When the electric field of a light wave encounters the sheet, the component parallel to the chains causes electrons to oscillate along the direction of that component (Ey in the above example), thus absorbing energy and inhibiting the component from passing through the sheet. Because electrons can not respond to the other component (Ex), it is readily transmitted.

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Other materials are nominally isotropic, but when they are bent or deformed in some way, they become anisotropic and therefore exhibit birefringence. This effect is widely used to study the mechanical properties of materials with optics.

The amount of light output in each polarization state can be determined by simply breaking up the incident light into its two polarization components (s and p), and then calculating how much of each intensity is transmitted and reflected. For systems based on incoherent light, this level of detail is usually sufficient to keep track of the impacts of components like optical filters on polarization.For some optical systems – particularly those based on coherent light and that utilize or are sensitive to interference effects, for example – the complete state of polarization should be tracked at every point through the system. In that case, it is important to understand that optical filters based on multilayer thin-film coatings not only reflect and transmit different amounts of intensity for the s and p polarization states, but also impart different phases to the two different states. And both the amplitude and phase contributions can depend strongly on the wavelength of light. Thus, in general, an optical filter can act like the combination of a partial polarizer and a birefringent waveplate, for both reflected and transmitted light.To determine the effect of an optical filter on the light in such a system, the incident light should first be broken up into the two fundamental components associated with the plane of incidence of the filter (s and p components). Then, the amplitude and phase responses of the filter for the s and p components should be applied separately to each of the incident light components to determine the amplitudes and phases of the reflected and transmitted light components. Finally, the reflected s and p components can be recombined to determine the total reflected light and its state of polarization, and likewise for the transmitted light. These steps are illustrated in the diagram below.

Notice from the graph above on the right that for the case of reflection from a higher-index region to a lower-index region (in this case glass-to-air, or ni = 1.5 and nt = 1.0), the reflectivity becomes 100% for all angles greater than the “critical angle” θc = arcsin(nt/ni) and for both polarizations. This phenomenon is known as “Total Internal Reflection” (TIR).For angles of incidence below the critical angle only the amplitudes of the different polarization components are affected by reflection or transmission at an interface. Except for discrete changes of p (or 180°), the phase of the light is unchanged. Thus, the state of polarization can change in only limited ways. For example, linearly polarized light remains linearly polarized, although its orientation (angle ) may rotate. However, for angles greater than θc, different polarizations experience different phase changes, and thus TIR can affect the state of polarization of a light wave in the same way birefringence does. Thus linearly polarized light may become elliptical, or vice versa, in addition to changes in the orientation.

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That is, E appears to oscillate along a line oriented at 45° with respect to the x axis. Hence this situation is called linear polarization.Notice that equivalently we could view the wave at a particular location (“fixed position”) and watch its amplitude evolve with time. Suppose we sit at the position z = 0. Then we see that

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All of the states of polarization described above are actually special cases of the most general state of polarization, called elliptical polarization, in which the tip of the electric field vector E traces out an ellipse in the x-y plane. The two components might have unequal amplitudes Ax  Ay , and also might contain a different relative phase, often denoted  That is, we may write generally

Have you ever had trouble sleeping after a night spent looking at your phone, your computer, your television and your tablet? This could be due to exposure to blue light.

We can see that in general the light emerges in a different state of elliptic polarization. In fact, for the example illustrated above, the particular choice of L for a given difference between nx and ny causes the linearly polarized light at the input end to be converted to circularly polarized light at the other end of the birefringent material. How did this happen? Let’s look at the math. Consider the phases accumulated by the two component waves as they travel through the birefringent material. The waves can be described by

An AR coating on your lenses can ease eye strain by reducing reflections to make your vision clearer. If you spend hours in front of a computer screen or on devices such as phones or iPads - particularly at night before bed - you may wish to choose an AR coating that also filters blue light.

