Optical Fiber Communication Questions and Answers for Viva

Answer-1: Optical fiber functions as a "light pipe," carrying light generated by lasers and other signal transmission sources to its destination.

Answer-2: Wavelength (?), Core radius (a), Index of Core* (n1),index of Cladding* (n2),Maximum intensity of light (Io),Numerical Aperature (NA),V-Number (V), Mode Type, Number of Modes, Spot size radius (wo), Mode Field Diameter (MFD), Power at MFD.

Answer-3: Numerical Aperature- NA = v (n12-n22)

Answer-4: V-number- V = 2*p*a*NA/??

Answer-5: An optical fiber consists of at least two distinct regions known as the core and cladding.

Answer-6: Methods of Optical Parameter Measurement-the method of comparing signal levels at the OF input and output; the method of controlling the radiation intensity in the far zone ,the pulse location ,the method of measuring the light energy emitted into the surrounding Medium , the bolometric method , the calorimetric method ; the photometric method ,the backscattering method , The method of comparing signal levels at the Optical fiber.

Answer-7: n1 must be slightly larger than n2 to guide light.

Answer-8: NA= .121

Answer-9: Single-mode fibers have a small core size (< 10 ?m) which permits only one mode or ray of light to be transmitted. Single-mode fibers have low attenuation and zero dispersion at 1310 nm. This fiber is a general-purpose fiber for systems of moderate distance, transmission rates and channel count.

Answer-10: Multimode fibers have larger cores that guide many modes or rays simultaneously. When one pulse of a signal is generated into a multimode fiber, the multiple modes enter the fiber core from different angles and each mode propagates at a different speed. This causes pulse broadening (modal dispersion), limiting the speed at which subsequent pulses may be generated without overlapping. Multimode fibers are generally used for short distance applications, such as within buildings.

Answer-11: Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber.

Answer-12: The digital bit stream enters the light source. If a one bit is present, the light source pulses light in that time slot, but if there is a zero bit, there is no light pulse (or vice versa, depending on how it is set up). The absence or presence of light therefore represents the discrete ones and zeros. Light energy, like other forms of energy, attenuates as it moves over a distance, so it has to run though amplification or repeating process.

Answer-13: Give example.Transmission medium (plural transmission media) is a material substance (solid, liquid, gas, or plasma) which can propagate energy waves. For example, the transmission medium for sound received by the ears is usually air, but solids and liquids may also act as transmission media for sound.

Answer-14: Time-division multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel.

Answer-15: A codec is a device or computer program capable of encoding and/or decoding a digital data stream or signal. The word codec is a portmanteau of 'compressor-decompressor' or, more commonly, 'coder-decoder'.

Answer-16: A digital video (using a DV codec) of a sports event needs to encode motion well but not necessarily exact colors, while a video of an art exhibit needs to perform well encoding color and surface texture.

Answer-17: A transmission medium can be classified as a:1. Linear medium, if different waves at any particular point in the medium can be superposed; 2.Bounded medium, if it is finite in extent, otherwise unbounded medium; 3.Uniform medium or homogeneous medium, if its physical properties are unchanged at different points; 4.Isotropic medium, if its physical properties are the same in different directions.

Answer-18: Transmission media are classified as one of the following:1.Guided (or bounded) - Waves are guided along a solid medium such as a transmission line.2.Wireless (or unguided) - Transmission and reception are achieved by means of an antenna.

Answer-19: An optical medium is material through which electromagnetic waves propagate. It is a form of transmission medium. The permittivity and permeability of the medium define how electromagnetic waves propagate in it.

Answer-20: An excitable medium is a nonlinear dynamical system which has the capacity to propagate a wave of some description, and which cannot support the passing of another wave until a certain amount of time has passed.

Answer-21: In telecommunication, Manchester code (also known as Phase Encoding, or PE) is a line code in which the encoding of each data bit has at least one transition and occupies the same time.

Answer-22: Reflection losses, Fiber separation, Lateral misalignment. Angular misalignment, Core and cladding diameter mismatch, Numerical aperture (NA) mismatch, Refractive index profile difference, Poor fiber end preparation.

Answer-23: Fiber-to-fiber connection loss is increased by Intrinsic coupling losses and Extrinsic coupling losses.

Answer-24: Propagation losses in an optical fiber (or other waveguide) caused by bending.

Answer-25: The power outputs of a transmitter or the input to receiver are "absolute" optical power measurements, that is, we measure the actual value of the power.

Answer-26: Loss is a "relative" power measurement, the difference between the power coupled into a component like a cable or a connector and the power that is transmitted through it. This difference is what we call optical loss and defines the performance of a cable, connector, splice, etc.

Answer-27: There are two methods that are used to measure loss, which we call "single-ended loss" and "double-ended loss".

Answer-28: The propagation of light through the core of an optical fiber is based on total internal reflection of the light wave. Rough and irregular surfaces, even at the molecular level, can cause light rays to be reflected in random directions. This is called diffuse reflection or scattering, and it is typically characterized by wide variety of reflection angles.

Answer-29: Attenuation results from the incoherent scattering of light at internal surfaces and interfaces.

Answer-30: Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses as well as crystalline materials like sapphire, are used for longer-wavelength infrared or other specialized applications. Silica and fluoride glasses usually have refractive indices of about 1.5, but some materials such as the chalcogenides can have indices as high as 3. Typically the index difference between core and cladding is less than one percent.

Answer-31: The cladding is coated by a "buffer" that protects it from moisture and physical damage.