Method of controlling a dynamic gain controller

• US 6,549,865 B2
• Filed: 03/15/2001
• Issued: 04/15/2003
• Est. Priority Date: 03/15/2001
• Status: Expired due to Fees

• Current Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Original Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Inventors: Tomlinson, W. John
• Primary Examiner(s): Bui, Bryan
• Assistant Examiner(s): VO, HIEN XUAN
• Application Number:
  US09/805,885
• Publication Number:
  US 20020177965A1
• Time in Patent Office: 761 Days
• Field of Search: 702/85, 702/40, 250/334, 250/339.02, 250/352, 385/37, 385/370.06, 385/370.08, 385/370.09, 385/252.1, 385/15, 385/24, 385/31, 385/39, 385/45, 349/115, 349/176, 349/74, 349/78, 349/98, 356/328, 359/124, 359/127, 359/237, 359/259
• US Class Current: 702/85
• CPC Class Codes: H04B 10/25073 using spectral equalisation, e.g. spectral filtering
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant
• CPC Class Codes: H04J 14/02216 by gain equalization

Abstract

A method of controlling a response function of a pixelated dynamic gain controller involving structuring the problem as a set of linear equations that are used to efficiently and accurately determine an initial set of pixel settings and further can be iterated to determine optimum pixel settings for a desired response function. In particular, the gain controller is comprised of an array of individually controllable pixels such as an array of liquid crystals. Adjusting drive conditions to each pixel controls the relative transmission of a narrow band of wavelengths through each pixel. The target response function is achieved by structuring the control conditions as a set of linear equations with which it is possible to accurately determine an initial set of pixel settings. The settings can be iterated to determine an optimum setting for a desired response function or change in response function. Additionally, compensating pixels at the edges of the array are used to compensate for edge effects.

Claims

1. In a system having an array of pixelated elements for controlling incident light thereon, and having a processor for processing control information related to response transmission characteristics of the array of pixelated elements, a method of controlling characteristics of the array of pixelated elements in response to input data comprising the steps of:

(a) acquiring calibration information related to the response characteristics of the array of pixelated elements;

(b) acquiring a target response function for the array of pixelated elements;

(c) converting the target response function into a set of pixel amplitude field linear equations; and

(d) determining a set of input data values for controlling the array of pixelated elements based on the calibration information and the pixel amplitude field linear equations.

2. The method of claim 1, wherein the array of pixelated elements operate in transmission mode.

3. The method of claim 1, wherein the array of pixelated elements operate in reflection mode.

4. The method of claim 1, further comprising the steps of:

(e) determining deviations from the desired response function based on the calibration information and the pixel amplitude field linear equations; and

(f) repeating step (c) and (d) when the deviations exceed a predetermine threshold.

5. The method of claim 1, wherein the array of pixelated elements are cells of a liquid crystal display.

6. The method of claim 5, wherein the processor controls input voltage to the liquid crystal display cells in order to vary characteristics thereof.

7. The method of claim 1, wherein the array of pixelated elements includes compensation pixels located at each end of the array of pixelated elements, wherein the compensation pixels do not have signal channels centered within a first area of a selected one of the array of pixelated elements and are sufficiently close to a further selected one of the array of pixelated elements such that reflectivity of the further selected pixelated element impacts reflectivity for signal channels.

8. The method of claim 1, wherein the set of pixelated amplitude field linear equations and the set of input data values are defined by:

