Control techniques and devices for an optical switch array

• US 20020186918A1
• Filed: 05/17/2002
• Published: 12/12/2002
• Est. Priority Date: 05/26/2000
• Status: Active Grant

• Current Assignee: Microsemi Communications, Inc. (Microchip Technology Incorporated)
• Original Assignee: Vitesse Semiconductor Sales Corp. (Microchip Technology Incorporated)
• Inventors: Burroughs, Alan C.
• Granted Patent: US 6,925,218 B2
• Time in Patent Office: Days
• US Class Current: 385/18
• CPC Class Codes: G02B 26/0816 by means of one or more reflecting elements
• 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 6/3572 Magnetic force magnetic forces controlling reflecting elements in general G02B26/085; magneto-optic devices G02F1/09
• 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: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 11/0062 Network aspects
• CPC Class Codes: H04Q 2011/0009 using wavelength filters
• CPC Class Codes: H04Q 2011/0011 using wavelength conversion
• CPC Class Codes: H04Q 2011/0013 using gating amplifiers
• CPC Class Codes: H04Q 2011/0016 using wavelength multiplexing or demultiplexing
• 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 2011/0041 Optical control
• CPC Class Codes: H04Q 2011/0043 Fault tolerance
• CPC Class Codes: H04Q 2011/0045 Synchronisation
• CPC Class Codes: H04Q 2011/0049 Crosstalk reduction; Noise; Power budget
• CPC Class Codes: H04Q 2011/0052 Interconnection of switches
• CPC Class Codes: H04Q 2011/0058 Crossbar; Matrix
• CPC Class Codes: H04Q 2011/0083 Testing; Monitoring
• CPC Class Codes: H04Q 2011/0088 : Signalling aspects

Abstract

Techniques and systems for controlling an optical switch array based on local and global optical monitoring and feedback controls. Each optical switch element includes a local optical monitoring mechanism to form a local feedback control to lock the switch element at a desired orientation. The global optical monitoring is used to adjust at least one switch element in the path of the signal beam to maintain an overall alignment.

Claims

1. An optical switch system, comprising:

an array of input optical ports each operable to receive a signal beam;

an array of first optical switch elements positioned to respectively receive light from said input optical ports, each first optical switch element having a first front reflector to receive and reflect said signal beam, a first back reflector fixed in position relative to said first front reflector to reflect a first local servo beam, a first optical position sensor to receive said first local servo beam and to produce a first position signal indicative of an orientation of said first front reflector, and a first actuator engaged to control an orientation of said first front reflector in response to said first position signal;

an array of second optical switch elements positioned to receive light from said first optical switch elements, each second optical switch element operable to receive and reflect said signal beam reflected from any first optical switch element, wherein each second optical switch element includes a second front reflector to receive and reflect said signal beam, a second back reflector fixed in position relative to said second front reflector to reflect a second local servo beam, a second optical position sensor to receive said second local servo beam and to produce a second position signal indicative of an orientation of said second front reflector, and a second actuator engaged to control an orientation of said second front reflector in response to said second position signal;

an array of output optical ports positioned to respectively receive light from said second optical switch elements, said signal beam reflected from said second optical switch element at one output optical port;

a plurality of output optical detectors respectively coupled to said array of output optical ports, each output optical detector operable to receive a fraction of output optical power of a corresponding output optical port to produce an output detector signal having information about an alignment of incident light at said corresponding output optical port; and

a switch control module coupled to receive output detector signals from said array of output optical detectors and to communicate with said first and said second optical switch elements, said switch control module responsive to a respective output detector signal and respective first and said second position signals to control orientations of respective first and second actuators in switching said signal beam from one input optical port to one output optical port.

2. The system as in claim 1, wherein each actuator is a galvanometer engaged to said front and said back reflectors.

3. The system as in claim 1, wherein said switch control module includes:

a set of first actuator control units to respectively control said first actuators and coupled to respectively receive said first position signals, wherein each first actuator control unit, a corresponding first actuator, and a corresponding first optical position sensor are coupled to form a feedback control loop to control said corresponding first actuator;

a set of second actuator control units to respectively control said second actuators and coupled to respectively receive said second position signals, wherein each second actuator control unit, a corresponding second actuator, and a corresponding second optical position sensor are coupled to form a feedback control loop to control said corresponding second actuator; and

a controller coupled to receive said output detector signals and operable to produce a control signal to each of said first and said second actuator control units to set a corresponding actuator to a selected orientation.

