Optical switch, optical switch control method and communication system

When a light intensity upon a perturbation is detected, an error calculation/correction unit (85) in a control unit (8) corrects and updates the above-described initial manipulated variables based on perturbation manipulated variables and manipulated variables, i.e., operation manipulated variables to obtain the maximum light intensity from the light intensity value at each perturbation manipulated variable, thereby adjusting the tilt angle of a mirror. More specifically, assuming that the time series data of an acquired output light intensity can be approximated to a cosine function, the error calculation/correction unit (85) calculates a phase difference θ between the cosine function and a sine or cosine function used to set x- and y-axis perturbation patterns for a circular trajectory perturbation. Manipulated variables at coordinates defined by the phase difference θ and polar coordinates of a radius voltage to perturb the mirror are calculated. Voltage values at coordinates defined by a function for setting the driving voltages of the mirror (230) are calculated and set as the driving voltages for one output port.

The present patent application is a Utility claiming the benefit of Application No. PCT/JP2007/066109, filed Aug. 20, 2007.

TECHNICAL FIELD

The present invention relates to an optical switch.

BACKGROUND ART

A technique of implementing an optical switch using a micromirror has been proposed (T. Yamamoto, et al., “A three-dimensional MEMS optical switching module having 100 input and 100 output ports”, Photonics Technology Letters, IEEE, Volume 15, Issue: 10).FIG. 37shows a conventional optical switch using a micromirror.

The optical switch shown inFIG. 37includes input ports1a, output ports1b, input-side micromirror array2a, and output-side micromirror array2b. Each of the input ports1aand output ports1bincludes a plurality of optical fibers arrayed two-dimensionally. Each of the micromirror arrays2aand2bincludes a plurality of micromirror devices3aand3barrayed two-dimensionally. The arrows inFIG. 37indicate a light beam traveling direction.

An optical signal which has outgone from a given input port1ais reflected by the mirror of a micromirror device3aof the input-side micromirror array2acorresponding to the input port1aso that the traveling direction changes. As will be described later, the mirror of the micromirror device3ais designed to pivot about two axes so as to direct light reflected by the micromirror device3ato an arbitrary micromirror device3bof the output-side micromirror array2b. The mirror of the micromirror device3bis also designed to pivot about two axes so as to direct light reflected by the micromirror device3bto an arbitrary output port1bby appropriately controlling the tilt angle of the mirror. It is therefore possible to switch the optical path and connect arbitrary two of the input ports1aand output ports1barrayed two-dimensionally by appropriately controlling the tilt angles of mirrors in the input-side micromirror array2aand output-side micromirror array2b.

The most characteristic constituent elements of the optical switch are the micromirror devices3aand3beach having a mirror. In a micromirror device, conventionally, a mirror substrate200having a mirror and an electrode substrate300having electrodes are arranged in parallel, as shown inFIGS. 38 and 39(see the above-described reference).

The mirror substrate200includes a plate-shaped frame portion210, a gimbal220arranged in the opening of the frame portion210, and a mirror230arranged in the opening of the gimbal220. The frame portion210, torsion springs211a,211b,221a, and221b, the gimbal220, and the mirror230are integrally formed from, e.g., single-crystal silicon. For example, a Ti/Pt/Au layer having a three layer structure is formed on the surface of the mirror230. The pair of torsion springs211aand211bconnect the frame portion210to the gimbal220. The gimbal220can pivot about a gimbal pivot axis X inFIG. 38which passes through the pair of torsion springs211aand211b. Similarly, the pair of torsion springs221aand221bconnect the frame portion230to the gimbal220. The mirror230can pivot about a mirror pivot axis Y inFIG. 38which passes through the pair of torsion springs221aand221b. The gimbal pivot axis X and the mirror pivot axis Y are perpendicular to each other. As a result, the mirror230pivots about the two axes which are perpendicular to each other.

The electrode substrate300includes a plate-shaped base portion310, and a terrace-shaped projecting portion320. The base portion310and the projecting portion320are made of, e.g., single-crystal silicon. The projecting portion320includes a second terrace322having a truncated pyramidal shape and formed on the upper surface of the base portion310, a first terrace321having a truncated pyramidal shape and formed on the upper surface of the second terrace322, and a pivot330having a columnar shape and formed on the upper surface of the first terrace321. Four electrodes340ato340dare formed on the four corners of the projecting portion320and the upper surface of the base portion310led out of the four corners. A pair of projecting portions360aand360bare formed on the upper surface of the base portion310to be juxtaposed while sandwiching the projecting portion320. Interconnections370are formed on the upper surface of the base portion310. The electrodes340ato340dare connected to the interconnections370via leads341ato341d. An insulating layer311made of, e.g., silicon oxide is formed on the surface of the base portion310. The electrodes340ato340d, leads341ato341d, and interconnections370are formed on the insulating layer311.

The lower surface of the frame portion210and the upper surfaces of the projecting portions360aand360bare bonded to each other to make the mirror230face the electrodes340ato340dso that the mirror substrate200and the electrode substrate300form a micromirror device shown inFIG. 39. In the micromirror device, the mirror230is grounded. A positive driving voltage is applied to the electrodes340ato340dsuch that an asymmetrical potential difference is generated between them, thereby attracting the mirror230by an electrostatic attraction and making it pivot in an arbitrary direction.

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

In the above-described optical switch, a change in the environment including the ambient temperature and humidity or an external vibration generates a positional error between the input/output ports and the mirrors or changes the tilt angle. This may gradually increase the shift from the optimum mirror tilt angle and result in drift so that the power loss of output light varies over time. If an optical switch used in a general optical network system causes a loss variation, the whole optical network system suffers profound influence. Hence, it is necessary to suppress the loss of optical connection intensity (output light intensity) within a predetermined tolerance.

However, if the drift amount per unit time is large, and no measure to suppress the drift is taken, the optical connection intensity may exceed the loss tolerance. To prevent this, an optical switch employs stabilizing control to obtain a stable optical connection intensity by monitoring the output light intensity. More specifically, the stabilizing control is done in accordance with the following procedure. First, a control device (not shown) for controlling the tilt angles of the mirrors230supplies periodically changing driving voltages to the micromirror devices3aand3b, thereby giving a perturbation (vibration) to the mirrors230. While doing so, an output light measuring device (not shown) provided on the output terminal side of the output ports1bmeasures the output light intensity. Next, the perturbation pattern of the driving voltage and the value of the output light intensity are held in the storage device of the control device. While comparing the maximum values of the perturbation pattern, a driving voltage that obtains a maximum optical connection intensity is calculated as an optimum driving voltage. The optimum driving voltage is obtained using, e.g., a hill-climbing method, in which the maximum value is searched for by perturbing the mirror within a voltage range ±ΔV set based on the initial output voltage and comparing the output intensities. Finally, the obtained optimum driving voltage is sequentially applied to the mirror repeatedly at a predetermined time interval. The optical connection intensity is stabilized by this technique.

In the optimum value search of so-called maximum value comparing type, if, for example, external noise affects the perturbation for the maximum light intensity search, the maximum light intensity may erroneously be recognized, and a wrong optimum driving voltage may be obtained. This problem is inevitable in the maximum value comparing type search.

It is an object of the present invention to calculate an optimum driving voltage even when, e.g., disturbance noise exists.

The above-described optimum value search of maximum value comparing type requires to perform a search a plurality of number of times to obtain an optimum value. Since the perturbation time in one search is about 10 ms, a time of several hundred ms is necessary in total. For this reason, this method is not applicable to a device which needs a switching speed of several ten ms. The application range of the optical switch as a switching device in a communication network apparatus is limited.

It is another object of the present invention to quickly obtain the optimum value of optical connection intensity.

In the above-described optimum value search, generally, the micromirror device3ais perturbed, and an error is detected and corrected based on the power variation at that time, and then, the micromirror device3bis perturbed, and an error is detected and corrected based on the power variation at that time. Since error detection and correction are done in each of the micromirror devices3aand3b, the time required for detection and correction of the optimum value becomes long. Additionally, since the error of each mirror230affects error detection of the other mirrors230, the optimum value detection accuracy is low.

It is still another object of the present invention to shorten the time required for detection and correction of an optimum value. It is still another object of the present invention to improve the optimum value detection accuracy.

Means of Solution to the Problem

In order to solve the above-described problems, according to an aspect of the present invention, there is provided an optical switch characterized by comprising at least one input port which inputs input light, at least one output port which outputs output light, at least one mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the input light input to the input port and making the input light selectively enter an arbitrary one of the at least one output port, a setting unit which sets, on a plane having coordinate axes represented by a manipulated variable Vxand a manipulated variable Vyto tilt the mirror about the x-axis and the y-axis, respectively, a perturbation pattern to change the manipulated variable Vxand the manipulated variable Vyso as to draw a circular trajectory based on a trigonometric function, a perturbation unit which perturbs the mirror by applying voltages to the electrodes based on the perturbation pattern, a detection unit which detects an intensity of output light which is input light input to one input port and output from one output port upon the perturbation of the mirror, and an error calculation/correction unit which calculates manipulated variables to obtain a tilt angle of the mirror corresponding to connection of the input port and the output port using a radius of the circular trajectory and a phase difference angle calculated based on an output light intensity waveform upon the perturbation of the mirror and perturbation waveforms used to draw the circular trajectory.

According to another aspect of the present invention, there is provided an optical switch characterized by comprising at least one input port which inputs input light, at least one output port which outputs output light, a first mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the first mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the input light, a second mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the second mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the light reflected by the first mirror device and outputting the light to the output port, a perturbation unit which perturbs the mirrors of the first mirror device and the second mirror device by applying voltages which periodically change around initial values of the driving voltages, an initial value generation unit which generates the initial values for the first mirror device and the second mirror device, a detection unit which detects an intensity of output light which is input light input to one input port and output from one output port upon the perturbation of the mirror, an error calculation unit which calculates an error of the manipulated variables based on the light intensity detected by the detection unit, and a correction unit which corrects the error based on the initial values using a predetermined time response waveform and updates the initial values, wherein the perturbation of the mirror of the first mirror device, the perturbation of the mirror of the second mirror device, and the detection of the light intensity are performed in synchronism.

According to still another aspect of the present invention, there is provided an optical switch characterized by comprising at least one input port which inputs input light, at least one output port which outputs output light, at least one mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the input light input to the input port and making the input light selectively enter an arbitrary one of the at least one output port, a perturbation unit which perturbs the mirror by applying, to the electrodes, driving voltages corresponding to manipulated variables which change within a predetermined range, a detection unit which detects an intensity of output light which is input light input to one input port and output from one output port upon the perturbation of the mirror, a setting unit which sets a perturbation pattern which changes the manipulated variables within the predetermined range, an error calculation/correction unit which determines a coefficient of each degree of a surface mathematical model assumed for a light intensity distribution in three-dimensional space by identifying a light intensity distribution function surface, and calculates optimum manipulated variables for the input port and the output port based on a maximum value of the surface, the three-dimensional space having coordinate axes represented by a manipulated variable Vxand a manipulated variable Vyto tilt the mirror about the x-axis and the y-axis, respectively, and the output light intensity detected by the detection unit, and a switching unit which applies driving voltages corresponding to the manipulated variables to the electrodes.

According to still another aspect of the present invention, there is provided an optical switch control method characterized by comprising the setting step of setting, for an optical switch including at least one input port which inputs input light, at least one output port which outputs output light, and at least one mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the input light input to the input port and making the input light selectively enter an arbitrary one of the at least one output port, on a plane having coordinate axes represented by a manipulated variable Vxand a manipulated variable Vyto tilt the mirror about the x-axis and the y-axis, respectively, a perturbation pattern to change the manipulated variable Vxand the manipulated variable Vyso as to draw a circular trajectory based on a trigonometric function, the perturbation step of perturbing the mirror by applying voltages to the electrodes based on the perturbation pattern, the detection step of detecting an intensity of output light which is input light input to one input port and output from one output port upon the perturbation of the mirror, and the error calculation/correction step of calculating manipulated variables to obtain a tilt angle of the mirror corresponding to connection of the input port and the output port using a radius of the circular trajectory and a phase difference angle calculated based on an output light intensity waveform upon the perturbation of the mirror and perturbation waveforms used to draw the circular trajectory.

According to still another aspect of the present invention, there is provided an optical switch control method of controlling an optical switch including at least one input port which inputs input light, at least one output port which outputs output light, a first mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the first mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the input light, and a second mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the second mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the light reflected by the first mirror device and outputting the light to the output port, characterized by comprising the first step of generating initial values of the driving voltages for the first mirror device and the second mirror device, the second step of perturbing the mirrors of the first mirror device and the second mirror device by applying voltages which periodically change around the initial values, the third step of calculating an error of the driving voltages based on an intensity of output light which is input light input to one input port and output from one output port upon the perturbation of the mirror, and the fourth step of correcting the error based on the initial values using a predetermined time response waveform and updates the initial values, wherein the second to fourth steps are repeated.

According to still another aspect of the present invention, there is provided an optical switch control method characterized by comprising the perturbation step of, for an optical switch including at least one input port which inputs input light, at least one output port which outputs output light, and at least one mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the input light input to the input port and making the input light selectively enter an arbitrary one of the at least one output port, perturbing the mirror by applying, to the electrodes, driving voltages corresponding to manipulated variables which change within a predetermined range, the detection step of detecting an intensity of output light which is input light input to one input port and output from one output port upon the perturbation of the mirror, the setting step of setting a perturbation pattern which changes the manipulated variables within the predetermined range, the perturbation step of perturbing the mirror based on the perturbation pattern set in the setting step, the error calculation/correction step of determining a coefficient of each degree of a surface mathematical model assumed for a light intensity distribution in three-dimensional space by identifying a light intensity distribution function surface, and calculates optimum manipulated variables for the input port and the output port based on a maximum value of the surface, the three-dimensional space having coordinate axes represented by a manipulated variable Vxand a manipulated variable Vyto tilt the mirror about the x-axis and the y-axis, respectively, and the output light intensity detected by the detection unit, and the switching unit of applying driving voltages corresponding to the manipulated variables to the electrodes.

