WO2019027724A1 - Filtre optique passe-bande - Google Patents

Filtre optique passe-bande Download PDF

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Publication number
WO2019027724A1
WO2019027724A1 PCT/US2018/043393 US2018043393W WO2019027724A1 WO 2019027724 A1 WO2019027724 A1 WO 2019027724A1 US 2018043393 W US2018043393 W US 2018043393W WO 2019027724 A1 WO2019027724 A1 WO 2019027724A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical
diffuser
bandpass
optical filter
broadband
Prior art date
Application number
PCT/US2018/043393
Other languages
English (en)
Inventor
Steven J. Byrnes
Jeffrey Korn
David J. Carter
Original Assignee
The Charles Stark Draper Laboratory, 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 The Charles Stark Draper Laboratory, Inc. filed Critical The Charles Stark Draper Laboratory, Inc.
Publication of WO2019027724A1 publication Critical patent/WO2019027724A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/20—Filters
    • G02B5/28—Interference filters
    • G02B5/284—Interference filters of etalon type comprising a resonant cavity other than a thin solid film, e.g. gas, air, solid plates
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/02—Diffusing elements; Afocal elements
    • G02B5/0205—Diffusing elements; Afocal elements characterised by the diffusing properties
    • G02B5/021—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures
    • G02B5/0221—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures the surface having an irregular structure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/50—Constructional details
    • H04N23/55—Optical parts specially adapted for electronic image sensors; Mounting thereof