Suppose the two components have equal amplitudes again, but now consider the case where these two components are not in phase, such that the angles of the sine functions are different. In particular, suppose there is a constant phase difference of p/2 between them, which corresponds to a distance of l/4 in the “fixed time” picture. The x component is

Polarization is a critical property of light for many optical systems and applications. This brief tutorial summarizes some of the most basic aspects of polarization, including how it is described, the impact of polarizing and birefringent elements on light, and how optical interfaces and filters can change the polarization of light.

You may experience a ‘halo’ effect around street lights or car headlights when driving at night. An AR coating can help this problem by virtually eliminating the reflections from your lenses.

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To understand the polarization of light, we must first recognize that light can be described as a classical wave. The most basic parameters that describe any wave are the amplitude and the wavelength. For example, the amplitude of a wave represents the longitudinal displacement of air molecules for a sound wave traveling through the air, or the transverse displacement of a string or water molecules for a wave on a guitar string or on the surface of a pond, respectively. We will refer to the amplitude of a light wave with the letter “E.” The amplitude of a light wave represents the potential for a charged particle (such as an electron) to feel a force – formally it may represent the “electric field” of an electromagnetic wave. Because this potential vibrates along the directions transverse to the direction the wave is traveling, light is a “transverse wave,” just like the waves on a string or water surface.Because light is a transverse wave, and because there are two transverse dimensions, there are fundamentally two distinct directions in which the light wave may oscillate. Let’s call these the x and y directions for a light wave traveling along the z direction. We’ll call the two distinct waves Ex and Ey, where we denote these by vectors to remind us that they point in (or oscillate along) a certain direction (the x and y directions, respectively).The amplitude of the light wave describes how the wave propagates in position and time. Mathematically, we can write it as a “sine wave” where the angle of the sine function is a linear combination of both position and time terms:

Some materials have a different index of refraction for light polarized along different directions. This phenomenon is called birefringence. For example, suppose light polarized along the x direction sees an index of nx, while light polarized along the y direction sees an index ny. Now suppose linearly polarized light passes through a piece of such a material of length L, where the linear polarization axis is oriented at 45° with respect to the x and y axes. The fixed time picture thus looks like:

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You might not have thought much about how glasses are made, but the care, science, and sheer technical expertise that goes into them really matters.

The polarization of light reflected and transmitted at an interface between two media or at a thin-film multilayer coating can be altered dramatically. These two cases are considered below.

However, if the optical system is in any way sensitive to polarization, even when the incident light is unpolarized, it is important to recognize that the beamsplitter can transmit and reflect different amounts of the “s” and “p” polarization states, as shown below.

and where, as before, E = Ex< + Ey. The three special cases described in sections a, b, and c above thus correspond to: (a) Ax = Ay and  = 0 (linear polarization; equal amplitudes); (b) 

When an optical filter is used at a non-normal angle of incidence, as is common with so-called “plate beamsplitters,” the filter can impact the polarization of the light. If the incident light is incoherent and unpolarized, and the optical system is “blind” to polarization, the standard intensity reflection and transmission functions R(l) and T(l) may be determined for the new angle of incidence, and they are sufficient to characterize the two emerging beams.

We all know how powerful the sense of sight is - but when we think of body health, we often don’t think about what our eyes need.

When you first have an eye test, your optometrist will get the lowdown on your eyes, vision, health and lifestyle in order to tailor the test to you.

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Please bring to your appointment:1) Your Medicare Card and Health Insurance Card (if applicable)2) Your previous spectacles (if any)3) Your previous contacts (if any)

Because of this relationship, a material with birefringence Dn of the appropriate thickness L to convert linear polarization to circular polarization is called a quarter-wave plate.What causes materials to be birefringent? Some materials, especially crystals, are naturally anisotropic at microscopic (sub-wavelength) size scales. For example, Calcite (CaCO3) is shown in the drawing below. The structure, and hence the response to polarized light, along the c direction is markedly different than that along the a and b directions, thus leading to a different index of refraction for light polarized along this direction.

You might not have thought much about how glasses are made, but the care, science, and sheer technical expertise that goes into them really matters.

