System and method for increasing signal-to-noise ratio in optical-based sensor systems

• US 7,897,907 B1
• Filed: 04/24/2008
• Issued: 03/01/2011
• Est. Priority Date: 04/24/2008
• Status: Active Grant

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Fralick, Mark S., Waters, Richard L.
• Primary Examiner(s): Luu; Thanh X
• Application Number:
  US12/108,829
• Time in Patent Office: 1,041 Days
• Field of Search: 250/205, 250/214.R
• US Class Current: 250/214.00R
• CPC Class Codes: G01J 1/04 Optical or mechanical part supplementary adjustable parts
• CPC Class Codes: G01J 1/0429 using polarisation elements
• CPC Class Codes: G01J 1/32 adapted for automatic variation of the measured or reference value regulation of light intensity G05D25/00

Abstract

A method includes passing a portion of an optical signal through an aperture of a sensor having a sensing element, wherein the portion of the optical signal that passes through the aperture is an inner portion of the optical signal and the portion of the optical signal that does not pass through the aperture is an outer portion of the optical signal; producing a sensed signal by sensing the outer portion of the optical signal with the sensing element; and controlling the source of the optical signal using the sensed signal. A system for implementing the method includes an optical energy source and a sensor having an optical sensing portion and an aperture therein. The system may also include an optical isolator, a detection element, and a controller for controlling the optical energy source. The system may be used within a MEMS-based system.

Claims

1. A method comprising the steps of:

passing a portion of an optical signal through an aperture of a sensor having a sensing element, wherein the portion of the optical signal that passes through the aperture is an inner portion of the optical signal and the portion of the optical signal that does not pass through the aperture is an outer portion of the optical signal;

producing a sensed signal by sensing the outer portion of the optical signal with the sensing element;

controlling the source of the optical signal using the sensed signal;

passing the inner portion of the optical signal through an optical isolation device, wherein the optical isolation device is a linear polarizer having a quarter-wave plate coupled thereto; and

detecting the inner portion of the optical signal with a detection element.

2. The method of claim 1, wherein the sensing element is ring-shaped, wherein the step of producing a sensed signal comprises sensing and integrating the outer portion of the optical signal about at least a first angle of the sensing element, wherein the first angle exceeds π

radians.

3. The method of claim 1, wherein the step of producing a sensed signal comprises sensing and integrating the outer portion of the optical signal over symmetrical segments of the sensing element.

4. The method of claim 1, wherein the step of controlling the source of the optical signal using the sensed signal comprises controlling the power level of the source of the optical signal.

5. The method of claim 1, wherein the sensor is a photodiode.

6. The method of claim 1, wherein the inner portion of the optical signal has a total noise source that correlates to a total noise source of the outer portion of the optical signal.

7. The method of claim 1, wherein the optical isolation device is coupled to the sensor.

8. The method of claim 1, wherein at least one side of the optical isolation device has an anti-reflective coating.

9. A system comprising:

an optical energy source configured to produce an optical signal having a power level;

a sensor having an optical sensing portion and an aperture therein, the optical sensing portion configured to sense at least a portion of the optical signal that does not pass through the aperture;

an optical isolator coupled to the sensor in the path of the optical signal, wherein the optical isolator is a linear polarizer having a quarter-wave plate coupled thereto; and

a detection element located adjacent to the optical isolator in the path of the optical signal

wherein the sensor is configured to produce a sensed signal by sensing the at least a portion of the optical signal that does not pass through the aperture with the optical sensing portion

wherein the sensor is configured to transmit the sensed signal to the optical energy source and the optical energy source is configured to receive the sensed signal and use the sensed signal to control the power level of the optical signal.

10. The system of claim 9, wherein the aperture is circular in shape and the optical sensing portion surrounds at least a portion of the perimeter of the aperture, wherein the optical sensing portion surrounding at least a portion of the perimeter of the aperture exceeds π

radians.

11. The system of claim 9, wherein at least one side of the optical isolator has an anti-reflective coating.

12. The system of claim 9, wherein the aperture is tapered from a first diameter to a second diameter, where the first diameter is greater than the second diameter, wherein the first diameter is located proximate to the optical energy source.

13. A system comprising:

an optical energy source configured to produce an optical signal; and

a sensor operatively coupled to the optical energy source, the sensor having an optical sensing portion and an aperture therein, the sensor configured to sense a first portion of the optical signal and to allow a second portion of the optical signal to pass through the aperture;

a controller operatively coupled to the sensor;

an optical isolator coupled to the sensor in the path of the optical signal, wherein the optical isolator is a linear polarizer having a quarter-wave plate coupled thereto; and

a detection element located adjacent to the optical isolator in the path of the optical signal

wherein the sensor is configured to produce a sensed signal by sensing the first portion of the optical signal

wherein the sensor is configured to transmit the sensed signal to the controller and the controller is configured to control the optical energy source based upon the sensed signal.

14. The system of claim 13, wherein the aperture is circular in shape and the optical sensing portion surrounds at least a portion of the perimeter of the aperture.

15. The system of claim 13, wherein the sensor is a monitor photodiode.

16. The system of claim 13, wherein at least one side of the optical isolator has an anti-reflective coating.

17. The system of claim 13, wherein the aperture is tapered from a first diameter to a second diameter, where the first diameter is greater than the second diameter, wherein the first diameter is located proximate to the optical energy source.