Resonator modulators and wavelength routing switches

• US 6,052,495 A
• Filed: 10/01/1997
• Issued: 04/18/2000
• Est. Priority Date: 10/01/1997
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Foresi, James S., Little, Brent E., Haus, Hermann A.
• Primary Examiner(s): Lee, John D.
• Assistant Examiner(s): Stahl, Michael J.
• Application Number:
  US08/944,009
• Time in Patent Office: 930 Days
• Field of Search: 385/1, 385/2, 385/8, 385/9, 385/14, 385/24, 385/27, 385/32, 385/39-41, 385/47, 385/50, 385/131, 385/132
• US Class Current: 385/2
• CPC Class Codes: G02F 1/011 in optical waveguides, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0155 modulating the optical absorption
• CPC Class Codes: G02F 1/3133 the optical waveguides being made of semiconducting materials
• CPC Class Codes: G02F 2203/055 wavelength filtering

Abstract

The invention provides an optical switch and modulator which uses a closed loop optical resonator. The optical resonator is a dielectric cavity whose primary function is to store optical power. Various structures are possible, and a particularly advantageous one is a ring shaped cavity. The wavelength response at the output port of a ring resonator side coupled to two waveguides is determined by the details of the resonator, and the coupling between the resonator and the waveguides. By coupling to adjacent resonators, the modulator response can be improved over that of a single resonator. One such improvement is in modulator efficiency, which is defined as the ratio of the change in optical intensity at the output, to a change in absorption in the ring waveguides. Absorption is used for switching and modulation without incurring significant optical attenuation. Another improvement involves making the resonance insensitive to small deviations in wavelength or index change. The latter improves fabrication tolerances and compensates for possible drift of the signal wavelength. Collectively, the behavior of multiple coupled resonators yields higher order responses.

Claims

1. A signal modulator comprising;

an input waveguide which carries a signal having a plurality of wavelengths including a desired wavelength;

an output waveguide; and

a closed loop resonator coupled between said input and output waveguides which allows transmission of said plurality of wavelengths except said desired wavelength through said input waveguide, said resonator being operable for selectively transferring said desired wavelength to said output waveguide in response to absorption characteristics of said resonator being varied.

2. The signal modulator of claim 1, wherein said signal comprises an optical signal.

3. The signal modulator of claim 1, wherein the absorption characteristics of said resonator are varied in response to an applied voltage or current to said resonator.

4. The signal modulator of claim 1, wherein said resonator has a modulation efficiency which corresponds to the spacing between said resonator and said input and output waveguides.

5. The signal modulator of claim 1, wherein said resonator comprises a ring resonator.

6. An optical signal modulator and wavelength router, comprising;

an input waveguide having an input port and an output port, said waveguide receiving an optical signal with an incident optical wavelength at said input port;

an output waveguide; and

at least one closed loop resonator coupled between said input and output waveguides, said resonator being tuned into and out of resonance with said incident optical wavelength by varying absorption characteristics to selectively route said wavelength between said output waveguide and said output port.

7. The optical signal modulator and wavelength router of claim 6 further comprising a plurality of closed loop resonators coupled between said input and output waveguides, at least one of said resonators being tuned into and out of resonance with said incident optical wavelength by varying absorption characteristics to selectively route said wavelength between said output waveguide and said output port.

8. The optical signal modulator and wavelength router of claim 6, wherein the absorption characteristics of said at least one resonator is varied in response to an applied voltage or current to said resonator.

9. The optical signal modulator and wavelength router of claim 6, wherein said at least one resonator has a modulation efficiency which corresponds to the spacing between said resonator and said input and output waveguides.

10. The optical signal modulator and wavelength router of claim 6, wherein said at least one resonator comprises a ring resonator.

11. An optical signal modulator and wavelength router, comprising;

an input waveguide having an input port and an output port, said waveguide receiving an optical signal with an incident optical wavelength at said input port;

an output waveguide;

at least one closed loop resonator coupled between said input and output waveguides, said at least one resonator being operable for selectively routing said incident wavelength between said output waveguide and said output port in response to being tuned into and out of resonance with said incident optical wavelength; and

means for tuning said at least one resonator into and out of resonance with said incident optical wavelength by inducing absorption in said at least one resonator.

12. The optical signal modulator and wavelength router of claim 11 further comprising a plurality of closed loop resonators coupled between said input and output waveguides, at least one of said resonators being tuned into and out of resonance with said incident optical wavelength by varying absorption characteristics to selectively route said wavelength between said output waveguide and said output port.

13. The optical signal modulator and wavelength router of claim 11, wherein the absorption characteristics of said at least one resonator is varied in response to said tuning means applying voltage or current to said at least one resonator.

14. The optical signal modulator and wavelength router of claim 11, wherein said at least one resonator has a modulation efficiency which corresponds to the spacing between said resonator and said input and output waveguides.

15. The optical signal modulator and wavelength router of claim 11, wherein said at least one resonator comprises a ring resonator.

16. A method of modulating an optical signal, comprising;

transmitting an optical signal with a plurality of incident optical wavelengths including a desired wavelength through an input waveguide; and

tuning at least one closed loop resonator, coupled between said input waveguide and an output waveguide, into and out of resonance with said desired wavelength by inducing absorption in said at least one resonator to selectively switch said desired wavelength to said output waveguide while allowing transmission of remaining wavelengths through said input waveguide.

17. The method of claim 16, wherein said tuning step comprises applying a voltage or current to said resonator to induce absorption in said resonator.

18. The method of claim 16, wherein said resonator has a modulation efficiency which corresponds to the spacing between said resonator and said input and output waveguides.

19. The method of claim 16, wherein said resonator comprises a ring resonator.

20. The method of claim 16 further comprising tuning a plurality of closed loop resonators, coupled between said input waveguide and an output waveguide, into and out of resonance with said desired wavelength.