Abstract: An objective lens is provided with plural optical functional regions including an inside optical functional region, an outside optical functional region and an intermediate optical functional region provided between the inside and outside optical functional regions. The absolute value of an amount of a spherical aberration of a light flux coming to the second optical information recording medium after having passed through the intermediate optical functional region is made larger than that of an amount of a spherical aberration of a light flux coming to the second optical information recording medium after having passed through the inside optical functional region when recording and/or reproducing information is conducted for the second optical information recording medium.

Abstract: An objective lens includes a first lens unit with positive refracting power and a second lens unit on the specimen side of the first lens unit. The first lens unit has at least one lens and the second lens unit has at least one optical element, satisfying the following conditions: v dLD > v dHD ⁢ - 0.56 ≦ φ II ⁢ / φ T ≦ 0.56 where &ngr;dLD is the Abbe's number of glass material of the lens, &ngr;dHD is the Abbe's number of glass material of the optical element, &phgr;II{circle around (1)} is the refracting power of a first surface of the second lens unit, and &phgr;T is the refracting power of the entire system of the objective lens.

Abstract: A formed lens produced by pressing an optical material so as to shape a predetermined configuration, has an optical surface having a light entrance side, a light exit side and an optical axis. When a normal line angle is defined as an angle formed between the optical axis and a normal line at an arbitrary point on the optical surface, the maximum normal angle is 60° to 90° and an intersection at which the maximum normal line forming the maximum normal line angle intersects with the optical axis is located at the light exit side from the point of the maximum normal line on the optical surface, and Abbe's number &ngr;d of the optical material is 60 or more.

Abstract: An objective light converging element for use in an optical pickup device and used to converge a light flux having a reference wavelength &lgr; (380 nm≦&lgr;0≦450 nm) emitted from a light source onto an information recording plane of an optical information recording medium equipped with a protective substrate having a thickness of 0.6 mm, has a lens structural section to refract a light flux emitted from the light source; and a ring-shaped diffractive structural section having an optical axis on a center and to diffract a light flux emitted from the light source.

Abstract: A low-cost bright image-pick up lens of a small size is provided which is short in total length, wherein the angle of field is beyond 30°; the angle of incidence onto the image pickup device is narrowed; and various aberrations are appropriately corrected. The image-pick up lens comprises, from the side of an object, an aperture stop, a biconvex positive lens, and a meniscus lens having a concave surface on the object side, and each of the lenses includes at least one aspheric surface.

Abstract: An optical pickup objective lens capable of correcting the spherical aberration effectively for a DVD and a CD while achieving downsizing and reduction of the costs is provided. The objective lens is divided into two types of lens portions, a DVD/CD common lens portion and a DVD-specific lens portion, which are different in contour. The surfaces of the incident side and the outgoing side of both lens portions are aspherical in shape. The aspherical shape of the incident surface of the DVD/CD common lens portion differs from that of the DVD-specific lens portion, and the joint portion therebetween is discontinuous. Likewise, the aspherical shape of the outgoing surface of the DVD/CD common lens portion differs from that of the DVD-specific lens portion, and the joint portion therebetween is also discontinuous.

Abstract: An optical pickup apparatus for at least two kinds of optical information recording media, comprises a first light source; a second light source; an optical converging system; and a photo detector. An optical element of the optical converging system comprises a first region including an optical axis and a second region adjoining the first region and locating at the outside of the first region, the first region is a refractive surface and the second region is a diffractive surface. When a first light flux passes through the second region, the light amount of n-th order diffracted ray of the first light flux is larger than that of any other order diffracted ray of the first light flux, and when a second light flux passes through the second region of the optical element, the light amount of n-th order diffracted ray of the second light flux is larger than that of any other order diffracted ray of the second light flux, where n is an integer except 0.

Abstract: When the DVD provided with the DVD substrate 2 having thickness t2of 0.6 mm is installed in the optical disc apparatus, the light beam 4 having wavelength &lgr;1=655 nm is used as luminous flux of numerical aperture NA=0.63 to be condensed on the information surface 2a on the DVD substrate 2. When the CD provided with the CD substrate 3 having thickness t2 of 1.2 mm is installed in the optical disc apparatus, the light beam 5 having wavelength &lgr;2=790 nm is effectively used as luminous flux of approximate numerical aperture NA=0.45 to be condensed on the information surface 3a on the DVD substrate 3. The wavefront aberration caused by a thickness difference between the DVD substrate 2 and CD substrate 3 is canceled out by the chromatic aberration caused by a wavelength difference between the light beams 4 and 5. Therefore, in spite of the difference in the transparent substrates, the light beams are suitably condensed respectively on the information surface 2a and 3a.

