Fiber optic communication, satellite communication, and radio communication are the three pillars of modern communication networks, with fiber optic
communication being the mainstay due to its many significant advantages
The History of Fiber Optic Communication
Using light for communication is not a completely new concept. Ancient my country's use of beacon towers for alarms is a prime example of visual optical communication, and Europeans' use of flag signals to transmit information can be seen as primitive forms of optical communication.
The form of modern optical communication can be traced back to the optical telephone invented by Alexander Graham Bell in 1880. He used sunlight as a light source, focusing the beam onto a vibrating mirror in front of the transmitter, causing the light intensity to change with the voice, thus modulating the light intensity. At the receiving end, a parabolic mirror reflected the light beam from the atmosphere onto a battery, and a selenium crystal acted as the optical receiver, converting the light signal into an electric current, thus successfully transmitting voice signals through the atmosphere. Due to the lack of an ideal light source and transmission medium at the time, this optical telephone had a very short transmission distance and no practical application, thus its development was slow. However, the optical telephone was still a great invention, proving the feasibility of using light waves as carrier waves to transmit information. Therefore, it can be said that the Bell optical telephone was the prototype of modern optical communication.
The invention of the lamp made it possible to construct simple optical communication systems and use them as light sources, such as communication between ships and between ships and land, car turn signals, and traffic lights. In fact, any type of indicator light is a basic optical communication system. In many cases, broadband fluorescent light-emitting diodes (LEDs) can be used as light sources.In 1960, American Robert Maiman invented the first ruby laser, which, in a sense, solved the problem of light sources and brought new hope to optical communication. Compared with ordinary light, lasers have narrow spectral width, excellent directionality, extremely high brightness, and good characteristics of relatively consistent frequency and phase. Lasers are highly coherent light, and their characteristics are similar to radio waves, making them an ideal optical carrier. Following the ruby laser, nitrogen-hydrogen (He-Ne) lasers and carbon dioxide (CO2) lasers appeared and were put into practical application. The invention and application of lasers ushered in a new era for optical communication, which had been dormant for 80 years.
Since Kao Kuen proposed the concept of optical fiber as a transmission medium in 1966, optical fiber communication has developed rapidly from research to application, with continuous technological upgrades, constantly improving communication capabilities (transmission rate and relay distance), and expanding application scope.
The five stages of fiber optic communication
The first stage was the development period from basic research to commercial application. Starting in 1976, following the pace of research and development, and after many field tests, the first-generation optical wave system operating at a wavelength of 0.8μm was officially put into commercial application in 1978.
The second stage was the practical application period, with the research goal of improving transmission rate and increasing transmission distance, and vigorously promoting its application.
The third stage focused on ultra-high capacity and ultra-long distance, with comprehensive and in-depth research into new technologies. During this period, 1.55μm dispersion-shifted single-mode optical fiber communication was achieved. This optical fiber communication system uses external modulation technology, achieving transmission rates of 2.5–10 Gbit/s and repeaterless transmission distances of 100–150 km. Even higher levels could be achieved in the laboratory.
The fourth stage of fiber optic communication systems is characterized by using optical amplifiers to increase repeater distances and employing wavelength division multiplexing (WDM) technology to increase bit rate and repeater distances. Because these systems sometimes use null-difference or heterodyne schemes, they are also called coherent optical communication systems.
The fifth stage of fiber optic communication systems is based on nonlinear compression to cancel fiber dispersion broadening, achieving conformal transmission of optical pulse signals, also known as optical soliton communication. This stage has spanned over 20 years and has achieved groundbreaking progress.
Applications of modern fiber optic communication
Optical fiber can transmit both digital and analog signals. Currently, 90% of global communication services rely on optical fiber transmission. With the development of optical fiber communication technology, many countries worldwide have incorporated optical fiber communication systems into their public telecommunications networks, relay networks, and access networks.
Optical fiber broadband backbone transmission networks and access networks are developing rapidly and are currently the main focus of research, development, and application.The various applications of optical fiber communication can be summarized as follows:
(1) Communication Networks:Fiber optic communication is widely used in communication networks and has become the mainstream method of modern communication.
(2) Computer local area networks (LANs) and wide area networks (WANs) constitute the Internet.
(3) Trunk and distribution networks of cable television networks, satellite earth stations of industrial television systems, microwave lines, antenna receivers, etc.
(4) Fiber optic access networks for integrated services.
(5) Fiber optic sensors. Strictly speaking, fiber optic sensors do not belong to the field of communication. However, fiber optic sensors are an extremely important application area of fiber optics.
