WO2003077592A1

WO2003077592A1 - Configuration system for optical switching arrangements

Info

Publication number: WO2003077592A1
Application number: PCT/GB2003/000981
Authority: WO
Inventors: Ugo Francesco Giuseppe Cerato; Robert Charles Goodfellow
Original assignee: Marconi Uk Intellectual Property Ltd
Priority date: 2002-03-08
Filing date: 2003-03-07
Publication date: 2003-09-18
Also published as: ITTO20020198A1; AU2003217001A1; ITTO20020198A0

Abstract

A configuration system adapted for use in an optical switching arrangement is provided. The arrangement comprises an array of input ports (40), an array of output ports (43) and a switching system (41, 42) configurable for switching a signal from each input port to a chosen output port, and the configuration system comprises an array of radiation sources (20), first and second optical elements (21, 22), a radiation detector (23) and a controller (24). Radiation from each source is directed onto the first optical element, to the switching system, the second optical element and the radiation detector. The radiation detector receives the radiation and sends the detected position thereof to the controller. The controller compares the detected position with an expected position, generated when the switching system is configured for switching of a signal from the input port corresponding to each radiation source to a chosen output port, and configures, as necessary, the switching system until the detected position is at least substantially similar to the expected position.

Description

CONFIGURATION SYSTEM FOR OPTICAL SWITCHING ARRANGEMENTS

This invention relates to a configuration system for use in optical switching arrangements, particularly optical switching arrangements for switching signals from an array of input ports to an array of output ports.

It is known to interconnect wavelength division multiplexed line and/or ring systems to form meshed optical networks. The interconnections may be formed using optical switching arrangements. These may comprise means for deflecting the signals from a two-dimensional input array of optical fibre ports to a two-dimensional output array of optical fibre ports. The number of ports will vary depending on requirements, and could be in the range 10 to 1000. The deflection means used may comprise, for example, an array of 0.5mm x 0.5mm optical mirrors fabricated in silicon using micro electromechanical system (MEMS) technology, or alternatively an optical collimator array combined with a piezo bending arrangement.

An example of a known optical switching arrangement is shown in Figure 1. This comprises an input optical fibre array 1, a first array of silicon MEMS mirrors 2, a second array of silicon MEMS mirrors 3 and an output optical fibre array 4. The MEMS mirrors are each mounted on gimbals or a trio of legs (not shown) for azimuthal and elevational angular deflection. Signals from the input fibre array 1 are switched, or coupled, to the output fibre array 4 by deflection by the mirror arrays 2 and 3. For example, the signal from an input fibre 5 is incident on a mirror 6 of mirror array 2, and, by suitable positioning of the mirror 6 and a mirror 7 of mirror array 3, the signal may be deflected to an output fibre 8. The signal from each input fibre in array 1 can therefore be switched to an output fibre in array 2 by deflection from a pair of mirrors, one from each of the mirror arrays 2, 3. It is desirable to position a mirror pair such that the intensity of the signal received by the output fibre from the input fibre is as high as possible. To do this, a probe signal is introduced into the input fibre and part of the signal received by the output fibre is coupled to, for example, a detector in a detector array. The azimuthal and elevational angles of the mirrors are adjusted, e.g. by means of electronic drives coupled to the gimbals or legs, whilst the signal received by the detector is monitored. The accuracy required in this process is very demanding, as the fibre cores are of the order of a few micrometres diameter and the optical path between fibres may need to be between lxlO⁴ and lxl0⁶μm, implying positional accuracies of between 1x10^ and lxl 0^"6 radians. When the signal maximum is identified, the configuration of the mirrors is maintained whilst that switch path is required. To carry out the above process, it is convenient to provide a detector for each fibre in the output array. This could be prohibitively expensive, and it is desirable to provide an alternative method of configuring the mirror pairs.

According to a first aspect of the present invention there is provided a configuration system adapted for use in an optical switching arrangement comprising an array of input ports, an array of output ports and a switching system configurable for switching a signal from each input port to a chosen output port, wherein the configuration system comprises an array of radiation sources, first and second optical elements, a radiation detector and a controller, and each radiation source corresponds to an input port i.e. the radiation from each radiation source and the signal from its corresponding input port are substantially coincident on the first optical element, radiation from each radiation source is directed onto the first optical element, from the first optical element to the switching system, from the switching system to the second optical element and from the second optical element to the radiation detector, the radiation detector receives the radiation and sends the detected position thereof to the controller, and the controller receives the detected position and compares it with an expected position generated when the switching system is configured for switching of a signal from the input port corresponding to each radiation source to a chosen output port, and configures, as necessary, the switching system until the detected position is at least substantially similar to the expected position.

The array of radiation sources may comprise an array of light emitting diodes (LEDs), or an array of semiconductor vertical cavity surface emitting lasers (VCSELs). The array of radiation sources may comprise an array of apertures illuminated using one or more sources of radiation. The array of radiation sources may comprise a mask illuminated by one or more sources of radiation. The array of radiation sources may comprise a digital MEMS mirror array illuminated using one or more sources of radiation. The array of radiation sources may be provided with an array of lenses. The array of lenses may provide a lens for each radiation source, which lens may act to collimate the radiation emitted from the radiation source.

The array of radiation sources may emit electromagnetic radiation having one or more wavelengths which may be in the infra red or visible region. The array of radiation sources may emit electromagnetic radiation having one or more wavelengths less than 1.1 μm. The array of radiation sources may emit electromagnetic radiation having one

or more wavelengths in the region 0.4μm to 0.98μm. The resolution of the configuration of the optical switching arrangement will be inversely proportional to the wavelength of the radiation emitted by the radiation sources. Using radiation in the infra red or visible regions will increase the resolution over that achievable if radiation having a longer wavelength is used. The radiation emitted from each radiation source may comprise a unique constitution. For example, the intensity of the radiation emitted from each radiation source may comprise a unique modulation or a unique wavelength.