Definitions

  • a bandpass optical filter comprises a broadband optical diffuser and a narrowband anti- diffuser disposed in a common optical path with the broadband optical diffuser.
  • the broadband optical diffuser comprises a substrate including pseudo-randomly arranged regions of a first thickness and regions of a second thickness less than the first thickness.
  • the narrowband anti-diffuser may include dielectric optical resonators disposed in opposed relation to one of either the regions of the first thickness and the regions of the second thickness.
  • the narrowband anti-diffuser includes dielectric optical resonators.
  • the dielectric optical resonators may be disposed on a substrate separated from the broadband optical diffuser.
  • the dielectric optical resonators may be disposed on the broadband optical diffuser.
  • the broadband optical diffuser is spaced from the narrowband anti-diffuser at a distance of less than about a central operating wavelength of the bandpass optical filter.
  • the broadband optical diffuser has an index of refraction and portions having a thickness that cause light having a wavelength at an operating wavelength of the bandpass optical filter to undergo a phase shift of ⁇ when passing through the portions of the broadband optical diffuser.
  • the narrowband anti-diffuser may include dielectric optical resonators having indices of refraction and dimensions that cause the light having the wavelength at the operating wavelength of the bandpass optical filter to undergo a further phase shift of ⁇ when passing through the narrowband anti- diffuser.
  • the bandpass optical filter has an optical pass-band that is independent of an incident angle of light upon the bandpass optical filter.
  • an optical instrument comprising an optical device having an aperture, and a bandpass optical filter disposed in front of the aperture of the optical device.
  • the bandpass optical filter comprises a broadband optical diffuser, and a narrowband anti-diffuser disposed in a common optical path with the broadband optical diffuser.
  • the optical instrument further comprises a second bandpass optical filter disposed between the bandpass optical filter and the aperture of the optical device.
  • the second bandpass optical filter may have a pass-band within a pass-band of the bandpass optical filter.
  • the optical device is one of a camera and a microscope.
  • a method of fabricating a bandpass optical filter comprises selecting an operating wavelength of the bandpass optical filter, fabricating a broadband optical diffuser from a substrate by forming first regions in the substrate with a first thickness that causes light at the operating wavelength of the bandpass optical filter to undergo a phase shift of ⁇ when passing through the first regions, and forming second regions in the substrate with a second thickness different from the first thickness, fabricating optical resonators having dimensions that cause light at the operating wavelength of the bandpass optical filter to undergo an additional phase shift of ⁇ when passing through the optical resonators, and mounting the optical resonators in a common light path with the first regions of the substrate.
  • the method further comprises one of forming and adhering the optical resonators on a second substrate separate from the broadband optical diffuser.
  • the method further comprises one of forming and adhering the optical resonators on the first regions of the broadband optical diffuser. In some embodiments, the method further comprises forming the first regions in the substrate in a pseudo-random pattern.
  • a method of obscuring an aperture of an optical device from view by an unaided eye of an observer and protecting the optical device from damage by optical radiation directed at the aperture of the optical device comprises disposing a narrowband optical filter including a broadband optical diffuser and a narrowband anti-diffuser disposed in a common optical path with the broadband optical diffuser in front of the optical device.
  • the method further comprises disposing a narrowband optical filter having a pass-band within a pass-band of the narrowband optical filter between the narrowband optical filter and the aperture of the optical device.
  • FIG. 1A illustrates a camera disposed behind a bandpass optical filter
  • FIG. IB illustrates a camera disposed behind a bandpass optical filter and an additional filter
  • FIG. 2A illustrates an embodiment of a bandpass optical filter
  • FIG. 2B illustrates another embodiment of a bandpass optical filter
  • FIG. 2C illustrates another embodiment of a bandpass optical filter
  • FIG. 2D illustrates another embodiment of a bandpass optical filter
  • FIG. 3A illustrates light having a wavelength within an operating pass-band of a bandpass optical filter passing through the bandpass optical filter
  • FIG. 3B illustrates light having a wavelength outside an operating pass-band of a bandpass optical filter passing through the bandpass optical filter.
  • a camera aperture or a bandpass optical filter placed in front of the camera aperture, to generally appear from the outside to be an opaque, matte (diffusely reflective) surface.
  • This can solve a number of problems.
  • surveillance cameras are well-known to be vulnerable to laser countermeasures, wherein an adversary may destroy the image sensor using a pulsed laser.
  • a matte aperture would prevent the laser from being focused onto the image sensor of a surveillance camera, dramatically reducing the effectiveness of this countermeasure— unless the laser happened to be in the (secret, narrow) operating wavelength pass-band of the diffusive filter.
  • an apparently-matte aperture would allow the camera to blend in seamlessly with a wall, object, or device, even when looking right at it, which is advantageous for both surveillance (hidden cameras) and consumer electronics (allowing a more seamless aesthetic for camera-carrying devices like cars, computers, cell phones, etc.).
  • FIG. 1A One camera/filter arrangement is illustrated in FIG. 1A.
  • a camera 10 including an optical aperture and lens 15 is disposed behind a bandpass optical filter 100.
  • an additional filter 200 may be disposed between the bandpass optical filter 100 and the optical aperture and lens 15 of the camera 10.
  • the additional filter 200 may prevent (or at least reduce an intensity of) light outside of an operating wavelength pass- band of the bandpass optical filter 100 from entering the optical aperture and lens 15 of the camera 10.
  • the bandpass optical filter 100 optionally in conjunction with the additional filter 200, may be utilized with other forms of optical devices, for example, a microscope, or two-way mirrors, privacy screens, etc.
  • a bandpass optical filter for use with a camera has an operating wavelength pass-band at which the bandpass optical filter does not diffuse the light, but rather lets it through unperturbed.
  • This wavelength pass-band may be narrow (for example, about 5nm), and may be in the visible, near infrared, or other wavelength ranges as desired for a particular
  • the narrow bandpass optical filter 100 is a combination of two adjacent components: A broadband diffuser 105 and a narrowband "anti-diffuser” 110 including dielectric optical resonators 115 disposed on a substrate 120.
  • the broadband diffuser 105 and a narrowband "anti-diffuser” 110 may be disposed parallel to one another.
  • an "optical resonator” is a structure in which there is an optical mode in which the light is confined to a small volume, for example, confined along all three spatial dimensions.
  • the broadband diffuser 105 may appear to diffuse light randomly, but may be manufactured in a deterministic way, for example, as a pseudorandom phase plate.
  • the narrowband anti-diffuser 110 may imprint an equal and opposite phase on light passing through the broadband diffuser 105, but only at wavelengths within the operating pass- band of the narrow bandpass optical filter 100.
  • the narrowband anti- diffuser 110 may consist of a pattern of high quality factor dielectric optical resonators 115 such as nano-spheres having dimensions (e.g., diameters) of ⁇ /2 ⁇ or approximately ⁇ /2 ⁇ , where ⁇ is the central operating wavelength of the bandpass optical filter and n is index of refraction of the material of the dielectric optical resonators 115.
  • the broadband diffuser 105, dielectric optical resonators 115, and substrate 120 may comprise one or more materials that are transparent to wavelengths in the pass-band of the narrow bandpass optical filter 100, for example, silicon dioxide or titanium dioxide or any of a variety of polymeric materials.
