CHIP-BASED LASER RESONATOR DEVICE FOR HIGHLY COHERENT LASER GENERATION

• US 20150092808A1
• Filed: 06/15/2012
• Published: 04/02/2015
• Est. Priority Date: 06/17/2011
• Status: Active Grant

• Current Assignee: California Institute of Technology
• Original Assignee: Li Jiang, Tong Chen
• Inventors: LI, Jiang, LEE, Hansuek, CHEN, Tong, VAHALA, Kerry
• Granted Patent: US 9,293,887 B2
• Time in Patent Office: Days
• US Class Current: 372/95
• CPC Class Codes: H01S 2301/02 ASE (amplified spontaneous emission), noise; Reduction thereof
• CPC Class Codes: H01S 3/0632 Thin film lasers in which light propagates in the plane of the thin film
• CPC Class Codes: H01S 3/083 Ring lasers fibre ring lasers H01S3/06791
• CPC Class Codes: H01S 3/094057 by tapered duct or homogenized light pipe, e.g. for concentrating pump light
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 3/176 silica or silicate glass
• CPC Class Codes: H01S 3/30 using scattering effects, e.g. stimulated Brillouin or Raman effects
• CPC Class Codes: H01S 5/1075 Disk lasers with special modes, e.g. whispering gallery lasers
• CPC Class Codes: H01S 5/2275 mesa created by etching

Abstract

A highly-coherent chip-based laser generating system includes a disk resonator incorporating a wedge structure fabricated from a silicon dioxide layer of a chip. The disk resonator is operable to generate a highly-coherent laser from a low-coherence optical pump input provided at an optical power level as low as 60 μW. The disk resonator is fabricated with sub-micron cavity size control that allows generation of a highly-coherent laser using a controllable Stimulated Brillouin Scattering process that includes matching of a cavity free-spectral-range to a Brillouin shift frequency in silica. While providing several advantages due to fabrication on a chip, the highly-coherent laser produced by the disk resonator may feature a Schawlow-Townes noise level as low as 0.06 Hz²/Hz (measured with the coherent laser at a power level of about 400 μW) and a technical noise that is at least 30 dB lower than the low-coherence optical pump input.

Claims

1. A highly-coherent chip-based laser generating system comprising:

a disk resonator comprising a wedge structure fabricated from a silicon dioxide layer of a chip, the disk resonator operable to generate a highly-coherent laser from a low-coherence optical pump input provided at an optical power level as low as 60 microwatts.

2. The system of claim 1, wherein the disk resonator is fabricated with a cavity size control that permits matching of a cavity free-spectral-range (FSR) to a Brillouin shift frequency in the chip for generating the highly-coherent laser.

3. The system of claim 2, wherein fabrication of the wedge structure from the silicon dioxide layer provides a diameter control of at least 1:

20,000.

4. The system of claim 2, wherein the generated highly-coherent laser is characterized at least in part, by a Schawlow-Townes noise level as low as 0.06 Hz²/Hz measured with the coherent laser at a power level of about 400 μ

W.

5. The system of claim 2, wherein the generated highly-coherent laser is characterized at least in part, by a technical noise that is at least 30 dB lower than the low-coherence optical pump input.

6. The system of claim 2, wherein the disk resonator is configured to operate as a chip-based spectral purifier for boosting a coherence level of the low-coherence optical pump input by several orders of magnitude.

7. The system of claim 6, wherein the disk resonator is a 10.8 GHz disk resonator providing a 0.5 MHz free-spectral-range (FSR) uncertainty.

8. The system of claim 2, wherein fabrication of the wedge structure comprises:

placing a silicon substrate in a furnace;

introducing steam into the furnace;

raising a temperature inside the furnace to a first temperature level wherein a silicon dioxide layer is formed on a major surface of the silicon substrate;

eliminating a moisture content in the silicon substrate by heating the silicon substrate at a second temperature level in an oxygen-rich environment;

forming a first assembly by applying a photo-resist layer upon a portion of the major surface of the silicon dioxide layer;

immersing the first assembly into a bath containing an etching solution selected for etching silicon dioxide;

forming a second assembly by allowing the etching solution to act upon the silicon dioxide layer of the first assembly for a first period of time that is selected in order to;

a) expose a portion of the silicon substrate, b) form the wedge structure in the silicon dioxide layer, and c) provide a cavity size control;

forming a third assembly by extending the first period of time by a second period of time in order to eliminate a foot region formed upon a sloping surface of the wedge structure;

after eliminating the foot region, forming a fourth assembly by removing the photo-resist layer from the third assembly; and

forming a waveguide portion from the fourth assembly by exposing the fourth assembly to a xenon difluoride (XeF₂) environment that eliminates a portion of the silicon substrate and forms a support pillar below the wedge structure.

9. The system of claim 8, wherein the silicon dioxide layer ranges from about 8 micron thickness to about 10 micron thickness.

10. The system of claim 8, wherein fabrication of the wedge structure from the silicon dioxide layer permits fabrication of a plurality of disk resonators with sub-micron precision control of a diameter dimension of each of the plurality of disk resonators.