The first and second optical elements preferably each have a transmission passband such as to allow signals from the array of input ports to pass to the array of output ports, and a reflection passband such as to pass the radiation from the array of radiation sources to the radiation detector. The first and second optical elements may each have a passband of approximately lOnm. The first and second optical elements may each comprise a mirror. The mirrors may be dichroic mirrors. The mirrors may each have a reflection coefficient of approximately 90% at the wavelength or wavelengths of the radiation from the array of radiation sources. The mirrors may be placed in the path of the signals from the array of input ports of the optical switching arrangement. The mirrors preferably then have a transmission coefficient of approximately unity at the wavelength or wavelengths of the signals from the array of input ports.

The detected position of the radiation may comprise x and y co-ordinates of the position in the radiation detector. The radiation detector may comprise a camera. The camera

preferably has a resolution in the range 1 to lOμm. The camera may be a silicon charge-coupled device (CCD). The camera may be a television camera. The radiation detector may comprise a plurality of detecting elements. The radiation received by the detector may illuminate a number of the detecting elements, and the detected radiation may appear as a finite spot having a gaussian-like power intensity profile. The detected position of the radiation may comprise the position in the radiation detector of the peak intensity of the power intensity profile. The detected position of the radiation may comprise x and y co-ordinates of the position in the radiation detector of the peak intensity of the power intensity profile. The radiation detector may be provided with an array of lenses. The array of lenses may magnify the radiation received by the detector. The resolution of the configuration of the optical switching arrangement may thereby be enhanced. The array of lenses provided with the radiation detector preferably has a different focal length than any array of lenses provided with the array of radiation sources. This may result in magnification of the radiation received by the detector, and enhancement of the resolution of the configuration. When the radiation from each radiation source comprises a unique constitution, the radiation detector may be configured to detect and to distinguish between each unique constitution.

The array of radiation sources may be positioned with respect to the first optical element and the array of input ports such that each radiation source corresponds to an input port. When the first optical element comprises a mirror, the array of radiation sources may be positioned with respect to the mirror and the array of input ports such that the virtual image of each radiation source in the mirror substantially coincides with its corresponding input port. The radiation from each radiation source and the signal from its corresponding input port will then be substantially coincident on the mirror. The array of radiation sources may be rigidly positioned with respect to the array of input ports. The array of radiation sources may be fixed to the array of input ports. The array of radiation sources may comprise a mechanical fixing with which it is positioned with respect to the array of input ports or fixed to the array of input ports. The radiation detector may be rigidly positioned with respect to the array of output ports. The radiation detector may be fixed to the array of output ports. The radiation detector may comprise a mechanical fixing with which it is positioned with respect to the array of output ports or fixed to the array of output ports.

The controller may comprise a digital signal processor integrated circuit or a microprocessor integrated circuit. Either circuit may be incorporated into the configuration system. Either circuit may be accessed using an interface, such as an Ethernet interface for example a dual speed 10/100 Base Tx RJ45 interface. The circuit and interface may interact using a communication protocol, such as a TCP/IP layer 4 transport service protocol from the TCP/IP protocol stack. The communication protocol may be a message-based protocol. The messages may be user messages, provided for the day-to-day operation of the optical switching arrangement and which may include commands to configure the switching system to change one or more optical paths in the arrangement, commands to determine and retrieve the status of the components of the arrangement or the configuration system, or commands to check for any alarm signals generated in the arrangement or the configuration system. The messages may be configuration messages, which may include commands for setting parameters which should not be altered during the day-to-day operation of the arrangement, for example programming of the controller. The controller may comprise a computer. The controller may comprise and/or be coupled to a memory. The controller may store the detected position of the radiation in the memory. The controller may retrieve the expected positions from the memory. The controller may record a final configuration of the switching system in the memory. The controller may be coupled to one or more components of, for example, a network to which the optical switching arrangement is connected for use. The controller may send control signals to the one or more components, and/or may receive control signals from the one or more components.

The controller may adjust the positioning of the switching system to configure the switching system. The controller may control the operation of moving means coupled to the switching system to adjust the positioning of the switching system. The controller may control the operation of the array of radiation sources. The controller may control the operation of the radiation detector. The controller may use at least one software algorithm to configure the switching system of the optical switching arrangement. The controller may use at least one software algorithm to control, for example, any, some, or all of: receipt of the detected position of the radiation, comparison of the detected position with the expected position, configuration of the switching system, adjustment of the positioning of the switching system, control of the operation of the moving means, control of the operation of the array of radiation sources, and control of the operation of the radiation detector. The software algorithm may be stored in the controller. The software algorithm may comprise one or more control loop algorithms, for example a multidimensional sampled proportional integrative control loop algorithm. The software algorithm may comprise one or more tree-based exploring algorithms. The expected positions may each comprise x and y co-ordinates of the position in the radiation detector. The expected positions may each comprise an optimum expected position generated when the switching system is configured for optimum switching of a signal from an input port to an output port, i.e. when a signal maximum is received by the output port from the input port. The optimum expected positions may each comprise x and y co-ordinates of the position in the radiation detector. The controller may control the generation of the expected positions. The controller may control the generation of the optimum expected positions. The controller may control the generation of the optimum expected positions by simply adjusting the positioning of the switching system until a signal maximum is received by each output port. Alternatively, the controller may control the generation of the optimum expected positions by using at least one software algorithm to configure the switching system until a signal maximum is received by each output port. The software algorithm may comprise a minimisation algorithm, for example a gradient method algorithm. The software algorithm may be stored in the controller. The expected positions may be stored in a memory, for example a memory of the controller. The expected positions may be stored as a database in the memory. When there are N input ports and N output ports and the expected positions each comprise x and y co-ordinates, the database may comprise 2xNxN elements. The configuration System may comprise a detector coupled to each output port in the array of output ports for use in generating the expected positions.

