What is the effect of temperature on semiconductors ?

When a semiconductor is heated, the conductance increases and the resistance decreases.  Semiconductors, thus, have a negative temperature coefficient of resistance.
When heat is applied to a semiconductor material, the outermost electrons in the atom gain energy.  These electrons are able to overcome the attraction of the nucleus and leave the atom.  Thus they become free electrons which can conduct. 
The number of electrons increase exponentially and this results in a large drop in the resistance. 
Electronic devices will behave erratically above a certain temperatures.  Hence, all electronic devices such as laptops will have a safe temperature beyond which they cannot function. 
The effect of vibration of the atomic lattice on the mobility of the electrons is offset by the large numbers of electrons which enter the conduction band. 

Joints in Optical Cables

In many instances, optical cables are needed to be jointed with one another.  Jointing in optical cables is different from jointing in electrical wires and cables.  The connection should be made such that there is minimum loss of the light energy. 
There are different methods of jointing optical cables
Fusion Jointing
In the method, the surface of the two optical fibres to be connected are heated and fused together.  This ensures that the light is conveyed from one fibre to another efficiently
Mechanical jointing
In this method, the surfaces of the ends are held firmly to make proper contact.  An gel or epoxy is used to match the different reflective indices of the materials.  The fibres are held together by mechanical splices. 

Optical Fibre Cleaver

A cleaver is a tool used to cleave optical fibres prior to splicing.  Optical fibres should have a plain and clear surface when they are cut.  The cut should be perpendicular to the longitudinal axis of the fibre.  This is essential to avoid loss of light or distortion.    The cleaving tool is used to cleave the fibre. 
Cleaving Tools generally use diamond tips and blades to cleave the fibres.
Certain mechanical cleaving tools use a diamond blade to make a wedge in the fibre and the twist the fibre to produce a clean break.  The cleave angle should be perfectly 90 degrees. 
The blade in the cleaver may have to be replaced after a certain number of splices.  Most manufacturers provide replacement blades. 
The cleave made is examined by the splicing machine prior to fusion

Optical Fusion Splicers-An Overview

Optical fusion Splicers are used to join two optical fibres using fusion.  The splicing is done by first heating the ends to be joined.

The fibres after being cleaved are fed into the splicer.  The two fibres to be joined are held against each other and the alignment is checked after which the fusion is done.  The heating is done by means of an electric arc or a laser.  The heating is done in about 15 seconds and the fusion is then carried out.  The device is battery operated. 

Splicers can be programmed for different types of fibre optic cables.  Most Splicers are portable and have a rugged construction.  The life of the heating electrodes is specified after which the electrode may have to be replaced. 

What is an Optical Time Domain Reflectometer ?

An optical time domain reflectometer is a device which is used to check the integrity of an optical fibre system detect and locate faults in optical cables. 

The optical time domain reflector sends out a series of optical pulses from one end of the cable.  The light which is reflected is analyzed.  This gives information about the state of the optical cable and its terminations.  If there is a drop in the quality of the light of if the distorted, it can indicate a problem such as a cut or an improper splice joint. 

The optical time domain reflectometer can also measure the attenuation of signals through the optical fibre.

What is the Q factor of an inductor ?

The Q factor of an inductor is a very important parameter.  The Q factor tell us how close the inductor to an ideal inductor. 

An ideal inductor is an inductor which has no losses.  That is, its series resistance is zero.  It is not possible to construct an ideal inductor as all inductors are made of wires which have resistances. 

Q factor is the ratio of the inductive reactance to the series resistance of the inductor  at a given frequency.

Q= X_L/ R

The Q factor is an crucial parameter when designing resonant circuits as it will affect the damping.  Higher the Q factor, higher is the efficiency of the inductor. 

Molded Chokes-An Overview

Moulded chokes are chokes which are moulded in a polymer or synthetic material.  These chokes are used in applications such as Led lighting, automotive electronic components, mobile  phones etc. 
Moulded chokes are small in size and highly compact. 
These chokes have very small inductance values from 10 microhenries to 1000 micro henries.