JP2007003948A - Apparatus for controlling optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain an electrooptical effect of high efficiency even in a temperature adjusting circuit having low temperature controlling accuracy. <P>SOLUTION: An apparatus for controlling an optical element 31 composed of a material having an electrooptical effect having temperature dependence is provided with a temperature detecting element 33 for detecting temperature of the optical element 31 and a driving circuit 35 for controlling the amplitude of driving voltage driving the optical element 31 according to the temperature detected by the temperature detecting element 33 so that influence of the electrooptical effect may be made to be fixed without depending on the temperature. The controlling apparatus may be further provided with a Pelletier element 32 for controlling the temperature of the optical element and a temperature controlling circuit 34 for driving the Pelletier element 32 according to the temperature detected by the temperature detecting element 33. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for an optical element, and more particularly to a control device for controlling the temperature of an optical element using an electro-optic effect, which is an optical element used in optical communication, optical measurement, or an electronic circuit.

A material made of KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1, hereinafter referred to as KTN) is expected to be applied to an optical element such as a wavelength conversion element. The KTN crystal has a nonlinear optical coefficient of 1200 to 8000 pm / V and an electro-optic coefficient of 600 pm / V or more under a constant bias electric field. For example, a conventionally used LiNbO ₃ (hereinafter referred to as LN) is used. Both are significantly larger than the optical coefficients of the. The electro-optic effect is very large when used in the paraelectric phase, particularly when used near the paraelectric / ferroelectric transition point.

  By the way, the electro-optic effect of the KTN crystal has a feature that the temperature dependence is very strong. FIG. 1 shows the temperature dependence of the electro-optic effect. The KTN crystal undergoes a phase transition at the paraelectric / ferroelectric transition temperature Tc, and the electrooptic effect is maximized in the vicinity of the temperature Tc. In order to stably operate an optical element using a KTN crystal regardless of temperature, a temperature adjustment circuit for the optical element is required. The temperature of the optical element is controlled to a constant temperature slightly higher than Tc by the temperature adjustment circuit (see, for example, Non-Patent Document 1).

S. Toyoda, et al., “Low driving voltage polarozaton-independent> 3GHz-response electro-optic switch using KTN waveguide” Proc. EOCE 2003

  In the case of an optical element using an LN crystal, it was not necessary to adjust the temperature. Therefore, an optical element using a KTN crystal has been required to reduce the size and cost of the temperature adjustment circuit. However, as shown in FIG. 1, the temperature dependence near the paraelectric-ferroelectric transition temperature Tc is very large, and the temperature adjustment circuit performs temperature control with a fast response speed with an accuracy of 0.1 degrees or less. There is a need. Such high-accuracy temperature control has a problem that the circuit scale of the temperature adjustment circuit becomes large, and the cost of an apparatus including an optical element using a KTN crystal increases.

When the electro-optic coefficient is E and the drive voltage amplitude is a constant value F, the intensity A of light that changes due to the electro-optic effect is
A = EF
It is expressed. In order to suppress the fluctuation range due to the temperature of the light intensity A to a certain range ΔA, the fluctuation range ΔE due to the temperature of the electro-optic coefficient is:
ΔE = ΔA / F
Must be kept within the range. FIG. 2 shows the accuracy required for temperature control of an optical element using a KTN crystal. In order to suppress the electro-optic coefficient to a certain range ΔE, it must be suppressed to a very small temperature range ΔT.

  Conventionally, a temperature detection element such as a thermistor is added to the outside as a method for detecting the temperature of the element, but the detection accuracy of the temperature detection element varies. Accordingly, there is a problem that it is expensive to select the temperature detection element in order to perform temperature control with high accuracy.

  The present invention has been made in view of such problems, and an object of the present invention is to control an optical element capable of obtaining a high electro-optic effect even in a temperature adjustment circuit with low temperature control accuracy. To provide an apparatus.

  In order to achieve such an object, the present invention provides a control device for controlling an optical element made of a material having an electro-optic effect having temperature dependence, wherein the temperature of the optical element is And a drive for controlling the amplitude of the drive voltage for driving the optical element so that the influence of the electro-optic effect is constant regardless of the temperature, according to the temperature detected by the detection means. And a circuit.

