Spatial polarization coding electro-optical transmitter

• US 4,103,260 A
• Filed: 01/03/1977
• Issued: 07/25/1978
• Est. Priority Date: 01/03/1977
• Status: Expired due to Term

• Current Assignee: Hughes Aircraft Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Buchman, William W.
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US05/756,292
• Time in Patent Office: 568 Days
• Field of Search: 332/7.51, 350/150, 350/151, 350/157, 350/160, 250/199
• US Class Current: 359/250
• CPC Class Codes: G02F 1/01 for the control of the intensity, phase, polarisation or colour G02F1/29, G02F1/35 take precedence
• CPC Class Codes: G02F 1/0121 Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
• CPC Class Codes: G02F 2201/16 series; tandem
• CPC Class Codes: H04B 10/532 Polarisation modulation

Abstract

A transmitter for producing an energy beam which has encoded thereon as a polarization state of the energy, angular position along a selected one of a plurality of dimensions across the beam. The transmitter comprises a laser unit for transmitting energy through a plurality of switchable modulators with each of said modulators comprising an electro-optical device, such as a 180° retarder or a 90° rotator, coupled between a pair of birefringent wedges. The wedges are configured such that when the associated electro-optical device is not energized the birefringence of the wedges cancel. When energized, the electro-optical device translates the polarization state of the energy passing therethrough such that the birefringence of the wedges add so as to cause a variation in the polarization across the beam. The spatial orientation of the two wedges in a given modulator determines the dimension across the beam encoded thereby.

Claims

1. A transmitter for producing an energy beam which has encoded thereon as a polarization state of the energy, position along a selected one of a plurality of dimensions across the beam, said transmitter comprising:

a laser unit which provides a beam of linearly polarized energy;

a plurality of switchable modulators arranged relative to said laser unit and to one another so that the laser energy passes sequentially through each of said modulators; and

with said modulators each comprising an electro-optical device coupled between a pair of birefringent wedges, with said electro-optical device including means for switching between a selected one of two states, with the polarization of the energy passing through said electro-optical device being transformed by a first amount when said electro-optical device is in its first state and transformed by a second amount when it is in its second state, and with said wedges having their fast and slow axes oriented at approximately 45 degress to the polarization of the energy provided by said laser unit and having their optical axes substantially perpendicular to the energy beam, and with said wedges being configured and oriented so that energy everywhere within the beam, in passing through said pair of wedges, passes through substantially the same amount of birefringent material and so that when said electro-optical device is in said first state the birefringence of said wedges combines so as to cause no substantial polarization encoding across the beam of energy at the output of said modulator and when said electro-optical device is in said second state the birefringence of said wedges combines so that the energy at the output of said modulator is polarization encoded along a preselected dimension across the beam.

2. The transmitter of claim 1 wherein said wedges are so configured that when said electro-optical device is in its first state their birefringence substantially cancels and when said device is in its second state their birefringence substantially adds.

3. The transmitter of claim 1 wherein the spatial orientation of the wedges is different in each of said modulators, whereby a different dimension across the beam is encoded by each respective modulator when said respective modulator is switched into its second state.

4. The transmitter of claim 1 wherein said electro-optical device passes energy with substantially zero polarization transformation when it is in its first state and when it is in its second state it changes the polarization of one component of the energy from horizontal to vertical and the polarization of the other component from vertical to horizontal.

5. The transmitter of claim 1 wherein said electro-optical device passes energy with substantially zero polarization transformation when it is in its first state and it functions as a 90°

rotator when it is in its second state.

6. The transmitter of claim 1 wherein said electro-optical device passes energy with substantially zero polarization transformation when it is in its first state and it functions as a 180°

linear retarder when in its second state.

7. The transmitter of claim 1 wherein said electro-optical device is a half-wave lithium niobate transverse Pockels cell.

8. The transmitter of claim 1 wherein said electro-optical device is a Faraday cell.

9. A transmitter for producing a polarization encoded energy beam comprising:

a laser unit which provides a beam of linearly polarized energy;

at least two switchable modulators arranged relative to said laser unit and to one another so that the laser energy passes sequentially through each of said modulators; and

with said modulators each comprising an electro-optical device coupled between a pair of birefringent wedges with said electro-optical device including means for switching between a first state in which substantially zero polarization transformation is impressed on energy passing therethrough and a second state in which an interchange of the horizontal and vertical components of the energy is effected, said wedges having their fast and slow axes oriented at approximately 45 degrees to the polarization of the energy provided by said laser unit and having their optical axes substantially perpendicular to the energy beam, and said wedges being configured and oriented so that energy everywhere within the beam, in passing through said pair of wedges, passes through substantially the same amount of birefringent material and so that when said electro-optical device is in one of its states the birefringence of said wedges combines so as to cause no substantial polarization encoding across the beam of energy at the output of said modulator and when said electro-optical device is in said other state the birefringence of said wedges combines so that the energy at the output of said modulator is polarization encoded and wherein the spatial orientation of said wedges is different in each of said modulators; and

means for controlling said modulators so that only one modulator at a time is selectively switched to said other state in which the beam passing through said modulator is polarization encoded.

10. The transmitter of claim 9 wherein said electro-optical device is a half-wave lithium niobate transverse Pockels cell.

11. The transmitter of claim 9 wherein said electro-optical device is a Faraday cell.

12. A modulator for selectively applying polarization encoding to a laser beam of linearly polarized energy, said modulator comprising:

first and second birefringent wedges;

an electro-optical device coupled between said wedges and including means for switching between a first state in which the polarization of the energy passing through said electro-optical device is transformed by a first amount and a second state in which the energy passing therethrough is transformed by a second amount; and

with said wedges having their fast and slow axes oriented at approximately 45°

to the polarization of the applied laser energy and having their optical axis substantially perpendicular to the energy beam, and said wedges being configured and oriented so that energy everywhere within the beam, in passing through said pair of wedges, passes through substantially the same amount of birefringent material and so that when said electro-optical device is in said first state the birefringence of said wedges combines so as to cause no substantial polarization encoding of energy at the output of said modulator and when said electro-optical device is in its second state the birefringence of said wedges combines so that the energy at the output of the modulator is polarization encoded.

13. The modulator of claim 12 wherein said wedges are so configured that when said electro-optical device is in its first state their birefringence substantially cancels and when said device is in its second state their birefringence substantially adds.

14. The modulator of claim 12 wherein said electro-optical device passes energy with substantially zero polarization transformation when it is in its first state and when it is in its second state it changes the polarization of one component of the energy from horizontal to vertical and the polarization of the other component from vertical to horizontal.

15. The modulator of claim 12 wherein said electro-optical devices passes energy with substantially zero polarization transformation when it is in its first state and it functions as a 90°

rotator when it is in its second state.

16. The modulator of claim 12 wherein said electro-optical device passes energy with substantially zero polarization transformation when its is in its first state and it functions as a 180°

retarder when it is in its second state.

17. The modulator of claim 12 wherein said electro-optical device is a half-wave lithium niobate transverse Pockels cell.

18. The modulator of claim 12 wherein said electro-optical device is a Faraday cell.