JP2006349855A - Variable dispersion compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a variable dispersion compensator having fast response speed. <P>SOLUTION: The control circuit 10 is equipped with first and second memory regions 12, 13. When the control circuit 10 receives a command to make a dispersion value variable, a plurality of first pulse currents respectively supplied to a plurality of heaters 7<SB>1</SB>-7<SB>n</SB>before the dispersion is made variable are stored in the first memory region 12, a plurality of second pulse currents to be respectively supplied to the plurality of heaters 7<SB>1</SB>-7<SB>n</SB>for the purpose of setting the dispersion to a desired value are stored in the second memory region 13, and subsequently differences between the second pulse currents and the first pulse currents are calculated, the calculated values are multiplied with a gradient coefficient, and sums of the multiplied values and the second pulse currents are calculated so as to calculate a plurality of third pulse currents, and subsequently the plurality of calculated third pulse currents are supplied to the respective plurality of heaters 7<SB>1</SB>-7<SB>n</SB>, and subsequently after a lapse of a predetermined length of time, the plurality of second pulse currents are supplied to the respective plurality of heaters 7<SB>1</SB>-7<SB>n</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a dispersion compensation technique for compensating chromatic dispersion of an optical signal in an optical fiber communication system, and more particularly to a tunable dispersion compensator in which a variable speed of dispersion compensation is increased.

  In an optical communication system using an optical fiber as a transmission line, the optical pulse is distorted by chromatic dispersion (hereinafter referred to as “dispersion”) of the optical fiber, so that signal degradation occurs. This is because the group velocities of the wave packets of the optical pulses having different wavelengths are different, and the time required for the wave packet of the optical pulses to propagate a certain distance, that is, the group delay time (unit: ps) is different. The inclination of the group delay time with respect to the wavelength is dispersion (unit: ps / nm). A single mode fiber (SMF) used for a normal optical fiber transmission line has a dispersion value of about 16 ps / (nm · km) per 1 km of the transmission line when the wavelength is around 1550 nm. This means that the difference in group delay time required for an optical pulse having a wavelength different by 1 nm to propagate through a 1 km SMF is 16 ps. For example, a group delay when an optical pulse having a wavelength different by 1 nm propagates through an optical fiber having a length of 100 km. The time is 100 times 1600 ps.

  On the other hand, the modulated optical pulse has several line spectrum spreads determined by the modulation method and the bit rate, and its envelope becomes a Gaussian distribution type. For example, in the RZ (return-to-zero) modulation method, the interval between the respective line spectra is 0.08 nm when the bit rate (transmission speed) is 10 Gbit / s, but when the bit rate is 40 Gbit / s. Is 0.32 nm. That is, the spread of the line spectrum increases in proportion to the bit rate. Further, in the NRZ (non-return-to-zero) modulation method, the line spectrum becomes half the spread in the RZ modulation method. Thus, as the bit rate increases, the interval of the line spectrum that is the component of the optical pulse increases, so the difference in group delay time when propagating through the optical fiber transmission line increases, and the distortion of the optical pulse increases. Further, the influence of the dispersion of the optical fiber transmission line that the optical pulse receives is increased in proportion to the square of the bit rate.

  In order to compensate for such dispersion, a dispersion compensating fiber, a chirped grating, and the like having a dispersion having a sign opposite to that of the optical fiber serving as a transmission line have been developed. On the other hand, there is a problem that the dispersion in the optical fiber changes with time due to the temperature variation of the optical fiber or the change in the stress of the optical fiber due to external force. There was a problem that such a problem could not be dealt with.

In order to solve this problem, various variable dispersion compensators that can vary the dispersion value that can be compensated have been proposed (see, for example, Patent Document 1).
In this conventional tunable dispersion compensator, an optical waveguide in which a chirped diffraction grating having a continuously changing grating pitch is formed is arranged on a large number of heaters formed in a line on a substrate. The pulse current is supplied to each heater. When a pulse current flows through the heater, each heater generates heat and the temperature of the optical waveguide rises. At this time, various temperature distributions can be formed by controlling the duty ratio of the pulse current flowing through each heater. When the temperature of the optical waveguide changes, the refractive index changes. As a result, the Bragg reflection wavelength of each part of the chirped diffraction grating changes, and the dispersion added to the optical signal incident on the optical waveguide changes.

