Abstract

It is shown how demodulation of rapidly modulated light beams can be achieved within a single charge-coupled device (CCD). Two interlaced image planes are created by optically masking every second CCD row and transferring the charges back and forth between the two image planes in synchrony with the modulation. The method has been successfully tested for modulation frequencies of 50 and 100 kHz, using integration times up to 1 s. No significant accumulated charge transfer losses are seen for integration times as long as 105 modulation cycles (1 s). This demonstrates the feasibility of a CCD polarimeter using piezoelastic modulation of the state of polarization.

© 1990 Optical Society of America

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References

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  1. J. C. Kemp, “Piezo-Optical Birefringence Modulators,” J. Opt. Soc. Am. 59, 950–954 (1969).
  2. J. O. Stenflo, “Solar Magnetic and Velocity-Field Measurements: New Instrument Concepts,” Appl. Opt. 23, 1267–1278 (1984).
    [CrossRef] [PubMed]
  3. J. O. Stenflo, H. Povel, “Astronomical Polarimeter with 2-D Detector Arrays,” Appl. Opt. 24, 3893–3898 (1985).
    [CrossRef] [PubMed]
  4. Hinds International, Inc., Hillsboro, OR 97124.
  5. English Electronic Valve Co., Ltd, Chelmsford, Essex, England.
  6. ELTEC Elektronik GmbH, D-6500 Mainz 42, F.R. Germany.

1985

1984

1969

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Figures (7)

Fig. 1
Fig. 1

Setup with a piezoelastic modulator, linear polarizer, photodetector, and synchronous demodulator.

Fig. 2
Fig. 2

Principle of a demodulator with a three-phase CCD image sensor. Shown is the position of the charge packets in a column during different modulation half-cycles.

Fig. 3
Fig. 3

Imaging of a slit mask on the CCD. The slits are parallel to the CCD rows and have a width that is 82% of the row width.

Fig. 4
Fig. 4

Block diagram of the electronics.

Fig. 5
Fig. 5

Demodulated signal P(α) for 50-kHz modulation as a function of phase shift α. Measured values are shown for 20-ms (circles) and 900-ms (squares) integration times. The curve is calculated from Eq. (10) as explained in the text.

Fig. 6
Fig. 6

Relative modulation amplitude for different integration times T between 20 and 1000 ms. The values are normalized with respect to the value at T = 20 ms.

Fig. 7
Fig. 7

Demodulated signal P(α) for 100-kHz modulation as a function of phase shift α. Measured values are shown for 20-ms (circles) and 900-ms (squares) integration times. The curve is calculated from Eq. (11) as explained in the text.

Equations (11)

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I c ( t ) = [ 1 + sin ϕ ( t ) ] / 2
I l ( t ) = [ 1 + cos ϕ ( t ) ] / 2
ϕ ( t ) = A sin ( Ω 0 t ) ,
I c ( t ) = ½ + J 1 ( A ) sin ( Ω 0 t ) + J 3 ( A ) sin ( 3 Ω 0 t ) + ,
I t ( t ) = [ 1 + J 0 ( A ) ] / 2 + J 2 ( A ) sin ( 2 Ω 0 t ) + .
P = I + - I - I + + I -
D ( Ω t ) = { 1 for 2 m π < Ω t < ( 2 m + 1 ) π , - 1 for ( 2 m + 1 ) π < Ω t < ( 2 m + 2 ) π .
F ( ω ) ~ k sinc [ ( k Ω - ω ) T ] , k = 1 , 3 , 5 , ,
P ( i , j ) = I + ( i , j ) - I - ( i , j ) I + ( i , j ) + I - ( i , j ) ,
P ( α ) = 4 π [ J 1 ( A ) sin ( α - α 0 ) - 1 3 J 3 ( A ) sin 3 ( α - α 0 ) + ] ,
P ( α ) = 4 π [ J 2 ( A ) sin ( α - α 0 ) + 1 3 J 6 ( A ) sin 3 ( α - α 0 ) + ] / [ 1 - J 0 ( A ) ] .

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