Optical switch

An optical switch changes the refractive index of an electro-optical crystal according to an electric field applied to the electro-optical crystal so as to switch depending on whether the electro-optical crystal enables incident light to pass through or whether the electro-optical crystal enables incident light to be totally reflected. The optical switch includes an electrode section including a plurality of electrodes and formed in the electro-optical crystal, a principal plane including the largest area of each electrode on a same plane of the electro-optical crystal; an insulator layer on at least one plane of the electro-optical crystal, the plane being parallel with the electrode section, the insulator layer made of an insulator with lower dielectric constant than the electro-optical crystal; and a temperature control device formed on and in contact with the insulator layer and controls a temperature of the electrode section or dissipates heat generated in the electrode section.

TECHNICAL FIELD

The present invention relates to optical switches that switch between transmission and the reflection of light.

BACKGROUND ART

In the field of optical communication, optical switches that perform switching of light according to a voltage that causes the refractive index of a crystal having an electro-optical effect (electro-optical crystal) to change are known.

Among those, waveguide type optical switches such as a directional coupling optical switch using the proximity effect of two waveguides, and a Mach-Zehnder interferometer-type photonic switch that generates a phase difference between lights that propagate the waveguides according to an external voltage applied between waveguides, and that uses optical interference that occurs therebetween have been proposed. Since these waveguide type optical switches can change the refractive index at high speed, they can perform switching at high speed.

As another type, an optical switch that uses the Bragg effect presented for example in Japanese Patent No. 2666805 (hereinafter referred to as Patent Document 1) is known.

FIG. 1is a perspective view showing a structure of an optical switch according to a related art reference.

As shown inFIG. 1, the optical switch according to the related art reference has optical waveguide layer2made of a non-linear optical substance having the electro-optical effect (electro-optical crystal); and first electrode group11and second electrode group12that are formed in optical waveguide layer2.

First electrode group11and second electrode group12each are composed of a plurality of planar electrodes1that can expand and make contact in the direction of the thickness of optical waveguide layer2. The individual electrodes of first electrode group11and those of second electrode group12are alternately arranged at a predetermined interval such that the cross-section of a plane of the electrodes perpendicular to the direction of the thickness of optical waveguide layer2is formed in the shape of a comb.

When a voltage is applied between first electrode group11and second electrode group12of the optical switch shown inFIG. 1, the refractive index of the nonlinear optical substance of optical waveguide layer2periodically changes. The portion of the nonlinear optical substance in which the refractive index periodically changes functions as a diffraction grating that reflects incident light, so called the Bragg reflection. On the other hand, when the voltage applied between the first and second electrode groups is stopped, since the portion does not function as a diffraction grating, the incident light passes through the region between the planar electrodes.

When the foregoing optical switch is used for optical communication or the like, the extinction ratio that represents the difference between the intensity of transmitted light in the ON state and that in the OFF state can be around 10:1. However, when the optical switch is used for example for an optical modulator of an image display device, an optical switch having a higher extinction ratio than is used for optical communication or the like is desired so as to improve the luminance and contrast ratio.

In addition, an optical switch used for an image display device or the like needs to have a high optical damage resistance. An optical switch used for an image display device needs to modulate light of several ten to several hundred mW or greater. The size of the waveguide used in the foregoing waveguide type optical switch is typically several μm. Since the intensity of light per unit square with which such a waveguide type optical switch is irradiated is high and thereby the nonlinear optical crystal or the like tends to be optically damaged, it is difficult to use such an optical switch for an image display device.

In addition, when the refractive index of the electro-optical crystal is caused to be changed according to an electric field applied thereto, the refractive index changes depending on the temperature of the crystal. When the magnitude for which the refractive index changes fluctuates according to the temperature, the intensity of output light of the optical switch also changes. Thus, to stably operate the optical switch, the temperature at which the refractive index changes in the electro-optical crystal needs to be maintained in an appropriate range.