The configuration system may comprise or be coupled to a temperature control system. The temperature control system may control the ambient temperature around the configuration system. The operation of the temperature control system may be controlled by the controller. The configuration system may comprise or be coupled to a temperature sensor. The temperature sensor may be used to measure the ambient temperature around the configuration system. The operation of the temperature sensor may be controlled by the controller. The temperature sensor may pass measurements of the temperature to the controller. The controller may use the temperature control system and the temperature sensor in order to compare the detected position detected at an ambient temperature to an expected position generated at that temperature or an expected position calculated for that temperature.

The configuration system may comprise a monitoring system for monitoring the signals from the array of input ports of the optical switching arrangement. The monitoring system may be used to determine one or more characteristics of the signals from the array of input ports. The monitoring system may be used to check that a signal is emitted from each of the input ports. The monitoring system may be used to determine the power level of the signal emitted from each input port. The monitoring system may be used to compare the power levels of the signals emitted from the input ports with one another. The monitoring system may comprise an alarm system, which may be activated, for example, if a signal is not emitted from each input port or if the power levels of the signals are not approximately similar. The alarm system may send an alarm signal to an operator of a network to which the optical switching arrangement is connected. The monitoring system may be used to check that each signal is switched to an output port. The monitoring system may be used to determine the power level of the signals from the input ports after passing through the switching system of the optical switching arrangement and before entry into the output ports. The monitoring system may be used to compare the power levels of the signals with one another. The alarm system may be activated, for example, if each signal is not switched to an output port or if the power levels of the signals after switching are not approximately similar. The alarm system may send an alarm signal to an operator of a network to which the optical switching arrangement is connected.

The monitoring system may comprise one or both of the first and second optical elements and the radiation detector. Alternatively or additionally, the monitoring system may comprise one or more optical elements and one or more detectors. In a preferred embodiment, the monitoring system comprises a first optical element which directs part of the signals emitted from the array of input ports to a first detector, and a second optical element which directs part of the signals switched to the array of output ports to a second detector. The first optical element may comprise a mirror placed in proximity to the array of input ports in the path of the signals emitted from the input ports. The mirror preferably has a transmission coefficient of approximately 95% and a reflection coefficient of approximately 5% at the wavelength or wavelengths of the signal emitted from the input ports. Most of these signals will then be transmitted by the mirror, and only part thereof will be deflected into the first detector. The first detector may, for example, determine the power level of each emitted signal. The operation of the first detector may be controlled by the controller. For example, the controller may control the frequency, timing and sampling duration for reading of the output of the first detector. The first detector may be coupled to the controller, and the controller may receive the power levels from the first detector. The controller may check whether or not a signal is emitted from each input port. The controller may compare the power levels with one another to check whether or not the power levels of the emitted signals are substantially similar. The second optical element may comprise a mirror placed in proximity to the array of output ports in the path of the signals switched to the output ports. The mirror preferably has a transmission coefficient of approximately 95% and a reflection coefficient of approximately 5% at the wavelength or wavelengths of the signal emitted from the input ports. Most of these signals will then be transmitted by the mirror, and only part thereof will be deflected into the second detector. The second detector may, for example, determine the power level of each switched signal. The operation of the second detector may be controlled by the controller. The second detector may be coupled to the controller, and the controller may receive the power levels from the second detector. The controller may check whether or not the signal from each input port is switched by the switching system. The controller may compare the power levels with one another to check whether or not the power levels of the switched signals are substantially similar. The first and second detectors may each comprise, for example, an indium gallium arsenide videcon or an infra red detecting 2-D detector array. In this preferred embodiment, detectors are provided which are used to monitor the signals from the array of input ports, and the radiation detector is used to receive radiation from the array of radiation sources. It is desirable that the radiation from the array of radiation sources has a wavelength or wavelengths in the infra red or visible region to enhance the resolution of the configuration. The signals from the array of input ports may, however, often comprise radiation whose wavelength or wavelengths are longer than this. By providing different detectors, each sensitive to radiation of different wavelength, it is possible to use radiation in the infra red or visible region for the configuration whilst still providing the ability to monitor the signals from the array of input ports of the optical switching arrangement.

The array of input ports of the optical switching arrangement may comprise or be coupled to an array of optical fibres or an array of waveguides or be an array of dense wavelength division multiplexed (DWDM) wavelength channels in the form of optical beams which may have been derived by diffraction of radiation from one or more fibres. The array of output ports of the optical switching arrangement may comprise or be coupled to an array of optical fibres or an array of waveguides or be an array of DWDM wavelength channels in the form of optical beams. The ports may each be provided with a collimator.

The input ports may each emit a signal having a wavelength or wavelengths in the range

1.25μm to 1.65μm. The input ports may each emit a signal having only one wavelength. The wavelength of each signal may be the same or may be different. The input ports may each emit a signal having a multiple of wavelengths.

