Method of automatic adjustment of dither amplitude of MEMS mirror arrays

• US 20070166034A1
• Filed: 08/03/2005
• Published: 07/19/2007
• Est. Priority Date: 08/03/2005
• Status: Active Grant

• Current Assignee: Capella Photonics, Inc. (Nokia Corporation)
• Original Assignee: Capella Photonics, Inc. (Nokia Corporation)
• Inventors: Tremaine, Brian
• Granted Patent: US 7,567,756 B2
• Time in Patent Office: Days
• US Class Current: 398/45
• CPC Class Codes: G02B 6/3512 the optical element being reflective, e.g. mirror
• CPC Class Codes: G02B 6/3546 NxM switch, i.e. a regular array of switches elements of matrix type constellation
• CPC Class Codes: G02B 6/356 in an optical cross-connect device, e.g. routing and switching aspects of interconnecting different paths propagating different wavelengths to (re)configure the various input and output links switching polarized beams G02B6/3594; power equalizers G02B6/356 and G02B6/3594; path selecting means H04Q11/0001
• CPC Class Codes: G02B 6/3588 of the processed beams, i.e. controlling during switching of orientation, alignment, or beam propagation properties such as intensity, size or shape
• CPC Class Codes: G02B 6/3594 Characterised by additional functional means, e.g. means for variably attenuating or branching or means for switching differently polarized beams
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 2011/0049 Crosstalk reduction; Noise; Power budget

Abstract

Methods for adjusting dither amplitude for MEMS mirrors in optical switches and optical switches employing such a method are disclosed. A dither amplitude of one or more MEMS mirrors may be adjusted in an optical switch having an input port, and an array of one or more MEMS mirrors that can be selectively optically coupled to one or more of N≧3 optical input/output (I/O) ports. The MEMS mirrors are aligned mirrors to achieve nominal peak coupling at each of the N collimators. Digital-to-analog (DAC) settings for positioning mirrors in an open control loop as a function of the selected collimator are stored to a non-volatile memory. The DAC settings are used to determine a dither amplitude DITHER(x) for one of the MEMS mirrors positioned to couple optical signals to an output port at a position x. The optical switch apparatus may comprise N≧3 optical input/output (I/O) ports, an array of one or more MEMS mirrors that can selectively reflect one or more spectral channels to one or more of the N ports, and a servo-control assembly in communication with said one or more of the MEMS mirrors. The servo control assembly includes memory containing digital-to-analog converter (DAC) settings for positioning each mirror in an open control loop as a function of a port position x. The servo control assembly is programmed to adjust dither amplitude of one or more of the MEMS mirrors using the stored DAC settings.

Claims

1. A method for adjusting a dither amplitude of one or more MEMS mirrors in an optical switch having an input port, and an array of one or more MEMS mirrors that can be selectively optically coupled to one or more of N optical input/output (I/O) ports, where N is an integer greater than or equal to 3, the method comprising the steps of:

aligning the one or more MEMS mirrors to achieve nominal peak coupling at each of the N collimators;

storing to a non-volatile memory digital-to-analog converter (DAC) settings for positioning each mirror in an open control loop as a function of the selected collimator; and

determining a dither amplitude DITHER(x) for one of the MEMS mirrors positioned to couple optical signals to an output port at a position x for using the stored DAC settings.

2. The method of claim 1 wherein the DAC settings include N signal values S_c, wherein each signal value S_c corresponds to a signal applied to the given mirror to position the mirror to couple an optical signal between the input port and a different one of the N output ports.

3. The method of claim 2 wherein determining the dither amplitude DITHER(x) includes:

fitting the N signal values to a polynomial of a parameter corresponding to a position of an output port;

determining a slope of the polynomial at a value of the parameter corresponding to a given output port;

determining the dither amplitude DITHER(x) based on the value of the slope.

4. The method of claim 3 wherein the polynomial is of the form a₃c³+a₂c²+a₁c+a_o=S_c, where c is an integer representing the position of an output port in an array.

5. The method of claim 4 wherein the dither amplitude DITHER(x) for an output port at position x is given by

DITHER(x)=REF_DITHER*slope(x)/REF_SLOPE,

where x is an integer representing the position of an output port in an array, REF_DITHER is a dither amplitude value determined from a design of the MEMS mirror, REF_SLOPE is a slope value determined from a design of a control system that controls an angle of the MEMS mirror and slope(x) is a value of the slope at output port position x.