According to still another aspect of the present invention, there is provided a communication system characterized by comprising a plurality of optical switches connected in series, each optical switch including at least one input port which inputs input light, at least one output port which outputs output light, at least one mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the input light input to the input port and making the input light selectively enter an arbitrary one of the at least one output port, a setting unit which sets, on a plane having coordinate axes represented by a manipulated variable Vxand a manipulated variable Vyto tilt the mirror about the x-axis and the y-axis, respectively, a perturbation pattern to change the manipulated variable Vxand the manipulated variable Vyso as to draw a circular trajectory based on a trigonometric function, a perturbation unit which perturbs the mirror by applying voltages to the electrodes based on the perturbation pattern, a detection unit which detects an intensity of output light which is input light input to one input port and output from one output port upon the perturbation of the mirror, and an error calculation/correction unit which calculates manipulated variables to obtain a tilt angle of the mirror corresponding to connection of the input port and the output port using a radius of the circular trajectory and a phase difference angle calculated based on an output light intensity waveform upon the perturbation of the mirror and perturbation waveforms used to draw the circular trajectory, and a management device which sends a control signal to control the perturbation of the mirror in each of the optical switches without synchronization of the perturbation of the mirror between the optical switches.

According to still another aspect of the present invention, there is provided a communication system characterized by comprising a plurality of optical switches connected in series, each optical switch including at least one input port which inputs input light, at least one output port which outputs output light, at least one mirror device which includes a mirror pivotally supported with respect to an x-axis and a y-axis perpendicular to the x-axis, and electrodes facing the mirror, the mirror device applying driving voltages corresponding to manipulated variables to the electrodes to tilt the mirror, thereby deflecting the input light input to the input port and making the input light selectively enter an arbitrary one of the at least one output port, a perturbation unit which perturbs the mirror by applying, to the electrodes, driving voltages corresponding to manipulated variables which change within a predetermined range, a detection unit which detects an intensity of output light which is input light input to one input port and output from one output port upon the perturbation of the mirror, a setting unit which sets a perturbation pattern which changes the manipulated variables within the predetermined range, an error calculation/correction unit which determines a coefficient of each degree of a surface mathematical model assumed for a light intensity distribution in three-dimensional space by identifying a light intensity distribution function surface, and calculates optimum manipulated variables for the input port and the output port based on a maximum value of the surface, the three-dimensional space having coordinate axes represented by a manipulated variable Vxand a manipulated variable Vyto tilt the mirror about the x-axis and the y-axis, respectively, and the output light intensity detected by the detection unit, and a switching unit which applies driving voltages corresponding to the manipulated variables to the electrodes, and a management device which sends a control signal to control the perturbation of the mirror in each of the optical switches without synchronization of the perturbation of the mirror between the optical switches.

Effects of the Invention

According to the present invention, voltage values on a plane specified by the radius of the circular trajectory and the phase difference angle between a trigonometric function which approximates the time series change in the light intensity upon the perturbation of the mirror and the trigonometric function used to set the perturbation pattern are set as optimum operating voltages. Even when a value deviates from a value that should be obtained due to the influence of disturbance noise at a certain timing, averaging using other acquired light intensities is implemented, and this enables to calculate a driving voltage for maximizing the light intensity. It is therefore possible to improve robustness against disturbance noise.

According to the present invention, perturbation voltages of a helical trajectory or a combined helical trajectory are output based on perturbation voltage patterns. The intensities of output light from the output port corresponding to the perturbation voltages are detected. Based on the combination of the perturbation voltage patterns and output light intensities, the coefficients of the degrees of an appropriate surface mathematical model in three-dimensional space assumed for the light intensity distribution are determined by identifying the surface using the relationship between the voltage outputs in the perturbation voltage patterns and the output light intensities detected in correspondence with the voltage outputs. The maximum value of the surface is obtained by numerical computation, thereby obtaining a control voltage for obtaining the maximum light intensity. It is consequently possible to end a search by one perturbation and implement high-speed switching.

According to the present invention, the perturbation of the mirror of the first mirror device, the perturbation of the mirror of the second mirror device, and light intensity detection are performed in synchronism. The error is corrected based on the initial values using a predetermined time response waveform, and the initial values are updated. This shortens the data collection time and increases the accuracy.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

An optical switch according to the first embodiment of the present invention will be described. The same names and reference numerals as in “Background Art” described with reference toFIGS. 37,38, and39denote the same constituent elements in this embodiment, and a description will be omitted as needed.

As well shown inFIG. 38, four electrodes340ato340dface a mirror230. The mirror230can be tilted in arbitrary directions about x- and y-axes by applying voltages to the electrodes340ato340d. Let θxbe the tilt angle of the mirror230about the x-axis, θybe the tilt angle about the y-axis, and Vxand Vybe the manipulated variables corresponding to the tilt angles θxand θyin a one-to-one correspondence. Voltages V1to V4applied to the electrodes340ato340d, respectively, are given by
V1=V0+Vx(101)
V2=V0+Vy(102)
V3=V0−Vx(103)
V4=V0−Vy(104)

where V0is a bias voltage which improves the linearity from the manipulated variable to the mirror tilt angle.

<Arrangement of Optical Switch>

As shown inFIG. 1, an optical switch10according to this embodiment includes an input port1a, output port1b, input-side micromirror device3a, output-side micromirror device3b, output light measuring device4, and control device5.

The output light measuring device4detects the intensity of output light which has outgone from the output port1band converts it into an electrical signal. The output light measuring device4can have an arrangement for extracting part of output light and measuring the output light intensity using a light-receiving element such as a photodiode.

The control device5includes a driving unit6, detection unit7, control unit8, and storage unit9.

The driving unit6applies driving voltages to the electrodes of the micromirror devices3aand3bto tilt the mirror230to a predetermined angle based on a manipulated variable generated by the control unit8.

The detection unit7detects the output light measurement result of the output light measuring device4when the driving unit6has driven the micromirror devices3aand3b. The detected measurement result is output to the control unit8.

The control unit8is a functional unit for controlling the operation of the entire optical switch and includes at least a switching unit81, perturbation pattern setting unit82, comparison/updating unit83, manipulated variable generation unit84, and error calculation/correction unit85.

When connecting the optical paths of the arbitrary input port1aand the arbitrary output port1b, the switching unit81reads out, from the storage unit9, manipulated variables corresponding to the initial tilt angles of the mirrors230of the micromirror devices3aand3bcorresponding to the ports, and applies driving voltages to the electrodes via the driving unit6.

The perturbation pattern setting unit82is a functional unit which sets a radius voltage Vs for determining the radius of a circle corresponding to the circular trajectory of the mirror230to be perturbed from the initial tilt angle and the number pt of division points (to be referred to as the “number of perturbation points” hereinafter) for the circular trajectory of a perturbation, and generates a manipulated variable based on the circular trajectory. The manipulated variable for each of the micromirror devices3aand3b, which is periodically changed to perturb the mirror230in accordance with the circular trajectory, will be referred to as a perturbation manipulated variable. Perturbation means applying driving voltages generated based on perturbation manipulated variables to the electrodes of the micromirror devices3aand3bso as to rotationally perturb each mirror230from the initial tilt angle. For example, when a micromirror device has the four electrodes340ato340d, as shown inFIGS. 38 and 39, driving voltages generated based on perturbation manipulated variables are applied to them, thereby perturbing the mirror230. In this case, the voltages to be applied to the electrodes are determined in accordance with, e.g., the positional relationship between the electrodes and the mirror230and the perturbation direction of the mirror230. Assume that the electrodes340aand340cdrive the mirror230about the x-axis at the tilt angle θx, and the direction in which the mirror230moves closer to the electrode340ais defined as the positive direction. Assume that the electrodes340band340ddrive the mirror230about the y-axis at the tilt angle θy, and the direction in which the mirror230moves closer to the electrode340dis defined as the positive direction. For example, when the manipulated variable in the x-axis direction is Vx=10 [V], and the perturbation manipulated variable in the y-axis direction is Vy=−20 [V], a voltage of 10 [V] is applied to the electrode340a, and a voltage of 20 [V] is applied to the electrode340d. For example, to increase the linearity from the manipulated variable to the tilt angle using the bias voltage, the manipulated variable is converted into the driving voltage in accordance with equations (101) to (104). When the bias voltage V0=30 [V], V0+Vx=40 [V] is applied to the electrode340a, V0+Vy=10 [V] is applied to the electrode340b, V0−Vx=20 [V] is applied to the electrode340c, and V0−Vy=50 [V] is applied to the electrode340d. The driving unit6converts the manipulated variables to the driving voltages. A voltage to be applied to rotate the mirror230in the x-axis direction will be referred to as an x-axis direction manipulated variable, and a voltage to be applied to rotate the mirror230in the y-axis direction will be referred to as a y-axis direction manipulated variable. The radius voltage Vs and the number pt of driving points set by the perturbation pattern setting unit82are stored in the storage unit9.

The comparison/updating unit83compares a loss variation range estimate ΔPp in the circular trajectory perturbation calculated by the error calculation/correction unit85with a loss variation tolerance ΔP stored in the storage unit9in advance, thereby calculating the radius voltage Vs to be used in the next circular trajectory perturbation. Based on the calculation result, the comparison/updating unit83updates the radius voltage Vs set by the perturbation pattern setting unit82. The updated radius voltage Vs is output to the perturbation pattern setting unit82.

In accordance with the initial manipulated variables representing the initial tilt angles for optical path connection, which are set by the switching unit81for the mirrors230of the arbitrary micromirror devices3aand3bcorresponding to the arbitrary input port1aand the arbitrary output port1bwhen connecting their optical paths, and the perturbation manipulated variables for the perturbation based on the circular trajectory radius voltage Vs and the number pt of driving points set by the perturbation pattern setting unit82, the manipulated variable generation unit84sets manipulated variables to be used to perturb the mirrors230so that the driving unit6applies the driving voltages to the micromirror devices3aand3b.

Based on the output light intensity detection result from the detection unit7upon perturbations of the mirrors230by the manipulated variable generation unit84, the error calculation/correction unit85calculates manipulated variables (to be referred to as “operation manipulated variables” hereinafter) to implement the optimum tilt angles of the mirrors230of the micromirror devices3aand3bcorresponding to the input port1aand output port1bwhose optical paths are connected. The error calculation/correction unit85also calculates the loss variation range estimate ΔPp upon circular trajectory perturbations of the mirrors230. The calculated operation manipulated variables and loss variation range estimate ΔPp are stored in the storage unit9. The loss variation range estimate ΔPp may be input to the comparison/updating unit83.

The storage unit9stores the radius voltage Vs and the number pt of driving points set by the perturbation pattern setting unit82, the preset loss variation tolerance ΔP, the perturbation voltage patterns set by the manipulated variable generation unit84, the operation manipulated variables, and a program for implementing the operation of the optical switch10.

The control device5is formed from a computer including an arithmetic device such as a CPU, a storage device such as a memory or an HDD (Hard Disk Drive), an input device such as a keyboard, mouse, pointing device, buttons, or touch panel to detect external information input, an I/F device which transmits/receives various kinds of information via a communication line such as the Internet, a LAN (Local Are Network), or a WAN (Wide Area Network), and a display device such as a CRT (Cathode Ray Tube), LCD (Liquid Crystal Display), FED (Field Emission Display), or organic EL (Electro Luminescence), and a program installed in the computer. That is, hardware resources and software resources cooperate so that the program controls the hardware resources, and the above-described driving unit6, detection unit7, control unit8, and storage unit9are implemented. The program may be recorded on a recording medium such as a flexible disk, CD-ROM, DVD-ROM, or memory card and provided.

<Operation of Control Device>

The operation of the control device of the optical switch according to this embodiment will be described next with reference toFIG. 3.

First, the switching unit81of the control unit8reads out, from the storage unit9, manipulated variables corresponding to the initial tilt angles of the mirrors230of the micromirror devices3aand3bcorresponding to the input port1aand output port1bwhose optical paths are to be connected, and sets initial manipulated variables. The manipulated variable generation unit84applies driving voltages to the corresponding electrodes of the micromirror devices3aand3bin accordance with the control units (step S0).

Next, the manipulated variable generation unit84of the control unit8applies, via the driving unit6, driving voltages to the corresponding electrodes of the micromirror devices3aand3bbased on the perturbation manipulated variables set by the perturbation pattern setting unit82, thereby perturbing the mirrors230from the initial tilt angles (step S1). A perturbation pattern setting operation for the perturbation will be described later in detail.

When the mirrors230are perturbed, the detection unit7detects the intensity of output light from the output port1bmeasured by the output light measuring device4(step S2). The detected light intensity is input to the error calculation/correction unit85.

When the light intensity at the time of perturbation is detected, the error calculation/correction unit85of the control unit8corrects and updates the above-described initial manipulated variables to manipulated variables for obtaining the maximum light intensity, i.e., operation manipulated variables based on the perturbation manipulated variables and light intensity value corresponding to each perturbation manipulated variable, thereby adjusting the tilt angles of the mirrors230(step S3). The optimum value search operation of the error calculation/correction unit85will be described later in detail. At this time, the error calculation/correction unit85calculates the loss variation range estimate ΔPp upon circular trajectory perturbations of the mirrors230.

When the operation manipulated variables are calculated, the comparison/updating unit83compares the loss variation range estimate ΔPp calculated by the error calculation/correction unit85with the loss variation tolerance ΔP stored in the storage unit9and updates the radius of the circle for the circular trajectory perturbation of the mirror230(step S4). The circular trajectory perturbation radius updating operation will be described later in detail.

If a process except the above-described steps S0to S4is requested (YES in step S5), the control device5performs another process (step S6). If no process except the above-described steps S0to S4is requested (NO in step S5), the control device5returns to the process in step S1and repeatedly performs the above-described process of stably operating the optical switch10(step S6).

The perturbation pattern setting operation of the perturbation pattern setting unit82of the control unit8will be described next in detail. The perturbation pattern setting operation is an operation of setting the perturbation manipulated variables to be supplied to the micromirror devices3aand3bto perturb the mirrors230. This operation will be described using an example in which a perturbation manipulated variable for circular trajectory (to be referred to as a circular trajectory perturbation manipulated variable hereinafter) to be supplied to the arbitrary micromirror device3ais set.

When setting the circular trajectory perturbation manipulated variable of the arbitrary micromirror device3a, the perturbation pattern setting unit82sets an initial value Vx0of the x-axis direction manipulated variable, an initial value Vy0of the y-axis direction manipulated variable, the radius voltage Vs, and the number Pt of driving points of the micromirror device3a, and calculates driving voltages at each driving point i in accordance with equations (1) and (2) below based on these values. Note that the initial values Vx0and Vy0, radius voltage Vs, and number Pt of driving points are stored in the storage unit9in advance. The x- and y-axes are set to be almost parallel to the mirror230and perpendicular to each other.
Vx[i]=Vx0+Vs*sin(i*2π/Pt)  (1)
Vy[i]=Vy0+Vs*cos(i*2π/Pt)+Vs(2)
where i is the identification number of a driving point.

