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Polarization of Light Interview Question with Answer

Polarization of Light Questions and Answers for Viva

Embark on an illuminating journey into the science of light polarization with our curated collection of Interview Questions and Answers. Whether you're a physics aficionado, a student exploring the wonders of optics, or simply curious about the fascinating phenomenon of light polarization, our comprehensive list covers a diverse range of topics. From the basics of polarization to advanced concepts, such as Brewster's angle and polarizers, our expertly crafted responses provide valuable insights and knowledge. Dive into our repository of interview questions to deepen your understanding of light polarization and impress your friends, colleagues, or interviewers with your newfound expertise. Explore the intriguing properties and applications of polarized light, and uncover the captivating facts and theories that illuminate this intriguing field of study.

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Interview Question and Answer of Polarization of Light

Question-1. State Malus law

Answer-1: When two pieces of Polaroid are placed in succession along the path of a light wave, the intensity of light received behind the two Polaroids is described by Malus’ Law. The law expresses light intensity, I, as a function of the angle which is the angle θ between the directions of polarization of the two filters. The law can be expressed as follows:

I = Imaxcos2 θ

where, Imax is the light intensity between the two sheets of Polaroid.

Question-2. What is meant by Plane Polarization?

Answer-2: Plane polarization is a type of polarization which allows waves to oscillate in only one plane.

Question-3. What is polarization of light?

Answer-3: The light which has acquired the property of one sidedness is called a polarized light.

Question-4. What is Circular polarization?

Answer-4: Circular polarization of an electromagnetic wave is a polarization in which the electric field of the passing wave does not change strength but only changes direction in a rotary manner.

Question-5. What types of waves may be polarized?

Answer-5: Transverse can be polarized as polarization is a property of th transverse waves.

Question-6. What are Dichroic substances

Answer-6: A dichroic material is a crystalline substance in which two preferred states of light polarization are propagated with different velocities, and more importantly, with different absorption.

Question-7. Define Dichroism

Answer-7: Dichroism has two related but distinct meanings in optics. A dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths (colours) (not to be confused with dispersion), or one in which light rays having different polarizations are absorbed by different amounts.

Question-8. Other than using a polarizing filter, give one way in which visible light may be polarized?

Answer-8: Visible light can be polarized on reflection.

Question-9. Distinguish between unpolarized and plane polarized light?

Answer-9: The unpolarized light is symmetrical about the direction of propagation while in case of plane polarized light, there is lack of symmetry about the direction of propagation.

Question-10. What is polaroid device

Answer-10: Polaroid is a device to produce plane polarized light. It consists of ultra - microscopic crystals of quinine iodo sulphate which are embedded in nitro - cellulose films in such a way that their optic axes are parallel to each other.

Question-11. For what kind of light does malus law hold?

Answer-11: Malus law is completely applicable for completely plane polarized light.

Question-12. Define plane of vibration and plane of polarization

Answer-12: The plane containing the direction of vibration as well as the direction of the propagation of light is called plane of vibration. On the other hand, the plane passing through the direction of propagation and containing no vibration is called plane of polarization.

Question-13. what is the use of photo detector

Answer-13: Photo Detector is an optical detector that converts light signals into electrical signals, which can then be amplified and processed. The photo detector is as essential an element of any fiber optic system as the optical fiber or the light source.

Question-14. What is the use of Polarizer?

Answer-14: Polarizer is an optical filter that passes light of a specific polarization and blocks waves of other polarizations. It can convert a beam of light of undefined or mixed polarization into a beam with well-defined polarization.

Question-15. What do you mean by plane of polarization

Answer-15: The plane of polarization of linearly polarized light or other electromagnetic radiation is the plane containing the electric vectors of the vibrations.

Question-16. Define plane of vibration and plane of polarization

Answer-16: The plane containing the direction of vibration as well as the direction of the propagation of light is called plane of vibration. On the other hand, the plane passing through the direction of propagation and containing no vibration is called plane of polarization.

Question-17. How does polarized light differ from ordinary light?

Answer-17: The ordinary light is symmetrical about the direction of propagation while in case of polarized light, there is lack of symmetry about the direction of propagation.

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Bi-quartz Polarimeter

Q.What is Polarimeter ?

A.It is a device used to measure the angle of rotation of plane of polarisation rotated by an optically active substance.

Q.What is specific rotation ?

A.Specific rotation of an optically active substance at a given temperature is the rotation in degrees of the plane of polarisation of incident polarized beam produced by one decimeter length of substance of unit concentration.

Q.What are optically active substances?

A.Optically active substances rotate the plane of polarisation or plane of vibration of plane polarised light when it passes through it.

Q.What are different optically active substances?

A. Right handed or dextro rotatory & left handed or leavo rotatory

Q.Define plane of polarisation

A.It is the plane passing through the direction of propagation of light.

Q.Define plane polarised light.

A.Light is said to be plane polarised if it has vibrations in a single direction perpendicular to direction of propagation.

Q.Define plane of vibration.

A.It is the plane containing the direction of vibration and direction of propagation.

Q.How does specific rotation depend on temperature?

A.In some substances it decreases with rise in temperature like turpentine while in quartz it increases.