  Since the conventional variable dispersion compensator changes the dispersion by forming the temperature distribution in the optical waveguide as described above, it takes a long time until the temperature distribution reaches a steady state. This means that the response speed of the tunable dispersion compensator is slow, but it is sufficient for the conventional tunable dispersion compensator that the response speed is about 30 seconds. This is because ultra-high-speed optical communication such as 40 Gbit / s is mostly used in long-distance transmission, and the cause of dispersion change in long-distance transmission is the temperature change and stress change of the fiber. This is because a change in a long cycle such as a half-day cycle is sufficient if it has a response speed corresponding to this.

  However, nowadays, a system has been constructed that automatically switches to another optical fiber transmission line when an error occurs in the transmission line (for example, see Non-Patent Document 1). At this time, since the distance of the optical fiber changes when the transmission path is switched, the dispersion value loaded on the optical signal also changes. At this time, it is necessary to carry out in less than 1 second from the occurrence of an error until the transmission line is switched and the dispersion compensation is completed. To cope with this, the variable dispersion compensator also requires a response speed of less than 1 second. Become.

JP 2004-258462 A Shiro Kasa and three others, "Chromatic dispersion compensation in ultra high-speed wavelength path network", 2004 Society of Electronics, Information and Communication Engineers Society Conference, BCS-1-1

  Since the conventional variable dispersion compensator has a response speed of about 30 seconds as described above, it cannot be applied to a system that requires a response speed of 1 second or less.

  An object of the present invention is to provide a variable dispersion compensator having a high response speed that can be applied to a system that requires a response speed of 1 second or less.

  The tunable dispersion compensator according to the present invention includes an optical waveguide having a diffraction grating, a plurality of heaters arranged in a line along the optical axis of the optical waveguide, and a plurality of pulse currents to generate a plurality of pulse currents. And a control circuit for supplying each of the plurality of heaters. When the control circuit includes a first storage area and a second storage area and receives a command for changing the dispersion value, the control circuit supplies each of the plurality of heaters before the dispersion is changed. A plurality of first pulse currents stored in the first storage area, and a plurality of second pulse currents supplied to each of the plurality of heaters in order to obtain a target dispersion value are stored in the second storage area, The difference between the second pulse current and the first pulse current is calculated, the value is multiplied by a gradient coefficient, and the sum of the value and the second pulse current is calculated to calculate a plurality of third pulse currents. The plurality of calculated first A pulse current is supplied to each of the plurality of heaters, it is then the plurality of second pulse current after a predetermined time to supply to each of said plurality of heaters.

  According to the present invention, when a command for varying the dispersion value is received, first, a third pulse current that forms a temperature distribution having a larger gradient than the temperature distribution from which the target dispersion value is obtained is supplied to each heater. It changes rapidly so as to obtain a temperature distribution formed by three pulse currents. Then, after a certain time has passed, that is, immediately before the temperature distribution becomes the temperature distribution at which the target dispersion value is obtained, the pulse current becomes the second pulse current that forms the temperature distribution from which the target dispersion value is obtained from the third pulse current. The dispersion value is maintained at the target value. As a result, when the dispersion value is made variable, the switching time from the current dispersion value to the desired dispersion value is significantly shortened compared to the case where the second pulse current is immediately supplied to the heater, and a high response speed is achieved. The tunable dispersion compensator is provided.

Embodiment 1 FIG.
1 is a schematic diagram showing the configuration of a variable dispersion compensator according to Embodiment 1 of the present invention, FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1, and FIG. 3 is a variable according to Embodiment 1 of the present invention. It is a block diagram which shows the control circuit part in a dispersion compensator.

1 and 2, the tunable dispersion compensator 1 includes an optical waveguide 2 having a chirped diffraction grating 5, n heaters 7 _{1 to} 7 _n that impart temperature distribution to the chirped diffraction grating 5 of the optical waveguide 2, and and n first electrodes ₈ 1 to 8 _n and one second electrode 9 for supplying power to the heaters _{7 i,} a control circuit 10 for controlling the pulse current supplied to the heaters _{7 i,} the interface circuit 11, It has.

