JP2014081577A - Optical device and temperature control method of optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device which can stably switch frequencies and optical control at high speed by effectively controlling influences of heat generation of the optical device as an amplitude of driving voltage and a frequency of the driving voltage change.SOLUTION: An optical device according to the present invention is provided with: an optical element 41 using an electro-optic crystal to be controlled; a Peltier element 42; a temperature detection element 43; a temperature control circuit 44 for performing PID control; and a driving circuit 45 for driving the optical device. The driving circuit 45 and the temperature control circuit 44 are connected, and the temperature control circuit 44 controls temperature of the optical element 41 on the basis of information from the driving circuit 45 given at the same time as the driving circuit 45 applies voltage.

Description

  The present invention relates to an optical device that requires temperature control. More particularly, the present invention relates to an optical device used for optical communication, optical measurement, or an electronic circuit, in which the temperature is controlled according to operation.

  A deflector is an optical device that changes the direction of light by applying an electric field. A deflector is used in various fields such as a display element in a projector. As the deflector, those using MEMS (Micro Electro Mechanical System) are widely used. However, in a deflector using MEMS, since a substance is mechanically moved by applying a voltage, deflection cannot be performed at a very high speed. Therefore, an optical switch or a deflector using a material having an electro-optic effect that can be deflected by applying an electric field has been devised.

Conventionally, research on the electro-optic effect has been advanced along with the development of an optical modulator. An optical phase modulator using an electro-optic crystal changes the phase of light by changing the speed of light passing through the crystal by changing the refractive index of the crystal. When the electro-optic crystal is installed in one of the optical waveguides of the Mach-Zehnder interferometer and the Michelson interferometer, the light intensity of the output of the interferometer changes according to the voltage applied to the crystal. In Patent Document 1, KTN (KTa _1-x Nb _x O ₃ (0 <x <1)) and KLTN (K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1) are used as electro-optic crystals. , 0 <y <1)), an optical phase modulator and an optical intensity modulator are disclosed.

In recent years, a material called KTa _1-x Nb _x O ₃ (abbreviated herein as KTN) has been noted and investigated for its large electro-optic coefficient. 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 relative dielectric constant of the KTN crystal. 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 actually use a large electro-optic effect, it is known that the temperature of the optical element is controlled to a constant temperature slightly higher than Tc (for example, see Non-Patent Document 1). In order to stably operate the optical element using the KTN crystal, it is necessary to keep the temperature of the optical element constant by adjusting the temperature of the optical element.

  In order to maintain the temperature of the optical element at a constant temperature, the operation of the optical element is appropriately controlled by using a Peltier element or a heater element as the electrothermal element. As a method for controlling the optical element, for example, a PID control method can be cited. The PID control method is a method of outputting a sum of a proportional action (Proportional Action), an integral action (Integral Action), and a derivative action (Derivative Action), and controlling toward a target value.

International Publication No. 2006/137408 Pamphlet JP 2007-3948 A

K. Nakamura, et al., "Space-charge-controlled electro-optic effect: Optical beam deflection by electro-optic effect and space-charge-controlled electrical conduction", JOURNAL OF APPLIED PHYSICS 104, 0131052008

  Since the KTN crystal is a dielectric, in an optical device composed of an optical element using the KTN crystal, it takes time to form polarization when operating at an AC voltage (particularly a high frequency voltage), and the phase between the applied voltage A delay occurs, and heat generation from the crystal itself due to dielectric loss becomes significant. Therefore, the temperature of the optical device changes immediately after switching the frequency of the drive voltage to the optical element using the KTN crystal.

  FIG. 2 shows an example of a conventional optical device. The optical device shown in FIG. 2 is for driving an optical element 21 using an electro-optic crystal to be controlled, a Peltier element 22, a temperature detecting element 23, a temperature control circuit 24 for performing PID control, and an optical device. Drive circuit 25.

  A specific operation of the optical device shown in FIG. 2 will be described with reference to a timing chart of FIG.

  In an optical device using a KTN crystal as an electro-optic crystal, first, the temperature of the optical element 21 is maintained at the target temperature T by the Peltier element 22 and the temperature control circuit 24. The reason for setting the temperature of the optical element 21 to the target temperature T is to use a huge electro-optic effect. At this time, since the drive voltage for developing the electro-optic effect is not applied, the calorific value of the optical device is zero.

