or permanent con- nection of two fibers. Semipermanent splices are made with the aid of a mechanical device holding the fiber ends together. Mechanical splices can be reentered, if necessary, without breaking or cutting the fiber. These splices can also be made without the use of expensive splicing tools. The fibers are simply held together with a connector that aligns them. The alignment is usually accomplished by adjusting the outer surface of the fiber. Mechanical splices are normally used to reduce splicing times. They involve some risk of temperature-induced misalignments that introduce Optics Primer variations in loss. Connector losses for a 12-fiber array splice have a loss of about 0.4 dB. Permanent splices are made either by electric-arc fusion or by chemical bonding. Electric-arc fusion splicing is the most widely used splicing method. The idea behind this method is to heat the fibers and fuse them together. Chemically bonding fibers together is the procedure of gluing two fiber ends together chemically. The adhesive material is typically a syn- thetic polyester. Because the fiber-end faces do not come in direct contact in this case, the adhesive must serve as an index-matching material to provide a consistent refractive index at the joint. Fusion or bonding undertaken under controlled conditions produces low-loss splices. Losses of 0.05 dB can be achieved with these methods. 2.3 Additional Details on Limitations of Fiber Links Fiber-optic transmission systems contain fundamental limitations on both the distance and the bit rate at which information can be transmitted. As discussed in the previous section, these limitations are determined by the attenuation of the signal and by the spreading of the digital pulses caused by modal and chromatic dispersion within the fiber media. For single-mode systems running up to 0.5 Gbps, link length before regeneration is limited by loss rather than by dispersion. At higher bit rates, however, the length is limited by dispersion. Length issues are generally more of a