When light is incident on an interface between two different media with different indexes of refraction, some of the light is reflected and some is transmitted. When the angle of incidence is not normal, different polarizations are reflected (and transmitted) by different amounts. This dependence was first properly described by Fresnel, and hence it is often called “Fresnel Reflection.” It is simplest to describe the polarization of the incident, reflected, and transmitted (refracted) light in terms of a vector component perpendicular to the plane of incidence, called the “s” component, and a component parallel to the plane of incidence, called the “p” component. The “plane of incidence” is the plane which contains the incident ray and the transmitted and reflected rays (i.e., all of these rays lie on one plane). In the example in the diagram below, the plane of incidence is the plane containing the x and z axes. That is, Es || y, while Ep lies in the x-z plane.

Cyber Sale*This offer is available to use at Bupa Optical for optical glasses and sunglasses from the Designer Range (does not apply to the Value Range, contact lenses or accessories) from 18 November to 2 December 2024. Offer must be applied in a single transaction and is available online and in-store. To receive $50 off, the customer must spend between $300 - $399 in one transaction after any discounts. Simply mention the promo code SAVE50 in-store or if purchasing online apply the code SAVE50 at checkout. To receive $75 off, the customer must spend between $400 to $499 in one transaction after any discounts. Simply mention the promo code SAVE75 in-store or if purchasing online apply the code SAVE75 at checkout. To receive $100 off, the customer must spend $500 or more in one transaction after any discounts. Simply mention the promo code SAVE100 in-store or if purchasing online apply the code SAVE100 at checkout. 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Bupa Optical Pty Ltd ABN 24 126 819 154.November Impact*Bupa Foundation will donate $5 AUD from every pair of prescription glasses or sunglasses, or packet of contact lens sold, online or in-store, between 6 and 30 November 2024 (donation period). The donation amount will be capped at $50,000 AUD. Donation does not apply to accessory or non-prescription glasses or sunglasses sales. Excludes all ADF contract sales. Customers are not eligible to claim any tax deduction or benefit. Eligible items that were purchased and then refunded or returned during the donation period will not be included in the final count to determine donation dollar amount. The final donation amount, as determined by the number of eligible items sold at $5 AUD per unit will be donated to The Brien Holden Vision Institute Foundation (ABN 86 081 872 586) within 90 days of the donation period ending. Chloe Jones Collection^From 6 November 2024, ongoing and until sold out (donation period), Bupa Foundation will donate $25 from every sale of glasses (prescription only) or sunglasses (prescription or non-prescription) from the Chloe Jones limited-edition range (1000 units available) to The Brien Holden Vision Institute Foundation (ABN 86 081 872 586) while stocks last. Donation does not apply to accessory or non-prescription glasses sales. Excludes all ADF contract sales. Customers are not eligible to claim any tax deduction or benefit. Eligible items that were purchased and then refunded or returned during the donation period will not be included in the final count to determine donation dollar amount. The final donation amount, as determined by the number of eligible items sold and will be donated to The Brien Holden Vision Institute Foundation (ABN 86 081 872 586) within 90 days of the donation period ending. Value Range*Offer available in-store and online at Bupa Optical. First complete pair(frame and single vision stock lens package) must be purchased from any ‘ValuePackage’ range (Range) at the first pair price for that Range. Second pair must be purchased in the same transaction or within 30 days of collection of an eligible first pair (in-store only). Second pair must be from the same or lower Range at the second pair price for that Range. Lens type upgrades and lens addons available on either pair at an additional cost and can differ between each pair. The prescription in each pair may also differ if both are clinically required by the customer. Frame only, may be purchased at the same amount as the frame & single vision stock lenses package price. Offer not available to goods supplied pursuant to any agreement between Bupa and any commonwealth government or associated entity. Members discount: 25% off Designer and sunglassesOffer available in-store and online at Bupa Optical. Bupa health insurance members buy any frames or sunglasses from the Designer range and receive 25% off the RRP on your first pair. Offer not available to goods supplied pursuant to any agreement between Bupa and any commonwealth government or associated entity. Bupa Optical Pty Ltd ABN 24 126 819 154.Members discount: 25% off Designer and sunglasses lenses & add-onsOffer available in-store and online at Bupa Optical. Bupa health insurance members buy any pair of prescription glasses or prescription sunglasses and receive 25% off RRP any lenses (excluding the value range), lens type upgrades and lens add-ons. Offer not available to goods supplied pursuant to any agreement between Bupa and any commonwealth government or associated entity. Bupa Optical Pty Ltd ABN 24 126 819 154.50% off 2nd pair Designer and sunglassesOffer available in-store and online at Bupa Optical. Buy any pair of prescription glasses or prescription sunglasses from the Designer range and receive 50% off RRP of any second prescription pair from the Designer range of equal or lesser value. You will also receive 50% off RRP for any lens type upgrades (not including lens add-ons) on the second pair from the Designer range. Alternatively, if you wish to purchase your second pair from the ‘Value Package’ range, you will only pay the 'Value Package' second pair price with 50% off lens type upgrades (not include lens add ons). Lens add-ons are always at an additional cost. Second pair in this offer must either be purchased in the same transaction, or if you are purchasing in-store it can also be within 30 days of collection of an eligible first pair. Offer not available to goods supplied pursuant to any agreement between Bupa and any commonwealth government or associated entity. Bupa Optical Pty Ltd ABN 24 126 819 15450% off lenses 2nd pair Value RangeOffer available in-store and online at Bupa Optical. Buy two pairs of prescription glasses from the Value range, received 50% off RRP lens type upgrades (does not include lens add ons) on the second pair. Lens add-ons are always at an additional cost. Second pair in this offer must either be purchased in the same transaction, or if you are purchasing in-store it can also be within 30 days of collection of an eligible first pair. Offer not available to goods supplied pursuant to any agreement between Bupa and any commonwealth government or associated entity. Bupa Optical Pty Ltd ABN 24 126 819 154Members discount: 20% off Contact LensesOffer available in-store and online at Bupa Optical. Bupa health insurance members receive 20% off the RRP on contact lenses. Offer not available to goods supplied pursuant to any agreement between Bupa and any commonwealth government or associated entity. Offer available instore and online by entering your Bupa member number at checkout on the Bupa Optical website Bupa Optical Pty Ltd ABN 24 126 819 154.EyeInspect and Microvascular Health Assessment

