Light wave at higher frequency range of electromagnetic spectrum (3 × 1011–3 × 1016 Hz) is used for transmission of information through fibers as transmitting medium in optical fiber communications. It can offer a large bandwidth (more than 50 THz) for data transmission. The emergence of fiber optics as a dominant technology for long-distance broadband services is discussed in this chapter. The basic configuration of optical fiber communication system comprises of an information source, a voltage-to-current converter, an optical source, a channel coupler, an optical fiber channel, an optical repeater, an optoelectronic detector, an electronic receiver, and the output device. The need, advantages, disadvantages, and wide range of applications of optical fiber communication are covered so as to generate interest to know more about the subject in subsequent chapters.
Optical fiber communication has been developed over the last two centuries. The first optical communication system, known as the ‘optical telegraph’, was invented in the 1790s by French engineer Claude Chappe. In 1880, Alexander Graham Bell patented the photophone—an optical telephone device for transmission of speech using a beam of light. During the 1920s, an experiment was conducted by J. L. Baird of England and C. W. Hansell of the USA, for transmission of images for TV/Facsimile systems using arrays of uncoated fiber cables. In the 1950s, A. V. Heel and H. Hopkins protected a bare glass fiber by covering it with a transparent cladding having lower index of refraction. As a result, crosstalk between fibers was greatly reduced in addition to providing protection from contamination. This led to the development of the flexible fiberscope, which is widely used in the medical field.
Note: In 1956, N. S. Kapany of England coined the term ‘fiber optics’. The initial applications of optical fiber were not in communications at all, because the early fibers were too lossy. Bundles of fibers were used for medical imaging to view inaccessible parts of the human body.
By 1960, attenuation of the order of 1 dB/m was achieved with glass-clad fibers. This was acceptable for medical imaging applications but not for voice/data transmissions. The invention of the lasers in the 1960s marked the beginning of a new era in modern optics, called Photonics.