 So, welcome to the next lecture that will be on same that is on the transmission characteristics second. So, these are the learning outcomes at end of this session students will be able to express a different types of scattering attenuation in optical signal. So, in the previous lecture we have seen the types of attenuation in the optical cable when the data is being transferred from the transmitter to the receiver. So, we have seen the material absorptions are due to the eccentric and eccentric conditions. So, we have seen that is the scattering problem is there one more problem is there on the dispersion and one more problem is there on the micro bending and the micro bending losses here. So, before starting to this basic of scattering losses just recall that what are the types of the attenuations we have studied in the previous video lecture and what we have seen is that the attenuation goes on decreasing when there is an increase in the wavelength here. So, is it right or wrong? So, we will start with the basic of scattering losses. This is due to the norm uniformity in the fiber optics while manufacturing that is the straight line path of light rays get deviated it is referred as a scattering. So, this is an optical cable fiber optical cable which consists of an the core and cladding inside this the light is being transmitted from the transmitter side here. So, the light should be follow the total internal reflection so that the data should be transmitted from the transmitter to the receiver side here. But this is due to the scattering is due to the non uniformity of the fiber optics while manufacturing. So, that is mainly caused due to the interaction of light with the density fluctuations in within the fiber. So, while manufacturing that the density is not same throughout the core here. So, the material which has been used to make this core and cladding here. So, what will happen when the light is going to be transmitted here it when it gets deflected due to that. So, the light will get transmitted from the core to the cladding and that data will be dispersed. So, such type of losses are known as in the scattering losses here. So, we will see the basic scattering mechanisms that is the scattering is being divided into two types that is the linear scattering as well as the non-linear scattering here. So, there is a difference between the linear scattering and the non-linear scattering here. So, the when the optical power is being transmitted from one mode to the another mode here, but there is no change in the frequency on the scattering here. So, such type of things are known as in the linear scattering here and there are two types of that is linear scattering are there that is Rayleigh scattering and the my scattering here. In the same manner if you see the non-linear scattering that when the optical power is being transmitted from one mode to the another mode or the some other or the same mode with a different frequency, there is a change in the frequency when the scattering will takes place here. So, there are two types of linear scattering that is the stimulated beryllian scattering that is S B S and the Raman scattering that is also known as the stimulated Raman scattering here. So, now in this video lecture we will be discussing the details about the Rayleigh's, my and the non-linear scattering that is S B S and the SRS here. So, this is the Rayleigh's scattering here. So, when does the Rayleigh's scattering occurs as the when the Rayleigh's got the size of the density fluctuation is less than one-tenth of the operating wavelength of the light here. So, when it is being transmitted when the size of the density fluctuation is less than one-tenth of the operating wavelength of the light. So, at that time the Rayleigh's scattering will occurs. So, this is the same figure when the light is being transmitted whose the density fluctuation is less than one-tenth of the operating wavelength. So, the light get scattered in this manner. So, the Rayleigh's scattering components can be reduced by the operating at the longest possible wavelength. So, we have seen that as we go on increasing where the wavelength the attenuation goes on decreasing. So, the Rayleigh's will also be the same here operating at the longest possible wavelength your Rayleigh's scattering will be less. So, how you are going to calculate the attenuation loss due to the Rayleigh's scattering it is denoted by y r that is an eta is equal to 8 pi cube n 8 p into beta c k f t f upon 3 lambda 4 here. So, where most important thing is your lambda that is then optical wavelength n is nothing but your the refractive index of the medium and p is the average photoelastic coefficient and beta c is the isothermal compressibility at the temperature t f and the k is nothing but your Boltzmann constant here. So, if you want to calculate that is how much loss is there due to the Rayleigh's scattering. So, we have to make use of this formula here. So, we will see afterwards that how the Rayleigh's scattering will be affected various wavelength here. So, we will take one 800 micrometer that is nanometer and then 1000 micro nanometers and then we will see the highest wavelength that is an 1500 nanometer here. So, from this we will understand that how we are going to increase the size of an wavelength at that time your the attenuation is going to be less here. So, we will solve one example on that. So, now it is the my scattering here it is the same like when the size of the defect is greater than the one-tenth of the wavelength of light and the scattering mechanism is called as an mass scattering here. So, when the size of a density fluctuation is less than one-tenth it is a Rayleigh's, but when the size of the defect is greater than one-tenth of the wavelength of light then the scattering mechanism is called as a mass scattering. So, the mass scattering is caused due to the last defect in the fiber core and the scatter lights out of the fiber core here. So, as we have seen in the Rayleigh's scattering, so when the light is is going to be scattered it is going to be into the cladding region here. But the mass scattering can be reduced by the removing imperfection during the glass manufacturing process. So, these losses are due to the manufacturing losses like Rayleigh's and the mass. So, it can be removed while removing the imperfections during the manufacturing process then controlling the coating of fiber means what we are going to make use of in the core and cladding and the mechanical coating on which is going to make use of the optical fiber and increase in the refractive index of the difference between the core and cladding. So, if you take care of all these three points, so the mass scattering will be less in that. So, now we will see the non-linear scattering that is known as the stimulated beryllium scattering that is known as the SBS here. So, when the light is passed through the optical fiber there are the variations in the electrical field of the beam here. These variations in the electrical field produce the acoustic vibrations in the optical cable as well as the scatter photon here. So, when the light is passed through then the optical cable there is a variations in the electrical field because the light is being transmitted in the form of electromagnetic waves as an light. So, it consists of electrical and the magnetic field. So, there is a variations in the electrical field which produces the acoustic vibrations and the scatter photon here. That scatter light aspects like an upper and the lower side bands which are the detached from the incident light by the modulation frequency. So, there is a change in the frequency because it scatters in the forward as well as in the backward direction here. Now, if you want to calculate that how much threshold optical power is there for the beryllium. So, it is given by pb 4.4 into 10 raise to minus 3 d square lambda square that is alpha it in db and then v watts. So, it is calculated in watts. So, where you know that d and lambda are the fiber core diameter and the operating wavelength respectively. Alpha db is nothing but the fiber attenuation in the decimal per kilometer and v is the source bandwidth in the gigahertz. So, it is important while measuring in the laser generation. So, when you are going to make use of a laser as then source to transmit the data here. So, at that time the stimulated beryllium scattering we have to see that there is no any scatter photon or the acoustic vibration here. In a similar manner if you are going to see the stimulated Raman scattering here it is also the same like an the SBS, but it is an high frequency optical photon is generated like an the SBS that the process is begun by the noise and the thermally made fluctuations in the optical field and active vibrational mode. So, due to which your the light is going to be scattered here. So, if you want to calculate the threshold optical power also for the Raman it is given by pr that is 5.6 into 10 raise to minus 2 d 2 lambda alpha db in watts. So, where you know that d and the lambda are at the fiber core diameter and the operating wavelength and alpha db is nothing but the fiber attenuation in the decimal per kilometer here. As the stimulated Raman is very high in the vat here now suppose we will see the examples on this also. So, pb if it comes to be a 1 milliwatt then it stimulated Raman scattering will appear at least 10 milliwatt here. So, the more threshold power is there for the Raman. So, this all all about the scattering. So, in which we have seen the linear and non-linear. So, in the linear we have seen that is Rayleigh's and my Rayleigh's will occur when it is the less than one-tenth of your operating wavelength that is the density fluctuation in the mice we have seen that is if it is greater than one-tenth of the operating wavelength and the Raman and the barrier will occurs due to the acoustic photons vibrations and the photons in being generated here. So, this was the related to your scattering. So, we will see now the examples how to calculate the Rayleigh's scattering now here. So, these are my references. Thank you.