Abstract: The present invention is concerned with an objective lens for an optical pickup, which is made up by a single lens of a meniscus structure, and which includes, looking sequentially from a light source side, a first surface S1 formed by an aspherical surface, having a positive refractive power, and a second surface S2, formed by an aspherical surface, having a negative refractive power, with the numerical aperture (NA) of the lens being not less than 0.8.

Abstract: An image pickup lens system includes a lens 1 of a meniscus shape having a first face as a convex face, and a diaphragm 2 disposed on an object side of the lens 1. The lens 1 meets the following conditions: Y′/fl equal to or larger than 0.6; Dt/Dc is equal to or smaller than 0.9 and equal to or larger than 0.5; and Ap2/Am2 is equal to or larger than 0.9. Thus, even when an image pickup element is of a reduced size, a desired optical performance can be maintained, and it is possible to produce a lens easily with a back focal length ensured.

Abstract: It is to provide an objective lens for being provided in an optical pickup device for firmly carrying out the reproduction/record for each of a plurality of optical information storing media in which the protect substrates have different thicknesses from each other. The optical functional surface of the optical lens is divided into the central region including the optical axis and the peripheral region arranged outside the central region. The diffractive structure is provided on the peripheral region. When the reproduction and/or the record is carried out for the first optical information storing medium, the diffracted light is condensed on the focal point.

Abstract: An objective lens for an optical pickup has a single lens element. One surface of the objective lens is divided into a central area and a peripheral area, and a step providing a level difference along a direction of the optical axis is formed at a boundary therebetween. The step provides a phase shift between light passing through the central area and the peripheral area. The level difference is formed such that a thickness on the peripheral area side is greater than a thickness on the central area side at the boundary.

Abstract: An objective lens for recording and/or reproducing information of an optical information recording medium, comprises a first lens group having a positive refractive power; and a second lens group having a positive refractive power. The first and second lens groups are arranged in this order from a light source side of the objective lens and are made of a plastic material respectively; and the following formula is satisfied: NA>0.85 where NA is a necessary image side numerical aperture for recording or reproducing information of the optical information recording medium.

Abstract: An objective lens and optical pickup device that uses it is disclosed having an optical diffraction surface on its surface nearest a light source which may be switched in wavelength for either CD or DVD recording/replaying. The optical diffraction surface causes a selected wavelength beam to converge or diverge more than the other wavelength beam. Superimposed in a peripheral region of the diffraction grating is a step change in height (higher or lower) which causes destructive interference for light in the peripheral region for only one of the beams. In this way, an objective lens is provided that, with a simple and compact structure, enables a light beam to be converged accurately into a spot on a selected recording medium, despite the need to have the converged beam have different wavelengths and numerical apertures, depending on the recording medium used.

Abstract: An optical pickup apparatus having an objective lens which is formed of a single lens such that the maximum slope angle of a surface of the lens is less than 55° with respect to a high NA of 0.7 or more. The objective lens can be manufactured to satisfy a condition of allowance in optical aberration and have a high NA of 0.7 or more unlike a typical objective lens formed of a single lens. Also, the optical pickup apparatus adopting the objective lens can be used for high density recording and reproduction and provide a reduced volume, a simple structure, and/or a low price. Also, since the optical pickup apparatus adopting the objective lens has a very short working distance, the first reflection surface recording method can be adopted. Accordingly, the thickness of the optical pickup apparatus can be manufactured as thin as a protective layer of a typical recording medium.

Abstract: An objective lens for converging two wavelengths of light to their predetermined positions is constituted by two or three lenses. Respective materials for forming adjacent lenses are chosen such that the respective refractive indices of adjacent lenses substantially equal each other with respect to only one of the two wavelengths of light, whereas the form of each lens surface is configured so as to suppress aberration in the objective lens as a whole.