The switching system of the optical switching arrangement may comprise one or more arrays of deflection elements. The deflection elements may comprise MEMS mirrors, or mirrors mounted on, for example, piezo bending arrangements, or piezo pointed fibres with collimators, or spatial light modulators e.g. reconfigurable diffraction grating elements implemented with liquid crystal technology or by means of deformable silicon filaments. The deflection of the array or arrays of deflection elements or the deflection of each deflection element within each array may be controlled by the controller of the configuration system by adjusting the positioning of the array or element. The array or arrays of deflection elements may be coupled to moving means, whose operation may be controlled by the controller. Each deflection element of the or each array may be coupled to moving means, whose operation may be controlled by the controller. The moving means may comprise one or more actuators or one or more electronic drives. When the deflection elements comprise one or more arrays of MEMS mirrors, the controller may adjust the positioning and hence deflection of each mirror by controlling the azimuthal and elevational angles of the mirror.

In one embodiment, the switching system of the optical switching arrangement may comprise first and second arrays of deflection elements, for example MEMS mirrors. The optical switching arrangement may be arranged such that the signal from a first input port is only incident on a first element in the first array of deflection elements, the signal from a second input port is only incident on a second element in the first array of deflection elements, and so on for all the input ports. Such an arrangement may be achieved by the providing each input port with a collimator. The switching system may be configurable such that each element in the first array of deflection elements may deflect its signal to any element in the second array of deflection elements. The optical switching arrangement may be arranged such that the signal from a first element in the second array of deflection elements is only deflected to a first output port in the array of output ports, the signal from a second element in the second array of deflection elements is only deflected to a second output port, and so on for all the elements in the second array of deflection elements. Such an arrangement may be achieved by the providing each output port with a collimator. Switching of, for example, the signal from a first input port to a fifth output port may then be achieved by configuring the first element in the first array of deflection elements to deflect its signal to the fifth element of the second array of deflection elements.

In such an embodiment, for each input port/chosen output port pair, configuration of the switching system involves configuring the deflection element of the first array of deflection elements which the signal from the input port is incident on to deflect its signal to the deflection element of the second array of deflection elements which deflects its signal to the chosen output port, i.e. involves configuration of a pair of deflection elements. For example, as stated above, configuration of the switching system to switch the signal from a first input port to a fifth output port is achieved by configuring the first element in the first array of deflection elements to deflect its signal to the fifth element of the second array of deflection elements. When the switching system has been configured, the connectivity of each deflection element pair, i.e. deflection of a signal from the first element of the pair to the second element of the pair, will be secured. Monitoring of the configuration of the switching system will allow monitoring of the connectivity of the deflection element pairs.

According to a second aspect of the present invention there is provided an optical switching arrangement comprising at least one configuration system according to the first aspect of the invention. According to a third aspect of the present invention there is provided a method of configuring an optical switching arrangement according to the second aspect of the invention comprising, for each input port signal to be switched to a chosen output port : (a) operating the radiation source corresponding to the input port, (b) directing the radiation from the radiation source onto the first optical element, from the first optical element to the switching system, from the switching system to the second optical element, and from the second optical element to the radiation detector, (c) operating the radiation detector to receive the radiation and to send the detected position thereof to the controller, (d) operating the controller to receive the detected position and to compare it to an expected position generated when the switching system is configured for switching a signal from the input port to the chosen output port, and

(e) operating the controller to configure, as necessary, the switching system until the detected position is at least substantially similar to the expected position.

Configuration of the switching system by the controller may comprise adjusting the positioning of the switching system, receiving the detected position of the radiation switched by the newly-positioned switching system, comparing this detected position with the expected position, and repeating this sequence until the detected position is at least substantially similar to the expected position. Configuration of the switching system by the controller may comprise using at least one software algorithm. The software algorithm may comprise one or more control loop algorithms, for example a multidimensional sampled proportional integrative control loop algorithm. The software algorithm may comprise one or more tree-based exploring algorithms. These may be used to increase the efficiency and dimensionality of any control loops used. When the switching system comprises one or more arrays of deflection elements, the software algorithm may be used to control adjustment of the positioning of the or each array, or to control adjustment of the positioning of each element in each array. For example, when the switching system comprises two arrays of MEMS mirrors, a control loop algorithm of the software algorithm may be used to control adjustment of the elevational angular positioning of each mirror and another control loop algorithm of the software algorithm may be used to control adjustment of the azimuthal angular positioning of each mirror. The control loop algorithms may be run simultaneously.

Configuration of the switching system may be carried out separately for each input port signal to be switched. This may comprise, for example, sequential activation of the radiation sources. However, if there a large number, e.g. 1000, of input ports, separate configuration for each of these may be prohibitively time consuming. Configuration of the switching system may be carried out substantially simultaneously for all the input port signals to be switched. This may comprise, for example, substantially simultaneous activation of the radiation sources. In such a configuration system, the radiation emitted from each radiation source may comprise a unique constitution. For example, the intensity of the radiation emitted from each radiation source may comprise a unique modulation. The radiation detector may be configured to detect and to distinguish between each unique constitution, e.g. intensity modulation, of the radiation emitted from the radiation sources. Configuration of the switching system may be carried out on one or more discrete occasions. Configuration of the switching system may be carried out when a user first receives the optical switching arrangement, for example to configure the switching system to the user requirements or to check that the manufacturer has so configured the switching system. Configuration of the switching system may also be carried out at regular occasions thereafter, for example to check that the current configuration matches the user's requirements or to change the configuration to match new requirements.

