Position-based response to light

• US 20070076210A1
• Filed: 12/04/2006
• Published: 04/05/2007
• Est. Priority Date: 08/23/2004
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Kiesel, Peter, Schmidt, Oliver
• Granted Patent: US 7,701,590 B2
• Time in Patent Office: Days
• US Class Current: 356/454
• CPC Class Codes: G01J 3/26 using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• CPC Class Codes: G01J 9/0246 Measuring optical wavelength

Abstract

Response to light with laterally varying photon energy distribution is based on position, such as position on a detector of a respective light spot or intensity maximum for a wavelength or photon energy subrange. A layered structure such as a coating over the detector can produce the laterally varying distribution, such as due to a laterally varying transmission property. A differential output or quantity can be obtained using sensing results from the detector and can then be used to monitor a light source'"'"'s wavelength. The light source can, for example, be a pulsed or continuous laser, in which case an optical component between the light source and the detector can be structured to prevent inhomogeneities such as speckle and also reflection back to the laser that could cause feedback. A tunable light source can be tuned in response to positions at which its light is detected.

Claims

1. Apparatus comprising:

a first component that includes one or more films, at least one of the films having a laterally varying transmission property;

the first component, in response to light that includes a shifting wavelength from a light source, transmitting the light and providing output light; and

a second component that receives output light from the first component on a photosensitive surface, the output light provided in response to the shifting wavelength including a respective light spot on the photosensitive surface, the light spot shifting through a sequence of two or more positions on the photosensitive surface, each shift in light spot position being caused by a respective shift in the shifting wavelength;

the second component including;

circuitry that, in response to the light spot, provides a differential output resulting from one or more positions of the light spot on the photosensitive surface and uses the differential output to monitor the shifting wavelength.

2. The apparatus of claim 1 in which the differential output results from the light spot'"'"'s shift between two positions in the sequence.

3. The apparatus of claim 1 in which the second component further includes:

a photosensing device that includes the photosensitive surface;

charge carriers being generated in the photosensing device in response to output light received from the first component;

the circuitry accumulating the generated charge carriers from the photosensing device during sensing periods, the circuitry using the accumulated charge carriers to obtain the differential output after one or more of the sensing periods.

4. The apparatus of claim 1, further comprising:

a support structure on which the first and second components are mounted;

the light source, mounted on the support structure; and

an optical component mounted on the support structure and positioned to receive light from the light source and to provide light to the first component;

the optical component being structured to prevent inhomogeneities in the light it provides to the first component and to prevent reflected light from the first component from reaching the light source.

5. The apparatus of claim 1 in which the differential output is a differential read-out of two currents.

6. A method of operating the apparatus of claim 1, the method comprising:

transmitting light from a light source through the first component;

the light from the light source including a shifting wavelength;

in response to the light, the first component transmitting the light and providing output light that includes, on the photosensitive surface of the second component, a respective light spot for the shifting wavelength, the light spot shifting through a sequence of two or more positions on the photosensitive surface, each shift in light spot position being caused by a respective shift in the shifting wavelength;

providing, in response to the shifting wavelength'"'"'s light spot, differential output resulting from one or more positions of the light spot on the photosensitive surface; and

using the differential output to monitor the shifting wavelength.

7. The method of claim 6 in which the act of using the differential output comprises:

determining a shift in the shifting wavelength from the light source based on a calibration curve.

8. A device comprising:

a photosensing component that photosenses quantities of photons provided at positions of a photosensing surface;

a layered transmission structure with entry and exit surfaces;

in response to light received at the entry surface, the layered transmission structure providing output light through the exit surface to the photosensing surface, the output light having laterally varying photon energy distribution on the photosensing surface;

in response to light with a changing subrange of photon energy received at the entry surface, the transmission structure providing output light that forms a respective moving light spot on the photosensing surface, the light spot moving through a sequence of two or more positions on the photosensing surface, each move of the light spot between positions in the sequence resulting from a respective change in the subrange'"'"'s photon energy; and

differential quantity circuitry that responds to quantities photosensed by the photosensing component in response to the moving light spot, providing a differential quantity that depends on one or more positions of the moving light spot on the photosensing surface.

9. A system that includes the device of claim 8, the system further comprising:

an optical input that receives light and provides the received light to the transmission structure'"'"'s entry surface, the received light being within a changing subrange of photon energy; and

monitor circuitry that uses the differential quantity to monitor the changing subrange.

10. The system of claim 9 in which the differential quantity depends on two positions in the sequence between which the light spot moves.

11. The system of claim 9, further comprising:

a support structure on which the optical input, layered transmission structure, and photosensing component are mounted; and

a light source mounted on the support structure and providing light to the optical input;

the optical input including;

an optical component mounted on the support structure and positioned to receive light from the light source and to provide light to the transmission structure;

the optical component being structured to prevent inhomogeneities in the light it provides to the transmission structure and to prevent reflected light from the transmission structure from reaching the light source.

12. The system of claim 9 in which the photosensing component includes a photosensing array, the photosensing array including first and second sets of one or more cells;

the relative quantities of photons received by the first and second sets of cells changing between first and second positions in the sequence between which the light spot moves;

the differential quantity indicating relative quantities of photons received by the first and second sets of cells.