The optical waveguide 2 is an optical fiber composed of a core 3 and a clad 4 formed so as to cover the periphery of the core 3, and a chirped diffraction grating 5 in which the grating pitch is continuously changed is formed. The n heaters 7 _{1 to} 7 _n are formed on the substrate 6 in almost one row. Also, n first electrodes 8 ₁ to 8 _n are formed on the substrate 6 so as to be electrically connected to the corresponding heater 7 i, and the second electrode 9 is electrically connected to the heaters 7 _{1 to} 7 _n. Thus, it is formed on the substrate 6. The second electrode 9 is grounded. The control circuit 10 is electrically connected to each first electrode 8 _i so that a pulse current can be supplied to each heater 7 _i .
The optical waveguide 2 is fixed on the substrate 6 with an adhesive or the like with the region where the chirped diffraction grating 5 is formed positioned on the heaters 7 _{1 to} 7 _n and in close contact therewith. Here, the heaters 7 _{1 to} 7 _n are arranged in a line along the optical axis of the optical waveguide 2. Then, a pulse current is passed from the first electrode heaters 8 ₁ to 8 _n to the heaters 7 _{1 to} 7 _n , and a desired temperature distribution is given to the chirped diffraction grating 5.

Here, although the optical waveguide 2 is assumed to use an optical fiber, a planar optical waveguide (PLC) may be used. Further, for example, a quartz substrate is used for the substrate 6, and tantalum nitride is used for each heater 7 _i , for example.

Next, the configuration of the control circuit 10 will be described with reference to FIG.
The control circuit 10 includes a first storage area 12 that stores n first pulse currents I _{a1 to} I _an that form a temperature distribution before dispersion variation, and a temperature distribution for obtaining a desired dispersion value. A second storage area 13 storing n second pulse currents I _{b1 to} I _bn forming a slope, a gradient coefficient storage area 14 storing a gradient coefficient k, a changeover switch 15, and a changeover switch 15 The counter 16 for defining the switching time of each of the above and the calculation portion 17 for performing each calculation are provided. The calculation part 17 includes a subtracter 18, a multiplier 19, and an adder 20.

  Here, the first storage area 12, the second storage area 13, and the gradient coefficient storage area 14 can be applied to any device capable of storing data, but a semiconductor memory such as a ROM is used from the viewpoint of reading speed and cost reduction. It is desirable to apply the storage device that was used.

There are various means for realizing the subtracter 18, the multiplier 19, and the adder 20. However, it is preferable that the means be realized by digital signal processing using an FPGA (Field Programmable Gate Array), a microcomputer, and an IC. The arithmetic portion 17, the signal processing in accordance with each of the heater 7 _i required. Therefore, in the analog signal processing, a signal processing circuit corresponding to each heater 7 _i is required, and the number of parts is large and the power consumption is increased. On the other hand, in digital processing using an FPGA or the like, many signal processing circuits can be realized with one device, and the circuit can be reduced in size and power consumption can be reduced. Even when the signal processing method is changed, it is possible to cope with the method change only by changing the program, and unlike the case of the analog signal processing, it is not necessary to change the circuit.

Next, the operation of the control circuit 10 will be described.
First, when a command for changing the dispersion value is transmitted to the variable dispersion compensator 1, the command is processed by the interface circuit 11, and a desired dispersion value is transmitted to the control circuit 10.
The control circuit 10 that has received the command stores the first pulse currents I _{a1 to} I _an that constitute the current dispersion value in the first storage area 12, and then the first circuit that constitutes the dispersion value corresponding to the received command. The two pulse currents I _{b1 to} I _bn are stored in the second storage area 13.
Next, the pulse current value to be passed through each heater 7 _i is calculated by the calculation portion 17 based on the pulse current values stored in the first and second storage areas 12 and 13.
First, the subtractor 18 calculates the difference between the second pulse current value stored in the second storage area 13 and the first pulse current value stored in the first storage area 12. Subsequently, the multiplier 19 multiplies the result by the gradient coefficient k stored in the gradient coefficient storage area 14, and the adder 20 further multiplies the result and the second pulse current value stored in the second storage area 13. And the sum is calculated.

