WO2010126643A1 - Dispositif de filtrage spectral accordable - Google Patents

Dispositif de filtrage spectral accordable Download PDF

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Publication number
WO2010126643A1
WO2010126643A1 PCT/US2010/024845 US2010024845W WO2010126643A1 WO 2010126643 A1 WO2010126643 A1 WO 2010126643A1 US 2010024845 W US2010024845 W US 2010024845W WO 2010126643 A1 WO2010126643 A1 WO 2010126643A1
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WIPO (PCT)
Prior art keywords
optical filter
incidence
angle
filtration device
tunable spectral
Prior art date
Application number
PCT/US2010/024845
Other languages
English (en)
Inventor
Gilbert D. Feke
Douglas L. Vizard
Original Assignee
Carestream Health, 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
Priority claimed from PCT/US2009/002610 external-priority patent/WO2010042139A1/fr
Priority claimed from US12/709,156 external-priority patent/US20100208348A1/en
Application filed by Carestream Health, Inc. filed Critical Carestream Health, Inc.
Publication of WO2010126643A1 publication Critical patent/WO2010126643A1/fr

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Classifications

    • 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
    • G02B27/10—Beam splitting or combining systems
    • G02B27/14—Beam splitting or combining systems operating by reflection only
    • G02B27/144—Beam splitting or combining systems operating by reflection only using partially transparent surfaces without spectral selectivity
    • 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
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0938—Using specific optical elements
    • G02B27/0988—Diaphragms, spatial filters, masks for removing or filtering a part of the beam
    • 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
    • G02B27/288—Filters employing polarising elements, e.g. Lyot or Solc filters

Definitions

  • This invention relates, generally, to spectral filtration devices and more particularly to such devices that are tunable to adjust the spectral output or transmitted frequencies of the device.
  • spectral filtration devices for illumination systems used to deliver electromagnetic radiation to a subject and for detection systems that receive electromagnetic radiation from a subject.
  • known spectral filtration devices selectively attenuate the transmitted frequencies of electromagnetic radiation in the range or spectrum of optical wavelengths. These ranges include from ultraviolet, through visible, to near- infrared wavelengths, which include the portion of the electromagnetic spectrum producing photoelectric effects, referred to herein as "light”.
  • Spectral filtration of light is performed in basically two ways, dispersion-based techniques and filter-based techniques.
  • Filters of the bandpass type substantially attenuate transmitted optical wavelengths which are less than a "cut-on" wavelength and greater than a "cut-off wavelength, and do not substantially attenuate transmitted optical wavelengths in between the "cut-on" and “cut-off wavelengths.
  • Filters of the short pass type substantially attenuate transmitted optical wavelengths that are greater than a "cut-off wavelength.
  • Filters of the long pass type substantially attenuate transmitted optical wavelengths that are less than a "cut-on” wavelength.
  • a bandpass filter is devised from a combination or construction of a shortpass and a longpass filter.
  • Filters are often comprised of transparent optical substrates upon which is deposited a multilayer interference filter coating which determines the spectral properties of the filter.
  • Discrete filters have a coating that is substantially uniform across the clear aperture of the filter.
  • Circularly variable filters and linearly variable filters have coatings that spatially vary by design across the clear aperture of the filter so that when the filter is rotated or translated with respect to a light path, the transmitted optical wavelengths vary accordingly.
  • Liquid crystal tunable filters and acousto-optic tunable filters have also been developed. In order to be useful in most applications, an optical filter that is designed to transmit certain wavelengths must sufficiently reject all other wavelengths for which source energy and detector sensitivity both exist.
  • the all-dielectric filters it is not uncommon for the all-dielectric filters to have upwards of 200 total layers. Typically, only a relatively few such layers can be formed on a single surface. Thus, these layers must be distributed over several surfaces, for example, over two to four surfaces on one or two substrates, to minimize and balance coating stresses. Otherwise, the use of two substrates with a small air space is acceptable, and in a number of applications it is perfectly acceptable to coat two surfaces of the same substrate.
  • optical wavelengths transmitted by a given interference filter through a given cross-section of its clear aperture are dependent upon both the angle of the incident light with respect to the multilayer interference coating and, in many cases, also the polarization of the incident light with respect to the angle. This dependence to a near approximation is described by the formula given as
  • ⁇ the magnitude of the angle of incidence
  • ⁇ the wavelength of the particular spectral feature of interest at angle of incidence with magnitude ⁇
  • ⁇ o the wavelength of the particular spectral feature of interest 0 degree angle of incidence
  • N the effective refractive index of the coating for the polarization state of the incident light
  • * indicates multiplication.
  • the effective refractive index of a coating is determined by the coating materials used and the sequence of thin-film layers in the coating. In the case of collimated light where all the rays of light are parallel, tilting the filter with respect to the light path axis causes the transmission spectrum of the filter to shift to shorter wavelengths.
