Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B13/00—Optical objectives specially designed for the purposes specified below
  • G02B13/001—Miniaturised objectives for electronic devices, e.g. portable telephones, webcams, PDAs, small digital cameras
  • G02B13/0055—Miniaturised objectives for electronic devices, e.g. portable telephones, webcams, PDAs, small digital cameras employing a special optical element
• • 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
  • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
  • G02B27/4205—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
  • G02B27/4211—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant correcting chromatic aberrations
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/18—Diffraction gratings
  • G02B5/1866—Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/18—Diffraction gratings
  • G02B5/1876—Diffractive Fresnel lenses; Zone plates; Kinoforms
  • G02B5/189—Structurally combined with optical elements not having diffractive power
  • G02B5/1895—Structurally combined with optical elements not having diffractive power such optical elements having dioptric power

Definitions

• the disclosure relates to an imaging system for an electronic device, the imaging system comprising a lens system and a sensor.
• Imaging systems e.g. cameras
• Electronic devices such as mobile phones preferably have as small outer dimensions as possible, while imaging systems inevitably require certain dimensions in order to provide sufficiently good image sharpness, spatial frequency, sensitivity etc.
• Diffractive optical elements are often combined with classical imaging optical systems to correct e.g. color aberrations.
• classical imaging optical systems to correct e.g. color aberrations.
• diffractive optical elements are mainly used in long total track length cameras, where the range of incident angles to diffractive element is small, and not in smaller electronic devices such as smartphones, where one challenge is to achieve as short track length as possible.
• an imaging system comprising a lens system comprising a plurality of lenses, a diffractive optical element, and a sensor, the lens system, diffractive optical element, and sensor sharing an optical axis, the diffractive optical element being arranged between the lens system and the sensor, incident rays of light entering the lens system at a plurality of first angles relative the optical axis, emergent rays of light reaching the sensor at a plurality of second angles relative the optical axis, the second angles being smaller than the first angles.
• This solution facilitates a comparatively short imaging system, i.e. having a short total track length. Due to the efficient light direction changing properties of the diffractive optical element, the ray angles can be controlled at a steep angle ray path which is subsequently directed towards the sensor by means of the diffractive optical element. This allows a shorter than usual imaging system for special applications such as time of flight or ultrawide angle fish eye lenses.
• the second angles are less than ⁇ 20° relative the optical axis. This small angle facilitates an as short track length as possible for the imaging system.
• the lens system redirects the rays of light such that the rays of light have third angles, the third angles being larger than the first angles and smaller than the second angles.
• the diffractive optical element is arranged closer to the sensor than the plurality of lenses along the optical axis, allowing the rays of light to reach an as large area as possible before turning them towards the sensor.
• the diffractive optical element comprises a grating, used to manipulate the phase, amplitude, and the propagation direction of incident rays of light.
• a configuration of the grating is asymmetrical in at least one direction perpendicular to the optical axis, allowing the configuration of the diffractive optical element to vary, from its center at the optical axis, with increasing light direction changing power.
• the grating comprises a plurality of slanted grating elements, and the configuration comprises adjusting periods between adjacent grating elements. Asymmetric gratings may be used to optimize the efficiency for higher angular and spectral ranges.
• angles of the grating element slants, in relation to the optical axis, increase when distances between the grating elements and the optical axis increase in a direction perpendicular to the optical axis.
• the period decreases when a distance between the grating element and the optical axis increases in the direction perpendicular to the optical axis.
• the chief ray incidence towards the diffractive optical element requires a large bending angle to the sensor.
• the grating period is smaller in this region, while the period increases laterally towards the optical axis where the bending needs to be less.
• no grating elements are located along the optical axis. As the period increases, it gives rise to parasitic diffraction orders lowering the diffraction efficiency in the desired direction. At the optical axis O, it is therefore preferred that the diffractive optical element does not have a grating configuration in order to avoid any stray light hitting the sensor.
• the lens system comprises ultra wide angle lenses, facilitating time of flight or other near-infrared imaging systems having large fields-of-view.