FIGS. 4A and 4Bshows examples of perturbation manipulated variables calculated by equations (1) and (2) assuming that the number of driving points is 20. For the micromirror device3a, a perturbation manipulated variable including manipulated variables arranged in a circular trajectory as shown inFIG. 4Ais set. Similarly, for the micromirror device3b, a perturbation manipulated variable including manipulated variables arranged in a circular trajectory as shown inFIG. 4Bis set. The series of manipulated variables included in a perturbation manipulated variable will be referred to as a perturbation pattern. Each point of the perturbation manipulated variables shown inFIGS. 4A and 4Bindicates a manipulated variable in the x and y direction.

The thus set perturbation patterns are used by the manipulated variable generation unit84in the following way.

Assume that an external optical signal is input to the input port1a, and its optical path is being connected to the output port1b. In this state, the manipulated variable generation unit84perturbs the mirrors230of the micromirror devices3aand3bcorresponding to the ports based on preset perturbation voltage patterns to search for optimum operation manipulated variables which minimize the connection loss of the propagating optical signal. The manipulated variable generation unit84also sets initial values Vx02and Vy02of the manipulated variables of the micromirror device3b, and causes the driving unit6to convert the manipulated variables at the 20 points set by the perturbation manipulated variable of the micromirror device3ainto driving voltages and sequentially output them, thereby perturbing the mirror230. The light intensity of the optical signal measured by the output light measuring device4via the detection unit7at this time is stored in the storage unit9.

After the mirror230is perturbed based on the perturbation pattern set for the micromirror device3a, the manipulated variables of the micromirror device3aare returned to initial values Vx01and Vy01. Then, the micromirror device3bis perturbed, like the micromirror device3a. The light intensity of the optical signal measured by the output light measuring device4via the detection unit7at this time is stored in the storage unit9. When the perturbation of the micromirror device3bhas ended, the manipulated variables of the micromirror device3bare returned to the initial values Vx02and Vy02.

The optimum value search operation of the error calculation/correction unit85will be described next. The perturbation manipulated variables along the x- and y-axes which are almost parallel to the mirror230and perpendicular to each other are calculated using a sine function complying with equation (1) concerning the x-axis direction and a cosine function complying with equation (2) concerning the y-axis direction. At this time, the perturbation patterns along the x- and y-axes are represented by manipulated variables Vx (a) and Vy (b) shown inFIG. 5. When driving voltages corresponding to the manipulated variables are applied in the x- and y-axis directions, the perturbation manipulated variable forms a circular trajectory on a Vx-Vyplane, as shown inFIG. 6. The mirror is perturbed in the circular trajectory, and the output light intensity detected upon making the mirror230pivot by applying driving voltages corresponding to the manipulated variables in the perturbation pattern is stored in the storage unit9.

Assume that the time series data of an acquired output light intensity P indicated by c inFIG. 5can be approximated to a cosine function represented by equation (3) below. A phase difference θ between the cosine function and the sine or cosine function used to set the x- and y-axis perturbation patterns for the circular trajectory perturbation is calculated. This calculation is done by, e.g., the least squares method, FFT of the light intensity P, or the product-sum operation and averaging of the light intensity P and the perturbation manipulated variables.
P=P0+ΔPp·cos(i*2π/Pt−θ)  (3)
where ΔPp is the variation range of the light intensity upon circular trajectory perturbation.

The phase difference calculated by equation (3) is defined as the direction angle θ for obtaining the maximum light intensity P. That is, it means that a driving voltage that ensures the maximum light intensity P exists in a direction d indicated by the arrow inFIG. 6. Hence, the manipulated variable at coordinates defined by polar coordinates represented by the direction angle θ and the radius voltage Vs is calculated. Voltage values at the coordinates defined by the function for setting the driving voltages of the mirror230are calculated and set as the driving voltages for one output port.

Equations (4) and (5) represent manipulated variables on the circular trajectory at the maximum direction angle for the micromirror device3a.
Vxp=Vxo+Vs*sin(θ)  (4)
Vyp=Vyo+Vs*cos(θ)+Vs(5)
where Vxpand Vypare the values of the x- and y-axis direction manipulated variables for obtaining the maximum output light intensity on the circular trajectory.

<Updating Operation of Circular Trajectory Perturbation Radius>

The circular trajectory perturbation radius voltage updating operation will be described next. The comparison/updating unit83compares the loss variation range estimate ΔPp in the circular trajectory perturbation calculated by the error calculation/correction unit85with the loss variation tolerance ΔP stored in the storage unit9, and sets the radius voltage Vs to be used in the next circular trajectory perturbation.

More specifically, based on the loss variation range estimate ΔPp calculated from the value of the output light intensity upon circular trajectory perturbation and the loss variation tolerance ΔP stored in the storage unit9in advance, the comparison/updating unit83calculates a next radius voltage Vs′ by equation (6) below. The comparison/updating unit83updates the radius voltage to be used for the circular trajectory perturbation by decreasing the radius of circular trajectory to be used in the next perturbation if the output light intensity variation range ΔPp is larger than the loss variation tolerance ΔP, and increasing the radius of circular trajectory to be used in the next perturbation if the output light intensity variation range ΔPp is smaller than the loss variation tolerance ΔP.
Vs′=Vs+(ΔP−ΔPp)·k(6)
where k is a parameter to determine the variation range of the radius voltage in one perturbation.

In this way, the comparison/updating unit83updates the radius voltage Vs set by the perturbation pattern setting unit82. The updated radius voltage Vs is output to the perturbation pattern setting unit82and used to set the next circular trajectory perturbation.

FIG. 7shows an experimental result obtained by executing optical connection according to the embodiment and performing stabilizing control of the optical connection intensity. As shown inFIG. 7, it was confirmed that it is possible to calculate a manipulated variable for obtaining the maximum light intensity and maintain the optical connection intensity within the set loss variation tolerance.

The loss variation tolerance ΔP may have a range from a loss variation tolerance minimum value ΔPpmin to a loss variation tolerance maximum value ΔPpmax. In this case, if the loss variation range estimate ΔPp is smaller than the loss variation tolerance minimum value ΔPpmin, the radius voltage is updated by increasing the radius of circular trajectory to be used in the next perturbation. On the other hand, if the loss variation range estimate ΔPp is larger than the loss variation tolerance maximum value ΔPpmax, the radius voltage is updated by decreasing the radius of circular trajectory.

As described above, according to this embodiment, even when a value deviates from a value that should be obtained due to the influence of disturbance noise at a certain timing, averaging using other acquired light intensities is implemented, and this enables to calculate a driving voltage for maximizing the light intensity. It is therefore possible to improve robustness against disturbance noise.

In this embodiment, an example has been described in which two micromirror devices exist. However, the arrangement is also applicable to a wavelength selective switch which arbitrarily switches the wavelength of input light and outputs the light from an output port, as shown inFIGS. 28 and 29to be described later. In this case, each micromirror device included in the wavelength selective switch is perturbed by the same method as described above, and the output light intensity at that time is detected, thereby calculating a driving voltage for maximizing the output light intensity.

Second Embodiment

The second embodiment of the present invention will be described next. The same names and reference numerals as in the first embodiment and “Background Art” described with reference toFIGS. 37,38, and39denote the same constituent elements in the second embodiment, and a description will be omitted as needed.

As shown inFIG. 1, an optical switch according to this embodiment includes an input port1a, output port1b, input-side micromirror device3a, output-side micromirror device3b, output light measuring device4, and control device5.

The control device5includes a driving unit6, detection unit7, storage unit9, and control unit10, as shown inFIG. 8.

The control unit10is a functional unit for controlling the operation of the entire optical switch and includes at least a switching unit101, perturbation pattern setting unit102, manipulated variable generation unit103, and error calculation/correction unit104.

When connecting the optical paths of the arbitrary input port1aand the arbitrary output port1b, the switching unit101reads out, from the storage unit9, manipulated variables corresponding to the initial tilt angles of mirrors230of the micromirror devices3aand3bcorresponding to the ports, and applies driving voltages to the electrodes via the driving unit6.

The perturbation pattern setting unit102is a functional unit which sets a radius voltage Vs for determining the radius of a circle corresponding to the circular trajectory of the mirror230to be perturbed from the initial tilt angle and the number pt of division points (to be referred to as the “number of perturbation points” hereinafter) for the circular trajectory of perturbation, and generates a manipulated variable based on the circular trajectory. The manipulated variable for each of the micromirror devices3aand3b, which is periodically changed to perturb the mirror230in accordance with the circular trajectory, will be referred to as a perturbation manipulated variable. Perturbation means applying driving voltages generated based on perturbation manipulated variables to the electrodes of the micromirror devices3aand3bso as to rotationally perturb each mirror230from the initial tilt angle. For example, when a micromirror device has four electrodes340ato340d, as shown inFIGS. 38 and 39, driving voltages generated based on perturbation manipulated variables are applied to them, thereby perturbing the mirror230. In this case, the voltages to be applied to the electrodes are determined in accordance with, e.g., the positional relationship between the electrodes and the mirror230and the perturbation direction of the mirror230. Assume that the electrodes340aand340cdrive the mirror230about the x-axis at a tilt angle θx, and the direction in which the mirror230moves closer to the electrode340ais defined as the positive direction. Assume that the electrodes340band340ddrive the mirror230about the y-axis at a tilt angle θy, and the direction in which the mirror230moves closer to the electrode340dis defined as the positive direction. For example, when the manipulated variable in the x-axis direction is Vx=10 [V], and the perturbation manipulated variable in the y-axis direction is Vy=−20 [V], a voltage of 10 [V] is applied to the electrode340a, and a voltage of 20 [V] is applied to the electrode340d. For example, to increase the linearity from the manipulated variable to the tilt angle using the bias voltage, the manipulated variable is converted into the driving voltage in accordance with equations (101) to (104). When a bias voltage V0=30 [V], V0+Vx=40 [V] is applied to the electrode340a, V0+Vy=10 [V] is applied to the electrode340b, V0−Vx=20 [V] is applied to the electrode340c, and V0−Vy=50 [V] is applied to the electrode340d. The driving unit6converts the manipulated variables to the driving voltages. A voltage to be applied to rotate the mirror230in the x-axis direction will be referred to as an x-axis direction manipulated variable, and a voltage to be applied to rotate the mirror230in the y-axis direction will be referred to as a y-axis direction manipulated variable. The radius voltage Vs and the number pt of driving points set by the perturbation pattern setting unit102are stored in the storage unit9.

In accordance with the initial manipulated variables generated by the switching unit101which sets, for optical path connection, the initial tilt angles of the mirrors230of the arbitrary micromirror devices3aand3bcorresponding to the arbitrary input port1aand the arbitrary output port1bwhen connecting their optical paths, and the perturbation manipulated variables for the perturbation based on the perturbation pattern setting unit102, the manipulated variable generation unit103generates the manipulated variables of the mirrors230so that the driving unit6applies the driving voltages to the micromirror devices3aand3b.

Based on the output light intensity detection result from the detection unit7upon perturbations of the mirrors230by the manipulated variable generation unit103, the error calculation/correction unit104calculates manipulated variables (to be referred to as “operation manipulated variables” hereinafter) to implement the optimum tilt angles of the mirrors230of the micromirror devices3aand3bcorresponding to the input port1aand output port1bwhose optical paths are connected, thereby correcting and updating the initial manipulated variables. The operation manipulated variables are stored in the storage unit9.

The control device5is formed from a computer including an arithmetic device such as a CPU, a storage device such as a memory or an HDD (Hard Disk Drive), an input device such as a keyboard, mouse, pointing device, buttons, or touch panel to detect external information input, an I/F device which transmits/receives various kinds of information via a communication line such as the Internet, a LAN (Local Are Network), or a WAN (Wide Area Network), and a display device such as a CRT (Cathode Ray Tube), LCD (Liquid Crystal Display), FED (Field Emission Display), or organic EL (Electro Luminescence), and a program installed in the computer. That is, hardware resources and software resources cooperate so that the program controls the hardware resources, and the above-described driving unit6, detection unit7, storage unit9, and control unit10are implemented. The program may be recorded on a recording medium such as a flexible disk, CD-ROM, DVD-ROM, or memory card and provided.

The perturbation pattern setting operation of the perturbation pattern setting unit102will be described next.

The perturbation pattern setting unit102generates a perturbation manipulated variable pattern to perturb a mirror based on an x-axis direction manipulated variable Vxo, y-axis direction manipulated variable Vyo, perturbation range ΔV, and the number Pt of perturbation points, which have initial values input by the user in advance for the start of perturbation.

A first example will be described in which setting the perturbation range ΔV to ΔVx1in the x-axis direction and ΔVy1in the y-axis direction of the micromirror device3a, and ΔVx2in the x-axis direction and ΔVy2in the y-axis direction of the micromirror device3b, perturbation manipulated variables are set at 25 points on a helical pattern. Note that the x- and y-axes are set to be almost parallel to the mirror230and perpendicular to each other. For the micromirror device3a, the pattern in the range defined by ΔVx1and ΔVy1is divided at 25 points at a predetermined interval, thereby setting the perturbation manipulated variables, as shown inFIG. 9A. For the micromirror device3bas well, the pattern in the range defined by ΔVx2and ΔVy2is divided at 25 points at a predetermined interval, thereby setting the perturbation manipulated variables, as shown inFIG. 9B. Each point of the perturbation manipulated variables shown inFIGS. 9A and 9Bindicates a manipulated variable in the x and y direction.

A second example of perturbation pattern setting will be described in which perturbation manipulated variables are set at 20 points on a combined helical pattern. In this case, the perturbation pattern setting unit102sets the initial value of a first helical pattern having a trajectory from the outside to the center and the final value of a second helical pattern having a trajectory from the center to the outside to the same manipulated variable, and the final value of the first helical pattern and the initial value of the second helical pattern to the same manipulated variable so that the manipulated variable sequentially changes from the first helical pattern to the second helical pattern. More specifically, for the micromirror device3a, the perturbation manipulated variables are set in a perturbation pattern as shown inFIG. 10A. For the micromirror device3bas well, the perturbation manipulated variables are set in a perturbation pattern as shown inFIG. 10B.

Assume that an external optical signal is input to the input port1a, and its optical path is being connected to the output port1b. In this state, the manipulated variable generation unit103perturbs the mirrors230of the micromirror devices3aand3bcorresponding to the ports based on preset perturbation voltage patterns to search for optimum operation manipulated variables which minimize the connection loss of the propagating optical signal. The manipulated variable generation unit103also sets initial values Vx02and Vy0.2of the perturbation voltages of the micromirror device3b, and causes the driving unit6to convert the manipulated variables at the 25 points set by the perturbation manipulated variable of the micromirror device3ainto driving voltages and sequentially output them, thereby perturbing the mirror230. The light intensity of the optical signal measured by the output light measuring device4via the detection unit7at this time is stored in the storage unit9.