  According to a second aspect of the present invention, in the control device for an optical element according to the first aspect, a current for driving the optical element is integrated between the optical element and the drive circuit, and the electric charge to be driven is integrated. A current integrating circuit for measuring the amount is provided, and the driving circuit controls the amplitude of the driving voltage for driving the optical element so that the driving charge becomes constant.

  According to a third aspect of the present invention, in the optical element control device according to the first or second aspect, the Peltier element that is thermally coupled to the optical element and controls the temperature of the optical element; And a temperature control circuit for driving the Peltier element according to the detected temperature.

According to a fourth aspect of the present invention, the material according to the first, second, or third aspect is characterized in that KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1), K _1-y Li _y Ta _1-x Nb _x O ₃ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) or (Pb, La) (Zr, Ti) O ₃ .

  As described above, according to the present invention, since the drive voltage for driving the optical element is controlled so that the influence of the electro-optic effect is constant regardless of the temperature, the temperature adjustment circuit with low temperature control accuracy can be used. Even if it exists, it becomes possible to implement | achieve a highly efficient electro-optic effect.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, based on the temperature detected by the temperature detection element, not only the temperature of the element is controlled, but also the amplitude of the drive voltage for driving the optical element is adjusted. Conventionally, the bias voltage applied to the optical element is controlled to compensate for the temperature dependence of the refractive index. Therefore, the drive voltage amplitude control for driving the optical element and the bias voltage control can be used in combination.

  FIG. 3 shows a control device for an optical element according to Example 1 of the present invention. A Peltier element 32 and a temperature detection element 33 are thermally coupled to the optical element 31 using the KTN crystal. The low precision temperature control circuit 34 controls the Peltier element 32 based on the temperature information of the optical element 31 detected by the temperature detection element 33. The drive circuit 35 adjusts the amplitude of the drive voltage that drives the optical element 31 based on the temperature information of the optical element 31 detected by the temperature detection element 33.

  With reference to FIG. 4, the method of temperature control in Example 1 is demonstrated. The low precision temperature control circuit 34 controls the temperature of the optical element 31 by controlling the Peltier element 32. First, the temperature of the optical element 31 is controlled to a constant temperature T1 higher than the paraelectric / ferroelectric transition temperature Tc, and the temperature is controlled within a range of ΔT1. When the temperature detected by the temperature detection element 33 is lower than the temperature T1 and the electro-optical effect is increased, the drive circuit 35 decreases the amplitude of the drive voltage, and the detected temperature is higher than the temperature T1. When the effect is reduced, the amplitude of the drive voltage is increased. That is, as shown by the dotted line in FIG. 4, the amplitude F of the drive voltage is increased with the decrease of the electro-optic coefficient E, and the light intensity A = EF is made constant.

  Here, by increasing the change amount of the amplitude F with respect to the temperature change, the light intensity can be made constant in a large temperature range. On the other hand, the temperature control range ΔT1 by the temperature control circuit is larger than ΔT shown in FIG. 1, and the accuracy required for temperature control is greatly relaxed. Therefore, a low-precision temperature control circuit may be used. Further, since the amplitude is changed by the drive circuit 35 which is an electric circuit, it can be made to follow much faster than the temperature control by the Peltier element 32.

  In principle, it is not necessary to perform temperature control by the Peltier element 32 only by adjusting the amplitude of the drive voltage for driving the optical element 31. However, considering the case where the temperature fluctuation becomes large, it is more effective to use the coarse adjustment by the Peltier element 32 and the fine adjustment by the drive circuit 35 in combination.

Here, the optical element 31 may be an optical switch, an optical modulator, a Q switch, a deflector, or the like as long as it is a device using the electro-optic effect. The material of the optical element 31 is not only KTN, but also KLTN (K _1-y Li _y Ta _1-x Nb _x O ₃ , 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), PLZT ((Pb, La) ( Any material that has an electro-optic effect, such as Zr, Ti) O ₃ ), may be used.

