Holographic gratings can also be made from computer-generated interference patterns. The patterns are written onto a chrome mask using an electron-beam machine. The patterns on the mask are then etched into a material, such as fused silica, using photolithographic masking and etching techniques. "Computer-generated gratings have really just reached maturity within the last two years," says Michael Feldman, of Digital Optics Corp. (Charlotte, NC). "They are very flexible and easy to mass-produce."

Kaiser Optical Systems Inc. (KOSI; Ann Arbor, MI), has developed an alternative to the classical or surface-relief holographic grating--the volume transmission holographic grating (see photo at top of this page; also Laser Focus World, Oct. 1995, p. 95). The grating is created in the traditional manner by recording interference patterns generated by two mutually coherent laser beams. After the pattern is defined in the photosensitive material, coated on glass, and the film developed, a top layer of glass is added, creating a totally transparent grating assembly. Light strikes the grating on one side and diffracts out through the other.

Lenticularlens

Aspherical lenses offer many advantages over traditional spherical lenses, such as a more natural field of view and thinner and lighter designs. However, aspherical lenses also have some disadvantages, including:

Optical lenses

Precision hot pressing is a highly precise manufacturing method that enables the mass production of aspheric lenses with exceptional accuracy and surface quality. By placing the lens material into a heated metal mold and applying high pressure at elevated temperatures, this technique allows for complete control over the shape and surface quality of the resulting lenses.

This article shows basic knowledge about aspheric lens and we hope it can not only offer you a complete explanation about what is a aspheric lens, but also give you some inspiration about its benefits and applications.

In short, an aspheric lens is a lens that provides higher-quality imaging. They adjust curvature and shape to correct problems such as spherical aberration, distortion, and peripheral astigmatism and have the advantages of greater precision, larger aperture, and improved efficiency. Due to its wide range of applications, aspheric lenses will be more and more widely used in the future.

Fiber Bragg gratings, another recent development in grating applications, are made within a fiberoptic cable. Fiber gratings are fabricated by exposing the core of a single-mode fiber, 8 to 10 µm thick, to a periodic pattern of intense ultraviolet light. This pattern is created when a 248- or 193-nm laser passes through a special diffractive phase mask. When a fiber is placed in the intense UV light pattern of the mask, a permanent modulation of the index of refraction is generated in the fiber core. This photo-generated index modulation acts as a grating.

Due to its high-precision imaging and targeted design, aspheric lenses are widely used in many application fields. Some of these application areas include:

Aspheric lenses have a more complex surface shape, are more susceptible to contamination and damage, and may require more frequent cleaning and maintenance.

Aspheric lenses require more precise measurements and positioning, thus requiring more skilled operators during fabrication, installation, and adjustment.

aspheric lenses中文

Commercial surface-relief gratings are produced using an epoxy casting replication process developed in the mid-1900s. The process involves pouring a liquid into a mold, allowing the liquid to harden, and then removing the hardened material from the mold without damaging either. The replication process yields a grating that is an optically identical copy of the original. The two basic types of grating masters are ruled and interference.

The concept of diffraction gratings is simple, yet elegant. For more than one hundred years, they have been used in dispersive optical systems. Applications for gratings are expanding as the fabrication technology grows. Fields as diverse as telecommunications, astronomy, microlithography, lasers, and metal analysis are driving these changes.

Aspheric lenses are unique lenses that have a non-spherical curvature. They are widely used because they can provide higher-quality imaging effects when compared with traditional spherical lenses. In this article by Noni, we will introduce what are aspheric lenses from their basic definition, compare them to spherical lenses, explain their working principles, and processing methods, list their advantages and disadvantages, and highlight their applications.

"The grooves are similar to the indentations made by a plow in soil," says John Hoose of Richardson Grating Laboratory (Rochester, NY), except that they are much closer together. Anywhere from one to 10,000 fine parallel lines per millimeter can be engraved. Light waves diffracted from these lines interfere, and all wavelengths but one are canceled in any particular direction through destructive interference. The depth of the groove changes the wavelength of the light wave being diffracted.

