Part A | Chapter 2 |Fiber Fabrication:Outside V-P oxidation vapour phase axial deposition, Modified CVD , Plasma activated CVD, Double – crucible method, Mechanical properties of fibers, Fiber optical cables, Fiber splicing, Optical connectors.

1) Discuss the mechanical properties of fiber?

2) Distinguish connectors from splices and discuss different types of splices and connectors?

3) Explain the ‘Plasma activated chemical vapour deposition’ process used for the optical fiber communication?

4) With the help of a neat diagram explain double – crucible method used for drawing optical fibers ?

5) Explain the structure of a typical six fiber optical cable used for optical communication?

6) What is a fiber splice? Explain two splicing techniques?

7) Derive the expression for the maximum optical power coupled in to a fiber ? 3rd question

8) Explain the optical power output V/S laser drive current characteristics?3rd question

9) With a neat diagram explain the modified CVD method of manufacture of optical fibers?

10) What are the different types of optical splices available in the industries? Briefly explain any two of them?

11) With help of cross sectional view explain the structure of a single core optical fiber ?

12) Explain Outside vapour phase oxidation ?

1) Discuss the mechanical properties of fiber?

Solution :

1. The fiber cable must able to withstand the stress and strain that generally occur during the cabling process.

2. The basic characteristics of fiber are strength and static fatigue. 3. The Main difference between metal and glass is that when stress is

applied to glass it extends elastically up to its breaking strength whereas the metal will be stretched plastically well beyond their true elastic range.

4. The Physical flaw model is show in the figure

5. The Elliptically shaped crack is generally referred as Griffith micro crack of width W and depth x and radius Row . the strength of crack for silica fiber is given by the relation k= YX1/2

2) & 7) Distinguish connectors from splices and discuss different types of splices and connectors? Or

10) What are the different types of optical splices available in the industries? Briefly explain any two of them?

Solution :

Splices Connector splicing is the act of joining two optical fibers end-to-end.

An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing.

Splices is a permanent or semi permanent joint between two fibers

Connector is a demountable joint between two fibers

These are typically used create long optical links

These are used for range from simple single channel fiber to multichannel fiber connectors.

Different types of Splices are:1.Fusion Splicing2.Mechanical Splicing3.Elastic tube splicing4.V – Groove optical fiber splicing

Different types of connectors are:1.Screw on2.twist on or snap on connectors

Different types of Splices are:

1.Fusion Splicing

2.Mechanical Splicing

2.1.Elastic tube splicing

2.2.V – Groove optical fiber splicing

1.Fusion Splicing :

Fusion splicing is the process of fusing or welding two fibers together usually by an electric arc. Fusion splicing is the most widely used method of splicing as it provides for the lowest loss and least reflectance, as well as providing the strongest and most reliable joint between two fibers.

Before optical fibers can be successfully fusion-spliced, they need to be carefully stripped of their outer jackets and polymer coating, thoroughly cleaned, and then precisely cleaved to form smooth, perpendicular end faces. Once all of this has been completed, each fiber is placed into a holder in the splicer’s enclosure. From this point on, the fiber optic fusion splicer takes over the rest of the process, which involves 3 steps:

Alignment: Using small, precise motors, the fusion splicer makes minute adjustments to the fibers’ positions until they’re properly aligned, so the finished splice will be as seamless and attenuation-free as possible. During the alignment process, the fiber optic technician is able to view the fiber alignment, thanks to magnification by optical power meter, video camera, or viewing scope.

 

Impurity Burn-Off: Since the slightest trace of dust or other impurities can wreak havoc on a splice’s ability to transmit optical signals, you can never be too clean when it comes to fusion splicing. Even though fibers are hand-cleaned before being inserted into the splicing device, many fusion splicers incorporate an extra precautionary cleaning step into the process: prior to fusing, they generate a small spark between the fiber ends to burn off any remaining dust or moisture.

