Nonlinear optical coupler using a doped optical waveguide

An apparatus for controlling an optical signal, comprising:

• an optical waveguide comprising an active medium, said waveguide having first and second spatial propagation modes, said first and second modes having first and second indices of refraction, respectively;
• a pump source coupled to introduce a pump signal into at least one of said spatial modes to optically perturb at least one of said first and second indices of refraction, the intensity of said pump signal being selected to produce a phase shift in a first optical signal component propagating in one of said modes such that said first component has a phase difference of approximately .pi. radians with respect to a second optical signal component propagating in the other of said modes, said optical signal having a spatial intensity distribution in said waveguide that varies as a function of said phase difference;
• and
• wherein said pump signal phase switches the optical energy of said optical signal from said first mode to said second mode and reciprocally.

An apparatus for controlling an optical signal, comprising:

• an optical waveguide comprising an active medium, said waveguide having first and second spatial propagating modes, said first and second modes having first and second indices of refraction, respectively;
• a pump source coupled to introduce a pump signal into at least one of said spatial modes to optically perturb at least one of said first and second indices of refraction, the intensity of said pump signal being selected to produce a phase shift in a first optical signal component propagating in one of said modes such that said first component has a phase difference of approximately .pi. radians with respect to a second optical signal component propagating in the other of said modes, said optical signal having a spatial intensity distribution in said waveguide that varies as a function of said phase difference;
• and
• wherein said pump signal has a pump power, said pump power being greater than P.sub.abs /1-exp(.sigma..sub.p N.sub.0 L+P.sub.abs /AI.sub.p,sat), wherein P.sub.abs is the total amount of pump power absorbed by the waveguide, .sigma..sub.p is the absorption cross section for said pump source, N.sub.0 is the total species population density for said active medium, L is the length of the optical waveguide, A is the area of the optical waveguide illuminated by the pump signal, and I.sub.p,sat is the pump saturation intensity for said active medium.

An apparatus for controlling an optical signal, comprising:

• an optical waveguide comprising an active medium, said waveguide having first and second spatial propagation modes, said first and second modes having first and second indices of refraction, respectively;
• a pump source coupled to introduce a pump signal into at least one of said spatial modes to optically perturb at least one of said first and second indices of refraction, said optical signal having a spatial intensity distribution in said waveguide that varies as a function of the perturbation;
• and
• wherein said optical signal has a first wavelength and said pump signal has a second wavelength, said second wavelength being proximate to an absorption transition of said active medium.

An apparatus for controlling an optical signal, comprising:

• an optical waveguide comprising an active medium 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 pump 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 can be selected 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 doped with an active medium 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 phase velocity 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.

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

• providing an optical waveguide doped with an active medium, said optical waveguide having at least first and second spatial propagation modes, said first and second spatial propagation modes having first and second refractive indices, respectively;
• inputting said optical signal having a first wavelength into said optical waveguide;
• inputting a pump signal having a second wavelength into said optical waveguide to optically perturb at least one of said first and second indices of refraction;
• selectively adjusting the intensity of said pump signal to controllably vary the spatial intensity distribution of said optical signal.