• an electronic device comprising the imaging system according to the above.
• FIG. 1 shows a schematic illustration of an imaging system in accordance with one embodiment of the present invention
• Fig. 2 shows a partial side view of a diffractive optical element of an imaging system in accordance with one embodiment of the present invention
• FIG. 3 shows a schematic illustration of an imaging system in accordance with a further embodiment of the present invention.
• the present invention relates to an electronic device (not shown) comprising an imaging system.
• the imaging system comprises a lens system 1 comprising a plurality of lenses 2, a diffractive optical element 3, and a sensor 4.
• the lens system 1, diffractive optical element 3, and sensor 4 share an optical axis O, and the diffractive optical element 3 is arranged between the lens system 1 and the sensor 4.
• the diffractive optical element 3 may be arranged closer to the sensor 4 than the plurality of lenses 2 along the optical axis O.
• the lens system 1 may comprise any suitable kind of lenses 2, including ultra-wide angle lenses, such as fish eye lenses, as shown in Fig. 3.
• Incident rays of light firstly pass through the lenses 2, secondly pass through the diffractive optical element 3, and thirdly reaches the sensor 4.
• the incident rays of light enter the lens system 1 at a plurality of first angles al relative the optical axis O, and emergent rays of light reach the sensor 4 at a plurality of second angles a2 relative the optical axis O.
• the second angles a2 are smaller than the first angles al, hence, the lenses 2 and the diffractive optical element 3 focuses the indecent light onto the sensor 4.
• the second angles a2 may be less than ⁇ 20° relative the optical axis O, i.e. cover a total area of up to 40°.
• the lens system 1 redirects the rays of light such that the rays of light have third angles a3, the third angles a3 being larger than the first angles al and smaller than the second angles a2.
• This solution facilitates a comparatively short imaging system, i.e. having a short total track length. Due to the efficient light direction changing properties of the diffractive optical element 3, the incident rays of light can be controlled at a steep angle ray path which is subsequently directed towards the sensor 4 by means of the diffractive optical element 3. This allows a shorter than usual imaging system for special applications such as time of flight or ultra-wide angle fish eye lenses.
• the total track length of the imaging system roughly depends on at how steep angles one can get the maximum field of view ray path to extend through the lenses 2 to the sensor 4. Nevertheless, it is also necessary to get the rays of light to the sensor pixels at small enough angles, typically the maximum chief ray angle to the sensor 4 is around 40°, as previously mentioned.
• the diffractive optical element 3 may comprise a grating 5, shown in more detail in Fig. 2.
• the diffractive optical element 3 is located on the object side, and configured on a planar substrate in order to reduce Fresnel losses.
• Gratings 5 may be used to manipulate the phase, amplitude, and the propagation direction of incident rays of light.
• Asymmetric gratings (ex: parallelograms) may be used to optimize the efficiency for higher angular and spectral ranges.
• the slant angle, height and the fill factor of the gratings are used for optimizing efficiency, and the periods are chosen to ensure the transmission of first diffraction order normal to the direction of the sensor 4.
• the chief ray incidence from the lenses 2 towards the diffractive optical element 3 requires a larger bending angle to the sensor 4.
• the grating period is smaller in this region, while the period increases laterally towards the optical axis O where the bending needs to be less. As the period increases, it gives rise to other parasitic diffraction orders lowering the diffraction efficiency in the desired direction.
• the diffractive optical element 3 does not have a grating configuration in order to avoid any stray light hitting the sensor 4.
• a configuration of the grating 5 is asymmetrical in at least one direction perpendicular to the optical axis O.
• the grating 5 may comprises a plurality of slanted grating elements 5a, and the configuration may comprise adjusting the periods between adjacent grating elements 5a.
• angles b of the grating element slants 5a, in relation to the optical axis O, may increase when the distances between the grating elements 5a and the optical axis O increase in a direction D1 perpendicular to the optical axis O.
• the period may decrease when the distance between a grating element 5a and the optical axis O increases in the direction D1 perpendicular to the optical axis O.
• the size if this no-grating area depends on the acceptance angle of the sensor 4. As such, the size of no-grating area grows with the tangent of the acceptance angle.
• a computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.
• a suitable medium such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Lenses (AREA)

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• 2020
  • 2020-02-25 EP EP20707397.4A patent/EP4085280A1/de active Pending
  • 2020-02-25 WO PCT/EP2020/054928 patent/WO2021170221A1/en not_active Ceased
  • 2020-02-25 CN CN202080097347.6A patent/CN115151844B/zh active Active

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