Abstract: An objective for an optical disk is made of a single double-sided aspherical lens having a numerical aperture (NA) equal to or greater than 0.75 and capable of minimizing axial aberration, off-axis aberration, surface-to-surface eccentricity aberration, and chromatic aberration. The objective (11) has a first aspherical surface (1). The vertex of the first surface has a radius of curvature R1 defined as follows: 0.95·A<R1<1.05·A A=B/C B=0.85f(n−1) C=n (0.60866−0.11·t/f−0.1272·d/f)(0.83+0.2·NA) where n is a refractive index of the lens, f is a focal length of the lens, t is a thickness along optical axis through the center of the lens and d is the thickness of a transmission layer of the optical disk.

Abstract: An optical pickup apparatus for first and second optical information recording medium, comprises first and second light sources to emit first and second light flux; a single objective lens made and a diaphragm having an aperture. The pitch of a plurality of ring-shaped diffractive zones provided on the objective lens, becomes gradually small from the optical axis to a point h and the pitch increases at the point h. At the time of conducting recording or reproducing information of the second optical information recording medium, the second light flux has a spherical aberration discontinuous portion at the point h where a spherical aberration-stepped amount is 7 &mgr;m to 40 &mgr;m, and a spherical aberration of a light ray of the second light flux having passed through the outermost portion of the aperture of the diaphragm is 7 &mgr;m to 40 &mgr;m.

Abstract: An objective lens is provided with plural optical functional regions including an inside optical functional region, an outside optical functional region and an intermediate optical functional region provided between the inside and outside optical functional regions. The absolute value of an amount of a spherical aberration of a light flux coming to the second optical information recording medium after having passed through the intermediate optical functional region is made larger than that of an amount of a spherical aberration of a light flux coming to the second optical information recording medium after having passed through the inside optical functional region when recording and/or reproducing information is conducted for the second optical information recording medium.

Abstract: The present invention provides an improved optical reading and recording system utilizing optical system employing an aspherical solid immersion lens (SIL). The improved optical system has an aspherical SIL between an objective lens and the recording media. The aspherical SIL reduces the focused electromagnetic radiation beam spot size by providing an increased numeric aperture (NA) of the optical system. The aspherical surface of the SIL provide greater manufacturing and operating tolerances between the objective lens and the aspherical SIL. Greater manufacturing tolerances provide an easier to manufacture optical system. Increased ease of manufacture reduces the cost of optical systems.

Abstract: An objective for an optical disk is made of a single double-sided aspherical lens having a numerical aperture (NA) equal to or greater than 0.75 and capable of minimizing axial aberration, off-axis aberration, surface-to-surface eccentricity aberration, and chromatic aberration.

Abstract: An objective lens unit used for an optical pickup device is made up of a plurality of lenses and has a numerical aperture (NA) not less than 0.7. The lenses (1) and (2) are secured within a cylindrically-shaped lens holder (3). The position of the lens(es) (2) other than one of the lenses secured within the lens holder is set with the position of the one lens (1) as reference.

Abstract: An objective lens system for optical pickups performing at least one of reading and writing of information by condensing a luminous flux from a light source on an information recording medium, has the following two lens elements from a light source side: a first lens element having a first surface convex to the light source side and a second surface convex to the light source side; and a second lens element having a third surface convex to the light source side and a plane fourth surface, wherein the first surface is an aspherical surface.

Abstract: An objective lens unit for an optical pickup used for recording and/or reproducing information signals fr an optical disc. The objective lens unit includes a resin layer (21) having, sequentially from an object side, a first surface S1 as an aspherical surface and a second surface S2 as an aspherical surface, at least one of the first surface and the second surface including a diffractive surface, and a lens of glass (22) having the second surface S2 as an aspherical surface and a third surface S3 as an aspherical surface. The lens unit is corrected for the chromatic aberration on an image surface on the optical axis with respect to the light of a reference wavelength not larger than 420 nm within several nm of the reference wavelength, with the numerical aperture of the lens unit being not less than 0.8. This objective lens unit is able to converge the laser light to close to the limit of diffraction on the image surface.

Abstract: A device is obtained for converting the intensity distribution of a laser beam in particular into an intensity distribution which falls constantly along an axis from one side to the other in that a homogenizer (10), which mutually superimposes the sub-beams of the laser beam such that when a laser beam with a specific intensity distribution passes through the homogenizer, a homogenization of the intensity distribution of the laser beam is promoted, is combined with at least one inverter (24, 26) which inverts the intensity distribution of a sub-region, in particular a sub-beam or a plurality of adjacent sub-beams, along at least one axis along which the intensity is to be converted. The extent of the fall in intensity from one side to the other can be controlled by means of the number of the inverters.

