Wavelength conversion apparatus with improved efficiency, easy adjustability, and polarization insensitivity

• US 5,946,129 A
• Filed: 08/29/1997
• Issued: 08/31/1999
• Est. Priority Date: 09/05/1996
• Status: Expired due to Term

• Current Assignee: Inphi Corporation
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Xu, Chang-Qing, Okayama, Hideaki, Shinozaki, Keisuke
• Primary Examiner(s): Lee, John D.
• Application Number:
  US08/920,884
• Time in Patent Office: 732 Days
• Field of Search: 359/326-332, 385/122, 372/21, 372/22
• US Class Current: 359/332
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 5/1071 Ring-lasers
• CPC Class Codes: H01S 5/50 Amplifier structures not provided for in groups H01S5/02 - H01S5/30

Abstract

A wavelength conversion apparatus has an optical amplifier, a wavelength converter, and an optical coupler coupled to form an optical ring resonator. The optical amplifier supplies pump light. The wavelength converter generates converted light, either from the pump light alone or by interaction between the pump light and signal light supplied from a signal source. The optical coupler extracts the converted light. The optical ring resonator preferably includes a tunable optical bandpass filter that defines the wavelength of the pump light. The optical coupler may also couple the signal light into the optical ring resonator, preferably through a polarization beam splitter and at least one polarization rotator, making the apparatus insensitive to the polarization of the signal light.

Claims

1. A wavelength conversion apparatus, comprising:

an optical resonator in which light circulates repeatedly along an optical path configured as a ring, said optical resonator including

an optical amplifier disposed on said optical path, for amplifying light of a first wavelength, and

a wavelength converter disposed on said optical path, for converting part of the light of the first wavelength to light of a second wavelength, different from the first wavelength; and

an optical coupler coupled to said optical resonator, for extracting the light of said second wavelength from said optical resonator.

2. The wavelength conversion apparatus of claim 1, wherein said optical resonator is configured using optical fiber.

3. The wavelength conversion apparatus of claim 2, wherein said optical fiber comprises polarization-maintaining fiber.

4. The wavelength conversion apparatus of claim 1, wherein said optical resonator also comprises a bandpass filter disposed on said optical path, for defining said first wavelength by transmitting light of said first wavelength and blocking light of wavelengths other than said first wavelength.

5. The wavelength conversion apparatus of claim 4, wherein said bandpass filter is tunable over a range of wavelengths including a wavelength at which said wavelength converter operates with maximum conversion efficiency.

6. The wavelength conversion apparatus of claim 1, wherein said optical amplifier comprises at least one semiconductor optical amplifier.

7. The wavelength conversion apparatus of claim 6, wherein said optical amplifier generates the light of said first wavelength by amplified spontaneous emission.

8. The wavelength conversion apparatus of claim 1, wherein said optical coupler has a pair of waveguides, and extracts the light of said second wavelength by optical tunneling between said waveguides.

9. The wavelength conversion apparatus of claim 1, wherein said optical coupler comprises:

a first selective reflector disposed on said optical path, for transmitting light of said first wavelength and reflecting light of said second wavelength; and

a first optical circulator disposed on said optical path between said wavelength converter and said first selective reflector, for transmitting light received from said wavelength converter to said first selective reflector, and extracting light received from said first selective reflector as output light.

10. The wavelength conversion apparatus of claim 9, wherein said first selective reflector comprises a fiber grating.

11. The wavelength conversion apparatus of claim 1, wherein said wavelength converter converts light from said first wavelength to said second wavelength by interaction with signal light having a third wavelength.

12. The wavelength conversion apparatus of claim 11, wherein said wavelength converter performs difference-frequency generation.

13. The wavelength conversion apparatus of claim 11, wherein said optical coupler comprises:

an input coupler disposed on said optical path, for coupling said signal light into said optical path;

a first selective reflector disposed on said optical path, for reflecting light of said second wavelength and transmitting light of other wavelengths;

a first optical circulator disposed on said optical path, for transmitting light to said first selective reflector, and extracting light received from said first selective reflector as output converted light;

a second selective reflector disposed on said optical path, for reflecting light of said third wavelength and transmitting light of other wavelengths; and

a second optical circulator disposed on said optical path, for transmitting light to said second selective reflector, and extracting light received from said second selective reflector as output signal light.

14. The wavelength conversion apparatus of claim 13, wherein said first selective reflector and said second selective reflector comprise respective fiber gratings.

15. A wavelength conversion apparatus, comprising:

an optical resonator in which light circulates repeatedly along an optical path configured as a ring, said optical resonator having

an optical amplifier disposed on said optical path, for amplifying light of a first wavelength, and

a wavelength converter disposed on said optical path, for converting part of the light of the first wavelength to light of a second wavelength, different from the first wavelength, wherein said wavelength converter converts light from said first wavelength to said second wavelength by interaction with signal light having a third wavelength; and

an optical coupler coupled to said optical ring resonator, for extracting the light of said second wavelength from said optical ring resonator, wherein the optical coupler comprises;

a polarization beam splitter, for separating said signal light into a first component having a first polarization and a second component having a second polarization;

a first multiplexing coupler disposed on said optical path, for coupling said first component onto said optical path;

a second multiplexing coupler disposed on said optical path, for coupling said second component onto said optical path; and

a first polarization rotator, disposed between said polarization beam splitter and said first multiplexing coupler, for rotating said first polarization to match said second polarization.

16. The wavelength conversion apparatus of claim 15, wherein said first multiplexing coupler and said second multiplexing coupler are disposed adjacent said wavelength converter, on opposite sides of said wavelength converter, and direct said signal light into said wavelength converter from mutually opposite directions.

