WO2008108628A1 - Retardateur optique achromatique - Google Patents

Retardateur optique achromatique Download PDF

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Publication number
WO2008108628A1
WO2008108628A1 PCT/NL2007/050087 NL2007050087W WO2008108628A1 WO 2008108628 A1 WO2008108628 A1 WO 2008108628A1 NL 2007050087 W NL2007050087 W NL 2007050087W WO 2008108628 A1 WO2008108628 A1 WO 2008108628A1
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WO
WIPO (PCT)
Prior art keywords
achromatic
optical retarder
birefringent material
retarder according
birefringent
Prior art date
Application number
PCT/NL2007/050087
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English (en)
Inventor
Jacob Tinbergen
Original Assignee
Stichting Astron
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 Stichting Astron filed Critical Stichting Astron
Priority to PCT/NL2007/050087 priority Critical patent/WO2008108628A1/fr
Priority to GB0917011A priority patent/GB2460206A/en
Publication of WO2008108628A1 publication Critical patent/WO2008108628A1/fr

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3083—Birefringent or phase retarding elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
    • G02B27/286—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another

Definitions

  • the invention relates to an achromatic optical retarder.
  • a retarder also known as a waveplate, is an optical device that modifies the polarization state of light by resolving it into two orthogonal polarization components (parallel to two orthogonal axes, commonly referred to as “fast axis” and “slow axis”) and producing a phase shift between them, i.e. birefringence.
  • the phase shift results from the two polarization components having different velocities within the retarder material.
  • a retarder produces a well defined phase shift (e.g. a quarter wavelength or half a wavelength) at a single frequency, i.e. the retarder is monochromatic.
  • Achromatic optical retarders are known per se.
  • a special type of achromatic retarder is the Pancharatnam achromatic retarders (S. Pancharatnam, "Achromatic combinations of birefringent plates. Part II: An achromatic quarterwa ⁇ e plate", Proc. Indian Acad. Sciences, A41, pp. 137-144, 1955).
  • Said achromatic Pancharatnam retarder usually comprises at least three layers, or slabs, of optical material, herein also referred to as "birefringent optical elements” or “birefringent components”, such as zero order polymer, quartz, magnesium fluoride or mechanically stressed fused silica, with their fast axes at oblique angles.
  • These achromatic retarders have a much wider spectral range over which they remain substantially quarter- or half-wave than conventional optical retarders.
  • a special class of retarder is the polarisation modulator.
  • a polarisation modulator is a retarder which provides a variable or varying retardance (phase shift).
  • a known polarisation modulator is the photo-elastic polarisation modulator (James C. Kemp, "Piezo-Optical Birefringence Modulators: New Use for a Long-Known Effect", Journal of the Optical Society of America, Vol. 59, No. 8 (Part 1), pp. 950-954, August, 1969).
  • This modulator comprises a slab of, generally isotropic, optical material. Applying uniaxial mechanical stress to the slab of optical material will change the birefringence of the material, thus allowing the phase shift to be changed.
  • An achromatic photo-elastic polarisation modulator (Pancharatnam achromatic polarisation modulator) is also known.
  • Said achromatic polarisation modulator usually comprises at least three monochromatic polarisation modulators, e.g. at least three slabs of optical material, such as zero order polymer or fused silica with their fast axes at oblique angles, which layers are mechanically vibrated in synchronism.
  • the achromatic retarder wherein an incident beam of light passes at least three birefringent elements with their fast axes at oblique angles, has the disadvantage that the at least three birefringent elements have to be accurately aligned with respect to each other to provide the achromatic retarder with the desired phase shift.
  • the process of alignment can be very cumbersome.
  • the achromatic retarder arranged as achromatic polarisation modulator wherein an incident beam of light passes at least three birefringent elements with their fast axes at oblique angles, has the disadvantage that the at least three elements have to be accurately aligned with respect to each other.
  • said achromatic polarisation modulator has the disadvantage that the at least three birefringent elements have to be mechanically actuated, e.g. vibrated, in synchronism and preferably with accurately controlled relative amplitudes.
  • the mechanical vibration is achieved by causing a standing sound wave in each of the elements, the dimensions of the elements must be equal within a very small tolerance in order to minimise differences in resonant frequencies of the elements.
  • complex and expensive actuators and control electronics are required to control the vibrations of the three birefringent elements under different ambient conditions, such as direction of gravity and gradients and/or changes in temperature SUMMARY OF THE INVENTION
