随着传输速度 企业光纤网络的传输速率提高到每秒10千兆(Gb/s)以上, 一个相对较新的术语——”laser-optimized纤维” – has crept into the industry’s vocabulary. What is laser-optimized纤维? What do you need to know about it? And what exactly does the term “laser- optimized” mean? 了解这些问题的答案将帮助您为企业网络光通信的最新浪潮做好准备.
Why have 光纤s been “optimized” for use with lasers?
Older “legacy” 光纤 systems (令牌环, 以太网, FDDI, ATM)用于以相对较慢的速度运行的室内应用程序，速度范围为每秒4至155兆比特(Mb/s). These systems utilized inexpensive light sources called Light Emitting Diodes (LEDs), which were perfectly adequate for these slower speeds. 多模光纤 used in these systems were rated to certain minimum b和widths, typically:
- 160兆赫/公里超过62.850 nm处5/125 μm光纤
- 500 MHz/km over 50/125 μm fiber at 850 nm
- 500 MHz/km over both products at 1300 nm
These fibers were tested for b和width using an Overfilled Launch (OFL) test method, which accurately replicated real-life performance with an LED.
随着对带宽和更高吞吐量需求的增加，特别是在建筑和 校园骨干在美国，led无法跟上步伐. With a maximum modulation rate of 622 Mb/s, LEDs would not support the 1 Gb/s 和 greater transmission rates required. One could make use of traditional lasers (Fabry-Perot, Distributed Feedback) typically used over single-mode fiber. 然而，由于在单模光纤上长距离传输需要更高的性能特征，这些都相当昂贵.
在回应, 业界开发了一种新的高速激光光源，称为垂直腔面发射激光器(VCSEL)。. 这些vcsel价格低廉，非常适合低成本的850纳米多模传输系统, allowing for data rates of 1 Gb/s 和 10 Gb/s in the enterprise. 随着这些vcsel的出现，多模光纤必须经过“优化”才能与激光器一起工作.
>> 现在下载我们的指南
What’s the Difference Between a VCSEL 和 an LED?
VCSELs提供 更高的功率，更窄的光谱宽度，更小的光斑尺寸和更快的数据速率比led. All of these advantages add up to a significant performance boost. This assumes, of course, the fiber itself does not hinder performance. To underst和 why this could occur, 我们需要认识到vcsel和led之间的区别，以及它们如何沿着多模光纤传输信号.
所有led产生 一个平滑的, 均匀输出，始终充满整个光纤芯，并激发光纤中的数百种模式. 光纤的带宽是由光纤中所有模式的综合性能决定的. If a few modes lag behind or get ahead due to modal dispersion, 它们对带宽的影响很小，因为许多其他模式承载了大部分信号.
The energy output of a VCSEL is smaller 和 more concentrated than that of an LED. 结果是, VCSELs do not excite all the modes in a multimode fiber, but rather only a restricted set of modes. The b和width of the fiber is dictated by this restricted set of modes, 和 any modes that lag or get ahead have a much greater influence on b和width.
通常，VCSEL的功率 would be concentrated in the center of the fiber, 旧的光纤容易出现折射率分布(光纤核心的关键光导特性)的缺陷或变化。, resulting in poor transmission of the signal. That is why some fibers may actually perform poorly with a VCSEL compared to an LED.
使事情复杂化, the power profile of a VCSEL is nonuniform 和 fluctuates constantly. It changes sharply across its face, varies from VCSEL to VCSEL 和 changes with temperature 和 vibrational fluctuations. 因此，在任何给定时间，单个vcsel将在特定光纤中激发不同的模式. And because different modes carry varying amounts of power, the fiber’s b和width can vary in an unpredictable manner.
Why are laser-optimized纤维s the best choice for use with VCSELs?
随着vcsel的出现, 很明显，用于LED系统的传统多模光纤并没有充分利用vcsel的性能优势.
为了充分利用VCSELs提供的优势，光纤制造商开发了 laser-optimized multimode fiber (LOMMF). LOMMF经过专门设计、制造和测试，可与vcsel一起高效、可靠地使用.
LOMMFs应该有一个精心设计和精心控制的折射率剖面，以确保最佳的光传输与VCSEL. Precise control of the refractive index profile minimizes modal dispersion, also known as Differential Mode Delay (DMD). 这确保了所有模式, 或者光路, in the fiber arrive at the receiver at about the same time, minimizing pulse spreading 和, 因此, 最大化的带宽. A good refractive index profile is best achieved through DMD testing.
vcsel和LOMMF提供了巨大的灵活性和成本效率，可以“释放”企业当前和未来的带宽瓶颈. LOMMF与led和其他光纤应用完全兼容(不需要特殊的连接器或终端，对衰减没有影响). 现在可以安装LOMMF并以较慢的数据速率使用，直到需要将网络速度提高到1 Gb/s甚至10 Gb/s. 此时，您只需要将光学模块升级到基于vcsel的收发器. There is no need to pull new cable.
>> 现在下载我们的指南
Can you use any laser-optimized纤维 for 10 Gb/s?
No — it is important to note that not all laser-optimized纤维 is 10 Gb/s capable. If 10 Gb/s capacity is in your future, 您必须确保现在安装的LOMMF能够处理10 Gb/s的速度. The first laser-optimized纤维s, introduced to the market in the mid-1990s, were designed for 1 Gb/s applications. 两种都有.5/125 µm 和 50/125 µm designs, 这些光纤扩展了1gb /s系统的覆盖能力，超出了行业标准的规定. 例如，OFS为1gb /s 激光优化62.5纤维 can go 300 meters in cost-effective, 1 Gb/s 850 nm (1000BASE-SX) systems. 50/125 µm fibers offer even greater performance, with a reach of 600 meters or more. 这些1gb /s的LOMMFs, 加上850纳米vcsel, 考虑到建设主干网和中短校园主干网的最低系统成本
How do you measure b和width for laser-optimized纤维?
由于led具有均匀一致的功率分布，可以激发多模光纤中的所有模式, 传统的OFL带宽测量方法可以准确地预测LED应用中光纤的带宽. But because VCSELs only excite some of the modes in a fiber, 以不同的方式, 如果光纤要用于VCSEL应用程序，OFL带宽测量不能预测光纤的带宽.
It should become clear now why fiber manufacturers developed laser-optimized纤维, 和 why DMD testing is so important. 折射率必须经过良好的设计和控制，以确保所有模式显示最小的DMD，并同时到达光纤的另一端. No matter which modes in the fiber are actually guiding the light, those modes will have minimal DMD 和 provide high b和width.
What should you look for in DMD testing?
DMD测试提供了一幅清晰的图像，显示各个模组如何在光纤中传输光, 和 which mode groups are causing DMD. 事实上, 这种情况是如此清楚，以至于标准要求光纤进行dmd测试，以确保有足够的带宽满足10gb /s应用程序的额定距离.
>> 现在下载我们的指南
托尼Irujo 是OFS的光纤销售工程师，OFS是世界领先的光纤设计、制造和供应商 光纤, 光缆, connectivity, fiber-to-the-subscriber (以前)和 specialty photonics products. Tony为多模和单模光纤提供技术销售和市场支持.
Tony在光纤制造，测试和应用方面拥有25年的经验. 1993年，他开始在SpecTran担任质量和工艺工程师，后来在朗讯和OFS担任更以客户为中心的职位. He represents OFS in the Fiber Optic LAN Section (FOLS) of the TIA, 撰写了几篇beat365登录光纤技术和应用的论文，并经常在行业活动中发表演讲. 托尼拥有斯普林菲尔德西部新英格兰学院机械工程学士学位, MA.