Q.What is the unit of specific rotation?

A.degree/decimeter/gm/cc

Q.name one practical use of polarimeter.

A.It is used to measure percentage of sugar in a solution.

Q.What is the function of analyzer and polariser ?

A. Polariser changer ordinary light to plane polarised light and analyzer is used to analyse light emitted through the optically active substance.

Q.What is Bi-quartz device?

A.It consists of two semicircular disc of right handed and left handed quartz which are cemented together to form a circular disc.

Bi-quartz polarimeter

3.5 Polarization of Light

Polarized light.

Polaroid sunglasses are familiar to most of us. They have a special ability to cut the glare of light reflected from water or glass. Polaroids have this ability because of a wave characteristic of light called polarization. What is polarization? How is it produced? What are some of its uses? The answers to these questions are related to the wave character of light.

Watch the first 6 minutes of the video below to see a practical overview of plane polarized light, using crossed polarizers, and how a third polarizer (which is how many minerals act) can be used to increase light output from crossed polarizers.

Electromagnetic waves are transverse waves consisting of varying electric and magnetic fields that oscillate perpendicular to the direction of propagation and perpendicular to each other.

The Sun and many other light sources produce waves in which E (and B , though it is not shown) are not preferentially oriented – they exist in every direction perpendicular to the direction of propagation (see Figure 2.3.11 ). Such light is said to be unpolarized because it is composed of many waves with all possible directions of polarization.

Figure 2.3.11. The slender arrow represents a ray of unpolarized light. The bold arrows represent the direction of polarization of the individual waves composing the ray. Since the light is unpolarized, the arrows point in all directions.

In contrast, light that is plane polarized (also called linearly polarized ) has E oriented in one specific direction in space ( Figure 2.3.12 ). The polarization direction is defined by the orientation of E (as opposed to B ).

Figure 2.3.12. The polarization direction of plane polarized light is defined as the vibration direction of the electric vector E.

Polarizers are composed of long molecules aligned in one direction. Thinking of the molecules as many slits, analogous to those for the oscillating ropes, we can understand why only light with a specific polarization can get through. The axis of a polarizing filter is the direction along which the filter passes the electric field of an EM wave (see Figure 2.3.13 ).

Figure 2.3.13. he transverse oscillations in one rope are in a vertical plane, and those in the other rope are in a horizontal plane. The first is said to be vertically polarized, and the other is said to be horizontally polarized. Vertical slits pass vertically polarized waves and block horizontally polarized waves.

To examine this further, consider the transverse waves in the ropes shown in Figure 2.3.13 . The oscillations in one rope are in a vertical plane and are said to be vertically polarized . Those in the other rope are in a horizontal plane and are horizontally polarized . If a vertical slit is placed on the first rope, the waves pass through. However, a vertical slit blocks the horizontally polarized waves. For EM waves, the direction of the electric field vector E is analogous to the disturbances on the ropes ( Figure 2.3.14 ).

Figure 2.3.14. A polarizing filter has a polarization axis that acts as a slit passing through electric fields parallel to its direction. The direction of polarization of an EM wave is defined to be the direction of its electric field.

ATOMIC EXPLANATION OF POLARIZING FILTERS

Polarizing filters have a polarization axis that acts as a slit. This slit passes electromagnetic waves (often visible light) that have an electric field parallel to the axis. This is accomplished with long molecules aligned perpendicular to the axis as shown in Figure 2.3.15 .

Figure 2.3.15. Long molecules are aligned perpendicular to the axis of a polarizing filter. The component of the electric field in an EM wave perpendicular to these molecules passes through the filter, while the component parallel to the molecules is absorbed.

Figure 2.3.16 illustrates how the component of the electric field parallel to the long molecules is absorbed. An electromagnetic wave is composed of oscillating electric and magnetic fields. The electric field is strong compared with the magnetic field and is more effective in exerting force on charges in the molecules. The most affected charged particles are the electrons in the molecules, since electron masses are small. If the electron is forced to oscillate, it can absorb energy from the EM wave. This reduces the fields in the wave and, hence, reduces its intensity. In long molecules, electrons can more easily oscillate parallel to the molecule than in the perpendicular direction. The electrons are bound to the molecule and are more restricted in their movement perpendicular to the molecule. Thus, the electrons can absorb EM waves that have a component of their electric field parallel to the molecule. The electrons are much less responsive to electric fields perpendicular to the molecule and will allow those fields to pass. Thus the axis of the polarizing filter is perpendicular to the length of the molecule.

Figure 2.3.16. Artist’s conception of an electron in a long molecule oscillating parallel to the molecule. The oscillation of the electron absorbs energy and reduces the intensity of the component of the EM wave that is parallel to the molecule.

Figure 2.3.17 shows the effect of two polarizing filters on originally unpolarized light. The first filter polarizes the light along its axis. When the axes of the first and second filters are aligned (parallel), then all of the polarized light passed by the first filter is also passed by the second. If the second polarizing filter is rotated, only the component of the light parallel to the second filter’s axis is passed. When the axes are perpendicular, no light is passed by the second.