  • an achromatic optical retarder in which the above disadvantage is at least reduced. Therefore, according to the invention, an achromatic optical retarder according to claim 1 is provided. It is a further goal of the invention to provide an achromatic retarder arranged as an achromatic polarisation modulator in which at least one of the above disadvantages is at least reduced.
  • Such achromatic optical retarder provides the advantage that the number of of birefringent elements can be reduced by at least one, since the beam of light passes at least two trajectories through one single element of birefringent material. Hence the number of birefringent elements that need to be aligned with respect to each other can also be reduced by at least one, rendering the alignment procedure less cumbersome.
  • the term "trajectory” is to be understood as a non-interrupted path travelled by a beam of light within a single optical element, such as a single bar of optical material, e.g. glass, from an entry point where the beam enters the element to an exit point where the beam exits the element.
  • a single optical element such as a single bar of optical material, e.g. glass
  • the term "birefringent material” is to be understood as a material that is at least birefringent in use.
  • the birefringent material may be an optical material that is at least birefringent when a variable or varying mechanical stress and/or electric field (e.g. by applying an electric voltage) is applied to the material.
  • the material need not necessarily be birefringent when no such stress and/or electric field is applied.
  • this provides the advantage that the achromatic optical retarder arranged as achromatic polarisation modulator does not alter the polarisation state of a beam traversing it when no stress and/or electric field is applied.
  • the birefringent material may be an optical material that is e.g. inherently birefringent, or is birefringent when a static mechanical stress and/or electric field is applied to the material.
  • the achromatic optical retarder comprises only one element of birefringent material for determining the phase shift. This provides the advantage that the beam of light can pass through that single element the required number of times. In this case no alignment of separate birefringent elements with respect to each other is required.
  • the achromatic retarder arranged as the achromatic polarisation modulator in which the phase shift is varied e.g.
  • At least the achromatic optical retarder wherein an incident beam of light passes three trajectories of birefringent material (which is the most simple and common embodiment of a Pancharatnam achromatic retarder or polarisation modulator) can be provided with the advantages of providing only a single element of birefringent material for determining the amplitude and/or timing of the variable phase shift.
  • the achromatic optical retarder comprises redirecting means for redirecting the beam of light transmitted by the element back to the element, for instance by means of reflection.
  • the beam of light can in a simple manner pass at least twice through a single element of birefringent material.
  • the redirecting means are arranged for changing the polarisation of the beam of light transmitted by the element before it re-enters the element.
  • the redirecting means may comprise a polarisation rotator for rotating the polarisation of the beam of light transmitted by the element before it re- enters the element, for example over 55-60 degrees.
  • the optical path within the polarisation rotator substantially extends in a flat plane, wherein the plane is arranged at a non-zero angle with respect to a fast axis of the element. Hence, the polarisation of the beam can easily be rotated.
  • Fig. 1 shows a schematic perspective view of a prior art achromatic optical retarder of the Pancharatnam design.
  • Fig. 2 shows a schematic perspective view of a first example of an embodiment of an achromatic optical retarder according to the invention.
  • Fig. 3 shows a schematic view of an example of an embodiment of an achromatic optical retarder, arranged as polarization modulator, according to the invention.
  • Figs. 4a-4k show schematic views of examples of achromatic retarders, to be used in polarisation rotators, for use in the redirecting unit of the achromatic optical retarder according to the invention.
  • Fig. 5a shows a schematic view of a third example of an embodiment of an achromatic optical retarder according to the invention.
  • Fig. 5b shows a top plan view of the retarder of Fig. 5a.
  • Fig. 1 shows a schematic, perspective view of a prior art achromatic optical retarder. Shown is a Pancharatnam achromatic retarder, comprising three plates Pl, P2, P3 of the same birefringent material, which are consecutively traversed by a beam of light 8.
  • the outer two plates Pl, P3 are of equal thickness and are oriented with their fast axes in parallel, in this case in the longitudinal direction of the outer plates Pl, P3.
  • the fast axes of all three plates Pl, P2, P3 are substantially perpendicular to a propagation direction of the beam of light 8.
  • the central plate P2 is a (chromatic) halfwave plate for the central wavelength of the desired passband.