Next, the effect of the above calculation will be described with reference to FIGS. 4 to 6, the vertical axis represents temperature, and the horizontal axis represents the heater number.
First, in FIG. 4, a temperature distribution 30 is a temperature distribution forming a current dispersion value, that is, a temperature distribution formed by applying the first pulse currents I _{a1 to} I _an to the heaters 7 _{1 to} 7 _n . In FIG. 4, a temperature distribution 31 is a temperature distribution forming a new dispersion value, that is, a temperature distribution formed by applying the second pulse currents I _{a1 to} I _an to the heaters 7 _{1 to} 7 _n .
Here, when a command for changing to a new dispersion value is transmitted to the tunable dispersion compensator 1 and the changeover switch 15 is switched to the second storage area 13 side, the second temperature distribution 31 constituting the new dispersion value is obtained. Pulse currents I _{b1 to} I _bn are passed through each heater 7 _i . At this time, if the current temperature distribution 30 changes to a new temperature distribution 31, it can be changed to a desired dispersion value. However, as described above, it takes a long time for the temperature to reach a steady state. End up.
The change in the dispersion value at this time is shown in FIG. As can be seen from the dispersion value change 33 shown in FIG. 7, it takes a long time to reach the desired dispersion value from the initial dispersion value.

In the first embodiment, when a command for changing to a new dispersion value is transmitted to the tunable dispersion compensator 1, the changeover switch 15 is switched to the output side of the calculation portion 17. The third pulse current is an operation result of the operation portion 17 is passed through the respective heaters 7 _i, the temperature distribution 32 shown in FIG. 5 is formed. For example, when the gradient coefficient k is 1, a temperature distribution 32 having a gradient twice as large as the difference between the temperature distribution 30 and the temperature distribution 31 is formed. In other words, for a heater whose temperature must be increased, a pulse current is applied so that the temperature is higher than the desired temperature, and for a heater whose temperature must be decreased, the temperature is lower than the desired temperature. A pulse current is applied to the.

  The gradient coefficient k is normally set to a number of 0 or more, and the gradient coefficient is changed according to the desired gradient. When the gradient coefficient k is 0, the temperature distributions 30 and 31 are the same temperature distribution, and when the gradient coefficient k is 1, the temperature distribution 32 has a gradient twice as large as the difference between the temperature distributions 30 and 31. . That is, the larger the gradient coefficient k, the higher the temperature distribution can be varied. However, if the gradient coefficient k is too large, the third pulse current value obtained as a result of the calculation may exceed the upper limit value of the heater or be lower than the lower limit value. It is preferable to do.

When the changeover switch 15 is switched to the output side of the calculation portion 17, the counter 16 is activated. Then, when the predetermined time set by the counter 16 is measured, a changeover signal is output to the changeover switch 15. Therefore, the changeover switch 15 is switched to the second storage area 13 side. That is, the counter 16 measures a predetermined time after the command to change to a new dispersion value is transmitted, and the second pulse current that forms the temperature distribution 31 by the third pulse current flowing through the heater. It is switched to I _b1 ~I _bn. Therefore, the second pulse currents I _{b1 to} I _bn are caused to flow through the heaters 7 _i , and as shown in FIG. 6, a temperature distribution 31 is formed and changed to a new dispersion value.
FIG. 8 shows changes in the dispersion value at this time. As can be seen from the variance value variation 34 shown in FIG. 8, the third pulse current time is applied to the heater 7 _i 35, because that is the large temperature distribution gradient which is determined by the slope factor k, The rate of change is greater than the variance value change 33. That is, the initial dispersion value can be varied in a short time from the desired dispersion value. Then, after reaching the desired dispersion value, the second pulse current is allowed to flow through the heater 7i for the time 36, and the desired dispersion value is maintained.

  Here, the changeover switch 15 may be a mechanical switch. However, the mechanical switch is not preferable because the switching speed is slow and precise switching speed cannot be controlled. Therefore, a switch capable of high-speed and precise time control can be easily realized by programming the switch portion in the FPGA or microcomputer used for the arithmetic processing.

