FREE SPACE OPTICS
NEXT GENERATION COMMUNICATION
V.LAXMANA VENKATA KUMAR
FSO may sound new and experimental but in fact it predates optical fiber and has its roots in wartime efforts to develop secure communication systems that did not require cable and could withstand radio jamming. FSO has been around for more than a decade, but it is only recently that interest in this technology has started to grow. Free Space Optics (FSO) communications, also called Free Space Photonics (FSP) or Optical Wireless, refers to the transmission of modulated visible or infrared (IR) beams through the atmosphere to obtain optical communications. Like fiber, Free Space Optics (FSO) uses lasers to transmit data, but instead of enclosing the data stream in a glass fiber, it is transmitted through the air. Free Space Optics (FSO) works on the same basic principle as Infrared television remote controls, wireless keyboards or wireless Palm® devices.
How Free Space Optics (FSO) Works
Free Space Optics (FSO) transmits invisible, eye-safe light beams from one "telescope" to another using low power infrared laser in the terahertz spectrum. The beams of light in Free Space Optics (FSO) systems are transmitted by laser light focused on highly sensitive photon detector receivers. These receivers are telescopic lenses able to collect the photon stream and transmit digital data containing a mix of Internet messages, video images, radio signals or computer files. Commercially available systems offer capacities in the range of 100 Mbps to 2.5 Gbps, and demonstration systems report data rates as high as 160 Gbps.
Free Space Optics (FSO) systems can function over distances of several kilometers. As long as there is a clear line of sight between the source and the destination, and enough transmitter power, Free Space Optics (FSO) communication is possible. [pic]
Free Space optics (fso) technology
Lasers are one of the most significant inventions of the 20th century - they can be found in many modern products, from CD players to fiber-optic networks. A laser generates light, either visible or infrared, through a process known as stimulated emission. To understand stimulated emission, understanding two basic concepts is necessary. The first is absorption which occurs when an atom absorbs energy or photons. The second is emission which occurs when an atom emits photons. Emission occurs when an atom is in an excited or high energy state and returns to a stable or ground state – when this occurs naturally it is called spontaneous emission because no outside trigger is required. Stimulated emission occurs when an already excited atom is bombarded by yet another photon causing it to release that photon along with the photon which previously excited it. Photons are particles, or more properly quanta, of light and a light beam is made up of what can be thought of as a stream of photons. [pic]
A basic laser uses a mirrored chamber or cavity to reflect light waves so they reinforce each other. An excitable substance – gas, liquid, or solid like the original ruby laser – is contained within the cavity and determines the wavelength of the resulting laser beam. Through a process called pumping, energy is introduced to the cavity exciting the atoms within and causing a population inversion. A population inversion is when there are more excited atoms than grounded atoms which then leads to stimulated emission. The released photons oscillate back and forth between the mirrors of the cavity, building energy and causing other atoms to release more photons. One of the mirrors allows some of the released photons to escape the cavity resulting in a laser beam emitting from one end of the cavity.
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