  • the fast axis of the central plate extends in the longitudinal direction of the central plate P2 and is oriented at a, non-zero, angle ⁇ with the fast axes of the outer plates Pl, P3.
  • the achromatic retarder is also a halfwave plate.
  • achromatic range may be traded for degree of achromatism merely by rotating, in a plane perpendicular to the direction of propagation of light, the fast axis of the central plate with respect to fast axes of the outer plates.
  • the angle ⁇ between the fast axis of the central plate and the fast axes of the outer plates is between 55 and 60 degrees, e.g. 57 degrees.
  • the achromatic range is zero, at approximately 55 degrees the maximum useful achromatic range is achieved, but the quality of achromatism is barely acceptable.
  • Fig. 2 shows a schematic, perspective view of a first example of an embodiment of an achromatic optical retarder 1 according to the invention.
  • the retarder 1 comprises a first element 2 of birefringent material and a second element 4 of birefringent material.
  • the first element 2 is of the same birefringent material as the second element 4.
  • the fast axis of the first element 2 extends in the longitudinal direction of the first element 2.
  • the fast axis of the second element 4 extends in the longitudinal direction of the second element 4.
  • the fast axis of the first element 2 is oriented at a non-zero angle with respect to the fast axis of the second element 4.
  • the achromatic retarder 1 in this example further comprises a redirecting unit 10.
  • the redirecting unit 10 comprises a mirror 20.
  • a beam of light 8 passes through the achromatic optical retarder 1.
  • the beam 8 enters the first element 2 at point A, in this example substantially perpendicular to the surface of the first element 2.
  • the beam of light 8 passes a first trajectory through birefringent material, which first trajectory extends through the first element 2 from point A to point B.
  • the first trajectory extends within the first element from an entry point, here point A, to an exit point, here point B.
  • the propagation direction of the beam of light is substantially perpendicular to the fast axis of the first element 2 at the first trajectory.
  • the beam 8 propagates, e.g. through air or vacuum, from the first element 2 to the redirecting unit 10.
  • the beam 8 is incident on the mirror 20 in point C, and is reflected. Next, the beam 8 propagates, e.g. through air or vacuum, from the redirecting unit 10 to the second element 4.
  • the beam 8 enters the second element 4 at point D, in this example substantially perpendicular to the surface of the second element 4.
  • the beam of light 8 passes a second trajectory through birefringent material, which second trajectory extends through the second element 4 from point D to point E, Hence, the second trajectory extends within the second element from an entry point, here point D, to an exit point, here point E.
  • the propagation direction of the beam of light is substantially perpendicular to the fast axis of the second element 4 at the second trajectory.
  • the beam 8 then enters the first element 2 again at point G, in this example substantially perpendicular to the surface of the first element 2.
  • point G coincides with point E as the first and second element 2,4 are positioned in contact with each other.
  • there also may be a distance between point G and E e.g with an optical medium, e.g. air, or vacuum.
  • the beam of light is substantially perpendicular to the fast axis of the first element 2.
  • the beam of light 8 passes a third trajectory through birefringent material, which third trajectory extends through the first element 2 from point G to point H.
  • the third trajectory extends within the first element from an entry point, here point G, to an exit point, here point H.
  • the propagation direction of the beam of light is substantially perpendicular to the fast axis of the first element 2 at the third trajectory.
  • achromatic retarder shown in Fig. 2 is, in its basis also a Pancharatnam achromatic retarder. Since, in this example, the first trajectory and the third trajectory both extend within the first element 2 of birefringent material, there is no need to align the birefringent material of the first trajectory with respect to the birefringent material of the second trajectory. Hence, alignment of the achromatic retarder is easier than when three separate elements are used.
  • Fig. 3 shows a schematic view of a second example of an embodiment of an achromatic optical retarder 1 according to the invention.
  • the achromatic optical retarder 1 is arranged as an achromatic polarisation modulator.
  • the achromatic polarisation modulator is essentially an achromatic optical retarder 1 which is further provided with means for varying, e.g. periodically, the induced phase shift.
  • the polarisation modulator 1 comprises a single element 2 of birefringent material.
  • the polarisation modulator 1 further comprises a transducer 18, e.g. a piezoelectric transducer.
  • the transducer 18 causes the element 2 to oscillate, for inducing a periodically varying uniaxial mechanical stress in the element 2.
  • the mechanical stress is applied in the longitudinal direction of the element 2.
  • the transducer 18 induces a standing sound wave in the element 2 in the longitudinal direction of the element 2.
