Posted by: dqie | September 17, 2008

Fiber Optic Splicing

What is Fiber Optic Splicing

Fibrlok Mechanical Splicing KitKnowledge of fiber optic splicing methods is vital to any company or fiber optic technician involved in Telecommunications or LAN and networking projects.

Simply put, fiber optic splicing involves joining two fiber optic cables together. The other, more common, method of joining fibers is called termination or connectorization. Fiber splicing typically results in lower light loss and back reflection than termination making it the preferred method when the cable runs are too long for a single length of fiber or when joining two different types of cable together, such as a 48-fiber cable to four 12-fiber cables. Splicing is also used to restore fiber optic cables when a buried cable is accidentally severed.

There are two methods of fiber optic splicing, fusion splicing & mechanical splicing. If you are just beginning to splice fiber, you might want to look at your long-term goals in this field in order to chose which technique best fits your economic and performance objectives.

Mechanical Splicing vs. Fusion Splicing

Fibrlok Mechanical SpliceMechanical Splicing:
Mechanical splices are simply alignment devices, designed to
hold the two fiber ends in a precisely aligned position thus enabling light to pass from one fiber into the other. (Typical loss: 0.3 dB)

Fibrlok Mechanical SpliceFusion Splicing:
In fusion splicing a machine is used to precisely align the two fiber ends then the glass ends are “fused” or “welded” together using some type of heat or electric arc. This produces a continuous connection between the fibers enabling very low loss light transmission. (Typical loss: 0.1 dB)

Which method is better?
The typical reason for choosing one method over the other is economics. Mechanical splicing has a low initial investment ($1,000 – $2,000) but costs more per splice ($12-$40 each). While the cost per splice for fusion splicing is lower ($0.50 – $1.50 each), the initial investment is much higher ($15,000 – $50,000 depending on the accuracy and features of the fusion splicing machine being purchased). The more precise you need the alignment (better alignment results in lower loss) the more you pay for the machine.

As for the performance of each splicing method, the decision is often based on what industry you are working in. Fusion splicing produces lower loss and less back reflection than mechanical splicing because the resulting fusion splice points are almost seamless. Fusion splices are used primarily with single mode fiber where as Mechanical splices work with both single and multi mode fiber.

Many Telecommunications and CATV companies invest in fusion splicing for their long haul singlemode networks, but will still use mechanical splicing for shorter, local cable runs. Since analog video signals require minimal reflection for optimal performance, fusion splicing is preferred for this application as well. The LAN industry has the choice of either method, as signal loss and reflection are minor concerns for most LAN applications.

Fusion Splicing Method
As mentioned previously, fusion splicing is a junction of two or more optical fibers that have been permanently affixed by welding them together by an electronic arc.

Fibrlok Mechanical SpliceFour basic steps to completing a proper fusion splice:

Step 1: Preparing the fiber – Strip the protective coatings, jackets, tubes, strength members, etc. leaving only the bare fiber showing. The main concern here is cleanliness.

Step 2: Cleave the fiber – Using a good fiber cleaver here is essential to a successful fusion splice. The cleaved end must be mirror-smooth and perpendicular to the fiber axis to obtain a proper splice. NOTE: The cleaver does not cut the fiber! It merely nicks the fiber and then pulls or flexes it to cause a clean break. The goal is to produce a cleaved end that is as perfectly perpendicular as possible. That is why a good cleaver for fusion splicing can often cost $1,000 to $3,000. These cleavers can consistently produce a cleave angle of 0.5 degree or less.

Step 3: Fuse the fiber – There are two steps within this step, alignment and heating. Alignment can be manual or automatic depending on what equipment you have. The higher priced equipment you use, the more accurate the alignment becomes. Once properly aligned the fusion splicer unit then uses an electrical arc to melt the fibers, permanently welding the two fiber ends together.

Step 4: Protect the fiber – Protecting the fiber from bending and tensile forces will ensure the splice not break during normal handling. A typical fusion splice has a tensile strength between 0.5 and 1.5 lbs and will not break during normal handling but it still requires protection from excessive bending and pulling forces. Using heat shrink tubing, silicone gel and/or mechanical crimp protectors will keep the splice protected from outside elements and breakage.

Mechanical Splicing Method
Fibrlok Mechanical Splicing KitMechanical splicing is an optical junction where the fibers are precisely aligned and held in place by a self-contained assembly, not a permanent bond. This method aligns the two fiber ends to a common centerline, aligning their cores so the light can pass from one fiber to another.

Four steps to performing a mechanical splice:

Fibrlok Mechanical SpliceStep 1: Preparing the fiber – Strip the protective coatings, jackets, tubes, strength members, etc. leaving only the bare fiber showing. The main concern here is cleanliness.

Step 2: Cleave the fiber – The process is identical to the cleaving for fusion splicing but the cleave precision is not as critical.