6. The method of claim 5 wherein the slope(x) has the form

slope(x)=3·

a₃c²+2·

a₂c+a₁

7. A method for adjusting dither amplitude of one or more MEMS mirrors in an optical switch having an input port, and an array of one or more MEMS mirrors that can be selectively optically coupled to one or more of N optical input/output (I/O) ports, where N is an integer greater than or equal to 3, the method comprising the steps of:

for a given one of the mirrors, determining N signal values S_c, wherein each signal value S_c corresponds to a signal applied to the given mirror to couple an optical signal between the input port and a different one of the N output ports;

fitting the N signal values to a polynomial of a parameter corresponding to a position of an output port;

determining a slope of the polynomial at a value corresponding to a given output port;

determining a dither amplitude based on the value of the slope.

8. An optical switch apparatus, comprising:

N optical input/output (I/O) ports, where N is an integer greater than or equal to 3;

and an array of one or more MEMS mirrors that can be selectively reflect one or more spectral channels to one or more of the N ports; and

a servo-control assembly in communication with said one or more of the MEMS mirrors, said servo-control assembly being adapted to control of said channel micromirrors and thereby maintaining a predetermined coupling of each reflected spectral channel into one of said output ports, wherein the servo control assembly includes memory containing digital-to-analog converter (DAC) settings for positioning each mirror in an open control loop as a function of a port position x, wherein the servo control assembly includes a processing unit programmed with a set of instructions for implementing a method of adjusting a dither amplitude of one or more of the MEMS mirrors, the set of instructions including an instruction for determining a dither amplitude DITHER(x) for one of the MEMS mirrors positioned to couple optical signals to an output port at a position x for using the stored DAC settings.

9. The apparatus of claim 8 wherein the DAC settings include N signal values S_c, wherein each signal value S_c corresponds to a signal applied to the given mirror to position the mirror to couple an optical signal between the input port and a different one of the N output ports.

10. The apparatus of claim 9 wherein determining the dither amplitude DITHER(x) includes:

fitting the N signal values to a polynomial of a parameter corresponding to a position of an output port;

determining a slope of the polynomial at a value of the parameter corresponding to a given output port;

determining the dither amplitude DITHER(x) based on the value of the slope.

11. The apparatus of claim 10 wherein the polynomial is of the form a₃c³+a₂c²+a₁c+a_o=S_c, where c is an integer representing the position of an output port in an array.

12. The apparatus of claim 11 wherein the dither amplitude DITHER(x) for an output port at position x is given by

DITHER(x)=REF_DITHER*slope(x)/REF_SLOPE,

where x is an integer representing the position of an output port in an array, REF_DITHER is a dither amplitude value determined from a design of the MEMS mirror, REF_SLOPE is a slope value determined from a design of a control system that controls an angle of the MEMS mirror and slope(x) is a value of the slope at output port position x.

13. The apparatus of claim 12 wherein the slope(x) has the form

slope(x)=3·

a₃c²+2·

a₂c+a₁

14. The apparatus of claim 8, wherein the N I/O ports include a plurality of fiber collimators, providing an input port for a multi-wavelength optical signal and a plurality of output ports.

15. The apparatus of claim 14, further comprising:

a wavelength-separator, for separating said multi-wavelength optical signal from said input port into multiple spectral channels; and

a beam-focuser, for focusing said spectral channels into corresponding spectral spots;

wherein the array of one or more MEMS mirrors is a spatial array of channel micromirrors positioned such that each channel micromirror receives one of said spectral channels, said channel micromirrors being individually and continuously controllable to reflect said spectral channels into selected ones of said output ports.

16. The apparatus of claim 15 wherein the spatial array of channel micromirrors is a one-dimensional array.

17. The apparatus of claim 15 wherein the spatial array of channel micromirrors is a two-dimensional array.

18. The apparatus of claim 8 wherein said servo-control assembly includes a spectral monitor for monitoring power levels of said spectral channels coupled into said output ports, and a processing unit responsive to said power levels for providing control of said channel micromirrors.

19. The apparatus of claim 8 wherein each MEMS mirror is rotatable about one or more axes.