  • the material of the element 2 is chosen such that the material is at least birefringent when the mechanical stress is applied to the material. Such material will herein also be referred to as birefringent material.
  • the degree of birefringence is proportional to the amount of mechanical stress applied to the material.
  • a beam of light 8 passes through the achromatic polarisation modulator 1.
  • the beam 8 enters the element 2 at point A, in this example substantially perpendicular to the surface of the element 2.
  • the beam of light 8 passes a first trajectory through birefringent material, which first trajectory extends through the element 2 from point A to point B.
  • the propagation direction of the beam of light is substantially perpendicular to the fast axis of the first element 2 at the first trajectory.
  • the beam 8 propagates, through an isotropic, i.e.
  • the redirecting unit 10 comprises a first mirror 20.
  • the beam 8 is reflected by the first mirror 20 back to the element 2.
  • the redirecting unit 10 further comprises a first polarisation rotator 24, e.g. an achromatic halfwave plate, arranged to rotate the orientation of the polarisation of the beam 8 before it enters the element 2 at point D.
  • the first polarisation rotator 24 rotates the polarisation of the beam 8 over a first angle.
  • the beam 8 then enters the element 2 at point D, in this example substantially perpendicular to the surface of the element 2.
  • the beam of light 8 passes a second trajectory through birefringent material, which second trajectory extends through the element 2 from point D to point E.
  • the propagation direction of the beam of light is substantially perpendicular to the fast axis of the first element 2 at the second trajectory.
  • the fast axis of the element 2 at the second trajectory is parallel to the fast axis of the element 2 at the first trajectory.
  • the beam 8 propagates, e.g. through an isotropic material such as air or vacuum, from the point E on the element 2 to the redirecting unit 10, this example to a second mirror 22 of the redirecting unit 10.
  • the beam 8 is reflected by the second mirror 22 back to the element 2.
  • the redirecting unit 10 further comprises a second polarisation rotator 26, e.g. an achromatic halfwave plate, arranged to rotate the orientation of the polarisation of the beam 8 before it enters the element 2 at point G.
  • the second polarisation rotator 26 rotates the polarisation of the beam 8 over a second angle.
  • the magnitude of the second angle is equal to the magnitude of the first angle
  • the sign of the second angle is opposite to the sign of the first angle.
  • the beam 8 then enters the element 2 at point G, in this example substantially perpendicular to the surface of the element 2.
  • the beam of light 8 passes a third trajectory through birefringent material, which third trajectory extends through the element 2 from point G to point H.
  • the propagation direction of the beam of light is substantially perpendicular to the fast axis of the first element 2 at the third trajectory. It will be appreciated that the fast axis of the element 2 at the third trajectory is parallel to the fast axis of the element 2 at the second trajectory.
  • the beam 8 exits the element 2.
  • the first, second and third trajectories extend within the single element 2 of birefringent material.
  • all trajectories through the birefringent material extend within the single element 2.
  • Providing the polarisation rotators 24,26 arranges that it is possible that the fast axis of the birefringent material at the second trajectory is oriented at a different angle with respect to a polarisation orientation of the beam of light than the fast axis of the birefringent material at the first and/or third trajectory, while the second and first and/or third trajectory extend within the same element of birefringent material.
  • the fast axes of the birefringent material at the outer two trajectories of the three trajectories are oriented substantially at the same angle with respect to the polarisation orientation of the beam of light
  • the fast axis of the birefringent material at the central trajectory of the three trajectories, here the second trajectory is oriented at a different angle with respect to the polarisation orientation of the beam of light than the fast axes of the birefringent material at at least one of the outer two trajectories, here both outer trajectories.
  • the Mueller matrix of rotation of the polarisation of the beam 8 by the polarisation rotator 24 or 26 is not exactly identical to the Mueller matrix of (geometric) rotation of the orientation of the fast axis of the birefringent material at the second trajectory with respect to the orientation of the fast axis of the birefringent material at the first and third trajectory (as in Fig. 1).
  • the inventor realised that this difference may be such that, depending on the intended use of the polarisation modulator, it does not provide a disadvantage which is not outweighed by the advantages of providing the achromatic retarder wherein at least two, or all, of the first, second and third trajectories extend within the single element 2 of birefringent material.