The method may further comprise generating an expected position for switching of a signal from each input port to a chosen output port, or from each input port to each output port. The expected positions may be generated using the configuration system. The controller may control the generation of the expected positions. Generation of the expected position for switching of a signal from an input port to an output port may comprise coupling the output port to a detector, activating emission of a signal from the input port, activating the detector coupled to the output port, configuring the switching system until the detector detects that the signal is switched to the output port, maintaining this configuration of the switching system, activating the radiation source corresponding to the input port, directing the radiation from the radiation source to the radiation detector via the switching system, activating the radiation detector to receive the radiation, sending the detected position to the controller, and operating the controller to record the detected position as the expected position. Preferably, the switching system is configured until the detector detects that a signal maximum is switched to the output port. This may be achieved by simply adjusting the positioning of the switching system until a signal maximum is received by the output port. Alternatively, this may be achieved by using at least one software algorithm to configure the switching system until a signal maximum is received by the output port. The software algorithm may comprise a minimisation algorithm, for example a gradient method algorithm. The software algorithm may be run by the controller. The expected positions may be generated at one or more temperatures. The expected positions generated at the one or more temperatures may be used to calculate expected positions for one or more other temperatures. For example, the expected positions may be generated for a high temperature, a low temperature, and a temperature intermediate the two. These expected positions may be used to calculate expected positions for one or more temperatures between the high temperature and the intermediate temperature and/or between the intermediate temperature and the low temperature.

Generation of the expected positions may be carried out separately for each position. Generation of the expected positions may be carried out substantially simultaneously for all the positions. This may comprise, for example, substantially simultaneous activation of the radiation sources. The radiation emitted from each radiation source may comprise a unique constitution. For example, the intensity of the radiation emitted from each radiation source may comprise a unique modulation. The radiation detector may be configured to detect and to distinguish between each unique constitution, e.g. intensity modulation, of the radiation emitted from the radiation sources.

Generation of the expected positions may be carried out on one or more discrete occasions. For example, generation of the expected positions may be carried out by a manufacturer of the optical switching arrangement prior to sending to a user, or may be carried out when a user first receives the arrangement, or may be carried out on either of these occasions and at one or more subsequent occasions. The expected positions generated on any subsequent occasion may be stored separately from expected positions generated on any or all previous occasions. Alternatively, the expected positions generated on any subsequent occasion may be used to replace expected positions generated on any or all previous occasions. The expected positions generated on any subsequent occasion may be compared to expected positions generated on any or all previous occasions. If the expected positions generated on any subsequent occasion are not at least substantially similar to expected positions generated on any or all previous occasions, the expected positions generated on the subsequent occasion may be used to replace the expected positions generated on any or all of the previous occasions. This may allow a user to, for example, check that the expected positions still correspond to positions generated when the switching system is configured for switching of a signal from an input port to a chosen output port, and particularly to check that the expected positions still correspond to positions generated when the switching system is configured for switching a signal maximum from an input port to a chosen output port. Generation of expected positions on one or more subsequent occasions may be initiated on request from an operator of a network to which the optical switching arrangement is connected for use.

According to a fourth aspect of the present invention there is provided a method of generating the expected positions in an optical switching arrangement according to the second aspect of the invention, comprising, for each input port signal to be switched to an output port: coupling each output port to a detector, activating emission of a signal from the input port, activating the detector coupled to the output port, configuring the switching system until the detector detects that the signal is switched to the output port, maintaining this configuration of the switching system, activating the radiation source corresponding to the input port, directing the radiation from the radiation source to the radiation detector via the switching system, activating the radiation detector to receive the radiation, sending the detected position to the controller, and operating the controller to record the detected position as the expected position.

The expected positions may be generated using the configuration system. The controller may control the generation of the expected positions. Preferably, the switching system is configured until the detector detects that a signal maximum is switched to the output port. This may be achieved by simply adjusting the positioning of the switching system until a signal maximum is received by the output port. Alternatively, this may be achieved by using at least one software algorithm to configure the switching system until a signal maximum is received by the output port. The software algorithm may comprise a minimisation algorithm, for example a gradient method algorithm. The software algorithm may be run by the controller. The expected positions may be generated at one or more temperatures. The expected positions generated at the one or more temperatures may be used to calculate expected positions for one or more other temperatures. For example, the expected positions may be generated for a high temperature, a low temperature, and a temperature intermediate the two. These expected positions may be used to calculate expected positions for one or more temperatures between the high temperature and the intermediate temperature and/or between the intermediate temperature and the low temperature.

Generation of the expected positions may be carried on one or more discrete occasions as before.

An embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of a known optical switching arrangement; and

Figure 2 is a schematic representation of an optical switching arrangement according to the second aspect of the present invention, incorporating a configuration system according to the first aspect of the invention. Figure 2 shows an optical switching arrangement incorporating a configuration system. The configuration system comprises an array of radiation sources 20, a first optical element 21, a second optical element 22, a radiation detector 23 and a controller 24. The array of radiation sources 20 comprises an array of apertures 25 illuminated by a source of visible radiation 26. An array of lenses 27 is provided in front of the apertures, and light from each aperture passes through and is collimated by a lens. The optical elements 21 and 22 are dichroic mirrors. The radiation detector 23 comprises a

