Control system for an optical fiber switch

• US 20040208425A1
• Filed: 05/07/2004
• Published: 10/21/2004
• Est. Priority Date: 10/24/2001
• Status: Active Grant

• Current Assignee: Jacek Maitan
• Original Assignee: Jacek Maitan
• Inventors: Maitan, Jacek
• Granted Patent: US 6,925,221 B2
• Time in Patent Office: Days
• US Class Current: 385/18
• CPC Class Codes: G02B 6/3512 the optical element being reflective, e.g. mirror
• CPC Class Codes: G02B 6/3556 NxM switch, i.e. regular arrays of switches elements of matrix type constellation
• CPC Class Codes: G02B 6/359 of the position of the moving element itself during switching, i.e. without monitoring the switched beams
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 2011/003 using switches based on microelectro-mechanical systems [MEMS]
• CPC Class Codes: H04Q 2011/0039 Electrical control
• CPC Class Codes: H04Q 2011/0083 Testing; Monitoring

Abstract

An optical switching fabric enables an optical signal entering the device on any one of multiple input ports to be directed to any one of multiple output ports. Light entering the switching fabric on an input port is reflected by individual mirrors on one or more mirror arrays to an output port. Methods of controlling optical switching fabrics compensate for distortions due to mechanical and environmental changes without the need to measure losses along all optical paths linking input ports and output ports. Reference input ports are interspersed among signal input ports and reference output ports are interspersed among signal output ports. Periodically, the positions of mirrors which maximize the intensity of light deflected from reference input ports and reference output ports, are measured. The measured positions are used to predict mirror positions to maximize the intensity of light deflected from signal input ports to signal output ports.

Claims

1. A method of controlling an optical switching fabric, comprising:

periodically measuring current optimum positions of at least two reference mirrors on at least one mirror array;

adjusting optimum positions for remaining mirrors on the at least one mirror array based on differences between the current optimum positions and previous optimum positions of the at least two reference mirrors.

2. The method of claim 1, wherein periodically measuring current optimum positions includes measuring optimum cross connect positions when differences between current optimum straight-through positions and previous optimum straight-through positions exceed threshold values.

3. The method of claim 1, wherein adjusting optimum positions includes recalculating positions in a look-up table by interpolating between optimum positions of reference mirrors.

4. A method of controlling an optical switch, the method comprising:

periodically measuring positions of mirrors in a first mirror array corresponding to reference input ports, the reference input ports being interspersed among signal input ports, and positions of mirrors in a second mirror array corresponding to reference output ports, the reference output ports being interspersed among signal output ports, the positions maximizing the intensity of reference light coupled from a reference light source to the reference input ports and directed to a reference detector coupled to the output reference ports, via the mirrors in the first mirror array corresponding to the reference input ports and the mirrors in the second mirror array corresponding to the reference output ports; and

using the measured positions to predict positions for mirrors in the first mirror array corresponding to signal input ports and for mirrors in the second mirror array corresponding to signal output ports to maximize the intensity of light directed from signal input ports to signal output ports, via the mirrors in the first mirror array corresponding to the signal input ports and the mirrors in the second mirror array corresponding to the signal output ports.

5. The method of claim 4 wherein the number of signal input ports is substantially greater than the number of reference input ports and the number of signal output ports is substantially greater than the number of reference output ports.

6. The method of claim 4 wherein the optical switch further comprises:

a first control light source illuminating the first mirror array with control light;

a first position sensing detector for detecting control light reflected by the first mirror array wherein signals from the first position sensing detector correspond to positions of mirrors in the first mirror array;

a second control light source illuminating the second mirror array with control light; and

a second position sensing detector for detecting control light reflected by the second mirror array wherein signals from the second position sensing detector correspond to positions of mirrors in the second mirror array; and

wherein periodically measuring positions of mirrors in the first mirror array and in the second mirror array comprises recording the signals from the first position sensing detector and the signals from the second position sensing detector.

7. The method of claim 4 further comprising determining the number of reference input ports and the placement of reference input ports, and determining the number of reference output ports and the placement of reference output ports.

8. The method of claim 7 wherein determining the number and placement of reference input ports and reference output ports comprises

forming a connection grid wherein each point of the grid corresponds to a connection between a particular input port and a particular output port;

associating a vector of mirror positions with each point of the grid;

selecting candidate reference input ports and candidate reference output ports;

fitting functional forms to the vectors of mirror positions across rows and columns of the connection grid using points of the grid corresponding to connections between the candidate reference input ports and the candidate reference output ports; and

selecting reference input ports and reference output ports to minimize a difference, at all points of the grid, between mirror positions predicted by interpolation using the functional forms and the candidate reference input ports and candidate reference output ports and mirror positions optimized in an initial calibration.

9. The method of claim 8 wherein using the measured positions to predict positions for mirrors in the first mirror array corresponding to signal input ports and for mirrors in the second mirror array corresponding to signal output ports comprises using the measured positions and the functional forms to interpolate between the points of the connection grid corresponding to reference input ports and reference output ports.

10. The method of claim 4 further comprising:

measuring positions of mirrors in a first mirror array and in a second mirror array if changes in positions of mirrors in a first mirror array corresponding to reference input ports and in positions of mirrors in a second mirror array corresponding to reference output ports with respect to previously measured positions, measured in a straight-through mode wherein a signal from an N^th reference input port is directed to an N^th reference output port, are greater than a predetermined threshold; and

otherwise, waiting until a next scheduled recalibration time.

11. An optical switch comprising:

a first plurality of ports comprising signal input ports and reference input ports;

a second plurality of ports comprising signal output ports and reference output ports;

a first plurality of mirrors disposed on a first surface;

a second plurality of mirrors disposed on a second surface;

wherein each one of the first plurality of mirrors is individually controllable to direct light incident from a corresponding one of the first plurality of ports to any one of the second plurality of mirrors, and

wherein each one of the second plurality of mirrors is individually controllable to direct to a corresponding one of the second plurality of ports, light incident from any one of the first plurality of mirrors;

a reference light source coupled to provide reference light to the reference input ports; and

a reference detector coupled to the reference output ports;

wherein measured changes in optimal positions of mirrors in the first plurality of mirrors and of mirrors in the second plurality of mirrors for directing reference light from reference input ports to reference output ports can be used to determine changes in optimal positions of mirrors in the first plurality of mirrors and of mirrors in the second plurality of mirrors for directing light from signal input ports to signal output ports.

12. The optical switch of claim 11 wherein the first plurality of ports comprise a two-dimensional array and wherein the reference input ports are interspersed among the signal input ports in two dimensions, and wherein the second plurality of ports comprise a two-dimensional array and wherein the reference output ports are interspersed among the signal output ports in two dimensions.

13. The optical switch of claim 11 further comprising:

a first control light source located to illuminate the first plurality of mirrors with control light;

a first position sensing detector located to detect control light that has been reflected by the first plurality of mirrors, wherein signals provided by the first position sensing detector correspond to the positions of the first plurality of mirrors;

a second control light source located to illuminate the second plurality of mirrors with control light; and

a second position sensing detector located to detect control light that has been reflected by the second plurality of mirrors, wherein signals provided by the second position sensing detector correspond to the positions of the second plurality of mirrors.