  • the redirecting unit comprises a mirror which has the function of reflecting the beam back towards the birefringent element(s) and an achromatic rotator which has the function of rotating the polarisation of the beam 8 over an angle. It will be appreciated that both functions may be embodied by a single optical component, e.g. a prism.
  • the first and second polarisation rotator 24,26 preferably are achromatic polarisation rotators, for example using the phase shift at total internal reflection, e.g. using a prism and/or mirror.
  • Figs. 4a-4k show schematic views of examples of achromatic retarders, which may be used within polarisation rotators for use in the redirecting unit.
  • Figs 4a-4e show examples of quarter wave total internal reflection retarders; two of these would be needed to construct a rotator.
  • Figs 4f-4k show examples of half wave achromatic total internal reflection polarisation rotators.
  • the polarisation rotators may comprise such components as a Fresnel rhomb 28 and/or prism 30 and/or mirror 32 and/or a plate 34.
  • the polarisation rotator shown in Fig. 4f utilises six internal reflections.
  • the field of view of the polarisation rotator of Fig. 4f is approximately 4.2 degrees.
  • the polarisation rotators shown in Figs. 4g and 4h utilise four internal reflections.
  • the refractive index of the optical elements 30,34 is, for instance, 1.55 (e.g. crown glass)
  • the field of view of the polarisation rotator of Figs. 4g and 4h is approximately 9.6 degrees.
  • the polarisation rotator shown in Fig. 4i utilises three internal reflections.
  • the refractive index of the optical elements 30,34 is, for instance, 1.7 (e.g.
  • the field of view of the polarisation rotator of Fig. 4i is approximately 18 degrees.
  • the refractive index of the prism 30 may for instance be 1.55 and the refractive index of the Fresnel rhomb may for instance be 1.5.
  • the polarisation rotator of Fig. 4k provides the advantage that the length of an optical path through the optical elements 30, in this example four prisms of fused silica, is minimised.
  • the plate 34 shown in Figs. 4f, 4h and 4i, serves as a substrate for constructional purposes.
  • the plate 34 may in the polarisation rotators according to these Figs, be omitted if so desired.
  • the optical path shown as the drawn (reflected) arrow OP, extends substantially in a single flat plane, which is parallel to the drawing plane in Figs. 4a-4k.
  • achromatic retarders shown in Figs 4a-4k may be used in the achromatic optical retarder or achromatic polarisation modulator according to the invention, e.g. in the polarisation modulator shown in Fig. 3.
  • the flat plane in which the optical path of the polarisation rotators extends will be at an angle with respect to the fast axis of the element 2, as will be further explained with respect to an example shown in Figs. 5a and 5b.
  • Figs. 5a and 5b show a schematic view of a third example of an embodiment of an achromatic optical retarder 1 according to the invention.
  • This example provides a more compact structure than the examples shown in Figs. 2 and 3.
  • the achromatic optical retarder is arranged as the achromatic polarisation modulator.
  • the polarisation modulator 1 comprises a single element 2 of birefringent material, here the birefringent material that is at least birefringent when the mechanical stress is applied to the material.
  • the fast axis of the element 2 extends in the longitudinal direction of the element 2, parallel to the line L in Figs. 5a and 5b.
  • the mechanical stress is applied in the longitudinal direction of the element 2.
  • the polarisation modulator 1 further comprises a transducer 18 as explained with respect to Fig. 3.
  • the polarisation modulator 1 comprises a redirecting unit 10.
  • the redirecting unit 10 comprises a first polarisation rotator 36 and a second polarisation rotator 38.
  • the first and second polarisation rotators 36,38 are in this example arranged according to Fig. 4f.
  • the first polarisation rotator 36 comprises three prisms 30.1,30.2,30.3 and a plate 34.1.
  • the second polarisation rotator 38 comprises three prisms 30.4,30.5,30.6 and a plate 34.2.
  • the optical path in the polarisation modulator as shown in Fig. 5a extends substantially in the plane of the drawing. This plane is indicated with R in Fig. 5b.
  • the retardance of the first or second polarisation rotator 36,38 can be tuned by changing the angle of incidence in two of the three prisms
  • the polarisation modulator 1 is arranged such that the beam of light emerging from the first polarisation rotator 36 is focussed in the centre of the element 2. This provides the advantage that the size of the prisms and hence the optical path length, and hence the chromatic retardance errors, are minimized for a given focal ratio of the beam.
  • the plane R in which the optical path extends extends at an angle with respect to the line L, and hence at an angle with respect to the fast axis of the element 2.
  • This angle is, in this example, related to the angle ⁇ for mechanical rotation of the central layer of birefringent material in the Pancharatnam achromatic retarder shown in Fig. 1.