17. The wavelength conversion apparatus of claim 16, wherein said wavelength converter is disposed at a point on said optical path where light of said first wavelength travels with equal intensity in both directions on said optical path.

18. The wavelength conversion apparatus of claim 16, wherein said first multiplexing coupler and said second multiplexing coupler comprise respective wavelength-division-multiplexing couplers.

19. The wavelength conversion apparatus of claim 16, wherein said first multiplexing coupler and said second multiplexing coupler also couple the light of said second wavelength from said optical path to said polarization beam splitter.

20. The wavelength conversion apparatus of claim 19, wherein said optical resonator also has a phase adjuster, disposed on said optical path, for adjusting a phase of the light of said first wavelength, thereby causing the light of said second wavelength coupled by said first multiplexing coupler and the light of said second wavelength coupled from said second multiplexing coupler to combine constructively in said polarization beam splitter.

21. The wavelength conversion apparatus of claim 19, wherein said optical coupler further comprises an optical isolator for transmitting said signal light into said polarization beam splitter, and blocking return of said signal light from said polarization beam splitter.

22. The wavelength conversion apparatus of claim 19, wherein said optical coupler further comprises an optical circulator, for transmitting said signal light into said polarization beam splitter from a first direction, and transmitting light received from said polarization beam splitter in a second direction different from said first direction.

23. The wavelength conversion apparatus of claim 19, wherein said first polarization rotator rotates said first polarization by forty-five degrees, and said optical coupler further comprises:

a second polarization rotator disposed between said polarization beam splitter and said second multiplexing coupler, for rotating said second polarization by forty-five degrees, thereby causing said first polarization and said second polarization to match.

24. The wavelength conversion apparatus of claim 23, wherein said signal light enters said polarization beam splitter from a first direction, and light of said second wavelength exits said polarization beam splitter in a second direction different from said first direction.

25. A wavelength conversion apparatus, comprising:

a pump light source for generating pump light having a certain polarization;

a polarization beam splitter, for receiving signal light, and splitting said signal light into a first component having a first polarization and a second component having a second polarization;

a pair of multiplexing couplers, coupled to said pump light source and said polarization beam splitter, for combining said first component and said second component with said pump light;

a wavelength converter coupled to said multiplexing couplers, for generating converted light by interaction of said pump light with said first component and said second component, said converted light differing in wavelength from said pump light; and

at least one polarization rotator, coupled to said polarization beam splitter, for rotating at least one polarization among said first polarization and said second polarization, thereby causing said first polarization and said second polarization both to match the polarization of said pump light.

26. The wavelength conversion apparatus of claim 25, comprising just one said polarization rotator, said polarization rotator rotating said first polarization by 90°

.

27. The wavelength conversion apparatus of claim 25, comprising a first said polarization rotator rotating said first polarization by 45°

, and a second said polarization rotator rotating said second polarization by 45°

.

28. The wavelength conversion apparatus of claim 25, wherein said multiplexing couplers are disposed on opposite sides of said wavelength converter.

29. The wavelength conversion apparatus of claim 28, wherein said wavelength converter receives said pump light with equal intensity from each of said multiplexing couplers.

30. The wavelength conversion apparatus of claim 28, wherein said pump light source comprises at least:

an optical amplifier for supplying said pump light to said multiplexing couplers, receiving said pump light from at least one of said multiplexing couplers after said pump light has passed through said wavelength converter, amplifying the pump light thus received, and supplying the amplified pump light again to said multiplexing couplers; and

an optical bandpass filter for limiting said pump light to a certain wavelength.

31. The wavelength conversion apparatus of claim 30, wherein said bandpass filter is tunable over a range of wavelengths including a wavelength at which said wavelength converter operates with maximum conversion efficiency.

32. The wavelength conversion apparatus of claim 30, further comprising optical fiber for coupling said optical amplifier, said bandpass filter, said wavelength converter, and said multiplexing couplers to form an optical ring resonator.

33. The wavelength conversion apparatus of claim 30, further comprising a pair of reflectors, wherein said optical amplifier, said bandpass filter, said wavelength converter, and said multiplexing couplers are disposed on an optical path between said pair of reflectors.

34. The wavelength conversion apparatus of claim 25, wherein said multiplexing couplers supply said converted light to said polarization beam splitter for provision as an output through said polarization beam splitter.

35. The wavelength conversion apparatus of claim 34, wherein said pump light source also comprises a phase adjuster for adjusting said pump light in phase, thereby also adjusting said converted light in phase and causing the converted light supplied from said multiplexing couplers to combine constructively in said polarization beam splitter.

36. The wavelength conversion apparatus of claim 34, further comprising an optical isolator for transmitting said signal light into said polarization beam splitter, and blocking return of said signal light from said polarization beam splitter.

37. The wavelength conversion apparatus of claim 34, further comprising an optical circulator, for transmitting said signal light into said polarization beam splitter from a first direction, and transmitting light received from said polarization beam splitter in a second direction different from said first direction.

38. The wavelength conversion apparatus of claim 34, comprising a first said polarization rotator rotating said first polarization by 45°

, and a second said polarization rotator rotating said second polarization by 45°

.

39. The wavelength conversion apparatus of claim 38, wherein said signal light enters said polarization beam splitter from a first direction and said converted light leaves said polarization beam splitter in a second direction different from said second direction.

40. The wavelength conversion apparatus of claim 25, wherein said multiplexing couplers are wavelength-division multiplexing couplers.

41. The wavelength conversion apparatus of claim 25, wherein said multiplexing couplers comprise dichroic mirrors that transmit said pump light, reflect said signal light, and reflect said converted light.

42. The wavelength conversion apparatus of claim 25, wherein said multiplexing couplers comprise dichroic mirrors that reflect said pump light, transmit said signal light, and transmit said converted light.