The change in the temperature distribution obtained by the first embodiment is determined by the set constant time (the application time of the third pulse current) and the gradient coefficient k. As described above, the larger the gradient coefficient k, the faster it changes, so it is better to make it as large as possible.
In addition, the product of the gradient coefficient k and a certain time (application time of the third pulse current) must be an optimum constant value. If this product is smaller than the optimum value, the pulse current value is switched from the third pulse current value to the second pulse current value before reaching the desired dispersion value, and the time until reaching the desired dispersion value is reached. It will take. On the other hand, if this product is larger than the optimum value, the pulse current value is switched from the third pulse current value to the second pulse current value after exceeding the desired dispersion value, and the dispersion value change curve overshoots, This also reduces the response speed. Therefore, a combination of the gradient coefficient k and the fixed time that makes the product of the gradient coefficient k and the fixed time the optimum value is found in advance and stored in the storage area in correspondence with the variable dispersion value after being transmitted. The gradient coefficient k and the fixed time corresponding to the new dispersion value obtained from the command are read out, and the calculation process in the calculation part 17 and the measurement process of the counter 16 are performed.

  Thus, by changing the pulse current applied to the heater 7i from the first pulse current → the third pulse current → the second pulse current, the temperature distribution 30 → the temperature distribution 31 → the temperature distribution 32 is changed. Switching from the dispersion value to the desired dispersion value can be accelerated. This makes it possible to realize a variable dispersion compensator having a high response speed that can be applied to a system that automatically switches to another optical fiber transmission line when an error occurs in the transmission line.

  In the first embodiment, the linear temperature distribution has been described. However, the temperature distribution need not be linear, and may be a non-linear temperature distribution or a temperature distribution change.

Embodiment 2. FIG.
FIG. 9 is a block diagram showing a control circuit portion in the tunable dispersion compensator according to Embodiment 2 of the present invention.
In FIG. 9, when the counter 16 measures a predetermined time after a command for changing to a new variance value is transmitted, the control circuit 10 </ b> A multiplies the gradient coefficient k = 0 from the gradient coefficient storage area 14. 19, the change-over switch 15 is omitted.
Other configurations are the same as those in the first embodiment.

Next, the operation of the control circuit 10A will be described.
First, when a command for changing the dispersion value is transmitted to the variable dispersion compensator 1, the command is processed by the interface circuit 11. A desired dispersion value is transmitted to the control circuit 10A.
Then, the control circuit 10A that has received the command stores the first pulse currents I _{a1 to} I _an constituting the current dispersion value in the first storage area 12, and then configures the first dispersion current corresponding to the received command. The two pulse currents I _{b1 to} I _bn are stored in the second storage area 13.
Next, the pulse current value that flows through each heater 7 i is calculated by the calculation portion 17 based on the pulse current values stored in the first and second storage areas 12 and 13.
First, the subtractor 18 calculates the difference between the second pulse current value stored in the second storage area 13 and the first pulse current value stored in the first storage area 12. Next, the multiplier 19 multiplies the result by the gradient coefficient stored in the gradient coefficient storage area 14, and the adder 20 further calculates the result and the second pulse current value stored in the second storage area 13. The sum of is calculated.

The third pulse current obtained from the result is caused to flow through each heater 7 _i . On the other hand, the counter 16 operates after receiving a command, and outputs a signal to the gradient coefficient storage area 14 when the set fixed time is measured. As a result, the gradient coefficient storage area 14 changes the value of the stored gradient coefficient k to “0”. Therefore, the multiplier 19 multiplies the calculated value of the subtracter 18 by 0, and the calculated value of the adder 20 becomes the second pulse current value stored in the second storage area 13. As a result, the third pulse current is applied to the heater from the time the command is received until the set time has elapsed, and the second pulse current is applied to the heater after the time has elapsed.

Therefore, also in the second embodiment, the same effect as in the first embodiment can be obtained.
Further, the changeover switch 15 is not required, and the configuration can be simplified.