  FIG. 5 shows an optical element control apparatus according to Embodiment 2 of the present invention. A Peltier element 52 and a capacitance measuring circuit 53 are coupled to the optical element 51 using a KTN crystal. The low-precision temperature control circuit 54 controls the Peltier element 52 based on the information on the capacitance of the optical element 51 detected by the capacitance measurement circuit 53. The drive circuit 55 adjusts the amplitude of the drive voltage for driving the optical element 51 based on the information on the capacitance of the optical element 51 detected by the capacitance measurement circuit 53.

  With reference to FIG. 6, a temperature control method according to the second embodiment will be described. As shown in FIG. 6, the electric capacity of the optical element 51 has the same temperature dependence as the electro-optic coefficient E. Therefore, when the capacitance detected by the capacitance measuring circuit 53 is lower than the predetermined capacitance and the electro-optic effect is increased, the drive circuit 55 reduces the amplitude of the drive voltage and the detected capacitance is predetermined. When the electro-optic effect is smaller than the capacity, the drive voltage amplitude is increased. For the measurement of electric capacity, measurement of an alternating current component of the current flowing through the optical element 51, a bridge method, an RF impedance method, or the like can be applied.

  FIG. 7 shows a control device for an optical element according to Example 3 of the present invention. A Peltier element 72 and a temperature detection element 73 are thermally coupled to the optical element 71 using the KTN crystal. The low accuracy temperature control circuit 74 controls the Peltier element 72 based on the temperature information of the optical element 71 detected by the temperature detection element 73. The drive circuit 75 adjusts the amplitude of the drive voltage for driving the optical element 71 based on the temperature information of the optical element 71 detected by the temperature detection element 73.

  When determining the amplitude of the driving voltage, the driving circuit 75 makes the driving charge constant. A current integration circuit 76 is inserted between the drive circuit 75 and the optical element 71. The current integration circuit 76 always measures and integrates the flowing current, and measures the changed amount of polarization as the amount of charge. The measured charge amount is fed back to the drive circuit 75. The drive circuit 75 changes the drive voltage until it drives an amount of charge proportional to the input signal. Thereby, since the value of the driven polarization becomes constant, the light intensity A = EF can be made constant.

  Similarly to the first embodiment, the light intensity can be made constant in a large temperature range by increasing the amount of change of the amplitude F with respect to the temperature change. In addition, since the accuracy required for temperature control is greatly relaxed, a low-accuracy temperature control circuit can be used.

It is a figure which shows the temperature dependence of an electro-optic effect. It is a figure which shows the precision required for temperature control of the optical element using a KTN crystal. It is a block diagram which shows the control apparatus of the optical element concerning Example 1 of this invention. 6 is a diagram for explaining a temperature control method in Embodiment 1. FIG. It is a block diagram which shows the control apparatus of the optical element concerning Example 2 of this invention. 6 is a diagram for explaining a temperature control method in Embodiment 2. FIG. It is a block diagram which shows the control apparatus of the optical element concerning Example 3 of this invention.

Explanation of symbols

31, 51, 71 Optical element 32, 52, 72 Peltier element 33, 73 Temperature detection element 34, 54, 74 Low-precision temperature control circuit 35, 55, 75 Drive circuit 53 Capacitance measurement circuit 76 Current integration circuit

Claims (4)

In a control device for controlling an optical element made of a material having an electro-optic effect having temperature dependence,
Detecting means for detecting the temperature of the optical element;
A drive circuit that controls the amplitude of the drive voltage for driving the optical element according to the temperature detected by the detection means so that the influence of the electro-optic effect is constant regardless of the temperature. An optical element control device. Between the optical element and the drive circuit, a current integration circuit for integrating the current for driving the optical element and measuring the amount of charge to be driven is provided.
2. The optical element control device according to claim 1, wherein the drive circuit controls an amplitude of a drive voltage for driving the optical element so that the electric charge to be driven becomes constant. 3. A Peltier element that is thermally coupled to the optical element and controls the temperature of the optical element;
The optical element control device according to claim 1, further comprising: a temperature control circuit that drives the Peltier element according to the temperature detected by the detection unit. The materials are KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1), K _1-y Li _y Ta _1-x Nb _x O ₃ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1), (Pb , La) (Zr, Ti) O ₃ , The optical element control device according to claim 1, 2 or 3.

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