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WO1999063367A1 - Elements a prisme optique de dispersion, a gradient d'indice de refraction - Google Patents

Elements a prisme optique de dispersion, a gradient d'indice de refraction Download PDF

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Publication number
WO1999063367A1
WO1999063367A1 PCT/US1999/009295 US9909295W WO9963367A1 WO 1999063367 A1 WO1999063367 A1 WO 1999063367A1 US 9909295 W US9909295 W US 9909295W WO 9963367 A1 WO9963367 A1 WO 9963367A1
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WO
WIPO (PCT)
Prior art keywords
prism
index
refraction
optical
gradient
Prior art date
Application number
PCT/US1999/009295
Other languages
English (en)
Inventor
Richard Blankenbecler
Andrew T. Zander
Ring-Ling Chien
Original Assignee
Varian, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Varian, Inc. filed Critical Varian, Inc.
Priority to AU38717/99A priority Critical patent/AU3871799A/en
Publication of WO1999063367A1 publication Critical patent/WO1999063367A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29371—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion
    • G02B6/29373—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion utilising a bulk dispersive element, e.g. prism
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B3/0087—Simple or compound lenses with index gradient
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/04—Prisms

Definitions

  • the present invention relates generally to unified focusing and dispersing prisms for use in optical systems, such as in beam transport, spectrographs and monochromators, and more particularly to lens-prism elements with a spatially varying, i.e. gradient, index of refraction.
  • a conventional prism element with planar surfaces and with a homogeneous index of refraction can be used to guide light in a beam transport system. They can also be used to disperse, or to separate, light beams into their different wave length components. Dispersion occurs because the angle of refraction of the beam depends upon the index of refraction of the prism material. Since the index of refraction varies as a function of the wave length of the light, the outgoing light beam is color separated. In a spectrograph, the angular deflection of an outgoing light ray is related to its wave length. Thus a spectrograph allows one to study a wide band of the light spectrum simultaneously. A monochromator, on the other hand, isolates a very narrow band of wave lengths for study. Monochromators are used in several instruments; examples are instruments (termed spectrophotometers) used to measure transmittance and reflection as a function of wave length.
  • Spectrographs and monochromators are used to study light across a broad range of wave lengths.
  • the three main classification regimes are termed the long wave lengths, infrared (IR), the visible region, and the ultraviolet (UV) which leads into the X-ray region of short wave lengths.
  • IR infrared
  • UV ultraviolet
  • the useful range in wave lengths for a prism instrument is limited by the transparency of the prism material. There are many possible choices for prism material that together allow a wide spectrum range to be spanned via overlapping regions.
  • Optical quality glass blanks that have a spatially varying index of refraction are commercially available from a variety of sources. These are termed gradient index blanks, or GRIN blanks, in the literature.
  • the index profile can be axial, i.e., varying in only one spatial direction, cylindrical, or possess a more general spatial variation, as desired by the optical designer.
  • GRIN blanks can be fabricated in a variety of materials that are suitable to cover the full wave length range.
  • One of the useful properties of an index gradient is that it can affect the direction of a ray path of light while it passes through the gradient region. The general rule is that the ray will turn in the direction of the increasing index of refraction since that is the side of the ray that has the lowest propagation velocity.
  • GRIN lens blanks are used to produce focusing lenses of the standard type with curved external surfaces generated by grinding and polishing.
  • gradient optical blanks can be made by several processes. In order to have suitable transmission properties in the IR the composition of the blank must be appropriately chosen. One of the most common choices for the IR region is zinc selenide or zinc sulfide for the active element. Suitable axial gradient index elements are commercially available from CVD, Inc. of Boston, MA; these blanks can be fabricated with a change in index as large as 0.2. In the visible range, the blanks for the fabrication of suitable optical gradient elements can be made by a variety of processes such as SOL-GEL, ion infusion, and atomic diffusion. In particular, there is the controlled diffusion processes that can produce macro lenses with a prescribable index of refraction axial profile.
  • optical blanks for the fabrication of gradient elements can be made by a few processes.
  • the composition of the element In order to have suitable transmission properties in the ultraviolet, the composition of the element must be appropriately chosen.
  • One of the best choices for the UV region is quartz or fused silica.
  • Such gradient index elements can be made by the chemical vapor deposition (CVD) process. Selected geometries are available from several sources including the Heraeus Corporation of Duluth, GA.
  • the dispersive power of the prism arises from the dependence of the index of refraction of the prism medium on the wave length of the incident light.