  • the rays of light which propagate at a nonzero angle with respect to the filter normal will experience a transmitted spectrum attenuation profile which is shifted to shorter wavelengths.
  • the parallel component in many cases, experiences a different shift of the transmission spectrum than the perpendicular component due to N being different for the different components.
  • tilting a single interference filter is effective for controlling the transmission spectrum when the light is collimated
  • the approach loses its effectiveness when the light is non-collimatcd, i.e., has divergent or convergent angular components. This loss occurs because the angles-of-incidence upon tilting are decreased for light rays which propagate in directions away from the direction of tilt and increased for light rays which propagate in directions toward the angle of tilt, so that the light rays with decreased angles of incidence experience a transmitted spectrum attenuation profile which is shifted to longer " wavelengths relative to the light path axis and the light rays with increased angles of incidence experience a transmitted spectrum attenuation profile which is shifted to shorter wavelengths relative to the light path axis, respectively.
  • the result is a smearing of the transmitted spectrum attenuation profile.
  • This smearing is advantageously smaller when the effective index N of the multilayer interference coating is larger, but a larger effective index N results in a smaller tuning range, which is a disadvantage.
  • the approach loses its effectiveness for light whose polarization state is a superposition of nonzero parallel and perpendicular components relative to the tilt axis because the parallel component, in many cases, experiences a different shift of the transmission spectrum than the perpendicular component due to N being different for the different components, thereby causing smearing of the transmitted spectrum attenuation profile.
  • the transmitted optical wavelengths of a single filter are limited to those available by tilting the filter with respect to a light path. Accordingly, there is a need for a tunable spectral filtration device that overcomes or avoids the above problems and limitations.
  • a tunable spectral filtration device that overcomes or avoids the above problems and limitations.
  • Laser sources provide sufficient spectral purity, often without the need to perform spectral filtration, and a high degree of polarization, but they are often undesirable due to high cost.
  • optical coherence effects characteristic of lasers often lead to system artifacts, such as ⁇ speckle.
  • LEDs Light emitting diodes
  • Monochromatic LEDs have a narrow spectral bandwidth, but do not provide the spectrally-pure light output necessary for many applications. Furthermore, LEDs do not provide collimated light output, and the degree of polarization of their light output is typically low, so therefore there is a need for a low-cost spectral filtration device for LEDs that can accommodate their light output.
  • the tunable spectral filtration devices of the present invention address the foregoing needs by substantially cancelling angle-of-incidence dependent spectral broadening and/or polarization dependent spectral broadening.
  • the tunable spectral filtration device comprises at least one optical filter for intersecting a first path of converging or diverging light comprising an axis at a first angle of incidence and at least one device positioned to enable a second path of converging or diverging light to pass through the at least one optical filter at a second angle of incidence.
  • the optical filter comprises at least one coating and is tiltable over a plurality of angles with respect to the axis of the light path.
  • the first angle of incidence is opposite in sign to the second angle of incidence, and the positioning of the first and second optical filters substantially cancels angle-of-incidence dependent spectral broadening.
  • the tunable spectral filtration device comprises the at least one optical filter and the at least one device, wherein the at least one device comprises a partially reflective surface positioned to redirect the converging or diverging light and a reflective surface positioned to reflect the converging or diverging light back through the optical filter.
  • the optical filter comprises at least one coating and is tiltable over a plurality of angles with respect to the axis of the light path. The positioning of the at least one optical filter and the partially reflective and reflective surfaces cancels angle-of-incidence dependent spectral broadening and/or polarization dependent spectral broadening of the converging or diverging light.
  • a tunable spectral filtration device comprises at least one optical filter for intersecting a first path of converging or diverging light comprising an axis at a first angle of incidence and at least one device positioned to enable a second path of the converging or diverging light to pass through the at least one optical filter at a second angle of incidence.
  • the at least one optical filter is capable of exhibiting substantially no polarization splitting and is tiltable over a plurality of angles with respect to the axis of the light path.
  • the first angle of incidence is opposite in sign to the second angle of incidence, and the positioning of the at least one optical filter and the at least one device substantially cancels angle-of-incidence dependent spectral broadening.
  • the present invention relates to methods of improving the spectral quality of filtered converging or diverging light.
  • the methods comprise providing converging or diverging light from a light source; providing a path for the converging or diverging light through at least one optical filter comprising an axis; and improving the spectral quality of the converging or diverging light by substantially canceling angle-of-incidence dependent spectral broadening and/or polarization dependent spectral broadening.
  • the at least one optical filter of this embodiment comprises at least one coating and is tiltablc over a plurality of angles with respect to the axis of the light path.
  • the foregoing embodiments may include various additional features and structures.
  • the first angle of incidence may be substantially equal in magnitude to the second angle of incidence.
  • the partially reflective surface may comprise a polarization-insensitive beamsplitter and the reflective surface may comprise a mirror.
  • the foregoing embodiments may further comprise a light source selected from the group consisting of a light emitting diode, a multicolor light emitting diode, a phosphor-coated light emitting diode, a halogen lamp, a xenon lamp and combinations thereof.
