Detection of a substance by refractive index change

• US 6,493,090 B1
• Filed: 07/24/2000
• Issued: 12/10/2002
• Est. Priority Date: 01/23/1998
• Status: Expired due to Fees

• Current Assignee: Torsana A/S (Hometown AS)
• Original Assignee: Torsana A/S (Hometown AS)
• Inventors: Lading, Lars, Lindvold, Lars
• Primary Examiner(s): Turner, Samuel A.
• Assistant Examiner(s): CONNOLLY, PATRICK J
• Application Number:
  US09/624,891
• Time in Patent Office: 869 Days
• Field of Search: 356/481, 356/480, 356/484, 385/12, 385/14, 250/227.19, 250/227.27, 250/227.18
• US Class Current: 356/484
• CPC Class Codes: G01D 5/268 using optical fibres G01D5/28 - G01D5/38 take precedence
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods
• CPC Class Codes: G01N 21/774 the reagent being on a grating or periodic structure
• CPC Class Codes: G01N 21/7746 the waveguide coupled to a cavity resonator

Abstract

A sensitive refractive index based detector comprises a first laser cavity (7) and a second laser cavity (7′) each for generating a respective laser light beam. Each laser cavity is defined in a planar waveguide. The surface of the waveguide of the first laser (7) receives a sample to be detected. Light from the two lasers is mixed using a coupling grating (3) and a beat frequency between the lasers dependent upon the refractive index of the substance is measured at a detector (4). Extremely sensitive measurement of small quantities of substance are made possible.

Claims

1. An apparatus for sensing the amount, concentration or presence of a substance through a change in refractive index, comprising

a first laser having a laser cavity defined by a waveguide for generation of a first laser light beam and a second laser having a laser cavity defined by a waveguide for generation of a second laser light beam,

the propagation of said laser light beam in said first laser cavity being characterised by a first propagation constant and the propagation of said laser light beam in said second laser cavity being characterised by a second propagation constant,

the waveguide defining the first laser cavity having a sensing surface for receiving a sample of a substance to be sensed, such that the presence of said substance at said sensing surface alters the said first propagation constant and the frequency of light in said first laser beam,

and means for combining said laser beams to produce beating between their respective frequencies and means for detecting a change in the said beating consequent upon a said change in said first propagation constant caused by the presence of said substance.

2. Apparatus as claimed in claim 1, wherein the laser cavities of the first laser and the second laser are separate from one another.

3. Apparatus as claimed in claim 1 or claim 2, wherein said means for combining said laser beams to produce beating between their respective frequencies and means for detecting a change in the said beating consequent upon a said change in said first propagation constant caused by the presence of said substance comprise

a detector which produces an electrical output signal in response to the intensity of light incident upon it,

first optical means for directing the first light beam emitted from the first laser towards the detector, and

second optical means for directing the second light beam emitted from the second laser towards the detector,

the first and second optical means being adapted to align the wavefronts of the first and second light beams at the detector for coherent detection of the light beams at the detector whereby the detector output signal has a component which is generated in response to the difference between the frequencies of the first and second light beams.

4. Apparatus as claimed in claim 3, wherein the first optical means comprises a first waveguide for transmission of the first light beam.

5. Apparatus as claimed in claim 4, wherein the second optical means comprise a second waveguide for transmission of the second light beam.

6. Apparatus as claimed in any preceding claim, wherein the first and second lasers are semiconductor lasers.

7. Apparatus as claimed in claim 6, wherein the first and second lasers are manufactured on a semiconductor chip.

8. Apparatus as claimed in claim 7, wherein the means for combining said laser beams to produce beating between their respective frequencies and means for detecting a change in the said beating consequent upon a said change in said first propagation constant caused by the presence of said substance are integrated in the semiconductor chip.

9. Apparatus as claimed in any one of claims 1 to 5, wherein the first and second lasers are polymer lasers.

10. Apparatus according to claim 9, wherein the lasers are manufactured on a device made of a polymer in which the means for combining said laser beams to produce beating between their respective frequencies and means for detecting a change in the said beating consequent upon a said change in. said first propagation constant caused by the presence of said substance are integrated.

11. Apparatus as claimed in any preceding claim, wherein the first and second laser cavities have cavity reflector gratings that are distributed along the length of the respective cavities.

12. The apparatus of claim 1, wherein said waveguide defining said laser cavity of said second laser is partially shared by said laser cavity of said first laser.

13. A method for sensing the amount, concentration or presence of a substance through a change of refractive index, which method comprises:

providing a first laser having a laser cavity defined by a waveguide for generation of a first laser light beam and a second laser having a laser cavity defined by a waveguide for generation of a second laser light beam, the propagation of said laser light beam in said first laser cavity being characterised by a first propagation constant and the propagation of said second laser light beam in said second laser cavity being characterised by a second propagation constant, the waveguide defining the first laser cavity having a sensing surface within an evanescent field of said first laser light beam;

receiving a sample of a substance to be sensed on said sensing surface such that the presence of said substance at said sensing surface alters the said first propagation constant and the frequency of light in said first laser light beam,

combining said first and second laser light beams to produce beating between their respective frequencies and

detecting a change in the said beating consequent upon a said change in said first propagation constant caused by the presence of said substance.

14. A method as claimed in claim 13 wherein said sensing surface has the ability to bind the substance to be detected.

15. A method as claimed in claim 14 wherein said sensing surface bears a specific binding partner for the substance to be detected.

16. A method as claimed in claim 15, wherein to increase detection sensitivity, the substance to be detected is bound to a refractive index change enhancing label.

17. A method as claimed in claim 16, wherein said label is a microparticle.

18. A method as claimed in claim 15 or claim 16, wherein said label is bound to the substance to be detected via a specific binding partner for said substance.

19. An apparatus for sensing the amount or presence of a substance comprising

a laser having a laser cavity comprising a free space gain portion for generation of laser light in two mutually orthogonally polarized modes and a bifurcated portion comprising a pair of arms,

means for splitting said laser light into two beams each of one said polarisation mode and for directing a respective beam into each of said arms of the bifurcated portion of the cavity,

the light of each said polarization mode having a respective frequency,

means for allowing a said substance to interact in one said arm with one of said two beams so as to alter the optical length of said arm and hence the frequency of the light of the polarization mode associated with that arm,

and means for detecting said change in frequency as a change in a beat frequency component produced by beating of the two said polarization modes.

20. Apparatus as claimed in claim 19, wherein said bifurcated portion of the laser cavity provides free space transmission of light.

21. Apparatus as claimed in claim 19, wherein said bifurcated portion of the laser cavity provides waveguide transmission of light.