4. The system as in claim 3, wherein each of said first and said second actuator control units includes:

a position circuit to extract an actual position of a corresponding actuator from a corresponding position signal generated by a corresponding optical position sensor;

a position error circuit coupled to said controller and said position circuit to determine an error in position from said control signal and said actual position; and

a loop compensator circuit connected to said position error circuit to produce an actuator control signal that drives said corresponding actuator.

5. The system as in claim 3, wherein each of said first and said second optical switch elements includes a local laser to produce a corresponding local servo beam that is used by a corresponding optical position sensor to produce a corresponding position signal, and wherein said of said first and said second actuator control units includes a laser controller circuit to receive and process a portion of said corresponding position signal to produce a laser power signal, and a laser driver circuit to control said local laser to stabilize a power of said local servo beam in response to said laser power signal.

6. The system as in claim 5, wherein local lasers in said optical switch elements are modulated to lase in pulses, and wherein local lasers in one group of said optical switch elements are turned on and local lasers in another group of said optical switch elements are turned off at a given time.

7. The system as in claim 3, wherein said controller includes a digital processor.

8. The system as in claim 3, further comprising an electrical amplifier connected between each output optical detector and said controller to amplify a corresponding output detector signal with a variable gain.

9. The system as in claim 1, wherein each of said first and said second actuators has two different rotation axes and is operable to independently rotate around said two different rotation axes.

10. The system as in claim 1, wherein said first optical switch element includes a local laser to produce said first local servo beam, a beam splitter in an optical path between said local laser and said first back reflector to direct said local servo beam reflected from said first back reflector to said first optical position sensor.

11. The system as in claim 1, wherein said first front reflector and said first back reflector are parallel to each other and face opposite directions.

13. The method as in claim 12, wherein said error in orientation in said local servo control loop is measured optically by:

directing a local servo beam to a back reflector fixed in said optical switch element;

using an optical position sensor to receive said local servo beam reflected from said back reflector to produce a position sensor signal; and

processing said position sensor signal to determine said error.

14. The method as in claim 13, wherein said processing includes comparing an actual orientation obtained from said position sensor signal to a desired orientation.

15. The method as in claim 12, wherein said error in said overall alignment is measured optically by:

measuring received optical power at an output optical port; and

comparing the measured power to a maximum power to determine said error in said overall alignment.

16. The method as in claim 12, wherein said error in said overall alignment is measured optically by:

directing a global servo beam to trace an optical path of said signal beam in parallel, wherein said global servo beam is at a wavelength different from a wavelength of said signal beam;

at an output optical port that receives said signal beam, directing said global servo beam to an optical position sensor to measure an actual position of said global servo beam; and

comparing said measured actual position to a desired position of said global servo beam to determine said error.

17. The method as in claim 12, further comprising:

measuring received optical power at an output optical port; and

adjusting at least one of said two different optical switch elements in an optical path of said signal beam to set the received optical power at a desired output level.

18. The method as in claim 12, further comprising adjusting each optical switch element with a variable adjustment speed, wherein the adjustment speed is less at the end of the adjustment than at a middle step of the adjustment.

19. The method as in claim 12, wherein each optical switch element includes a local laser to produce the local servo beam, and said method further comprising:

modulating each local laser to produce pulses; and

turning one group of local lasers when turning off other local lasers to reduce a total power consumption at a given time.

12. A method, comprising:

providing an optical switching array with a plurality of optical switch elements to direct a signal beam;

providing a local servo control loop to actively control an orientation of each optical switch element in said optical switch array, wherein said active control includes;

optically measuring an orientation of each optical switch element by an optical position sensor in the local servo control loop,

using the measured orientation to determine an error in orientation with respect to a desired orientation, and

adjusting the optical switch element to reduce said error;

optically measuring an overall alignment of said signal beam that is directed by at least two different optical switch elements in said optical switch array; and

adjusting at least one of said two different optical switch elements in an optical path of said signal beam to reduce an error in said overall alignment.