  • first and second optical filters may be substantially identical and set in various positions, including in series to intersect the converging or diverging light.
  • the first optical filter may be tilted at an angle opposite in sign to the tilt angle of the second optical filter.
  • the first optical filter may be tilted at an angle with equal magnitude to the second optical filter and/or the tilt angles of the first and second optical filters may be substantially identical.
  • the first and second filters may be mounted in filter selection members and selectable from a collection of optical filters mounted in such selection members.
  • the optical filters may exhibit substantially no polarization splitting, provide a steep edge absorption at angles of incidence ranging in magnitude from 0° to 60° and /or provide a substantially uniform transmission spectrum.
  • FIGS. IA and IB are a pair of graphs for reference showing the transmittance for S and P polarizations of a 542 nm central wavelength, 20 nm bandpass filter as functions of wavelength and angle of incidence.
  • FIG. 2A illustrates a known configuration wherein a filter is intersecting an unpolarized collimated light path at normal incidence.
  • FIG. 2B illustrates transmittance vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter for the configuration of FIG. 2A.
  • FIG. 3A illustrates a known configuration wherein a filter is intersecting an unpolarized non-collimated light path at normal incidence.
  • FlG. 3B illustrates transmittance vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter for the configuration of FlG. 3 A.
  • FlG. 4A illustrates a known configuration wherein a filter is intersecting an unpolarized collimated light path at a pitch angle of -30 degrees.
  • FIG. 4B illustrates transmittance vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter for the configuration of FlG. 4A.
  • FIG. 5A illustrates a configuration wherein a filter is intersecting an unpolarized non-collimated light path at a pitch angle of -30 degrees.
  • FIG. 5B illustrates transmittance vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter for the configuration of FIG. 5A.
  • FIG. 6A is an illustration of a configuration wherein two filters are intersecting an unpolarized non-collimated light path, both at pitch angle of -30 degrees.
  • FIG. 6B illustrates transmittance vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter for the configuration of FIG. 6A.
  • FIG. 7A illustrates an embodiment of the invention comprising a configuration wherein two filters are intersecting an unpolarized non-collimated light path, one at a pitch angle of -30 degrees and the other at a pitch angle of +30 degrees.
  • FIG. 7B illustrates transmittance vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter for the configuration of FIG. 7A.
  • FIG. 7C illustrates an embodiment of the invention comprising the configuration of FIG. 7 A wherein the layers of the multilayer interference coatings are evenly distributed between the two filters.
  • FIG. 8A illustrates another embodiment of the invention comprising a configuration wherein two filters are intersecting an unpolarized non-collimated light path, one at a pitch angle of -30 degrees and the other at a yaw angle of -30 degrees.
  • FIG. 8B illustrates transmittance vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter for the configuration of FIG. 8A.
  • FIG. 9A illustrates a further embodiment of the invention comprising a configuration wherein four filters are intersecting an unpolarized non-collimated light path, one at a pitch angle of -30 degrees, another at a pitch angle of +30 degrees, another at a yaw angle of +30 degrees, and another at a yaw angle of -30 degrees.
  • FIG. 9B illustrates transmittance vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter for the configuration of FIG. 9A.
  • FIG. 10 is a graph showing transmittance vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter for all the configurations of FIGS. 2B, 3B, 4B, 5B, 6B, 7B, 8B and 9B.
  • FIG. 1 1 illustrates yet another embodiment of the invention wherein four filters are selected from loose piece collections of filters, tilted and fixedly mounted, whereby the selection and tilting are made permanent.
  • FlG. 12A illustrates still another embodiment of the invention wherein four filters are selected from loose piece collections of filters, tilted and adjustably mounted, whereby the selection and tilting are adjustable.
  • FlG. 12B illustrates schematically the adjustable fixture of FlG. 12A.
  • FIG. 13 illustrates an embodiment of the invention wherein four filters are selected from collections of filters mounted in rotatable wheels, and tilted, whereby the selection and tilting are adjustable.
  • FIG. 14 illustrates an embodiment of the invention wherein four filters are selected from collections of filters mounted in translatable sliders, and tilted, whereby the selection and tilting are adjustable.
  • FIG. 15 illustrates an embodiment wherein four filters are selected, tilted, and positioned intersecting a light path from a light source, the filtered output light being directed toward a capture device.
  • FIG. 16 illustrates an embodiment of the invention comprising a configuration where two VersaChrome filters arc intersecting an unpolarized non- coUimated light path, one at a pitch angle of -30 degrees and the other at a pitch angle of +30 degrees.
  • FIG. 17 illustrates yet another embodiment of the invention where two VersaChrome filters are selected from loose piece collections of VersaChrome filters, tilted and fixedly mounted, whereby the selection and tilting are made permanent.
  • FIG. 18A illustrates still another embodiment of the invention where two VersaChrome filters are selected from loose piece collections of VersaChrome filters, tilted and adjustably mounted, whereby the selection and tilting are adjustable.