$\begin{array}{cc}{t}_j=\underset{i=0}{\overset{N-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>M_{j,i}·<br><br>r_i;<br><br>& \left(i\right)\\ M_{j,j\pm <br><br>n}={\left(\frac{8}{\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>W^2}\right)}^{1/2}<br><br>{\int <br><br>}_{-0.5+\mathrm{gap}/2}^{0.5-\mathrm{gap}/2}<br><br>\text{\hspace{1em}<br><br>}<br><br>\exp <br><br>\text{\hspace{1em}<br><br>}\left[-8<br><br>{\left(y\pm <br><br>n\right)}^2/W^2\right]<br><br><br><br>y;<br><br>\mathrm{and}& \left(\mathrm{ii}\right)\\ r_i=\underset{j=0}{\overset{N-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>M_{j,i}^{-1}·<br><br>t_j,& \left(\mathrm{iii}\right)\end{array}$

t_j represents a set of pixel amplitude field reflectivities or transmissions, M_j,i represents a matrix element at wavelength j to the setting of pixel i that is independent of the wavelength and depends on the position of pixel i relative to the pixel where wavelength j is centered;

W is the e<sup>−

2</sup> intensity full width of a monochromatic input signal, at a pixel plane, measured in units of pixel pitch;

r_i represents the set of input data values of desired pixel amplitude field reflectivities or transmissions and gap represents a gap width between pixels in the array measured in units of pixel pitch.

9. A method of controlling the optical characteristics of individual pixelated elements in a dynamic gain equalizer having an array of controllable pixelated elements, and having a processor for processing control information related to a response function of the dynamic gain equalizer, said method comprising the steps of:

acquiring a predetermined target response function for the array of pixelated elements from a system controller;

calculating initial attenuation settings for individual pixels of the array of pixelated elements based on stored data;

calculating spectral attenuation that would result from the initial attenuation settings for individual pixels and determining deviations between the initial settings and settings to satisfy said target response;

calculating input data for use by said processor to control said individual pixels if said deviations are within set limits; and

sending said input data to said processor.

10. The method of claim 9, wherein said spectral information is recalculated if said deviations are not within said set limits.

11. The method of claim 10, wherein the array of pixelated elements includes compensation pixels located at each end of the array of pixelated elements, wherein the compensation pixels do not have signal channels centered within a first area of a selected one of the array of pixelated elements and are sufficiently close to a further selected one of the array of pixelated elements such that reflectivity of the further selected pixelated element impacts reflectivity for signal channels.

12. The method of claim 10, wherein the set of pixelated amplitude field linear equations and the set of input data values are defined by:

$\begin{array}{cc}{t}_j<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>\underset{i<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>0}{\overset{N<br><br>\text{\hspace{1em}<br><br>}-\text{\hspace{1em}<br><br>}<br><br>1}{\sum <br><br>}}<br><br>M_{j,\text{\hspace{1em}<br><br>}<br><br>i}·<br><br>r_i;<br><br>& \left(i\right)\\ M_{j,\text{\hspace{1em}<br><br>}<br><br>j<br><br>\text{\hspace{1em}<br><br>}\pm <br><br>\text{\hspace{1em}<br><br>}<br><br>n}<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>{\left(\frac{8}{\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>W^2}\right)}^{1/2}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\int <br><br>}_{-0.5<br><br>\text{\hspace{1em}<br><br>}+\text{\hspace{1em}<br><br>}<br><br>\mathrm{gap}/2}^{0.5<br><br>\text{\hspace{1em}<br><br>}-\text{\hspace{1em}<br><br>}<br><br>\mathrm{gap}/2}<br><br>\exp [\text{\hspace{1em}<br><br>}<br><br>-8<br><br>\text{\hspace{1em}<br><br>}<br><br>{\left(y<br><br>\text{\hspace{1em}<br><br>}\pm <br><br>\text{\hspace{1em}<br><br>}<br><br>n\right)}^2/W^2]<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>y;<br><br>\mathrm{and}& \left(i<br><br>\text{\hspace{1em}<br><br>}<br><br>i\right)\\ r_i<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>\underset{j<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>0}{\overset{N<br><br>\text{\hspace{1em}<br><br>}-\text{\hspace{1em}<br><br>}<br><br>1}{\sum <br><br>}}<br><br>M_{j,\text{\hspace{1em}<br><br>}<br><br>i}^{-1}·<br><br>t_j,& \left(i<br><br>\text{\hspace{1em}<br><br>}<br><br>i<br><br>\text{\hspace{1em}<br><br>}<br><br>i\right)\end{array}$

t_j represents a set of pixel amplitude field reflectivities or transmissions, M_j,i represents a matrix element at wavelength j to the setting of pixel i that is independent of the wavelength and depends on the position of pixel i relative to the pixel where wavelength j is centered;