Fibrlok Mechanical Splicing KitStep 3: Mechanically join the fibers – There is no heat used in this method. Simply position the fiber ends together inside the mechanical splice unit. The index matching gel inside the mechanical splice apparatus will help couple the light from one fiber end to the other. Older apparatus will have an epoxy rather than the index matching gel holding the cores together.

Step 4: Protect the fiber – the completed mechanical splice provides its own protection for the splice.

Tips for Better Splices:

1. Thoroughly and frequently clean your splicing tools. When working with fiber, keep in mind that particles not visible to the naked eye could cause tremendous problems when working with fiber optics. “Excessive” cleaning of your fiber and tools will save you time and money down the road.

Clauss Fiber Cleaver2. Properly maintain and operate your cleaver. The cleaver is your most valuable tool in fiber splicing. Within mechanical splicing you need the proper angle to insure proper end faces or too much light escaping into the air gaps between the two fibers will occur. The index matching gel will eliminate most of the light escape but cannot overcome a low quality cleave. You should expect to spend around $200 to $1,000 for a good quality cleaver suitable for mechanical splicing.

For Fusion splicing, you need an even more precise cleaver to achieve the exceptional low loss (0.05 dB and less). If you have a poor cleave the fiber ends might not melt together properly causing light loss and high reflection problems. Expect to pay $1,000 to $4,000 for a good cleaver to handle the precision required for fusion splicing. Maintaining your cleaver by following manufacturer instructions for cleaning as well as using the tool properly will provide you with a long lasting piece of equipment and ensuring the job is done right the first time.

3. Fusion parameters must be adjusted minimally and methodically (fusion splicing only). If you start changing the fusion parameters on the splicer as soon as there is a hint of a problem you might lose your desired setting. Dirty equipment should be your first check and them continue with the parameters. Fusion time and fusion current are the two key factors for splicing. Different variables of these two factors can produce the same splice results. High time and low current result in the same outcome as high current and low time. Make sure to change one variable at a time and keep checking until you have found the right fusion parameters for your fiber type.

Fibrlok Mechanical Splicing Kit
Tecra Tools offers a large selection of fiber optic tool kits and fiber optic supplies.
We currently stock Fibrlok Mechanical Splicing Kit from 3M and the Miller Fiber Optic Cleaver.

Click here to see our Fiber Splicing Kit and let us help you find the right tools for all your fiber optic needs.

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Mengenal Komunikasi Serat Optik

Media komunikasi digital pada dasarnya hanya ada tiga, tembaga, udara dan kaca. Tembaga kita kenal sebagai media komunikasi sejak lama, telah berevolusi dari hanya penghantar listrik menjadi penghantar elektromagnetik yang membawa pesan, suara, gambar dan data digital. Berkembangnya teknologi frekuensi radio menambah alternatif lain media komunikasi, kita sebut nirkabel atau wireless, sebuah komunikasi dengan udara sebagai penghantar. Tahun 1980-an kita mulai mengenal media komunikasi yang lain yang sekarang menjadi tulang punggung komunikasi dunia, yaitu serat optik, sebuah media yang memanfaatkan pulsa cahaya dalam sebuah ruang kaca berbentuk kabel, total internal reflection.

Kabel Serat Optik

Sebuah kabel serat optik dibuat sekecil-kecilnya (mikroskopis) agar tak mudah patah/retak, tentunya dengan perlindungan khusus sehingga besaran wujud kabel akhirnya tetap mudah dipasang. Satu kabel serat optik disebut sebagai core. Untuk satu sambungan/link komunikasi serat optik dibutuhkan dua core, satu sebagai transmitter dan satu lagi sebagai receiver. Variasi kabel yang dijual sangat beragam sesuai kebutuhan, ada kabel 4 core, 6 core, 8 core, 12 core, 16 core, 24 core, 36 core hingga 48 core. Satu core serat optik yang terlihat oleh mata kita adalah masih berupa lapisan pelindungnya (coated), sedangkan kacanya sendiri yang menjadi inti transmisi data berukuran mikroskopis, tak terlihat oleh mata.

Detil core kabel serat optik

Bentuk kabel dikenal dua macam, kabel udara (KU) dan kabel tanah (KT). Kabel udara diperkuat oleh kabel baja untuk keperluan penarikan kabel di atas tiang. Baik KU maupun KT pada lapisan intinya paling tengah diperkuat oleh kabel khusus untuk menahan kabel tidak mudah bengkok (biasanya serat plastik yang keras). Di sekeliling inti tersebut dipasang beberapa selubung yang isinya adalah core serat optik, dilapisi gel (katanya berfungsi juga sebagai racun tikus) dan serat nilon, dibungkus lagi dengan bahan metal tipis hingga ke lapisan terluar kabel berupa plastik tebal. Dari berbagai jenis jumlah core, besaran wujud akhir kabel tidaklah terlalu signifikan ukuran diameternya.