Figure 2.3.17. The effect of rotating two polarizing filters, where the first polarizes the light. (a) All of the polarized light is passed by the second polarizing filter, because its axis is parallel to the first. (b) As the second is rotated, only part of the light is passed. (c) When the second is perpendicular to the first, no light is passed. (d) In this photograph, a polarizing filter is placed above two others. Its axis is perpendicular to the filter on the right (dark area) and parallel to the filter on the left (lighter area). (credit: P.P. Urone)

Only the component of the EM wave parallel to the axis of a filter is passed. Let us call the angle between the direction of polarization and the axis of a filter θ . If the electric field has an amplitude E , then the transmitted part of the wave has an amplitude E cos θ (see Figure 2.3.18 ). Since the intensity of a wave is proportional to its amplitude squared, the intensity I of the transmitted wave is related to the incident wave by I = I 0 cos2 θ, where I 0 is the intensity of the polarized wave before passing through the filter.

Figure 2.3.18. A polarizing filter transmits only the component of the wave parallel to its axis, Ecosθ , reducing the intensity of any light not polarized parallel to its axis.

Liquid Crystal DISPLAYS and Optically Active Materials

While you are undoubtedly aware of liquid crystal displays (LCDs) found in watches, calculators, computer screens, cellphones, flat screen televisions, and other myriad places, you may not be aware that they are based on polarization. Liquid crystals are so named because their molecules can be aligned even though they are in a liquid. Liquid crystals have the property that they can rotate the polarization of light passing through them by 90 degrees. Furthermore, this property can be turned off by the application of a voltage, as illustrated in Figure 2.3.19 . It is possible to manipulate this characteristic quickly and in small well-defined regions to create the contrast patterns we see in so many LCD devices.

Figure 2.3.19. (a) Polarized light is rotated 90º by a liquid crystal and then passed by a polarizing filter that has its axis perpendicular to the original polarization direction. (b) When a voltage is applied to the liquid crystal, the polarized light is not rotated and is blocked by the filter, making the region dark in comparison with its surroundings. (c) LCDs can be made color specific, small, and fast enough to use in laptop computers and TVs. (credit: Jon Sullivan)

In flat screen LCD televisions, there is a large light at the back of the TV. The light travels to the front screen through millions of tiny units called pixels (picture elements). One of these is shown in Figure 2.3.19 (a) and (b). Each unit has three cells, with red, blue, or green filters, each controlled independently. When the voltage across a liquid crystal is switched off, the liquid crystal passes the light through the particular filter. One can vary the picture contrast by varying the strength of the voltage applied to the liquid crystal.

Figure 2.3.20. Optical activity is the ability of some substances to rotate the plane of polarization of light passing through them. The rotation is detected with a polarizing filter or analyzer.

Many crystals and solutions rotate the plane of polarization of light passing through them. Such substances are said to be optically active . Examples include sugar water, insulin, and collagen (see Figure 2.3.20 ). In addition to depending on the type of substance, the amount and direction of rotation depends on a number of factors. Among these is the concentration of the substance, the distance the light travels through it, and the wavelength of light. Optical activity is due to the asymmetric shape of molecules in the substance, such as being helical. Measurements of the rotation of polarized light passing through substances can thus be used to measure concentrations, a standard technique for sugars. It can also give information on the shapes of molecules, such as proteins, and factors that affect their shapes, such as temperature and pH.

Figure 2.3.21. Optical stress analysis of a plastic lens placed between crossed polarizers. (credit: Infopro, Wikimedia Commons)

Glass and plastic become optically active when stressed; the greater the stress, the greater the effect. Optical stress analysis on complicated shapes can be performed by making plastic models of them and observing them through crossed filters, as seen in Figure 2.3. 21 . It is apparent that the effect depends on wavelength as well as stress. The wavelength dependence is sometimes also used for artistic purposes.

Birefrigence

Another interesting phenomenon associated with polarized light is the ability of some minerals and other crystals to split an unpolarized beam of light into two polarized beams ( Figure 2.3.22 ). Such crystals are said to be birefringent .

Each of the separated rays has a specific polarization. One behaves normally and is called the ordinary ray (o or ω) , whereas the other does not obey Snell’s law and is called the extraordinary ray (e or ε) . Birefringent crystals can be used to produce polarized beams from unpolarized light. Some birefringent materials preferentially absorb one of the polarizations. These materials are called dichroic and can produce polarization by this preferential absorption. This is fundamentally how polarizing filters and other polarizers work. We will use the property of birefringence to help us identify and distinguish minerals in thin section!

Figure 2.3.22. Birefringent materials, such as the common mineral calcite, split unpolarized beams of light into two. The ordinary ray behaves as expected, but the extraordinary ray does not obey Snell’s law.

Analytical Methods in Geosciences Copyright © by Elizabeth Johnson and Juhong Christie Liu is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License , except where otherwise noted.

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Polarisation and Malus’ Law – Practice

1) Polarised light with an intensity of 40cd passes through a analysing filter at an angle of 72° to the plane of the incident light. Calculate the intensity of the light as it passes through the polarising filter:

2) At what angle must an analysing filter be orientated at for the intensity of the light to be 50% of its original intensity?

