Dynamic couplers using two-mode optical waveguides

An apparatus for controlling an optical signal, comprising:

• an optical waveguide comprising a light propagation medium that supports at least first and second spatial propagation modes, said optical waveguide having a first effective refractive index for light propagating in said first spatial propagation mode and a second effective refractive index, said second effective refractive index different from said first effective refractive index, for light propagating in said second spatial propagation mode so that light propagating in one of said modes propagates at a phase propagation velocity that is different from the phase propagation velocity of light propagating in the other of said modes;
• an optical signal- source that supplies a first optical input signal to said optical waveguide at a first optical wavelength, said first optical wavelength selected so that said first optical input signal has a first spatial mode component that propagates in said optical waveguide in said first spatial propagation mode and a second spatial mode component that propagates in said second spatial propagation mode, said first spatial mode- component being shifted in phase with respect to said second spatial mode component as said first optical input signal propagates in said optical waveguide;
• and
• a perturbational signal source that supplies a second optical input signal to said optical waveguide at a second optical wavelength, said second optical wavelength selected so that said second optical input signal propagates in said optical waveguide in at least said first spatial propagation mode, said second optical input signal having an intensity that is selectable to perturb said first effective refractive index relative to said second effective refractive index to change the amount by which said first spatial propagation mode component of said first optical input signal is shifted in phase with respect to said second spatial mode component of said first optical input signal as said first and second spatial propagation mode components propagate in said optical waveguide.

A method of controlling an optical signal in an optical waveguide, comprising the steps of:

• providing an optical waveguide having a geometry selected so that said optical waveguide supports at least first and second spatial propagation modes light propagating therein, said first and second spatial propagation modes having first and second effective refractive indices, respectively, such that light propagating in one of said first and second spatial propagation modes propagates at a phasevelocity that is different from the phase propagation velocity of light propagating in the other of said first and second spatial propagation modes;
• inputting a first optical signal having a first wavelength into said optical waveguide so that said first optical signal propagates in said optical waveguide with substantially equal light intensities in said first and second spatial propagation modes in said waveguide, the light propagating in said first spatial propagation mode propagating at a phase velocity that is different from the phase propagation velocity of the light propagating in said second spatial propagation mode thereby causing an optical phase difference between the light propagating in said first spatial propagation mode and the light propagating in said second spatial propagation mode, said optical phase difference varying along the length of said optical waveguide;
• inputting a second optical signal having a second wavelength into said optical waveguide to control said first optical signal, said second optical signal propagating in said optical waveguide in said first spatial propagation mode;
• and
• selectively adjusting the intensity of said second optical signal so that said second optical signal has an intensity sufficiently large to perturb said first effective refractive index with respect to said second effective refractive index to change the ' phase velocity of the light of said first optical signal propagating in said first spatial propagation mode, thereby introducing an additional optical phase difference between the light propagating in said first spatial propagation mode and the light propagating in said second spatial propagation mode, said additional optical phase difference causing a change in the intensities in first and second lobes of an optical intensity distribution pattern at the output of said optical waveguide.