  • the angle between a line Q which extends in the drawing plane of Fig. 5b perpendicular to the line L, and the plane R is half of the angle ⁇ , wherein ⁇ is between 55 and 60 degrees, e.g. 57 degrees. It will be appreciated that thus the polarisation orientation of the beam of light will be rotated over the angle ⁇ .
  • the desired combination of achromatic quality and achromatic range depends on the exact value of the angle ⁇ .
  • the second trajectory through the birefringent material extends through the center of the element 2.
  • the amplitude of the birefringence due to the periodically varying uniaxial mechanical stress induced by the transducer 18 will be maximum, in this example, since the transducer induces a standing sound wave in the longitudinal direction in the element 2.
  • the first trajectory through the birefringent material, from point A to point B, and the third trajectory through the birefringent material, from point G to point H do not extend through the centre of the element 2 in Figs 5a and 5b.
  • the beam 8 passes through the birefringent material which has a smaller birefringence than at the second trajectory.
  • the distance, measured in the longitudinal direction of the element 2, between the first and the second trajectory is small, e.g. ⁇ 30%, preferably ⁇ 10%, with respect to the distance, measured in the longitudinal direction of the element 2, between an edge 40 of the element 2 and the first trajectory. Then, the difference in birefringence at the first, second and third trajectory will be sufficiently small.
  • the achromatic optical retarder according to the invention may be used in situations where high polarimetric precision is needed over an extended wavelength range, for example, but not limited to, imaging polarimetry, spectropolarimetry, astronomy.
  • a beam of light consecutively passes at least three trajectories through birefringent material, wherein a fast axis of the birefringent material is oriented substantially perpendicular to the propagation direction of the beam of light at each of the at least three trajectories.
  • the fast axes of the birefringent material at the outer two trajectories of the at least three trajectories are oriented substantially at the same angle with respect to a polarisation orientation of the beam of light.
  • the fast axis of the birefringent material at the central trajectory of the at least three trajectories is oriented at a different angle with respect to the polarisation orientation of the beam of light than the fast axes of the birefringent material at the outer two trajectories of the at least three trajectories.
  • other configurations are conceivable.
  • achromatism may be further perfected by suitable coatings on internal reflection surfaces.
  • the redirecting unit may be encased in sound- absorbing material to reduce acoustical coupling to the element(s).
  • Polarisation modulation may be used together with (digital) gating on a detector for detecting the modulated beam of light. Thus, selected pats of the modulation cycle may be measured.
  • the transducer is arranged for inducing a periodically varying mechanical stress, and hence a periodically varying birefringence and thus periodically varying the polarisation change. It will be appreciated that it is also possible that the transducer is arranged for inducing a predetermined, variable or constant, mechanical stress, and hence a predetermined, variable or constant, birefringence and thus a predetermined, variable or constant, polaristion change.
  • the embodiment of the optical retarder shown in Fig. 2 may also be provided with the transducer for applying a varying or variable mechanical stress, so that an achromatic polarisation modulator may be obtained.
  • polarisation modulator shown in Figs. 3, 5a and 5b may also be provided without the transducer for applying a varying or variable mechanical stress, so that a constant achromatic optical retarder may be obtained.
  • polarisation rotators shown in Figs 4a-4k may also be applied in the achromatic optical retarder according to Fig. 2.
  • the beam of light passes three trajectories through birefringent material. It is also possible that the beam passes more than three trajectories through birefringent material, e.g. five or seven trajectories.
  • a static, variable or varying mechanical stress may be applied to the element(s) of birefringent material for obtaining a static, variable or varying birefringence.
  • a static, variable or varying electric field is applied to the element(s) of birefringent material, e.g. by applying a static, variable or varying electric voltage to the element(s) of birefringent material for obtaining a static, variable or varying birefringence.
  • the element(s) may also comprise other birefringent material, such as material which is at least birefringent when a magnetic field is applied to the material.
  • any reference signs placed between parentheses shall not be construed as limiting the claim.
  • the word 'comprising' does not exclude the presence of other elements or steps than those listed in a claim.
  • the words 'a' and 'an' shall not be construed as limited to 'only one', but instead are used to mean 'at least one', and do not exclude a plurality.
  • the mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Mechanical Light Control Or Optical Switches (AREA)
  • Polarising Elements (AREA)