  Application of a drive voltage is started at time t0, and operations such as light deflection and light modulation follow. At this time, the KTN crystal generates heat due to dielectric loss (heat generation amount J). The temperature detection element 23 detects the temperature rise of the optical device due to the heat generation, and the detected information is fed back to the temperature control circuit 24. The temperature control circuit 24 again controls the temperature of the optical element 21 to the target temperature T that was initially controlled by feedback control. Before the optical device generates heat, the current amount to the Peltier element is i0, but after the optical device generates heat, the optical device itself raises the temperature, so the current amount to the Peltier element after re-control is i1 Change (decrease) to In this feedback control, since the amount of current to the Peltier element is adjusted after the temperature of the optical element 21 to be controlled starts to change, the problem that a time delay Δt1 until the start of adjustment is unavoidable.

  On the other hand, a method has been proposed in which the operation of the element is kept stable by the amplitude of the driving voltage even if the temperature of the electro-optic crystal changes (see, for example, Patent Document 2). However, in this method, while the temperature of the optical device changes and is controlled again to the target temperature, there is a case where a phase change of the crystal in the electro-optic crystal is caused as the temperature decreases. In this case, since the electro-optical characteristics themselves change, there is a problem that the original operations such as optical deflection and optical phase modulation cannot be realized before the operation amount of the optical device is stabilized.

  In the drive circuit, electrical resonance including the electro-optic element can be used. Optical deflection and optical phase modulation using an electro-optic element are controlled by an applied voltage. When an optical device composed of a capacitive optical element such as an optical element using a KTN crystal is driven at a high frequency, the frequency is adjusted. The charging current increases proportionally and the required power supply capacity also increases. As a result, the power supply size becomes enormous.

  On the other hand, the resonance circuit can apply a voltage to the electro-optic element while storing a certain amount of energy in the circuit, and thus a small power source can be formed.

The Q value is used as an index indicating the characteristics of the resonance circuit. In the parallel resonance circuit, the current flowing through the element is multiplied by Q the power supply current. The Q value at this time can be written as (Equation 1) below.
Q = jωCR (Formula 1)
Here, ω is a driving frequency, C is a capacitance of the electro-optic element, and R is an effective resistance existing in the resonance circuit.

  Since the Q value is proportional to the capacitance C of the electro-optic element, the temperature and dielectric constant of the electro-optic element change when the amplitude and frequency of the applied voltage are changed. As a result, the Q value also changes. Since the change in the Q value leads to a change in the current value in the circuit, the resonance operation becomes unstable. Furthermore, since the Q value indicates the energy that can be stored in the circuit at the time of resonance, if the Q value decreases significantly, the energy required for resonance cannot be stored in the circuit, and the resonance itself stops. There was also the problem of end up.

  The present invention has been made in view of the above problems. The object of the present invention is to control the frequency and light control at high speed and stably by effectively controlling the influence of heat generation of the optical device accompanying the change in the amplitude and frequency of the drive voltage. It is to provide an optical device.

  The present invention is an optical device comprising an optical element comprising an electro-optic crystal having an electro-optic effect, a temperature control circuit for adjusting the temperature of the optical element, and a drive circuit for applying a voltage to the optical element. The control circuit adjusts the temperature of the optical element based on information from the drive circuit that is given at the same time that the drive circuit applies the voltage.

  The optical device according to the present invention has a configuration in which a control amount corresponding to a change in the heat generation amount can be added from the outside to a temperature control circuit that controls the temperature of the optical element. With this configuration, in the optical device according to the present invention, even if the amount of heat generated by the optical element changes, the temperature is instantaneously controlled to the target temperature, so that the frequency and light control can be switched at high speed and stably.

  Furthermore, when the optical element is driven by a resonance type power source, even if the calorific value of the optical element changes, the capacitance of the optical element can be kept constant, so that it is stable without deviating from the resonance condition. It is possible to apply the applied voltage.

It is a graph which shows the temperature dependence of the dielectric constant of a KTN crystal. It is a block diagram for demonstrating the temperature control performed in the conventional optical device. It is a timing chart which shows operation | movement of each part regarding the temperature control performed in the conventional optical device. It is a block diagram for demonstrating the temperature control performed in the optical device which concerns on one Embodiment of this invention. It is a timing chart which shows operation | movement of each part regarding the temperature control performed in the optical device which concerns on one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 4 shows an example of an optical device according to an embodiment of the present invention. The optical device shown in FIG. 4 is for driving an optical element 41 using an electro-optic crystal to be controlled, a Peltier element 42, a temperature detecting element 43, a temperature control circuit 44 for performing PID control, and an optical device. Drive circuit 45.

  The optical device shown in FIG. 4 is different from the optical device shown in FIG. 2 in that a path for directly connecting the drive circuit 45 and the temperature control circuit 44 is provided.

The electro-optic crystals used in the optical element 41 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), or (Pb, La) (Zr, Ti) O ₃ or the like.