The optical switch presented in Patent Document 1 does not have a structure that takes into account how the refractive index of the electro-optical crystal changes depending on the temperature. Thus, when the first and second electrode groups are irradiated with light and thereby their temperatures rise, since the refractive index based on the applied voltage also changes, the wavelength and direction of light reflected by the diffraction grating may become unstable, namely, the operation of the optical switch may become unstable depending on the environment and surrounding temperature of the optical switch.

CITATION LIST

Patent Document

SUMMARY

Therefore, an object of the present invention is to provide optical switches that have a higher extinction ratio, optical damage resistance, and temperature stability, and that can perform higher speed operation and lower power consumption operation, and that have smaller structures than previously.

To accomplish the foregoing object, an exemplary aspect of the optical switch of the present invention is an optical switch that changes the refractive index of an electro-optical crystal according to an electric field applied to the electro-optical crystal so as to switch depending on whether the electro-optical crystal enables incident light to pass through or whether the electro-optical crystal enables incident light to be totally reflected, comprising:

an electrode section that is composed of a plurality of electrodes and that is formed in the electro-optical crystal, a principal plane including the largest area of each of the plurality of electrodes being present on a same plane of the electro-optical crystal;

an insulator layer that is formed on at least one plane of the electro-optical crystal, the plane being parallel with the electrode section, the insulator layer being made of an insulator having a lower dielectric constant than the electro-optical crystal; and

a temperature control device that is formed to be in contact with the insulator layer and that controls a temperature of the electrode section or that dissipates heat generated in the electrode section.

Alternatively, an exemplary aspect of the optical switch of the present invention is an optical switch that changes a refractive index of an electro-optical crystal according to an electric field applied to the electro-optical crystal so as to switch depending on whether the electro-optical crystal enables incident light to pass through or whether the electro-optical crystal enables incident light to be totally reflected, comprising:

an electrode section that is composed of a plurality of electrodes and that is formed in the electro-optical crystal, a principal plane including the largest area of each of the plurality of electrodes being present on a same plane of the electro-optical crystal;

an insulator layer that is formed on at least one plane of the electro-optical crystal, the plane being parallel with the electrode section, the insulator layer being made of an insulator having a lower dielectric constant than the electro-optical crystal; and

a temperature control device that is formed to be in contact with the insulator layer and that controls a temperature of the electrode section or that dissipates heat generated in the electrode section,

wherein the electro-optical crystal has a refractive index change section whose refractive index changes according to the electric field that is applied to the electrode section, the refractive index change section fully covers the electrode section, and a refractive index interface of the refractive index change section is evenly formed.

Alternatively, an exemplary aspect of the optical switch of the present invention is an optical switch that changes a refractive index of an electro-optical crystal according to an electric field applied to the electro-optical crystal so as to switch depending on whether the electro-optical crystal enables incident light to pass through or whether the electro-optical crystal enables incident light to be totally reflected, comprising:

an electrode section that is composed of a plurality of electrodes and that is formed in the electro-optical crystal, a principal plane including the largest area of each of the plurality of electrodes being present on a same plane of the electro-optical crystal,

wherein anti reflection coats are formed respectively on a light incident plane to which light enters and on at least one plane from among a light exit plane from which transmitted light exits and a light exit plane from which reflected light exits.

Alternatively, an exemplary aspect of the optical switch of the present invention is an optical switch that changes a refractive index of an electro-optical crystal according to an electric field applied to the electro-optical crystal so as to switch depending on whether the electro-optical crystal enables incident light to pass through or whether the electro-optical crystal enables incident light to be totally reflected, comprising:

an electrode section that is composed of a plurality of electrodes and that is formed in the electro-optical crystal and that applies the electric field to the electro-optical crystal;

anti reflection coats formed respectively on a light incident plane to which light enters and on at least one plane from among a light exit plane from which transmitted light exits and a light exit plane from which reflected light exits,

wherein the electro-optical crystal has a refractive index change section whose refractive index changes according to the electric field that is applied to the electrode section, the refractive index change section fully covers the electrode section, and a refractive index interface of the refractive index change section is evenly formed.