After the mirror is sequentially moved based on the 25 points set as the perturbation manipulated variables of the micromirror device3a, the manipulated variables of the micromirror device3aare returned to initial values Vx01and Vy01. Then, the micromirror device3bis perturbed, like the micromirror device3a. The light intensity of the optical signal measured by the output light measuring device4via the detection unit7at this time is stored in the storage unit9. When the perturbation of the micromirror device3bhas ended, the manipulated variables of the micromirror device3bare returned to the initial values Vx02and Vy02.

<Calculation Operation of Optimum Driving Voltage>

The optimum driving voltage calculation operation of the error calculation/correction unit104will be described next with reference toFIG. 11. An example will be described in which an ellipsoidal quadric surface model to be described below is assumed to be a light intensity distribution function.

First, the switching unit101of the control unit10reads out, from the storage unit9, manipulated variables corresponding to the initial tilt angles of the mirrors230of the micromirror devices3aand3bcorresponding to the input port1aand output port1bwhose optical paths are to be connected, and sets initial manipulated variables. The manipulated variable generation unit103applies driving voltages to the corresponding electrodes of the micromirror devices3aand3bin accordance with the control units (step S10).

The perturbation pattern setting unit102causes the driving unit6to sequentially apply the driving voltages in accordance with the set perturbation manipulated variables. The output light intensity measured via the detection unit7at this time is stored in the storage unit9. Next, the error calculation/correction unit104reads out, from the storage unit9, perturbation voltage patterns Vx[i] and Vy[i] set by the perturbation pattern setting unit102and an output light intensity P[i] (step S11). In this case, i represents the number of driving points.

The error calculation/correction unit104substitutes data to an ellipsoidal quadric surface equation given by
P[i]=a×Vx[i]2+b×Vx[i]+c×Vy[i]2+d×Vy[i]+e
[i=0, . . . , ]  (7)
where coefficientsa, b, c, d, and e are parameters representing the shape of the ellipsoidal quadric surface (step S12).

After substituting the data, the error calculation/correction unit104reads out, from the storage unit9, the perturbation voltage patterns of the micromirror device3aand the corresponding output light intensity information as sequence data Vx[0] to Vx[n], Vy[0] to Vy[n], and P[0] to P[n], and substitutes them to the ellipsoidal quadric surface equation to create simultaneous linear equations (step S13).

The simultaneous linear equations are solved by numerical computation using, e.g., the least squares method, thereby calculating a coefficient matrix [a,b,c,d,e] (step S14). When the coefficient matrix is calculated, the error calculation/correction unit104calculates optimum manipulated variables (step S15). For the ellipsoidal quadric surface set as the model, an optimum manipulated variable Vxp1is calculated as −b/2a, and Vyp1is calculated as −d/2c. For the micromirror device3bas well, Vxp2and Vyp2can be calculated by the same method. The initial manipulated variables are updated by the thus calculated optimum manipulated variables Vxp1, Vyp1, Vxp2, and Vyp2. When converted driving voltages are applied to the micromirror devices3aand3b, output light having the maximum light intensity can be obtained.

FIG. 12shows an experimental result obtained by executing optical connection according to the embodiment. InFIG. 12, e represents the output light intensity, and f represents the driving voltage updating section of the micromirror device3a. As is apparent fromFIG. 12, it was confirmed that it is possible to calculate a driving voltage for obtaining the maximum light intensity and implement a high-speed switching operation.

As described above, according to this embodiment, perturbation manipulated variables of a helical trajectory or a combined helical trajectory are output based on the perturbation voltage patterns set by the perturbation pattern setting unit102, and the intensities of output light from the output port corresponding to the perturbation manipulated variables are detected. The error calculation/correction unit104determines, based on the combination of the perturbation voltage patterns and output light intensities, the coefficients of the degrees of an appropriate surface mathematical model in three-dimensional space assumed for the light intensity distribution by identifying the surface using the relationship between the voltage outputs in the perturbation voltage patterns and the output light intensities detected in correspondence with the voltage outputs, and obtains the maximum value of the surface by numerical computation, thereby obtaining a control voltage for obtaining the maximum light intensity. It is consequently possible to end the search by one perturbation and implement high-speed switching.

Use of the helical trajectory combined perturbation voltage pattern of this embodiment allows to reduce the driving speed near the end point of the helical trajectory. This makes it possible to reduce residual vibration after the perturbation and decrease the time lag until control voltage applying to move to the optimum value. It is therefore possible to implement a quicker switching operation.

In this embodiment, a helical trajectory or a combined helical trajectory is set as a perturbation voltage pattern. However, various kinds of geometrical trajectories can be adopted without departing from the spirit of the embodiment. The function model of the light intensity distribution has been described as an ellipsoidal quadric surface. However, various kinds of surface models can be adopted without departing from the spirit of the embodiment.

In this embodiment, an example has been described in which two micromirror devices exist. However, the arrangement is also applicable to a wavelength selective switch which arbitrarily switches the wavelength of input light and outputs the light from an output port, as shown inFIGS. 28 and 29to be described later. In this case, each micromirror device included in the wavelength selective switch is perturbed by the same method as described above, and the output light intensity at that time is detected, thereby calculating a driving voltage for maximizing the output light intensity.

Third Embodiment

The third embodiment of the present invention will be described next. The same names and reference numerals as in the first and second embodiments and “Background Art” described with reference toFIGS. 37,38, and39denote the same constituent elements in the third embodiment, and a description will be omitted as needed.

As shown inFIG. 38, a mirror230is supported by a gimbal220via torsion springs221aand221babout the y-axis. The gimbal220is supported by a frame portion210around the gimbal220via torsion springs211aand211babout the x-axis so that a gimbal structure is formed. The mirror can tilt in arbitrary directions about the x- and y-axes. Let θxand θybe the tilt angles of the mirror230. Four electrodes340ato340dface the mirror230. The mirror230can be tilted by an electrostatic force generated by voltages applied to the electrodes. Voltages V1to V4applied to the electrodes are given by, e.g.,
V1=Vo+Vx(8)
V2=Vo+Vy(9)
V3=Vo−Vx(10)
V4=Vo−Vy(11)

where Vo is a bias voltage which improves the linearity from the electrode application voltage to the mirror tilt angle, and Vx and Vy are manipulated variables corresponding to the tilt angles θx and θy of the mirror in a one-to-one correspondence. It is possible to tilt the mirror230in arbitrary directions by operating Vx and Vy.

FIG. 37shows the arrangement of an optical switch using two micromirror arrays each having the above-described micromirror devices arrayed two-dimensionally. Referring toFIG. 37, an optical signal which has outgone from a given input port1ais reflected by the mirror of a micromirror device3aof an input-side micromirror array2acorresponding to the input port1aso that the traveling direction changes. As will be described later, the mirror of the micromirror device3ais designed to pivot about two axes so as to direct light reflected by the micromirror device3ato an arbitrary micromirror device3bof an output-side micromirror array2b. The mirror of the micromirror device3bis also designed to pivot about two axes so as to direct light reflected by the micromirror device3bto an arbitrary output port1bby appropriately controlling the tilt angle of the mirror. It is therefore possible to switch the optical path and connect arbitrary two of the input ports1aand output ports1barrayed two-dimensionally by appropriately controlling the tilt angles of mirrors in the input-side micromirror array2aand output-side micromirror array2b. An output light measuring device monitors the light intensity of the optical signal which has outgone from the output port1b. Examples of the output light measuring device are a photodiode (PD), or a Tap-PD which guides part of optical power in a fiber to a PD and monitors it.

To adjust the mirror tilt angle to obtain optimum output light power in such an optical switch, a method of perturbing the micromirror devices3aand3band searching for an optimum value based on the power variation of the light intensity at that time is used. In this method, generally, the micromirror device3ais perturbed, and an error is detected and corrected based on the power variation at that time, and then, the micromirror device3bis perturbed, and an error is detected and corrected based on the power variation at that time. Since error detection and correction are done in each of the micromirror devices3aand3b, the time required for detection and correction of the optimum value becomes long. Additionally, since the error of each mirror230affects error detection of the other mirrors230, the optimum value detection accuracy is low.

An object of this embodiment is to shorten the time required for detection and correction of an optimum value. Another object is to improve the optimum value detection accuracy.

<Arrangement of Optical Switch>

As shown inFIG. 1, an optical switch according to this embodiment includes the input port1a, the output port1b, the input-side micromirror device3a, the output-side micromirror device3b, an output light measuring device4, and a control device5. In the optical switch, to adjust the tilt angles of the mirrors230of the micromirror devices3aand3bto obtain an optimum output light intensity, the control device5perturbs each mirror230. The output light measuring device4monitors the output light intensity at that time. The control device5calculates and corrects the tilt angle error based on the measurement result of the output light measuring device4. The tilt angle of each mirror corresponds to a manipulated variable output from the control device5in a one-to-one correspondence. The mirrors230are driven by converting the manipulated variables into voltages to be applied to the electrodes of the mirrors and applying them.

The control device5includes a driving unit6, detection unit7, and control unit11, as shown inFIG. 13.

The control unit11is a functional unit for controlling the operation of the entire optical switch and includes at least an error calculation unit111, correction unit112, initial value generation unit113, perturbation generation unit114, and waveform storage unit115.

The error calculation unit111calculates the error of each manipulated variable based on the output light intensity monitored by the output light measuring device4in synchronism with the perturbation of the mirror230.

The correction unit112corrects and updates initial manipulated variables based on the manipulated variable errors calculated by the error calculation unit111.

The initial value generation unit113sets manipulated variables corresponding to the initial tilt angles of the mirrors230.

The perturbation generation unit114sets manipulated variables to give a periodical perturbation around the manipulated variables generated by the initial value generation unit113.

The waveform storage unit115stores waveforms to perturb the mirrors230, which are set by the perturbation generation unit114.

The control device5is formed from a computer including an arithmetic device such as a CPU, a storage device such as a memory or an HDD (Hard Disk Drive), an input device such as a keyboard, mouse, pointing device, buttons, or touch panel to detect external information input, an I/F device which transmits/receives various kinds of information via a communication line such as the Internet, a LAN (Local Are Network), or a WAN (Wide Area Network), and a display device such as a CRT (Cathode Ray Tube), LCD (Liquid Crystal Display), FED (Field Emission Display), or organic EL (Electro Luminescence), and a program installed in the computer. That is, hardware resources and software resources cooperate so that the program controls the hardware resources, and the above-described driving unit6, detection unit7, and control unit11are implemented. The program may be recorded on a recording medium such as a flexible disk, CD-ROM, DVD-ROM, or memory card and provided.

An operation of adjusting the tilt angle of the mirror230in the optical switch according to this embodiment will be described next with reference toFIG. 14.

First, the initial value generation unit113sets manipulated variables corresponding to the initial tilt angle of each mirror230(step S21). When the initial value generation unit113sets the manipulated variables, the perturbation generation unit114sets manipulated variables to give a periodical perturbation around the manipulated variables. The driving unit6applies driving voltages based on the manipulated variables set by the perturbation generation unit114to the micromirror devices3aand3bto perturb their mirrors230simultaneously. In an example to be explained below, the optical path of a mirror230aof the micromirror device3aand that of a mirror230bof the micromirror device3bare connected, for the descriptive convenience.

When the mirrors230aand230bare perturbed, the error calculation unit111detects the light intensity of output light monitored by the output light measuring device4in synchronism with the perturbations of the mirrors230aand230b(step S22).

Upon detecting the output light intensity, the error calculation unit111calculates manipulated variable errors based on the value of the light intensity (step S23). The perturbations of the mirrors230aand230bare in synchronism so that they perform the perturbation operation simultaneously. The output light measuring device4also monitors the output light intensity in synchronism with the perturbations of the mirrors230aand230b. For example, a light intensity P(t) of output light obtained by giving a perturbation Sin ωt to the mirrors230aand230bhas no time shift, and a power variation during the same time as the perturbation is monitored. The operation of the error calculation unit111will be described later in detail.

When the manipulated variable errors are calculated, the correction unit112corrects and updates the initial manipulated variables based on the errors (step S24). The operation of the correction unit112will be described later in detail.

When the initial manipulated variables are updated, and the process is to be continued (NO in step S25), the control device5returns to the process in step S22. On the other hand, to end the process (YES in step S25), the control device5ends the process.

<Operation of Error Calculation Unit>

The processing operation of the error calculation unit111will be described next in detail.

The output light intensity measured by the output light measuring device4includes the influence of the perturbations of the mirrors230aand230b. For this reason, it is necessary to obtain the manipulated variable errors of each of the mirrors230aand230bbased on the detected light intensity. To do this, both the mirrors230aand230bare perturbed such that the trajectory of the light beam reflected by the mirror forms a conical shape having a vertex on the mirror surface.FIGS. 15A and 15Bshow reflected light beam trajectories upon perturbations of the mirrors.

One mirror will be exemplified. As described above, the mirror can tilt about two axes almost perpendicular to each other on the mirror surface. Tilt angles θx and θy about the axes are controlled by two manipulated variables Vx and Vy. The light beam reflected by the mirror230draws a conical trajectory when Vx and Vy are given by
Vx=Vx0+Vr·Cos(2πft)  (12)
Vy=Vy0+Vr·Sin(2πft)  (13)
where Vx0and Vy0are the initial values of the manipulated variables around which a perturbations is given, and Vr is a parameter to determine the radius of the conical perturbation.

To obtain the manipulated variable errors of the mirrors230aand230b, different frequencies are set for the perturbations of the two mirrors230aand230b, as expressed by
Vx1=Vx10+Vr1·Cos(2πf1t)  (14)
Vy1=Vy10+Vr1·Sin(2πf1t)  (15)
Vx2=Vx20+Vr2·Cos(2πf2t)  (16)
Vy2=Vy20+Vr2·Sin(2πf2t)  (17)
where Vx1and Vy1are the manipulated variables of the mirror230a, Vx2and Vy2are the manipulated variables of the mirror230b, Vx10and Vy10are the initial manipulated variables of the mirror230a, Vx20and Vy20are the initial manipulated variables of the mirror230b, Vr1and Vr2are parameters to determine the conical radius of the perturbation of each mirror, f1is the perturbation frequency of the mirror230a, and f2is the perturbation frequency of the mirror230b.

When the two perturbation frequencies f1and f2are different, the manipulated variable errors of the two mirrors can separately be calculated by, e.g., analyzing the frequency of the optical power response.

