PREDICTION METHODS OF RAYLEIGH

SCATTERING LOSSESPREPARED BY

DARSHAN BHATT(150320705001)

INTRODUCTION■ Scattering losses in glass arise from microscopic variation in material

density, from structural decomposition and structural inhomogeinity.

SCATTERING LOSSES

Stimulated Brillouin

Scattering(SBS)

Stimulated Raman

Scattering(SRS)

Non-Linear Scattering Losses

RayleighScattering

Linear Scattering Losses

Mie Scattering

RAYLEIGH SCATTERING IN OPTICAL FIBER

• Rayleigh scattering named after the British physicist Lord Rayleigh.

• Also known as elastic scattering.

• It is a linear type of scattering mechanism.

• It is a parametric process.

• It is the reason for blue color of sky. Figure 1 : Lord Rayleigh [1]

Why the sky is blue..................?

FIGURE 2 – RAY LEIGH SCATTERING PHENOMENA

Expression for Rayleigh Scattering Coefficient

■ Rayleigh scattering is an important component of the scattering of optical

signals in optical fibers.

■ Microscopic variations of density and refractive index: These give rise

to energy losses due to the scattered light, with the following coefficient -

Prediction Methods for Rayleigh Scattering Losses■ To reduce the attenuation losses due to Rayleigh scattering in optical

fibers –

1. Improved Fabrication Processes

2. Thermal Treatment of glass fibers■ Fabrication processes – OVPO, MCVD, VAD■ Better Fabrication process – Vapor-Phase Axial Deposition (VAD)■ The Rayleigh scattering coefficient is strictly dependent on fictive

temperature (TF) and it is inversely proportional to the 4th power of the wavelength.

■ If fictive temperature (TF) ↓ γR↓

Rayleigh Scattering Reduction Method using VAD Technique

■ Effect of temperature on Rayleigh Scattering : γR ↑ (5 to 10%) at 1800 deg. C

■ To reduce γR drawing the fiber at low temperature.

Consideration:

■ GeO2 doped Silica core SMF with minimum loss 0.16 dB/km at 1.55 μm.

Reduction Method :

Vapor Phase Axial Deposition (VAD) which is developed by Izawa.

Sub Processes in VADFour processes in VAD technique :

1. Consolidation - Process of uniting or unification of two or more components

2. Annealing – Heating than cooling

3. Air cooling

4. Re-heating

To reduce scattering losses – ■ Consolidation – At 1400 deg. C■ Annealing – At 1250 to 1400 deg C■ Cooling Rate – 5 deg C / min■ Air cooling – At room temp.

Thermal Treatment Diagram

Expression for R.S.C for GeO2 and F doped fiber

■Rayleigh scattering coefficient of GeO2 and F doped Silica fiber is

given by –

■Here, [GeO2] and [F] are the refractive index differences, AGeO2-F and

ASiO2 are Rayleigh scattering co-efficients for GeO2 & F doped Silica

fiber and SiO2 doped glass fiber.

Overall Spectral Loss

■ By analysis of loss components in fiber the total spectral loss is expressed by α of an optical fiber is expanded as –

■ Here A = Rayleigh scattering coefficient, αIM = Imperfection loss

αIR = Infrared Absorption loss,

αOH = OH Absorption loss

Generalized form of R.S.C

■ In general the Rayleigh scattering coefficient ‘A’ is expressed by the equation –

■ Here Ad = density fluctuations and Ac = Concentration fluctuations

where Ad is defined by -

Relation between Rayleigh scattering

coefficient and drawing

temperature

Conclusion■The Rayleigh scattering coefficients of the glasses increased 5–

10% by heating them to 1800 C.

■A method for reducing the Rayleigh scattering of silica-based optical fibers by drawing them slowly at low temperatures.

■This is because the fictive temperature of the fiber decreased as the drawing temperature decreased.

References[1]. https://en.wikipedia.org/wiki/John_William_Strutt,_3rd_Baron_Rayleigh

[2]. www.slideshare.net

[3]. K.T.Katsuske, Member IEEE, K Shiraki, I Sankawa, “Method for predicting Rayleigh scattering loss of silica based optical fiber”, vol. 25, no.8, Aug 2007.

[4]. K Tsujikawa, K Tajima, M. Ohashi, Senior member IEEE, “Rayleigh scattering reduction method for silica based optical fiber”, vol 18, no 11, Nov 2000.

[5] Book – John M Senior, Optical fiber communications, Principles & practice, second edition

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