W is the e<sup>−

2</sup> intensity full width of a monochromatic input signal, at a pixel plane, measured in units of pixel pitch;

r_i represents the set of input data values of desired pixel amplitude field reflectivities or transmissions and gap represents a gap width between pixels in the array measured in units of pixel pitch.

13. A computer program product for a system having an array of pixelated elements for controlling incident light thereon, and having a processor for processing control information related to response transmission characteristics of the array of pixelated elements, the computer program product comprising computer readable program code devices for controlling characteristics of the array of pixelated elements in response to input data comprising:

(a) acquiring calibration information related to the response characteristics of the array of pixelated elements;

(b) acquiring a target response function for the array of pixelated elements;

(c) converting the target response function into a set of pixel amplitude field linear equations; and

(d) determining a set of input data values for controlling the array of pixelated elements based on the calibration information and the pixel amplitude field linear equations.

14. The computer program product of claim 13, further comprising (e) determining deviations from the desired response function based on the calibration information and the pixel amplitude field linear equations;

and (f) repeating step (d) and (e) when the deviations exceed a predetermine threshold.

15. The computer program product of claim 13, wherein the array of pixelated elements includes compensation pixels located at each end of the array of pixelated elements, wherein the compensation pixels do not have signal channels centered within a first area of a selected one of the array of pixelated elements and are sufficiently close to a further selected one of the array of pixelated elements such that reflectivity of the further selected pixelated element impacts reflectivity for signal channels.

16. The computer program product of claim 13, wherein the set of pixelated amplitude field linear equations and the set of input data values are defined by:

$\begin{array}{cc}{t}_j<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>\underset{i<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>0}{\overset{N<br><br>\text{\hspace{1em}<br><br>}-\text{\hspace{1em}<br><br>}<br><br>1}{\sum <br><br>}}<br><br>M_{j,\text{\hspace{1em}<br><br>}<br><br>i}·<br><br>r_i;<br><br>& \left(i\right)\\ M_{j,\text{\hspace{1em}<br><br>}<br><br>j<br><br>\text{\hspace{1em}<br><br>}\pm <br><br>\text{\hspace{1em}<br><br>}<br><br>n}<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>{\left(\frac{8}{\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>W^2}\right)}^{1/2}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\int <br><br>}_{-0.5<br><br>\text{\hspace{1em}<br><br>}+\text{\hspace{1em}<br><br>}<br><br>\mathrm{gap}/2}^{0.5<br><br>\text{\hspace{1em}<br><br>}-\text{\hspace{1em}<br><br>}<br><br>\mathrm{gap}/2}<br><br>\exp [\text{\hspace{1em}<br><br>}<br><br>-8<br><br>\text{\hspace{1em}<br><br>}<br><br>{\left(y<br><br>\text{\hspace{1em}<br><br>}\pm <br><br>\text{\hspace{1em}<br><br>}<br><br>n\right)}^2/W^2]<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>y;<br><br>\mathrm{and}& \left(i<br><br>\text{\hspace{1em}<br><br>}<br><br>i\right)\\ r_i<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>\underset{j<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>0}{\overset{N<br><br>\text{\hspace{1em}<br><br>}-\text{\hspace{1em}<br><br>}<br><br>1}{\sum <br><br>}}<br><br>M_{j,\text{\hspace{1em}<br><br>}<br><br>i}^{-1}·<br><br>t_j,& \left(i<br><br>\text{\hspace{1em}<br><br>}<br><br>i<br><br>\text{\hspace{1em}<br><br>}<br><br>i\right)\end{array}$

where

t_j represents a set of pixel amplitude field reflectivities or transmissions, M_j,i represents a matrix element at wavelength j to the setting of pixel i that is independent of the wavelength and depends on the position of pixel i relative to the pixel where wavelength j is centered;

W is the e<sup>−

2</sup> intensity full width of a monochromatic input signal, at a pixel plane, measured in units of pixel pitch;

r_i represents the set of input data values of desired pixel amplitude field reflectivities or transmissions and gap represents a gap width between pixels in the array measured in units of pixel pitch.

