JP4715099B2 - Light intensity variable device and control method thereof - Google Patents

Description

  The present invention relates to a light intensity variable device used for optical communication and optical information processing, and a control method thereof.

  In the optical communication field, as an effective technique for increasing the transmission capacity, a wavelength multiplexing transmission system that transmits signal light of a plurality of wavelengths through one optical fiber has been put into practical use. An optical fiber amplifier for amplifying the attenuated signal light is required in a wavelength multiplexing transmission system, particularly in a system that performs long-distance transmission and add / drop of signal light of each wavelength (ODAM: Optical Add Drop Multiplexing). Become.

  The gain of the optical fiber amplifier is not always constant with respect to the wavelength, and has a unique wavelength characteristic for each amplifier. For this reason, in the case of using an optical fiber amplifier, in multi-relay transmission and OADM that require multi-stage connection of optical amplifiers, the light intensity is generated depending on the wavelength of the signal light. The case where it disappears occurs. In order to solve this problem, it is necessary to adjust the signal light level of each wavelength channel in accordance with the gain characteristic of the optical fiber amplifier in a single transmission station or a plurality of network nodes (Patent Documents 1, 2, and 5). 3, 4, 5).

  As devices for adjusting the signal light level of each wavelength channel in accordance with an optical fiber amplifier, a variable optical attenuator (VOA), a VMUX (VOA-MUX) combined with a wavelength filter, and the like have been studied. For example, a combination of an arrayed waveguide grating wavelength multiplexer / demultiplexer (AWG) shown in FIG. 7 and a plurality of optical variable attenuators has been proposed as an example of VMUX (see Patent Document 6). ).

  The VMUX includes an AWG composed of two slab waveguides 514 and 512 and an arrayed waveguide 515 for optically connecting them, a plurality of Mach-Zehnder interference type optical attenuators 516 and a light intensity monitor using the thermo-optic effect. Monitor waveguide 517 is formed on the same substrate 520. The light intensity is adjusted by the optical attenuator 516 so that the signal light having each wavelength entered from one end of the substrate 520 can obtain an optimum transmission characteristic according to the gain characteristic wavelength of an optical fiber amplifier (not shown). The light intensity adjustment by the optical attenuator 516 is controlled by a control device (not shown) according to the intensity of the signal light guided through the monitor waveguide 517. In this control, for example, digital or analog PID control is used.

The applicant has not yet found prior art documents related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in this specification.
Japanese Patent Laid-Open No. 10-020348 JP 2000-019471 A JP 2000-180803 A Japanese Patent Laid-Open No. 200303699 JP 2001-339366 A JP 2002-062443 A

  However, in recent optical network communication systems, high-speed and high-precision operation with a response time of about 50 ms and a light intensity variation of about ± 0.1 dB is required in the above-described control of the optical or variable attenuator. However, a control method that satisfies this requirement has not been proposed in the Mach-Zehnder interference type optical attenuator using the thermo-optic effect.

  In the Mach-Zehnder interference type optical attenuator using the thermo-optic effect, it is necessary to control the temperature of the heater, and generally PI or PID control is used. However, in this control, the determination of the control factor is empirical and cumbersome, and the high speed is not always satisfied. In addition, a control method having tolerance is not clarified with respect to variations in the response speed (time constant) of the Mach-Zehnder interference type optical attenuator using the thermo-optic effect, making it difficult to put it into practical use.

  The present invention has been made in order to solve the above-described problems, and is easy to handle such as having few control parameters, has tolerance against variations in response speed, and has high speed and high accuracy. The purpose is to enable strength control.

The control method of the light intensity variable device according to the present invention provides the light intensity of the signal light output from the light intensity variable section by giving a control value to the light intensity variable section for the light intensity variable state of the light intensity variable section. In the control method of the light intensity variable device for controlling the intensity close to the intensity , an initial control value is continuously given to the light intensity variable section from the control start time to a time after the first time interval, and the first time interval from the control start time. At a later time , an initial control value is given and a first control change value proportional to the difference between the light intensity of the output signal light output from the light intensity variable unit and the design light intensity is obtained, and the first control change value is obtained. obtains a first control value obtained by adding the initial control value, from the time after the first time interval, until after the second time interval different from the first time interval, kept giving a first control value to the light intensity varying portion, the at a later point in time intervals of two hours, allowed to output from the optical intensity varying portion giving first control value The light intensity of the force signal light, obtains a second control change value proportional to the difference between the design light intensity, it obtains a second control value obtained by adding the second control change value to the first control value, after a second time interval from the time of giving a second control value to the light intensity varying portion, the first time interval, is obtained by the so that is longer than the second time interval.