Abstract: An optical element has diffractive grooves. Each diffractive groove includes a first surface approximated by a predetermined optical function; a second surface extending in a direction to cross the first surface and being parallel to the optical axis; and a third surface to connect the first surface and the second surface. A width of the third surface in the direction perpendicular to the optical axis is 0.5% to 15% of the sum of a width of the first surface in the direction perpendicular to the optical axis and the width of the third surface in the direction perpendicular to the optical axis.

Abstract: A single lens that has a small spot size across a large field of view and a small height. The lens has a first surface for performing color correction functions and a second surface for primarily performing light ray bending functions. The first surface has diffraction efficiency improvement mechanism for improving the resolution of the lens. The lens also has a vignetting reducing mechanism for reducing the amount of vignetting in the corners of the image.

Abstract: An objective lens comprises an inner optically functional region an inner optically functional region allowing a light flux to pass through for conducting recording and/or reproducing information for a first and second optical information recording mediums, an outer optically functional region allowing a light flux to pass through for conducting recording and/or reproducing information for the first optical information recording medium; and a diffractive structure provided on the outer optically functional region. The objective lens satisfies the following formulas: &lgr;>700 nm, NA1>0.65 and t1<t2 wherein &lgr; is a wavelength, NA1 is a numerical aperture, t1 and t2 are a thickness of a transparent base board of the first information recording medium and the second information recording medium.

Abstract: A single-element objective lens for an optical pick-up directs an incident light beam to a data recording surface of an optical disc through a cover layer to form a beam spot thereon. A numerical aperture of the objective lens is 0.7 or more. The objective lens is configured to compensate for coma such that a characteristic of a change of spherical aberration due to a degree of divergence/convergence of the incident beam is comparable with respect to a characteristic of a change of spherical aberration due to variation of the cover layer so that the change of spherical aberration due to variation of the cover layer can be cancelled by the change of spherical aberration due to a degree of divergence/convergence of the incident beam.

Abstract: An optical element has diffractive grooves. Each diffractive groove includes a first surface approximated by a predetermined optical function; a second surface extending in a direction to cross the first surface and being parallel to the optical axis; and a third surface to connect the first surface and the second surface. A width of the third surface in the direction perpendicular to the optical axis is 0.5% to 15% of the sum of a width of the first surface in the direction perpendicular to the optical axis and the width of the third surface in the direction perpendicular to the optical axis.

Abstract: A single-element objective lens for an optical pick-up is configured to converge substantially parallel light rays incident thereon onto a data recording surface of an optical recording medium. The objective lens includes, a first surface, which is a light incident side surface, and a second surface, which is an optical recording medium side surface. The first surface is an aspherical surface having a positive power, and the second surface is an aspherical surface having positive or negative power. The objective lens is designed such that paraxial wavefront aberration is 0.07&lgr; rms or less when a decentering amount between the first and second surfaces is 2 &mgr;m or less so as to converge the incident light substantially to a diffraction limit. A numerical aperture of the objective lens is 0.8 or more.

Abstract: When the DVD provided with the DVD substrate 2 having thickness t2of 0.6 mm is installed in the optical disc apparatus, the light beam 4 having wavelength &lgr;1=655 nm is used as luminous flux of numerical aperture NA=0.63 to be condensed on the information surface 2a on the DVD substrate 2. When the CD provided with the CD substrate 3 having thickness t2 of 1.2 mm is installed in the optical disc apparatus, the light beam 5 having wavelength &lgr;2=790 nm is effectively used as luminous flux of approximate numerical aperture NA=0.45 to be condensed on the information surface 3a on the DVD substrate 3. The wavefront aberration caused by a thickness difference between the DVD substrate 2 and CD substrate 3 is canceled out by the chromatic aberration caused by a wavelength difference between the light beams 4 and 5. Therefore, in spite of the difference in the transparent substrates, the light beams are suitably condensed respectively on the information surface 2a and 3a.

