Presents readers with the basic science, technology, and applications for every type of adaptive lens
An adaptive lens is a lens whose shape has been changed to a different focal length by an external stimulus such as pressure, electric field, magnetic field, or temperature. Introduction to Adaptive Lenses is the first book ever to address all of the fundamental operation principles, device characteristics, and potential applications of various types of adaptive lenses.
This comprehensive book covers basic material properties, device structures and performance, image processing and zooming, optical communications, and biomedical imaging. Readers will find homework problems and solutions included at the end of each chapterāand based on the described device structures, they will have the knowledge to fabricate adaptive lenses for practical applications or develop new adaptive devices or concepts for advanced investigation.
Introduction to Adaptive Lenses includes chapters on:
Optical lenses
Elastomeric membrane lenses
Electro-wetting lenses
Dielectrophoretic lenses
Mechanical-wetting lenses
Liquid crystal lenses
This is an important reference for optical engineers, research scientists, graduate students, and undergraduate seniors.
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Yes, you can access Introduction to Adaptive Lenses by Hongwen Ren, Shin-Tson Wu in PDF and/or ePUB format, as well as other popular books in Naturwissenschaften & Optik & Licht. We have over one million books available in our catalogue for you to explore.
Light carries information from the world to our eyes and brains. Therefore, we can see colors and shapes of the objects. It has been verified that light is a kind of electromagnetic radiation. The electromagnetic radiation is generated by the oscillation or acceleration of electrons or other electrically charged particles. The energy produced by this vibration travels in the form of electromagnetic waves. Like a water wave or the wave formed by swinging a rope, a light wave has the properties of wavelength, amplitude, period, frequency, and speed. Figure 1.1a shows light as a wave with those properties. In Figure 1.1a, wavelength is the distance between adjacent crests or troughs, measured in meters, while amplitude is the height of the wave, measured in meters. The period is the time it takes for one complete wave to pass a given point, measured in seconds. The frequency is the number of complete waves that pass a point in one second, measured in inverse seconds, or hertz (Hz). The speed is the horizontal speed of a point on a wave as it propagates, measured in meter/second. For light traveling in vacuum, the speed of light is commonly given the symbol c. It is a universal constant that has the value c = 3 Ć 108 m/sec. The speed of light in a medium is generally expressed as v = c/n, where n is the refractive index of the medium. Since the propagation direction and the vibration direction of a light wave are perpendicular, light is a transverse wave.
Figure 1.1 Property of light as (a) a wave and (b) particles.
To human eyes, the visible wavelength of a light wave is distributed in a range from ā¼ 380 to ā¼ 780 nm. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light.
Besides the wave property, light can also be considered as particles, as shown in Figure 1.1b. These particles are called photons, which carry a specific amount of energy. Light exhibits wave and particle duality, depending on what we do with it and what we try to observe. For example, light manifests wave properties through interference and diffraction, while it can be treated as particles (photons) through photoelectric effect (1). The wave and particle duality nature can be linked nicely by the de Broglie relation: p = h/Ī», where p is the momentum of the particle, Ī» is the wavelength, and h is Planck's constant.
When light interacts with matter, several phenomena could take place, such as reflection, refraction, absorption, diffraction, interference, and polarization (2). In order to control or modulate light to achieve these optical properties, various optical devices have been developed. For example, we have mirrors to reflect light, eyeglasses to see better, telescopes to see farther, and microscopes to see objects hundreds or thousands of times larger than they actually are. Light can also be used for medicine and communication. The light from a laser can be used to perform tissue surgery. Many internet and telephone cables are now being replaced by optical fibers, which carry an enormous amount of information in a small space (3).
Many different optical devices have been developed. There is no doubt that the lens is the most widely used optical device. The lens has been studied and developed for a long history. The oldest man-made lens can be dated back to 3000 years ago. It may have been used as a magnifying glass, or as a burning glass to start fires by concentrating sunlight. Lenses have become indispensible devices in many areas. Owing to the development of optical materials, fabrication techniques, and new operation mechanisms, the performances of lenses have been improved significantly. A typical lens is made of glass, plastic, polymer, or polycarbonate. From the aspect of geometrical structure, a lens has two refraction surfaces with a perfect or approximate axial symmetry; at least one surface is a segment of a sphere. Conventional lenses are used to form images by converging or diverging the incident beam. They are used in building various optical devices and instruments, such as cameras, telescopes, microscope, projectors, optical readers, laser scanners, laser printers, fiber optical switches, and many more. Optical lenses are now the key elements in image processing, information storage, optical communication, vision correction, three-dimensional (3D) displays, and other scientific applications. The market of optical lenses is huge, and the demand of optical lenses has been growing continually. On the other hand, the development of novel optical and electronic products has evoked new concept lens. Thus, conventional solid lenses are insufficient due to their inherent shortcomings.
In this chapter, we will introduce the operation mechanism of a solid lens based on the law of light refraction. Through a lens or a lens system, the relationship between image and object are given. The merits and demerits of the lens or lens system are discussed. Inspired from the structure of human eye and human eye's operation mechanism, two possible ways of realizing an eye-like lens are anticipated.
1.2 Conventional Lens
1.2.1 Refraction of Light
When light from a vacuum enters a medium, such as glass, water, or clear oil, it travels at a different speed. The speed of light in a given medium is related to a quantity called the index of refraction (n), which is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v): n = c/v. When light propagates from one medium with n = n1 to another with n = n2, its speed changes. The change in speed is responsible for the bending of light, that is, refraction. The refraction occurs at the boundary of two media having different refractive indices. Figure 1.2 depicts the refraction of light propagating from medium 1 to medium 2.
Figure 1.2 The refraction of light at the interface of two different mediums.
The angles of incidence and refraction are measured relative to a line perpendicular to the boundary between the media called the normal. The media that the light passes from and to are transparent. The light will bend based on the following relationship, called Snell's law:
1.1
where n1 is the refractive index of medium 1, Īøi is the angle of incidence between the incident ray and the normal, n2 is the refractive index of medium 2, and Īør is the angle of refraction between the refracted ray and the normal.
When a beam of light with parallel rays enters medium 2 at a tilted angle, the rays are bent with the same refraction angle without crossing, as shown in Figure 1.3a. As a comparison, if the surface is polished with a spherical shape, then the parallel rays of the beam are refracted with different refraction angles. Let us suppose n1 < n2, the rays come together at a point in the medium on the axis, as shown in Figure 1.3b. The point where the rays focus together is...