13. A method of using the device of claim 8, the method comprising:

receiving light within a changing subrange of photon energies through the layered transmission structure;

in response, the layered transmission structure transmitting a portion of the received light onto the photosensing surface, providing a respective light spot for the changing subrange on the photosensing surface, the light spot moving through a sequence of two or more positions on the photosensing surface, each move of the light spot between positions in the sequence resulting from a respective change in the subrange;

with the differential quantity circuitry, obtaining a differential quantity that depends on one or more positions of the changing subrange'"'"'s light spot; and

using the differential quantity to monitor the changing subrange.

14. A system comprising:

a tunable light source that can provide light within subranges of a photon energy range, each subrange having a respective central energy;

a detector that receives light from the tunable light source;

the detector including a photosensitive surface and a layered structure that responds to the received light by providing light with laterally varying photon energy distributions on the photosensitive surface;

the central energy of the received light'"'"'s subrange having a respective position on the photosensitive surface;

the detector providing sensing results that depend on the central energy'"'"'s position; and

circuitry that can, in response to the sensing results, cause the tunable light source to change the light it provides to be within a different subrange of the photon energy range.

15. The system of claim 14 in which the received light'"'"'s subrange changes, the central energy'"'"'s position moving through a sequence of two or more positions on the photosensitive surface, each move of the central energy'"'"'s position in the sequence resulting from a respective change in the received light'"'"'s subrange;

the detector providing sensing results that depend on two or more positions in the sequence.

16. The system of claim 14 in which the tunable light source includes a laser cavity;

the central energy of each subrange being a peak energy of light from the laser cavity.

17. The system of claim 14 in which the detector includes:

a transmission structure with an entry surface at which it receives light from the tunable light source and with an exit surface, the transmission structure including the layered structure; and

a photosensing component that photosenses quantities of photons provided at positions of the exit surface;

the photosensing component including the photosensitive surface.

18. The system of claim 14, further comprising:

an optical fiber that receives light provided by the tunable light source and guides the light to the detector.

19. The system of claim 18 in which the optical fiber is a single-mode optical fiber.

20. The system of claim 14, further comprising:

a support structure on which the tunable light source and detector are mounted; and

an optical component mounted on the support structure between the light source and the layered structure, positioned to receive light from the light source and to provide light to the layered structure;

the optical component being structured to prevent inhomogeneities in the light it provides to the layered structure and to prevent reflected light from the layered structure from reaching the light source.

21. A method of operating the system of claim 14, the method comprising:

operating the tunable light source to provide first input light to the photosensitive surface through the layered structure;

the tunable light source providing the first input light within a first subrange;

the layered structure responding to the first input light by providing output light with a laterally varying photon energy distribution in which the first subrange'"'"'s central energy has a respective position on the photosensitive surface; and

operating the circuitry to respond to the sensing results, causing the tunable light source to provide light within a second subrange of the photon energy range, the second subrange being different than the first.

22. The method of claim 21 in which the act of operating the circuitry comprises:

based on the sensing results, determining that the first input light has changed from a previous central energy to a current central energy; and

causing the tunable light source to provide light in the second subrange, the second subrange'"'"'s central energy being closer to the previous central energy than the current central energy is.

23. The method of claim 22 in which the sensing results include position signals;

the act of determining that the first input light has changed comprising;

using the position signals to obtaining an absolute measurement of the current central energy; and

comparing the absolute measurement of the current central energy with an absolute measurement of the previous central energy.

24. The method of claim 21 in which the act of operating the circuitry comprises:

based on the sensing results, determining that the first input light has changed; and

without using calibration data, causing the tunable light source to provide light in the second subrange, the second subrange'"'"'s central energy being incrementally closer to the previous central energy than the current central energy is.

25. A device comprising:

a support structure;

mounted on the support structure, a tunable light source that can provide light within subranges of a photon energy range, each subrange having a respective central energy;

the tunable light source responding to tuning signals by changing between subranges with different central energies;

mounted on the support structure, an optical component that includes a single-mode optical fiber positioned to receive light from the light source;

mounted on the support structure, a detector that receives light from the tunable light source through the optical component;

the detector including a photosensitive surface and a layered structure that, in response to the received light, provides light with a laterally varying photon energy distribution on the photosensitive surface;

the detector being positioned relative to the optical component so that, for each of a set of the subranges, the subrange'"'"'s central energy has a respective position on the photosensitive surface;

the detector providing sensing results that depend on the central energy'"'"'s position; and

connection circuitry connected to the tunable light source and to the detector and being connectible to external circuitry that receives the sensing results from the detector through the connection circuitry and, in response, provides the tuning signals to the tunable light source through the connection circuitry;

the single-mode optical fiber being structured to prevent inhomogeneities in the light it provides to the layered structure and to prevent reflected light from the layered structure from reaching the light source.

26. The device of claim 25 in which the tunable light source is a laser.

27. The device of claim 25 in which the optical component includes a single-mode optical fiber.

28. A method of producing the device of claim 25, the method comprising:

mounting the tunable light source, the optical component, and the detector on a support structure, positioned so that the detector receives the light from the tunable light source through the optical component with a substantially stable and homogeneous light distribution across the layered structure.