Wavelength-independent polarization converter

A wavelength-independent electrooptical polarization mode converter, comprising:

• an electrooptical crystal substrate of lithium niobate, which has its optical axis in the z-axis direction, and is cut in a plane defined by a direction perpendicular to the optical or z axis;
• an optical waveguide formed by diffusion of titanium into a surface of the substrate, the waveguide being oriented to provide for the propagation of light from one end of the waveguide to the other, in a direction parallel with the z axis of the substrate;
• and
• electrode means disposed on the surface of the substrate and positioned with respect to the waveguide to provide control of a coupling coefficient for conversion between a transverse-electric (TE) polarization mode a transverse-magnetic (TM) polarization mode, and control of phase mismatch between the two modes;
• whereby both modes experience the same material refractive index, in the x and y directions orthogonal to the optical axis, and any phase mismatch between the modes can be corrected by applying a suitable bias voltage through the electrode means.

A wavelength-independent electrooptical polarization mode converter, comprising:

• an electrooptical crystal substrate of x-cut lithium niobate, which has its optical axis in the z-axis direction;
• an optical waveguide formed by diffusion of titanium into a surface of the substrate, the waveguide being oriented to provide for the propagation of light from one end of the waveguide to the other, in a direction parallel with the z axis of the substrate;
• a first electrode positioned immediately over the waveguide;
• a second electrode parallel to the waveguide and displaced laterally to one side;
• and
• a third and common electrode parallel to the waveguide and displaced laterally to the other side;
• and wherein a first bias voltage is applied between the first and third electrodes to generate an electric field that is predominantly in the x direction, and a second bias voltage is applied between the second and third electrodes to generate an electric field that is predominantly in the y direction;
• and wherein the first bias voltage is used to control the degree of coupling between transverse-electric (TE) and transverse-magnetic (TM) polarization modes, and the second bias voltage is used to control the phase velocity mismatch between the two modes;
• whereby both modes experience the same material refractive index, in the x and y directions orthogonal to the optical axis, and any phase mismatch between the modes can be corrected by applying a suitable bias voltage through the electrode means.

A wavelength-independent electrooptical polarization angle modulator, comprising:

• an electrooptical crystal substrate of lithium niobate, which has it optical axis in the z-axis direction, and is cut in a plane defined by a direction perpendicular to the optical or z axis;
• an optical waveguide formed by diffusion of titanium into a surface of the substrate, the waveguide being oriented to provide for the propagation of light from one end of the waveguide to the other, in a direction parallel with the z axis of the substrate;
• and
• first electrode means disposed on the surface of the substrate and positioned with respect to the waveguide to provide control of a coupling coefficient for conversion between a transverse-electric (TE) polarization mode a transverse-magnetic (TM) polarization mode;
• and
• second electrode means, to control phase mismatch between the two modes;
• whereby both modes experience the same material refractive index, in the x and y directions orthogonal to the optical axis, and any phase mismatch between the modes can be corrected by applying a suitable bias voltage through the electrode means, after which control of the polarization mode coupling coefficient permits control of the polarization angle of light output from the device.

A wavelength-independent electrooptical polarization angle modulator, comprising:

• an electrooptical crystal substrate of x-cut lithium niobate, which has its optical axis in the z-axis direction;
• an optical waveguide formed by diffusion of titanium into a surface of the substrate, the waveguide being oriented to provide for the propagation of light from one end of the waveguide to the other, in a direction parallel with the z axis of the substrate;
• a first electrode positioned immediately over the waveguide;
• a second electrode parallel to the waveguide and displaced laterally to one side;
• and
• a third and common electrode parallel to the waveguide and displaced laterally to the other side;
• and wherein a first bias voltage is applied between the first and third electrodes to generate an electric field that is predominantly in the x direction, and a second bias voltage is applied between the second and third electrodes to generate an electric field that is predominantly in the y direction;
• and wherein the first bias voltage is used to control the degree of coupling between transverse-electric (TE) and transverse-magnetic (TM) polarization modes, and therefore to control the polarization angle if the phase velocity mismatch is eliminated, and the second bias voltage is used to control and eliminate the phase velocity mismatch between the two modes;
• whereby both modes experience the same material refractive index, in the x and y directions orthogonal to the optical axis, and any phase mismatch between the modes can be corrected by applying a suitable bias voltage through the electrode means.

An optical communication link employing polarization angle modulation, comprising:

• an optical source;
• a polarization angle modulator that is insensitive to wavelength, including means for correcting phase velocity mismatch between polarizaiton modes and means for independently varying the polarization mode coupling coefficient, and therefore varying the polarization angle of light output from the modulator;
• means for separating the modulated light into its polarization mode components;
• means for detecting the polarization mode components and producing corresponding electrical signal;
• and
• means combining the component signals in such a way as to produce and output signal that is proportional to the modulating signal but is independent of any variations in the intensity of the optical source.