3) A student placed two polarising filters together to reduce the intensity of light passing through them. They were originally placed at an angle of 10° and the student still wanted to reduce the intensity of the light. At what angle should the student place the analysing filter if they want the light intensity to be 1/5 of the intensity when the angle was 10°?

Quick Answers:

Worked Answers:

IIT JEE Study Material

Malus law is crucial if we want to learn or understand the polarisation properties of light. The law helps us to study the light intensity relation of the polariser-analyser. Malus law is named after Étienne-Louis Malus, who, in the year 1808, discovered that natural incident light could be polarised when it was reflected by a glass surface. He used calcite crystal for his experiment.

After observing the results, he further put forth a concept that natural light consisted of the s- and p-polarisation and that they were perpendicular to each other. Today, this law is used to define the intrinsic connection between optics and electromagnetism as well as demonstrate the transverse nature of electromagnetic waves.

What is malus law, malus law formula, solved problems and questions.

Malus law states that the intensity of plane-polarised light that passes through an analyser varies as the square of the cosine of the angle between the plane of the polariser and the transmission axes of the analyser.

Also Read: Electromagnetic Spectrum and Electromagnetic Waves

The law helps us quantitatively verify the nature of polarised light. Let us understand the expression of Malus law.

Point 1 – When unpolarised light is incident on an ideal polariser, the intensity of the transmitted light is exactly half that of the incident unpolarised light, no matter how the polarising axis is oriented.

Point 2 – An ideal polarising filter passes 100% of incident unpolarised light, which is polarised in the direction of the filter’s (Polariser) polarising axis.

From point (1) and point (2), we can assume I = I o cos 2 ϕ

The average value of I (< I >):

Which satisfies point (2) mentioned above.

To show point (1), let us consider ϕ = 0

That implies cos 2 ϕ = 1

To determine the direction of polarisation, we need one polariser, which is known as analyser oriented, making an angle (p) with the polariser.

Frequently Asked Questions on Malus Law

What is the use of malus law.

The law helps us understand the polarising properties of light.

State Malus law.

The Malus law states that the intensity of the plane-polarised light that passes through the analyser is directly proportional to the square of the cosine of the angle between the plane of the polariser and the transmission axis of the analyser.

Which wave can be polarised?

Lightwaves can be polarised. The phenomenon of polarisation takes place only in the transverse nature of waves. So, sound waves cannot be polarised.

Who is the Malus law named after?

The Malus law is named after Etienne Malus, who published this law in 1809.

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Engineering Physics Questions and Answers – Polarisation of Light

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Polarisation of Light”.

The following graph shows a circularly polarized light obtained by using a polarizer

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Optical Communication Viva Question

Optical fiber and their properties, 1. what is an optical fiber and also mention its type.

Optical fiber is the technology associated with data transmission using light pulses travelling along with a long fiber which is usually made of plastic or glass. Metal wires are preferred for transmission in optical fiber communication as signals travel with fewer damages. The types of optical fibers depend on the refractive index, materials used, and mode of propagation of light. The classification based on the refractive index is as follows:  Step Index Fibers  Graded Index Fibers The classification based on the materials used is as follows:  Plastic Optical Fibers  Glass Fibers The classification based on the mode of propagation of light is as follows:  Single-Mode Fibers  Multimode Fibers The mode of propagation and refractive index of the core is used to form four combination types of optic fibers as follows:  Step index-single mode fibers  Graded index-Single mode fibers  Step index-Multimode fibers  Graded index-Multimode fibers

2.What is a Optical Fiber Communication System and what are its basic elements?

The technique of transmitting data from one location to another by transmitting infrared light pulses using optical fiber is known as fiber optic communication. Here, the light is in the form of a carrier signal that is changed to hold the data. Basic elements of optical Fiber Communication System are: 1. Transmitter(Compact Light Source) 2. Optical Fiber Cable 3. Receiver(Photo Detector)

3State Advantages of Optical Fiber Communication.

a)Enormous Potential Bandwidth b)Signal Security c)Electrical Isolation d)Low Transmission Loss

4.What are the characteristics of light ?

a) Intensity b) Wavelength c) Spectral Width d) Polarization Intensity, wavelength and spectral width treat light as a scalar quantity but polarization treats light as vector quantity.

5.State Snell’s law.

A law stating that the ratio of the sines of the angles of incidence and refraction of a wave are constant when it passes between two given media.

6What do you mean by Total Internal Reflection?

Total Internal Reflection (TIR) is a phenomenon , by which light experiences complete reflection at an interface between two media. i.e When the light ray is travelling from denser medium to less denser medium, the angle of incidence becomes greater than the critical angle no refraction will take place and the light rays are reflected back in the same medium.

7. What are the types of Modes in Planar guide(Optical fiber) ?

There are 3 types of modes waveguide modes : a) Transverse Electric wave b) Transverse Magnetic wave c) Transverse Electromagnetic wave (hybrid wave propagation)

8.Define Critical Angle.

Critical angle is the minimum angle of incident beyond which the total internal reflection occurs for light travelling from a medium of higher to one of lower refractive index.

9.Define V-number.

V-number is defined by : V = 2πa/λ. N A. It is a dimensionless number gives a measure of the number of modes a fiber can support.