  In the second embodiment, the temperature distribution is changed by selecting a preset gradient coefficient k and “0” when changing from the initial dispersion value to a desired dispersion value. The slope coefficient is not limited to two and may be three or more. By changing three or more gradient coefficients with time change, it is possible to more accurately control time change of temperature distribution.

Embodiment 3 FIG.
FIG. 10 is a block diagram showing a control circuit portion in a tunable dispersion compensator according to Embodiment 3 of the present invention, and FIG. 11 is a diagram for explaining the thermistor mounting position in the tunable dispersion compensator according to Embodiment 3 of the present invention. is there.
In FIG. 10, in the control circuit 10B, the temperature monitor 21 monitors the temperature of the thermistor 22, and when the temperature of the thermistor 22 reaches the set temperature, the changeover switch 15 is switched from the calculation portion 17 side to the second storage area 13 side. It is configured as follows. The thermistor 22 measures the temperature of the heater 7 _i.
Other configurations are the same as those in the first embodiment.

Next, the operation of the control circuit 10B will be described.
First, when a command for changing the dispersion value is transmitted to the variable dispersion compensator 1, the command is processed by the interface circuit 11. A desired dispersion value is transmitted to the control circuit 10B.
Then, the control circuit 10B that received the command stores the first pulse currents I _{a1 to} I _an constituting the current dispersion value in the first storage area 12, and then configures the first dispersion current corresponding to the received command. The two pulse currents I _{b1 to} I _bn are stored in the second storage area 13.
Next, the pulse current value that flows through each heater 7 i is calculated by the calculation portion 17 based on the pulse current values stored in the first and second storage areas 12 and 13.
First, the subtractor 18 calculates the difference between the second pulse current value stored in the second storage area 13 and the first pulse current value stored in the first storage area 12. Next, the multiplier 19 multiplies the result by the gradient coefficient stored in the gradient coefficient storage area 14, and the adder 20 further calculates the result and the second pulse current value stored in the second storage area 13. The sum of is calculated.

The third pulse current obtained from the result is caused to flow through each heater 7 _i .
On the other hand, the temperature monitor 21 monitors the temperature of a predetermined heater via the thermistor 22, and outputs a switching signal to the changeover switch 15 when the temperature of the heater reaches a set temperature. Accordingly, the changeover switch 15 is switched to the second storage area 13 side, and the second pulse current stored in the second storage area 13 is caused to flow to each heater 7 _i .

Therefore, also in the third embodiment, the same effect as in the first embodiment can be obtained.
In the third embodiment, the temperature of a specific heater is monitored, the third pulse current is applied until the heater temperature reaches the set temperature, and the second pulse current is applied after the set temperature is reached. I am doing so. Therefore, even if disturbances such as fluctuations in the resistance value of the heater and fluctuations in the supply voltage to the control circuit 10B occur, it is possible to accurately approximate the desired temperature distribution.
In the first and second embodiments, the optimum value of the product of the gradient coefficient k and the predetermined time needs to be found in advance corresponding to the variance value after the variable. In the third embodiment, Since feedback control is performed to monitor the heater temperature and reflect the result, the concept of optimum value is not required, and the manufacturing process can be simplified.

  In the third embodiment, when the heater temperature detected by the thermistor 22 reaches the set temperature, the changeover switch 15 is switched to change the pulse current applied to the heater from the third pulse current value to the second pulse current value. Although switching is performed, the present invention can be applied to the control circuit 10A of the second embodiment. That is, when the heater temperature detected by the thermistor 22 reaches the set temperature, the pulse current applied to the heater is switched from the third pulse current value to the second pulse current value by changing the gradient coefficient k to “0”. You may do it. Furthermore, the gradient coefficient can be changed according to the heater temperature detected by the thermistor 22.

Next, the mounting position of the thermistor 22 will be described.
When one thermistor 22 is mounted, it is preferable that the thermistor 22 is mounted on _{one of} the heaters 7 ₁ and 7 _n located at both ends of the heater array, as shown by mounting positions 23 and 24 in FIG.
When the dispersion value is varied, the temperature gradient is changed around the central heater. This is to make the total power consumption compensated by the heater equal for all dispersion values. That is, the central heater temperature is constant at all dispersion values. For this reason, if the thermistor 22 is arranged in the central heater, the temperature change cannot be detected even if the dispersion value is changed, and information on the temporal change of the temperature distribution cannot be obtained. On the other hand, since the heater at the end has the largest temperature change when the dispersion value is varied, the temporal change in the temperature distribution can be detected.