11. The system of claim 8, wherein fabrication of the wedge structure from the silicon dioxide layer permits manufacturing of a batch of disk resonators with sub-micron precision control of a diameter dimension, and obtaining a Q factor of at least 100 million and as high as 875 million in each disk resonator.

12. A highly-coherent chip-based laser generating system comprising:

a disk resonator fabricated from a silicon substrate with a sub-micron cavity size control, the disk resonator operable to generate a highly-coherent laser using stimulated Brillouin scattering on a chip, the highly-coherent laser characterized in part, by a Schawlow-Townes noise level as low as 0.06 Hz²/Hz at a power level of about 400 μ

W.

13. The system of claim 12, wherein the disk resonator is configured to generate the highly-coherent laser from a low-coherence optical pump input provided at an optical power level as low as 60 μ

W.

14. The system of claim 13, wherein fabrication of the disk resonator from the silicon substrate permits manufacturing of a hatch of disk resonators with i) sub-micron precision control of a diameter dimension and ii) substantially similar Q factors.

15. The system of claim 14, wherein the sub-micron precision control comprises using an etching procedure that provides a diameter control of at least 1:

20,000.

16. The system of claim 14, wherein fabrication of the disk resonator from the silicon substrate comprises:

placing the silicon substrate in a furnace;

introducing steam into the furnace;

raising a temperature inside the furnace to a first temperature level wherein a silicon dioxide layer is formed on a major surface of the silicon substrate;

eliminating a moisture content in the silicon substrate by heating the silicon substrate at a second temperature level in an oxygen-rich environment;

forming a first assembly by applying a photo-resist layer upon a portion of the major surface of the silicon dioxide layer;

immersing the first assembly into a bath containing an etching solution selected for etching silicon dioxide;

forming a second assembly by allowing the etching solution to act upon the silicon dioxide layer of the first assembly for a first period of time that is selected in order to;

a) expose a portion of the silicon substrate, and b) form a wedge structure in the silicon dioxide layer;

forming a third assembly by extending the first period of time by a second period of time in order to eliminate a foot region formed upon a sloping surface of the wedge structure;

after eliminating the foot region, forming a fourth assembly by removing the photo-resist layer from the third assembly; and

forming a waveguide portion from the fourth assembly by exposing the fourth assembly to a xenon difluoride (XeF₂) environment that eliminates a portion of the silicon substrate and forms a support pillar below the wedge structure.

17. The system of claim 16, wherein the silicon dioxide layer ranges from about 8 micron thickness to about 10 micron thickness.

18. A method of manufacturing chip-based laser devices for one or more coherent laser generating systems, the method comprising:

fabricating a batch of disk resonators from a silicon substrate, the fabricating comprising precision control of a diameter dimension to obtain a substantial similar Q factor in each disk resonator.

19. The method of claim 18, wherein the substantial similar Q factor is at least 100 million and as high as 875 million.

20. The method of claim 19, wherein each disk resonator is configurable as to generate a coherent laser that is characterized in part, by a Schawlow-Townes noise level as low as 0.06 Hz²/Hz at a power level of about 400 μ

W.

21. The method of claim 20, wherein the fabricating comprises:

placing the silicon substrate in a furnace;

introducing steam into the furnace;

raising a temperature inside the fur lace to a first temperature level wherein a silicon dioxide layer is formed on a major surface of the silicon substrate;

eliminating a moisture content in the silicon substrate by heating the silicon substrate at a second temperature level in an oxygen-rich environment;

forming a first assembly by applying a photo-resist layer upon a portion of the major surface of the silicon dioxide layer;

immersing the first assembly into a bath containing an etching solution selected for etching silicon dioxide;

forming a second assembly by allowing the etching solution to act upon the silicon dioxide layer of the first assembly for a first period of time that is selected in order to;

a) expose a portion of the silicon substrate, and b) form at least one wedge structure in the silicon dioxide layer;

forming a third assembly by extending the first period of time by a second period of time in order to eliminate a foot region formed upon a sloping surface of the at least one wedge structure;

after eliminating the foot region, forming a fourth assembly by removing the photo-resist layer from the third assembly; and

forming at least one waveguide portion from the fourth assembly by exposing the fourth assembly to a xenon difluoride (XeF₂) environment that eliminates a portion of the silicon substrate and forms a support pillar below the at least one wedge structure.

22. The method of claim 21, wherein the silicon dioxide layer ranges from about 8 micron thickness to about 10 micron thickness.

23. The method of claim 21, wherein the first period of time is further selected to allow the etching solution to act upon the silicon dioxide layer to form a slope angle ranging from about 7 degrees to about 90 degrees in the sloping surface of the at least one wedge structure.

24. The method of claim 23, wherein an adhesion promoter is incorporated into the photo-resist layer, the adhesion promoter providing an adhesion factor between the photo-resist layer and the silicon dioxide layer, the adhesion factor selected in accordance with the first period of time and the slope angle.