  • An overall summary for homogeneous glass can be found in the book “Handbook of Glass Properties” by N. P. Bansal and R. H. Doremus, Academic Press, New York 1986. A general discussion can also be found in "Applied Optics” by L. Levi, John Wiley, New York 1982.
  • the dispersion dependence of selected GRIN glass compositions has also been studied.
  • lead silicate glasses useful for the near-infrared and visible regimes, a detailed study has been published by P. K. Manhart and R. J.
  • a prism element to separate the different wave lengths of light also implies the use of conventional focusing optical elements to provide an image on a detector plane. This system usually requires several elements and requires very careful chromatic design so that the different wave lengths are focused sharply with no loss in resolution. GRIN prism elements allow a design with fewer elements, good chromatic properties, and improved performance.
  • axial index gradients for focusing in optical elements with tilted planar surfaces was described in US patents 5,541,774 and 5,703,722, both issued to Blankenbecler. These patents describe compound optical elements containing at least one internal tilted surface that exposes an axial index gradient whose profile is chosen to achieve focussing of light rays.
  • wave length regimes such as the infrared (long wave lengths), visible, and ultraviolet (short wavelength or X-rays).
  • the present invention utilizes prisms made out of glass blanks that have a spatially varying index of refraction.
  • a gradient prism provides an optical element for the spectrograph designer that can be used to achieve many desirable optical functions.
  • the basic property used in such instruments is that the index of refraction and its spatial derivative have a different dependence on wave length.
  • the designer may choose to decrease the nonlinear dispersive behavior, in order to simplify the light detector, to improve the resolution of the instrument by increasing the nonlinear dispersion, or alternatively to make the dispersion very small for use in certain light beam guides. Therefore GRIN prisms can be used in various arrangements that combine these two properties in different ways to affect its overall dispersive properties.
  • an axial gradient wedge prism having a spherical or cylindrical front surface, an optical axis, and a planar but tilted rear surface.
  • the light rays refract as they pass through the curved front surface and refract again as they pass through the tilted rear surface.
  • the rays are very slightly bent by the axial gradient index as they traverse the interior of the prism.
  • the total deflection of the rays is a combination of these mechanisms. Since these physical mechanisms have a different wave length dependence, it is possible to affect the overall dispersive power of the prism.
  • the front surface is chosen to focus the rays with a chosen focal length.
  • the refraction at the final tilted surface depends upon the index of refraction at the exit point and the wave length. If the index varies appropriately from the bottom to the top of the rear surface, the rays can be focused as from a positive or a negative cylindrical lens.
  • the optical element consists of a compound lens/prism.
  • the front section consists of a homogeneous lens with a spherical or cylindrical front surface. Its rear surface is preferably planar.
  • the second element is a wedge prism with planar surfaces and possessing an index gradient.
  • the front surface of the prism is arranged perpendicular to the optical axis of the lens. The light rays are refracted and focused as they pass through the front surface of the first element.
  • the axial index of refraction of the prism element may be chosen to vary either along the optical axis or perpendicular to this axis.
  • the GRIN index profile of the prism can be either axial or cylindrical in geometry, or indeed, of more general variation.
  • Figure 1 A is a homogeneous wedge prism of the prior art. A sample ray is drawn.
  • Figure IB is a two element compound homogeneous prism of the prior art.
  • Figure 2A is a wedge prism with an index that varies along the optical axis.
  • Figure 2B is a wedge prism with an index that varies perpendicular to the optical axis.
  • Figure 3 is a wedge GRIN prism with a curved front surface.
  • Figure 4A is a compound element - a homogeneous lens and an axial GRIN wedge prism.
  • Figure 4B is a compound element - a homogeneous lens and a transverse GRIN wedge prism.
  • Figures 5A and 5B define the coordinates and quantities used in the theoretical treatment.
  • Figure 6 defines the coordinates and quantities used in further theoretical treatment.
  • Figure 7A is a raytrace output from a commercial optical design package for a GRIN prism with spherical front surface.
  • Figure 7B is a raytrace output from a commercial optical design package for a GRIN prism with cylindrical diverging lens
  • a prism with a gradient index of refraction is provided.
  • the angle of refraction of a light ray passing through a surface depends upon the angle between the ray and the normal to the surface and the indices of refraction on either side of the surface.
  • the deflection of a light ray in passing through a gradient index medium depends upon the index gradient and the length of path in the GRIN region.
  • the index of refraction has a different dependence on wave length than its spatial gradient.
  • the ratio of the two depends upon the vertex angle of the prism, the thickness (or path length) in the GRIN medium and the sign of the index gradient.
  • the simplest GRIN prism is a wedge prism as shown in Figure 2 A and 2B.
