Continuously operated spatial light modulator apparatus and method for adaptive optics

A spatial light modulator (SLM) for controlling the pixelized phase pattern of an input optical beam in response to the pixelized optical intensity pattern of a control beam, comprising:

• a charge transfer plate comprising a pixelized array of conductive charge transfer pins extending through a substrate,
• means responsive to said control beam for accumulating charge on said charge transfer pins in a pixelized charge pattern that corresponds to the pixelized optical intensity pattern of said control beam,
• a deformable mirror adjacent an output side of said charge transfer plate, said deformable mirror being positioned to receive said input beam and responding to a pixelized charge accumulation on said pins with a corresponding pixelized deformation to impose a pixelized phase modulation on said input beam,
• means for connecting to a reference voltage that drains the charge accumulated on said pins, and
• resistance and capacitance means between said pins and said reference voltage connection, said resistance means being selected to establish, together with said capacitance, a common time constant for draining charge from said pins that allows for a continuous operation of said SLM without inter-frame charge erasures, and
• further comprising an array of shield conductors that extend through said charge transfer plate generally parallel to said charge transfer pins to electrically shield said pin pixels from each other.

An adaptive optics system for removing undesired phase aberrations from an input target beam that accompanies a returned laser beam upon which similar aberrations have been imposed, comprising:

• a spatial light modulator (SLM) having an input side for receiving said aberrated input target beam and said aberrated returned laser beam and a control side for receiving a control beam, said SLM adjusting the pixelized phase pattern of said aberrated input target beam and said aberrated returned laser beam in response to the pixelized intensity pattern of a control beam, said SLM being positioned so that its input side receives said aberrated input target beam and said aberrated returned laser beam,
• means for beating said aberrated returned laser beam against an unaberrated reference beam to produce a control beam having a pixelized intensity pattern that corresponds to said aberrations, and for directing said control beam onto the control side of said SLM, said control beam causing said SLM to adjust the pixelized phase pattern of said aberrated input target beam and said aberrated returned laser beam so as to substantially remove said aberrations, and
• means for directing said input target beam after processing by said SLM as an output beam,
• said SLM comprising:
• a charge transfer plate comprising a substrate, a pixelized array of conductive charge transfer pins extending through said substrate, a spacer layer on one face of said substrate, said spacer layer having openings established therein forming cavities,
• means responsive to said control beam for accumulating charge on said charge transfer pins in a pixelized charge pattern that corresponds to the pixelized optical intensity pattern of said control beam,
• a deformable mirror adjacent said one face of said charge transfer plate, said deformable mirror being positioned to receive said input target beam and having mirror pixels for responding to a pixelized charge accumulation on corresponding said pins with which respective said mirror pixels are aligned with a corresponding pixelized deformation into said cavities to impose a pixelized phase modulation on said input target beam, said charge transfer pins, cavities and mirror pixels being aligned,
• means for connecting to a reference voltage that drains the charge accumulated on said pins, and
• resistance and capacitance means between said pins and said reference voltage connection, said resistance means being selected to establish, together with said capacitance, a time constant for draining charge from said pins that allows for a continuous operation of said SLM without inter-frame charge erasures, wherein said capacitance means comprises pin-to-pin capacitances associated with said charge transfer pins and mirror-to-pin capacitances between said deformable mirror and said charge transfer pins and pin-to-reference voltage connection capacitance associated with said pins and said reference voltage connection, and wherein a pin-to-ground capacitance is larger than the pin-to-pin capacitance.

An adaptive optics system for removing undesired phase aberrations from an input optical target beam that accompanies a returned laser beam upon which similar aberrations have been imposed, comprising:

• a spatial light modulator (SLM) having an input side for receiving said aberrated input target beam and said aberrated returned laser beam and a control side for receiving a control beam, said SLM adjusting the pixelized phase pattern of said aberrated input target beam and said aberrated returned laser beam in response to the pixelized intensity pattern of said control beam, said SLM being positioned so that its input side receives said aberrated input target beam and said aberrated returned laser beam,
• means for beating said aberrated returned laser beam against an unaberrated reference beam to produce said control beam having a pixelized intensity pattern that corresponds to said aberrations, and for directing said control beam onto the control side of said SLM, said control beam causing said SLM to adjust the pixelized phase pattern of said aberrated input target beam and said aberrated returned laser beam so as to substantially remove said aberrations, and
• means for directing said input target beam after processing by said SLM as an output beam,
• said SLM comprising:
• opto-electric conversion means for converting a pixelized optical intensity pattern of Said control beam to a pixelized charge pattern,
• a deformable mirror having mirror pixels positioned to be deformed by said pixelized charge pattern in a pixelized array of curved mirror deformations, said deformations having generally flat curvature bases, and
• optical focusing means comprising an array of lenslets that are aligned with respective mirror pixels positioned in an input beam path to pixelize and focus said input beam onto the curvature bases of said mirror pixels.

A method of operating a spatial light modulator (SLM)in a continuous mode, the SLM including a charge transfer plate that accumulates a pixelized charge pattern in response to the pixelized optical intensity pattern of a control beam, and modulates the pixelized deformation of a deformable mirror having an array of mirror pixels to adjust the pixelized phase pattern of an input beam, said method comprising:

• applying charge to said charge transfer plate to accumulate a pixelized charge pattern thereon in response to said control beam, said charge transfer plate comprising a pixelized array of conductive charge transfer pins extending through a substrate,
• deforming said deformable mirror so that the mirror deformation at each pixel location is in response to accumulated charge on a corresponding charge transfer pin with which said mirror pixel location is spatially aligned so that the deformation at each pixel location varies as a function of the amount of phase distortion present at the corresponding pixel location in the input beam,
• draining charge from each of said pins of said charge transfer plate at a controlled rate through respective R-C circuits for each of said pixels, and
• continuing to accumulate charge on said charge transfer plate for the duration of said control beam under the control of said beam,
• the rate at which charge is drained from said charge transfer plate being selected to be slow enough to sustain an accumulated charge for a constant rate of charge application to the charge transfer plate, but fast enough for the accumulated charge to respond to a change in the rate of charge application within a desired response rate.