10.What are the ways in which a light ray can be launched inside a fiber?

We can launch a ray inside a fiber in two ways: i) Meridinal Ray : When the Ray which we launch in the fiber and axis of the fiber lies in the same plane then such a ray is known as meridinal ray.

Ray : These Rays are not confined to a single plan but instead tends to follow a helical type path along the fiber.

11. Why is cladding necessary for an optical fiber?

Cladding is necessary for an optical fiber for the following reasons: • Provide proper light guidance inside the core. • And to avoid leakage of light from the fiber.

12.Define Acceptance Angle , Numerical Aperture

Acceptance Angle : The maximum incidence angle of a light ray which can be used for injecting light into a fiber core or waveguide is known as acceptance angle

Numerical Aperture: For an optical fiber with core refractive index of n1 and cladding refractive index of n2 , Numerical Aperture(NA) is defined as :

13.Diffrence between multimode fiber and Single mode fiber?

PARAMETER	SINGLE-MODE OPTICAL FIBER	MULTIMODE OPTICAL FIBER
Number of propagating mode	Only one	More than one
Core diameter	Small	Large
Optical source	LASER	LED
Bandwidth	More	Less
Handling and coupling	Difficult	Easy
Initial cost of fiber	Low	High
Attenuation	Less	More
Transmission Rate	High	Low

Transmission Characteristics of Optical Fiber

1.what are the mechanisms of losses occurs in optical fiber.

The mechanisms of losses that occur in an optical fiber are: 1. Absorption (fiber material) 2. Scattering ( fiber material + structural imperfection) 3. Radiative effects 4. Pulse broadening.

2.AWhat is the difference between intermodal and intramodal dispersion?

Intermodal dispersion: Dispersion caused by the delay between different modes. Typically, it is the delay between the shortest path (zero mode) and the longest path (critical mode). Intramodal dispersion: Dispersion that is independent of modes, related to the line width of the source and caused by variations in the refractive index as a function of wavelength.

3.Define Attenuation loss and Bending loss.

Attenuation loss(or path propagation loss) is the reduction in power density (attenuation) of an electromagnetic wave as it propagates through space. Attenuation occurring as a result of either a bend in an optical fiber that exceeds the minimum bend radius or an abrupt discontinuity in the core/cladding interface is called bending loss.

4.What is macro bend and micro bend losses?

Macro bend losses occur when radius of curvature is large compared to the fiber diameter. Micro bend losses are small scale fluctuation in radius of curvature of fiber axis

5.What is polarization?

Polarization is the electric field orientation of a light signal. Also, it can vary significantly along the length of a fiber polarization state. Thus, it is a fundamental property of an optical signal.

Optical Sources

1.why do you prefer laser diode over leds for communication applications.

• It allows high intensity radiation. • Because laser diode has narrow spectral width of its laser source which is preferable.

2. What are the difference between LED and Laser diode?

` =

LED	LASER
Optical output is incoherent.	Optical output is nearly coherent.
No optical cavity exists for wavelength selectivity.	The optical energy is produced in an optical resonant cavity.
No spatial and temporal coherence	Optical energy has spatial and temporal coherence.
The output radiation has a broad spectral width	The output beam has very directional and narrow spectral width.

3.State the essential components of a laser?

The major components of lasers are: • Amplifying medium • An optical feedback • Finally, the pumping source.

4.Give some important photo detector materials.

The important materials are: 1. InGaAs 2. InAlGaAs.

5.What is Quantum Efficiency?

As we know re combination could be radiative and non radiative . also energy photon generated may or may not enter the fiber so there are two types of efficiencies 1. Internal Quantum Efficiency 2. External Quantum Efficiency

6.List the advantages and disadvantages of LED

Advantages • Simpler fabrication • Low cost • Less temperature dependent • Linearity Disadvantages • Incoherent source of light • Usually lower modulation Bandwidth • Harmonic distortion • Large Spectral

7.What is Laser Diode?

Lasers comes in many forms but for optical fiber communication “Laser diodes” are used exclusively.Laser diodes have response times less than 1ns and spectral widths of 2nm or less. Lasers are used in systems in which requirements are more than 200MHz

Optical Detectors

1.what are the desirable characteristics of optical sources.

 Emission within the low loss window of the fiber.  Narrow spectral width  Ease and linearity of modulation  High reliability

2. What are the possible noises that occur in optical receivers?

The possible noises that occur in optical receivers are as follows: 1. Photo detector noise 2. Quantum noise 3. Dark current noise ( bulk dark current, surface dark current ) 4. Amplifier noise 5. Lastly the thermal noise or Johnson noise.

3. Define fiber splicing.

Fiber splicing is a Permanent joint formed between two individual optical fibers in the field or factory.

4. What is a fiber coupler?

Optical fiber coupler is a device that distributes light from a main fiber into one or more branch fibers. Thus, we use a directional coupler to combine and split optical signals in an optical network.

5.What is Optical signal to noise ratio (OSNR)?

It is the ratio of signal power to noise power, over a specific spectral bandwidth, at any point in an optical link. Noise power can be defined as any undesirable signal interference.