When two thermistors 22 are mounted, it is preferable to mount one thermistor 22 on one of the heaters 7 ₁ and 7 _n located at both ends of the heater array. The remaining one thermistor 22 may be mounted on any heater, but is preferably mounted on a heater located at the center or end.

For example, when the thermistor 22 is mounted on each of the end heater and the center heater, the thermistor 22 mounted on the end heater detects a temporal change in temperature distribution and uses it to control the changeover switch 15. The thermistor 22 mounted on the central heater cannot detect a temporal change in the temperature distribution, but can detect a change in the environmental temperature. Therefore, when the environmental temperature changes, the thermistor 22 is controlled so as to absorb it. Can be used.
The correspondence to the environmental temperature is realized by the temperature of the Peltier element as described in the prior document 1. However, in this prior art, since the temperature of the Peltier element under the heater is detected by the thermistor, there is an error between the temperature transmitted to the actual fiber grating. Furthermore, the location detected by the thermistor and the location of the actual temperature are separated from each other, and thermal resistance is generated, causing instability such as oscillation of temperature control. In the third embodiment, since the heater temperature is directly detected, control instability as in the prior art does not occur, and stable control can be performed.

Further, when the thermistors 22 are respectively mounted on the heaters at both ends, both thermistors 22 can detect a temporal change in temperature distribution. As a result, not only a linear temperature change but also a non-linear temperature change can be detected. For example, even if there is a gradient difference between the heater that raises the temperature and the heater that lowers the temperature, the temperature can be detected, and the gradient coefficient for the heater that raises the temperature and the heater that lowers the temperature are changed. It is also possible to add a time difference to the timing. Moreover, if the average value of the temperature detected by the thermistors at both ends is calculated, a change in the environmental temperature can be detected.
Note that the number of thermistors 22 may be three or more, and the larger the number, the more preferable temperature distribution can be detected.

Embodiment 4 FIG.
In the first to third embodiments, when calculating the third pulse current value, the gradient coefficient is determined so as not to exceed the upper limit value or lower limit value of the heater. However, when the variable range of the variance value is changed, there is a possibility that the upper limit value or lower limit value of the heater may be exceeded with the same gradient coefficient. In particular, when the upper limit is exceeded, there is a possibility of causing fatal defects that cannot be repaired, such as cutting of the heater and deterioration of the adhesive for fixing the fiber grating. Therefore, it is effective to provide the variable dispersion compensator with a heater protection function which is a function for setting the pulse current value equal to or higher than the upper limit value to the upper limit value and the pulse current value equal to or lower than the lower limit value to the lower limit value.

  Here, the upper limit value of the heater protection function is determined by the maximum current that can flow through the heater and the heat resistance temperature of the fixing adhesive. The heater used in the present invention uses a thin film heater such as tantalum nitride, and when a current exceeding the maximum current flows, the thin film abnormally generates heat and is cut. This maximum current depends on the shape of the thin film, and the smaller the cross-sectional area, the easier it is to cut. Moreover, a silicone-based adhesive is often used as the fixing adhesive, and it is generally said that silicone deteriorates when the temperature exceeds approximately 150 ° C. The upper limit value of the heater is determined by the above two points. The thin film heater used in the present invention has a performance capable of being heated to a temperature of 150 ° C. or higher. The heat-resistant temperature is the determining factor for the upper limit. On the other hand, the lower limit value may be any value as long as it is less than or equal to the upper limit value. However, even if the heater protection function is activated, it is more preferable that the total power consumption of the heater is constant. It is preferable to set the difference so that the upper limit value and the lower limit value are equal. The heater protection function can be easily realized by programming a comparator in the FPGA or microcomputer. An analog signal processing circuit may be used, but since it is necessary to install circuits in all the heaters, it is preferable to use a digital signal processing circuit.

