Since the commercialization of optical fibers, with the continuous advancement of technology, the types of optical fibers have gone through several important developmental stages.
Today, let's take a brief look back at this journey:
#### Stage One: Multimode Fiber (First Window)
In July 1966, the Chinese-American scientist Charles Kao published a historically significant paper on the prospects of optical fiber transmission. The paper analyzed the main causes of optical fiber transmission loss and theoretically demonstrated the possibility of reducing the loss to 20 dB/km. It also proposed that such fibers could be used for communication.
In 2009, Kao was awarded the Nobel Prize in Physics for his outstanding contributions to the fiber optic industry.
Guided by this theory, four years later, in 1970, Corning Inc. in the United States successfully drew an optical fiber with a loss of 20 dB/km, proving the feasibility of using optical fibers as a communication medium.
At the same time, Bell Labs in the United States invented the semiconductor laser using gallium arsenide (GaAs) as the material. Thanks to its small size, it was widely used in fiber optic communication systems.
In 1972, the transmission loss of optical fibers was reduced to 4 dB/km.
From this point on, the era of fiber optic communication officially began.
From 1972 to 1981, it was the research and application period for multimode fibers.
The first wavelength used in fiber optic communication was 850 nm, known as the first window.
The early multimode fibers developed were step-index multimode fibers. Subsequently, graded-index multimode fibers of the A1a category (50/125) were developed. These fibers had an attenuation of 3.0-3.5 dB/km, a bandwidth of 200-800 MHz·km, and a numerical aperture of 0.20±0.02 or 0.23±0.02.
Later on, graded-index multimode fibers of the A1b category (62.5/125) were developed and used. These fibers had an attenuation of 3.0-3.5 dB/km, a bandwidth of 100-800 MHz·km, and a numerical aperture of 0.275±0.015.
These two types of fibers, combined with light-emitting diodes (LEDs) operating near the 850 nm wavelength, formed the early optical communication systems.
At that time, the spectral width of the LED was 40 nm, the injected optical power was 5 or 20 μW, and the maximum data rate was 5 or 60 Mb/s.
#### Stage Two: Multimode Fiber (Second Window)
At the end of the 1970s and the beginning of the 1980s, fiber manufacturers developed the second window (1300 nm).
The A1a category fibers had an attenuation of 0.8-1.5 dB/km and a bandwidth of 200-1200 MHz·km. The A1b category fibers had an attenuation of 0.8-1.5 dB/km and a bandwidth of 200-1000 MHz·km.
These fibers were used in conjunction with high-radiation LEDs, which had a spectral width of 120 nm, an injected optical power of 20 μW, and a maximum data rate of 100 Mb/s.
#### Stage Three: G.652, G.653, and G.654 Single-Mode Fibers (Second and Third Windows)
From 1982 to 1992, it was the large-scale application period for G.652, G.653, and G.654 single-mode fibers, which opened the second window (1310 nm) and the third window (1550 nm) for optical fibers.
Between 1973 and 1977, major fiber manufacturers worldwide developed various advanced preform manufacturing processes. Corning developed the OVD (Outside Vapor Deposition) technology; NTT, Sumitomo, Furukawa, and Fujikura in Japan jointly developed the VAD (Vapor Axial Deposition) technology; Lucent improved the MCVD (Modified Chemical Vapor Deposition) technology; and Philips in the Netherlands developed the PCVD (Plasma Chemical Vapor Deposition) technology.
In 1982, starting with the United States, followed by Japan and Germany, the global construction of long-haul projects using G.652 single-mode fibers began. The large market demand for single-mode fibers stimulated mass production.
At this time, Corning's OVD further increased the deposition rate, and VAD, MCVD, and PCVD all added outer jackets to increase the size of the preforms.
Subsequently, all manufacturers followed the two-step hybrid process to enlarge the preforms.
In the 1990s, Alcatel in France developed the APVD (Atmospheric Pressure VAD) technology (MCVD + plasma spraying process).
Significant advancements in manufacturing technology by major fiber manufacturers created better conditions for the widespread application of conventional single-mode fibers.
In 1984, the third window (1550 nm) was put into use.
In the same year, the CCITT (International Telegraph and Telephone Consultative Committee) issued the G.651 and G.652 standards.
By 1985, the attenuation of G.652 fibers had reached 0.35 dB/km at 1310 nm and 0.21 dB/km at 1550 nm.
In 1985, the dispersion-shifted fiber (G.653) developed by Japan and the United States was commercialized. Its characteristic was to shift the zero-dispersion point from the second window to the third window. At the 1550 nm wavelength, not only was the loss the lowest, but the dispersion was also the smallest.
In 1988, the CCITT issued the G.653 standard. This fiber was widely used in Japan's communication trunk lines.
In the early 1990s, the erbium-doped fiber amplifier (EDFA) began to be commercialized, prompting the consideration of dense wavelength division multiplexing (DWDM).
However, the zero dispersion at the 1550 nm wavelength of G.653 fibers caused severe nonlinear interference between channels in DWDM systems, so it was not widely promoted worldwide.
In 1995, China constructed the Beijing-Kowloon optical cable project, using six G.653 fibers out of 24 cores, which were never activated. Since then, China has not used G.653 fibers.
During this period, a cut-off wavelength shifted fiber was also developed. It not only had low loss at 1550 nm but also low microbend loss, making it suitable for long-haul systems using optical amplifiers and submarine cable systems.
In 1988, the CCITT issued the G.654 standard.
#### Stage Four: Full Opening of Fiber Windows and Comprehensive Development of Characteristics
From 1993 to 2006, the fiber communication windows expanded to the fourth and fifth windows and the S band, with the full opening of fiber communication windows. Four new types of fibers were developed, and the characteristics of fibers became more comprehensive.
(1) Non-Zero Dispersion Shifted Single-Mode Fiber G.655 (Third and Fourth Windows)
To suppress four-wave mixing (FWM) and cross-phase modulation (XPM) in dense wavelength division multiplexing (DWDM) systems and reduce nonlinear interference between optical channels, non-zero dispersion shifted fiber (NZDSF) was introduced in 1993.
First, Lucent launched the TrueWave fiber, followed by Corning's introduction of the large effective area LEAF fiber.
These fibers initially operated in the third window, i.e., the C band (1530-1565 nm). After 1995, they were extended to the fourth window, i.e., the L band (1565-1625 nm).
In 1996, the ITU-T established the G.655 standard. After 1998, it was widely used worldwide.
(2) Low-Water-Peak Single-Mode Fiber G.652C (Fifth Window)
In 1998, Lucent introduced the TrueWave fiber (i.e., low-water-peak fiber), which almost eliminated the water peak at 1383 nm (attenuation < 0.31 dB/km), opening the fifth window of optical fibers, i.e., the E band (1360-1460 nm).
In 1999, China began to use all-wave fibers for cables in Jiujiang Telecommunications.
In 2000, the ITU-T established the G.652C standard.
In 2001, Corning produced low-water-peak fibers.
In 2002, G.652C fiber was promoted worldwide.
Since then, single-mode fibers have exhibited excellent attenuation performance across the wavelength range from 1260 nm to 1625 nm.
In May 2002, the ITU-T divided the optical wavelength bands for single-mode fiber communication systems into O, E, S, C, L, and U.
The 850 nm wavelength for multimode fibers is referred to as the first window. For single-mode fibers, the O band is the second window, the C band is the third window, the L band is the fourth window, and the E band is the fifth window.
