3.1 Introduction

As you would expect, since this unit deals with systems engineering, it embodies the principles and methods associated with a systems perspective. So it is important that you understand systems and the systems perspective at the beginning of the unit.

To have engineered a system successfully, all its features – the technology, control systems, people and related aspects of the physical environment – have to contribute to the achievement of its objectives. In other words, it h
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4.4.1 FTTCab, FTTC, FTTB and hybrid coaxial fibre

The equipment needed at optical-fibre transmitters and receivers (lasers, photodiodes and the associated electronics) is more expensive than the equivalent for transmission over copper cables. With FTTH this equipment is needed in every home, and a substantial cost reduction is possible with schemes where the fibre doesn't go all the way to the home, but stops short, and copper links run from a shared fibre to several homes (Author(s): The Open University

3.3 Optical amplifiers

Figure 22 shows in outline one possible structure for an Erbium-doped fibre amplifier (EDFA).

Figure 22
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2.4.3 Polarization mode distortion

Because light is an electromagnetic wave, it has a ‘state of polarization’, which, for light in single-mode fibre, is at right angles to the path of the fibre. If you've not encountered electromagnetic waves before, all you need to appreciate is that as light travels down the fibre the electromagnetic field has an orientation across the fibre (Author(s): The Open University

2.4.1 Multimode distortion

With multimode fibre, the main cause of pulses spreading is the multiple paths that signals can traverse as they travel along the fibre. This phenomenon of multimode distortion is illustrated in Figure 5.


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2.2 Fibre types

A strand of glass (or plastic, but the best performance comes from glass) has a core surrounded by a cladding, where the refractive index of the glass in the core is higher than that of the cladding (see the box on ‘Refractive index>’).

Light is contained within the core by <
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1.1 Uses of optical fibre in communication

Using optical fibres, very high data rates (gigabits per second and higher) can be transmitted over long distances (tens of kilometres) without amplifiers or regenerators. As a consequence, optical fibre has completely superseded copper wires as the primary medium for cabled transmission over long distances. Until recently, however, optical fibre has been used less in LANs, where twisted-pair copper cable has been dominant. Similarly, fibre has been slow to penetrate the access network, from
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Learning outcomes

After studying this unit you should be able to:

  • convert between wavelengths and frequencies;

  • describe the main differences between lasers and LEDs as used as light sources for optical-fibre communications systems;

  • describe the difference between direct and external modulation of a laser;

  • describe the difference in structure and performance of step-index multimode, graded-index multimode and single-mode optical fibres;

  • d
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Acknowledgements

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Grateful acknowledgement is made to the following sources for permission to reproduce material within this unit:


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Introduction

Ethics is an established area of academic interest, but it is only fairly recently that the relevance of ethics to Information and Computer Sciences (ICS) started to emerge clearly outside philosophical studies. Professional bodies in Engineering and ICS have begun to require, as a condition for accreditation, the study of ethics-related topics, and, partially in response to these requirements, new pedagogies for teaching and learning these topics are gradually emerging.

This unit expl
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2 An introduction to the process view of business operations

As we touched on in Section 1, the course that this unit is taken from is concerned with how best to manage the set of business processes that are directly responsible for converting a variety of resources (such as materials, money and the effort of people) into outputs (such as manufactured goods and/or
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Introduction

This unit is adapted from the Open University course Business operations: delivering value (T883_1), which is about the essence of any enterprise – that core set of processes needed to convert various resources (such as materials, money and the effort of people) into outputs (such as manufactured goods and/or delivered services) that provide value to customers and other stakeholders. T
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7.4.3 Chemical vapour deposition (CVD)

If step coverage or equipment cost is more critical than purity, then PVD is supplanted by CVD.

There are many variants on the chemical vapour deposition technique, but the concept is simple: gases adsorb onto the wafer surface where a chemical reaction forms a solid product. Any other products are gases, or at least volatile liquids, and are pumped away.

There is one obvious restriction: the wafer surface must be the only place where the reaction can occur. If it is not, particle
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7.3.6 Laser ablation deposition

Another close cousin to sputter deposition is laser ablation deposition. Ion bombardment of the target is replaced by a focused pulse of light from an ultraviolet laser. Although each pulse may carry only 1 J of energy, this is delivered within 1 ns to a 1 mm spot on the target surface. This represents an astonishing power density and the target surface explodes into vapour that can be caught on the waiting wafer surface. It is vital to scan the focus point across the target surface or you wi
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7.3.5 Ion beam deposition

PVD still has some limitations, however. It must operate in a gaseous atmosphere (to provide the plasma) so is not well suited to the long-throw, directional line-of-sight mode accessible to low-pressure evaporation. Also, if magnets behind the target are used to generate a magnetic field for magnetron sputtering the technique cannot be easily used to deposit magnetic metals such as nickel and cobalt, owing to the influence from the magnetic field on the deposition process.

In an altern
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4.3 PZT

The above requirements lead us to a range of ceramic materials with crystalline structure. One such material is lead zirconate titanate (PZT), which is an oxide alloy of lead, zirconium and titanium. It is often used in a specific composition (sometimes with additives) in order to achieve a particular crystal structure and the desired piezoelectric response. Author(s): The Open University

4.2 The piezoelectric effect at the atomic scale

It has been mentioned above that by changing the state of polarisation of a piezoelectric material we can generate movement, and vice versa. Let's examine a little more deeply what is meant by ‘state of polarisation’ and how we can maximise its effect to get the best out of electrically controlled micro-actuators.

In order to electrically polarise a material we need, by definition, to cause a separation of charges within the material. The more we can do this the greater the d
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3.2 The principles of scanning probe microscopes

Scanning probe microscopy is a term that is applied to a set of imaging methods based on a common element: a fine stylus. In many ways, what scanning probe microscopes do is similar to what a gramophone does. A gramophone stylus scans a spiral groove (by travelling along it) on which information has been encoded in the form of undulations in the groove wall. Side-to-side and up-and-down movements of the stylus (which is mounted on one end of a rod supported and pivoted at its centre) as it fo
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3.1 Introduction

The atomic force microscope is a key visualisation tool for the ‘invisible’ world of micro and nano technology. Within it, right at the heart, is a probe tip that is itself a triumph of nanotechnology.

This section is going to begin with a fair amount of detail about how scanning probe microscopes of various types work, starting with a description of the scanning tunnelling microscope (STM). After that I want to concentrate on its close relative, the atomic force microscope. Then we
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1.4 Sensitivity

Since a biased MOS structure builds up a depletion region with an electric field similar to that in a p–n junction, it's worth thinking about what would happen if light were to be absorbed in an MOS capacitor, generating electron–hole pairs.

Exercise 2

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