Transcript Advantages of Optical Fiber Communication

叠加,重叠
复杂的,高级的,现代化的
同轴的
恶化,降级
失真,畸变
衰减
停止
拖运的距离
明白的,易懂的
雪崩
光敏电阻
[1] 虽然具有光纤系统的模拟调制易于实现,但其效率较低,
且要求在接收端有比数字调制高得多的信噪比.
linearity:线性度
[2]:前置放大器与均衡器或滤波器跟在雪崩二极管检测器的后面
以获得增益、线性信号处理及噪声带宽的抑制。
Passage B
Advantages of Optical Fiber Communication
Communication using an optical carrier wave guided along a glass
fiber has a number of extremely attractive features, several of which
were apparent when the technique was originally conceived.
Furthermore,the advance in the technology to date have surpassed
even the most optimistic predictions,creating additional advantages.
Hence it is useful to consider the merits and special features offered
by optical fiber communications over more conventional electrical
communications. In this context we commence with the originally
foreseen advantages and then consider additional features which
have become apparent as the technology has been developed.
巨大的潜在带宽
金属的
[1]目前,传输100km的几GHz的调制信号和传输300km的几百MHz
的调制信号都是可能的,因此,光纤系统的可用带宽并没有得到充
分利用.
参数,参量
[2]应用波分复用(技术),尤其是密集波分复用(或者说,实质上的精
细频分复用),使光纤的信息载容量能超过电缆或宽带无线系统好
多个数量级.
小尺寸和轻重量
缓解
电绝缘 通道
充满,拥挤,阻塞
危险的
电弧
磨损
抗干扰和无串话
系统可靠和维护方便
潜在低成本
购买
提高
起源于
稀有的
可拆卸的
招致
handling
视线
天线
合理
全长
Many advantages are therefore provided by the use of a lightwave carrier within a transmission medium consisting of an
optical fiber. The fundamental principles giving rise to these
enhanced performance characteristics, together with their practical
realization, are described in the following chapter. However, a
general understanding of the basic nature and properties of light is
assumed.
Passage C
Fiber-optics Communication
Even though optical fibers are much smaller than wire pairs, and
silica (the most widely used material in fibers) is vastly more
abundant than copper, the cost of preparing the rods(棒) from
which optical fibers are drawn is several times greater than the
cost of producing wires. Moreover, studies suggest that this may
be the case for some time.
However, fiber system is so many telephone conversations at the
same time than wire pairs, and can carry them so much farther
without amplification or regeneration(更新), that when there are
many telephone calls to be carried between points such as
switching(交换) offices, fiber systems are economically attractive.
Thus the interoffice trunk(干线) network will be the first to benefit
from this new technology.
Competition is more difficult, though, with existing high-capacity
systems that use coaxial transmission lines, wave-guide, microwave
radio and satellites. Larger fiber bandwidth,lower loss,and more
reliable optical sources would make optical fiber more competitive
in this sector.
The heart of an optical communication system is something
which transmits electrical signals: a telephone, computer or cable
TV. A light emitting diode or laser converts those signals into
light pulse, which travel along a glass fiber. At the receiving end,
a photo detector converts them back to electrical signals.
The system provides significant advantages over conventional ones
which rely heavily on electrical signals and copper wire, including
the handling of large amounts of information; a high-performance
laser can produce up to a half-billion(十亿) light pulses a second.
As a result, it is possible to transmit the entire 30-volume
Encyclopedia(百科全书) Britannica in a tenth of a second. Since
optical communications are free from electromagnetic interference
which can cause noise in copper cable, they produce clear signals,
despite nearly power lines or electric motors.
Copper wires, although they are insulted(攻击), can leak electrical
signals and cause cross-talk in nearby wires. Not so with optical
communication equipment. A glass fiber cable, moreover, weights
only about 1% as much as the copper cable carrying the same
number of signals. Indeed, one a half-inch thick can carry as many
signals as a copper-cable as big as a man’s arm. Then, too, since
glass fibers carry light rather than electricity, there’s no danger of
sparks in dangerous environments like chemical plants or nuclear
reactors.