افت اضافی ناشی از جوش دادن تارهای چندمدی ۵۰ و ۵ ̸ ۶۲ میکرونی به یکدیگر

Excess Loss for splicing MM 62.5 to MM 50 micron fibers

Technicians who are designing or installing an Optical Network should avoid using of different fibers in a link which having different MFD or Core Diameter .

We have to keep it in our mind that any deviation in MFD of single mode fibers or Core Diameter of MM fibers will result to an excess loss in the network .

In this article , we are trying to show how much extra loss will be added to the network by splicing two different multimode fibers to each other , say MM 62.5 to MM 50 micron .

When an Optical Fiber Network consists of two section one with MM62.5 and the other with MM 50 , regardless of the length of each section , a part of signal will be lost if MM62.5 be at the transmitter side and the MM50 at the receiver side .

We may compare it by dropping the water from the bulk to the hose . Pictures below will give a better idea about such problem :

Though by changing the location of transmitter and the receiver , such unpleasant case will not be happened but as the network will be mostly designed that both sending and receiving signals transmitted via the same fiber , so in any case excess loss will exist in the network .

The following table getting from FOA reports showing the approximate range of excess loss in dB for splicing two different type of MM fibers .

Dimension  Of Core/Clad Transmission Side
۶۲٫۵/۱۲۵ ۸۵/۱۲۵ ۱۰۰/۱۴۰
Receiver Side ۵۰/۱۲۵ ۰٫۹-۱٫۶ dB ۳٫۰-۴٫۶ dB ۴٫۷-۹٫۰ dB
۶۲٫۵/۱۲۵ ۰٫۹ dB ۲٫۱-۴٫۱ dB
۸۵/۱۲۵ ۰٫۹-۱٫۴ dB

By injection of optical signal to a Multimode fibers , different modes of propagation will be produced in them due their special construction as well as launching condition of the light source . MPD as an abbreviation to the Modal Power Distribution will determine that how many modes will be supported by the fiber . therefore the existing formula which calculating the excess loss in splicing dissimilar commercial SM fibers and the other special type of SM like DS or NZDS fibers will not be practically applicable for MM fibers .We are in the idea that values of excess loss due to mismatching of two MM fibers are more higher than what stated in FOA table . In order to be more closer to the real figures , one should study about modal distribution of optical signal in the fiber core as excess loss will entirely depending on such distribution profile . We did more investigated in the other documents and found out that Corning and Fluke data for excess loss in splicing MM62.5 to MM50 are between 3 to 5 dB which such values are more close to the reality figures .

Conclusion :

With respect to the above reason , it is not recommended to splice MM 62.5 micron fibers to MM 50 , even technicians should be careful to use of the same dimension of MM fiber pigtail and patchcord as end termination to avoid unexpected excess loss .

If by any reason splicing of two dissimilar MM fibers is unavoidable , the highest amount of excess loss to be taken into consideration for loss budgeting of the network . Furthermore , effect of this high excess loss on the quality of transmission to be also measured and observed .

Afshan Cable Co.

Tehran – Iran

آیا رطوبت به فیبرنوری آسیب می رساند؟

Does water damage fibers ?

Though silica is not a hygroscopic material and doesn’t absorb water but moisture and water will cause optical fibers to be deteriorated in long term .

Technicians who are currently installing, maintaining or working continuously with fibers , should have special concern about micro crack or stress corrosion in them .

If optical fibers specially on their splice points be under pressure , effect of moisture in long term will cause flaw or crack grow up gradually till breaking the fiber .

This extreme condition in the fibers will happen in case that all three following ingredients be present :  Flaw , Tension and Moisture

People usually have less knowledge about existence of flaw and tension in fibers which are under service . therefore they should always be careful that Closures are sealed enough to protect fibers against penetration of water and moisture .

For a better monitoring the network , water or aqua-sensor to detect the presence of water inside the closure should also be installed in the closures .

These sensors will immediately act to the presence of water inside the closures so prior facing with any deterioration , will send an alarm signal to the monitoring station for immediate network repairing .

Afshan Cable Co.

Tehran – Iran

کاربرد فیبرنوری در نظارت بر تاسیسات زیربنایی


ساختار تارهای نوری ، عکس العمل آنها در قبال انتشار امواج الکترو مغناطیسی و ایجاد پدیده های مختلف در آنها ، وضعیت خاصی را به وجود آورده که علاوه بر خاصیت موجبری به عنوان حسگر های دقیق حرارتی ، لرزشی ، شتاب ، ولتاژ، فرکانس ، فشار ، تنش و کرنش نیز می توانند مورد استفاده قرار گیرند. از خاصیت حسگر بودن فیبرنوری برای حفاظت و نظارت بر سلامت تاسیسات مهم نفت ، گاز و سایر زیرساخت های ارتباطی و صنعتی درمقابل آسیب های فیزیکی  ، حفاری های غیر مجاز و … استفاده می شود.