GRINlens

Holoplexing, a technique devised by KOSI in which two gratings are placed together in the same structure to cover multiple spectral ranges at one time, is useful for imaging on charge-coupled-device (CCD) cameras for broadband applications. Holographic transmission gratings are also used in Raman spectroscopy and for pulse compression in ultrafast lasers.

Since aspheric lenses can freely adjust their curvature as needed, they can add relatively larger apertures while maintaining high imaging quality. This means that aspherical lenses can provide a larger field of view and a wider field of view in a smaller size, making them particularly suitable for photography and video applications that require high resolution.

Conventional lenses also produce distortion in the peripheral region. This is due to the shape of the lens limiting how much light can be bent. In contrast, aspheric lenses can freely adjust the curvature as needed, thereby eliminating distortion.

An advantage of a transmission volume grating is its relative insensitivity to angle, says James Arns of KOSI. A Bragg-type structure follows the classical grating equation concerning image position but with the added ability to adjust the intensity profile over a range of wavelengths. To describe the capability, Arns compares a Venetian blind to lines painted on a window. When the blind is positioned with the slats horizontal, it diffracts light in the same way as the painted lines or a surface-relief grating. When the slats are angled, the element of depth is added to how the light is diffracted. Because of this added dimension, the grating efficiency can be adjusted over the wavelength bandwidth to favor one side or the other. Also, the low sensitivity to incidence angle means the grating can be angularly tuned without influencing the image position.

Spherical lenses produce spherical aberration in the peripheral region. This means that when light rays pass through the lens, they will be focused on different points due to different angles and positions, resulting in image distortion. Aspherical lenses can correct spherical aberration through complex curves, thus providing more accurate imaging effects.

Aspherical lenses can be freely adjusted in curvature and shape as required, allowing them to provide higher optical efficiency. This makes them the preferred choice in many application areas, such as laser systems, lighting systems, and optical sensors.

An aspheric lens is a type of lens that differs from the traditional spherical or cylindrical shape. It boasts complex and asymmetrical curves that allow it to correct common lens problems like distortion, peripheral astigmatism, and spherical aberration.

For the case where customized aspheric lenses are required, factors such as development cost, sample cost, batch price, and delivery cycle also need to be considered.

Aspheric lenses, on the other hand, can be manufactured in a variety of curvatures as needed, so problems such as spherical aberration, distortion, and peripheral astigmatism can be better corrected, making them better adaptable to various imaging needs.

Aspheric lenses are designed to better correct spherical distortion, but they are also prone to other types of optical distortion, such as lateral astigmatism and longitudinal astigmatism.