17. A computer program product for controlling the optical characteristics of individual pixelated elements in a dynamic gain equalizer having an array of controllable pixelated elements, and having a processor for processing control information related to a response function of the dynamic gain equalizer, the computer program product comprising computer readable program code devices for:

acquiring a predetermined target response function for the array of pixelated elements from a system controller;

calculating initial attenuation settings for individual pixels of the array of pixelated elements based on stored data;

calculating spectral attenuation that would result from the initial attenuation settings for individual pixels and determining deviations between the initial settings and settings to satisfy said target response;

calculating input data for use by said processor to control said individual pixels if said deviations are within set limits; and

sending said input data to said processor.

18. The computer program product of claim 17, wherein said spectral information is re-calculated if said deviations are not within said set limits.

19. The computer program product of claim 17, wherein the set of pixelated amplitude field linear equations and the set of input data values are defined by:

$\begin{array}{cc}{t}_j<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>\underset{i<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>0}{\overset{N<br><br>\text{\hspace{1em}<br><br>}-\text{\hspace{1em}<br><br>}<br><br>1}{\sum <br><br>}}<br><br>M_{j,\text{\hspace{1em}<br><br>}<br><br>i}·<br><br>r_i;<br><br>& \left(i\right)\\ M_{j,\text{\hspace{1em}<br><br>}<br><br>j<br><br>\text{\hspace{1em}<br><br>}\pm <br><br>\text{\hspace{1em}<br><br>}<br><br>n}<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>{\left(\frac{8}{\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>W^2}\right)}^{1/2}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\int <br><br>}_{-0.5<br><br>\text{\hspace{1em}<br><br>}+\text{\hspace{1em}<br><br>}<br><br>\mathrm{gap}/2}^{0.5<br><br>\text{\hspace{1em}<br><br>}-\text{\hspace{1em}<br><br>}<br><br>\mathrm{gap}/2}<br><br>\exp [\text{\hspace{1em}<br><br>}<br><br>-8<br><br>\text{\hspace{1em}<br><br>}<br><br>{\left(y<br><br>\text{\hspace{1em}<br><br>}\pm <br><br>\text{\hspace{1em}<br><br>}<br><br>n\right)}^2/W^2]<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>y;<br><br>\mathrm{and}& \left(i<br><br>\text{\hspace{1em}<br><br>}<br><br>i\right)\\ r_i<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>\underset{j<br><br>\text{\hspace{1em}<br><br>}=\text{\hspace{1em}<br><br>}<br><br>0}{\overset{N<br><br>\text{\hspace{1em}<br><br>}-\text{\hspace{1em}<br><br>}<br><br>1}{\sum <br><br>}}<br><br>M_{j,\text{\hspace{1em}<br><br>}<br><br>i}^{-1}·<br><br>t_j,& \left(i<br><br>\text{\hspace{1em}<br><br>}<br><br>i<br><br>\text{\hspace{1em}<br><br>}<br><br>i\right)\end{array}$

t_j represents a set of pixel amplitude field reflectivities or transmissions, M_j,i represents a matrix element at wavelength j to the setting of pixel i that is independent of the wavelength and depends on the position of pixel i relative to the pixel where wavelength j is centered;

W is the e<sup>−

2</sup> intensity full width of a monochromatic input signal, at a pixel plane, measured in units of pixel pitch;

r_i represents the set of input data values of desired pixel amplitude field reflectivities or transmissions and gap represents a gap width between pixels in the array measured in units of pixel pitch.