نظارت از راه دور

امروزه اطلاعات زیاد و متنوعی بر روی شبکه های فیبرنوری منتقل می شود و هرروز بر حجم و اهمیت این اطلاعات و همچنین ضرورت نظارت بر سلامت عملکرد شبکه انتقال افزوده می شود . از طرف دیگر کاربران از شرکت های ارائه کننده خدمات ،  تقاضای تضمین کیفیت و ارائه مستنداتی دال بر قابلیت اطمینان و دردسترس بودن شبکه را دارند .
این مسئله باعث می شود تا شرکت ها و ارائه دهندگان خدمات ، اقدام به اجرای سیستم هایی برای نظارت و کنترل دائمی سلامت شبکه های خود نمایند .
راه های مختلفی برای رسیدن به این هدف وجود دارد . برخی از سیستم های ارائه شده با این فرض که هر اتفاق مهمی که برای یکی از تارهای داخل کابل بیافتد سایر تارها را نیز تحت تاثیر قرار می دهد ، راهکار نظارت و مانیتورینگ یک یا چند تار بلا استفاده ( Dark Fiber ) را  پیشنهاد می کنند .
در مقابل روش دیگری نیز ارائه شده است که  بر تارهای زیر بار (Active)  نظارت می کند . در این روش از قابلیت تسهیم طول موج استفاده می شود ، به این ترتیب که اگر شبکه در طول موج ۱۵۵۰ کار می کند عمل نظارت در طول موج دیگری  برروی همان تار صورت می گیرد.
البته طراحان شبکه می توانند ترکیبی از این روش ها را نیز بکارگیرند .

برخی از عواملی که در این سیستم ها تحت نظارت و مانیتورینگ قرار می گیرند به شرح زیر است :

  • ایجاد خرابی و قطع شدن کابل
  • ایجاد خمش غیر مجاز در کابل
  • ورود آب به اتصالات موجود در شبکه
  • ایجاد خرابی در اتصالات موجود در شبکه
  • افت کیفیت شبکه به مرور زمان

تاریخچه تکامل فیبرنوری

Fiber Optic Historical Development

Since ancient times , it was necessary that man communicate with each other . For such need they actually starting investigation to find a media for exchanging information  . Light in a form of smoke, signal fires or even sunlight have been used for this purpose . As a legend , in 1185 BC , Qeen Clytemnestra got informed through  a series of 9 signal fires that Troy had fallen and her husband King Agamemnon was passing a distance of 800 Km back to the palace in Argos . By development of Civilization , other shape of light signal or media were used for quick and easy communication which most of them are still found today . Light House for navigation , traffic signal and torches on the top of high mountains are few examples and reminders of this type of communication .

In 1793 , Claude Chappe as a French Doctor and inventor , introduced Optical Telegraph and built a link of 230 Km with 15 stations between Paris and Lille . Though this system rapidly developed in Europe during the first half of nineteenth century but by the invention of Electric Morse Telegraph in 1850 it gradually put out of the service and the modern world of telecommunication began . In 1860 , James Clark Maxwell a Scottish mathematician , physicist and professor of Cambridge University succeeded to present the theory of Electromagnetic Wave Propagation in Waveguides which is now the basic calculation and formula for Optical fibers .

In 1870 , Tyndall an English inventor , succeeded to make a path of light through a bend water jet . This invention opened a new era to the transmission of Optical waves into the light conductors . In 1960 Professor Ali Javan an Iranian scientist succeeded to produce the first Gas Laser .

In 1962 , the first type of Semiconductor Laser introduced and the inventor got the Nobel Prize for that in 1964 . In 1966 , three scientists Charles H. Kao , George A. Hockham and Alain Werts found that Silica Waveguides having total reflection are the best media for the transmission of Optical waves and made the first optical fiber with the loss of 1000 dB/Km . Dr. Kao who got his Nobel Prize for this invention in 2009 , about 43 years later , was in the idea that high loss is due to impurities of glass while others thought that it is the effect of high dispersion of the fiber . As time goes , by development of fiber technology , it proved that the idea of Kao was correct and by removing the impurities from fibers during production the loss will be highly reduced .

In 1970 , Corning glass of United States made the first step Index fiber with the loss of 17 dB/Km at wavelength of 633 nm . Today the commercially made fibers having a loss less than 0.2 dB/Km at wavelength of 1550 nm which is almost close to the theoretical value .

By the application of WDM ( Wavelength Division Multiplexing ) technology having EDFA for Amplification of Optical signals and G.655 NZDS fiber as media , the transmission speed of 45 Mb/s in 1978 exceed 40 Gb/s in these days .

Afshan Cable Co.

Tehran – Iran