  • the pass-band of the narrow bandpass optical filter 100 may become narrower as the quality factor of the resonators 115 increases.
  • the dielectric optical resonators 115 may be introduced onto the surface of the substrate 120 suspended in solution in a carrier fluid and positioned and adhered to the substrate 120 utilizing methods know in the art. Additionally or alternatively, the dielectric optical resonators 115 may be created using cleanroom-type processes such as lithography, etching, thin-film deposition, liftoff, etc.
  • the narrow bandpass optical filter 100 may have the same optical pass-band regardless of the incoming angle of the light. This may be facilitated by techniques such as keeping the broadband diffuser 105 and anti-diffuser 110 in very close proximity, for example, separated by a distance d which is about equal to or less than the central operating wavelength of the narrow bandpass optical diffuser 100.
  • the distance d may be defined between centers of the dielectric optical resonators 115 and opposing surfaces of the broadband diffuser 105.
  • the camera 10 should ideally only be sensitive to the non-scattered light in the operating wavelength pass-band of the bandpass optical filter 100.
  • This can be accomplished using a second bandpass filter 200 (FIG. IB) that prevents the diffusely- scattered wavelengths from reaching the image sensor of the camera 10.
  • This second filter 200 will help reduce the background light level even if its pass-band is wider than that of the filter 100. It can also be done by engineering the image sensor of the camera 10 itself— for example, using quantum wells or quantum dots to absorb light specifically in the pass-band.
  • the functionality of the second bandpass filter 200 could be reproduced by only reading one of the three R,G,B color channels of a color image sensor.
  • the system could potentially have more than one pass band, for example red, green, and blue for color imaging. This may be accomplished by providing the broadband diffuser 105 with portions of different thicknesses and corresponding opposed anti-diffusers 110 or optical resonators, the portions of different thicknesses and corresponding different optical resonators having thicknesses and indices of refraction selected to selectively pass the desired different wavelengths of light.
  • a longpass optical diffuser rather than a bandpass optical filter, i.e., a diffuser that diffusely scatters visible light while allowing longer- wavelength infrared light through unperturbed.
  • the dielectric resonators 115 may be spherical, ellipsoidal, cylindrical, or boxlike (a.k.a. rectangular parallelepiped) in shape.
  • the salient features of the dielectric resonators are low loss to allow high Q, and sub- wavelength in size.
  • the dielectric resonators 115 may possess circular, square, or other such symmetric cross-sections in planes parallel to the substrate 120.
  • the dielectric resonators 115 may have ellipsoidal, cylindrical, or box- like cross-sections in planes parallel to the substrate 120.
  • the broadband diffuser (BBD) 105 functions like a frosted plate of glass.
  • the BBD 105 may comprise a transparent (transparent within the operational wavelength range) substrate of thickness L in full thickness regions 105 A.
  • the optical path length through the BBD 105 is "nxL" where "n” is the index of refraction of the material of the BBD 105.
  • the optical path length becomes: "nx(L-Lb) + (l)xLb" where (1) is the index of refraction of the air or vacuum.
  • dielectric optical resonators 115 are placed into correspondence with either the full thickness regions 105A having the longer optical path length or the reduced thickness regions 105B having the shorter optical path.
  • the effect of the resonators 115 is to add an additional optical path length such that the difference, at one wavelength, is now zero and the "diffuser" effect goes away for that wavelength.
  • FIGS. 3 A and 3B illustrate the effect of the bandpass optical filter on light having a wavelength within the operating pass-band of the bandpass optical filter and light having a wavelength outside the operating pass-band of the bandpass optical filter, respectively.
  • the bandpass optical filter 100 may be operated with light passing through in the direction illustrated in FIGS. 3A and 3B or in the opposite direction or at an angle relative to the BBD 105 of the bandpass optical filter 100.
  • the substrate or resonators could be birefringent, in which instances for two states of polarization two different wavelengths exhibit the non-diffuser effect.
  • FIG. 2B illustrates an alternative configuration for a bandpass optical filter 100.
  • the substrate 120 is omitted, and the dielectric optical resonators 115 are grown, deposited, or coated directly on the full thickness regions 105A of the BBD 105.
  • the dielectric optical resonators 115 are grown, deposited or coated on the substrate 120 opposite the reduced thickness regions 105B of the BBD 105.
  • the reduced thickness regions 105B of the BBD 105 have a thickness of L and cause light at the central operating wavelength of the BBD 105 passing through the reduced thickness regions 105B to undergo a phase shift of ⁇ .
  • the dielectric optical resonators 115 cause the phase shifted light to undergo a further phase shift of ⁇ , thus undoing the diffusion effect of the BBD 105 for light having a wavelength in the operating passband of the bandpass optical filter 100.
  • FIG. 2D illustrates a further alternate arrangement for the bandpass optical filter
  • FIG. 2D The embodiment illustrated in FIG. 2D is similar to that illustrated in FIG. 2B in that the substrate 120 is omitted, and the dielectric optical resonators 115 are disposed directly on the BBD 105. Unlike the embodiment illustrated in FIG. 2B, however, in the embodiment illustrated in FIG. 2D the dielectric optical resonators 115 are disposed on the reduced thickness regions 105B of the BBD 105 rather than the full thickness regions 105 A.
  • a method of fabricating a bandpass optical filter comprising selecting an operating wavelength of the bandpass optical filter.
  • the operating wavelength may be in the infrared band such that the bandpass optical filter may appear to have a matte or opaque surface to an observer.
  • the operating wavelength may be a visual light wavelength or an ultraviolet wavelength.
  • the method further includes fabricating a broadband optical diffuser from a substrate.
  • the substrate may be transparent to light at the selected operating wavelength of the bandpass optical filter.
  • the broadband optical diffuser may be fabricated by forming first regions in the substrate with a first thickness that causes light at the operating wavelength of the bandpass optical filter to undergo a phase shift of ⁇ (or ⁇ , X being an odd number) when passing through the first regions, and forming second regions in the substrate with a second thickness different from the first thickness.
  • the first and second regions may be formed in a pseudo-random pattern, a pattern that appears random, but which is known to one fabricating the broadband optical diffuser and which may be reproducible.
  • the first and second regions may be formed by, for example, etching the substrate using methods such as those utilized in the semiconductor fabrication industry.
  • the first thickness may be greater or lesser than the second thickness.
  • the second thickness causes light at the operating wavelength of the bandpass optical filter to undergo a phase shift other than ⁇ (or ⁇ , X being an odd number)
  • the method further includes fabricating optical resonators having dimensions that cause light at the operating wavelength of the bandpass optical filter to undergo an additional phase shift of ⁇ (or ⁇ , X being an odd number) when passing through the optical resonators.
  • the optical resonators may be formed from a dielectric material and may be transparent to light at the selected operating wavelength of the bandpass optical filter.
  • the optical resonators are mounted in a common light path with the first regions of the substrate.
  • the optical resonators may be formed on or adhered to a second substrate separate from the broadband optical diffuser.
  • the second substrate may be transparent to light at the selected operating wavelength of the bandpass optical filter.
  • the optical resonators may be formed or adhered on the first regions of the broadband optical diffuser.
  • the optical resonators may be formed by deposition on the first regions of the broadband optical diffuser or by etching of portions of the first regions of the broadband optical diffuser using methods such as those utilized in the

