber optic telecommunication wavelength (1.3 µm to 1.6 µm), silicon is nearly transparent and generally does not interact with the light, making it an exceptional medium for guiding optical data streams between active components. But no practical modification to silicon has yet been conceived which gives efficient generation of light. Thus it required the light source as an external component which was a drawback.
There are two parallel approaches being pursued for achieving opto-electronic integration in silicon. The first is to look for specific cases where close integration of an optical component and an electronic circuit can improve overall system performance. One such case would be to integrate a SiGe photodetector with a Complementary Metal-Oxide-Semiconductor (CMOS) transimpedance amplifier. The second is to achieve a high level of photonic integration with the goal of maximizing the level of optical functionality and optical performance. This is possible by increasing light emitting efficiency of silicon. The paper basically deals with this aspect.
Chapter 1
INTRODUCTION

Silicon photonics is an evolving technology in which data is transferred among computer chips by optical rays. Optical rays can carry far more data in less time than electrical conductors. Its overarching goal is to develop high volume, bolt-and-go optical components using silicon. While silicon is opaque in the visible spectrum, it is transparent at the infrared wavelengths used in optical transmission, hence it can guide light.
Why silicon photonics?
The big success of today’s microelectronic industry is based on various factors, among others
• the presence of a single material, silicon, which is widely available, can be purified to an unprecedented level, is easy to handle and to manufacture and shows very good thermal and mechanical properties which render the processing of devices based on it easy ,
• the availability of a natural oxide of silicon, SiO2, which effectively passivates the surface of silicon, is an excellent insulator, is an effective diffusion barrier and has a very high etching selectivity with respect to Si,
• the presence of a single dominating processing technology, CMOS, which accounts for more than 95% of the whole market of semiconductor chips,
• the possibility to integrate more and more devices, 55 000 000 transistors in PENTIUM® 4 (figure), on larger and larger wafers (300 mm process and 400 mm research) with a single transistor size which is decreasing (gate lengths of 180 nm are in production while 15 nm have been demonstrated), yielding a significant reduction in cost per bit,
• the ability of the silicon industry to face improvements when the technology is hitting the so-called red brick wall, e.g. the use of SiGe for high frequency operation and the introduction of low k-materials and of Cu to reduce RC delays,
All these factors have rendered the microelectronics industry very successful. However, in recent years some concerns about the evolution of this industry have been raised which seem related to fundamental materials and processing aspects.
Technology Challenges:
Silicon photonics aims to determine how to use silicon and standard silicon processing techniques to build optical devices. The concept is based on developing optical building blocks that give active functionality, rather than simple, passive optical wave-guiding. In the future, these tiny silicon building blocks can be selectively placed into optical modules, reducing cost and size.
Today, both home and business computers are limited less by processor performance than by the rate at which data can be transmitted between the processor and the outside world. Major corporations, financial institutions, and virtually all businesses and consumers demand instant and reliable transmissions, whether their data is traveling across the street or around the world. Corporate LAN and Internet traffic already exceeds telephony traffic, and Internet traffic has been doubling every year.
Copper-based networking can no longer keep up, so the telecommunications industry has turned to fiber optics to fulfill the growth demands of Internet traffic. But optical networks are arcane and expensive. Because of their high costs, their use has been limited primarily to long-haul and backbone networks.
The evolution toward faster data rates will drive the fiber-optic industry to move next to 40 Gbps, and to even higher data rates in the future. With the combination of higher data rates and DWDM capabilities, telecommunication companies will be able to transmit a trillion bits of data per second on a single fiber — a rate that would exceed the total traffic on the entire Internet today.
Chapter 2
EXTERNAL CAVITY LASER
Silicon Light Source:

In this section the use of silicon photonics applied to the light source is discussed. While a silicon laser is still out of reach, work is being done worldwide on silicon light emitters that emit both visible and infrared radiation. A silicon emitter is the missing piece for monolithic integration as it would enable all optical elements and drive electronics to be fabricated on a common substrate. Because we are using silicon waveguides to guide light, the emitter must be in the infrared region of the wavelength spectrum (> 1.1 μm) where optical absorption loss is low.
We first summarize the different paths researchers are investigating to achieve electrically pumped light emission, known as Electro Luminescence (EL), from silicon. Until reliable and efficient silicon emitter can be produced, hybrid integration must be considered (i.e., using a non-silicon-based light source coupled to silicon waveguides). In such a hybrid integrated approach, we show how a simple gain element (III-V gain chip) coupled to a silicon-based Bragg filter can be used to form an ECL. Proof of principal of this tunable, single mode laser is discussed.
Device Architecture
This section describes how a silicon wave guide based Bragg grating can be used in an external cavity to alter the lasing properties of a III-V gain chip to produce a useful source for optical communications. The strong thermo-optic effect in silicon can be used to tune the lasing wavelength by heating the silicon grating. The driving force behind this is to produce an inexpensive narrow line-width source suitable for optical communications.
The Bragg grating is fabricated by etching a set of 1.2x2.3 μm, 3.4 μm deep, trenches into a 4 μm thick Silicon-on- Insulator (SOI) wafer. One thousand of these trenches are laid out in a line along the waveguide with a range of periods around 2.445 μm (although these were laid out as rectangular trenches, due to litho resolution, they were rounded after processing). These trenches are then filled with poly-silicon and annealed to reduce the loss
due to the poly-silicon. The poly-silicon is then chemically/mechanically polished to obtain a planar surface and the 3.5 μm wide, 0.9 μm deep rib is patterned using standard lithography and etching. The last step in the fabrication is to deposit a final, 0.5 μm thick, low temperature layer of oxide to provide the necessary upper cladding for the rib waveguides. A schematic of the Bragg grating is shown in Figure 1.
The novel property of this Bragg grating is that it only reflects a narrow, 0.5 nm wide range of wavelengths back through the waveguide with a reflectivity of 70%. An example of a reflection spectrum from a 1500- trench grating filter is shown in Figure. As a separate component these Bragg filters can be used in optical communication networks as channel filters for wavelength division multiplexed systems.
The ECL is formed by butt coupling a Single Angled Facet (SAF) gain chip to a waveguide containing the polycrystalline/crystalline silicon Bragg grating. The laser cavity is formed between the Bragg grating as one end mirror, and a 90% high-reflection coating of the gain chip as the other mirror. The 8º angled facet between the two chips decreased the effective reflectivity of that facet to ~10-3. Combining an angled facet with a 1% antireflection coating resulted in an effective facet reflectivity of ~10-5. The output of the laser was taken from the 90% high-reflectivity coated side of the laser diode with a conical polished (140º) lensed single-mode fiber [Figure 3]. The purpose of this lensed optical fiber was to increase the coupling between the laser and the optical fiber.
Chapter 2.1
CONTINUOUS SILICON LASER
The 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. As their state changes, they release a photon, which is the particle that composes light. This generation of photons can be stimulated in many materials, but not silicon due to its material properties. However, an alternate process called the Raman Effect can be used to amplify light in silicon and other materials, such as glass fiber. 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.
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 (Figure 1a). By reflecting light back and forth through the fiber, the repeated action of the Raman Effect can produce a pure laser beam (see sidebar on lasers). 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 (Figure 1b). By using the Raman Effect and an optical pump beam, silicon can now be used to make useful amplifiers and lasers.
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