Aspheric lenses, due to their complex manufacturing process and materials, can be more delicate and susceptible to damage if not handled properly. They require careful handling and storage to maintain their precision and performance. On the other hand, spherical lenses, being simpler in design and construction, tend to be more robust and less prone to damage, making them a durable option for rugged applications and environments.

Fresnellens

In the field of photography, aspheric lenses are prized for their ability to minimize distortion and provide high image clarity, making them essential in professional-grade cameras and high-end smartphones. They help achieve sharp images with accurate focus, important for detailed photography and videography. Spherical lenses, while not as advanced in reducing aberrations, are commonly used in entry-level cameras where cost-efficiency is a priority.

Two optical power measurements are needed to estimate the DUT's extinction ratio. The measurement of the maximum power (Pmax ) transmitted to the power sensor requires the DUT's transmission axis to be oriented parallel to the polarization direction of the incident light. The measurement of the minimum power (Pmin ) transmitted by the DUT requires the DUT's transmission axis to be oriented perpendicular to the polarization direction of the incident light. These two orientations of the DUT's transmission axis are indicated by the dashed gold lines in Figure 1, assuming the polarization direction of the source light is vertical.

Selecting the right lens for your imaging application is important to achieving optimal performance. Lenses come in various shapes and forms, each with its own unique characteristics and advantages. Understanding the differences between spherical and aspheric lenses can help you make an informed decision that meets your specific needs. In this blog, you will learn more about the intricacies of both lenses, including their design, how they work, their applications, and the main considerations in choosing the right lens for an optical system.

Lenticularlens

Focusing the light through a spherical lens depends upon its curvature, refractive indices of materials used in its construction and wavelengths of light that pass through it. Spherical lenses suffer from distortion due to their uniform curve; light hitting their edges being refracted more than those striking its center, thus leading to different focus locations along an optical axis.

Finding an aspherical or spherical lens suitable to your needs requires considering several key aspects, particularly within photonics. Photonics is an expansive field that encompasses everything from telecom systems and laser beam systems through medical photonics as well as sensors requiring lenses – this comprehensive guide can assist in selecting an appropriate type of lens in photonics applications.

The maintenance requirements for aspheric lenses are typically higher due to their complex surface profiles, which can make cleaning and alignment more challenging. Special tools and techniques might be needed to ensure they remain in optimal condition. Spherical lenses, with their simpler curvature, are easier to clean and maintain, reducing the time and cost associated with their upkeep.

VR and AR systems demand lenses that can deliver a wide field of view with minimal distortion. Aspheric lenses are well-suited for these applications due to their ability to provide clear and immersive visuals, enhancing the user experience. The precision in aspheric lenses ensures that users perceive virtual objects with minimal optical flaws, which is critical for maintaining realism and immersion in VR and AR environments.

Aspherical lens designs offer several advantages that outweigh their challenges, including enhanced optical performance or more compact lens configurations.

Improve the Extinction Ratio of the Source LightThe extinction ratio of the light incident on the DUT can potentially limit the value of ERest  to a value substantially less than ERDUT . The value of ERest  only approaches the value of ERDUT  when the extinction ratio of the incident light is significantly higher than the extinction ratio of the light incident on the DUT. For example, when the extinction ratio of the incident light equals the value of ERDUT , ERest  is only ~50% of the value of ERDUT . When the extinction ratio of the incident light is two orders of magnitude higher than ERDUT , ERest  is ~99% of the value of ERDUT .

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Figure 1: The extinction ratio of the optic under test (DUT) can be estimated from two optical power measurements. One, Pmax , requires the transmission axis of the DUT to be parallel with the polarization direction of the incident light, which is vertical in this illustration. The second measurement, Pmin , requires the DUT's transmission axis to be perpendicular (crossed with) the incident light's polarization direction. The estimate's accuracy is better when the extinction ratio of the light incident on DUT is much higher than the DUT's extinction ratio. One or more linear polarizers inserted between the source and DUT may be needed to improve the light's extinction ratio, since light from lasers described as linearly polarized often has an extinction ratio too low to achieve the desired accuracy.