It is the schematic which shows the structure of the variable dispersion compensator which concerns on Embodiment 1 of this invention. It is II-II arrow sectional drawing of FIG. It is a block diagram which shows the control circuit part in the variable dispersion compensator which concerns on Embodiment 1 of this invention. It is a figure which shows temperature distribution at the time of applying the 1st pulse current in the variable dispersion compensator which concerns on Embodiment 1 of this invention. It is a figure which shows temperature distribution at the time of applying the 3rd pulse current in the variable dispersion compensator which concerns on Embodiment 1 of this invention. It is a figure which shows temperature distribution at the time of applying the 2nd pulse current in the variable dispersion compensator which concerns on Embodiment 1 of this invention. It is a figure which shows the dispersion value change in the variable dispersion compensator of the comparative example of this invention. It is a figure which shows the dispersion value change in the variable dispersion compensator which concerns on Embodiment 1 of this invention. It is a block diagram which shows the control circuit part in the variable dispersion compensator which concerns on Embodiment 2 of this invention. It is a block diagram which shows the control circuit part in the variable dispersion compensator which concerns on Embodiment 3 of this invention. It is a figure explaining the thermistor mounting position in the variable dispersion compensator concerning Embodiment 3 of this invention.

Explanation of symbols

1 variable dispersion compensator, second optical waveguides, 5 chirped _grating, 7 1 to _7-n heater, 10, 10A, 10B control circuit, 12 a first storage area, 13 the second storage area, 15 changeover switch, 16 a counter, 17 Operation part, 18 subtractor, 19 multiplier, 20 adder, 21 temperature monitor, 22 thermistor.

Claims (4)

An optical waveguide having a diffraction grating;
A plurality of heaters arranged in a line along the optical axis of the optical waveguide;
In a variable dispersion compensator comprising a control circuit that generates a plurality of pulse currents and supplies each of the plurality of heaters,
The control circuit includes first and second storage areas, and when receiving a command for changing a dispersion value, the control circuit supplies a plurality of first pulse currents supplied to each of the plurality of heaters before the dispersion is changed. A plurality of second pulse currents stored in the storage area and supplied to each of the plurality of heaters to obtain a target dispersion value are stored in the second storage area, and then the second pulse current and the first pulse current are stored. And the value is multiplied by a gradient coefficient, the sum of the value and the second pulse current is calculated to calculate a plurality of third pulse currents, and the calculated third pulse currents are calculated. Is supplied to each of the plurality of heaters, and then the plurality of second pulse currents are supplied to each of the plurality of heaters after a predetermined time has elapsed. An optical waveguide having a diffraction grating;
A plurality of heaters arranged in a line along the optical axis of the optical waveguide;
A control circuit that generates a plurality of pulse currents and supplies each of the plurality of heaters;
A variable dispersion compensator comprising: a thermistor that detects at least one heater temperature of the plurality of heaters;
The control circuit includes first and second storage areas, and when receiving a command for changing a dispersion value, the control circuit supplies a plurality of first pulse currents supplied to each of the plurality of heaters before the dispersion is changed. A plurality of second pulse currents stored in the storage area and supplied to each of the plurality of heaters to obtain a target dispersion value are stored in the second storage area, and then the second pulse current and the first pulse current are stored. And the value is multiplied by a gradient coefficient, the sum of the value and the second pulse current is calculated to calculate a plurality of third pulse currents, and the calculated third pulse currents are calculated. Is supplied to each of the plurality of heaters, and after the heater temperature detected by the thermistor reaches a set value, the plurality of second pulse currents are supplied to each of the plurality of heaters. Dispersion compensation .   3. The variable dispersion compensator according to claim 1, wherein the first and second storage areas are semiconductor memories.   In the control circuit, when the upper limit value and the lower limit value of the plurality of third pulse currents are set and the calculated third pulse currents are equal to or more than the upper limit value, the third pulse currents Is set to the upper limit value, and when the calculated third pulse currents are equal to or lower than the lower limit value, the third pulse current is set to the upper limit value. 4. The variable dispersion compensator according to any one of 3 above.

Images