  • the dotted lines in all figures represent planes of constant value of the refractive index. Refraction takes place at the front and rear surfaces. The deflection due to the index gradient takes place as the ray passes through the wedge GRIN medium. The dispersive behavior of the total deflection angle depends upon the mixture of these effects.
  • a ray at normal incidence parallel to the prism axis is not deflected as it enters the prism. As the ray traverses the medium, it is bent by the transverse refraction index gradient in Figure 2B. The ray is again refracted as it leaves the prism.
  • the prescribability of the resultant dispersive power of the prism is achieved by the combination of these various effects.
  • the dispersive effects of the index of refraction is different from the dispersive effects of the gradient of the index of refraction and their combination permits the control of the overall dispersive power.
  • a GRIN wedge prism with an axial GRIN profile and a curved front surface is illustrated in Figure 3.
  • the necessary chromatic corrections can be accomplished by choosing the axial gradient to function as a diverging lens.
  • the major chromatic effects are canceled between the converging front lens surface and the diverging GRIN rear surface.
  • More general mixed combinations are possible, depending upon the performance and properties required by the optical designer. For example, it is possible to have the front surface shaped as a concave or diverging lens and then have the axial gradient function as a converging lens.
  • GRIN prisms can be fabricated from a variety of basic compositions. These include plastics, glass compositions, quartz, and fused silica. All of these compositions are available commercially, but are presently limited in the geometries that are available.
  • Figure 5 A depicts a diverging GRIN prism lens which has both F z and F y negative.
  • Figure 5B depicts a converging GRIN prism lens which has both F r and F y positive.
  • the dispersive property of the GRIN prism is characterized by the dependence of F z and F y on the wave length ⁇ ; they in turn depend upon the behavior of the index of refraction upon wave length.
  • the goal of a good design is to have a large dispersion yet to have each wave length sharply focused on the image plane for maximum resolution.
  • the way to make these chromatic corrections can be anticipated by noting that the chromatic changes in the focal length arise from the wave length dependence of the front curved surface and the refraction at the rear surface. If the index profile is chosen so that the rear face acts as a diverging lens, then the index rises from the front to the rear of the prism while its Abbe value decreases.
  • This negative focal length is then combined with the positive focal length from the front surface with its larger Abbe value to produce the total focal length of the system. It will be shown below that the two sources of chromatic shift in the z focal length, F z , can be arranged to cancel while the dispersion measure, F y , still depends strongly upon wave length.
  • the axial index profile is expanded as (6) n(z) - w(0) + n z + n 2 z 2 +...
  • (F z - L) on the left is the focal length of the total GRIN prism system.
  • the first term on the right side is the focal length of the front spherical or cylindrical lens if the rear surface were perpendicular to the optical axis.
  • the second term is the focal length of a GRIN index profile with a surface inclined at an angle A. It is seen that if «, is positive, this acts as a diverging cylindrical lens while if n, is negative, it acts as a converging cylindrical lens.
  • One of the goals of the invention is to provide an optical system that not only disperses the wave length spectrum of the incident light, but also to sharply focus all wave lengths on the image plane. That is, F z is to be independent of wave length, but F y is to depend on wave length.
  • An alternative design choice is to choose a diverging front surface shape, that is, R ⁇ 0, and a decreasing axial index profile.
  • R ⁇ a diverging front surface shape
  • F z can be made to be independent of wave length.
  • the following designs were done using the ZEMAX optical design program.
  • the source was at infinity
  • the radius of curvature on the front surface was 100mm
  • the lens diameter was 10mm
  • the parameter F was fixed at 217.6mm.
  • the glass was a lead silicate glass whose dispersive properties were described by Manhart and Pagano.
  • the total change in F y of the spectrum over the wave length range 0.45-0.65 microns is 2.683mm.
  • the resolution width in y of a given wave length is approximately 0.012mm.
  • FIGs 7 A and B This design is illustrated in Figures 7 A and B for one wave length.
  • a side view of the GRIN prism with its spherical front surface is depicted in Figure 7A.
  • the effect of the GRIN cylindrical diverging lens is seen in Figure 7B.
  • the top view shows the rays converging well in front of the image plane.
  • the side view shows the refraction of the rays by the tilted rear surface and the focusing effect.
  • the source was at a finite distance of 400mm from the front surface.
  • the other parameters were unchanged except that F z was 663.6mm.
  • the total change in F y over the same wave length range is 9.486mm.
  • the resolution width in y of a given wave length is approximately 0.05mm.
  • the maximum index change over the length of the prism is 0.106.
  • index gradient may be oriented in any direction desired to achieve the goals of a particular optical design.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Optical Elements Other Than Lenses (AREA)