Selecting the right lens type for your imaging application involves a thorough understanding of the specific requirements and constraints of your project. Spherical lenses offer simplicity and cost-effectiveness for less demanding applications, while aspheric lenses provide superior optical performance for high-precision tasks. By considering factors such as clarity, field of view, compactness, cost, and supplier capabilities, you can make an informed decision that meets your needs. Innovations in lens technology continue to expand the possibilities, making it an exciting time for developments in optical systems.

Aspherical and spherical optical lenses differ both in terms of shape and light handling capabilities, creating different advantages and disadvantages depending on which application the lens will be used in. Here is a detailed comparison.

Accurately estimating a DUT's extinction ratio requires linearly polarized incident light, whose extinction ratio is much higher than that of the DUT, as well as an optical power sensor. It is sometimes the case that a linearly polarized source provides light whose extinction ratio is adequate (see the discussion in the following section), but it is typically necessary to include one or more linear polarizers between the source and DUT (Figure 1).

Aspheric lenses feature more intricate profiles with changing curvatures from center to edge that enable more precise focusing and less distortion from spherical distortion, resulting in clearer images with sharper contrast. Although aspherics lenses may cost more and be harder to produce than regular lens designs, their superior optical performance make it worthwhile in high precision applications.

If the positions of the linear polarizer and the DUT are switched, so that the DUT is placed closest to the source, the effect can be modeled by exchanging the ERDUT  and ERref  variables in this equation. This change worsens the model's (and the measurement's) estimate of ERDUT . For best results, the set of linear polarizers should be located closest to the source.

Figure 2: The difference between the measured value (ERest = Pmax / Pmin ) and the actual value (ERDUT ) of the DUT's extinction ratio strongly depends on the extinction ratio of the light incident on the DUT. The incident light's extinction ratio is the product of the extinction ratios of the source (ERsource ) and the linear polarizer (ERref ) inserted between the source and DUT. Modelled values (blue curve) and experimental data (triangles and circles) are plotted. In this work, ERsource < ERDUT . The measurements obtained with no polarizer between the source and DUT corresponds to ERref  = 1 and are indicated by triangles. The measurement data obtained with a linear polarizer between the source and DUT are indicated by circles. These data show that without the added linear polarizer, the estimated values of the DUT's extinction ratio were substantially lower than the actual value.

Effect of Improving the Incident Light's Extinction RatioThe value of ERest  can be modeled for sources with different extinction ratios as well as configurations that do and do not include linear polarizer(s) between the source and the DUT. The modelled value (ERmodel ),

Selecting an aspherical or spherical lens for photonics applications involves careful consideration of application requirements, design factors, cost versus performance considerations and supplier collaboration – to achieve desired performance from your photonics system through lens selection in an organized manner.

References[1] Michael Kraemer and Tom Baur, "Extinction ratio measurements on high purity linear polarizers," Proc. SPIE Polarization: Measurement, Analysis, and Remote Sensing XIII, 10655, 1065505 (2018).

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whose value can be used to estimate the DUT's extinction ratio (ERDUT ). The estimated and actual values can differ by a large amount, and the difference strongly depends on the extinction ratio of the light incident on the DUT. The most accurate estimates of ERDUT  are provided when the incident light's extinction ratio is orders of magnitude higher than ERDUT . This is discussed in the following two sections.

Convexlens

Aspherical lens

In general, the extinction ratio of light from most lasers is too low to be suitable for measuring the extinction ratios of highly polarizing DUTs, such as linear polarizers. In this case, a linear polarizer placed before the DUT (as shown in Figure 1) can improve the extinction ratio of the incident light. By the same principle, adding an additional linear polarizer at this location will further improve the extinction ratio. The transmission axes of the two polarizers should be aligned exactly parallel to obtain the highest extinction ratio.