Abstract: An objective lens is used in an optical pickup apparatus. The objective lens is a single lens and satisfies the following formulas: 0.1<f<1 0.50<NA<0.90 350 nm<&lgr;<850 nm 1/10<|m|<⅓ the objective lens satisfying the following formula: 0.0 &lgr;rms<&dgr;Wtemp+&dgr;Wheight<0.07 &lgr;rms where &dgr;Wtemp represents an aberration of the objective lens when an ambient temperature of the optical pickup apparatus is changed from a room temperature by 30° C. and &dgr;Wheight represents an aberration of the objective lens at an image height Y of 0.02 mm.

Abstract: An aspheric lens focuses light emitting from a light-emitting diode (LED) of a light-generating dental device for curing light-curable compounds during dental procedures. The LED is preferably affixed to the end of an extension arm extending away from a light-generating dental device. A transparent shield, which is removably attachable to the extension arm, protects the aspheric lens from physical contact during use. The aspheric lens, which has a flat end and an aspheric end, is held in place by the extension arm and/or the transparent shield with the flat end of the aspheric lens being held in close proximity to the LED. Light emitted from the LED enters the flat end of the lens and exists the aspheric end of the lens, which focuses the light for curing light-curable compounds during dental procedures.

Abstract: The present invention relates to an optical pickup having a constant numerical aperture even if spherical aberration is compensated for. The optical pickup is used in an information recording and/or reproducing machine. The information recording and/or reproducing machine records and/or reproduces information in a recording medium upon radiation of a light beam from a light source. The optical pickup includes a condensing optical system for condensing the light beam from the light source onto a recording layer of the recording medium. The condensing optical system includes an object lens. The condensing optical system also includes an aperture positioned about a focal length of the object lens apart from a position of a principal incidence plane of the object lens toward the light source along an optical axis of the condensing optical system.

Abstract: A coma compensating element has two refraction surfaces. The refraction surfaces provide, as a whole, no aberration with respect to rays perpendicularly incident thereon, while the refraction surfaces provide coma with respect to rays obliquely incident thereon.

Abstract: Disclosed are holographic storage systems and lenses for holographic storage systems. The lens units can be of a single-component design. The lenses can be used to both record to photorefractive storage media and to read from photorefractive storage media.

Abstract: An objective lens for use in an optical pickup apparatus has a diffractive optical surface. A first light flux having a first wavelength of &lgr;1 is converged as a first number diffraction order diffracted-ray other than the zero-th order diffracted-ray onto an information recording plane of the first optical information recording medium having a thinner protective substrate t1 by the diffractive optical surface and a second light flux having a second wavelength of &lgr;2 (&lgr;1<&lgr;2) is converged as a second number diffraction order diffracted-ray other than the zero-th order diffracted-ray onto the information recording plane of the second optical information recording medium having a thicker protective substrate t2 (t1<t2) by the diffractive optical surface. The second number diffraction order is different from the first number diffraction order.

Abstract: An image pickup lens includes a lens body 1 which meets the following conditions:

Abstract: An objective lens for use in an optical pickup apparatus in which first and second light sources are provided on a same flat surface, converges each of the light fluxes from the first and second light sources onto an information recording plane through each of transparent substrates of a first and second optical information recording mediums and has a coma aberration of 0.015 &lgr;1 rms or less when recording or reproducing information is conducted for the first optical information recording medium, and a coma aberration of 0.015 &lgr;2 rms or less when recording or reproducing information is conducted for the second optical information recording medium.

Abstract: An optical scanning device is used for scanning first and second information layers with first and second radiation beams. The device includes a radiation source and an objective lens assembly (31). The lens assembly includes a doublet-lens system (61, 62) including a first objective lens (61) with a first cross-section having a first diameter (d1) and a second objective lens (62) with a second cross-section having a second diameter (d2). The first and second lenses are arranged for transforming the first radiation beam to a first focused radiation beam having a first numerical aperture. The objective lens assembly further includes a third objective lens (63) for transforming the second radiation beam to a second focused radiation beam having a second, smaller numerical aperture. The second and third objective lenses (62, 63) are integrally formed in one body (64). In a preferred embodiment of the objective lens assembly, the second diameter is smaller than the first diameter.

Abstract: In an optical lens for use in an optical information recording and reproducing apparatus conducting at least one of recording information on an optical recording medium and reproducing of information recorded on the optical recording medium, by converging light on the optical recording medium, the optical lens includes: lens surfaces provided on both sides of the optical lens; and an antireflection coating provided on the lens surface on at least one side thereof. Thickness of the antireflection coating on a peripheral portion of the lens surface is greater than that of the antireflection coating provided on a center portion of the lens surface.