In the control method of the light intensity variable device, the first time interval may be in the range of 6 to 8 times the time constant of the light intensity variable unit.

The light intensity variable device according to the present invention measures the light intensity of the signal light output from the light intensity variable section and the light intensity variable section that changes and outputs the light intensity of the signal light input according to the given control value. A light intensity measuring means that controls the light intensity of the signal light output from the light intensity variable section by giving a control value to the light intensity variable section, and the control section controls The initial control value is continuously given to the light intensity variable unit from the start time to the time after the first time interval , and the initial control value is given from the light intensity variable unit at the time after the first time interval from the control start time. A first control change value proportional to the difference between the output light intensity of the output signal light and the design light intensity is obtained, a first control value obtained by adding the first control change value to the initial control value is obtained, and a first time is obtained. from the time after the interval, until after different second time interval from the first time interval, light intensity variable It continued to receive the first control value at the time after the second time interval, and the light intensity of the output signal light is output from the optical intensity varying portion giving first control value is proportional to the difference between the design light intensity A second control change value is obtained, a second control value obtained by adding the second control change value to the first control value is obtained, and the second control value is given to the light intensity variable unit from the time after the second time interval , 1 hour interval is obtained by the so that is longer than the second time interval.

In the light intensity variable device, the first time interval may be in the range of 6 to 8 times the time constant of the light intensity variable unit. Further, a Mach-Zehnder optical attenuator based on a thermo-optic effect can be used for the light intensity variable unit.

As described above, according to the present invention, the braking becomes better than control parameters only proportional constant, there is tolerance for variations in the response speed, excellent effect that it is possible to high-speed, high-precision light intensity control Is obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram schematically showing a configuration example of a light intensity variable device in an embodiment of the present invention. In the following, a case where a Mach-Zehnder interference type optical attenuator is used as the light intensity variable unit will be described as an example. However, the present invention is not limited to this, and the present invention can be applied to other light intensity variable devices.

  1 includes a Mach-Zehnder interference optical waveguide 102 formed on a quartz substrate 101, and a directional coupler 103 provided in a waveguide on the output side of the Mach-Zehnder interference optical waveguide 102. The heater 104 provided in one of the branched waveguides of the Mach-Zehnder interference optical waveguide 102, the heater control unit 105 that controls the operation of the heater 104, and the signal light branched by the directional coupler 103 And a light receiving portion (light intensity measuring means) 106 for receiving light.

  The heater control unit 105 controls the driving of the heater 104 by, for example, determining input power based on a signal output from the light receiving unit 106 that has received the signal light branched by the directional coupler 103. The intensity of the signal light output from the Mach-Zehnder interference type optical waveguide 102 is attenuated by the heating of the heater 104 that is driven and controlled in this way. Accordingly, the light intensity variabler shown in FIG. 1 is such that the attenuation of the signal light by the Mach-Zehnder interference optical waveguide 102 is feedback-controlled by the intensity of the signal light output from the Mach-Zehnder interference optical waveguide 102.

Next, the control operation of the light intensity variable unit shown in FIG. 1, that is, the control operation in the heater control unit 105 will be described with reference to the flowchart of FIG.
First, the design output value P _{0 that} is the target value of the signal light output and the allowable deviation Δe ₀ with respect to the design output value P ₀ are set in the heater control unit 105 (step S201). For example, the initial data can be input by inputting the above-described values from an input unit (not shown) of the heater control unit 105.

  Next, the heater control unit 105 first inputs a photoelectric conversion signal output from the light receiving unit 106 (step S202). Next, the heater control unit 105 calculates an output light intensity value P (t0) at time t0 when the photoelectric conversion signal is output based on the input photoelectric conversion signal, and performs control based on a control function prepared in advance. A value t0 is determined (step S203).

  For example, the heater control unit 105 determines the relationship between the input power to the heater 104 and the light transmittance of the waveguide where the heater 104 is provided, as shown in FIG. It is provided as a control function indicating the relationship with the rate. The heater control unit 105 determines an initial control value t0 based on the control function.

