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Photonics

Photonics Essentials, Second Edition by Thomas Pearsall [McGraw-Hill Professional] The development of electronics and the development of photonics have followed different routes. The development of integrated circuits has focussed on the design, fabrication, and characterization of two basic devices: memory and microprocessor chips. This element of simplicity is one important reason for the extraordinary growth and success of the integrated circuit industry.

This unique book teaches photonics through the hands-on measurement techniques common to all photonic devices. Perfect for students and engineers looking for practical expertise rather than abstract theory, this tutorial does more than explain the workings of photonic applications in standard devices like lasers and photodetectors--it offers worked examples of measurement and characterization problems. Filled with these real-world examples that feature commercially available instruments, this practice-based book enables you to analyze, characterize, and handle any kind of photonic device.

On the other hand, there is a wide variety of photonic devices: light emitters, detectors, modulators, phototransistors, waveguides, and switches, to name a few examples. While integrated circuits are made out of silicon and silicon dioxide, photonic circuits are made from many different materials, III-V semiconductors, polymers, oxides, plastics, and yes, silicon and silicon dioxide. The physics and technologies of these devices cover a very wide range of disciplines because of the large number of functions and because of the number of materials.

Since the publication of the first edition of this book in 2003, there have been some significant changes in photonics components and applications:

• Photographic film for the amateur photography market has been nearly totally replaced by photonic imaging chips.
• LEDs have been commercialized in automotive lighting, and Audi has introduced the LED automotive headlight.
• Television using OLED emission flat-panel displays has been commercialized by Sony.
• Broadband communication access by fiber to the home is widespread.
• The modulation rate of commercially available telecommunications lasers has increased from 2 to 40 Gbit/sec.
• The production of photovoltaic panels has increased by a factor of 10.
• Since 2003 Two Nobel Prizes have been awarded in photonics research:
• 2008 in Chemistry for the discovery of the green fluorescent protein GFP
• 2005 in Physics for the quantum theory of lasers, and for high-precision laser measurements of time

By 2008, the annual revenue generated by photonics businesses world-wide was 20% greater than the total generated by microelectronics. Furthermore, in comparison to microelectronics, photonics is a high-growth business. Photonics will continue to move into the mainstream of economic activity only if there is a large cadre of trained engineers. The presence of photonics courses in the undergraduate curriculum will help make this happen by teaching photonics to an audience with wider interests and at an earlier stage in the educational cycle. Teaching photonics to undergraduates requires an approach that is different from that of the typical graduate-level course.

This text stresses understanding and mastery of four key scientific concepts that have shaped not only our understanding of photonics but also our current scientific view of the world in general. These are

• The Boltzmann relationship: n1/n2 = e-(E1-E2)/kT
• The Planck equation that relates energy to frequency: E =
• The de Broglie relationship that equates momentum to wavelength: p = h/L.
• Conservation of energy and momentum

The approach in this text is to present and develop these concepts, introducing ideas of quantum mechanics as necessary to support the understanding and use of these principles, which appear as revolutionary to students now as they appeared to scientists when they were introduced over a century ago. The full beauty of quantum mechanics and statistical mechanics is left for treatment in graduate-level courses.

A key feature of this text is the emphasis on experimental measurement as a teaching tool. It is my experience that the unusual features of quantum mechanical behavior of electrons and photons are much more quickly understood if they are encountered both in the laboratory and in the classroom. But an equally important reason to teach photonics from an experimental viewpoint has to do with the diverse nature of the technologies.

While the number and variety of photonic devices are large, the measurement techniques used to characterize photonic devices are relatively standard: current-voltage measurements, capacitance-voltage measurements, optical characterization using a spectrometer or monochromator, lock-in amplifier, and lenses. These methods are routinely used to understand and quantify the performance of almost all photonic devices. Mastery of the basic laboratory techniques in this book will enable the students to study a large number of photonic devices. The instruments can usually be found in any department that has research activities in optics or optoelectronics. The specific devices used here have been chosen because they are widely available and inexpensive. Thus, the budget needed to run a laboratory section is modest and the pedagogical rewards can be significant.

