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光纤的工作原理

How Does LIGHT Carry Data?

If you’ve ever built a tree fort
如果你曾建造过树堡
You’ve probably also tried to send a secret message to your friend
你可能也尝试过用摩斯密码和手电筒
using Morse code and a flashlight.
给朋友发送秘密信息
And fundamentally, fiber optic networking works in the same way:
本质上讲 光纤网络也以相同的方式工作
Encoding data, impulses of light that travel around the world,
编码数据 以及遍布全世界的光脉冲
carrying our phone calls, business conference,
传输着我们的电话 商务会议
and important internet data.
和重要的互联网数据
But, now hold on a second.
但是 等一下
How exactly do you send light
你究竟是如何把光
over great distances
传送到很远的地方
and still manage to extract information from it?
并且依然可以从中获取信息?
I mean, fiber optic cables have to carry light,
我的意思是 实际上光纤要携带着光
for literally, thousands of miles, like across oceans.
跨越几千里 例如跨越海洋
Yet, if you’ve ever shined a flashlight down a long hallway,
然而 如果你曾经用手电筒照过长长的走廊
you’ll know that over any more than a short distance,
你就会知道光穿过一小段距离
the light scatters,
就发生散射
and eventually becomes too dim to make out.
最终会变得太暗 从而无法看清
Well, that is where optical fibers come in.
而这就使光纤有了用武之地
Those really skinny tubes that make your Christmas tree look nice
这些纤细的管子能把圣诞树打扮得漂亮
without having to string up any messy lights,
而不必挂乱糟糟的灯
have some special characteristics that allow them to work over incredible distances.
它们具有的一些特性使之能超远距离传输光线
The main way that fiber optics behave differently than your flashlight
光纤和手电筒主要的不同点在于
is that they take advantages of a physical phenomenon,
光纤利用了一种
called Total Internal Reflection.
叫做“全反射”的物理现象
You see, a fiber optic system
如你所见 光纤系统
doesn’t just shine light down any random hollow tube.
不是单单让光通过任意的中空管
Instead, optical cables are made up of the core of glass or plastic,
与此相反 光缆由一根玻璃或塑料“纤芯”
surrounded by an outer layer called Cladding.
和包裹于外侧的“包层”组成
Both the glass and the cladding have an inherent property,
玻璃纤芯和包层都有一个固有特性
called a refractive index,
叫做“折射率”
which is basically a measure of how fast light can travel through something.
这是一个度量光在物体中传播速度的基本参数
For the system to work properly,
为了使系统正常运作
the cladding needs to have a slightly lower index of refraction than the core.
包层要比纤芯的折射率略小一些
Now sometimes this is achieved by using
有时候纤芯采用的是
pure glass that is silicon dioxide for the core,
二氧化硅这种纯玻璃
and then doping the cladding with chemicals to lower its refractive index
然后在包层中掺杂化学物质以降低折射率
while other times,
而其他时候
the core itself can be doped to raise the same value.
可以掺杂纤芯来提高折射率
Either way, this difference means
总之 这个折射率差异意味着
that if light hits the cladding at a shallow enough angle,
如果光线以一个足够小的角度射向包层
it would be completely reflected at the same angle
它会按照相同的角度完全反射
instead of passing through the cladding.
而不是穿过包层
That means that it can continue on down the fiber
这就意味着光线可以沿光纤
in a zigzag pattern indefinitely.
按锯齿形路径一直传播
Well, not quite.
当然 也不完全是这样
Although in theory, the optical signal should
尽管从理论上讲 光信号应该
just keep going all the way until it reaches the other end of the fiber.
一直传递 直到另一端为止
The pesky real world
但这个讨厌的现实世界
always has a way of throwing a wrench in the pudding.
总有办法搞破坏
No matter how high-end and pure an optical cable is,
无论一根光缆多高端 多纯净
there will always be some imperfections,
总会有一些瑕疵
even if they are so small
即便它们非常微小