Contact lenses are popular for a reason - they make life much easier for many people with vision issues. However, they might not be the right option for everyone.

We can see that the tip of E traces out a circle as we follow the wave along the z axis at a fixed time. Similarly, if we sit at a fixed position, the tip of E appears to trace out a circle as time evolves. Hence this type of polarization is called circular polarization.

It is also possible to take advantage of an appreciable difference in reflected or transmitted phase for p- and s-polarized light over a region of the spectrum where the reflected and transmitted intensities are essentially equal, thus forming a waveplate.

where A is called the “amplitude factor,” the variable l (“lambda”) is the “wavelength” (units of nm), and the variable v (“nu”) is the “frequency” (units of Hz, or sec–1). If a snapshot of the wave could be taken at a fixed time, l would be the distance from one wave peak to the next. If one sits at a fixed point in space and counts the wave peaks as they pass by, v gives the frequency of these counts, or 1/v gives the time between peaks. The sign between the position and time terms determines the direction the wave travels: when the two terms have the opposite sign (i.e., the “–” sign is chosen), the wave travels in the positive z direction. For convenience we often use two new variables called the “wavenumber” k = 2p/l and the “angular frequency” 2pv (“omega”), which absorb the factor of 2p, so that the wave amplitude can now be written more compactly as

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Some polarizers eliminate the non-passed polarization component (Ey in the above example) by absorbing it, while others reflect this component. Absorbing polarizers are convenient when it is desirable to completely eliminate one polarization component from the system. A disadvantage  of absorbing polarizers is that they are not very durable and may be damaged by high intensity light (as found in many laser applications).When a reflective polarizer is operated in such a way that the blocked (i.e., reflected) polarization component is deflected into a convenient direction, such as 90° relative to the transmitted polarization component, then the polarizer acts like a polarizing beamsplitter, as shown below.

