Scattering, reflections and refractions are the major loss contributors in the field of optical fiber communication. There are some methods described in this presentation for reduction of the special case of scattering loss called rayleigh scattering loss.

1. PREDICTION METHODS OF
RAYLEIGH SCATTERING
LOSSES
PREPARED BY
DARSHAN BHATT
(150320705001)

2. 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
Rayleigh
Scattering
Linear Scattering Losses
Mie Scattering

3. 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]

4. Why the sky is blue..................?
FIGURE 2 – RAY LEIGH SCATTERING PHENOMENA

5. 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 -

6. 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↓

7. 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.

8. Sub Processes inVAD
Four 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.

9. ThermalTreatment Diagram

10. 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.

11. 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

12. 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 -

13. Relation between
Rayleigh
scattering
coefficient and
drawing
temperature

14. 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.

15. 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