Integrated opto-electronic oscillators having optical resonators
Systems and techniques of incorporating an optical resonator in an optical part of a feedback loop in opto-electronic oscillators. This optical resonator provides a sufficiently long energy storage time and hence to produce an oscillation of a narrow linewidth and low phase noise. Certain mode matching conditions are required. For example, the mode spacing of the optical resonator is equal to one mode spacing, or a multiplicity of the mode spacing, of an opto-electronic feedback loop that receives a modulated optical signal and to produce an electrical oscillating signal.
1. A opto-electronic device, comprising:
a substrate formed of a semiconductor;
a semiconductor laser formed on said substrate to produce a laser beam;
a semiconductor optical modulator formed on said substrate to receive and modulate said laser beam from said semiconductor laser in response to an electrical modulation signal;
a first waveguide formed on said substrate and coupled to receive a modulated optical signal from said optical modulator;
an optical resonator formed on said substrate and coupled to said first waveguide to receive a portion of said modulated optical signal;
a second waveguide formed on said substrate and coupled to receive a portion of said modulated optical signal in said optical resonator;
a semiconductor photodetector formed on said substrate to receive and convert an optical output from said second waveguide into an electrical signal; and
an electrical link formed on said substrate and coupled between said photodetector and said optical modulator to produce said electrical modulation signal from said electrical signal.
2. A device as in claim 1 , wherein said optical resonator is a micro resonator in whispering gallery modes.
3. A device as in claim 2 , wherein said micro resonator is a dielectric sphere.
4. A device as in claim 2 , wherein said first and second waveguides include coupling sections adjacent to said micro resonator to couple optical energy to and from said micro resonator via evanescent coupling.
5. A device as in claim 1 , wherein said photodetector and said optical modulator have a substantially matched impedance.
6. A device as in claim 1 , wherein said electrical link does not have a signal amplifier between said photodetector and said optical modulator.
7. A device as in claim 1 , wherein said optical modulator is an electro absorption modulator.
8. A device as in claim 7 , wherein said photodetector is a device which is structurally identical to said electro absorption modulator but is biased to operate as a photodetector.
9. A device as in claim 1 , wherein said optical resonator has a free spectral range that is greater by a factor of an integer than a mode spacing of modes in an opto-electronic loop formed by said optical modulator, said first and second waveguides, said photodetector, and said electrical link.
10. A opto-electronic device, comprising:
a substrate formed of a semiconductor;
a semiconductor optical modulator formed on said substrate to modulate an optical beam in response to an electrical modulation signal, said optical modulator having a first side and an opposing second side that define an optical path;
an optical reflector formed on said first side of said optical modulator;
a first waveguide formed on said substrate having a first end that is to receive a modulated optical signal from said optical modulator and is insulated from said optical modulator, and a second end that has an angled facet;
an optical resonator operating in whispering gallery modes and formed on said substrate and coupled to said angled facet of said first waveguide via evanescent coupling;
a second waveguide formed on said substrate and having a first end with an angled facet which is coupled to said optical resonator via evanescent coupling, and a second end;
a semiconductor photodetector formed on said substrate and spaced from said second end of said second waveguide to receive and convert an optical output from said second waveguide into an electrical signal; and
an electrical link formed on said substrate and coupled between said photodetector and said optical modulator to produce said electrical modulation signal from said electrical signal,
wherein said first and second waveguides are doped to produce an optical gain to produce a laser oscillation in a laser cavity formed between said optical reflector and said second end of said second waveguide.
11. A device as in claim 10 , wherein said photodetector and said optical modulator have a substantially matched impedance.
12. A device as in claim 10 , wherein said electrical link does not have a signal amplifier between said photodetector and said optical modulator.
13. A device as in claim 10 , wherein said optical modulator is an electro absorption modulator.
14. A device as in claim 13 , wherein said photodetector is a device which is structurally identical to said electro absorption modulator but is biased to operate as a photodetector.
15. A device as in claim 10 , wherein said optical resonator has a free spectral range that is greater by a factor of an integer thin a mode spacing of modes in an opto-electronic loop formed by said optical modulator, said first and second waveguides, said photodetector, and said electrical link.
16. A device as claimed in claim 10 , wherein said optical resonator is a sphere formed of a dielectric material.