What if the two components Ex and Ey have unequal amplitude factors? We can see that the light wave is still linearly polarized.

An AR coating will help to prevent sunlight from reflecting into your eyes when the sun is behind you. This can help if you tend to experience those annoying reflections or ‘ghost’ images when wearing sunglasses.

Multilayer thin-film coatings have a large number of interfaces, since they are generally comprised of alternating layers of a high- and low-index layer materials. The fraction of incident light intensity Iin that is reflected (IR) and transmitted (IT) through a thin-film coating can be calculated from the indexes of refraction and the precise thicknesses of each layer. These intensity reflection and transmission functions R(l) and T(l), respectively, generally depend strongly on the wavelength of the light, because the total amount of light reflected from and transmitted through the coating comes from the interference of many individual waves that arise from the partial reflection and transmission at each interface. That is why optical filters based on thin-film coatings are called “interference filters.”

Unpolarized light can be polarized using a “polarizer” or “polarizing beamsplitter,” and the state of already polarized light can be altered using a polarizer and/or optical components that are “birefringent.” In this section we explore some examples of these types of components.

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Because the polarization response of a tilted multilayer thin-film coating can be very strong, optical filters can make excellent polarizers. For example, a basic edge filter at a high angle of incidence exhibits “edge splitting” – the edge wavelength for light at normal incidence shifts to a different wavelength for p-polarized light than it does for s-polarized light. As a result, there is a range of wavelengths for which p-polarized light is highly transmitted while s-polarized light ishighly reflected, as shown below.

Using this description of a single transverse orientation of a light wave, we can now consider multiple orientations to describe different states of polarization.

To place an order with anti-reflective lens coating, when entering your prescription details select ‘anti-reflective’ on the lens coating page.

Most polarizing beamsplitters are very efficient polarizers for the transmitted light (i.e., the ratio of desired to undesired polarization is very high); however, the reflected light generally contains some of both polarization components.How does a polarizer work? There are different ways of making a polarizer, and they are not described in detail here (see [1] for more examples). However, as an example consider one of the most popular absorbing polarizers: the well-known Polaroid “H-Sheet.” This polarizer, invented by E. H. Land in 1938, is a plastic, Poly-Vinyl Alcohol (PVA) sheet that has been heated and then stretched in one direction, forming long, nearly parallel hydrocarbon molecule chains. After dipping the sheet into an iodine-rich ink, long iodine chains form along the hydrocarbon molecules. Electrons freely move along the iodine chains, but do not easily move perpendicular to the chains. This ability for electrons to move freely in one direction but not the perpendicular direction is the key principle upon which most absorbing polarizers are based.

Polarization is a fundamental property of light. While many optical applications are based on systems that are “blind” to polarization, a very large number are not. Some applications rely directly on polarization as a key measurement variable, such as those based on how much an object depolarizes or rotates a polarized probe beam. For other applications, variations due to polarization are a source of noise, and thus throughout the system light must maintain a fixed state of polarization – or remain completely depolarized – to eliminate these variations. And for applications based on interference of non-parallel light beams, polarization greatly impacts contrast. As a result, for a large number of applications control of polarization is just as critical as control of ray propagation, diffraction, or the spectrum of the light. Yet despite its importance, polarization is often considered a more esoteric property of light that is not so well understood. In this article our aim is to answer some basic questions about the polarization of light, including: what polarization is and how it is described, how it is controlled by optical components, and when it matters in optical systems.

Anti-reflective lenses have a coating (sometimes referred to as an AR coating, multicoat or anti-glare coating) which reduces the amount of light that reflects off your lenses. Essentially, it allows more light to pass through your lenses to your eye, giving you clearer vision.

Have you ever had trouble sleeping after a night spent looking at your phone, your computer, your television and your tablet? This could be due to exposure to blue light.

A polarizer transmits only a single orientation of linear polarization, and blocks the rest of the light. For example, a polarizer oriented along x passes x and blocks Ey.