The tilt operation of the mirror230about each axis can be modeled by a mass system supported by torsion springs. The mirror230therefore has a dynamic characteristic with a resonance frequency as shown inFIG. 16, which is expressed as a so-called spring-mass system. The above-described perturbation frequency is not limited by the resonance frequency of the mirror230and can also be set to be equal to or higher than the resonance frequency. The higher the perturbation frequency is, the shorter the time required for manipulated variable error detection is.

As the conical radius of the reflected beam trajectory upon perturbation, a suitable value is determined based on optical characteristics including the input/output fiber collimator. More specifically, if the radius is too large, the optical power variation is too large, and nonlinearity needs to be taken into consideration. If the radius is too small, the variation is too small, and the S/N ratio in the optical power response degrades. Hence, the conical radius upon perturbation is preferably constant independently of the dynamic characteristic or perturbation frequency of the mirror230. The conical radius upon perturbation corresponds to the vertical angle of the cone in a one-to-one correspondence. For this reason, when the conical radius is constant, the tilt angle of the mirror230perturbed is also constant. To obtain a constant tilt angle of the perturbed mirror230, voltage setting must be done in consideration of the dynamic characteristic of the mirror230.FIG. 17Ashows the gain characteristic of the tilt angle with respect to the manipulated variable of the mirror about the x-axis. When the perturbation frequency exceeds the resonance frequency, the gain characteristic is lower than 1. To set the perturbation frequency more than the resonance frequency, perturbation voltages need to be higher than in perturbation at a frequency equal to or lower than the resonance frequency in consideration of the gain attenuation. The higher the perturbation frequency is, the larger the gain attenuation is. It is therefore necessary to set high perturbation voltages.

The dynamic characteristic may change between tilt about the x-axis and that about the y-axis of the mirror230, or between the mirrors230aand230b. In this case, since the dynamic characteristic changes between the axes, voltage setting must be done in consideration of the gain characteristic for each axis. For example,FIG. 17Bshows the overlaid dynamic characteristics of the mirror230aabout the x- and y-axes. The resonance frequency about the x-axis is lower than that about the y-axis. For this reason, at a frequency higher than the resonance frequency, the gain attenuation is larger about the x-axis than about the y-axis. The mirror230ais perturbed about the x- and the y-axes at the same frequency. However, when the dynamic characteristic changes, as described above, the voltage for the perturbation about the x-axis must be higher than that for the perturbation about the y-axis. More specifically, to perturb the mirror at a frequency higher than the resonance frequency, it is necessary to set a higher perturbation voltage as the frequency separates from the resonance frequency or a lower perturbation voltage as the frequency becomes closer to the resonance frequency.

The perturbation voltage will be described. As described above, the manipulated variables in perturbation are represented by equations (14) to (17). Vr1and Vr2are manipulated variables associate with the radius of perturbation. The mirror230awill be exemplified. When the above-described equations to calculate the voltages of four electrode are employed, the voltages to be applied to the four electrodes of the mirror230aare given by
V1=Vo+Vx1=Vo+Vx10+Vr1·Cos(2πf1t)  (18)
V2=Vo+Vy1=Vo+Vy10+Vr1·Sin(2πf1t)  (19)
V3=Vo−Vx1=Vo−Vx10−Vr1·Cos(2πf1t)  (20)
V4=Vo−Vy1=Vo−Vy10−Vr1·Sin(2πf1t)  (21)

The radius voltage changes between the x-axis and the y-axis when the dynamic characteristic or perturbation frequency of the mirror230is taken into consideration. Hence, when parameters Vr1x, Vr1y, Vr2x, and Vr2yassociated with the perturbation radius considering the dynamic characteristic are introduced, equations (18) to (21) are rewritten to
Vx1=Vx10+Vr1x·Cos(2πf1t)  (22)
Vy1=Vy10+Vr1y·Sin(2πf1t)  (23)
Vx2=Vx20+Vr2x·Cos(2πf2t)  (24)
Vy2=Vy20+Vr2y·Sin(2πf2t)  (25)
where Vr1x, Vr1y, yr2x, and Vr2yare values obtained by multiplying Vr by the reciprocal of the gain attenuation determined by the dynamic characteristic and perturbation frequency of the mirror. For example, if the gain at the perturbation frequency is 1/10 due to the dynamic characteristic of the mirror, Vr is multiplied by 10.

A method of calculating each manipulated variable error will be described next. An example will be explained in which only the mirror230ais perturbed such that the reflected beam draws a conical trajectory.

The relationship between the tilt angles θx and θy of the mirror230aand the output light intensity exhibits a shape close to a Gaussian distribution whose peak corresponds to the optimum mirror tilt angle at which the output light intensity is maximum. As described above, voltages are applied to the mirror230in consideration of its dynamic characteristic and perturbation frequency such that a predetermined perturbation tilt angle is obtained. More specifically, a perturbation which draws a circular trajectory on a θx-θy plane is given. If a perturbation is given with errors in the tilt angles, the output light intensity exhibits a variation at the same frequency as the perturbation frequency. Upon perturbation in the optimum value direction, the variation of the light intensity is maximum. It is therefore possible to know the peak direction by obtaining the phase difference between the perturbation component and the optical output response.

Since the relationship between the output light intensity and the tilt angles can be approximated to a Gaussian distribution, the ratio of the light intensity variation in perturbation to the tilt angle amplitude of the perturbation corresponds to a value obtained by differentiating the Gaussian distribution by the tilt angle. When the output light intensity is expressed by dBm, the relationship between the tilt angle and the light intensity forms a paraboloid, as shown inFIG. 18. The ratio of the light intensity variation in the perturbation to the amplitude of perturbation at that time represents the differential value of the paraboloid in a plane including the optimum value and the initial tilt angle as the center of the perturbation, as shown inFIG. 19. The tilt angle error amount can be estimated by multiplying the ratio by a constant. This is because the differential value of a parabola with respect to the tilt angle draws a straight line, the differential value is zero at the optimum position, and the tilt angle error is proportional to the differential value. The mirrors is perturbed at a constant perturbation radius. Hence, the error amount can be estimated by multiplying the variation range of the light intensity by a constant. The above-described method enables to estimate the manipulated variable error amount based on the phase and amplitude of the light intensity at the perturbation frequency.

A method of perturbing two mirrors simultaneously and extracting one frequency component from an optical power response in which two frequencies are mixed will be described next. Assume that a light intensity p of output light is given by
p=p1·sin(2πf1t+φ1)+p2·sin(2πf2t+φ2)  (26)
including two frequency components,

where f1is the perturbation frequency of the mirror230a, and f2is the perturbation frequency of the mirror230b. The average of the sums of products of p and cos(2πf1t) is given by

The first term of equation (27) includes a phase φ1and amplitude p1necessary for error calculation. Phase information and amplitude information are obtained using this term. The second, third, and fourth terms are unnecessary. When an appropriate integration time is selected to make these terms zero, the accuracy of the first term increases, and the error detection accuracy can be increased. When the period of the frequency f1is T1=1/f1, and the period of the frequency f2is T2=1/f2, the second, third, and fourth terms are periodical signals having periods ½f1=T1/2, 1/(f2+f1)=T1·T2/(T1+T2), and 1/(f2−f1)=T1·T2/(T1−T2), respectively. Hence, when the least common multiple of T1and T2is selected as the integration time, the second, third, and fourth terms can be made zero. Similarly, when the average value of the sums of products of p and cos(2πf1t) is obtained at a time interval corresponding to the least common multiple of T1and T2, p1·cos(φ1))/2 can be obtained. The amplitude p1and phase φ1can be obtained based on p1·cos(φ1))/2 obtained by the above-described method. For the mirror230bas well, an amplitude p2and phase φ2can be obtained by obtaining the sums of products of each of sin(2πf2t) and cos(2πf2t) at the time interval corresponding to the least common multiple of T1and T2. This method enables more accurate error calculation in a shorter time than FFT or the like. It is also possible to shorten the data collection time and increase the accuracy by acquiring and calculation data at the time interval corresponding to the least common multiple of T1and T2.

Note that the phase information and amplitude information at each perturbation frequency can also be obtained by analyzing the frequency of the optical power response using a general FFT calculation tool. In this case as well, it is possible to increase the accuracy and shorten the data collection time by setting the data interval to the least common multiple of T1and T2.

The phase obtained by equation (27) corresponds to the phase delay from the driving signal of perturbation to the optical power response. Hence, it includes the delay generated by the mirror dynamic characteristic at the perturbation frequency, and the phase representing the optimum value direction generated due to the shift of the initial manipulated variable of the mirror from the optimum value. To accurately obtain the peak direction, the phase delay caused by the dynamic characteristic of the mirror needs to be subtracted from the phase information obtained by the above-described method. This process allows more accurate error detection.

The perturbation frequency f1of the mirror230aand the perturbation frequency f2of the mirror230bcan arbitrarily be selected if they are not equal. At this time, when f1is an integer multiple of f2, or f2is an integer multiple of f1, errors may be generated when obtaining manipulated variable errors from the output light intensity. This is because the output light intensity can include not only the linear combination of a perturbation and a frequency component, as assumed in above description, but also a component corresponding to the nth power of the perturbation. It is therefore preferable to avoid the perturbation frequency combination.

The correction value calculation/updating operation of the correction unit112will be described next.

To calculate a manipulated variable correction value, the variation range of output light intensity is multiplied by a constant. The optimum value of the constant changes depending on the tilt angle when the voltage vs. tilt angle characteristic of the mirror has nonlinearity. Even when the perturbation manipulated variable range does not change, the perturbation tilt angle becomes small if the initial mirror tilt angle is small. Hence, the influence of nonlinearity can be reduced by making the constant larger as the initial value becomes small. Similarly, when the voltage vs. tilt angle characteristic changes between the mirrors, the value of the constant is changed depending on the mirror, i.e., the constant is made large for a mirror whose tilt angle is small even upon applying the same voltage, thereby reducing the influence of the characteristic difference.

When the initial manipulated variable is corrected and updated using the calculated manipulated variable correction value by changing the manipulated variable stepwise, a vibration occurs near the resonance frequency of the mirror. If optical power response data for the next manipulated variable error calculation are collected during the vibration, the error calculation accuracy degrades. To correct the manipulated variable without causing the vibration of the mirror, the initial manipulated variable is corrected not stepwise but in accordance with a waveform without the component near the resonance frequency of the mirror. Use of such a waveform prevents any excitation of the mirror at the resonance frequency and suppresses the vibration in correcting the initial manipulated variable. When the high-frequency component in the waveform is made large, the mirror can be operated at a high speed.

For manipulated variable correction using such a waveform, the control device5stores a coefficient sequence corresponding to the waveform. For example, the time response of the waveform is sampled at a predetermined interval, and the sample values are normalized by the difference between the prestart value and the final value of the waveform. These values are stored in the waveform storage unit115. When the manipulated variable correction value is multiplied by the coefficient sequence stored in the waveform storage unit115, and the product is added to the initial manipulated variable, as shown inFIG. 20, correction using an arbitrary response waveform can be performed.FIG. 21shows an example of a driving voltage waveform obtained by sampling at an interval. This method ensures a high stability without any divergence of the calculation result because the calculation is easy and includes no feedback loop, unlike calculation using an IIR filter.

In the flowchart shown inFIG. 14, when the mirror230starts or stops perturbation, the accuracy of manipulated variable error calculation may degrade because the mirror230moves while vibrating near the resonance frequency. To prevent this, even in the manipulated variable error calculation step and the initial manipulated variable correction/updating step, the perturbation of the mirror230is continuously repeated without stop. This prevents any excitation of vibration of the mirror near the resonance frequency and increases the accuracy. As described above, the output light intensity detection is preferably done at a time interval corresponding to the least common multiple of the perturbation period of the mirror230aand that of the mirror230b. If the perturbation in the first optical power response detection and the perturbation in the second optical power response detection after the first initial manipulated variable correction/updating have a phase shift, the phase shift causes an error in the phase information at the time of calculation. To prevent this, the total time of manipulated variable error calculation and initial manipulated variable correction/updating of one time is preferably an integer multiple of the optical power response detection time to make the phases match, as shown inFIG. 22.

When a perturbation starts in the second step after setting the initial manipulated variables, the mirror vibrates near the resonance frequency. To prevent this, the perturbation preferably starts from the initial manipulated variable setting point in the first step. When the initial manipulated variables are set in the first step, the vibration of the mirror near the resonance frequency is excited. The accuracy can be increased further by starting data acquisition after attenuation of the vibration.

The perturbation radius is set such that the output light intensity variation has a predetermined value when one point on the perturbation trajectory has the optimum value. For example, only the mirror230ais perturbed, and the perturbation radius is determined such that the variation range of the output light power response at that time becomes 0.5 dB. For the mirror230bas well, only the mirror230bis perturbed, and the perturbation radius is set such that the power response variation range at that time becomes 0.5 dB.

If the manipulated variables have errors, and the driving voltages shift from the optimum values, the optical response variation range is larger than the above-described predetermined value, i.e., 0.5 dB in the above example if the perturbation radius is constant, as is apparent from the light intensity distribution described with reference toFIG. 18. Hence, when the variation range of the output light intensity becomes smaller than the predetermined value, it can be determined that the optimum value is obtained, and the process advances to a termination process.

The mirror230vibrates also when the perturbation abruptly stops in the termination process. To avoid this, the perturbation amplitude is reduced over time and finally made zero. This process suppresses an end-time optical power variation. The perturbation amplitude can be reduced either stepwise in each correction cycle from the second step to the fourth step, as shown inFIG. 23A, or over time, as shown inFIG. 23B. In this embodiment, since both the mirrors230aand230bare perturbed simultaneously, and their errors are detected simultaneously, the influence of one mirror's error on the other mirror's error detection accuracy can be reduced, and the accuracy can be increased. For example, when error detection and correction are performed for the mirrors230aand230bin turn, the mirror230bhas an error at the time of error detection of the mirror230a. If the optimum value for the mirror230ais detected in this state, the output light power is maximized in correspondence with a value shifted from the true optimum value due to the influence of the error of the mirror230b. For this reason, the error remains even after correction of the mirror230a. The same error detection accuracy degradation occurs even at the time of error detection of the mirror230b. In this embodiment, however, since the errors of the mirrors230aand230bare detected simultaneously, the accuracy can be improved.

Fourth Embodiment

The fourth embodiment of the present invention will be described next.