  • FIG. 18B illustrates schematically the adjustable fixture of FIG. 18A.
  • FIG. 19 illustrates an embodiment of the invention where two VersaChrome filters are selected from collections of VersaChrome filters mounted in rotatable wheels, and tilted, whereby the selection and tilting are adjustable.
  • FIG. 20 illustrates an embodiment of the invention where two VersaChrome filters arc selected from collections of VersaChrome filters mounted in translatable sliders, and tilted, whereby the selection and tilting are adjustable.
  • FIG. 21 illustrates an embodiment wherein two VersaChrome filters are selected, tilted, and positioned intersecting a light path from a light source, the filtered output light being directed toward a capture device.
  • FIG. 22 illustrates an embodiment of the invention where a non- collimated light path is diverted by a polarization-insensitive beamsplitter into a filter at a given pitch angle, and then reflected by a mirror back through the filter toward a capture device.
  • the tunable spectral filtration device of the presently claimed invention comprises at least one optical filter for intersecting a first path of converging or diverging light comprising an axis at a first angle of incidence and at least one device positioned to enable a second path of converging or diverging light to pass through the at least one optical filter at a second angle of incidence.
  • the optical filter comprises at least one coating and is tiltable over a plurality of angles with respect to the axis of the light path.
  • the at least one device may comprise a second optical filter, which is positioned in series with the first, while in others, the at least one device may comprise a beamsplitter for diverging the first light path and a mirror for reflecting the light path back through the optical filter.
  • Figures IA and B respectively show the transmittance for S and P polarizations of a 542 nm central wavelength, 20 nm bandpass filter as functions of wavelength and angle of incidence as calculated using equation (1).
  • the graphs are based on published product data from Semrock, Inc., for 0 degrees angle-of- incidence and exemplary values for the effective index for S and P polarizations as suggested in published information by Semrock, Inc. Data published by Semrock, Inc., also indicates that Equation 1 is a valid approximation out to at least 45 degree angle-of-incidence.
  • a filter of the bandpass type was selected for illustration of the preferred embodiments because this type is comprised of both a cut-on edge and a cut-off edge, and the behavior of these edges is individually applicable to filters of other types.
  • Figures I A and B show that for a light ray with any given combination of wavelength, angle-of-incidence, and polarization components, the transmittance is mostly either rather high or rather low, i.e., that the transmittance is a sharp function of wavelength, angle-of-incidencc, and polarization.
  • Figures IA and B are provided as a reference for the detailed description of the preferred embodiments.
  • Figure 2A shows a known configuration wherein a filter 1 1 is intersecting an unpolarized collimated light path 12 at normal, i.e., 0 degree angle of, incidence with respect to the incident light path axis 2.
  • the transmitted light path axis docs not undergo a translational shift.
  • the transmittance spectrum of this configuration is represented by the average of the O degree angle-of-incidence slices of the S and P polarization graphs shown in Figures I A and B, which are in fact identical.
  • Figure 2B shows transmittance relative to peak vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter as described in Figures IA and B for the configuration in Figure 2A as simulated by TraccPro optical modeling software from Lambda Research Corporation using a circular grid source.
  • Figure 3A shows a known configuration wherein filter 11 is intersecting an unpolarized non-collimated light path 1 at normal, i.e., 0 degree angle of, incidence with respect to incident light path axis 2.
  • the transmitted light path axis does not undergo a translational shift.
  • the non-collimated light was given a Lambertian angular weighting within a 15 degree half cone.
  • the transmittance spectrum of this configuration is therefore represented by the Lambertian weighted average over angle of the average of the S and P polarization slices between 0 and 15 degree angle-of-incidence as shown in Figures I A and B.
  • Figure 3B shows transmittance relative to peak vs.
  • the transmittance spectrum of this configuration is represented by the average of the 30 degree angle-of-incidcnce slices of the S and P polarization graphs shown in Figures A and B.
  • Figure 4B shows transmittance relative to peak vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter as described in Figures IA and B for the configuration in Figure 4A as simulated using a circular grid source.
  • the resulting central wavelength is shown to have shifted significantly to shorter wavelength compared to the central wavelength of the configuration shown in Figure 2A. This is due to the large angle of incidence.
  • the resulting bandwidth is shown to have increased compared to the bandwidth of the configuration shown in Figure 2 A, with a characteristic "ziggurat" shape of the transmittance spectrum, due to the difference in the effective index for the S and P polarization components.
  • Figure 5A shows a known configuration wherein filter 3 is intersecting unpolarized non-collimated light path 1 at a pitch angle of -30 degrees with respect to incident light path axis 2.
  • the transmitted light path axis undergoes a translational shift.
  • the non-collimated light was given a Lambertian angular weighting within a 15 degree half cone.
  • the transmittance spectrum of this configuration is therefore represented by the Lambertian weighted average over angle of the average of the S and P polarization slices between 15 degree and 45 degree anglc-of-incidence as shown in Figures IA and B.