  The heater control unit 105 that has determined the initial control value t0 controls the driving of the heater 104 based on the determined control value t0 (step S204). For example, the control value is the power to be applied to the heater 104, and the heater control unit 105 continues to apply the power of the determined initial input power value to the heater 104 for a predetermined time Δt.

Next, the heater control unit 105 determines whether or not to continue the control (step S205). When the heater control unit 105 continues, after a predetermined time Δt has elapsed from the time when the previous control of the heater 104 was performed (power-on start time) ( First, a photoelectric conversion signal output from the light receiving unit 106 is input (step S207). Next, the heater control unit 105 calculates an output light intensity value P (t1) at the time t1 when the photoelectric conversion signal is input based on the input photoelectric conversion signal, and outputs an output light intensity value P (with respect to the design output value P ₀ . A new control value t1 is calculated based on the deviation of t1) and the previous control value t0 (step S208).

After calculating the control value t1, Heater control unit 105 changes the control value t0 determined at time t0 to the new control value t1 (step S209), drives the heater 104 by the new control value t1 has been changed Control (step S204). In other words, the heater control unit 105 continues to input power of the determined new input power value for a predetermined time Δt.

  The heater control unit 105 continues the series of operations described above until it is determined in step S205 that the control is to be stopped in step S205. Accordingly, the heater 104 is driven with a new control value (input power) every time indicated by Δt. It should be noted that when the deviation is substantially 0, the power supplied to the heater 104 is not changed.

Next, the calculation of the control value of the heater control unit 105 in step S208 will be described in more detail. In the following, it is assumed that the control value is input power to the heater 104. That is, it is assumed that the control value t0 is the input power w0.
The heater control unit 105 first calculates a deviation e = (design output value P ₀ -output light intensity value P (t1)), and multiplies the deviation e by a predetermined proportional constant kp to obtain a differential power value Δw. The difference power value Δw is added to the initial input power w0 to obtain a new input power w1, that is, a control value t1.

The heater control unit 105 repeats steps S204 to S209 described above, calculates a new control value tm (m = 1, 2, 3,...) Every time Δt, and changes the light intensity variable shown in FIG. Control is performed so that the light intensity of the signal light output more closely approaches the designed value.
Here, when the response time by the above-described control is calculated using the proportionality constant kp and the control interval time Δt as parameters, regions having the same response time are distributed as shown in FIG.

  In FIG. 3, the time constant (RC) based on the time point when power is supplied to the heater 104 is used as the unit of the horizontal axis. Also, in FIG. 3, the control response time (seconds) required for the light intensity after control to fall within the range of ± 0.1 dB with respect to the design value of the light intensity is shown numerically. Each region where the same response time is obtained is indicated by a different density (grayscale), and the region with a shorter response time is indicated by a darker color. As shown in FIG. 3, the combination of the proportionality constant kp and the control interval Δt that gives a control response time of 0.05 seconds or less is shown in the darkest black region.

  Next, the time when the power of the initial applied power value determined in step S203 of FIG. 2A is turned on is set as an interval Δt1, and the time when the power of the input power value changed at step S209 is turned on is set as an interval Δt2. FIG. 4 shows a calculation example of the control response time using kp and Δt2 as parameters for the response time when Δt1 and Δt2 are different values. 4A shows a case where Δt1 is twice the time constant RC, FIG. 4B shows a case where Δt1 is four times the time constant RC, and FIG. 4C shows a case where Δt1 is When the time constant RC is 5 times, FIG. 4D shows the case where Δt1 is 6 times the time constant RC.

  In FIG. 4, the time constant (RC) is the unit of the horizontal axis, and the control response time required until the light intensity after control falls within the range of ± 0.1 dB with respect to the design value of the light intensity. (Second) is indicated by a numerical value in the figure, each region where the same response time is obtained is indicated by a different density (grayscale), and a region with a shorter response time is indicated by a darker color.

  When attention is paid to a region where the control response time indicated by a numerical value in the figure is 0.05 seconds or less, the larger Δt1, the wider. For example, the area of 0.05 seconds or less (the area closest to black) in FIG. 4D, which shows the case where Δt1 is set to 6 times the time constant, is greatly enlarged compared to the case shown in FIG. ing. This shows that the tolerance to each control parameter and time constant for the fast response is increasing.