Memotong kabel serat optik sangat mudah, cukup menggunakan gergaji kecil. Sering terjadi maling-maling tembaga salah mencuri, niatnya mencuri kabel tembaga yang laku di pasar besi/loak malah menggergaji kabel serat optik. Yang sulit adalah mengupasnya, namun hal ini dipermudah dengan pabrikan kabel menyertakan serat nilon khusus di bawah lapisan terluar yang keras sehingga cukup dikupas sedikit dan nilon tersebut berfungsi membelah lapisan terluar hingga panjang yang diinginkan untuk dikupas.

Untuk apa dikupas? Tentunya untuk keperluan penyambungan atau terminasi. Kita lihat dulu bagaimana pulsa cahaya bekerja di dalam serat kaca yang sangat sempit ini. Kabel serat optik yang paling umum dikenal dua macam, multi-mode dan single-mode. Transmitter cahaya berupa Light Emitting Diode (LED) atau Injection Laser Diode (ILD) menembakkan pulsa cahaya ke dalam kabel serat optik. Dalam kabel multi-mode pulsa cahaya selain lurus searah panjang kabel juga berpantulan ke dinding core hingga sampai ke tujuan, sisi receiver. Pada kabel single-mode pulsa cahaya ditembakkan hanya lurus searah panjang kabel. Kabel single-mode memberi kelebihan kapasitas bandwidth dan jarak yang lebih tinggi, hingga puluhan kilometer dengan skala bandwidth gigabit.

Pulsa cahaya serat optik multi-modePulsa cahaya serat optik single-mode

Inti kaca kabel single-mode umumnya berdiameter 8,3-10 mikron (jauh lebih kecil dari diameter rambut), dan pada multi-mode berukuran 50-100 mikron. Pulsa cahaya yang ditembakkan pada single mode adalah cahaya dengan panjang gelombang 1310-1550nm, sedangkan pada multi-mode adalah 850-1300nm.

OTB wallmount
OTB rackmount

Ujung kabel serat optik berakhir di sebuah terminasi, untuk hal tersebut dibutuhkan penyambungan kabel serat optik dengan pigtail serat optik di Optical Termination Board (OTB), bisa wallmount atau 1U rackmount. Dari OTB kabel serat optik tinggal disambung dengan patchcord serat optik ke perangkat multiplexer, switch atau bridge (converter to ethernet UTP).

Penyambungan kabel serat optik disebut sebagai splicing. Splicing menggunakan alat khusus yang memadukan dua ujung kabel seukuran rambut secara presisi, dibakar pada suhu tertentu sehingga kaca meleleh tersambung tanpa bagian coated-nya ikut meleleh. Setelah tersambung, bagian sambungan ditutup dengan selubung yang dipanaskan. Alat ini mudah dioperasikan, namun sangat mahal harganya. Inilah sebabnya meskipun harga kabel fiber optik sudah jauh lebih murah namun alat dan biaya lainnya masih mahal, terutama pada biaya pemasangan kabel, splicing dan terminasinya.

Berbagai jenis konektor kabel serat optik

Pigtail yang disambungkan ke kabel optik bisa bermacam-macam konektornya, yang paling umum adalah konektor FC. Dari konektor FC di OTB ini kita tinggal menggunakan patchcord yang sesuai untuk disambungkan ke perangkat. Umumnya perangkat optik seperti switch atau bridge menggunakan konektor SC atau LC. Cukup menyulitkan ketika menyebut jenis konektor yang kita kehendaki kepada penjual, FC, SC, ST, atau LC.

Setelah kabel optik terpasang di OTB dilakukan pengujian end-to-end dengan menggunakan Optical Time Domain Reflectometer (OTDR). Dengan OTDR akan didapatkan kualitas kabel, seberapa besar loss cahaya dan berapa panjang kabel totalnya. Harga perangkat OTDR ini sangat mahal, meskipun pengoperasiannya relatif mudah. OTDR ini digunakan pula pada saat terjadi gangguan putusnya kabel laut atau terestrial antar kota, sehingga bisa ditentukan di titik mana kabel harus diperbaiki dan disambung kembali.

Untuk keperluan sederhana misalnya sambungan fiber optik antar gedung pada jarak ratusan meter (hingga 15km) kini teknologi bridge/converter-nya sudah semakin murah dengan kapasitas 100Mbps, sedangkan untuk full gigabit harga switch/module-switch-nya masih mahal. Jadi, meskipun harga kabel serat optik sudah di kisaran Rp10.000/m namun total pemasangannya membengkak karena ada biaya SDM yang menarik dan memasang kabel, biaya splicing setiap core-nya, pemasangan OTB, pengujian OTDR, penyediaan patchcord dan perangkat optiknya sendiri (switch/bridge).

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