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Cutoff Wavelength In Fibre Optics

presenting cutoff wavelength of optical fibres its principal measurements and specifications

Gorakh
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Cutoff Wavelength In Fibre Optics

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  1. CUTOFF WAVELENGTH I n F I b r e o p t I c s JUNE 21 2021 Mon CREATED BY GORAKH VANJARE

  2. TABLE OF CONTENTS • INTRODUCTION • DEFINATION • REFRACTIVE INDEX • TOTAL INTERNAL REFLECTION • MEASURMENTS SPECIFICATIONS • MEASURMENTS PROCEDURE • REFERENCES ©GV4779

  3. INTRODUCTION IzaaA n optical fibre is a flexible transparent fibre made by drawing glass silica, Optical fibres are used to transmit light between the two ends of the fibre and wide uses in fibre optic communications. Where they permit transmission over longer distances at higher bandwidth [data transfer rates] than electrical cables. Optical fiber goes under various measurements parameter in which cut-off wavelength is one of important parameter of them, cut-off wavelength is important for single mode fibres as it is the characteristic unique to single mode fibres. INTRODUCTION

  4. DEFINATION C ut-off wavelength is the wavelength above which an optical fibre will allow single mode transmission. In other words the wavelength below which multimode transmission starts. Single mode fibre design to have one mode for propagation typically SMF used in telecommunication cables having core diameter 8㎛ and MFD 9㎛. For multimode fibres cutoff wavelength is not important why? The answer is simple as the defination of cutoff wavelength itself is the wavelength below which multimode transmission starts hence cutoff is a single mode fibre characteristic. »»

  5. 10m To understand cut off it is better to think about the analogy of a road having a width of 10 meters. Theoretically, if the car width is 5 meters, then two cars can travel in that road. If the car width is 5.1, only one car can travel in that road at a time. Then, 5.1 is the cut-off for this road. Cut-off wavelength is important for single mode optical fibers as it is the characteristic unique to single mode optical fibers. Cut-off wavelength is the minimum wavelength below which a single mode fiber will act as multimode fibers, meaning it will allow propagation of more than one mode at a time. Thus it is clear that cut-off wavelength determines the fate of single mode transmission. ITU-T recommendation for single mode fibers ITU-T G.652 specify a cut-off wavelength of less than or equal to 1260nm. This means the wavelength below 1260nm is acceptable for a single mode.

  6. REFRACTIVE INDEX T he cutoff wavelength is determined by fibres refractive index profile the length and bend of the fibre Refractive index is measure of bending of a ray of light when passing one medium into another. Optical fibers typically include a core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by the phenomenon of total internal reflection. which causes the fiber to act as a waveguide. Optical fibre rely on total internal reflection for their operation Refractive Index Optical fibres work even when the fibre is bent

  7. Ttotal internal reflection • When light is incident upon a medium of lesser index of refraction, the ray is bent away from the normal, so the exit angle is greater than the incident angle. Such reflection is commonly called “internal reflection". The exit angle will then approach 90° for some critical incident angle θc, and for incident angles greater than the critical angle there will be total internal reflection. Fig: Total internal reflection Example of Total Internal Reflection MIRAGE : It is an optical illusion that is responsible for the appearance of the water layer at short distances in a desert or on the road. Mirage is an example of total internal reflection which occurs due to atmospheric refraction. •There appear to be water on the road though there is not.

  8. MEASUREMENT SPECIFICATIONS SCOPE → This part of IEC 60793 establishes uniform requirements for measuring the cut-off wavelength of single-mode optical fibre, thereby assisting in the inspection of fibres and cables for commercial purposes. METHOD USED →IEC 60793 Optical Fibres-Part 1-44: [INTERNATIONAL TELECOMMUNICATION UNION]ITU-T G650 1 TIA/EIA FOTP 80… INSTRUMENT → PK2200

  9. Measurment instrument specification The cutoff wavelength of single mode fibers depends on the fiber length and bend conditions.

  10. E1 E2 Cutoff Specifications for itu-t g.657a1,g.657A2 NEW • CABLE CUTOFF ONLY CONSIDER WHEN CUTOFF WAVELENGTH VALUE EXCEEDS ABOVE 1320nm

  11. Cable cutoff specifications for DOF ITU-T G655E.G656, G.655.c TYPE A TYPE Q

  12. MEASUREMENT PROCEDURES Determining the cutoff wavelength of a single mode fiber involves finding the wavelength above which the power transmitted through the fiber decreased abruptly. This power decrease occurs when the second-order mode propagating in the fiber is cut off. The cutoff wavelength of single mode fibers depends on the fiber length and bend conditions. The effects of length and bending are different on different fibers Cutoff wavelength may be measured on uncabled or cabled single mode fibers. A slightly different procedure is used in each case, but the basic measurment process is the same. The test method for uncabled single mode fiber cutoff wavelength is EIA/TIA-455-80. The test method for cabled single mode fiber cutoff wavelength is EIA/TIA-455-170. EIA/TIA-455-80 →September 1, 1998. FOTP-80 Measurement of Cut-Off Wavelength of Single-Mode Fiber by Transmitted Power. This method is intended to measure the cut-off wavelength of single-mode fiber by determining the wavelength at which the fiber transmission abruptly changes.

  13. Each test method describes the test equipment (input optics, mode filters, and cladding-mode strippers) necessary for the test. BEND REFERENCE TECHNIQUE (FIBRE CUTOFF) : the cutoff wavelength was measured using bend reference technique described by fiber optic test procedure (FOTP)-80, on a 2 meter single mode fabricated silica fiber using the experimental setup viz; Photon Kinetics Model 2200.

  14. E1 E3 E2 G 657 A2 G 657 A1 Fibre cutoff measurment for ITU-t • Scan the fibre ID • Enter operator ID • Enter length as 2mtr • Take 2mtr length fibre • Cleave it • Select the menu for measuring cutoff wavelength • Lay the fibre on flat surface instrument table give 28㎝ loop • Allign the input and output ends of the fibre specimens to the detection optics • Press F1 to measure fibre cutoff wavelength then give 6㎝ guide loop press F1 after measurment the value as well as the graph will display.

  15. Cable cutoff wavelength (multimode reference) E2 E1 PROCEDURE FOR CABLE CUTOFF FOR ITU-T G 697 A1,A2 • When fibre cutoff greater than 1320㎚ from top end it goes for cable cutoff The test sample shall be 22 m of uncabled fiber coiled into a loop with a minimum 280㎜ to conservatively simulate cabling effects. To simulate the effects of a splice organizer, apply two loop of 80㎜ diameter near one end, as shown in Figure TYPE Q TYPE A FOR ITU-T G655E.656(DOF), G.655.C,D(DOF) SMF IN THIS TYPE OF FIBRE CUTOFF DOES NOT MEASURE AT 1310㎚ AS ITS CUTOFF ALREADY HIGH SO IT CAN BE MEASURE AT 1550㎚ IN CABLE CUTOFF. ◇◆◇◆◇◆◇◆◇◆◇◆

  16. REFERENCES • https://www.researchgate.net/publication/37464067_Cut-off_wavelength_measurement • https://standards.globalspec.com • https://www.stl.tech/optical-interconnect-products/optical-fibre-cable/ • Optiwave • https://fibercore.humaneticsgroup.com/services-support/fiberpaedia/c/cut-wavelength

  17. END OF PRESENTATION END OF PRESENTATION

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