  FIG. 5 is a characteristic diagram showing the relationship between the proportion of the parameter area where the control response time is 0.05 seconds or less and Δt1, and the proportion is obtained by setting Δt1 to 6 to 8 times the time constant RC. Is significantly larger. This is a phenomenon that is generally applied to a heater-type VOA having a time constant. Therefore, Δt1 may be set in the range of 6 to 8 times the time constant RC. Thus, according to the control described above, the control can be performed with a short response time of 0.05 seconds or less by appropriately setting the proportionality constant kp and the control interval Δt.

  Here, as the control value tm + 1 at time t + 1, the control value tm (m = 0, 1, 2,...) At the time before Δt from time t + 1 is used, and “control value tm + 1 = control value tm + kp × em” is obtained. Can show. This may be expressed as “control value tm + 1 = control value t0 + kp × (e0 + e1 + e2 + e3 +... Em)”.

In the above control method, the control value t0, which is the initial value of the control value, is set to a value that gives the output target value P ₀ in a steady state. For a sufficiently large value of m, “e0 + e1 + e2 + e3 +. "Asymptotically approaches 0 and becomes" control value tm + 1 = control value t0 ".
Further, the time constant of the light intensity variable device is changed by changing the value of the time interval Δt from the time when the light intensity variable device is controlled by the initial control value t0 until the next control is performed, and the subsequent time interval Δt. Even if there is variation, it is possible to make asymptotic in a short time by the light output target value.

Hereinafter, the control method of the present embodiment described above and the conventional digital PID control will be compared.
In general, in digital PID control, a control value is expressed as “control value = deviation proportional component + deviation integral component + deviation derivative component” with respect to the deviation.
When the output is stabilized by the control, the deviation gradually approaches zero. Therefore, in the above equation, the deviation proportional component and the deviation derivative component asymptotically approach zero, and asymptotically approach only a finite value having only the deviation integral component.

  Since the asymptotic value of the deviation integral component corresponds to the value of the control value for obtaining the output target value, the output target value cannot be obtained with high accuracy without this component. Therefore, in the conventional digital PID control, at least a deviation proportional component and a deviation integral component are necessary, and at least two control parameters are necessary.

  On the other hand, in the control method according to the present embodiment described above, the deviation asymptotically approaches zero, as is apparent from “control value tm + 1 = control value t0 + kp × (e0 + e1 + e2 + e3 +... Em)”. Even so, the control value can be made asymptotic to a finite value, and high-precision control can be realized with only the proportionality constant kp.

  In the above description, the case where the light intensity variable unit is configured as shown in FIG. 1 has been described. However, the present invention is not limited to this, and as shown in FIG. The present invention can also be applied to control of an optical intensity variable array composed of variable elements. FIG. 6 is a configuration diagram showing a configuration example of a light intensity variable array including an optical attenuator array 602 including a plurality of Mach-Zehnder optical attenuators and a control plate 603 inside the module box 601. .

  The input signal light is input to each Mach-Zehnder interference optical waveguide of the optical attenuator array 602 disposed inside the module box 601 by the input optical fiber array 606. On the other hand, signal light output from each Mach-Zehnder interference type optical waveguide is output from the output optical fiber array 607 to the outside of the module box 601.

  The control plate 603 provided in the module box 601 includes a light receiving unit 631, a heater driving unit 632, an arithmetic processing unit 633, and an interface 634. Electric power is supplied to each heater 621 provided in each Mach-Zehnder interference optical waveguide of the optical attenuator array 602 by the heater driving unit 632. Power is supplied by the wiring array 605. A directional coupler 622 is provided in the output side waveguide of each Mach-Zehnder interference type optical waveguide of the optical attenuator array 602 so that a part of the output signal light can be taken out.

  Each signal light branched by each directional coupler 622 is received by the light receiving unit 106 via the detection optical fiber array 604. Each received signal light is photoelectrically converted by the light receiving unit 106, and the photoelectrically converted signal is output to the arithmetic processing unit 633. The arithmetic processing unit 633 that has input the photoelectrically converted signal calculates a control value for each heater 621 based on the input photoelectric conversion signal, and outputs the calculated control value to the heater driving unit 632.

The arithmetic processing unit 633 performs the processing shown in the flowchart of FIG. 2 based on the design output value P _{0 that} is the target value of the signal light output input from the interface unit 632 and the allowable deviation Δe ₀ . Each control value is generated.
The heater driving unit 632 that receives the control values generated by the arithmetic processing unit 633 supplies power to the heaters 621 in accordance with the input control values.