As shown inFIGS. 37 to 39, in the conventional optical switch, generally, the mirrors are perturbed to determine the optimum tilt angles to set the optical path between an input port1aand an output port1b. More specifically, a control device (not shown) for controlling the tilt angles of mirrors230supplies periodically changing driving voltages to micromirror devices3aand3b, thereby giving a perturbation (vibration) to the mirrors230. While doing so, an output light measuring device (not shown) provided on the output terminal side of the output ports1bmeasures the output light intensity. The relationship between the driving voltages and the output light intensity is obtained, thereby obtaining optimum driving voltages which ensure the optimum tilt angles of the mirrors230(e.g., driving voltages which maximize the output light intensity).

However, the output light measuring device provided on the output terminal side of the output port1bin the conventional optical switch may measure not only the variation in the output light intensity due to the perturbation of the mirror230but also the variation in the input light intensity. Examples of the input light intensity variation are an intensity variation near the bit rate caused by light modulation and the intensity variation of a low-frequency component caused by the signal periodicity. If the control device obtains the relationship between the driving voltages and the output light intensity in this state, proper driving voltage generation is impossible, and the mirror230cannot be controlled to an optimum angle because of the influence of the variation in the input optical signal strength. For example, if the control device controls the tilt angle of a mirror by obtaining optimum driving voltages based on the relationship between the driving voltages and the output light intensity while the input optical signal strength is varying, the angle actually shifts from the optimum angle by an amount corresponding to the variation in the input optical signal strength. This results in the loss of the output light intensity and may degrade the communication quality.

It is therefore an object of this embodiment to provide an optical switch capable of properly controlling driving of a mirror device without any influence of the variation in the input optical signal strength.

According to this embodiment, it is possible to remove the signal frequency component of an optical signal by determining the tilt angle of a mirror based on a change in the intensity of a signal obtained by removing the signal frequency component of the optical signal from a change in the intensity of the optical signal measured by the output light measuring device. This allows to control driving of a mirror device without any influence of the variation in the optical signal strength. Since any decrease in the intensity of the optical signal to be output can be prevented, degradation in the communication quality can be prevented.

The optical switch according to the fourth embodiment of the present invention will be described below in detail with reference to the accompanying drawings. The same names and reference numerals as in the first to third embodiments and “Background Art” described with reference toFIGS. 37,38, and39denote the same constituent elements in the fourth embodiment, and a description will be omitted as needed.

As shown inFIG. 24, the optical switch according to this embodiment includes the input port1a, the output port1b, the input-side micromirror device3a, the output-side micromirror device3b, an output light measuring device4, a filter12, and a control device5.

The output light measuring device4detects the intensity of output light which has outgone from the output port1band converts it into an electrical signal. The output light measuring device4can have an arrangement for extracting part of output light and measuring the output light intensity using a light-receiving element such as a photodiode.

The filter12removes a predetermined frequency component from the electrical signal generated by the output light measuring device4. An optical signal is modulated by a signal serving as a carrier wave and therefore contains an intensity variation in the frequency band of the signal. To eliminate this, the filter12removes a component near the frequency of the signal used to modulate the light from the electrical signal representing the output light intensity measured by the output light measuring device4. The electrical signal obtained by removing the signal frequency component is sent to a driving voltage determination unit13. As the filter12, for example, a low-pass filter which cuts off components not more than the frequency of the carrier wave is used.

The driving voltage determination unit13determines driving voltages necessary for implementing the pivot angles of the mirrors230to connect the optical path of the output port1bto that of the output port1bbased on the output light intensity measured by the output light measuring device4when the mirrors230are perturbed in accordance with an instruction output to the control device5. The driving voltage determination unit13also outputs an instruction to the control device5to tilt the mirrors230to the determined pivot angles. The mirrors230need not always be perturbed. They need to be perturbed only when determining or correcting the driving voltages.

The control device5supplies the driving voltages to the micromirror devices3aand3bto perturb the mirrors230or tilt the mirrors230to predetermined tilt angles based on the instruction from the driving voltage determination unit13.

In this optical switch, input light which has outgone from the input port1ais reflected by the mirrors of the input-side micromirror device3aand output-side micromirror device3band enters the output port1b. At this time, the driving voltage determination unit13performs the following operation to obtain optimum driving voltages capable of obtaining the pivot angles of the mirrors230at which the output light intensity is maximized. The optimum output light intensity means a light intensity at which the optical loss is minimum or a desired light intensity based on a requirement of the system. A driving voltage for implementing the pivot angle of the mirror230at which such a light intensity is obtained will be referred to as an optimum driving voltage.

The driving voltage determination unit13causes the control device5to supply periodically changing driving voltages to the micromirror devices3aand3bto give a perturbation (vibration) to the mirrors230. The output light measuring device4detects the intensity of output light which has entered the output port1bat this time and converts it into an electrical signal. The filter12removes the signal frequency component of the optical signal from the electrical signal representing the output light intensity measured by the output light measuring device4. The driving voltage determination unit13determines driving voltages to control the mirrors of the micromirror devices3aand3bto proper angles at which the output light intensity has an optimum value based on the signal obtained by causing the filter12to remove the signal frequency component from the electrical signal of the output light measured by the output light measuring device4. This process is performed for each of the micromirror devices3aand3b, and the control device5supplies the obtained driving voltages to the micromirror devices3aand3b.

An example of the method of detecting optimum driving voltages will be described below. As shown inFIGS. 26A and 26B, a perturbation voltage range designated in advance is divided by a series of driving points (a1to a4inFIG. 26A, and b1to e4inFIG. 26B) formed from several points (four points inFIGS. 26A and 26B). The voltages of the driving points are sequentially supplied to perturb the mirrors230. For example, the micromirror device3ashown inFIG. 26Ais driven at the driving point a1. In this state, the micromirror device3bshown inFIG. 26Bis driven at the series of driving points b1to e1. Next, the micromirror device3bis driven at the next series of driving points b2to e2. In this way, the micromirror device3bis driven at all the series of driving points b1to e4. Then, the micromirror device3ais driven at the next driving point a2, and the micromirror device3bis driven at all the series of driving points, as described above. In this way, the micromirror device3bis driven at all the series of driving points b1to e4in correspondence with each of the driving points a1to a4of the micromirror device3a. This enables to drive the micromirror devices3aand3bin all combinations of the driving points. A driving point combination of the micromirror devices3aand3bat which the output light power is optimum is searched for from the measurement result of the output light measuring device4at each driving point. The driving voltages at the driving points are detected as optimum driving voltages.

As described above, according to this embodiment, when causing the control device5to give a perturbation to the mirrors of the micromirror devices3aand3band obtaining driving voltages capable of obtaining the pivot angles of the mirrors230at which the output light intensity is maximized based on the relationship between the driving voltages and the output light intensity, the filter12removes the intensity variation component of the input optical signal. This allows proper driving control of the mirror device. This makes it possible to prevent a decrease in the output light intensity and a degradation in the communication quality.

Note that the functions and effects of this embodiment and the first to third embodiments can be obtained even by combining the fourth embodiment with the above-described first to third embodiments.

Fifth Embodiment

The fifth embodiment of the present invention will be described next. In this embodiment, instead of providing the filter12as in the fourth embodiment, the gain characteristic of an output light measuring device4is appropriately selected, thereby removing the signal frequency component of input light, as shown inFIG. 25. The same names and reference numerals as in the fourth embodiment denote the same constituent elements in the fifth embodiment, and a description will be omitted as needed.

The output light measuring device4of this embodiment uses a light-receiving element4ahaving a frequency response characteristic representing that the gain in the signal frequency band of an optical signal is lower than those in other frequency bands. Generally, when the light-receiving element4aresponds to the signal frequency band of input light, an intensity variation caused by the signal affects the measurement value of the output light measuring device4. When the light-receiving element4ahaving the above-described frequency response characteristic is used, the influence of the signal component of the optical signal can be eliminated or reduced. As the light-receiving element4a, a light-receiving element whose gain characteristic decreases the variation caused by the signal component of an optical signal with respect to the variation tolerance of an optical switch is used. The “variation tolerance” is the allowance ratio with respect to the maximum value of the output light intensity. For example, as shown inFIG. 27, when the variation tolerance is 0.1 dB (about 3%), a light-receiving element whose gain in the signal frequency band is 3% or less, i.e., −16 dB (corresponding to 3%) or less with respect to the DC component is used. This enables to almost eliminate the influence of the intensity variation in the signal frequency band of an optical signal.

In this optical switch, input light which has outgone from an input port1ais reflected by the mirrors of an input-side micromirror device3aand an output-side micromirror device3band enters an output port1b. At this time, a driving voltage determination unit13performs the following operation to obtain optimum driving voltages capable of obtaining the pivot angles of mirrors230at which the output light intensity is maximized.

The driving voltage determination unit13causes a control device5to supply periodically changing driving voltages to the micromirror devices3aand3bto give a perturbation (vibration) to the mirrors230. The output light measuring device4detects the intensity of output light which has entered the output port1bat this time and converts it into an electrical signal. The light-receiving element of the output light measuring device4eliminates or reduces the influence of the signal component of the optical signal in the electrical signal. The driving voltage determination unit13determines driving voltages to control the mirrors of the micromirror devices3aand3bto proper angles at which the output light intensity has an optimum value based on the signal obtained by removing the signal frequency component measured by the output light measuring device4. This process is performed for each of the micromirror devices3aand3b, and the control device5supplies the obtained driving voltages to the micromirror devices3aand3b.

As described above, according to this embodiment, when causing the control device5to give a perturbation to the mirrors of the micromirror devices3aand3band obtaining driving voltages capable of obtaining the pivot angles of the mirrors230at which the output light intensity is maximized based on the relationship between the driving voltages and the output light intensity, the intensity variation component of the input optical signal is removed or attenuated using a light-receiving element having a frequency response characteristic representing that the gain in the signal frequency band of the optical signal is lower than those in other frequency bands. This allows proper driving control of the mirror device. This makes it possible to prevent a decrease in the output light intensity and a degradation in the communication quality.

Note that the functions and effects of this embodiment and the first to fourth embodiments can be obtained even by combining the fifth embodiment with the above-described first to third embodiments.

Sixth Embodiment

The sixth embodiment of the present invention will be described next.FIG. 28is a block diagram schematically showing the arrangement of a wavelength selective switch according to the sixth embodiment of the present invention. In this embodiment, the present invention is applied to a wavelength selective switch (WSS) as a kind of optical switch. Referring toFIG. 28, reference numeral210denotes an input port;211aand211b, output ports;212, a micromirror array;214, a main lens;215, a reflection grating;216, a collimator lens;217aand217b, output light measuring devices provided at the output ports211aand211b, respectively;218, a filter;219, a driving voltage determination unit; and220, a control device. The micromirror array212includes a plurality of micromirror devices213a,213b, and213carrayed one-dimensionally.

The input port210outputs, to the main lens214, a wavelength multiplexed signal221formed by multiplexing a plurality of optical signals having different wavelengths. The wavelength multiplexed signal221which has passed through the main lens214enters the reflection grating215. The wavelength multiplexed signal221which has entered the reflection grating215is reflected by the reflection grating215and demultiplexed into a plurality of optical signals222a,222b, and222chaving different wavelengths. The demultiplexed optical signals222a,222b, and222cpass through the main lens214again and enter the predetermined micromirror devices213a,213b, and213c, respectively.

The optical signals222a,222b, and222care reflected by the mirrors of the corresponding micromirror devices213a,213b, and213c, respectively. Then, the optical signals222a,222b, and222care collimated by the collimator lens216to optical signals223a,223b, and223cand enter the reflection grating215via the main lens214. Each of the optical signals223a,223b, and223cis reflected by the reflection grating215, passes through the main lens214again, and enters one of the plurality of output ports211aand211b. In the example shown inFIG. 28, the optical signals223aand223creflected by the micromirror devices213aand213center the output port211a, and the optical signal223breflected by the micromirror device213benters the output port211b.

In this way, the wavelength multiplexed signal221from the input port210is input to the reflection grating215and demultiplexed into a plurality of optical signals. Each of the demultiplexed optical signals is input to a corresponding one of the micromirror devices213a,213b, and213c. At this time, the control device220appropriately controls the direction of each mirror. An optical signal having a wavelength, or one or a plurality of sets of a plurality of optical signals having different wavelengths are extracted. The optical signals of each set can be combined and input to a desired one of the output ports211aand211b.

Each of the micromirror devices213a,213b, and213chas the same arrangement as that of the micromirror devices3aand3bof the first embodiment.

As in the fourth embodiment, each of the output light measuring devices217aand217bdetects the intensity of output light that has entered the corresponding to one of the output ports211aand211band converts it into an electrical signal.

As in the fourth embodiment, the filter218removes a predetermined frequency component from the electrical signal generated by the output light measuring device217a,217b.

As in the fourth embodiment, the driving voltage determination unit219determines driving voltages to control the mirrors of the micromirror devices213a,213b, and213cto proper angles based on the output light intensity measured by each of the output light measuring devices217aand217bwhen the mirrors of the micromirror devices213a,213b, and213care perturbed in accordance with an instruction output to the control device220.

As in the fourth embodiment, the control device220supplies the driving voltages to the micromirror devices213a,213b, and213cto perturb the mirrors or tilt the mirrors to predetermined tilt angles based on an instruction from the driving voltage determination unit219.

As described above, in the example shown inFIG. 28, the optical signals reflected by the micromirror devices213aand213center the output port211a, and the optical signal reflected by the micromirror device213benters the output port211b. Hence, the driving voltage determination unit219determines the driving voltages to be supplied to the micromirror devices213aand213csuch that the output light intensity detected by the output light measuring device217ais optimum, and the driving voltages of the micromirror device213bsuch that the output light intensity detected by the output light measuring device217bis optimum.

The driving voltage determination unit219causes the control device220to supply periodically changing driving voltages to the micromirror devices213a,213b, and213cto give a perturbation (vibration) to the mirrors. Each of the output light measuring devices217aand217bdetects the intensity of output light which has entered the corresponding one of the output ports211aand211bat this time and converts it into an electrical signal. The filter218removes the signal frequency component of the optical signal from the electrical signal of the output light intensity measured by each of the output light measuring devices217aand217b. The driving voltage determination unit219determines driving voltages to control the mirrors of the micromirror devices213a,213b, and213cto proper angles at which the output light intensity has an optimum value based on the signal obtained by causing the filter218to remove the signal frequency component from the electrical signal of the output light measured by each of the output light measuring devices217aand217b. The control device220supplies the driving voltages determined by the driving voltage determination unit219to the micromirror devices213a,213b, and213cso that the mirrors of the micromirror devices213a,213b, and213cpivot to the pivot angles at which the output light intensity is optimum. In this way, according to this embodiment, the same effects as in the fourth embodiment can be obtained in the wavelength selective switch.

