White Paper: Elimination Of Moisture For Low-Water Peak Fiber
•White Paper: Elimination of Moisture for Low-Water Peak Fiber
The production of "low-water peak" optical fiber (LWPF) is achieved by processes that remove water and/or prevent it from diffusing into the silica matrix. As demand for LWPF increases, fiber makers have resorted to new materials and manufacturing steps to reach more difficult attenuation specifications for this fiber type.
The appearance of the "water peak" in conventional optical fibers has historically eliminated wavelengths between 1360 and 1460 nm, about 30% of the available channels, due to high light attenuation. Many fiber manufacturers are focused on making LWPF as a means to provide the most light-carrying capacity for their products. Production volumes of LWPF are expected to show a compound annual growth rate of greater than 20% from 2003-2007.
Process improvements that allow the manufacture of low-water peak fiber require water levels in the glass to be reduced from 10 ppb to less than 1 ppb.
The advent of wave-division multiplexing (WDM) has led to development of optical fibers with reduced attenuation, nonlinearities and inter-channel mixing across the spectrum from 1260 nm to 1625 nm (1, 2). The ITU-T specification 652.C and the related 652.D codify the properties of fibers that can be used in these systems, which are referred to generically as "low water peak fiber" (LWPF).
Central to these specifications is the requirement that at the water-peak wavelength (1383 nm) the "attenuation average at this wavelength shall be less than or equal to the value specified at 1310 nm after hydrogen ageing". Thus, the manufacture of LWPF requires enough moisture control in the fabrication and post treatment of the fiber that the water peak attenuation is < 0.4 dB/km. A survey of LWPF available on the market shows that the typical measured water peak attenuation is between 0.31 and 0.35 dB/km.
A concentration of several parts per billion (ppb) of hydroxyl groups in a conventional single mode fiber core causes the attenuation for wavelengths around the water peak to be several times higher than that at lower or higher wavelengths. Process improvements that allow the manufacture of low-water peak fiber require water levels in the glass to be reduced from 10 ppb to less than 1 ppb.
Downloads:
•White Paper: Elimination of Moisture for Low-Water Peak Fiber