As shown in FIG. 6, even when a plurality of optical attenuators are provided, as described above, the proportional constant kp and the control interval Δt are appropriately set to control with a short response time of 0.05 seconds or less. Can be done.
Note that a VMUX module can be realized by connecting a multiplexer / demultiplexer such as an AWG filter to a portion where the signal light of each optical attenuator is output. This is a useful module in a wavelength division multiplexing communication system.

It is a block diagram which shows typically the structural example of the light intensity variable device in embodiment of this invention. It is a flowchart explaining the example of control operation in embodiment of this invention. It is a characteristic view which shows the result of having calculated the response time by control of the light intensity variable device shown in FIG. 1 by making into a parameter the proportionality constant kp and (DELTA) t which is the time of a control interval. It is a characteristic view which shows the result of having calculated the response time by control of the light intensity variable device shown in FIG. 1 by making into a parameter the proportionality constant kp and (DELTA) t which is the time of a control interval. FIG. 6 is a characteristic diagram illustrating a relationship between a ratio of a parameter region in which a control response time is 0.05 seconds or less and Δt1. It is a block diagram which shows typically the structural example of the light intensity variable device array which consists of several light intensity variable devices in other embodiment of this invention. It is a block diagram which shows the structure of an array waveguide diffraction grating type | mold wavelength multiplexer / demultiplexer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Quartz substrate, 102 ... Mach-Zehnder interference type optical waveguide, 103 ... Directional coupler, 104 ... Heater, 105 ... Heater control part, 106 ... Light-receiving part (light intensity measurement means).

Claims (6)

A light intensity variable device for controlling the light intensity of the signal light output from the light intensity variable section to be close to the designed light intensity by giving a control value to the light intensity variable section for the light intensity variable state of the light intensity variable section. In the control method,
From the start of control until the time after the first time interval, the light intensity variable unit continues to give an initial control value,
At a later point in time a first time interval from the beginning of the control, the proportional and the light intensity of the initial control value output signal light is outputted from the optical intensity varying portion giving, to the difference between the design light intensity 1 Find the control change value,
A first control value obtained by adding the first control change value to the initial control value;
From the time after the first time interval until the second time interval different from the first time interval continues to give the first control value to the light intensity variable unit,
A second control change value that is proportional to the difference between the light intensity of the output signal light that is output from the light intensity variable unit by giving the first control value at the time after the second time interval, and the design light intensity. Seeking
A second control value obtained by adding the second control change value to the first control value;
From the time point after the second time interval, give the second control value to the light intensity variable unit ,
The method of controlling a light intensity variable device, wherein the first time interval is longer than the second time interval . In the control method of the light intensity variable device according to claim 1 ,
The method of controlling a light intensity variable device, wherein the first time interval is in a range of 6 to 8 times a time constant of the light intensity variable section. In the control method of the light intensity variable device according to claim 2 ,
The light intensity variable unit is a Mach-Zehnder optical attenuator based on a thermo-optic effect . A light intensity variable section that changes and outputs the light intensity of the input signal light according to a given control value;
A light intensity measuring means for measuring the light intensity of the signal light outputted from the light intensity varying portion,
A control unit for controlling the light intensity of the signal light output from the light intensity variable unit to be close to the design light intensity by giving the control value to the light intensity variable unit;
The controller is
From the start of control until the time after the first time interval, the light intensity variable unit continues to give an initial control value,
At a later point in time a first time interval from the beginning of the control, the proportional and the light intensity of the initial control value output signal light is outputted from the optical intensity varying portion giving, to the difference between the design light intensity 1 Find the control change value,
A first control value obtained by adding the first control change value to the initial control value;
From time after the first time interval until said different post second time interval from the first time interval, kept giving the first control value in the light intensity varying portion,
A second control change value that is proportional to the difference between the light intensity of the output signal light that is output from the light intensity variable unit by giving the first control value at the time after the second time interval, and the design light intensity. Seeking
A second control value obtained by adding the second control change value to the first control value;
From the time point after the second time interval, give the second control value to the light intensity variable unit ,
The light intensity variable device, wherein the first time interval is longer than the second time interval . The light intensity variable device according to claim 4, wherein
The light intensity variable device , wherein the first time interval is in a range of 6 to 8 times a time constant of the light intensity variable unit. The light intensity variable device according to claim 5 , wherein
The light intensity variable unit is a Mach-Zehnder optical attenuator based on a thermo-optic effect.
A light intensity variable device characterized by that.

Images