Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
  • G02F1/0305—Constructional arrangements
  • G02F1/0311—Structural association of optical elements, e.g. lenses, polarizers, phase plates, with the crystal
• • 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
• • 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
  • G02B27/283—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising used for beam splitting or combining
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F2203/00—Function characteristic
  • G02F2203/48—Variable attenuator

Definitions

• This invention relates to electro-optic devices such as, for example, modulators or shutters which use birefringent material.
• the transmissivity in the on-state may be maximized by adjusting the electric field such that the birefringent cell Cl behaves as a half-wave retardation plate, such that light is linearly polarised at the output of the cell Cl with the plane of polarisation being
• Figure 2 illustrates another optical shutter which has improved extinction, acceptance angle and power consumption compared to the shutter shown in Figure 1.
• two birefringent cells Cl and C2 are spatially arranged alternately along the optical path with three polarisers PI, P2 and P3. If the two cells Cl and C2 are each identical with the single cell Cl of the Figure 1 device, the same effect can be achieved at the output using approximately half the voltage applied across each of the cells.
• voltage pulses of 600V were applied across the cell Cl to switch it between states
• each cell Cl and C2 is subjected to pulses of 300V, leading to a faster response time and increased repetition rate.
• Other improvements may be achieved by including coatings on the surfaces of the optical elements and by appropriate selection of the chemical composition of the birefringent material.
• an electro-optic device comprising: a polarising beam splitter which produces first and second differently polarised components from applied unpolarised optical radiation; first and second optical paths along which the first and second components respectively are directed; and birefringent cell means in the first and second paths.
• a device in accordance with the invention may have a significantly higher transmission characteristic than previously known devices.
• the initial polariser cuts down transmission through the system as a whole by 50% at least, with other components in the optical path adding to the reduction in transmission.
• the significantly improved transmission obtainable by making use of the invention means that devices based on the electro-optic effect become practicable in applications for which previously they would not have been considered.
• a device in accordance with the invention does not require a collimated, polarised or monochromatic illuminant source in order to work.
• a prior art arrangement such as that shown in Figure 1 may have a transmission of approximately 42% whereas in a comparable device in accordance with the invention, transmissions of 80% may be achieved.
• a device in accordance with the invention may be used as a shutter in applications such as for example gated TV cameras (which may use CCD or other solid state sensors), laser gated TV cameras, multicolour cameras and displays, holographic displays, mid-infra-red range thermal cameras (operating at wavelengths of 3 to 5 microns for example), and thermal modulators for thermal cameras.
• gated TV cameras which may use CCD or other solid state sensors
• laser gated TV cameras multicolour cameras and displays
• holographic displays holographic displays
• mid-infra-red range thermal cameras operating at wavelengths of 3 to 5 microns for example
• thermal modulators for thermal cameras such as for example gated TV cameras (which may use CCD or other solid state sensors), laser gated TV cameras, multicolour cameras and displays, holographic displays, mid-infra-red range thermal cameras (operating at wavelengths of 3 to 5 microns for example), and thermal modulators for thermal cameras.
• a device may be used as a voltage controlled attenuator.
• a varying voltage may be applied to the birefringent cell means to control transmission through the device.
• the transmission may be controlled such that the sensor is operated at its optimum level of incident light.
• the transmission may be controlled using a separate circuit but in one advantageous embodiment, a control signal is derived from a sensor receiving the output from the device.
• a CCD sensor output may be used to provide a feedback signal for the birefringent cell means.
• the device may be used to control light transmission where the output is to be received in turn by different sensors having different characteristics and/or where the input optical radiation to the device has changing characteristics, for example to view a scene under daylight conditions and also at night when illuminated by a laser source.
• the birefringent cell means may comprise a Pockel cell or cells, Kerr cell or cells or LCD cells.
• a particularly suitable material for use in a birefringent cell means is lanthanum- modified lead zirconate titanate (PLZT).
• PZT lead zirconate titanate
• Such materials may be tailored so as to control the magnitude of the birefringence for example by adjusting the percentage of lanthanum included in the material.
• the cell means comprises a first cell in the first path and a second different cell in the second path.
• the cell means may comprise a single cell which is included in the both the first and second paths, the first and second components being applied to different regions of the single cell.
• Glan-Thompson polarizer gives 40°.
• the cell means includes a plurality of birefringent cells in the first path and a plurality of birefringent cells in the second
• the optical outputs of the first and second optical paths are kept separate. These outputs may be separately processed subsequently or may be combined following conversion from optical form into, say, electrical signals.