Grating applicationsLight incident on a diffraction grating is dispersed away from the grating surface at an angle dependent on its wavelength, allowing a grating to be used to select a narrow spectral band from a much wider band. This ability of a grating is particularly useful for laser tuning, especially in the visible region of the spectrum. Two primary configurations for selecting a narrow wavelength are Littrow and Littman. In the Littrow configuration, the wavelength of interest diffracts at exactly the same angle as the light incident on the grating. Littrow tuning is done either with fine-pitch first-order gratings (typically 1800 or 2400 grooves/mm, either ruled or holographic) or a coarser grating used in higher orders. The alternative approach is to use the grating in a fixed grazing incidence mode together with a rotating reflecting mirror. Pairs of diffraction gratings can also be used to compress or stretch a laser pulse. When a spectrally broad laser pulse is incident on a diffraction grating, the various wavelengths that make up the pulse will diffract from the grating at angles determined by those wavelengths. If the pulse is chirped so that the frequency changes linearly during the length of the pulse, then diffraction will spread the pulse out across the second grating. When the light diffracts from the second grating, which is oriented parallel to the first grating, the different parts of the pulse will diffract at angles that yield a pulse whose parts are synchronized. This increases the peak power while the total energy remains the same. Pulse compression uses two gratings with the same groove frequency and efficiencies peaked for the polarization and wavelength of the laser. If the gratings are arranged in a nonparallel arrangement, a pulse can be stretched. Pulse stretching uses two identical gratings, allowing lower peak power to be transmitted through the laser system and increasing the amount of stored energy that can be extracted. Since the invention of the replication technique, diffraction gratings have replaced prisms in many commercial spectrometers. A prism will bend short wavelengths more than longer ones (see Laser Focus World, Jan. 1997, p. 101). Prisms that transmit visible light absorb most UV and infrared wavelengths, whereas reflection gratings can be suitably coated for high reflectivity in wide spectral regions. Gratings are considered superior to prisms in many applications. Seeking to combine the best of both, Richardson Grating Laboratory has fabricated a "grism," a part-grating, part-prism optical element useful in spectrometers that require in-line presentation of the spectrum, as in astronomy. The light diffracted by the grating is bent back in line by the refracting effect of the prism. The dispersion of the grism is not linear, because the dispersive effects of the prism and grating are superimposed.New fabrication techniquesKaiser Optical Systems Inc. (KOSI; Ann Arbor, MI), has developed an alternative to the classical or surface-relief holographic grating--the volume transmission holographic grating (see photo at top of this page; also Laser Focus World, Oct. 1995, p. 95). The grating is created in the traditional manner by recording interference patterns generated by two mutually coherent laser beams. After the pattern is defined in the photosensitive material, coated on glass, and the film developed, a top layer of glass is added, creating a totally transparent grating assembly. Light strikes the grating on one side and diffracts out through the other.An advantage of a transmission volume grating is its relative insensitivity to angle, says James Arns of KOSI. A Bragg-type structure follows the classical grating equation concerning image position but with the added ability to adjust the intensity profile over a range of wavelengths. To describe the capability, Arns compares a Venetian blind to lines painted on a window. When the blind is positioned with the slats horizontal, it diffracts light in the same way as the painted lines or a surface-relief grating. When the slats are angled, the element of depth is added to how the light is diffracted. Because of this added dimension, the grating efficiency can be adjusted over the wavelength bandwidth to favor one side or the other. Also, the low sensitivity to incidence angle means the grating can be angularly tuned without influencing the image position."It also has a high efficiency," says Arns. "Depending on the configuration, the grating can produce 90% efficiency in the first order. If the thickness or the frequency of the grating is high enough, higher orders that otherwise might be propagated are extinguished." Another advantage, says Arns, is that the element can be handled and cleaned in the same fashion as a high-quality cemented lens because the grating is sandwiched between two layers of glass. Also, because the Bragg-type grating is a transmission device, optical elements and instruments can be brought close to it, resulting in a compact design.Holoplexing, a technique devised by KOSI in which two gratings are placed together in the same structure to cover multiple spectral ranges at one time, is useful for imaging on charge-coupled-device (CCD) cameras for broadband applications. Holographic transmission gratings are also used in Raman spectroscopy and for pulse compression in ultrafast lasers.Holographic gratings can also be made from computer-generated interference patterns. The patterns are written onto a chrome mask using an electron-beam machine. The patterns on the mask are then etched into a material, such as fused silica, using photolithographic masking and etching techniques. "Computer-generated gratings have really just reached maturity within the last two years," says Michael Feldman, of Digital Optics Corp. (Charlotte, NC). "They are very flexible and easy to mass-produce." Their versatility offers many advantages. "Ruled and holographic gratings are limited to relatively simple structures by the fabrication methods that are used," says W. Hudson Welch, also of Digital Optics. "The flexibility provided by computer-generated gratings allows the creation of essentially arbitrary grating patterns."Fiber gratingsFiber Bragg gratings, another recent development in grating applications, are made within a fiberoptic cable. Fiber gratings are fabricated by exposing the core of a single-mode fiber, 8 to 10 µm thick, to a periodic pattern of intense ultraviolet light. This pattern is created when a 248- or 193-nm laser passes through a special diffractive phase mask. When a fiber is placed in the intense UV light pattern of the mask, a permanent modulation of the index of refraction is generated in the fiber core. This photo-generated index modulation acts as a grating. Light traveling along the fiber core impinges on the grating, and each area of different refractive index scatters a small portion of the beam. If the wavelength of the signal is twice the distance between the periodic refractive elements (typically <1 µm), then the signals scattered back down the fiber core will add constructively to give a large reflection. The wavelength at which the reflection occurs is the Bragg wavelength. A Bragg grating can operate at precise wavelengths that can be accurately preset and maintained, says Keith Brundin at 3M Specialty Optical Fibers (West Haven, CT).There are also long-period fiber gratings that have index modulations with periods of hundreds of microns (see Laser Focus World, June 1996, p. 293). Instead of producing a reflected signal, these gratings create a phase-matching, or Bragg, condition that couples a forward-traveling signal into forward-traveling cladding modes. The signals coupled into the cladding are absorbed by the coating, creating a loss. Long-period gratings thus act as wavelength-selective absorption filters and are used in wavelength-division-multiplexing networks and in gain-shaping filters for rare-earth-doped fiber amplifiers. Fiber Bragg gratings have been commercially available only since 1995. They are becoming increasingly popular in telecommunications and the laser industry for such applications as external reflectors for stabilizing semiconductor lasers (see Fig. 4) and single- frequency fiber lasers.

