# US 7,612,931 B2 · MEMS control system gain normalization

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- Number: US 7,612,931 B2
- Document ID: US7612931B2
- Status: Granted
- Kind: B2
- Application number: 11/437,026
- Filed: 2006-05-19
- Published: 2007-11-22
- Granted: 2009-11-03
- Earliest claimed: 2006-05-19
- Assignees: JDS Uniphase Corporation
- Inventors: David Schneider; Darrel Kanagy
- Web page: https://patentgrep.com/patent/US7612931B2

## CPC

- 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}
- G02B 6/3512: {the optical element being reflective, e.g. mirror}
- G02B 6/3594: {Characterised by additional functional means, e.g. means for variably attenuating or branching or means for switching differently polarized beams}
- G02B 6/3598: {Switching means directly located between an optoelectronic element and waveguides, including direct displacement of either the element or the waveguide, e.g. optical pulse generation (based on changing the optical properties of the medium G02F1/00; optical pulse generation in optical transmitters H04B10/508; optical pulse generation by controlling laser operation H01S3/00)}
- G02B 26/0833: {the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD (G02B26/0825 takes precedence; micromechanical devices in general B81B)}
- H01S 5/0071: {for beam steering, e.g. using a mirror outside the cavity to change the beam direction}
- H01S 5/4025: {Array arrangements, e.g. constituted by discrete laser diodes or laser bar (H01S5/42 takes precedence)}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL

## Abstract

A method and system for providing gain normalization in a MEMS control system and/or device includes moving a MEMS structure from a first position wherein light is redirected from a first input port to an output port to a second position wherein light is redirected from a second input port to the output port, dithering an orientation of the MEMS structure, monitoring an intensity of the dithered light and providing a feedback signal in dependence upon the monitored intensity, and using the feedback signal, determining a control loop gain for active alignment of the MEMS structure. Gain normalization is achieved by applying a fitting function, which is split into a gain control loop gain part and a mechanical part.

## Claims

### Claim 1

An optical system comprising:
a MEMS structure movable between a first position in which light is redirected from a first input port to an output port and a second position in which light is redirected from a second input port to the output port, the first input port spatially separated from the second input port;
a MEMS actuator for moving the MEMS structure between the first and second positions, and for dithering an orientation of the MEMS structure about the first and second positions;
a detector optically coupled to the output port for monitoring an intensity of the dithered light and for providing a feedback signal in dependence upon the monitored intensity; and
a controller for receiving the feedback signal from the detector, for determining a control loop gain used in active alignment of the MEMS structure, for applying a first normalization function to the control loop gain, and for applying a second normalization function to a dither magnitude,
wherein the first normalization function is selected in dependence on the second normalization function,
wherein the first input port transmits light from a first laser in a laser array, and the second input port transmits light from a second laser in the laser array,
wherein the output port transmits light into an input waveguide of an optical modulator, and
wherein the feedback signal is shared between four separate control loops, a first control loop for actively aligning the MEMS structure in a first dimension, a second control loop for actively aligning the MEMS structure in a second other dimension, a third control loop for controlling the bias of the optical modulator, and a fourth control loop for controlling a driver voltage of the optical modulator, the control loop gain corresponding to a gain provided in the first control loop.

### Claim 2 (depends on 1)

An optical system according to claim 1, wherein the feedback signal is AC coupled.

### Claim 3 (depends on 1)

An optical system according to claim 1, wherein the first and second normalization functions are determined using fixed point calculations.

### Claim 4 (depends on 3)

An optical system according to claim 3, wherein the first and second normalization functions are limited to a square term.

### Claim 5 (depends on 3)

An optical system according to claim 3, wherein each of the first and second normalization functions is calculated from
Normalization
⁢
⁢
(
LSBs
)
=
3
⁢
,
⁢
200
⁢
,
⁢
000
(
LSBs
/
200
)
2
+
140
+
130
⁢
.

### Claim 6 (depends on 1)

An optical system according to claim 1, wherein the MEMS structure is an electrostatically actuated two-axis MEMS mirror.

### Claim 7 (depends on 6)

An optical system according to claim 6, wherein the detector is a photodiode integrated with the optical modulator.

### Claim 8 (depends on 7)

An optical system according to claim 7, comprising a collimating lens for collimating light transmitted from the laser array to the MEMS minor and a focusing lens for focusing collimated light redirected from the MEMS minor to the input waveguide of the optical modulator.

### Claim 9 (depends on 8)

An optical system according to claim 8, comprising a first tap for redirecting a portion of the light redirected from the MEMS mirror to a wavelength detector, and a second tap for redirecting light another portion of the light redirected from the MEMS mirror to a quadrant detector.

### Claim 10 (depends on 1)

An optical system according to claim 1, wherein a same dither voltage provides different dither magnitudes for the first and second positions, and wherein the second normalization function is selected to reduce the difference in the dither magnitudes.

### Claim 11 (depends on 1)

An optical system according to claim 1, wherein each of the first and second normalization functions is selected to compensate for non-linearity in MEMS actuation, the non-linearity including a non-linear relationship between MEMS deflection angle and applied deflection voltage.

### Claim 12 (depends on 1)

An optical system according to claim 1, wherein each of the first and second normalization functions is a curve corresponding to the square-root of total dither compensation.

### Claim 13 (depends on 1)

An optical system according to claim 1, wherein each of the first and second normalization functions is selected to provide only partial gain normalization.