  In FIG. 4, the temperature control circuit 44 controls the temperature of the optical element 41 by controlling the current value to the Peltier element 42. At this time, control is performed so that the temperature of the optical element 41 becomes a target value based on the temperature information of the optical element 41 detected by the temperature detection element 43. After the optical element 41 is controlled to an appropriate temperature, the drive voltage output from the drive circuit 45 is applied to the optical element 41 via the metal blocks 46 and 47. With this drive voltage, the laser light incident on the optical element 41 can be deflected.

  Although the optical element 41 before the drive voltage is applied does not generate heat, the optical element 41 generates heat due to the above-described dielectric loss when an AC voltage for continuous deflection operation is applied. The temperature change due to the heat generation of the optical element 41 is detected by the temperature detection element 43 and fed back to the temperature control circuit 44. Using the fed back temperature change information, the temperature control circuit 44 performs control so that the temperature of the optical element 41 becomes the target temperature.

  However, this series of control is performed after the temperature change of the optical element 41 occurs. Therefore, the deflection operation in this series of control differs from the steady deflection operation until the temperature of the optical element 41 is controlled again after reaching the target value after the temperature of the optical element 41 is changed. Will decrease.

  When the laser beam is deflected continuously at a single frequency, the drive voltage is also an AC voltage with a single frequency, so the amount of heat generated by the optical element 41 is constant. Accordingly, the temperature increase due to the heat generation of the optical element 41 can be detected by the temperature detection element 43, and the temperature control circuit 44 can control the temperature of the optical element 41 to be a target value. Variation of the deflection angle is unavoidable until the temperature is controlled again to the target temperature.

  On the other hand, in the embodiment of the present invention, in advance, a change in the amount of heat generated due to a short-time change in the amplitude of the drive voltage and / or a change in the amount of heat generated due to a short-time change in the frequency of the drive voltage -Measure with voltage characteristics phase difference or thermo viewer. At the same time as applying the drive voltage to the optical element 41, a control amount corresponding to a change in the calorific value measured in advance is added to the temperature control circuit 44. The control amount at this time is a current and a voltage for controlling the heat absorption amount of the Peltier element 42.

  When the laser beam is deflected continuously at a single frequency, that is, when the drive voltage is an AC voltage having a single frequency, the amount of heat generated by the optical element 41 changes due to the change in the amplitude of the AC voltage.

  In high-speed optical deflection using a KTN crystal as an electro-optic crystal, the deflection angle increases in proportion to the applied voltage. That is, when the laser beam is deflected over a wide range, a voltage with a large amplitude is applied, and when the laser beam is deflected within a narrow range, the amplitude of the applied voltage may be small. In optical measurement or the like, measurement may be performed while sequentially switching between a broad range of broad measurements and a narrow range of detailed measurements.

  At this time, if the control for canceling the change in the heat generation amount of the optical element 41 corresponding to the change in the amplitude of the AC voltage is performed simultaneously with the change in the amplitude of the AC voltage, the temperature does not change regardless of the change in the heat generation amount of the optical element 41. It is always kept constant and stable operation can be obtained.

  A specific operation of the optical device shown in FIG. 4 will be described with reference to a timing chart of FIG.

  In an optical device including an optical element 41 using a KTN crystal as an electro-optic crystal, first, the temperature of the optical element 41 is maintained at the target temperature T by the Peltier element 42 and the temperature control circuit 44. The reason for setting the temperature of the optical element 41 to the target temperature T is to use a huge electro-optic effect. At this time, since the drive voltage for developing the electro-optic effect is not applied, the calorific value of the optical device is zero.

  Application of a drive voltage is started at time t0, and operations such as light deflection and light modulation follow. At this time, the KTN crystal generates heat due to dielectric loss (heat generation amount J). Simultaneously with the application of the drive voltage, a current change Δi that cancels the heat generation amount J is added to the current amount to the Peltier element. The current change Δi depends on the frequency change of the drive voltage and the amplitude change of the drive voltage, and the current change Δi necessary for canceling the heat generation amount J is measured in advance and stored in the database. After the current change Δi is applied to the amount of current to the Peltier element, the temperature change of the optical element 41 is detected by the temperature detection element 43 and controlled again to the target temperature T that was initially controlled by feedback control. Although this control is performed by normal PID control, since the temperature change of the optical element 41 is suppressed in the first place by applying the current change Δi, a steady deflection operation can be obtained immediately after the drive voltage is applied. In this embodiment, the control after the start of application from the state where the drive voltage is not applied has been described. However, the present invention can be applied to a case where the amount of heat generated by the optical device changes due to a change in the applied voltage. That is, the present invention can be applied if the change in the amount of generated heat is measured in advance when the applied voltage is changed to a different amplitude or frequency from the state in which the voltage is already applied.

