Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/06—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the phase of light
• • 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 
  • G02F1/0147—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 thermo-optic effects
• • 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
  • G02F2203/18—Function characteristic adaptive optics, e.g. wavefront correction

Definitions

• a thin film adaptive optical component is provided.
• This invention relates to optical systems, and particularly to a modifiable transfer function type of optical component.
• optical components either of the transmissive or the reflective type, whose response characteristics to electromagnetic radiation within a given frequency band can be varied to some extent by a surface modification of the substrate which forms their optically active element.
• Such so-called adaptive components have a particular application in optical systems which can change their optical characteristics automatically, e.g. to compensate for aberration, alter the radiation wave front, optimize the system spatial resolution, etc.
• the substrate surface can be modified in a number of ways, e.g. using mechanical and piezoelectric actuators which ⁇ by exerting on the substrate a pressure distributed in accordance with a criterion that depends on the correction sought ⁇ will deform it locally so as to obtain a corresponding distribution of phase lags for the optical field being propagated through that surface or reflected therefrom.
• An object of this invention is to provide an adaptive optical component which is simple construction-wise, requires no high working voltages, has low operating power requirements, and enables continuous deformation of the optical substrate.
• Another object of the invention is to provide a method of manufacturing such an optical component.
• Figure 1 shows in schematic form and in cross-section an optical component according to the invention.
• Figure 2 shows in cross-section this optical component at various stages of the manufacturing method according to the invention.
• the operation of the optical component of this invention is based on Joule effect, that is on the fact that a conductor through which an electric current is flown will become heated proportionally to the product of the voltage applied to its terminals by the current flowing through it, or stated otherwise, proportionally to the product of its electric resistance by the square of the current flowing through it.
• An electric conductor in the form of a thin film, is formed on the surface of an optical substrate which may be a glass or crystal for a transmissive optical component, or a mirror-finished metal or metallized glass for a reflective optical component.
• the film is disposed and patterned such that, on flowing an electric current therethrough which may be a direct or alternating or pulsive current, it will become a heat source capable of heating the substrate in a selective fashion.
• k 1 is the thermal conductivity
• D 1 is the thermal diffusivity
• Q is the heat flux generated at time t at point x, y, z, and
• T is the temperature
• ⁇ I is induced by the expansion of the optical surface
• ⁇ II is induced by the thermal lens effect
• the term ⁇ II is zero because the thermal lens forms not only on the surface of the component to which the heating conductor is applied, but also on the other surface thereof, so that the "output" thermal lens effect will compensate for that of the "input” thermal lens, whereas in the instance of a reflective optical component, the term ⁇ I is negligible compared to the term ⁇ II , because the latter is to be regarded as twice as great due to the double path travelled by the light through the thermal lens over the component surface.
• response times of an adaptive optical component of the kind described hereinabove are on the order of a tenth of a second.
• an appropriate layout of the heating conductor that is by forming a conductive pattern on the substrate, such as in the form of a uniform cross-section strip that follows a predetermined path to apply greater or lesser amounts of heat to different areas of the component;
• a heating conductive pattern or combination of patterns formed with the foregoing methods is designed by computing the distribution of the heat Q (x,y,z;t) generated by the conductor to obtain a predetermined distribution of the temperature T (x,y,z;t) and, therefore, the phase modulation sought using formula (1) above.
• a method of making an adaptive optical component from a transparent or reflective substrate in a given radiation band will be now described with reference to Figure 2 and assuming that the substrate is either electrically insulative or coated with an electrically insulating layer.
• the pattern sought for the heating conductor is first defined on the substrate, shown at 10 in Figure 2, that is, a complementary photoresist mask 11 is formed for the pattern by a conventional photolithographic process.
• a conductive material 12 e.g. an indium-tin oxide layer
• the mask 11 is removed along with the overlying portion of the layer of conductive material (12) to provide the heating conductor pattern 13 on the substrate.
• the method just explained may be repeated, following deposition of a layer of an electrically insulating layer, to form more conductive patterns in accordance with the method under 3) above.
• the heating conductor is to cover the entire substrate surface uniformly, e.g. with a modulated thickness of the electrically conductive film, the method would be made simpler by the omission of the photolithographic masking step.
• the invention yields an adaptive optical component exhibiting a continuous deformation of its surface which can be adjusted in a most fine fashion, has very low operating power requirements (typically of 0.2 Watt/cm 2 ), can be implemented in a most simple manner, and requires no mechanical parts for its operation.
• the thin film processing of the inventive method is compatible with the other customary treatments for optical components such as, for example, antiflare and/or reflecting, polarizing or non-polarizing multilayer treatments.

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Citations (4)

• 1991
  • 1991-07-12 IT ITMI911942A patent/IT1251281B/it active IP Right Grant
• 1992
  • 1992-07-07 WO PCT/EP1992/001528 patent/WO1993001513A1/en active Application Filing

Patent Citations (4)

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