Diffraction gratings are fundamental optical elements that have a precise pattern of grooves superimposed on them. These minute, periodic structures diffract, or disperse, incident light in such a way that the individual wavelengths making up the incident light can be differentiated. Gratings are indispensable in helping physicists determine the structure of atoms or helping astronomers calculate the chemical composition of stars and the rotation of galaxies. Applications are expanding; one of the fastest growing areas for gratings—laser pulse compression—didn’t even exist until a few years ago.

If have particular specifications for aspheric lens or other optics in customization, or you need support in the R&D and manufacturing of tailored optics of higher accuracy and special sizes for your projects or applications, Noni is ready to be a reliable helper with our custom abilities to exceed your expectations via the one-package solution.

We provide off-axis paraboloid, ellipsoid, hyperboloid, and other aspheric lenses. At the same time, we can also provide aspheric lenses of various infrared materials, such as germanium, zinc selenide, zinc sulfide, and more.

Optical aspheric replication molding technology is a cost-effective and efficient method for manufacturing high-quality aspheric lenses. This technique involves transferring the surface of a master mold onto a base, resulting in the transformation of a spherical surface into an aspherical one. Unlike other aspheric surface processing methods, this technology requires minimal equipment and eliminates the need for substrate polishing, making it ideal for the mass production of sub-mirrors with identical specifications or spliced mirror surfaces.

Our use of aspheric grinding CNC machine tools to produce lenses results in larger sizes, improved surface quality, and better maintenance of the M-square value of the input beam when compared to corresponding molded aspheric lenses. This technology is particularly suitable for small-batch production and product prototype manufacturing, thereby meeting the needs of diverse industries.

The radius of curvature varies everywhere on one of the surfaces with a height from the optical axis to minimize spherical aberration. The other side is convex or flat.

Joseph Fraunhofer first used diffraction gratings in 1819 to observe the spectrum of the sun. Earliest devices were multiple-slit assemblies, consisting of a grid of fine wire or thread wound about and extending between two parallel screws, which served as spacers. A wavefront that passed through the system was confronted by alternate opaque and transparent regions, so that it underwent a modulation in amplitude.

Since the invention of the replication technique, diffraction gratings have replaced prisms in many commercial spectrometers. A prism will bend short wavelengths more than longer ones (see Laser Focus World, Jan. 1997, p. 101). Prisms that transmit visible light absorb most UV and infrared wavelengths, whereas reflection gratings can be suitably coated for high reflectivity in wide spectral regions. Gratings are considered superior to prisms in many applications. Seeking to combine the best of both, Richardson Grating Laboratory has fabricated a "grism," a part-grating, part-prism optical element useful in spectrometers that require in-line presentation of the spectrum, as in astronomy. The light diffracted by the grating is bent back in line by the refracting effect of the prism. The dispersion of the grism is not linear, because the dispersive effects of the prism and grating are superimposed.

Aspheric lenses provide higher-quality imaging and are correct for issues such as spherical aberration, distortion, and peripheral astigmatism. This makes them particularly suitable for applications requiring high-precision imaging, such as astronomy, medicine, and industry.

Aspheric lens CNC grinding is a highly precise processing method that utilizes CNC machine tools to cut and process aspheric lenses from bulk materials, producing lenses with exceptional shape and surface quality. This technique is widely employed in modern optical manufacturing due to its ability to produce high-precision aspheric lenses.