Abstract

L'invention concerne un élément à prisme optique de concentration à utiliser dans certains système optiques. Le prisme possède une surface avant courbe et une surface arrière plane et contient un indice de réfraction variant dans l'espace. On l'appelle élément à prisme GRIN. On peut fabriquer des prismes à éléments multiples en combinant un lentille homogène et un prisme GRIN. Le gradient de l'indice de réfraction peut avoir une géométrie de profil axiale, cyclindrique ou plus générale. Si le gradient d'indice est choisi de sorte que la surface arrière agisse comme une lentille divergente, la dépendance chromatique de la longueur focale longitudinale peut être faible. L'utilisation d'un prisme GRIN comme élément dispersif dans un spectrographe est également décrite.
PCT/US1999/009295 1998-06-04 1999-04-28 Elements a prisme optique de dispersion, a gradient d'indice de refraction WO1999063367A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU38717/99A AU3871799A (en) 1998-06-04 1999-04-28 Dispersing optical prism elements with graded index of refraction

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US9077698A 1998-06-04 1998-06-04
US09/090,776 1998-06-04

Publications (1)

Publication Number Publication Date
WO1999063367A1 true WO1999063367A1 (fr) 1999-12-09

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2021146474A1 (fr) * 2020-01-16 2021-07-22 Akalana Management Llc Systèmes optiques ayant des structures optiques à indice de gradient
US12442967B2 (en) 2021-09-22 2025-10-14 Apple Inc. Optical systems having gradient index optical structures

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58205108A (ja) * 1982-05-26 1983-11-30 Mitsubishi Electric Corp 光回路
US4783591A (en) * 1987-11-09 1988-11-08 Honeywell Inc. Color mark sensor
US4895433A (en) * 1986-02-17 1990-01-23 Olympus Optical Co., Ltd. Visual field converting optical system
JPH05150148A (ja) * 1991-11-29 1993-06-18 Mitsubishi Electric Corp レーザモジユール
WO1996027809A1 (fr) * 1995-03-08 1996-09-12 Lightpath Technologies, Inc. Lentilles a gradient d'indice et procede de fabrication
JPH09236724A (ja) * 1996-03-01 1997-09-09 Matsushita Electric Ind Co Ltd 光合分波器及びその製造方法

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58205108A (ja) * 1982-05-26 1983-11-30 Mitsubishi Electric Corp 光回路
US4895433A (en) * 1986-02-17 1990-01-23 Olympus Optical Co., Ltd. Visual field converting optical system
US4783591A (en) * 1987-11-09 1988-11-08 Honeywell Inc. Color mark sensor
JPH05150148A (ja) * 1991-11-29 1993-06-18 Mitsubishi Electric Corp レーザモジユール
WO1996027809A1 (fr) * 1995-03-08 1996-09-12 Lightpath Technologies, Inc. Lentilles a gradient d'indice et procede de fabrication
JPH09236724A (ja) * 1996-03-01 1997-09-09 Matsushita Electric Ind Co Ltd 光合分波器及びその製造方法

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
MANHART P K ET AL: "FUNDAMENTALS OF MACRO AXIAL GRADIENT INDEX OPTICAL DESIGN AND ENGINEERING", OPTICAL ENGINEERING, vol. 36, no. 6, 1 June 1997 (1997-06-01), pages 1607 - 1621, XP000693506, ISSN: 0091-3286 *
PATENT ABSTRACTS OF JAPAN vol. 008, no. 055 (P - 260) 13 March 1984 (1984-03-13) *
PATENT ABSTRACTS OF JAPAN vol. 017, no. 539 (P - 1621) 28 September 1993 (1993-09-28) *
PATENT ABSTRACTS OF JAPAN vol. 098, no. 001 30 January 1998 (1998-01-30) *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2021146474A1 (fr) * 2020-01-16 2021-07-22 Akalana Management Llc Systèmes optiques ayant des structures optiques à indice de gradient
US12442967B2 (en) 2021-09-22 2025-10-14 Apple Inc. Optical systems having gradient index optical structures

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Publication number Publication date
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