Optical control element
An optical control modulator comprises an input to receive light from a light source; a polarization divider to divide the light into two orthogonal plane-polarized light components; a Faraday material which, upon being energized, rotates the plane of polarization of the plane-polarized light as it passes through the material; and an output. The light travels through the Faraday material in opposite directions on a common path. In one embodiment, the light passes once through the Faraday material on a loop path. In another embodiment, the light passes twice through the Faraday material by being reflected by a mirror disposed at a back face of the Faraday material.
1. A modulator comprising
an input to receive light from a light source and modulate data onto it,
a polarization divider to convert the light into plane-polarized light,
a material which upon being energized rotates the plane of polarization of the plane-polarized light as it passes through the material such that energizing and de-energizing the material modulates data onto the light, and
an output wherein the light travels through the material in opposite directions on a common path.
2. A modulator according to claim 1 in which the intensity of the light is modulated by changing its polarization state.
3. A modulator according to claim 1 in which the light is divided into two components having different respective polarization states.
4. A modulator according to claim 3 in which the polarization state of each of the light components is changed after the light is divided.
5. A modulator according to claim 1 in which the input and the output commonly comprise an input/output.
6. A modulator according to claim 1 in which the material is energized when subjected to a magnetic field.
7. A modulator according to claim 1 in which the material is a Faraday material.
8. A modulator according to claim 1 in which the material is energized when subjected to an electric field.
9. A modulator according to claim 8 which comprises a Pockels cell.
10. A modulator according to claim 1 which comprises a magnetic field generator for applying a magnetic field to the material.
11. A modulator according to claim 10 in which the magnetic field generator is a coil and a power supply for causing current flow in the coil.
12. A modulator according to claim 11 which comprises a modulation control unit for controlling the power supply.
13. A modulator according to claim 1 in which there are two common paths.
14. A modulator according to claim 13 in which the light is split into a first part and a second part wherein the first part travels on a first common path firstly in a first direction and then secondly in a second opposite direction and the second part travels on a second common path firstly in a first direction and then secondly in a second opposite direction.
15. A modulator according to claim 13 which comprises a reflecting element.
16. A modulator according to claim 1 in which the light passes once through the material.
17. A modulator according to claim 1 in which the light is split into a first part and a second part wherein the first part travels on the common path in a first direction and the second part travels on the common path in a second opposite direction.
18. A modulator according to claim 1 which produces“0” and “1” signals according to whether the material is energized.
19. A modulator according to claim 1 which produces analog signals according to whether the material is energized.
20. An optical network unit for an optical transmission system comprising a modulator, wherein the modulator comprises
an input to receive light from a light source and modulate data onto it,
a polarization divider to convert the light into plane-polarized light,
a material which upon being energized rotates the plane of polarization of the plane-polarized light as it passes through the material such that de-energizing and energizing the material modulates data onto the light, and
an output wherein the light travels through the material in opposite directions on a common path.
21. An optical transmission system comprising at least one modulator, wherein the at least one modulator comprises
an input to receive light from a light source and modulate data onto it,
a polarization divider to convert the light into plane-polarized light,
a material which upon being energized rotates the plane of polarization of the plane-polarized light as it passes through the material such that energizing and de-energizing the material modulates data onto the light, and
an output wherein the light travels through the material in opposite directions on a common path.
22. A method of modulating light comprising the steps of:
receiving light from a light source;
using a polarization divider to convert the light into plane-polarized light;
sending the light in opposite directions on a common path through an energizable material; and
energizing the material to rotate the plane of polarization of the plane-polarized light as it travels on the common path such that energizing and de-energizing the material modulates data onto the light.