US 5,347,382 A · Liquid crystal cell retarder with driving beyond retardance value and two cells for high speed

Abstract

A fast response liquid crystal optical retarder system. A liquid crystal retarder system employs one or more liquid crystal cells and corresponding drive circuits. The drive circuits provide to the cell a rectangular wave ac voltage signal whose RMS voltage is controlled. To switch from one retardance to another, the voltage is increased or decreased beyond the voltage corresponding to the target retardance and then, prior to or when the target retardance is reached, the applied voltage is switched to the voltage corresponding to the target retardance. One or more pairs of liquid crystal cells provided sequentially along the path of light propagation and with their eigen-axis orthogonal to one another to increase or decrease the total retardance rapidly. The retarder system is incorporated in a polarization control system and in a fiber-optic link.

Claims21

Dependent claims

An optical retarder system, comprising:

(a) first retarder means for controlling the retardance of light passing therethrough along a first eigen-axis thereof relative to a second eigen-axis thereof in response to the application of a first signal thereto;
and
(b) first drive means, connected to said first retarder means, for supplying said first signal to said first retarder means, said drive means including first control means for changing said retardance from a first retardance to a second retardance by causing said first signal to change, in a direction to move toward said second retardance, from a first amplitude which is required for said first retardance to a second amplitude, beyond a third amplitude which is required for said second retardance, for a period of time, and then causing said first signal to change to the said second amplitude required for a second retardance.

An optical retarder system, comprising:

(a) first retarder means, including liquid crystal material and having a fast axis and a slow axis, for controlling the retardance of light passing therethrough along said fast axis thereof relative to said slow axis thereof by the application of an electric field to said liquid crystal material, said first retarder means having a minimum retardance and a maximum retardance;
(b) first drive means for supplying to said first retarder means a first drive signal for producing said electric field;
(c) second retarder means, including liquid crystal material and having a fast axis and a slow axis, for controlling the retardance of light passing therethrough said fast axis thereof relative to said slow axis thereof by applying a second electric field to liquid crystal material of said second retarder means, said second retarder means being disposed relative to said first retarder means so that said light passes through said first retarder means and said second retarder means sequentially, said fast axis of said second retarder means being substantially co-planer with said slow axis of said first retarder means, and said slow axis of said second retarder means being substantially co-planer with said fast axis of said first retarder means, said second retarder means having a minimum retardance and a maximum retardance;
(d) second drive means for supplying to said second retarder means a second drive signal for producing said second electric field;
and
(e) difference control means, connected to said first drive means and to said second drive means, for adjusting the retardance of said first retarder means and the retardance of said second retarder means to respective intermediate values between said respective minimum and maximum retardances thereof so that the difference in retardance between the two is a predetermined amount.

3 more elements

An optical polarization control system, comprising:

(a) a coherent optical input signal source;
(b) a coherent optical reference signal source;
(c) detector means for receiving light from said input signal source and from said reference signal source and producing an output signal representative of the intensity of the light illuminating said detector;
(d) an optical retarder system, disposed between said input signal source or said reference signal source and said detector means, for controlling the retardance of light passing therethrough, said optical retarder system having:
(i) first retarder means, for controlling the retardance of light passing therethrough along a fast axis thereof relative to a slow axis thereof by the application of a first signal thereto;
(ii) first drive means for supplying to said first retarder means said first signal;
(iii) second retarder means for controlling the retardance of light passing therethrough along a fast axis thereof relative to a slow axis thereof by applying a second electric field to liquid crystal material of said second retarder means, said second retarder means being disposed relative to said first retarder means so that said light passes through said first retarder means and said second retarder means sequentially, said fast axis of said second retarder means being substantially co-planer with said slow axis of said first retarder means, and said slow axis of said second retarder means being substantially co-planer with said fast axis of said first retarder means;
(iv) second drive means for supplying to said second retarder means a second signal for producing said second signal;
and
(v) difference control means, connected to said first drive means and to said second drive means, for adjusting the retardance of said first retarder means and the retardance of said second retarder means so that the difference between the two is a predetermined amount;
and
(e) control means, responsive to said output signal and connected to said drive means, for maintaining a predetermined polarization relationship between said input signal and said reference signal.

9 more elements

Dependencies are inferred from the claim text.

Liquid crystal cell retarder with driving beyond retardance value and two cells for high speed

Life of this patent

Liquid crystal cell retarder with driving beyond retardance value and two cells for high speed

Life of this patent

Abstract

Claims21