In the first eight chapters, the operating principles of some basic and important photonic devices such as p-n junction diodes, photodiodes, LEDs, and laser diodes are taught through analysis in the classroom and experimental measurement in the laboratory. From this starting point, the course can be continued by covering further analytical material on devices that are not generally available, such as waveguides, modula-tors and switches, or the course can be concluded with a design project. Some examples are

• Optical data links with a grand variety of modulation schemes
• Laser interferometer
• Measurement of the oxygen content in the bloodstream
• Using a CCD array to make a spectrograph, particularly appreciated by students after having characterized a laser using a conventional scanning spectrometer

Photons have been around ever since the Big Bang, which is a long time. Photons, by definition, are always on the move: 3 x 10 10 cm/sec in air. Some of the important milestones in the history of the human civilization are those at which we have improved our ability to control the movement of photons. A few notable examples are the control of fire, the design of lenses, the conception of Maxwell's equations, the invention of photography, broadcast radio, and the laser.

Photonics is the study of how photons and electronics interact, how electrical current can be used to create photons as in a semiconductor laser diode, and how photons can create an electrical current, as in a solar cell. The field of photonics is in its infancy. Great discoveries remain to be made in using photonics to improve our lives.

The list of applications in photonics is long. Some of the rapidly growing areas are:

Ecology:
Solar cell energy generation
Air quality and pollution monitoring

Imaging:
Camcorders
Satellite weather pictures
Digital cameras
Night vision
Military surveillance

Information displays:
Computer terminals
Traffic signals
Operating displays in automobiles and appliances

Information storage:
CD-ROM
DVD

Life Sciences:
Identification of molecules and proteins
Lighting

Medicine:
Minimally invasive diagnostics
Photodynamic chemotherapy

Telecommunications:
Lasers
Photodetectors
Light modulators

Telecommunications is an application of considerable activity and economic importance because of the transformation of the worldwide communications network from one that used to support only voice traffic to one that now supports media transmitted through the Internet, including voice, data, music, and video. Of course, in the digital world these different media are all transmitted by ones and zeros. However, if a picture can be said to be worth more than a thousand words, a transmitted picture counts for about a million words. The growth of the Internet and its capacity to transmit both images and sound has been made possible only because of the vast improvements in speed and capacity of fiber optic telecommunications. At the heart of this revolution are the semiconductor laser, fast light modulators, photodiodes, and communications-grade optical fiber.

From this text you can learn what makes these key devices work and how they perform. Laboratory measurements are emphasized for an important reason: There are many different kinds of photonic devices, but only a few basic characterization measurements. When you learn these laboratory techniques, you can measure and understand almost any kind of device. The experiments are based on components that you can find easily in any electronics store. This means that the laboratory fees should be reasonable, and that you can quickly find a replacement device when you need one.

This course is an excellent preparation for subsequent work in the physics of semiconductor devices, the design of biomedical instrumentation, optical fiber telecommunications, sensors, and micro opto-electro mechanical systems (MOEMS). You may also want to consider a summer internship as a test and measurement engineer with one of the growing number of start-up companies in the opto-electronics industry.

The largest market for photonic devices today is the telecommunications industry. Historically, this industry has been growing at about 5% per year. The development of the optical fiber and the Internet have changed all that.

An optical fiber is generally a thin strand of glass that is used to carry a beam of light. Once the light is introduced in the fiber, by using a lens, for example, it can only escape by propagating to the other end of the fiber. The light beam is prevented from leaking out of the sidewalls by an effect called total internal reflection. Thus, the fiber acts as a guide for photons. When engineers showed that sending high-speed communications by light waves was far superior to sending communications by electricity, growth rates in the industry changed dramatically. This is the definition of a disruptive technology.

An important side effect of this growth is that the composition of the telecommunications industry is changing rapidly. Old-line companies, like Alcatel, Lucent, and Philips, that were masters at handling slow growth and predictable schedules for deployment of new technology are going through radical changes to adapt to the rapid evolution of technology innovation and manufacture. For example, Alcatel has recently announced that it intends to own no factories by 2010. These are being replaced in the photonic devices industry sector by a very large number of smaller companies, many of which have been in business for only a few years. Not all of these companies will succeed. Making a career in the photonics industry is both exciting and punctuated occasionally by moments of instability provoked by the reorganization of this industry resulting from the implementation of new technologies, takeovers, and creation of new start-up companies. Fortunately, there is a strong and steady growth rate, much greater than 5%, that is underlying this effervescence. To succeed, you need to keep a close watch on both the technology and the opportunities.

 

 

 

 

 

 

 

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