Nanoscale Object Detection Using A Whispering Gallery Mode Resonator

• US 20110139970A1
• Filed: 12/13/2010
• Published: 06/16/2011
• Est. Priority Date: 12/11/2009
• Status: Active Grant

• Current Assignee: Washington University In St Louis
• Original Assignee: Washington University In St Louis
• Inventors: He, Lina, Yang, Lan, Ozdemir, Sahin Kaya, Chen, Da-Ren, Zhu, Jiangang
• Granted Patent: US 8,704,155 B2
• Time in Patent Office: Days
• US Class Current: 250/227.18
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: G01N 21/7746 the waveguide coupled to a cavity resonator

Abstract

Detection of individual objects using a light source and a whispering gallery mode (WGM) resonator. Light from the whispering gallery mode (WGM) resonator is analyzed. The presence of an object is determined based on mode splitting associated with the light received by the photodetector. For example, the presence of the object may be determined based on the distance between two whispering gallery modes and/or the linewidths of the two modes in a transmission spectrum. Alternatively, the presence of the object may be determined based on a beat frequency that is determined based on a heterodyne beat signal produced by combining split laser modes in the received light from a WGM microcavity laser.

Claims

1. A system for detecting an object, said device comprising:

a photodetector configured to receive light from a whispering gallery mode (WGM) resonator;

a processor coupled to the photodetector and programmed to;

create a transmission spectrum based on the received light;

identify within the transmission spectrum a first mode and a second mode, each of the first mode and the second mode representing a portion of the transmission spectrum associated with decreased transmission of light; and

determine a presence of an object proximate to the WGM resonator based on the first mode and the second mode.

2. The system of claim 1, wherein the processor is programmed to determine the presence of the object based on a distance between the first mode and the second mode.

3. The system of claim 2, wherein the processor is programmed to determine the presence of the object further based on a linewidth of the first mode and a linewidth of the second mode.

4. The system of claim 1, wherein the object is a first object, wherein the processor is further programmed to determine a presence of a second object based on the first mode and the second mode.

5. The system of claim 1, wherein the photodetector is a first photodetector configured to receive light from a first WGM resonator, and the object is a first object, said device comprising a second photodetector coupled to the processor and configured to receive light from a second WGM resonator, wherein the processor is further configured to determine a presence of a second object based on the light received by the second photodetector.

6. The system of claim 1, wherein the processor is further programmed to determine, based on the first mode and the second mode, one or more of the following:

a size of the object and a refractive index of the object.

7. The system of claim 1, further comprising a communication interface coupled to the processor and configured to transmit a detection signal indicating the presence of the object.

8. A system for detecting an object, said device comprising:

a photodetector configured to;

receive light emitted by a whispering gallery mode (WGM) resonator, wherein the received light includes a first laser mode and a second laser mode, each of the first mode and the second mode representing light transmission in a frequency range; and

combine the first laser mode and the second laser mode to create a heterodyne beat signal; and

a processor coupled to the photodetector and programmed to;

determine a beat frequency based on the heterodyne beat signal; and

determine a presence of an object proximate to the WGM resonator based on the beat frequency.

9. The system of claim 8, wherein the beat frequency is a first beat frequency determined at a first time, and the processor is further programmed to:

determine a second beat frequency of the heterodyne signal at a second time subsequent to the first time;

determine the presence of the object further based on comparing the first beat frequency to the second beat frequency.

10. The system of claim 8, wherein the light coupled out of the WGM resonator further includes residual light from a light source, the system further comprising a wavelength-division multiplexer coupled to the photodetector and configured to:

receive the light coupled out of by the WGM resonator; and

separate the residual light from the received light to create filtered light, wherein the photodetector receives the filtered light from the wavelength-division multiplexer.

11. The system of claim 8, wherein the processor is programmed to determine the beat frequency at least in part by applying a fast Fourier transform to the heterodyne beat signal.

12. The system of claim 8, further comprising:

the WGM resonator;

a light source; and

an optical fiber extending from the light source to the photodetector and proximate to the WGM resonator, wherein the optical fiber is configured to;

transmit light from the light source to the WGM resonator; and

transmit the light emitted by the WGM resonator to the photodetector.

13. The system of claim 12, wherein the WGM resonator comprises a cavity that includes a gain medium.

14. The system of claim 12, wherein the WGM resonator comprises a surface including an object adhesive, wherein the object adhesive is selected to bind the object to the surface.

15. The system of claim 12, wherein the light source comprises a substantially monochromatic laser.

16. A method comprising:

receiving, by a photodetector, light emitted by a whispering gallery mode (WGM) resonator;

creating, by the photodetector a heterodyne beat signal based on the received light;

determining, by a processor, a beat frequency based on the heterodyne beat signal; and

determining, by the processor, a presence of an object proximate to the WGM resonator based on the beat frequency.

17. The method of claim 16, wherein the received light includes a first laser mode representing light transmission in a first frequency range and a second laser mode representing light transmission in a second frequency range, and creating the heterodyne beat signal comprises combining the first laser mode and the second laser mode.

18. The method of claim 17, wherein the beat frequency is a first beat frequency, the received light further includes a third laser mode and a fourth laser mode, and creating the heterodyne beat signal further comprises combining the third laser mode and the fourth laser mode.

19. The method of claim 18, further comprising:

determining a second beat frequency based on the heterodyne beat signal; and

determining the presence of the object based further on the second beat frequency.

20. The method of claim 16, wherein determining the beat frequency comprises determining a first beat frequency at a first time, the method further comprising:

determining a second beat frequency based on the heterodyne beat signal at a second time subsequent to the first time; and

determining the presence of the object based at least in part on a comparison of the first beat frequency to the second beat frequency.