that you could only see them at the molecular level.
以至于只能在分子水平上才可以观察到
And these will cause some of that light to scatter,
而这些瑕疵会导致一些光线散射
weakening the signal over distance until eventually
使信号随着距离增加而不断减弱
it can’t be understood by the equipment at the other end.
直到它最终无法被另一端设备识别
So, to combat this,
因此 为了防止这一点
long distance fiber runs are assisted by Repeaters or Amplifiers.
远距离光纤传输需要中继器和放大器辅助
A repeater gets placed at a point down the fiber
中继器被安装在沿着光纤
where the signal will have weakened significantly,
某个信号强度明显减弱的位置
but it’s still strong enough to be read.
但至少要强到可以被读取
Once the light hits the repeater,
一旦光线传到中继器
it’s turned into the corresponding electronic signal,
就会被转为对应的电信号
which is then turned back into light
然后电信号再转成光
much as it was at the origination point
和它最初发射出来时一样
and then sent along on its merry way.
然后一路顺利地传送下去
Repeaters come with a latency
但是 中继器会以延迟
and a complexity cost though.
和复杂化作为代价
So many modern long-distance systems now use amplifiers instead.
因此现在许多现代远程光纤系统改用放大器
These gadgets have optical fibers which are doped with chemicals
这些小设备拥有掺杂化学物质的光纤
that directly amplify light when the weakened signal hits them.
当衰减的信号传入时 能直接增强光线
So the ions in the fibers themselves
即光纤内的离子
will re-emit the same signal,
会再次发射相同的信号
but much more strongly than what came in,
但要比进入时的光线强得多
and it continues down the cable.
然后 光会沿光缆继续传播
In this way, optical fibers runs can be designed to be really long,
通过这种方式 光纤可以被设计得很长
making them a more viable choice for long distance communication than copper.
这使得它们比铜线更适合远程通信
Optical fibers are not only more cost effective than copper wiring,
光纤不仅比铜线更省钱
it’s more power efficient,
而且也更节能
and it even goes farther without requiring a boost.
甚至无需增压就能传播更远
Also, because it’s thinner,
另外 因为光纤更细
and doesn’t cause electromagnetic interference to the cables around it.
而且不会对周围的电缆造成电磁干扰
It’s common to bundle a bunch of optical fibers,
把很多光纤塞进一根大光缆
each of which can carry multiple wavelength of light,
是很常见的
into one large cable,
每根光纤能传输携带多种波长
making it possible to transmit enormous amounts of data
从而使传送海量数据
without taking up too much space.
而不占据太多空间成为可能
This versatility means that fiber optics have found uses outside of just communication,
这种通用性意味着光纤有通信之外的用处
such as an endoscopy,
例如内窥镜检查
where the flexibility allows a user to light up,
它的柔韧性允许使用者照亮
and view inside very hard-to-reach spaces.
并观察身体内部难以触及的地方
This is useful in fields like engineering, plumbing, and even medicine.
这在工程 管道甚至医学等领域都很有用
Speaking of which,
说到这里
I got to run and get to a doctor’s appointment,
我得赶紧去看医生了
and hopefully doesn’t involve sticking a fiber optic scope up somewhere embarrassing.
希望不要把内窥镜插入什么尴尬的地方
Oh, I know what the doctor ordered.
噢 我知道医生怎么吩咐的了
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So thanks for watching, guys.
感谢大家的收看
Like, dislike, leave a comment.
无论是否喜欢 敬请评论
If you have a suggestion for a future, fast as possible.
如果你对今后的节目有什么建议 请尽快评论
And I’ll see you next time.
下次见

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视频概述

光纤的原理是什么?光线又如何在光纤中持续传播,跨越数千公里的距离?它通过什么办法保证了信息的准确性?它有哪些有优点?有那些方面的应用?

听录译者

Raven

翻译译者

F̶a̶n̶t̶丶̶子̶夜̶

审核员

审核员SR

视频来源

https://www.youtube.com/watch?v=G1Ke-H8I1uk

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