• a first CCD sensor may receive the optical component from the first path and a second CCD sensor the component from the second path and the electrical outputs of the CCDs combined to give an output video signal.
• the optical outputs of the first and second paths are optically combined. In a shutter, for example, this combined output may then be applied to a single optical sensor, such as a single CCD sensor or camera tube.
• the optical paths must be adjusted such that when the outputs are combined, they are in register with one another. It may be useful for some devices to include a moveable reflective surface, such as a prism , within the device for adjustment of the paths relative to one another to permit correct registration to be obtained.
• the polarising beam splitter and birefringent cell means form part of a single component.
• the component may also incorporate an optical combiner in those embodiments where the optical outputs are combined. This is particularly advantageous as it enables the geometry of the device and the properties of the components to be selected during assembly and subsequently the single component may be handled, for example, for shipping or when assembling it into a larger arrangement whilst maintaining the correct alignments, removing the need for subsequent adjustments.
• the optical combiner may be a cube or a prism, for example.
• the device may be incorporated in the focussing system, for example, being located between elements of the focussing system itself.
• a device in accordance with the invention may be used to extract from a viewed scene details of either vertically or horizontally polarised components which occur in that scene.
• Figure 3 schematically illustrates an optical arrangement incorporating a device in accordance with the invention and having two CCD sensors;
• Figure 4 schematically illustrates a cascaded parallel shutter in accordance with the invention;
• Figure 5 schematically shows another arrangement in accordance with the invention having a single output
• FIG. 6 schematically illustrates another device in accordance with the invention.
• FIGs 7, 8 and 9 are explanatory diagrams relating to the device of Figure 6; and Figures 10, 11, 12 13 and 14 schematically show other devices in accordance with the invention.
• a shutter arrangement includes a polarising beam splitter cube 1 at which unpolarised input radiation is received in the direction shown by the arrow.
• the cube 1 acts to split randomly polarised input light into two components, one being transmitted straight through the cube 1 to give a beam 2 which is linearly polarised with P-polarisation, and the other component being reflected through 90 ° to give an output beam 3 which is also highly polarised having a linear S-polarisation.
• the reflected beam 3 is applied to a prism 4 where it is redirected onto a first birefringent cell Cl, the output of which is directed to an analyser, in this case an output polariser P2.
• This first optical path also includes a CCD sensor 5 arranged to receive the output from polariser P2.
• a second optical path through the system parallel to the first path which includes a second birefringent cell C2, a second output polariser P4 and a second CCD sensor 6. Any light incident on the CCD sensors 5 and 6 produces a charge pattern representative of the amount of radiation incident thereon which can be electronically read out and combined at combiner 7 to give a video output signal at 8.
• T 0N (Ux PI x Cl x P2) + (U x PI x C2 x P4) which is approximately PI x Cl x P2 giving a transmission of approximately 80%, U being 0.5 (being the conversion of unpolarised light to polarised light), PI and P2 are both approximately 0.9 and the transmission of Cl is approximately 0.9.
• the material used in the birefringent cells Cl and C2 is PLZT which is commercially available.
• the first and second cells Cl and C2 could be replaced by a single cell which is extensive across both optical paths.
• a shutter in accordance with the invention includes the components of the device shown in Figure 3 and having the same reference numerals for clarity.
• the first optical path also includes a second birefringent cell C2 which uses PLZT and a second polariser P3 interposed between the first polariser P2 and the CCD sensor 5.
• the second optical path which is parallel to the first, includes an additional birefringent cell C4, again of PLZT, and a second polariser P5 located in front of the CCD sensor 6. Again, the outputs of the CCDs 5 and 6 are combined at 7 to give a video output at 8.
• the polarising beam splitter cube 1 produces a transmitted beam of one polarisation and a reflected beam of another polarisation.
• both beam components contribute to the final output signal.
• the Figure 3 device In a variation of this configuration, the cells Cl and C3 are replaced by a larger single cell, and cells C2 and C4 are replaced by a second larger single cell.
• a shutter in accordance with the invention has an input polarising beam splitter 1.
• Linearly polarised light reflected at 1 is transmitted along a first path via prism 4 to a first birefringent cell C, and passes via a combiner 8 to a CCD sensor 9.
• Light transmitted by the beam splitter 1 and polarised orthogonal to that in the first path is transmitted to a second cell C 3 and is then directed onto the combiner 8 by a second prism 10 where it is reflected and combined with light from the first path to give a single output to the CCD 9.
• this shows another shutter in accordance with the invention which includes two parallel optical paths each of which incorporates cascaded birefringent cells.
• Input radiation is applied to the polarising beam splitter 1.
• the reflected component is transmitted via a first cell C, and onto a reflecting polariser P2 from whence it is directed onto a second C 2 and to a combiner 8 which includes a polariser 11, which acts as the analyser.
• the light is then incident on a single CCD camera 9.