6. What is dark current noise?

The dark current noise arises from electrons/holes which are thermally generated in the PN junction of the photodiode. Thus, this current continues to flow through the bias circuit of the device when no light is incident on the photodiode

Fiber Optic Components

1.what are leaky modes in optical fiber.

A leaky mode in an optical fiber is a mode having electric field that decays monotonically for a finite distance in the transverse direction but becomes oscillatory everywhere beyond the finite distance

2. What is Eye Diagrams?

The eye diagram is a powerful measurement tool for assessing the data handling ability of a digital transmission. The eye pattern measurements are done in time domain and allow the effects of waveform distortion to be shown immediately on the display of standard BER test equipment

3.Define Point to Point fiber optic data links

4.What do you mean by WDM?

WDM is wavelength division multiplexing .The optical beam consists of different wavelengths and several channel information is transmitted over a single channel.

5. What is Power Penalties?

The ratio of the reduced received power (or power received due to signal impairments) to the ideal received power is known as power penalties

6. What is Neighborhood processing?

7. . What is a quantum limit?

It is possible that we find the minimum optical power that we receive, required for a specific bit error rate performance in a digital system. Hence,we refer to this minimum received power level as the quantum limit

8. What is the cutoff wavelength of fiber?

We define the cutoff wavelength as the minimum value of wavelength that can be transmitted through the fiber. Additionally, the wavelength greater than the cutoff wavelength can be transmitted.

9. What is BER(Bit Error Ratio)?

It is an approach to divide the number .No .of. Errors occurring over a certain time interval t by the number N of pulses transmitted during this interval

10. What is BER(Bit Error Ratio)?

Avalanche Photodiode: An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. PIN Photodiode: PIN photodiode is a kind of photo detector; it can convert optical signals into electrical signals.

Module 6- Image Segmentation

1. define point to point fiber optic data links.

2. List Down the application of radio-over-fiber links.

1. Access to dead zones An important application of RoF is its use to provide wireless coverage in the area where wireless backhaul link is not possible. 2. FTTA (Fiber to the Antenna) By using an optical connection directly to the antenna, the equipment vendor can gain several advantages like low line losses, immunity to lightening strikes/electric discharges etc.

3.What is the purpose of rise time budget analysis?

Rise time budget: A rise-time budget analysis is a convenient method to determine the dispersion limitation of an optical link. The power budget involves the power level calculations from the transmitter to the receiver.

4.What are the key parameters required for analyzing the optical ?

Along with the primary design criteria, there are some additional parameters which facilitate better design and quality analysis of the optical link. These factors consist of the scheme of modulation, the system fidelity, cost, upgradeability, commercial availability etc.

5.What is Fiber Optic Communication System Design Considerations?

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Polarisation ( AQA A Level Physics )

Revision note.

Polarisation

Polarisation is when:

Particle oscillations occur in only one of the directions perpendicular to the direction of wave propagation

This is because transverse waves oscillate in any plane perpendicular to the propagation direction
Vibrations are restricted to one direction
These vibrations are still perpendicular to the direction of propagation / energy transfer
The difference between unpolarised and polarised waves is shown in the diagram below:

Polarised waves diagram, downloadable AS & A Level Physics revision notes

Diagram showing the displacement of unpolarised and polarised transverse waves

This is because they oscillate parallel to the direction of travel
This only allows oscillations in a certain plane to be transmitted

Waves through a polariser, downloadable AS & A Level Physics revision notes

Diagram showing an unpolarised and polarised wave travelling through polarisers

Only unpolarised waves can be polarised
When a polarised wave passes through a filter with a transmission axis perpendicular to the wave, none of the wave will pass through
Light can also be polarised through reflection, refraction and scattering

Investigating Light Intensity with Two Polarisers

Filter A will polarise the light in a certain axis
All of the polarised light will pass through filter B unaffected
In this case, the maximum intensity of light is transmitted

Polarised Light Intensity(1), downloadable AS & A Level Physics revision notes

When both polarisers have the same transmission axis, the intensity of the transmitted light is at its maximum

As the polarising filter B is rotated anticlockwise, the intensity of the light observed changes periodically depending on the angle B is rotated through
This time none of the polarised light will pass through filter B
In this case, the minimum intensity of light is transmitted

Polarised Light Intensity (2), downloadable AS & A Level Physics revision notes

When one of the polarisers is rotated through 90°, the intensity of the transmitted light drops to zero

The resulting graph of the light intensity with angle, as the second polariser is rotated through 360°, looks as follows:

Intensity v Angle Graph, downloadable AS & A Level Physics revision notes

Graph showing how the intensity of the transmitted beam varies with the angle between the transmission axes of the two polarisers

In real life, the intensity of the unpolarised electromagnetic wave reduces after it passes through a polarising filter

Worked example

Which statement below describes a situation in which polarisation should happen? A. Radio waves pass through a metal grid B. Surface water waves are diffracted C. Sound waves are reflected D. Ultrasound waves pass through a metal grid

Radio waves are transverse waves - they can be polarised by a metal grid so only the waves that fit through the grid will be transmitted, therefore, A is correct
B cannot be correct as waves are not polarised when diffracted, but are polarised only when reflected , refracted or scattered
C & D cannot be correct as polarisation only occurs for transverse waves , therefore, C & D can be ruled out as sound and ultrasound are both longitudinal waves

You may be expected to describe the intensity, or even draw the graph of intensity v angle, for light with two polarisers, however, the good news is that you won't be expected to perform any calculations (Malus's Law) in relation to this.