Alternatively, an exemplary aspect of the optical switch of the present invention is an optical switch that changes a refractive index of an electro-optical crystal according to an electric field applied to the electro-optical crystal so as to switch depending on whether the electro-optical crystal enables incident light to pass through or whether the electro-optical crystal enables incident light to be totally reflected, comprising:

an electrode section that is composed of a plurality of electrodes and that is formed in the electro-optical crystal, a principal plane including the largest area of each of the plurality of electrodes being present on a same plane of the electro-optical crystal;

an insulation section that is formed in contact with at least part of the electrode section that has a higher thermal conductivity and a lower dielectric constant than the electro-optical crystal; and

a temperature control section that is formed on a plane of the insulation section and dissipates heat generated in the electrode section or controls a temperature of the electrode section.

Alternatively, an exemplary aspect of the optical switch of the present invention is an optical switch that changes a refractive index of an electro-optical crystal according to an electric field applied to the electro-optical crystal so as to switch depending on whether the electro-optical crystal enables incident light to pass through or whether the electro-optical crystal enables incident light to be totally reflected, comprising:

an electrode section that is composed of a plurality of electrodes and that is formed in the electro-optical crystal that applies the electric field to the electro-optical crystal;

an insulation section that is formed in contact with at least part of the electrode section that has a higher thermal conductivity and a lower dielectric constant than the electro-optical crystal; and

a temperature control section that is formed on a plane of the insulation section and controls a temperature of the electrode section or dissipates heat generated in the electrode section,

wherein the electro-optical crystal has a refractive index change section whose refractive index changes according to the electric field applied to the electrode section, the refractive index change section fully covers the electrode section, and a refractive index interface of the refractive index change section is evenly formed.

EXEMPLARY EMBODIMENT

Next, with reference to drawings, the present invention will be described.

As described above, the optical switch presented in Patent Document 1 controls transmission and diffraction of incident light using a diffraction grating that occurs as the refractive index changes. Instead of the structure in which transmission and diffraction of incident light are controlled by such a diffraction grating, an optical switch that controls transmission and reflection of incident light using a refractive index change section that occurs in an electro-optical crystal that is formed in the proximity of electrodes according to a voltage applied to the electrodes and to, the refractive index change section covering the electrodes, is known.FIG. 2is a perspective view showing a structure of the optical switch.

In the optical switch shown inFIG. 2, a plurality of rod shaped electrodes105are arranged at a relatively narrow interval in electro-optical crystal104and a voltage is applied from external power supply107to each of electrodes105such that adjacent electrodes have different polarities. Light is obliquely entered into electro-optical crystal104to the normal direction of electrode section106composed of electrodes105that are arranged along a straight line. Electrode section106is composed of electrodes105that are arranged in such a manner that a principal plane including the maximum area is present on the same plane, electrodes106have the same film thickness and are arranged in parallel and at an equal interval. As described above, a voltage is applied to electrodes105such that the polarities of adjacent polarities become different from each other.

When a voltage is not applied to electrode section106, as shown inFIG. 3(a), since the diffractive index of electro-optical crystal104in the proximity of electrode section106does not change, incident light101passes through electrode section106and exits to the outside (transmitted light). On the other hand, when a voltage is applied to electrode section106, as shown inFIG. 3(b), since an electric field occurs between electrodes105, the refractive index of electro-optical crystal104in the proximity of electrode section106changes and thereby refractive index change section108occurs. At this point, refractive index change section108occurs such that it entirely covers electrodes105and a refractive index interface nearly occurs evenly. Thus, incident light having an incident angle equal to or greater than the critical angle totally reflects on refractive index change section108and then the reflected light exits to the outside.

Thus, the optical switch shown inFIG. 2can switch between exit planes of light depending on whether or not a voltage is applied to electrode section106and thereby can perform switching of light.