  • Figure 5B shows transmittance relative to peak vs.
  • Figure 6B shows transmittance relative to peak vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter as described in Figures I A and B for the configuration in Figure 6A as simulated using a circular grid source.
  • Figure 6B shows that the transmittance spectrum is very similar to that shown in Figure 5B, with only a very slight decrease in transmittance at the extremes of the spectrum. This is because every incident ray with a given wavelength, angle of incidence, and polarization state experiences a sharp transmittance spectrum as shown in Figures IA and B, so that a light ray that this transmitted by the first filter with near unity transmittance relative to peak in fact has its properties preserved upon incidence onto the second filter, which also transmits the light ray with near unity transmittance relative to peak.
  • Figure 7A shows an embodiment wherein two identical filters are intersecting unpolarized non-collimated light path 1 , one filter 3 at a pitch angle of -30 degrees and the other filter 4 at a pitch angle of +30 degrees with respect to incident light path 2. Jn this configuration the transmitted light path axis undergoes a translational shift upon transmission through the first filter and another translational shift of the same magnitude and opposite direction upon transmission through the second filter, the result being zero net translational shift.
  • These two filters comprise a matched pair 5 oppositely tilted in pitch angle according to the invention.
  • the non-collimated light was given a Lambertian angular weighting within a 15 degree half cone.
  • Figure 7B shows transmittance relative to peak vs.
  • FIG. 7 A shows an embodiment wherein the layers 110.of the multilayer interference coatings on substrates 100 are' evenly distributed between two identical filters of Figure 7A to achieve the desired spectral profile.
  • the distribution of the layers need not be exactly evenly distributed.
  • Figure 8A shows a preferred embodiment wherein two identical filters are intersecting unpolarized non-collimated light path 1, one filter 3 at a pitch angle of -30 degrees and the other filter 7 at a yaw angle of -30 degrees with respect to incident light path 2.
  • the transmitted light path axis undergoes a translational shift upon transmission through the first filter and another translational shift of the same magnitude and orthogonal direction upon transmission through the second filter.
  • These two filters comprise a matched pair 9 wherein one filter is tilted by the same amount as the other filter and is tilted along a tilt axis perpendicular to the tilt axis of the other filter.
  • Figure 8B shows transmittance relative to peak vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter as described in Figures IA and B for the configuration in Figure 8A as simulated using a circular grid source.
  • Figure 8B shows that the resulting bandwidth is decreased compared to the bandwidth of the configuration shown in Figures 5A and 6A.
  • any given light ray transmitted through the first filter at a pitch angle magnitude of the absolute value of (-30 + x) degrees and a yaw angle magnitude of the absolute value of y degrees is incident upon the second filter at a pitch angle magnitude of the absolute value of x degrees and a yaw angle magnitude of the absolute value of (-30 + y) degrees, where x and y are between -15 degrees and 15 degrees. Therefore the S polarization components of the light rays transmitted by the first filter are the P polarization components of the light rays incident upon the second filter, and the P polarization components of the light rays transmitted by the first filter are the S polarization components of the light rays incident upon the second filter.
  • Figure 9A shows another embodiment wherein four interleaved, identical filters are intersecting unpolarized non-collimated light path 1, one input filter 3 at a pitch angle of -30 degrees, another output filter 4 at a pitch angle of +30 degrees, another input filter 6 at a yaw angle of +30 degrees, and another output filter 7 at a yaw angle of -30 degrees, with respect to incident light path 2.
  • the transmitted light path axis undergoes a translational shift upon transmission through the first filter, another translational shift of the same magnitude and opposite direction upon transmission through the second filter, another translational shift of the same magnitude and direction orthogonal to the direction of translational shift provided by the first two filters upon transmission through the third filter, and another translational shift of the same magnitude and opposite direction as the translational shift provided by the third filter upon transmission through the fourth filter, the result being zero net translational shift.
  • Filters 3 and 4 comprise a matched pair 5 oppositely tilted in pitch angle according to the invention.
  • Filters 6 and 7 comprise a matched pair 8 oppositely tilted in yaw angle according to the invention.
  • Matched pairs 5 and 8 comprise a super pair 10 according to the invention wherein one of the matched filter pairs comprises filters that are tilted along a tilt axis perpendicular to the tilt axis of the filters comprising the other of the matched filter pairs.
  • the non-collimated light was given a Lambertian angular weighting within a 15 degree half cone.
  • Figure 9B shows transmittance relative to peak vs. wavelength of the 542 nm central wavelength, 20 nm bandpass filter as described in Figures IA and B for the configuration in Figure 9A as simulated using a circular grid source.
  • Figure 9B shows hat the resulting bandwidth is decreased compared to the bandwidth of the configuration shown in Figures 7A and 8 A.
  • filters 3, 4, 6 and 7 arc selected from loose piece collections of filters 13, 14, 16 and 17 and tilted, resulting in two matched pairs 5 and 8, and one super pair 10.