silicon CCD, having a resolution in the range 1 to lOμm. An array of lenses 28 is provided adjacent the CCD, and light received by the CCD first passes through and is magnified by the array of lenses. The controller 24 comprises a digital signal processing integrated circuit, coupled to an interface (not shown). The controller 24 is coupled to and controls the operation of the visible radiation source 26 illuminating the array of apertures 25. The controller 24 is coupled to and controls the operation of the CCD 23. A temperature sensor and a temperature control system (not shown) are coupled to the controller, and are used to measure and control the ambient temperature around the configuration system and the optical switching arrangement. The controller controls the operation of the temperature sensor and the temperature control system. The configuration system further includes a signal monitoring system which comprises a mirror 29, a detector 30, a mirror 31 and a detector 32. Signals deflected from the mirror 29 are received by the detector 30 and sent to the controller 24, and signals deflected from the mirror 31 are received by the detector 32 and sent to the controller 24. The optical switching arrangement comprises an array of input ports 40, a switching system comprising a first array of deflection elements 41 and a second array of deflection elements 42, and an array of output ports 43. The array of input ports 40 is coupled to an array of input optical fibres. An array of lenses 44 is provided in front of the input ports, such that the signal emitted by each port is collimated by a lens. The array of output ports 43 is coupled to an array of output optical fibres. An array of lenses 45 is provided before the output ports, such that the signal entering each port is collimated by a lens. Each output fibre is coupled to a detector of an array of detectors 46. The deflection element arrays 41, 42 each comprise an array of MEMS mirrors. Each mirror of each array is mounted on a gimbal (not shown), and an actuator (not shown) is attached to and drives each gimbal. The actuators are coupled to and their operation is controlled by the controller 24 of the configuration system. The array of input ports 40 is positioned relative to the first array of mirrors 41 and their collimators such that the signal from a first input port is only incident on a first mirror in the array 41, the signal from a second input port is only incident on a second mirror in the array 41, and so on for all the input ports. The mirrors in each array 41, 42 are capable of elevational and azimuthal angular positioning such that each mirror in the array 41 may deflect its signal onto any mirror in the array 42. The array of output ports 43 is positioned relative to the second array of mirrors 42 and their collimators such that the signal from a first mirror in the array is only deflected to a first output port in the array 43, the signal from a second mirror is only deflected to a second output port, and so on for all the mirrors in the second array of mirrors 42. The array of radiation sources 20 is located and fixed relative to the array of input ports

40 using a mechanical fixing (not shown), such that the virtual image of a first radiation source (aperture) is coincident with a first input port as viewed by the dichroic mirror

21, the virtual image of a second radiation source (aperture) is coincident with a second input port as viewed by the dichroic mirror 21 and so on for all the radiation sources, i.e. each radiation source has a corresponding input port. The radiation from the first radiation source will then be incident on the first mirror of the array 41, and the radiation from the second radiation source will then be incident on the second mirror of the array 41, and so on for all the radiation sources. The radiation detector 23 is located and fixed relative to the array of output ports 43 using a mechanical fixing (not shown). The mirrors 21, 22 are positioned in the path of the radiation from the array of radiation sources 20 and the path of the signals from the array of input ports 40, as shown. The mirrors each have a reflection coefficient of approximately 90% at the wavelength or wavelengths of the radiation from the array of radiation sources, and a transmission coefficient of approximately unity at the wavelength or wavelengths of the signals from the array of input ports. Radiation from the array of radiation sources 20 will be substantially deflected by the mirrors, but the signals from the array of input ports 40 will be substantially transmitted by the mirrors.

The switching system of the optical switching arrangement is configured as follows. First, the expected position for switching of a signal from each input port to each output port is generated. The ambient temperature around the configuration system and the optical switching arrangement is measured using the temperature sensor, and the temperature measurement is sent to the controller 24. The controller receives the temperature measurement, and controls the operation of the temperature control system and the temperature sensor, as necessary, until the ambient temperature is set at a minimum desired operating temperature for the optical switching arrangement. The controller 24 activates emission of a signal from a fibre coupled to a first port of the array of input ports 40, and activates the detector of the detector array 46 coupled to a first port of the array of output ports 43. The controller 24 uses a gradient method software algorithm to configure the switching system until a signal maximum is switched from the first input port to the first output port. This involves controlling the operation of the actuator coupled to a MEMS mirror from each of the arrays 41, 42, to adjust the azimuthal and elevational angular positioning of the mirrors whilst the signal received by the port is monitored by the detector. In this case, the signal from the first input port will be incident on the first mirror of the array 41 , and the switching system is configured such that the first mirror of array 41 deflects the signal to the first mirror of array 42, and the first mirror of array 42 then deflects the signal to the first output port. When the controller determines that receipt of a signal maximum is detected by the detector coupled to the first output port, the configuration of the switching system is maintained. The controller 24 then controls operation of the first radiation source of the array of radiation sources 20 (corresponding to the first input port of the array of input ports 40). The radiation from the first radiation source is directed to the radiation detector 23 via the switching system, and the controller 24 controls the operation of the radiation detector 23 to receive the radiation. The x and y co-ordinates of the detected position of the radiation in the detector are sent to the controller 24, where they are recorded in a memory thereof as the expected position in the detector generated for switching of the signal from the first input port to the first output port. The above steps are repeated for each input port to each output port, to generate an expected position for switching of a signal from each input port to each output port for the minimum operating temperature. The expected positions for that temperature are stored as a 2xNxN database in the memory of the controller 24, where N is the number of input ports and the number of output ports. This process is repeated for a number of ambient temperatures, for example 4 or 5, up to a maximum operating temperature of the optical switching arrangement. The expected positions are generated and recorded for each temperature, and the results are interpolated to obtain expected positions for intermediate temperatures with a resolution of 1°C between the minimum and maximum operating temperatures.