Applications of Polarisers

Polaroid sunglasses.

This means the glasses do not allow any horizontally polarised light to pass through

Polaroid sunglasses contain vertically oriented polarising filters which block out any horizontally polarised light

This means if the surface is horizontal, a proportion of the reflected light will oscillate more in the horizontal plane than the vertical plane
Therefore, polaroid sunglasses are useful in reducing the glare on the surface of the water (or any reflective surface) as the partially-polarised light will be eliminated by the polarising filter
As a result of this, objects under the surface of the water can be viewed more clearly

Polaroid Sunglasses (2), downloadable AS & A Level Physics revision notes

When sunlight reflects off a horizontal reflective surface, such as water, the light becomes horizontally polarised. This is where polaroid sunglasses come in useful with their vertically aligned filter

Polaroid Photography

They are very useful for capturing intensified colour and reducing glare on particularly bright sunny days
This is because the light reflected on the surface of the water is partially polarised in the horizontal plane
This glare is eliminated by the polarising lens
However, the light from the underwater object is refracted by the surface of the water, not reflected, so it is not plane-polarised
Therefore, the light from the underwater object is more intense than the glare and shows up much more brightly in the photo

As well as giving a cool look to photographs, polaroid filters are extremely useful for reducing glare in photos and snapping pictures of objects underwater

Polarisation of Radio & Microwave Signals

Radio and television services are broadcast either horizontally-polarised or vertically-polarised
The particular orientation of an aerial will depend on the transmitter it is pointing towards and the polarity of the services being broadcast

Aerial Polarisation, downloadable AS & A Level Physics revision notes

Broadcasting towers always transmit either vertically or horizontally polarised signals. This is why aerials must be positioned accordingly otherwise they won't pick up the TV signal correctly

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Author: Katie M

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

What Is America’s Gender War Actually About?

The political parties are more divided by their views on gender than they are divided by gender itself.

Red and blue hands inserting ballots in box

Produced by ElevenLabs and News Over Audio (NOA) using AI narration.

This is Work in Progress, a newsletter about work, technology, and how to solve some of America’s biggest problems. Sign up here .

The United States is politically polarized along several lines, including race, geography, and education. Heading into a general election that will once again offer voters a choice between a Democratic woman and a Republican man, gender may seem like the clearest split of all. But surveys, polls, and political scientists are torn on how dramatically men and women are divided, or what their division actually means for American politics. The gender war is much weirder than it initially appears.

By several measures, men and women in America are indeed drifting apart. For most of the past 50 years, they held surprisingly similar views on abortion, for example. Then, in the past decade, the pro-choice position surged among women. In 1995, women were just 1 percentage point more likely to say they were pro-choice than men. Today women are 14 points more likely to say they’re pro-choice—the highest margin on record.

In 1999, women ages 18 to 29 were five percentage points more likely than men to say they were “very liberal.” In 2023, the gap expanded to 15 percentage points . While young women are clearly moving left, some evidence suggests that young men are drifting right. From 2017 to 2024, the share of men under 30 who said the U.S. has gone “too far” promoting gender equality more than doubled, according to data shared by Daniel Cox, a senior fellow at the American Enterprise Institute, a free-market think tank. Gallup data show that young men are now leaning toward the Republican Party more than at any other point this century.

Read: The gender war is over in Britain

So far, this seems like a straightforward story: Men (especially young men) are racing right, while women (especially young women) are lurching left. Alas, it’s not so simple. Arguably, men and women aren’t rapidly diverging in their politics at all, as my colleague Rose Horowitch reported . At the ballot box, the gender gap is about the same as it’s long been. Men have for decades preferred Republican candidates, while women have for decades leaned Democratic. In a 2024 analysis of voter data, Catalist, a progressive firm that models election results, “found that the gender divide was roughly the same for all age groups in recent elections,” Horowitch wrote .

One suggested explanation for these apparent contradictions is that the most alarming surveys are showing us the future, and this November will establish a new high-water mark in gender polarization, with women breaking hard for Kamala Harris and men voting overwhelmingly for Donald Trump. Another possibility is that these surveys are a little misleading, and gender polarization has already peaked, in which case this is much ado about nothing.

A third possibility interests me the most. John Sides, a political scientist at Vanderbilt University, says the gender gap is real; it’s just not what many people think it is. “The parties are more polarized by gender attitudes than by gender itself,” he told me.

If that sounds a bit academic, try a thought experiment to make it more concrete. Imagine that you are standing on the opposite side of a wall from 100 American voters you cannot see. Your job is to accurately guess how many of the folks on the other side of the wall are Republicans. You can only ask one of the following two questions: “Are you a man?” or “Do you think that men face meaningful discrimination in America today?” The first question is about gender. The second question is about gender attitudes , or how society treats men and women. According to Sides, the second question will lead to a much more accurate estimate of party affiliation than the first. That’s because the parties aren’t remotely united by gender, Sides says. After all, millions of women will vote for Trump this year. But the parties are sharply divided by their cultural attitudes toward gender roles and the experience of being a man or woman in America.