  • the selection and tilting are made permanent by a fixture 20.
  • filters 3, 4 may have pitch angles that are equal in magnitude and opposite in sign
  • filters 6, 7 may have yaw angles that are equal in magnitude and opposite in sign.
  • the respective pitch and yaw angles may not be exactly equal in magnitude.
  • filters 3, 4, 6 and 7 are selected from loose piece collections of filters 13, 14, 16 and 17 and tilted, resulting in two matched pairs 5 and 8, and one super pair 10.
  • the selection and tilting may be adjustable, via a movable fixture 22.
  • filters 3, 4 may have pitch angles that are equal in magnitude and opposite in sign
  • filters 6, 7 may have yaw angles that are equal in magnitude and opposite in sign.
  • the respective pitch and yaw angles may not be exactly equal in magnitude.
  • fixture 22 may be rotatable, thereby providing mechanical control of the tilt angle of the filters with respect to the light path.
  • Fixture 22 also may allow for both mounting and releasing of filters, thereby providing mechanical control of the filter selection.
  • collection 13 of filters 3, 4, 6 and 7 is mounted rotationally on a filter wheel 28.
  • the collections 14, 16 and 17 of filters 3, 4, 6 and 7 arc mounted rotationally on wheels 30, 32 and 34, respectively.
  • Each filter wheel also has a blank hole 36.
  • Each filter wheel may be moved to a position so that four identical filters mounted on the filter wheel are rotated to intersect unpolarized non- collimated light path 1 as indicted by arrow 40, with one filter 3 at a pitch angle of -30 degrees, another filter 4 at a pitch angle of +30 degrees, another filter 6 at a yaw angle of +30 degrees, and another filter 7 at a yaw angle of -30 degrees, with respect to incident light path 2, resulting in two matched pairs 5 and 8, and one super pair 10.
  • the position of the pitch or tilt of each filter wheel may be selected as indicated by arrow 42 and the position of the yaw of each filter wheel may be selected as indicated by arrow 44.
  • Adjustments of pitch and yaw may be performed via a device 50 and may be automatically controlled via a control computer 46 shown in Figure 15.
  • the previously mentioned applications of Harder et al and Hall et al disclose features for adjusting tilt of filters that are useful in the present invention.
  • filters 3, 4, 6 and 7 are selected from collections 60 of filters mounted on translatable sliders 62, resulting in two matched pairs 5 and 8, and one super pair 10.
  • Each of filters 3, 4, 6 and 7 is selected and moved into and out of position via a plurality of translatable sliders 62 running laterally on a corresponding plurality of tracks 64.
  • the selection of each filter, the position of the pitch of each filter and the position of the yaw of each filter are performed via the translatable sliders 62 and may be automatically controlled via the control computer 46 shown in Figure 15.
  • filters 3, 4 may be set to pitch angles that are equal in magnitude and opposite in sign
  • filters 6, 7 may be set to yaw angles that are equal in magnitude and opposite in sign.
  • the respective pitch and yaw angles may not be exactly equal in magnitude.
  • Figure 15 shows schematically how four selected filters 3, 4, 6 and 7, resulting in two matched pairs 5 and 8, and one super pair 10 are tilted and positioned to intersect light path 2.
  • filters 3, 4 may have pitch angles that are equal in magnitude and opposite in sign
  • filters 6, 7 may have yaw angles that are equal in magnitude and opposite in sign.
  • the respective pitch and yaw angles may not be exactly equal in magnitude.
  • a light source 70 provides the light that forms an image on a screen 72. The image is captured by a capture device 74.
  • Light source 70 and capture device 70 are connected to a computer 46 via cables 48 and may be automatically controlled by computer 46.
  • Light source 70 may be, but is not limited to, one of monochromatic light emitting diode (LED), a polychromatic LED, a "white” (i.e., phosphor-coated) LED, a halogen lamp or a xenon lamp.
  • Capture device 74 may be, but is not limited to, one of a photodiode, a film camera, a digital camera, or a digital video camera.
  • a folded configuration may also substantially cancel angle-of-incidence dependent spectral broadening and/or polarization dependent spectral broadening of converging or diverging light.
  • Figure 22 shows an embodiment where non- collimated light from light source 70 travels twice through filter 203 before forming an image on screen 72 and is captured by capture device 74.
  • light path 2 is first diverted by a partially reflective surface, in this case a polarization-insensitive beamsplitter 209, which directs light path 2 through filter 203, tilted at a pitch angle to achieve the desired wavelength transmission.
  • Light path 2 then travels toward mirror 207, and is reflected back through filter 203 at a pitch angle of opposite sign.
  • Light source 70 and capture device 74 are connected to computer 46 via cables 48 and may be automatically controlled by computer 46.
  • Light source 70 may be, but is not limited to, one of monochromatic light emitting diode (LED), a polychromatic LED, a "white” (i.e., phosphor-coated) LED, a halogen lamp or a xenon lamp.