If the difference between the two phase values is p/2, then the wave emerging from the material (say into air) will be circularly polarized. This occurs when

The angle of the reflected ray,θr, is always equal to the angle of the incident ray, θi, this result is called the “law of reflection.” The angle of the transmitted (or refracted) ray, θT, is related to the angle of incidence by the well-known “Snell’s Law” relationship: ni sin θinbsp;= nt sin θT. It turns out that s-polarized light is always more highly reflected than p-polarized light. In fact, at a special angle called “Brewster’s Angle,” denoted θB, the p-polarized component sees no reflection, or is completely transmitted. Brewster’s angle is given by θB = arctan(nt/ni). The power or intensity reflection coefficients for a light wave (i.e., the squares of the amplitude reflection coefficients) for air-to-glass (left) and glass-to-air (right) look like:

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If you proceed with EyeInspect or Microvasular Health Assessment (MHA) (retinal screenings), Bupa Optical Pty Ltd ABN 24 126 819 154 (Bupa, we, us or our) will collect your personal information (PI) (your age, patient ID, gender and retinal images) from you for the purpose of conducting the retinal screening and reporting to you. The findings in your report will be based upon your retinal screening, but will not constitute a clinical diagnosis, recommended treatment or medication, nor be a substitute for advice from your eye health professional or other health care practitioner. We will disclose your PI to the providers of the retinal screening tool we use, Eyetelligence Pty Ltd, for the purpose of conducting the retinal screening and generating the retinal screening report. If you do not provide all of the PI requested, we may not be able to conduct the retinal screening or provide you with your retinal screening report. Bupa handles your PI in accordance with its Privacy Policy found at https://bupaoptical.bupa.com.au/pages/privacy-policy. This Privacy Policy lets you know how to access and correct your PI, how to make a complaint if you believe we have not complied with the Australian Privacy Principles and how we will handle your complaint. You can also contact us at Bupa Optical Head Office – Level 15, 33 Exhibition Street, Melbourne VIC 3000, or via email at feedback@bupaoptical.com.auMicrovascular Health Assessment: Free for Bupa members ^This offer is available for Bupa Health Insurance members between the ages of 40 and 80 to use at Bupa Optical for a free Microvascular Health Assessment (valued at $25). Microvascular Health Assessments are suitable for people between the ages of 40 and 80. Offer must be applied in a single transaction and is available in-store only. The offer may be redeemed once per person and once per transaction. This offer is not transferable and not available in conjunction with any other offer or discount, except Bupa Health Insurance member discounts. Any Bupa Health Insurance member discounts (if applicable) will be applied prior to the discount amount of this offer. Offer not available to goods supplied pursuant to any agreement between Bupa and any Commonwealth government or associated entity. Bupa Optical Pty Ltd ABN 24 126 819 154.Hearing~Available to customers 18 years and older.^Offer available on hearing aids from a higher technology level than the Hearing Services Program (HSP) range (Eligible Products). For HSP customers, 25% discount will apply to the balance owing on Eligible Products once any applicable HSP funding is applied. Offer available for the duration of the Bupa and Amplifon partnership. This offer cannot be used in conjunction with any other offer.^^Discount available on any in-store hearing offer at Bupa Optical & Hearing or Amplifon stores for the duration of the Bupa and Amplifon partnership.

Yes – everyone can benefit from anti-reflective lenses, particularly if you find yourself looking at your devices for long hours or driving regularly at night.

The amplitude E, or the potential for a charged particle to feel a force, is vibrating along both the x and y directions. An actual charged particle would feel both of these fields simultaneously, or it would feel

If Ax  Ay , the total wave E is linearly polarized, but it is no longer oriented at 45° with respect to the x axis. In fact we can see that it is oriented at an angle  where

AR lenses these days are treated so they repel water - and they also resist water spots forming, which means you’ll spend less time removing those pesky smears and fingerprints. Just ensure you use lens cleaning products suitable for coated lenses, so you don’t damage the surface.

In other words, if we look down the propagation axis in the positive x direction, the vector E at various locations (and at t = 0) now looks like: