Abstract

The design, construction, and evaluation of a laser beam steerer that uses two binary ferroelectric liquid-crystal (FLC) spatial light modulators (SLMs) operated in conjunction are presented. The system is characterized by having few components and is in principle lossless. Experimentally, a throughput of ∼20% was achieved. The simple system design was achieved because of the high tilt angle FLC material used in the SLMs, which were specifically designed and manufactured for this study. By coherently imaging the first SLM onto the second SLM, pixel by pixel, we obtained an effective four-level phase structure with a phase step of 90°. An appropriate alignment procedure is presented. The beam steering performance of the system is reported and analyzed.

© 2004 Optical Society of America

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  1. M. Gotlieb, C. L. M. Ireland, J. M. Lay, “Electro-Optic and Acousto-Optic Scanning and Deflection,” Vol. 3 of Optical Engineering Series (Marcel Dekker, New York, 1983), p. 198.
  2. S. Lee, L. Huang, C. Kim, M. C. Wu, “Free-space fiber-optic switches based on MEMS vertical torsion mirrors,” J. Lightwave Technol. 17, 7–13 (1999).
    [CrossRef]
  3. R. F. Cartland, A. Madhukar, “High contrast, 2D spatial light modulators (SLMs) using InGas/AlGaAs quantum wells operating at 980 nm,” in Spatial Light Modulators (Optical Society of America, Washington, D.C., 1997), pp. 55–57.
  4. W. D. Cowan, M. K. Lee, B. M. Welsh, V. M. Bright, M. C. Roggemann, “Surface micromachined segmented mirrors for adaptive optics,” IEEE J. Sel. Top. Quantum Electron. 5, 90–101 (1999).
    [CrossRef]
  5. P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
    [CrossRef]
  6. N. A. Clark, S. T. Lagerwall, “Submicrosecond bistable electro-optic switching in liquid crystals,” Appl. Phys. Lett. 36, 899–901 (1980).
    [CrossRef]
  7. W. Crossland, T. D. Wilkinson, “Nondisplay applications of liquid crystals,” in Handbook of Liquid Crystals, D. Demus, J. Goodby, G. W. Gray, H.-W. Spiess, V. Vill, eds. (Wiley-VCH, Weiheim, Germany, 1998), Vol. 1, pp. 763–822.
  8. M. O. Freeman, T. A. Brown, D. M. Walba, “Quantized complex ferroelectric liquid crystal spatial light modulators,” Appl. Opt. 31, 3917–3929 (1992).
    [CrossRef] [PubMed]
  9. S. E. Broomfield, M. A. A. Neil, E. G. S. Paige, “Programmable multiple-level phase modulation that uses ferroelectric liquid-crystal spatial light modulators,” Appl. Opt. 34, 6652–6665 (1995).
    [CrossRef] [PubMed]
  10. A. Magnusson, S. Hård, “Four-level phase grating generated by combination of two binary gratings through coherent imaging,” Appl. Opt. 39, 5936–5939 (2000).
    [CrossRef]
  11. High-tilt FLCs are notoriously difficult to align in electro-optic cells, and the alignment achieved after the virgin cooling of the CS-2005 LC from the isotropic to the smectic C* phase is often rather inhomogeneous. Hence the boundary conditions (buffed polyimide layers) are by themselves not sufficient for providing satisfactory alignment. However, by cycling the temperature through the nematic to smectic C* transition while applying ac electric fields (with amplitudes similar to the addressing signals), one can significantly improve the alignment.
  12. The distributing circuit, which accepts only positive voltages, contains one binary switch per pixel. When a switch is set in one of its positions, zero voltage is applied to its pixel electrode. When it is set in its other position the raw driving voltage is applied to its pixel electrode. To generate the required positive and negative pixel-cell voltages the common SLM electrode is fed with half of the instantaneous raw driving voltage (virtual ground). The switch settings are controlled by the microprocessor.
  13. The reason why the grating with period 2Np gets repeated after only N pixel shifts is that the phase steps of the SLM pixels are π and π/2.

2000

1999

S. Lee, L. Huang, C. Kim, M. C. Wu, “Free-space fiber-optic switches based on MEMS vertical torsion mirrors,” J. Lightwave Technol. 17, 7–13 (1999).
[CrossRef]

W. D. Cowan, M. K. Lee, B. M. Welsh, V. M. Bright, M. C. Roggemann, “Surface micromachined segmented mirrors for adaptive optics,” IEEE J. Sel. Top. Quantum Electron. 5, 90–101 (1999).
[CrossRef]

1996

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

1995

1992

1980

N. A. Clark, S. T. Lagerwall, “Submicrosecond bistable electro-optic switching in liquid crystals,” Appl. Phys. Lett. 36, 899–901 (1980).
[CrossRef]

Bright, V. M.

W. D. Cowan, M. K. Lee, B. M. Welsh, V. M. Bright, M. C. Roggemann, “Surface micromachined segmented mirrors for adaptive optics,” IEEE J. Sel. Top. Quantum Electron. 5, 90–101 (1999).
[CrossRef]

Broomfield, S. E.

Brown, T. A.

Cartland, R. F.

R. F. Cartland, A. Madhukar, “High contrast, 2D spatial light modulators (SLMs) using InGas/AlGaAs quantum wells operating at 980 nm,” in Spatial Light Modulators (Optical Society of America, Washington, D.C., 1997), pp. 55–57.

Clark, N. A.

N. A. Clark, S. T. Lagerwall, “Submicrosecond bistable electro-optic switching in liquid crystals,” Appl. Phys. Lett. 36, 899–901 (1980).
[CrossRef]

Corkum, D. L.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Cowan, W. D.

W. D. Cowan, M. K. Lee, B. M. Welsh, V. M. Bright, M. C. Roggemann, “Surface micromachined segmented mirrors for adaptive optics,” IEEE J. Sel. Top. Quantum Electron. 5, 90–101 (1999).
[CrossRef]

Crossland, W.

W. Crossland, T. D. Wilkinson, “Nondisplay applications of liquid crystals,” in Handbook of Liquid Crystals, D. Demus, J. Goodby, G. W. Gray, H.-W. Spiess, V. Vill, eds. (Wiley-VCH, Weiheim, Germany, 1998), Vol. 1, pp. 763–822.

Dorschner, T. A.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Freeman, M. O.

Friedman, L. J.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Gotlieb, M.

M. Gotlieb, C. L. M. Ireland, J. M. Lay, “Electro-Optic and Acousto-Optic Scanning and Deflection,” Vol. 3 of Optical Engineering Series (Marcel Dekker, New York, 1983), p. 198.

Hård, S.

Hobbs, D. S.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Holtz, M.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Huang, L.

Ireland, C. L. M.

M. Gotlieb, C. L. M. Ireland, J. M. Lay, “Electro-Optic and Acousto-Optic Scanning and Deflection,” Vol. 3 of Optical Engineering Series (Marcel Dekker, New York, 1983), p. 198.

Kim, C.

Lagerwall, S. T.

N. A. Clark, S. T. Lagerwall, “Submicrosecond bistable electro-optic switching in liquid crystals,” Appl. Phys. Lett. 36, 899–901 (1980).
[CrossRef]

Lay, J. M.

M. Gotlieb, C. L. M. Ireland, J. M. Lay, “Electro-Optic and Acousto-Optic Scanning and Deflection,” Vol. 3 of Optical Engineering Series (Marcel Dekker, New York, 1983), p. 198.

Lee, M. K.

W. D. Cowan, M. K. Lee, B. M. Welsh, V. M. Bright, M. C. Roggemann, “Surface micromachined segmented mirrors for adaptive optics,” IEEE J. Sel. Top. Quantum Electron. 5, 90–101 (1999).
[CrossRef]

Lee, S.

Liberman, S.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Madhukar, A.

R. F. Cartland, A. Madhukar, “High contrast, 2D spatial light modulators (SLMs) using InGas/AlGaAs quantum wells operating at 980 nm,” in Spatial Light Modulators (Optical Society of America, Washington, D.C., 1997), pp. 55–57.

Magnusson, A.

McManamon, P. F.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Neil, M. A. A.

Nguyen, H. Q.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Paige, E. G. S.

Resler, D. P.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Roggemann, M. C.

W. D. Cowan, M. K. Lee, B. M. Welsh, V. M. Bright, M. C. Roggemann, “Surface micromachined segmented mirrors for adaptive optics,” IEEE J. Sel. Top. Quantum Electron. 5, 90–101 (1999).
[CrossRef]

Sharp, R. C.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Walba, D. M.

Watson, E. A.

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Welsh, B. M.

W. D. Cowan, M. K. Lee, B. M. Welsh, V. M. Bright, M. C. Roggemann, “Surface micromachined segmented mirrors for adaptive optics,” IEEE J. Sel. Top. Quantum Electron. 5, 90–101 (1999).
[CrossRef]

Wilkinson, T. D.

W. Crossland, T. D. Wilkinson, “Nondisplay applications of liquid crystals,” in Handbook of Liquid Crystals, D. Demus, J. Goodby, G. W. Gray, H.-W. Spiess, V. Vill, eds. (Wiley-VCH, Weiheim, Germany, 1998), Vol. 1, pp. 763–822.

Wu, M. C.

Appl. Opt.

Appl. Phys. Lett.

N. A. Clark, S. T. Lagerwall, “Submicrosecond bistable electro-optic switching in liquid crystals,” Appl. Phys. Lett. 36, 899–901 (1980).
[CrossRef]

IEEE J. Sel. Top. Quantum Electron.

W. D. Cowan, M. K. Lee, B. M. Welsh, V. M. Bright, M. C. Roggemann, “Surface micromachined segmented mirrors for adaptive optics,” IEEE J. Sel. Top. Quantum Electron. 5, 90–101 (1999).
[CrossRef]

J. Lightwave Technol.

Proc. IEEE

P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holtz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, E. A. Watson, “Optical phased array technology,” Proc. IEEE 84, 268–298 (1996).
[CrossRef]

Other

R. F. Cartland, A. Madhukar, “High contrast, 2D spatial light modulators (SLMs) using InGas/AlGaAs quantum wells operating at 980 nm,” in Spatial Light Modulators (Optical Society of America, Washington, D.C., 1997), pp. 55–57.

W. Crossland, T. D. Wilkinson, “Nondisplay applications of liquid crystals,” in Handbook of Liquid Crystals, D. Demus, J. Goodby, G. W. Gray, H.-W. Spiess, V. Vill, eds. (Wiley-VCH, Weiheim, Germany, 1998), Vol. 1, pp. 763–822.

M. Gotlieb, C. L. M. Ireland, J. M. Lay, “Electro-Optic and Acousto-Optic Scanning and Deflection,” Vol. 3 of Optical Engineering Series (Marcel Dekker, New York, 1983), p. 198.

High-tilt FLCs are notoriously difficult to align in electro-optic cells, and the alignment achieved after the virgin cooling of the CS-2005 LC from the isotropic to the smectic C* phase is often rather inhomogeneous. Hence the boundary conditions (buffed polyimide layers) are by themselves not sufficient for providing satisfactory alignment. However, by cycling the temperature through the nematic to smectic C* transition while applying ac electric fields (with amplitudes similar to the addressing signals), one can significantly improve the alignment.

The distributing circuit, which accepts only positive voltages, contains one binary switch per pixel. When a switch is set in one of its positions, zero voltage is applied to its pixel electrode. When it is set in its other position the raw driving voltage is applied to its pixel electrode. To generate the required positive and negative pixel-cell voltages the common SLM electrode is fed with half of the instantaneous raw driving voltage (virtual ground). The switch settings are controlled by the microprocessor.

The reason why the grating with period 2Np gets repeated after only N pixel shifts is that the phase steps of the SLM pixels are π and π/2.

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Figures (15)

Fig. 1
Fig. 1

Schematic of the effective four-phase level beam steerer studied here. Both SLM1 and SLM2 are of the surface-stabilized FLC type, with the same pixel configuration. The phase steps are π and π/2, respectively, for the wavelength used. SLM1 is coherently imaged onto SLM2 at unit magnification.

Fig. 2
Fig. 2

Schematic showing the orientation of the FLC molecules in the smectic layers for our θ ≈ 45° FLC material. The orientation depends on the polarity of controlling electric field E.

Fig. 3
Fig. 3

Phase modulation at a pixel in the FLC SLM as experienced by a linearly polarized laser beam incident upon a rotatable birefringent plate whose optic axis can be directed either vertically (state 1) or horizontally (state 2) as determined by the polarity of the electric field controlling the pixel. The phase difference between the two states is Γ = (2π/λ0nd, where Δn is the birefringence of the material, d is the cell thickness, and λ0 is the wavelength of light in vacuum.

Fig. 4
Fig. 4

FLC SLM cell with glued so-called flexprints. The arrow indicates the active area of the SLM.

Fig. 5
Fig. 5

Photo of the two-SLM beam steering setup. The physical distance between the SLMs is 200 mm.

Fig. 6
Fig. 6

Flow chart of the drive electronics. The shapes of the raw driving signals are indicated. The picture is oversimplified: In actuality there is one connector to each electrode from the distributing circuits.

Fig. 7
Fig. 7

Switching performance of SLM1 viewed in a polarizing microscope. (To illustrate the two pixel settings we added a passive λ/4 plate.) (a) The voltage alternated between minus voltage and plus voltage at every second pixel. (b) The same as in (a) but with reversed voltages.

Fig. 8
Fig. 8

(a) Setup for phase step measurement of a SLM as a function of wavelength: M, monochromator; P, polarizer; A, circular aperture; L, lens. (b) Captured CCD frames for SLM1 at wavelengths of 450, 550, and 750 nm from left to right.

Fig. 9
Fig. 9

Measured powers in the zeroth and two first diffraction orders as a function of wavelength for (a) SLM1 and (b) SLM2. The values are normalized to the total power detected by the CCD.

Fig. 10
Fig. 10

Examples of measured beam deflection in the pixel identification procedure. Each picture is a stripe composite showing the diffraction patterns for N = 9 equidistant deflection angles plus the pattern at zero deflection; the stripes are oriented vertically side by side. Each subimage shows the result obtained when the structures set on the two SLMs are shifted in steps of 1 pixel. The subimages should be read in alphabetical order. Subimage (h) shows the measured diffraction patterns at correct positioning of the phase structures on SLM1 and SLM2 characterized by a continuous slanting trace. Maximum deflection angle, αmax = λ/(2p).

Fig. 11
Fig. 11

Measured diffraction patterns from the beam deflection experiment. The picture is a composite, showing a stack of vertical stripes of the diffraction patterns from 513 phase structures made to steer the beam into 513 equidistant deflection angles, including the pattern at zero deflection.

Fig. 12
Fig. 12

Relative power steered in 513 aimed directions as a function of steering angle. Dots show the measured data. The solid curve shows simulated values (number of values, 5001). Each measured value is normalized to the total power in the corresponding CCD stripe. The angular stripe width is ±4.3αmax. A corresponding normalization was done for the simulated values.

Fig. 13
Fig. 13

Relative power in the second most powerful diffracted beam for each of the 513 phase structures. Dots show the measured data. The solid curve shows simulated values (number of values, 5001). Each measured value is normalized to the total power in the corresponding CCD stripe. The angular stripe width is ±4.3αmax. A corresponding normalization was done for the simulated values. The numbering of the phase structures is the same as in Fig. 12.

Fig. 14
Fig. 14

Measured locations of the most powerful diffracted beams (slanted curve of dots) and of the second most powerful diffracted beams (open circles) within operating angular range ±αmax for the 513 phase structures studied.

Fig. 15
Fig. 15

Simulated locations of the most powerful diffracted beams (slanted curve of dots) and the second most powerful diffracted beams (open circles) within operating angular range ±αmax for the 513 phase structures studied.

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