Once the expected positions have been generated, the switching system may be subsequently configured for switching of the signal from any input port of the array of input ports to a chosen output port of the array of output ports. For example, the switching system may be configured for switching of the signal from the first input port of the array of input ports 40 to the first output port of the array of output ports 43, as follows. The controller 24 activates the temperature sensor and receives the measurement of the ambient temperature. The controller 24 controls operation of the first radiation source of the array of radiation sources 20 (corresponding to the first input port). The radiation from the first radiation source is directed onto the first optical element 21 of the configuration system, from the first optical element 21 to the first mirror of array 41 , from the first mirror of array 41 to the first mirror of array 42, from the first mirror of array 42 to the second optical element 22, and from the second optical element 22 to the radiation detector 23. The controller 24 controls the operation of the radiation detector 23 to receive the radiation and to send the x and y co-ordinates of the detected position of the radiation to the controller 24. The controller receives the detected position and compares it to an expected position generated when the switching system is configured for switching of a signal from the first input port to the first output port at the same temperature as the measured ambient temperature. If the two positions are not at least substantially similar, the controller 24 controls the operation of the actuators attached to the first mirror in each array 41, 42 to adjust their azimuthal and elevational angular positioning. Comparison and adjustment are repeated until the detected and expected positions are at least substantially similar. This sequence of events is controlled using a software control loop algorithm stored in the controller 24. The above process is repeated for each input port signal to be switched to a chosen output port. The required configuration of the switching system can thus be achieved. The configuration of the switching system may also, in the same way, be monitored and maintained or adjusted. The latter may be necessary, for example, as the configuration of the switching system may change due to, for example, drift in the positioning of the mirrors in the arrays 41, 42. Such drift may thus be detected and corrected for as above.

The configuration system also provides for the monitoring of the signals emitted by the array of input ports. The mirror 29 of the signal monitoring system is placed in proximity to the array of input ports 40 of the optical switching arrangement. The mirror has a transmission coefficient of approximately 95% and a reflection coefficient of approximately 5% at the wavelength or wavelengths of the signal emitted from each input port. Most of these signals are transmitted by the mirror, but part thereof is deflected into the detector 30, which determines the power level of each emitted signal. These power level signals are sent to the controller 24, which uses them to check that a signal is emitted from each input port, and compares the signals with one another to check whether the power levels are substantially similar. If either of these is not the case, the controller may send an alarm signal to an operator of a network to which the optical switching arrangement is connected for use. The mirror 31 of the configuration system is placed in proximity to the array of output ports 43. The mirror has a transmission coefficient of approximately 95% and a reflection coefficient of approximately 5% at the wavelength or wavelengths of the signal emitted from each input port. Most of these signals are transmitted by the mirror, but part thereof is deflected by the mirror into the detector 32, which determines the power level of each switched signal. These power level signals are also sent to the controller 24, which uses them to check that each signal from the input ports is switched through the switching system, and compares the signals with one another to check whether the switched power levels are substantially similar. If either of these is not the case, the controller may again send an alarm signal to an operator of a network to which the optical switching arrangement is connected for use.

It will be appreciated that the generation of the expected values of the radiation in the detector may be performed separately from any subsequent configuration of the optical switching arrangement. For example, the expected positions may be generated 'in- factory' before the optical switching arrangement with the configuration system is supplied to a user. In this case the user may purchase the arrangement without the array of detectors 46 coupled to the array of output ports, which will significantly reduce the cost of the arrangement. The required configuration of the switching system of the optical switching arrangement may be specified by the user and also set in the factory. When the user receives the arrangement the configuration may be monitored and maintained as necessary using the expected positions. Alternatively, the user may wish to have the capability of generating the expected positions, and of checking and regenerating these positions as necessary.

Claims

1. A configuration system adapted for use in an optical switching arrangement comprising an array of input ports, an array of output ports and a switching system configurable for switching a signal from each input port to a chosen output port, wherein the configuration system comprises an array of radiation sources, first and second optical elements, a radiation detector and a controller, and each radiation source corresponds to an input port i.e. the radiation from each radiation source and the signal from its corresponding input port are substantially coincident on the first optical element, radiation from each radiation source is directed onto the first optical element, from the first optical element to the switching system, from the switching system to the second optical element and from the second optical element to the radiation detector, the radiation detector receives the radiation and sends the detected position thereof to the controller, and the controller receives the detected position and compares it with an expected position generated when the switching system is configured for switching of a signal from the input port corresponding to each radiation source to a chosen output port, and configures, as necessary, the switching system until the detected position is at least substantially similar to the expected position.

2. A system according to claim 1 in which the array of radiation sources comprises an array of apertures illuminated using one or more sources of radiation.

3. A system according to claim 1 or claim 2 in which the array of radiation sources emit electromagnetic radiation having one or more wavelengths in the infra red or visible regions.

4. A system according to any preceding claim in which the first and second optical elements each comprise a dichroic mirror.

5. A system according to any preceding claim in which the detected position of the radiation in the radiation detector comprises x and y co-ordinates of the position.

6. A system according to any preceding claim in which the radiation detector

comprises a camera, having a resolution in the range 1 to lOμm.

7. A system according to any preceding claim in which the radiation detector comprises a plurality of detecting elements, and the radiation received by the detector illuminates a number of the detecting elements, and the detected radiation appears as a finite spot having a gaussian-like power intensity profile.

8. A system according to claim 7 in which the detected position of the radiation comprises x and y co-ordinates of the position in the radiation detector of the peak intensity of the power intensity profile.

9. A system according to any preceding claim in which the first optical element comprises a mirror, and the array of radiation sources is positioned with respect to the mirror and the array of input ports such that the virtual image of each radiation source in the mirror substantially coincides with its corresponding input port.

10. A system according to any preceding claim in which the controller comprises a digital signal processor integrated circuit.

11. A system according to any preceding claim in which the controller adjusts the positioning of the switching system to configure the optical switching arrangement.

12. A system according to any preceding claim in which the controller uses at least one software algorithm to configure the switching system of the optical switching arrangement.

