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Chapter 28:
Integrated Plasmonic Antennas with Active Optical Devices
A laser can be thought of as an optical cavity with two mirrors within which light bounces back and forth many times. Because the optical mode is strongly coupled to the cavity, a slight change to either mirror can cause a change to the cavity and to the operation of the laser. Increasing the interaction strength between changes to the mirror and the cavity can lead to interesting operational methods for the laser. Recently developed fabrication techniques have made it possible to integrate metallic nanostructures with lasers, creating a hybrid device with applications in the medical, communication, commercial, and defense fields. Using an optical antenna creates an area of very high electric-field concentration; by placing one of these antennas in close proximity to the laser cavity, the antenna can perturb this area, influencing the whole cavity mode. We will show that by modulating the laser mode by interacting it with the near field of the antenna, one can perform the following: determine the near-field and optical force profiles of different antenna geometries, frequency modulate a laser, amplitude modulate a laser, and detect biomolecules with high sensitivity. With the development of nanofabrication techniques, optical antennas can be made and further explored in the visible region of the optical spectrum. These antennas are similar to radio frequency (RF) antennas in that they are structures that are designed to be resonant with specific wavelengths through both their geometrical and material properties as well as their external surroundings. Though both RF and optical antennas have the same basic goal of controlling radiation patterns, there is an important difference. RF antennas are designed to optimize far-field characteristics in order to obtain better transmission and reception of signals, while optical antennas are designed to optimize the near-field characteristics, in order to, for example, create a spot size that is smaller than the wavelength of incoming light. The different operating wavelengths of these antennas also impose an orders-of-magnitude size mismatch between the two classes of antennas.
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