 

Fusion: After fibers have been properly positioned and any remaining moisture and dust have been burned off, it’s time to fuse the fibers ends together to form a permanent splice. The splicer emits a second, larger spark that melts the optical fiber end faces without causing the fibers’ cladding and molten glass core to run together (keeping the cladding and core separate is vital for a good splice – it minimizes optical loss). The melted fiber tips are then joined together, forming the final fusion splice. Estimated splice-loss tests are then performed, with most fiber fusion splices showing a typical optical loss of 0.1 dB or less

2.Mechanical Splicing :

Mechanical splices are used to create permanent joints between two fibers by holding the fibers in an alignment fixture and reducing loss and reflectance with a transparent gel or optical adhesive between the fibers that matches the optical properties of the glass. Mechanical splices generally have higher loss and greater reflectance than fusion splices, and because the fibers are crimped to hold them in place, do not have as good fiber retention or pull-out strength. The splice component itself, which includes a precision alignment mechanism, is more expensive than the simple protection sleeve needed by a fusion splice. Mechanical splices are most popular for fast, temporary restoration or for splicing multimode fibers in a premises installation. They are also used - without crimping the fibers - as temporary splices for testing bare fibers with OTDRs or OLTSs. Of course most prepolished splice connectors use an internal mechanical splice (several actually have fusion splices) so the mechanisms and techniques described here apply to those also.The advantage of mechanical splices is they do not need an expensive machine to make the splices. A relatively simple cleaver and some cable preparation tools are all that's needed, although a visual fault locator (VFL) is useful to optimize some types of splices.

Alignment MechanismsThe biggest difference between mechanical splices is the way the fibers are aligned. Here are some typical methods.

Capillary Tube

The simplest method of making a mechanical splice is to align two fibers in a small glass tube with a hole just slightly larger than the outside diameter of the fibers. This type of splice works well with UV-cured adhesive as well as index-matching gel between the fibers. The Ultrasplice is a capillary splice.

V-Groove

V-groove splices are quite simple and work well. They work for single fibers or even for fiber ribbons as shown here. The Grooved alignment plates can be made of many types of materials and are quite inexpensive.

The 3M Fiberlok is a version of a V-groove splice that uses a metal stamping inside a plastic case to both align fibers and crimp them. It's elegant design and good performance has made it one of the most popular mechanical splices.

This method has a more complex alignment mechanism, made from four small glass rods fused together with a bend in the middle. The fibers follow the grooves made by the joint of two rods. The complexity and expense of this, especially compared to a simple V-groove, limited its use.

Elastomeric

The GTE Elastomeric splice (still available from Corning) uses soft elastomers to hold the fibers in position. It's similar to a v-groove, but the grooves are soft so they accomodate

slight variations in fiber diameter easily.

Rotary Splice

The AT&T Rotary splice was more like a connector. The fibers were glued into glass ferrules and polished. They were then inserted into an alignment sleeve and rotated until the lowest loss was obtained. Again, complexity and cost, plus labor required, limited their popularity.

3) Explain the ‘Plasma activated chemical vapour deposition’ process used for the optical fiber communication?

Solution :

4) With the help of a neat diagram explain double – crucible method used for drawing optical fibers ?

Solution :

6)Explain the structure of a typical six fiber optical cable used for optical communication?

Solution :

7) ) Derive the expression for the maximum optical power coupled in to a fiber ?

Solution: 3rd chapter question

8) Explain the optical power output V/S laser drive current characteristics?

Solution : 3rd chapter question

9) With a neat diagram explain the modified CVD method of manufacture of optical fibers?

Solution :

12) Explain Outside vapour phase oxidation ?

Solution :

11) With help of cross sectional view explain the structure of a single core optical fiber ?

Solution :

In fiber-optic communication, a single-mode optical fiber (SMF) is an optical fiber designed to carry light only directly down the fibre - the transverse mode. Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining Maxwell's equations and the boundary conditions. These modes define the way the wave travels through space, i.e. how the wave is distributed in space. Waves can have the same mode but have different frequencies. This is the case in single-mode fibers, where we can have waves with different frequencies, but of the same mode, which means that they are distributed in space in the same way, and that gives us a single ray of light. Although the ray travels parallel to the length of the fiber, it is often called transverse mode since its electromagneticvibrations occur perpendicular (transverse) to the length of the fiber. The 2009 Nobel Prize in Physics was awarded to Charles K. Kao for his theoretical work on the single-mode optical fiber

A typical single mode optical fiber has a core diameter between 8 and 10.5 µm [5]  and a cladding diameter of 125 µm. There are a number of special types of single-mode optical fiber which have been chemically or

physically altered to give special properties, such as dispersion-shifted fiber and nonzero dispersion-shifted fiber. Data rates are limited bypolarization mode dispersion and chromatic dispersion. As of 2005, data rates of up to 10 gigabits per second were possible at distances of over 80 km (50 mi) with commercially available transceivers (Xenpak). By using optical amplifiers and dispersion-compensating devices, state-of-the-art DWDM optical systems can span thousands of kilometers at 10 Gbit/s, and several hundred kilometers at 40 Gbit/s.