OPTICAL CAVITY SYSTEM HAVING AN ORTHOGONAL INPUT

• US 20090014670A1
• Filed: 06/28/2007
• Published: 01/15/2009
• Est. Priority Date: 09/28/2004
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Cole, Barrett E., Zook, J. David, Cox, James A.
• Granted Patent: US 7,586,114 B2
• Time in Patent Office: Days
• US Class Current: 250/573
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 2021/0378 Shapes
• CPC Class Codes: G01N 2021/399 Diode laser
• CPC Class Codes: G01N 21/03 Cuvette constructions
• CPC Class Codes: G01N 21/0303 Optical path conditioning in cuvettes, e.g. windows; adapted optical elements or systems; path modifying or adjustment G01N21/031 - G01N21/15 take precedence
• CPC Class Codes: G01N 21/031 Multipass arrangements
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/39 using tunable lasers

Abstract

An optical system having a closed loop light path with a source for providing light in a direction parallel to the normal of an input to the light path. The light may be provided via a diffracting mechanism to the input. The system may be a cavity ring-down sensor or some other optical device. The light path may be formed in a laser gyroscope type cavity. A light source may have a beam aligned to a spot, indicator or mark near the input of the cavity. The location of the spot, indicator or mark may be determined in accordance with parameters of the diffracting mechanism and/or cavity. A fixture for holding the light source may be secured so that placement of the source in the fixture will automatically result in an aligned light source. Then the diffracting mechanism may be inserted to further complete fabrication of the optical system.

Claims

1. An optical system comprising:

a cavity having an internal loop light path and having an input coupled to the light path;

a light source for providing light in a direction approximately parallel to a normal of the input; and

a light diffracting mechanism optically coupled between the light source and the input.

2. The system of claim 1, wherein the light source is aligned relative to an alignment indicator situated on the cavity proximate to the input.

3. The system of claim 2, wherein:

a location of the alignment indicator determined according to parameters of the diffracting mechanism; and

the light source is aligned prior to a placement of the diffracting mechanism

4. The system of claim 1, further comprising:

an output coupled to the light path;

a light detector optically connected to the output;

a port connected to the cavity for entering a fluid sample in the cavity; and

a processor connected to the light detector for measuring a decay of intensity of light in the light path after the light source stops providing light.

5. The system of claim 1, wherein;

the cavity is situated in a block of material and comprising a plurality of bores in the block connected end to end; and

the light path from bore to another bore is connected with a reflective mechanism situated between the bores.

6. The system of claim 5, wherein the reflective mechanism is moveable for adjusting a length of the light path to tune the path for a particular wavelength.

7. The system of claim 1, wherein the light source is tunable for providing a light having a wavelength for absorption by at least a portion of the fluid sample;

8. A method for sensing comprising:

providing light from a source to an input of a chamber having a closed light path, in a direction parallel to a normal of the input; and

detecting light from the light path through an output of the chamber; and

wherein the light is provided to the chamber via a diffracting optics and the input.

9. The method of claim 8, wherein:

a position of the light relative to the input is determined according to an alignment indicator proximate to the input; and

the alignment indicator is located relative to the input according to at least one or more parameters of the diffracting optics.

10. The method of claim 9, further comprising:

injecting a fluid sample into the chamber; and

measuring at least one parameter of the light from the output of the chamber which is indicative of a property of the fluid sample.

11. The method of claim 10, further comprising processing the at least one parameter of the light from the chamber to determine an identity of the sample and/or a concentration of the sample in the chamber.

12. The method of claim 10, wherein the at least one parameter of the light is a period of time that light remains in the path after a ceasing of the providing light to the input of the chamber.

13. The method of claim 8, wherein:

the diffracting optics is a prism having a first surface for entry of light and a second surface for exit of the light to the input of the chamber; and

a first angle between the first surface and second surface has a magnitude set for the light to enter the light path from the second surface in alignment with the light path upon entry from the input of the chamber.

14. The method of claim 13, wherein:

the second surface is perpendicular to the normal of the input;

the light goes through the prism at a second angle relative to a normal of the first surface;

the light exits the second surface at a third angle relative to the normal of the input;

n₁ sin θ

₁=n₂ sin θ

₂;

n₂ sin(θ

₁−

θ

₂)=n₃ sin θ

₃;

n₁ is an index of refraction of a medium of the incident light beam to the first surface;

n₂ is an index of refraction of the medium in the prism;

n₃ is an index of refraction of the medium in the light path;

θ

₁ is the first angle;

θ

₂ is the second angle; and

θ

₃ is the third angle.

15. A sensor system comprising:

a cavity having a ring-like path for propagation of light;

an optical input connected to the cavity;

a light diffracting prism optically connected to the input; and

a source for providing light to the prism, the light having a direction approximately parallel to a normal of the input.

16. The system of claim 15, further comprising:

an alignment indicator proximate to the input; and

wherein;

a location of the alignment indicator is determined according to relevant optical properties of the light diffracting prism; and

the source is aligned according to the indicator.

17. The system of claim 15, further comprising:

a port connected to the cavity for conveying a sample of fluid into the cavity;

an optical output connected to the cavity; and

a detector proximate to the optical output for measuring one or more parameters of light from the cavity via the output.

18. The system of claim 16, further comprising:

readout electronics connected to the detector; and

wherein the readout electronics comprises a dual FET charge amplifier.

19. The system of claim 15, wherein the cavity is situated in a ring laser gyroscope structure.

20. The system of claim 15, wherein the light path is tunable to a particular wavelength.