Noni is a leading custom optics production and development company with extensive experience in the industry of optical components and systems. Since our establishment in 2014, we have been committed to providing exceptional services to our clients worldwide. Our team comprises experts who have been in the optics field since 2008, ensuring that we deliver top-quality products and reliable services to meet our client’s diverse needs.

There are also long-period fiber gratings that have index modulations with periods of hundreds of microns (see Laser Focus World, June 1996, p. 293). Instead of producing a reflected signal, these gratings create a phase-matching, or Bragg, condition that couples a forward-traveling signal into forward-traveling cladding modes. The signals coupled into the cladding are absorbed by the coating, creating a loss. Long-period gratings thus act as wavelength-selective absorption filters and are used in wavelength-division-multiplexing networks and in gain-shaping filters for rare-earth-doped fiber amplifiers.

Due to their complex design and manufacturing process, aspheric lenses are usually more expensive than traditional spherical lenses.

Aspherical lens

The author wishes to thank John Hoose of Richardson Grating Laboratory (Rochester, NY) for his help in preparing this article.

"It also has a high efficiency," says Arns. "Depending on the configuration, the grating can produce 90% efficiency in the first order. If the thickness or the frequency of the grating is high enough, higher orders that otherwise might be propagated are extinguished." Another advantage, says Arns, is that the element can be handled and cleaned in the same fashion as a high-quality cemented lens because the grating is sandwiched between two layers of glass. Also, because the Bragg-type grating is a transmission device, optical elements and instruments can be brought close to it, resulting in a compact design.

Light traveling along the fiber core impinges on the grating, and each area of different refractive index scatters a small portion of the beam. If the wavelength of the signal is twice the distance between the periodic refractive elements (typically <1 µm), then the signals scattered back down the fiber core will add constructively to give a large reflection. The wavelength at which the reflection occurs is the Bragg wavelength. A Bragg grating can operate at precise wavelengths that can be accurately preset and maintained, says Keith Brundin at 3M Specialty Optical Fibers (West Haven, CT).

Light incident on a diffraction grating is dispersed away from the grating surface at an angle dependent on its wavelength, allowing a grating to be used to select a narrow spectral band from a much wider band. This ability of a grating is particularly useful for laser tuning, especially in the visible region of the spectrum. Two primary configurations for selecting a narrow wavelength are Littrow and Littman. In the Littrow configuration, the wavelength of interest diffracts at exactly the same angle as the light incident on the grating. Littrow tuning is done either with fine-pitch first-order gratings (typically 1800 or 2400 grooves/mm, either ruled or holographic) or a coarser grating used in higher orders. The alternative approach is to use the grating in a fixed grazing incidence mode together with a rotating reflecting mirror.

Pairs of diffraction gratings can also be used to compress or stretch a laser pulse. When a spectrally broad laser pulse is incident on a diffraction grating, the various wavelengths that make up the pulse will diffract from the grating at angles determined by those wavelengths. If the pulse is chirped so that the frequency changes linearly during the length of the pulse, then diffraction will spread the pulse out across the second grating. When the light diffracts from the second grating, which is oriented parallel to the first grating, the different parts of the pulse will diffract at angles that yield a pulse whose parts are synchronized. This increases the peak power while the total energy remains the same. Pulse compression uses two gratings with the same groove frequency and efficiencies peaked for the polarization and wavelength of the laser.

Convexlens

If the gratings are arranged in a nonparallel arrangement, a pulse can be stretched. Pulse stretching uses two identical gratings, allowing lower peak power to be transmitted through the laser system and increasing the amount of stored energy that can be extracted.

Astronomy is one of the most widely used fields of aspheric lenses. Telescopes and astronomical telescopes require high-precision imaging to observe galaxies and stars, and aspheric lenses can correct spherical aberration and distortion to provide higher-quality imaging.

In 1882, Henry A. Rowland invented the process of ruling, or scratching parallel notches into metal deposited onto the surface of a flat, clear glass plate—a method that produced gratings of exceptionally high quality. Modern ruled gratings can be either reflective or transmissive and are fabricated with a single diamond point that burnishes grooves on flat or concave surfaces.