Abstract

Un filtre optique passe-bande comprend un diffuseur optique à large bande et un antidiffuseur à bande étroite disposé dans un trajet optique commun avec le diffuseur optique à large bande.
PCT/US2018/043393 2017-08-02 2018-07-24 Filtre optique passe-bande WO2019027724A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201762540257P 2017-08-02 2017-08-02
US62/540,257 2017-08-02

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WO2019027724A1 true WO2019027724A1 (fr) 2019-02-07

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4757289A (en) * 1985-07-22 1988-07-12 Nec Corporation Filter with dielectric resonators
US20150171234A1 (en) * 2013-12-12 2015-06-18 Raytheon Company Broadband graphene-based optical limiter for the protection of backside illuminated cmos detectors
US20150219494A1 (en) * 2014-01-31 2015-08-06 Jds Uniphase Corporation Optical filter and spectrometer
WO2016125164A2 (fr) * 2015-02-05 2016-08-11 Verifood, Ltd. Applications d'un système de spectrométrie
WO2016145523A1 (fr) * 2015-03-19 2016-09-22 Institut National De La Recherche Scientifique Système laser verrouillé en mode passif et procédé pour génération d'impulsions longues
WO2017070178A1 (fr) * 2015-10-19 2017-04-27 The Board Of Trustees Of The Leland Stanford Junior University Procédés et appareil permettant une imagerie par cohérence optique dépourvue de chatoiement

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4757289A (en) * 1985-07-22 1988-07-12 Nec Corporation Filter with dielectric resonators
US20150171234A1 (en) * 2013-12-12 2015-06-18 Raytheon Company Broadband graphene-based optical limiter for the protection of backside illuminated cmos detectors
US20150219494A1 (en) * 2014-01-31 2015-08-06 Jds Uniphase Corporation Optical filter and spectrometer
WO2016125164A2 (fr) * 2015-02-05 2016-08-11 Verifood, Ltd. Applications d'un système de spectrométrie
WO2016145523A1 (fr) * 2015-03-19 2016-09-22 Institut National De La Recherche Scientifique Système laser verrouillé en mode passif et procédé pour génération d'impulsions longues
WO2017070178A1 (fr) * 2015-10-19 2017-04-27 The Board Of Trustees Of The Leland Stanford Junior University Procédés et appareil permettant une imagerie par cohérence optique dépourvue de chatoiement

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