Optical lenses

Cylindricallens

Spherical and aspherical lenses should be selected based on your application requirements, including optical performance, design complexity and cost considerations. Aspherical lenses offer higher precision while at the same time remaining an affordable solution for many general-purpose uses; on the contrary aspherical lenses tend to offer superior image quality than their spherical counterparts.

GRINlens

It can be difficult to accurately measure the values of Pmin , and errors in these measurements can have a substantial negative impact on the the value of ERest . Following some guidelines can provide the first steps to improving the accuracy of low-power-signal measurements. Note that an unpolarized source can also be used to measure the extinction ratio of a DUT.

is plotted as the blue curve in Figure 2. This equation assumes a single linear polarizer is placed between the source and DUT, and that the extinction ratio of the source is ERsource . The value of ERsource  is set to 1 when the source is unpolarized. The extinction ratio of this polarizer is ERref . If a set of polarizers is used instead, the value ERref  should be replaced with the set's effective extinction ratio. If there are no polarizers located between the source and the DUT, replace ERref  with a value of 1.

A sphere-shaped lens features an even curvature across its entire surface and is relatively inexpensive and easy to manufacture, aspherics being more so. However, Spherical lenses may suffer from an effect called Spherical Aberration which causes light rays passing through their edges not focusing correctly in comparison with those passing through its center; images produced can appear blurry due to this phenomenon using wider apertures or high magnification magnification levels.

Aspherical lenses work by controlling the direction that light rays pass through through a process known as refraction, similar to how spherical ones do, yet feature significant variations in surface curvature; their profiles tend to be more complex than spherical ones which typically feature uniform curvatures; as such they’re better at correcting aberrations (especially spherical) more effectively due to non-uniform surface curvatures; as such they focus light more precisely onto one focal point; correct aberrations while correct aberrations more effectively due to non-uniform surface curvatures as opposed to uniform curvatures featured by their counterparts spherical counterparts which feature uniform curvatures; they also focus light more efficiently onto one point when focused onto one point than traditional counterparts would allow.

Refraction occurs when light rays pass through spherical lenses which bend them as they pass. Their basic principle lies within their circular design: light entering such lenses interact with its curvilinear surface, leading them either towards convergence (convex lenses) or divergence (concave lenses).

Consider all requirements of your application when choosing lenses, including image quality, field of view requirements, compactness of lens design and cost. Aspheric lenses tend to perform better for applications involving aberrations; spherical ones might suffice if less demanding or cost-conscious applications exist.

The extinction ratio of an optical component under test (DUT) can be measured using light from a laser or other linearly polarized source, but it is often necessary to insert a linear polarizer between the source and the DUT. The linear polarizer is needed when the light from the source has an extinction ratio that is not significantly higher than the extinction ratio of the DUT, which is frequently the case. Obtaining an accurate measurement of the DUT's extinction ratio requires the incident light's extinction ratio to be substantially higher than the DUT's. Inserting one or more linear polarizers between the source and the DUT is one way to improve the extinction ratio of the light incident on the DUT.

Estimating the Extinction Ratio of the DUTIt is important to note that this approach estimates the absolute extinction ratio of the DUT, rather than the extinction ratio of the light.

In display technologies such as projectors and augmented reality displays, the choice between spherical and aspheric lenses can impact image quality and device compactness. Aspheric lenses help in producing uniform and high-quality images across the entire display surface, while spherical lenses might be used in more cost-effective solutions where high precision is not as important.

The longevity and upkeep of optical systems are important factors when choosing between spherical and aspheric lenses. Each type offers different maintenance challenges and durability characteristics.

Both spherical and aspheric lenses play significant roles in consumer electronics, each bringing distinct advantages to various devices.

In terms of replacement and repair, spherical lenses offer more straightforward solutions. Their widespread use and simpler design mean that replacements are generally more readily available and less expensive. Aspheric lenses, due to their specialized nature, might involve longer lead times for replacements and higher costs, especially if custom designs are required.