The fable above plays out in survey data, too. In the March 2024 Views of the Electorate Research (VOTER) Survey, 39 percent of men identified as Republican versus 33 percent of women. That’s a six-point gap. But when the VOTER Survey asked participants how society treats, or ought to treat, men and women, the gender gap exploded. Sixty-one percent of Democrats said women face “a lot” or “a great deal” of discrimination while only 19 percent of Republicans said so. In this case, the gender- attitude gap was more than six times larger than the more commonly discussed gender gap.

To Sides, the conclusion is obvious: The political parties are more divided by their views on gender than they are divided by gender itself. It’s not “men are from Mars, and women are from Venus.” It’s “Republican men and women are from Mars, and Democratic men and women are from Venus.”

America’s parties engage in highly gendered messaging, and the news media contributes to the sense that the parties stand in for masculine and feminine archetypes. “This is the boys vs. girls election,” Mike Allen and Jim VandeHei wrote in Axios before Harris became the Democrats’ presumptive nominee. In the article, they quote Trump advisers who played up the Republican National Convention as an opportunity to sell the GOP as “the testosterone party” that pits “Donald Trump’s chest-beating macho appeals vs. Joe Biden’s softer, reproductive-rights-dominated, all-gender inclusivity.”

Political language today is so coded by gender that it’s easy to identify blind quotes by party. If you hear a politician complain that the opposing party is dominated “by a bunch of childless cat ladies,” well, it’s obviously a Republican speaking. (That would be J. D. Vance in an interview a few years ago with Tucker Carlson .) If you hear a politician accuse the opposing party of becoming a “He-Man woman-hater’s club," well, it’s obviously a Democrat talking. (In this case, the Democrat is Minnesota Governor Tim Walz describing the GOP presidential ticket and this month’s Republican National Convention.)

Read: Women exit the party of Trump

But there’s a difference between distinct gender rhetoric and a coherent vision of womanliness or manliness. For its part, the GOP plays host to several visions of masculinity, awkwardly mushed together. Trump is a thrice-married Lothario who combines the showmanship of a pro-wrestling heel with the wounded rage of a country-club rejectee. The result is a potent mix of cosmetic macho bluster and marrow-deep elite resentment. For the purpose of containing this multitude in a phrase, let’s call it “alpha-victim masculinity.”

Adding to the muddle, for the third straight election Trump is sharing the ticket with a devoutly Christian vice-presidential candidate whose vision of gender relations is distinctly conservative and traditional.

Whereas Trump flaunted his promiscuity, his vice president, Mike Pence, broadcasted his chastity. Whereas Trump’s alone time with women ultimately led to felony convictions, Pence refused to eat alone with any woman except his wife. Whereas Trump has divorced twice, his new running mate, Vance, has called into question the very institution of divorce . He said in 2021 that the ability to quickly end marriages is “one of the great tricks that I think the sexual revolution pulled on the American populace” and slammed the idea that we should make “it easier for people to shift spouses like they change their underwear.”

If the GOP’s gender politics are fragmented by decorum and divorce, the glue tying the party together may be a nostalgia for social-dominance hierarchies and opposition to the cosmopolitan mores of the left. As the Cambridge University historian Gary Gerstle has written, the progressive movement originating with the New Left of the 1960s and ’70s has embraced a cultural politics that is “free of tradition, inheritance, and prescribed social roles” and that “rejected the notion that the patriarchal, heterosexual family should be celebrated.” The watchword of progressive gender politics is not tradition but liberation, a full break from the pull of history. Tradition, which conservatives see as a guardrail, progressives see as a straitjacket.

Women make up a majority of the electorate , outvoting men by millions of ballots each election. So it might be strategic for Democrats to adopt a political language and policy platform that appeals disproportionately to female voters. The problem, as Richard Reeves, the author of the book Of Boys and Men , has told me , is that men vote, too. The left has become more adept at shaming toxic masculinity than at showcasing a positive masculinity that is distinct from femininity. Progressive readers of the previous sentence might roll their eyes at the notion that it is the job of any left-wing political movement to coddle men’s feelings. But if a large shift rightward among young male voters helps Trump eke out a victory in November, Democrats will have little choice but to think up a new message to stop the young-male exodus.

“The Democratic Party appears to have made a conscious choice not to make young men a political priority,” Cox told me, just as “the GOP under Trump seems unconcerned about the ways it may be alienating young women.” If American politics in 2024 is a gender war, it is not yet a conflict between the genders. Let’s hope it never gets to that. But it is a conflict between the parties over the role of gender, the meaning of gender, the definition of gender. And that, frankly, is strange enough.

About the Author

IMAGES

Polarization of Light Interactive Demo
Polarisation Questions 3 to 4 IAL As Physics Unit 2 Lecture 6 Part c
Polarisation Exam Questions
Polarization
Questions with Answers on Polarisation
Important Viva Questions for determination of Planck's constant by photoelectric effect

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