  • Capture device 74 may be, but is not limited to, one of a photodiode, a film camera, a digital camera, or a digital video camera. Additionally, the optical filters used in any of the foregoing embodiments may be replaced with filters that exhibit substantially no polarization splitting. Filters with this quality include those commercially available from Semrock, Inc. under the trademark VersaChrome.
  • VersaChrome filters include (a) Semrock Part Number TBPO 1-440/ 16-25x36 (which has a CWL Range of 390 - 440 nm when tilted from 60 degrees to 0 degrees, and > 90% average transmission over a 16 nm bandwidth), (b) Semrock Part Number TBPO 1 -490/15-25x36 (which has a CWL Range of 440 - 490 nm when tilted from 60 degrees to 0 degrees, and > 90% average transmission over a 15 nm bandwidth, (c) Semrock Part Number TBPO 1-550/15-25x36 (which has a CWL Range of 490 - 550 nm when tilted from 60 degrees to 0 degrees, and > 90% average transmission over a 15 nm bandwidth, (d) Semrock Part Number TBP01-620/14-25x36 (which has a CWL Range of 550 - 620 nm when tilted from 60 degrees to 0 degrees, and > 90% average transmission over a 14 nm bandwidth
  • Such filters substantially eliminate the polarization dependence of the transmission spectra as a function of angle. Further, they offer wavelength tunability over a very wide range of wavelengths by adjusting the angle of incidence with essentially no change in spectral performance. For example, with a tuning range of greater than 12% of the normal-incidence wavelength (by varying the angle of incidence from 0 degrees to 60 degrees), only five Versachrome filters are needed to cover the full visible spectrum.
  • VersaChrome tunable filters filters offer an average transmission greater than 90% with steep edges and wideband blocking of bandpass for applications like fluorescence imaging. More particularly, such filters provide a steep edge absorption at angles of incidence ranging in magnitude from 0° to 60° and are capable of producing a substantially uniform transmission spectrum.
  • FIG. 9A, 1 1 , 12A, 13, 14 and 15 When Versachrome filters are employed, the second pair of optical filters shown in Figures. 9A, 1 1 , 12A, 13, 14 and 15 is unnecessary.
  • Embodiments employing Versachrome filters arc shown at Figures 18-21.
  • Figure 16 shows an embodiment where two identical VersaChrome filters are intersecting unpolarized non-collimated light path 1, with first VersaChrome filter 203 positioned at a pitch angle of -30 degrees and second VersaChrome filter 204 positioned at a pitch angle of +30 degrees with respect to incident light path 2.
  • First light path 216 intersects first VersaChrome filter 203 and second light path 218 intersects second VersaChrome filter 204.
  • the transmitted light path axis undergoes a translational shift upon transmission through first VersaChrome filter 203 and another translational shift of the same magnitude and opposite direction upon transmission through second VersaChrome filter 204, the result being zero net translational shift.
  • These two VersaChrome filters comprise a matched VersaChrome pair 205 oppositely tilted in pitch angle according to the invention.
  • the resulting bandwidth is decreased compared to the bandwidth of known configurations. This is because any given light ray transmitted through first VersaChrome filter 203 at a pitch angle magnitude of the absolute value of (- 30 + x) degrees is incident upon second VersaChrome filter 204 at a pitch angle magnitude of the absolute value of (30 + x) degrees, where x is between -15 degrees and 15 degrees.
  • first VersaChrome filter 203 Because of a relatively smaller magnitude of angle of incidence but arc rejected by second VersaChrome filter 203 because of a relatively larger magnitude of angle of incidence; and some light rays with wavelengths shorter than the central wavelength are transmitted by first VersaChrome filter 203 because of a relatively larger magnitude of angle of incidence but are rejected by second VersaChrome filter 204 because of a relatively smaller magnitude of angle of incidence.
  • the resulting transmission spectrum is not further broadened.
  • Versachrome filters 203 and 204 may have pitch angles that are equal in magnitude and opposite ⁇ n sign. As illustrated in Figs. 17 and 18A, two VersaChrome filters 203 and 204 are selected from loose piece collections and tilted, resulting in a matched VersaChrome pair 205. The selection and tilting are made permanent by fixture 20. As illustrated, VersaChrome filters 203, 204 may be positioned so that they have pitch angles that are equal in magnitude and opposite in sign.
  • first path of light 216 passes through first VersaChrome filter 203 and second path of light 218 passes through second VersaChrome filter 204.
  • fixture 22 may be rotatable, thereby providing mechanical control of the tilt angle of the filters with respect to the light path.
  • Fixture 19 also may allow for both mounting and releasing of filters, thereby providing mechanical control of filter selection.
  • the VersaChrome filters or a collection of Versachrome filters may also be mounted rotationally on a filter wheel 28, as shown in Fig. 19.