13. A system according to any preceding claim in which the expected positions each comprise x and y co-ordinates of the position.

14. A system according to any preceding claim in which the expected positions each comprise x and y co-ordinates of an optimum expected position generated when the switching system is configured for optimum switching of a signal from an input port to a chosen output port, i.e. when a signal maximum is received by the chosen output port from the input port.

15. A system according to claim 14 in which the controller controls the generation of the optimum expected positions by using at least one software algorithm to configure the switching system until a signal maximum is received by each output port.

16. A system according to any preceding claim in which the configuration system comprises a detector coupled to each output port of the array of output ports for use in generating the expected positions.

17. A system according to any preceding claim in which the configuration system comprises a temperature control system which controls the ambient temperature around the configuration system, and a temperature sensor used to measure the ambient temperature around the configuration system, and the controller uses the temperature control system and the temperature sensor in order to compare the detected position detected at an ambient temperature to an expected position generated at that temperature or an expected position calculated for that temperature.

18. A system according to any preceding claim in which the configuration system comprises a monitoring system for monitoring the signals from the array of input ports of the optical switching arrangement.

19. A system according to claim 18 in which the monitoring system is used to check that a signal is emitted from each input port, and that each signal emitted from an input port is switched to an output port, and the monitoring system is used to determine the power level of the signal emitted from each input port, and the power level of each signal after it has passed through the switching system.

20. A system according to any preceding claim in which the switching system of the optical switching arrangement comprises first and second arrays of deflection elements, and the signal from a first input port is only incident on a first element in the first array of deflection elements, the signal from a second input port is only incident on a second element in the first array of deflection elements, and so on for all the input ports, each element in the first array of deflection elements deflects its signal to any element in the second array of deflection elements, and the signal from a first element in the second array of deflection elements is only deflected to a first output port in the array of output ports, the signal from a second element in the second array of deflection elements is only deflected to a second output port, and so on for all the elements in the second array of deflection elements.

21. An optical switching arrangement comprising at least one configuration system according to any of claims 1 to 20.

22. A method of configuring an optical switching arrangement according to claim 21 comprising, for each input port signal to be switched to a chosen output port: (a) operating the radiation source corresponding to the input port, (b) directing the radiation from the radiation source onto the first optical element, from the first optical element to the switching system, from the switching system to the second optical element, and from the second optical element to the radiation detector,

(c) operating the radiation detector to receive the radiation and to send the detected position thereof to the controller,

(d) operating the controller to receive the detected position and to compare it to an expected position generated when the switching system is configured for switching a signal from the input port to a chosen output port, and

23. A method according to claim 22 in which configuration of the switching system by the controller comprises adjusting the positioning of the switching system, receiving the detected position of the radiation switched by the newly-positioned switching system, comparing this detected position with the expected position, and repeating this sequence until the detected position is at least substantially similar to the expected position.

24. A method according to claim 22 or claim 23 in which configuration of the switching system by the controller comprises using at least one software algorithm.

25. A method according to any of claims 22 to 24 in which configuration of the switching system is carried out separately for each input port signal to be switched.

26. A method according to claim 25 in which configuration of the switching system comprises sequential activation of the radiation sources.

27. A method according to any of claims 22 to 24 in which configuration of the switching system is carried out substantially simultaneously for all the input port signals to be switched.

28. A method according to claim 27 in which configuration of the switching system comprises substantially simultaneous activation of the radiation sources.

29. A method according to claim 28 in which the radiation emitted from each radiation source comprises a unique constitution, and the radiation detector is configured to detect and to distinguish between each unique constitution of the radiation emitted from the radiation sources.

30. A method according to any of claims 22 to 29 further comprising generating an expected position for switching of a signal from each input port to each output port.

31. A method according to claim 30 in which generation of the expected position for switching of a signal from an input port to an output port comprises coupling the output port to a detector, activating emission of a signal from the input port, activating the detector coupled to the output port, configuring the switching system until the detector detects that the signal is switched to the output port, maintaining this configuration of the switching system, activating the radiation source corresponding to the input port, directing the radiation from the radiation source to the radiation detector via the switching system, activating the radiation detector to receive the radiation, sending the detected position to the controller, and operating the controller to record the detected position as the expected position.

32. A method according to claim 31 in which the switching system is configured until the detector detects that a signal maximum is switched to the output port, achieved by using at least one software algorithm comprising a minimisation algorithm.

33. A method according to any of claims 30 to 32 in which the expected positions are generated at one or more temperatures, and are used to calculate expected positions for one or more other temperatures.

34. A method according to any of claims 30 to 33 in which generation of the expected positions is carried out separately for each position.

35. A method according to any of claims 30 to 33 in which generation of the expected positions is carried out substantially simultaneously for all the positions.

36. A method according to claim 35 in which generation of the expected positions comprises substantially simultaneous activation of the radiation sources.

37. A method according to claim 36 in which the radiation emitted from each radiation source comprises a unique constitution, and the radiation detector is configured to detect and to distinguish between each unique constitution of the radiation emitted from the radiation sources.

38. A method of generating the expected positions in an optical switching arrangement according to claim 21, comprising, for each input port to be switched to an output port: coupling each output port to a detector, activating emission of a signal from the input port, activating the detector coupled to the output port, configuring the switching system until the detector detects that the signal is switched to the output port, maintaining this configuration of the switching system, activating the radiation source corresponding to the input port, directing the radiation from the radiation source to the radiation detector via the switching system, activating the radiation detector to receive the radiation, sending the detected position to the controller, and operating the controller to record the detected position as the expected position.