Abstract: A molded glass lens is taught that includes a molded two-dimensional reference surface at a first end of the lens body, a first molded optical surface that is longitudinally displaced from the two-dimensional reference surface, and a molded second optical surface at a second end of the lens body. The first and second optical surfaces may be plano, convex or concave. The molded two-dimensional reference surface is planar and preferable annular. By physically locating the lens with the molded two-dimensional reference surface and one of the first or second optical surfaces, the lens can be held in a given orientation. Thus, the molded reference surface at the end of the cylindrical body allows for accurate and safe capture, positioning, handling, and placement for subsequent finishing operations, allowing for the creation of one or more additional lens datums.

Abstract: The present invention is characterized in that by laser beam being slantly incident to the convex lens, an aberration such as astigmatism or the like is occurred, and the shape of the laser beam is made linear on the irradiation surface or in its neighborhood. Since the present invention has a very simple configuration, the optical adjustment is easier, and the device becomes compact in size. Furthermore, since the beam is slantly incident with respect to the irradiated body, the return beam can be prevented.

Abstract: A beam shaping optical system which is provided with a first wedge prism having two refractive surfaces defining a first principal section, and a second wedge prism having two refractive surfaces defining a second principal section that is parallel to the first principal section, wherein a reference ray of light forms incident angles at each of the refractive surfaces of the prisms satisfying the following condition (1): &LeftBracketingBar; ∑ j = 1 L ⁢ α j &RightBracketingBar; < 0.020 .

Abstract: An image pickup lens system includes, in sequence from an object side to an image side, an aperture stop, a plano-convex lens having positive power and oriented such that a planar surface of the plano-convex lens faces the object side and a convex surface of the plano-convex lens faces the image side, the convex surface being aspheric, and another stop.

Abstract: A non-imaging optical coupler that is a figure of revolution combining a light-transmitting body defining a recessed input cavity, a transparent droplet-shaped encapsulant of a light-emitting diode, or array of diodes in the cavity, the body having a curved side wall shaped to totally internally reflect all the light emitted from the LED and encapsulant, traveling toward the side wall, within a predetermined distance from the diode or center of array, the body having a cylindrical transition section extending from a curved side wall and forwardly, and a planar exit face at the forward end of the body, transverse to the central axis of the figure of revolution.

Abstract: An image pickup lens system includes a lens 1 of a meniscus shape having a first face as a convex face, and a diaphragm 2 disposed on an object side of the lens 1. The lens 1 meets the following conditions: Y′/fl equal to or larger than 0.6; Dt/Dc is equal to or smaller than 0.9 and equal to or larger than 0.5; and Ap2/Am2 is equal to or larger than 0.9. Thus, even when an image pickup element is of a reduced size, a desired optical performance can be maintained, and it is possible to produce a lens easily with a back focal length ensured.

Abstract: One surface of an objective lens is provided with a zonal part which acts such that the quantity of light having a wavelength of &lgr;1 is apparently canceled in the outer peripheral portion of the luminous flux due to an interference effect, whereas the quantity of light having a wavelength of &lgr;2 in the outer peripheral part is kept as it is. The zonal part has such a step that light supposed to pass a position corresponding to the zonal part if the zonal part does not exist and light passing a position at which the zonal part is formed if the zonal part exists generate therebetween a phase difference satisfying a predetermined conditional expression. The numerical aperture at a boundary position of the step has a value between two numerical apertures for the respective wavelengths &lgr;1 and &lgr;2.

Abstract: Disclosed is an objective lens of an optical pick-up that converges light beams of two different wavelengths onto recording layers of optical discs of two different standards, respectively. The objective lens includes a refractive lens having a positive power and a diffractive lens structure formed on one surface of the refractive lens. The diffractive lens structure has a plurality of concentric ring areas with minute steps at the boundaries therebetween. The diffractive lens structure maximizes the diffraction efficiency of the third order diffracted light at the shorter wavelength and maximizes the diffraction efficiency of the second order diffracted light at the longer wavelength. This enables the diffractive lens structure to correct the chromatic aberration at the respective wavelengths with keeping high diffraction efficiency.