The greatest advantage of precision hot pressing is its ability to produce high-precision and smooth-surfaced aspheric lenses with sub-micron-level accuracy. Although the use of high-precision metal molds and materials that can withstand high temperatures and pressure may result in higher production costs. Furthermore, this method is ideal for producing relatively simple aspheric lenses due to the simplicity of their shapes.

When selecting an aspheric lens, it is necessary to consider aspheric lenses’ advantages and disadvantages to determine which lens is most suitable for a specific application.  Based on our experience of decades, the key factors into consideration include volume, quality, and cost.  Here, you can check the requirements for different types of lenses as follows:

Cylindricallens

Medical imaging also requires high-precision imaging to ensure accurate diagnosis and treatment. Aspherical lenses are widely used in the field of medical imaging, such as intraocular lenses in eye surgery, X-ray imaging systems, and MRI machines.

CNC grinding technology achieves sub-micron level precision in lens manufacturing and allows for more complex designs of aspheric lenses. Additionally, it provides higher production efficiency and superior surface quality compared to other methods, reducing production costs while enhancing lens performance.

Mainly used in projectors, amplifiers, spotlights, and other projection and lighting fields. Two condenser lenses of the same focal length can be combined to form a system with half the focal length of a single lens. Primarily used in high-efficiency illumination systems, aspheric condensers feature excellent aberration correction.

Peripheral astigmatism is a common lens problem that produces bright or dark spots in the peripheral areas. This is due to the shape of the lens so that light is scattered in different directions. Aspherical lenses can eliminate marginal astigmatism by adjusting the curvature, thereby improving imaging.

Spherical lenses have the same curvature, while aspheric lenses have different curvatures. Due to the fixed surface curvature of spherical lenses, they only provide the best image quality in certain situations. Specifically, spherical lenses provide optimal imaging when the object is located at the infinity of the spherical lens.

Their versatility offers many advantages. "Ruled and holographic gratings are limited to relatively simple structures by the fabrication methods that are used," says W. Hudson Welch, also of Digital Optics. "The flexibility provided by computer-generated gratings allows the creation of essentially arbitrary grating patterns."

Fresnellens

Both spherical and aspheric lenses are common lens types, and the main difference between them is the curvature of the lens.

While optical aspheric surface replication molding technology can achieve high precision and excellent surface quality, it may have limitations in terms of replication accuracy and surface quality. Therefore, it may not be suitable for all types of aspheric lens manufacturing needs. Nonetheless, when used appropriately, this technology serves as a valuable solution for various industries seeking to produce high-quality aspheric lenses efficiently and cost-effectively.

Aspheric lenses have several advantages over conventional lenses, including improved accuracy in the light collection and the ability to eliminate spherical chromatic aberration. Additionally, they have a simple structure that can replace multi-lens systems, reducing weight, volume, and cost. Unlike traditional lenses, aspheric lenses have varying radii of curvature from the center to the surface’s edge. This unique feature enables them to eliminate errors that standard lenses cannot.

spheric lenses are commonly used in a variety of optical systems to reduce aberrations and improve image quality. Here are some additional types of aspheric lenses:

These lenses can focus light at short focal lengths that cannot be achieved with spherical lenses. Generally, it is made of B270-ultra-clear glass, so it is convenient to realize the manufacture of complex surfaces that are not easy to grind. The design condition of this type of lens is infinity conjugate, and the design wavelength is 587.6nm (yellow helium line). Condenser lenses concentrate light into a projection beam.

The industrial field also requires high-precision imaging to ensure product quality and efficiency. Aspheric lenses can provide more accurate imaging in applications such as automated manufacturing, machine vision, and laser imaging, thereby increasing production efficiency and reducing costs.

The use of aspheric lenses has two major advantages: one is to improve the imaging quality of the entire optical system; the other is to reduce the weight and size of the finished product. Advantages include a reduced number of back reflections that occur in the system resulting in higher total light transmission, reduced system heating when some kilowatt-level high power light is transmitted, advanced process technology reduces damage to subsurface layers, the spherical surface is precisely polished to improve the collimation accuracy.