• the transmitted component from beam splitter 1 is similarly directed via a cell C 3 ,a reflecting polariser P4 and a second cell C 4 , being finally incident on a second reflecting polariser 11 where it is combined with the originally reflected component to give a single output.
• the device offers improved transmission enabling a TV camera to be used, for example, for pulsed laser viewing under total darkness conditions.
• the cells C 1; C 2 , C 3 and C 4 may be operated so as to give a three-state transmission path
• Figure 7 is an explanatory diagram concerning the generation of the three transmission states.
• Figure 7a shows the PLZT transfer function, giving the transmission achieved for a particular applied voltage, the three voltage levels being 400 volts, 500 volts and 700 volts.
• Figure 7b illustrates the temporal function of the PLZT material, showing transmission against response time.
• the transmissive sfates are as illustrated in Figures 8a, 8b and 8c.
• the laser pulse is emitted at time tl shown at Figure 8a and the return received at time t2.
• Figure 8b shows the state of the shutter, which during time period a the shutter is fully
• Figure 9 schematically shows two cells Cl and C2 in series connected so as to achieve the three state drive. This is repeated for the other two cells C3 and C4 in the other optical path through the device.
• the digital electrodes laid down on the surfaces of the cells C, to C 4 are arranged so such that they are angled with respect to each other to avoid aliasing.
• the angles of the electrodes of C are + 22%, for C 2 + 45%, for C 3 - 22% and C 4 - 45%.
• a control signal from the ccD 9 may be applied to the cells Cl, C2, C3 and C4 to adjust transmission to ensure that the CCD 9 operates at optimum illumination levels. This may act, for example, to adjust for slowly varying ambient light conditions in a viewed scene.
• the cells Cl, C2, C3 and C4 may also be controlled so as to block transmission to the
• the vertical and horizontal polarised components in a scene may be separately viewed by firstly switching off C 3 and C 4 and viewing the scene transmitted via C, and C 2 and then switching off C, and C 2 and viewing via C 3 and
• the device of Figure 6 may be modified by incorporating, for example, a blue pass filter in the first path and a red pass filter in the second path.
• P2 may be a blue pass filter and P4 a red pass filter.
• Colour separation may be achieved using a standard dichroic prism in which, say, blue light is reflected and red/green light is transmitted, or a triple colour dichroic arrangement in which light is separated into blue, red and green components.
• the device shown in Figure 4 may also be used for polar viewing without the
• FIG. 10 Another embodiment of the invention is illustrated in Figure 10. This has an input polar splitter 1 followed by a birefringent cell Cl and C2 in the respective reflected and transmitted paths.
• the light transmitted via cell Cl is reflected at P2 and is incident on a first CCD sensor 12.
• the transmitted light passes via cell C2 to a second CCD sensor 13. This arrangement avoids lateral inversion but involves unequal first and second path lengths.
• FIG 11 Another device is illustrated in Figure 11 and includes a polar splitter 1 which divides the incident radiation. Light reflected at PI is transmitted via a birefringent cell Cl to a reflective surface P2 followed by another surface P3 to a polar combiner 14 where it is combined with light transmitted via polar splitter 1 and a second birefringent cell C2, the combined output being received by a single CCD sensor 15.
• a polar splitter 1 which divides the incident radiation.
• Light reflected at PI is transmitted via a birefringent cell Cl to a reflective surface P2 followed by another surface P3 to a polar combiner 14 where it is combined with light transmitted via polar splitter 1 and a second birefringent cell C2, the combined output being received by a single CCD sensor 15.
• another device includes a polar splitter 1 following which in each path is located a birefringent cell Cl and C2 the output of which is directed towards prisms 16 and 17, the light then being recombined at polar combiner 18 and the output directed towards a CCD sensor 19.
• the prism 17 is adjustable in position so as to enable precise adjustment of the light paths to be achieved. Thus, registration may be adjusted by moving one prism only.
• This device requires a single CCD only and also presents equal path lengths on both the first and second paths through the device.
• another device includes two polarising cubes and two polarisers.
• One cube acts as a polar splitter 1 and the second cube as a combiner 20.
• Two prisms 21 and 22 are located in the first and second optical paths and birefringent cells Cl, C2, C3 and C4 are located between the cubes and prisms.
• two polarisers PI and P2 are incorporated in the first and second optical paths.
• a device 23 similar to that shown in Figure 13 is located as a shutter between an input lens 24 and a CCD 25.
• the insertion of device 23 results in a longer system compared to an arrangement in which the device 23 is absent as illustrated in Figure 14b.
• the entry cube 1 of the device 23 is longer than the exit cube 20 because of the acceptance angle which is aperture and focal length dependent.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Nonlinear Science (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Crystallography & Structural Chemistry (AREA)
• Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=10854069

Family Applications (1)

Country Status (4)

Families Citing this family (7)

Family Cites Families (12)

• 1999
  • 1999-05-24 GB GBGB9912072.7A patent/GB9912072D0/en not_active Ceased
• 2000
  • 2000-05-24 GB GB0012655A patent/GB2351356A/en not_active Withdrawn
  • 2000-05-24 WO PCT/GB2000/001979 patent/WO2000072079A2/en not_active Application Discontinuation
  • 2000-05-24 EP EP00935314A patent/EP1185899A2/en not_active Withdrawn
  • 2000-05-24 JP JP2000620410A patent/JP2003500693A/ja not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events