Abstract

La présente invention concerne un retardateur optique achromatique dans lequel, lorsqu'il est utilisé, un faisceau incident de lumière passe consécutivement à travers un matériau biréfringent (2, 4) selon une première (AB), une deuxième (DE) et une troisième (GH) trajectoire ; un axe rapide du matériau (4) est orienté au niveau de la deuxième trajectoire à un angle différent par rapport à une orientation de polarisation du faisceau lumineux de l'axe rapide du matériau biréfringent (2) au niveau de la première et/ou de la troisième trajectoire, sachant qu'au moins deux des trajectoires (AB, GH) se déploient avec un élément unique (2) de matériau biréfringent.
PCT/NL2007/050087 2007-03-02 2007-03-02 Retardateur optique achromatique WO2008108628A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/NL2007/050087 WO2008108628A1 (fr) 2007-03-02 2007-03-02 Retardateur optique achromatique
GB0917011A GB2460206A (en) 2007-03-02 2007-03-02 Achromatic optical retarder

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/NL2007/050087 WO2008108628A1 (fr) 2007-03-02 2007-03-02 Retardateur optique achromatique

Publications (1)

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WO2008108628A1 true WO2008108628A1 (fr) 2008-09-12

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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5469279A (en) * 1989-10-30 1995-11-21 The University Of Colorado Foundation, Inc. Chiral smectic liquid crystal multipass optical filters including a variable retarder (and a variable isotropic spacer)
EP0840160A2 (fr) * 1996-10-31 1998-05-06 Sharp Kabushiki Kaisha Dispositif à cristaux liquides du type réflectif
WO2000036462A1 (fr) * 1998-12-18 2000-06-22 Colorlink, Inc. Retardateur composite achromatique
WO2001044862A1 (fr) * 1999-12-17 2001-06-21 Deutsche Telekom Ag Modulateur de phase optique
EP1139146A2 (fr) * 2000-03-21 2001-10-04 Lucent Technologies Inc. Filtre polarisant birefringent à double passage
US6380997B1 (en) * 1995-04-07 2002-04-30 Colorlink, Inc. Achromatic polarization inverters for displaying inverse frames in DC balanced liquid crystal displays
US6546159B1 (en) * 2001-08-22 2003-04-08 Avanex Corporation Method and apparatus for compensating differential group delay
US20060146682A1 (en) * 2004-12-16 2006-07-06 Colorlink, Inc. Achromatic polarization devices for optical disc pickup heads

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5469279A (en) * 1989-10-30 1995-11-21 The University Of Colorado Foundation, Inc. Chiral smectic liquid crystal multipass optical filters including a variable retarder (and a variable isotropic spacer)
US6380997B1 (en) * 1995-04-07 2002-04-30 Colorlink, Inc. Achromatic polarization inverters for displaying inverse frames in DC balanced liquid crystal displays
EP0840160A2 (fr) * 1996-10-31 1998-05-06 Sharp Kabushiki Kaisha Dispositif à cristaux liquides du type réflectif
WO2000036462A1 (fr) * 1998-12-18 2000-06-22 Colorlink, Inc. Retardateur composite achromatique
WO2001044862A1 (fr) * 1999-12-17 2001-06-21 Deutsche Telekom Ag Modulateur de phase optique
EP1139146A2 (fr) * 2000-03-21 2001-10-04 Lucent Technologies Inc. Filtre polarisant birefringent à double passage
US6546159B1 (en) * 2001-08-22 2003-04-08 Avanex Corporation Method and apparatus for compensating differential group delay
US20060146682A1 (en) * 2004-12-16 2006-07-06 Colorlink, Inc. Achromatic polarization devices for optical disc pickup heads

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GB2460206A (en) 2009-11-25
GB0917011D0 (en) 2009-11-11

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