  • Each filter wheel 28 comprises a blank hole 36, and may be positioned so that a plurality of filters mounted on the filter wheel are rotated to intersect unpolarized non-collimated light path 1 as indicted by arrow 40, with first VersaChrome filter 203 at a pitch angle of -30 degrees, and second VersaChrome filter 204 at a pitch angle of +30 degrees, with respect to incident light path 2, resulting in a matched VersaChrome pair 205.
  • each filter wheel may be selected as indicated by arrow 42, such that first path of light 216 passes through a first filter and second path of light 218 passes through a second filter. Adjustments of pitch may be performed via device 50 and may be automatically controlled via a control computer 46, shown in Figure 21.
  • the previously mentioned applications of Harder et al. and Hall et al. disclose features for adjusting tilt of filters that are useful in the present invention.
  • four pluralities of VersaChrome filters 203 and 204 may be selected from collections 260 of VersaChrome filters mounted on translatable sliders 62, resulting in a matched VersaChrome pair 205.
  • each VersaChrome filter 203 and 204 is selected and moved into and out of position via a plurality of translatable sliders 62 running laterally on a corresponding plurality of tracks 64.
  • the selection of each VersaChrome filter, and the positioning of the pitch of each VersaChrome filter are carried out via the translatable sliders 62 and may be automatically controlled via the control computer 46 shown in Figure 21.
  • VersaChrome filters 203, 204 may be set to pitch angles that are equal in magnitude and opposite in sign. However, those skilled in the art will appreciate that in some applications, the pitch angles may not be exactly equal and opposite.
  • Figure 21 shows schematically how two selected VersaChrome filters 203 and 204, resulting in a matched VersaChrome pair 205 are tilted and positioned to intersect light path 2.
  • First path of light 216 passes through first VersaChrome filter 203 and second path of light 218 passes through second VersaChrome filter 204.
  • VersaChrome filters 203, 204 have pitch angles that are equal in magnitude and opposite in sign. However, those skilled in the art will appreciate that in some applications, the pitch angles may not be exactly equal in magnitude.
  • a light source 70 provides the light that forms an image on a screen 72. The image is captured by a capture device 74.
  • Light source 70 and capture device 74 are connected to computer 46 via cables 48 and may be automatically controlled by computer 46.
  • Light source 70 may be, but is not limited to, one of monochromatic light emitting diode (LED), a polychromatic LED, a "white” (i.e., phosphor-coated) LED, a halogen lamp or a xenon lamp.
  • Capture device 74 may be, but is not limited to, one of a photodiode, a film camera, a digital camera, or a digital video camera.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Polarising Elements (AREA)

Abstract

L'invention porte sur un dispositif de filtrage spectral accordable qui comprend au moins un filtre optique pour croiser un premier trajet de lumière convergente ou divergente comprenant un axe à un premier angle d'incidence, et au moins un dispositif positionné pour permettre à un second trajet de la lumière convergente ou divergente de passer par le au moins un filtre optique à un second angle d'incidence. Le filtre optique comprend au moins un revêtement et est inclinable suivant une pluralité d'angles par rapport à l'axe. Le premier angle d'incidence est de signe opposé au second angle d'incidence, de telle sorte que le positionnement du au moins un filtre optique et du au moins un dispositif annule sensiblement l'élargissement spectral dépendant de l'angle d'incidence et/ou l'élargissement spectral dépendant de la polarisation, de la lumière convergente ou divergente.
PCT/US2010/024845 2009-04-29 2010-02-20 Dispositif de filtrage spectral accordable WO2010126643A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
PCT/US2009/002610 WO2010042139A1 (fr) 2008-10-10 2009-04-29 Dispositif de filtrage spectral accordable
USPCT/US2009/002610 2009-04-29
US12/709,156 2010-02-19
US12/709,156 US20100208348A1 (en) 2008-08-22 2010-02-19 Tunable spectral filtration device

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WO2010126643A1 true WO2010126643A1 (fr) 2010-11-04

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050207014A1 (en) * 2004-03-05 2005-09-22 Coronado Instruments, Inc. Solar tunable filter assembly
US7197208B2 (en) * 2004-04-13 2007-03-27 Agilent Technologies Wavelength tunable light sources and methods of operating the same
US7218650B2 (en) * 2003-12-31 2007-05-15 Intel Corporation Wavelength reference filter
US20080208297A1 (en) * 2005-01-25 2008-08-28 Allux Medical, Inc. Optical Therapy Devices, Systems, Kits and Methods for Providing Therapy to a body Cavity

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7218650B2 (en) * 2003-12-31 2007-05-15 Intel Corporation Wavelength reference filter
US20050207014A1 (en) * 2004-03-05 2005-09-22 Coronado Instruments, Inc. Solar tunable filter assembly
US7197208B2 (en) * 2004-04-13 2007-03-27 Agilent Technologies Wavelength tunable light sources and methods of operating the same
US20080208297A1 (en) * 2005-01-25 2008-08-28 Allux Medical, Inc. Optical Therapy Devices, Systems, Kits and Methods for Providing Therapy to a body Cavity

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