  The embodiments of the present invention described above can be applied to optical devices such as a phase modulator, a light intensity modulator, and a variable focus lens. However, it should be noted that it is not the essence of the present invention to which optical device the embodiment of the present invention is applied. It is the essence of the present invention to suppress the temperature change of the optical element accompanying the change in the amount of generated heat when the amplitude or frequency of the voltage applied to the optical element using the electro-optic crystal having the electro-optic effect is changed. . Therefore, the embodiment of the present invention can be applied to any optical device using an electro-optic crystal as a light guiding region and an operation temperature change is not preferable. .

  The temperature control performed in the optical device according to the embodiment of the present invention will be described below with reference to FIG. 4 again.

  In this embodiment, the temperature control circuit 44 controls the temperature of the optical element 41 using the KTN crystal by controlling the amount of current to the Peltier element 42. At this time, the temperature control circuit 44 controls the temperature based on the temperature information of the optical element 41 detected by the temperature detection element 43.

  As for the KTN crystal used in the optical element 41, a block was cut out from the KTN single crystal and formed into a shape of 4.0 mm × 3.2 mm × 1.0 mm. The surface of 3.2 mm × 1.0 mm was used as the optical incident surface, and the surface of 4.0 mm × 3.2 mm was used as the electrode surface. The electrode structure was a Ti / Pt / Au structure in which Ti, Pt, and Au were laminated in this order from the crystal plane. Both the optical incident surface and the electrode surface of the KTN crystal used in the optical element 41 are subjected to optical polishing.

  The temperature of the KTN crystal used in the optical element 41 is controlled at 35 ° C. so that the relative dielectric constant is 20,000. A voltage of 200 kHz and ± 300 V was applied through the metal blocks 46 and 47, and the calorific value was measured by current-voltage characteristics.

  When control information in accordance with the change in the driving state is not sent from the driving circuit 55 to the temperature control circuit 44 (when the present invention is not applied), the KTN crystal used in the optical element 41 after the voltage application is the target. It took 1 minute or more to be controlled at the controlled temperature.

  The deflection angle was smaller than the steady value until the temperature of the optical element 41 reached the target temperature, and after the temperature of the optical element 41 reached the target temperature, the deflection angle gradually recovered to the steady value.

  At this time, the room temperature is 25 ° C., which is lower than the target temperature of 35 ° C., and the temperature difference between the room temperature and the target temperature is 10 ° C. Under such circumstances, the Peltier element 42 is operated at a current value of 0.20 A in a steady state before voltage application and at a current value of 0.05 A in a steady state after voltage application.

  On the other hand, when the present invention is applied, immediately after the voltage is applied, the control information is transmitted from the drive circuit 55 to the temperature control circuit 44, and the temperature control circuit 44 decreases the current value of 0.15A corresponding to the heat generation amount of 1W. By controlling the current value to the Peltier element 42, a steady deflection operation can be obtained immediately after voltage application.

  In FIG. 4, the temperature control circuit 44 and the drive circuit 45 may be separately controlled from a computer or the like.

21, 41 Optical elements
22, 42 Peltier element
23, 43 Temperature sensing element
24, 44 Temperature control circuit
25, 45 Drive circuit
26, 27, 46, 47 Metal block

Claims (6)

An optical element comprising an electro-optic crystal having an electro-optic effect;
A temperature control circuit for adjusting the temperature of the optical element;
An optical device comprising a drive circuit for applying a voltage to the optical element,
The optical device is characterized in that the temperature control circuit adjusts the temperature of the optical element based on information from the drive circuit that is given at the same time that the drive circuit applies a voltage.   2. The light according to claim 1, wherein the temperature of the electro-optic crystal changes according to a change in amplitude of a drive voltage applied by the drive circuit and a change in frequency of the drive voltage applied by the drive circuit. device.   The optical device according to claim 1, wherein the temperature adjustment circuit adjusts the temperature of the optical element using a control amount corresponding to information from the drive circuit. The electro-optic crystal includes 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), The optical device according to claim 1, wherein the optical device is (Pb, La) (Zr, Ti) O ₃ .   2. The optical device according to claim 1, wherein information from the driving circuit given at the same time when the driving circuit applies a voltage is measured in advance and stored in a database. A method for adjusting the temperature of an optical device comprising an optical element comprising an electro-optic crystal having an electro-optic effect, a temperature control circuit for regulating the temperature of the optical element, and a drive circuit for applying a voltage to the optical element. There,
The drive circuit applying a voltage to the optical element;
Simultaneously with the step of applying a voltage to the optical element, the drive circuit transmitting control information to the temperature control circuit;
The temperature control circuit includes a step of adjusting the temperature of the optical element based on the control information. A method of adjusting the temperature of the optical device.

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