Note that the functions and effects of this embodiment and the first to third embodiments can be obtained even by combining the sixth embodiment with the above-described first to fourth embodiments.

Seventh Embodiment

The seventh embodiment of the present invention will be described next. In this embodiment, instead of providing the filter218in a wavelength selective switch of the seventh embodiment, the gain characteristic of each of output light measuring devices217aand217bis appropriately selected, as in the second embodiment, thereby removing the signal frequency component of input light, as shown inFIG. 29. The same names and reference numerals as in the fourth to sixth embodiments denote the same constituent elements in the seventh embodiment, and a description will be omitted as needed.

As in the fifth embodiment, each of the output light measuring devices217aand217bof this embodiment uses a light-receiving element having a frequency response characteristic representing that the gain in the signal frequency band of an optical signal is lower than those in other frequency bands.

In the example shown inFIG. 29, optical signals reflected by micromirror devices213aand213center an output port211a, and an optical signal reflected by a micromirror device213benters an output port211b, as in the above-described sixth embodiment. Hence, a driving voltage determination unit219determines the driving voltages to be supplied to the micromirror devices213aand213csuch that the output light intensity detected by the output light measuring device217ais optimum, and the driving voltages of the micromirror device213bsuch that the output light intensity detected by the output light measuring device217bis optimum.

The driving voltage determination unit219causes a control device220to supply periodically changing driving voltages to the micromirror devices213a,213b, and213cto give a perturbation (vibration) to the mirrors. Each of the output light measuring devices217aand217bdetects the intensity of output light which has entered the corresponding one of the output ports211aand211bat this time and converts it into an electrical signal. The light-receiving element of each of the output light measuring devices217aand217beliminates or reduces the influence of the signal component of the optical signal in the electrical signal. The driving voltage determination unit219determines driving voltages to control the mirrors of the micromirror devices213a,213b, and213cto proper angles at which the output light intensity has an optimum value based on the signal obtained by removing the signal frequency component measured by each of the output light measuring devices217aand217b. The control device220supplies the driving voltages determined by the driving voltage determination unit219to the micromirror devices213a,213b, and213cso that the mirrors of the micromirror devices213a,213b, and213cpivot to the pivot angles at which the output light intensity is optimum.

In this way, according to this embodiment, the same effects as in the fifth embodiment can be obtained in the wavelength selective switch.

InFIGS. 28 and 29, two output ports and three micromirror devices are used. However, the number of output ports and the number of micromirror devices are not limited to those and can freely be set as needed. As a preferable example, micromirror devices equal in number to the wavelengths of optical signals input from the input port are provided, and the number of output ports is set to be equal to or smaller than the number of wavelengths.

Note that the functions and effects of this embodiment and the first to third embodiments can be obtained even by combining the seventh embodiment with the above-described first to third embodiments.

Eighth Embodiment

The eighth embodiment of the present invention will be described next.

As shown inFIGS. 37 to 39, in the above-described optical switch, generally, a control device (not shown) for controlling the tilt angles of mirrors230supplies periodically changing driving voltages to micromirror devices3aand3b, thereby giving a perturbation (vibration) to the mirrors230. While doing so, an output light measuring device (not shown) provided on the output terminal side of an output ports1bmeasures the output light intensity. The relationship between the driving voltages and the output light intensity is obtained, thereby obtaining optimum driving voltages which ensure the optimum tilt angles of the mirrors230(e.g., driving voltages which optimize the output light intensity).

When a perturbation is given, the output light power varies. This variation is very small in one optical switch. However, when a plurality of optical switches as described above are connected in series, like a ring-shaped network, and the perturbations of the switches synchronize, the variation in the output light power is amplified. When the power variation is amplified, the output light power becomes unstable. This makes it difficult to obtain optimum driving voltages and also degrades the communication quality.

This embodiment has been made to overcome the above-described problems, and has as its object to prevent a degradation in communication quality in a communication system formed by connecting a plurality of optical switches in series.

According to this embodiment, the control device can perturb the mirror of a mirror device without any synchronization with other optical switches, thereby preventing amplification of the variation in the output light power. This makes it possible to detect optimum driving voltages and prevent a degradation in communication quality.

The eighth embodiment of the present invention will be described below in detail with reference to the accompanying drawings. The same names and reference numerals as in the first to seventh embodiments and “Background Art” described with reference toFIGS. 37 to 39denote the same constituent elements in the eighth embodiment, and a description will be omitted as needed.

As shown inFIG. 30, the communication system having optical switches according to this embodiment includes optical switches10ato10cwhich are connected in series into a ring shape via a ring-shaped network30, and a management device20connected to the optical switches. The optical switches10ato10chave the same arrangement.

<Arrangement of Optical Switch>

As shown inFIG. 31, an optical switch10which forms each of the optical switches10ato10cincludes an input port1a, the output port1b, the input-side micromirror device3a, the output-side micromirror device3b, an output light measuring device4, and a control device5.

The output light measuring device4detects the power, i.e., intensity of output light which has outgone from the output port1band converts it into an electrical signal. The output light measuring device4can have an arrangement for extracting part of output light and measuring the output light power using a light-receiving element such as a photodiode.

The control device5supplies voltages (to be referred to as “driving voltages” hereinafter) to the micromirror devices3aand3bto tilt the mirrors230to predetermined angles. The control device5also gives a small variation to the driving voltages to perturb the mirrors230based on a control signal from the management device to be described later. At this time, the optimum driving voltages of the mirror devices3aand3bare obtained based on the electrical signal from the output light measuring device4.

<Arrangement of Management Device>

As shown inFIG. 31, the management device20includes an output unit21, signal generation unit22, and control unit23.

The output unit21sends control signals generated by the signal generation unit22to the optical switches10ato10cbased on an instruction from the control unit23.

The signal generation unit22generates a control signal to be sent to each optical switch10to control the perturbation of the mirror230. Each control signal is generated such that the mirrors230of the optical switches10ato10care perturbed without synchronization with the mirrors230of other optical switches10. Synchronization means that the perturbations of the mirrors230of two or more optical switches10match in terms of, e.g., the points of time of generation, generation period, frequency, and phase. If the perturbations of the mirrors230of two or more optical switches synchronize, the variation in the output light power caused by the perturbation of one optical switch is amplified by the perturbations of the other optical switches. For example, if the optical switches10are connected in series into a ring shape via the network30as shown inFIG. 30, and the perturbations of the mirrors230of the optical switches10synchronize, the variation in the output light power of each optical switch10is amplified, and the output light power becomes unstable. In this embodiment, the signal generation unit22generates control signals, and each optical switch10performs a perturbation based on the control signal, thereby preventing synchronization of the perturbations of the optical switches10.

In this embodiment, the management device20specifies the perturbation timing of each mirror230based on a control signal. More specifically, the signal generation unit22generates control signals to perturb the mirrors230of the optical switches10in different periods and not simultaneously with the mirrors230of other optical switches10.

The control unit23sends the control signals generated by the signal generation unit22to the optical switches10ato10cvia the output unit21.

<Operation of Communication System>

The operation of the communication system according to this embodiment will be described next.

First, the management device20causes the signal generation unit22to generate control signals to specify the perturbation timings of the optical switches10ato10cand sends the control signals to the optical switches10ato10cvia the output unit21. The sending is done continuously or at a predetermined interval.

The optical switches10ato10cperform a perturbation operation based on the control signals received from the management device20. More specifically, the control device5supplies driving voltages to each of the input-side micromirror device3aand output-side micromirror device3bto tilt the mirrors of the arbitrary micromirror devices3aand3bto predetermined angles and causes the input light which has outgone from the input port1ato outgo from the specific output port1b. At this time, the control device5gives a small periodical voltage change to the driving voltages to slightly perturb (vibrate) the mirrors230to obtain optimum driving voltages at which the pivot angles of the mirrors230optimize the output light intensity. The perturbation is done at a timing specified by each control signal received from the management device20.

The output light measuring device4measures the power of output light which has entered the output port1bin a perturbed state and outputs the measurement value to the control device5. Based on the measurement value, the control device5detects driving voltages at which the output light power has an optimum value and supplies the driving voltages to the micromirror devices3aand3b. The mirrors of the micromirror devices3aand3bare controlled to the angles at which the power of output light which has outgone from the output port1bhas an optimum value.

In this way, the control device5perturbs the mirrors230of the micromirror devices3aand3bbased on the control signals from the management device20and obtains optimum driving voltages capable of obtaining an optimum output light power based on the relationship between the driving voltages and the output light power. The control signal of each optical switch10is generated such that the perturbation period does not overlap with those of the remaining optical switches10. Hence, the mirror230of each of the optical switches10ato10cis perturbed without synchronization with the mirrors230of other optical switches10. Hence, only one optical switch10performs a perturbation at a time. This prevents synchronization of the perturbations of the mirrors230of the optical switches10ato10c. Since the variation in the output light power stabilizes, optimum driving voltages can be detected, and the degradation in the communication quality can be prevented.

The optimum output light power means an output light power at which the optical loss with respect to the input light is minimum or a desired output light power based on a requirement of the system. A driving voltage for implementing the pivot angle of a mirror at which such an output light power is obtained will be referred to as an optimum driving voltage.

In this embodiment, the signal generation unit22generates a control signal associated with the timing of a perturbation. However, the signal generation unit22may generate a signal to specify not the timing but the frequency or phase of a perturbation.

For example, when control signals to specify frequencies are generated, the control device5of each of the optical switches10ato10cperturbs the mirror230at the frequency specified by the control signal. Each control signal is generated such that the frequency at which the mirror230is perturbed is different from those of the remaining control signals and is not an integer multiple of each of the perturbation frequencies specified by the remaining control signals. Hence, the mirror230of each of the optical switches10ato10cis perturbed at different frequencies. This prevents synchronization of the perturbations of the mirrors230of the optical switches10ato10c. It is consequently possible to prevent the degradation in the communication quality.

For example, when control signals to specify phases are generated, the control device5of each of the optical switches10ato10cperturbs the mirror230at the phase specified by the control signal. Each control signal is generated by, e.g., adding time lags to signals of the same frequency such that the phase of the perturbation of the mirror230shifts from those of the remaining control signals. Hence, the mirrors230of the optical switches10ato10care perturbed with phase shifts, respectively. This prevents synchronization of the perturbations of the mirrors230of the optical switches10ato10cwith zero phase difference. It is consequently possible to prevent the degradation in the communication quality.

As described above, according to this embodiment, the management device20generates control signals to perturb the mirrors230of the optical switches10ato10casynchronously with the mirrors230of other optical switches10. This prevents synchronization of the perturbations in the optical switches10ato10cand consequently prevents the degradation in the communication quality.

Note that the functions and effects of this embodiment and the first to third embodiments can be obtained even by combining the eighth embodiment with the above-described first to third embodiments.

Ninth Embodiment

The ninth embodiment of the present invention will be described next. In this embodiment, instead of providing the management device20as in the eighth embodiment, an input light measuring device14and a detection device15are arranged in each optical switch10, as shown inFIG. 32. Each optical switch10performs a perturbation based on the measurement result of the detection device15. The remaining components are the same as in the eighth embodiment. The same names and reference numerals as in the eighth embodiment denote the same constituent elements in the ninth embodiment, and a description will be omitted as needed.

The input light measuring device14measures the power of input light to be input to an input port1a. The input light measuring device14can have an arrangement for extracting part of input light and measuring the input light power using a light-receiving element such as a photodiode.

The detection device15detects, based on the measurement result of the input light measuring device14, the presence/absence of the perturbation of a mirror in another optical switch10, the perturbation frequency, and the perturbation phase.

<Operation of Optical Switch>

The operation of the optical switch10according to this embodiment will be described next.

To perform the switching operation of the optical switch10, a control device5supplies driving voltages to an input-side micromirror device3aand an output-side micromirror device3bto tilt the mirrors of the arbitrary micromirror devices3aand3bto predetermined angles and causes the input light which has outgone from the input port1ato outgo from a specific output port1b. At this time, the control device5gives a small periodical voltage change to the driving voltages to slightly perturb (vibrate) mirrors230based on the detection result of the perturbation of each mirror230detected by the detection device15, to obtain driving voltages at which the pivot angles of the mirrors230optimize the output light intensity. In the following explanation, the optical switch10sequentially sets the following three states to perform a perturbation at a timing different from those of other optical switches10without synchronization with the perturbations of the mirrors230of the other optical switches10. The three states are “perturbation” in which a perturbation is performed, “measurement” in which the state of the optical switch10of the preceding state is measured, and “standby” in which neither perturbation nor measurement is done. The transition of the three states will be described with reference toFIG. 33.

When optical switches10ato10care connected in series as shown inFIG. 30, each of the optical switches10ato10cperforms a perturbation, standby, and measurement in this order without overlap with the remaining optical switches10, as shown inFIG. 33, thereby preventing synchronization with the perturbations of the remaining optical switches10.

Assume that the optical switch10ais performing a perturbation in Phase1. At this time, the optical switch10bof the succeeding stage of the optical switch10ameasures the variation in the output light power of the optical switch10aand detects the presence/absence of the perturbation of the optical switch10a. The optical switch10cof the succeeding stage of the optical switch10bstands by for a predetermined time.

When the perturbation of the optical switch10aends, the state shifts to Phase2. In Phase2, the optical switch10astands by for a predetermined time. The predetermined standby time can freely be set to, e.g., the perturbation time of the optical switch10a. Upon detecting based on the variation in the output light power of the optical switch10athat the perturbation of the optical switch10ahas ended, the optical switch10bstarts a perturbation. The perturbation is done for a predetermined time. After standing by for a predetermined time, the optical switch10cmeasures the variation in the output light power of the optical switch10bof the preceding stage and detects the presence/absence of the perturbation of the optical switch10bof the preceding stage.

When the perturbation of the optical switch10bends, the state shifts to Phase3. In Phase3, after standing by for a predetermined time, the optical switch10ameasures the variation in the output light power of the optical switch10cof the preceding stage and detects the presence/absence of the perturbation of the optical switch10cof the preceding stage. When the perturbation has ended, the optical switch10bstands by for a predetermined time. Upon detecting based on the variation in the output light power of the optical switch10bthat the perturbation of the optical switch10bhas ended, the optical switch10cstarts a perturbation.

In this way, the optical switches10ato10csequentially selectively perform “perturbation”, “standby”, and “measurement” in Phases. Each of the optical switches10ato10ccan perform the perturbation without overlap with the remaining optical switches10This prevents synchronization of the perturbations of the mirrors230of other optical switches10. It is consequently possible to prevent the degradation in the communication quality.

When the detection device15detects the frequency of the perturbation of the optical switch10of the preceding stage, the control device5perturbs the mirror230at a frequency which is different from the detected frequency and is not an integer multiple of it. The optical switches10perturb the mirrors230at different frequencies. This prevents synchronization of the perturbations of the plurality of optical switches10even when they are connected in series. It is consequently possible to prevent the degradation in the communication quality.

When the detection device15detects the phase of the perturbation of the optical switch10cof the preceding stage, the control device5perturbs the mirror230at a phase shifted from the detected phase. The optical switches10perturb the mirrors230at different phases. This prevents synchronization of the perturbations of the plurality of optical switches10even when they are connected in series. It is consequently possible to prevent the loss of the output light power.

As described above, according to this embodiment, the input light measuring device14detects perturbation information about the perturbation of the optical switch10of the preceding stage. This makes it possible to perturb the mirror230without synchronization with the remaining optical switches10. Since the variation in the output light power stabilizes, optimum driving voltages can be detected, and the degradation in the communication quality can be prevented.

Note that the functions and effects of this embodiment and the first to third embodiments can be obtained even by combining the ninth embodiment with the above-described first to third embodiments.

The 10th embodiment of the present invention will be described next.

In the optical switch shown inFIGS. 37 to 39, a change in the environment including the ambient temperature and humidity generates a positional error between the input/output ports and the mirrors or changes the mirror tilt angle. This gradually increases the shift from the optimum mirror tilt angle and results in drift so that the power loss of output light varies over time.

However, if the drift per unit time is large, the relationship between voltages applied to electrodes340ato340dand the output light intensity largely changes even during a perturbation. This may lead to find a wrong maximum value of output light intensity.

For example, if the voltages applied to the electrodes340ato340dand the output light intensity have the relationship shown inFIG. 40A, the maximum value of the light intensity within a range ΔV from a voltage V1[V] to a voltage V2[V] is a light intensity I2at the voltage V2. However, if the shift amount from the optimum mirror tilt angle per unit time largely drifts, for example, a light intensity I1at time t=0 is erroneously determined as the maximum value, although the actual maximum value is a light intensity I4at time t=2Δt after the sampling time, as shown inFIG. 40B. In this case, it is also impossible to search for driving voltages at which the light intensity is maximum because the range ΔV is narrow.

It is an object of this embodiment to provide an optical switch capable of accurately searching for the optimum posture of a deflecting element.

According to this embodiment, a predetermined range is set based on the change amount of the mirror tilt angle per unit time. This makes it possible to search for the maximum value of output light power without any influence of drift and consequently accurately search for the optimum deflection angle of a mirror.

This embodiment will be described below in detail with reference to the accompanying drawings. The same names and reference numerals as in the first to ninth embodiments and “Background Art” described with reference toFIGS. 37 to 39denote the same constituent elements in this embodiment, and a description will be omitted as needed.

<Arrangement of Optical Switch>

As shown inFIG. 34A, an optical switch10according to this embodiment includes an input port1a, output port1b, input-side micromirror device3a, output-side micromirror device3b, output light measuring device4, and control device5.

The output light measuring device4detects the intensity of output light which has outgone from the output port1band converts it into an electrical signal. The output light measuring device4can have an arrangement for extracting part of output light and measuring the output light intensity using a light-receiving element such as a photodiode.

The control device5includes a driving unit6, detection unit7, control unit16, and storage unit9.

The driving unit6supplies driving voltages to the micromirror devices3aand3bto tilt mirrors230to predetermined angles or give a very small variation to the driving voltages and perturb the mirrors230based on an instruction from the control unit16.

The detection unit7detects the output light measurement result of the output light measuring device4when the driving unit6has driven the micromirror devices3aand3b. The detected measurement result is output to the control unit16.

The control unit16is a functional unit for controlling the operation of the entire optical switch10and includes at least a search setting unit161, perturbation unit162, error calculation/correction unit163, and switching unit164.

The search setting unit161is a functional unit which sets the perturbation range and time of the mirror230to be perturbed by the perturbation unit162in accordance with the drift amount of the power loss of output light. The search setting unit161includes a measuring unit161awhich measures the drift amount of the power loss of output light at a predetermined unit time (to be referred to as a “sampling time” hereinafter) interval, a range setting unit161bwhich sets a predetermined range (to be referred to as a “search range” hereinafter) in which the mirror230is to be perturbed based on the measurement result of the measuring unit161a, and a time setting unit161cwhich sets a predetermined time (to be referred to as a “search time” hereinafter) in which the mirror230is to be perturbed based on the measurement result of the measuring unit161a. The search range means the range of a periodically changing manipulated variable (to be referred to as a “perturbation manipulated variable” hereinafter) to be supplied to each of the micromirror devices3aand3bto perturb the mirrors230. The search time means the time required to perturb the mirrors230based on all perturbation manipulated variables set within the search range. Perturbation means supplying driving voltages converted from manipulated variables to the electrodes of the micromirror devices3aand3bso as to perturb the mirrors230. For example, when a micromirror device has the four electrodes340ato340d, as shown inFIGS. 5 and 6, perturbation manipulated variables are supplied to them, thereby perturbing the mirror230. The search range and search time set by the search setting unit161are stored in the storage unit9.

When connecting the optical paths of the arbitrary input port1aand the arbitrary output port1b, the perturbation unit162sets perturbation manipulated variables to perturb the mirrors230based on the search range set by the range setting unit161b, and supplies the perturbation manipulated variables to the micromirror devices3aand3bvia the driving unit6. The perturbation manipulated variable supply is done to perturb the mirrors230based on the perturbation manipulated variables within the search time set by the time setting unit161c.

The error calculation/correction unit163detects, from the output light intensity detection result of detection unit7when the perturbation unit162has perturbed the mirrors230, driving voltages (to be referred to as “operation manipulated variables” hereinafter) for implementing the optimum deflection angles, i.e., tilt angles of the mirrors230to connect the optical paths of the arbitrary input port1aand the arbitrary output port1b.

When connecting the optical paths of the arbitrary input port1aand the arbitrary output port1b, the switching unit164supplies the operation manipulated variables to the corresponding micromirror devices3aand3bvia the driving unit6based on the operation manipulated variables stored in the storage unit9.

The storage unit9stores the search range and search time set by the search setting unit161, the perturbation manipulated variables set by the perturbation unit162, and a program for implementing the operation of the optical switch10.

The control device5is formed from a computer including an arithmetic device such as a CPU, a storage device such as a memory or an HDD (Hard Disk Drive), an input device such as a keyboard, mouse, pointing device, buttons, or touch panel to detect external information input, an I/F device which transmits/receives various kinds of information via a communication line such as the Internet, a LAN (Local Are Network), or a WAN (Wide Area Network), and a display device such as a CRT (Cathode Ray Tube), LCD (Liquid Crystal Display), or FED (Field Emission Display), and a program installed in the computer. That is, hardware devices and software resources cooperate so that the program controls the hardware resources, and the above-described driving unit6, detection unit7, control unit16, and storage unit9are implemented. The program may be recorded on a recording medium such as a flexible disk, CD-ROM, DVD-ROM, or memory card and provided.

The search range and search time setting operation of the search setting unit161will be described next.

First, the measuring unit161aof the search setting unit161measures the drift amount of the power loss of output light at the sampling time interval. This measurement is done based on the measurement result of the output light measuring device4, which is obtained by supplying predetermined operation manipulated variables to the arbitrary micromirror devices3aand3bas the drift amount measurement target to tilt the mirrors230to predetermined angles and connect the optical paths between the micromirror devices and inputting an external optical signal having a predetermined light intensity distribution from the input port1ato the micromirror device3a. That is, the output light intensity is detected at the sampling time interval, and the values at the respective sampling times are compared, thereby measuring the drift amount.

When the drift amount is measured, the range setting unit161bof the search setting unit161sets a search range which is wider than the range of voltages applied to the electrodes340ato340dto tilt the mirrors more than the drift amount, i.e., in an angular shift amount corresponding to the drift. The search range is set for each sampling time. The perturbation unit162sets perturbation manipulated variables based on the search range. The time setting unit161cof the search setting unit161sets the search time to not more than a value obtained by dividing the tilt angle range of the mirror230corresponding to a preset output light power loss amount by the drift amount per sampling time.

Even when drift has occurred, the above-described search range setting enables to search for the peak of the output light intensity in a range wider than the drift. It is therefore possible to search for the optimum posture of the mirror230. The above-described search time setting enables a search at an interval shorter than that for an output light intensity loss of a predetermined value or more. Since a search can be performed near the peak of the output light intensity, it is consequently possible to search for the optimum posture of the mirror230.

An example of the search range and search time setting operation will be described next with reference toFIG. 35.FIG. 35is a graph which shows the drift of the output light loss as a function of time and illustrates the relationship between the output light loss and the tilt angle of the mirror230in a one-dimensional model which increases the pivot angle error in one direction along, e.g., the mirror pivot axis or the gimbal pivot axis. An example will be described with reference toFIG. 35, in which the maximum value of the output light intensity is determined by comparing three points. Hence, curves y1to y3inFIG. 35represent the first search, and y4represents the second search. The symbols inFIG. 35have the following meanings.

Δθ: search range

Δt: sampling time

ΔL: angle corresponding to target loss variation range

TL: search time of one cycle

α: drift time conversion factor per unit time (angle/unit time): a factor obtained by converting the loss drift per unit time into a drift angle

αΔt: drift angle amount in one perturbation time

ΔTL: drift angle amount in one search cycle

The angle-loss distribution in each sampling time represented by each of the curves y1to y4is a quadratic function model. Since a drift angle amount α1is generated in time t, the loss distribution function is as follows.

In this one-dimensional model, the search range and search time are set to satisfy conditions [1] and [2].

[1] A condition to find the peak value by comparing three points in the presence of drift

Since y3>y2, a value found 2Δt after is larger. Hence, the search range is set to not less than the drift angle amount per sampling time, as represented by
Δθ>αΔt(28)

[2] A condition to do a search within the range of the preset loss variation value even in the presence of drift.

The angle corresponding to the preset loss variation value is set to be smaller than the drift angle amount in a time required for one search cycle, as represented by
ΔL>αTL(29)

where ΔL is set based on the operation manipulated variables stored in the storage unit9. For example when the loss variation range is set at 0.5 dB, the value of an angular width corresponding to an angle smaller than the angle at the peak position by 0.5 dB is obtained. The time required for one search cycle is equal to or less than a value obtained by dividing the angular width determined based on the preset loss variation value by the drift factor.

The range setting unit161band time setting unit161cof the search setting unit161set the search range and search time to satisfy the above-described conditions. Hence, even when drift has occurred, it is possible to search for the peak of the output light intensity. This allows to more accurately search for the optimum posture of the mirror230.

The system environment where the optical switch is used may require to prevent the loss variation caused by the perturbation in the search from exceeding a certain preset value. In this case, if the preset value is a “preset perturbation range value”, the search range Δθ is set such that the difference between the maximum value and the minimum value of the loss within the search range Δθ is equal to or smaller than the preset loss range value.

The perturbation operation of the perturbation unit162will be described next.

When the search range is set by the above-described method, the perturbation unit162sets perturbation manipulated variables based on the search range. The perturbation manipulated variables are set for each sampling time. The first perturbation manipulated variables are set based on the search range around the operation manipulated variables stored in the storage unit9in advance. The next perturbation manipulated variables are applied after the elapse of sampling time from the first perturbation manipulated variable application, and set based on the search range set in accordance with the drift amount at that time. For this reason, the search range at this time shifts from the first search range in a predetermined direction or becomes wider than the first search range. The perturbation manipulated variables are values obtained by dividing the set search range at a predetermined interval. A detailed example will be described below.

Assume that the x-direction search range of the micromirror device3ais set to X1, and the y-direction search range is set to Y1. If a perturbation manipulated variable is set in a spiral pattern, the range defined by X1and Y1is divided at a predetermined interval in consideration of the number of turns of the spiral, thereby setting perturbation manipulated variables, as shown inFIG. 36. For the micromirror device3bas well, the perturbation manipulated variables are set in the same way. The spiral pattern indicates the trajectory of a movement which converges into a coil shape while sequentially changing the direction in the x and y directions. More specifically, in the example shown inFIG. 36, the trajectory is drawn by repeatedly moving from an arbitrary point in the positive x direction by an arbitrary distance, moving from that position in the negative y direction by an arbitrary distance, moving from that position in the negative x direction by an arbitrary distance, and moving from that position to an arbitrary position in the y direction while decreasing or increasing the arbitrary moving distance. InFIG. 36, perturbation manipulated variables are set at 25 points. The number of perturbation manipulated variables can freely be set. The pattern of perturbation manipulated variables to be set is not limited to the spiral pattern, and any other pattern such as an almost N-shaped pattern or a lattice pattern can freely be set.

Perturbation manipulated variables are set when connecting the optical paths of the micromirror devices3aand3bby inputting an external optical signal having a predetermined light intensity distribution from the input port1a. The perturbation unit162inputs the external optical signal having a predetermined light intensity distribution from the input port1ato the micromirror device3ato search for optimum operation manipulated variables which minimize the connection loss of the propagating optical signal. The perturbation unit162then perturbs the mirrors230while fixing the perturbation manipulated variables of the micromirror device3bat the outermost peripheral points and sequentially moving through the points where the perturbation manipulated variables of the micromirror device3aare set. The perturbation is performed within the search time while moving through the points. That is, the search of one cycle is done within the search time while performing the perturbation based on all the set perturbation manipulated variables. The light intensity of the optical signal measured by the output light measuring device4via the detection unit7at this time is stored in the storage unit9.

After the perturbation manipulated variables of the micromirror device3aare sequentially moved through the respective set points, the perturbation manipulated variables of the micromirror device3bare moved to the next point. The mirrors230are perturbed while sequentially moving through the points where the perturbation manipulated variables of the micromirror device3aare set. After moving to the final values of the perturbation manipulated variables of the micromirror device3b, the light intensity at each point is stored in the storage unit9. The optimum value detection unit84sets the perturbation manipulated variables corresponding to the maximum value of the light intensities at the respective points, which are stored in the storage unit9, as the optimum operation manipulated variables to connect the optical paths of the arbitrary input port1aand the arbitrary output port1b. The operation manipulated variable search is performed within the search time.

As described above, according to this embodiment, a search range not less than the drift amount in the sampling time is set. This makes it possible to search for the peak of output light without any influence of drift and consequently more accurately search for the optimum posture of the mirror230.

Note that the functions and effects of this embodiment and the first to third embodiments can be obtained even by combining the 10th embodiment with the above-described first to third embodiments.