In addition, the optical switch shown inFIG. 2is a bulk type optical switch where light passes through electro-optical crystal104that does not need to provide a waveguide structure. Thus, the optical switch allows the intensity of light irradiated per unit volume to be lowered and thereby the optical damage resistance to be improved in comparison with waveguide type optical switches. As a result, the optical switch can switch an optical beam with a relatively larger aperture (several ten to several hundred μm) than waveguide type optical switches.

In addition, since the optical switch shown inFIG. 2has a structure in which electrodes105are arranged at an equal interval of several μm to several ten μm, namely a relatively narrow interval, a relatively low voltage allows a strong electric field to be generated in the electro-optical crystal between electrodes105and thereby allows a refractive index change section to occur. Thus, the voltage applied to electrode section106can be lowered. In addition, since the cross section of each of electrodes105is relatively small, the inter-electrode capacitance can be lower than that of the optical switch presented in Patent Document 1 that uses planar electrodes.

Since the power consumption at a high speed operation of the optical switch is proportional to both the second power of the applied voltage and the inter-electrode capacitance, when the applied voltage and the inter-electrode capacitance are lowered, the power consumption can be reduced in comparison with the optical switch presented in Patent Document 1. Moreover, since the operational frequency bandwidth is reversely proportional to the inter-electrode capacitance, when the inter-electrode capacitance is decreased, the operational frequency band can be widened. In other words, when compared with the optical switch presented in Patent Document 1, the switching operation of the optical switch shown inFIG. 2can be performed at high speed.

AlthoughFIG. 2shows an exemplary structure in which electrodes105are arranged perpendicular to the traveling direction of incident light, electrodes105may be arranged in the same direction as the traveling direction of incident light.

In the following, with reference to drawings, the present invention will be described based on the foregoing optical switch.

FIRST EMBODIMENT

FIG. 4shows a structure of an optical switch according to a first embodiment: (a) is a perspective view of the drawing; (b) is a sectional view of the drawing taken along line A-A of the optical switch shown inFIG. 4(a); (c) is a sectional view of the drawing taken along line B-B of the optical switch shown inFIG. 4(a).

The optical switch according to the first embodiment has the same structure as the optical switch shown inFIG. 2except that temperature control device111is formed through insulator layer110on a lower plane of electro-optical crystal104, the lower plane being parallel with electrode section106.FIGS. 4(a) to (c) show an exemplary structure in which electrodes105are arranged in the same direction as the traveling direction of incident light.

As described above, when the refractive index of electro-optical crystal104is changed according to an electric field applied thereon, the refractive index changes depending on the temperature of the crystal. When the magnitude of change of the refractive index fluctuates as the temperature changes, the intensity of output light of the optical switch also changes. Thus, to stabilize the operation of the optical switch, the temperatures at which the refractive index changes in electro-optical crystal104need to be maintained in a proper range.

Since the optical switch shown inFIG. 2has the structure in which electrode section106is formed on an optical path of incident light, when electrode section106is irradiated with light, the temperature of electrode section106tends to rise. When the temperature of electro-optical crystal104in the proximity of electrode section106changes as the temperature of electrode section106rises, the refractive index corresponding to the applied voltage also changes and thereby it becomes difficult to maintain the flatness of the refractive index interface of refractive index change section108. Thus, in the optical switch shown inFIG. 2, it is preferred that the temperatures of electrode section106and electro-optical crystal104formed in the proximity thereof be maintained constant.

Thus, in the optical switch according to the first embodiment, temperature control device111is formed on a plane of electro-optical crystal104, the plane being closest to electrode section106that is formed on the optical path of incident light and whose characteristic fluctuates the most as the temperature changes.

Temperature control device111is a thermoelectric transducer such as a Peltier device that serves to control the temperature of electrode section106or a heat dissipating device such as a heat sink that serves to dissipate heat generated in electrode section106.

When temperature control device111is a thermoelectric transducer, a temperature sensor is attached to the optical switch so as to detect the temperature in the electrode forming region including electrode section106and refractive index change section108.

When a current is supplied from a current source (not shown) to the thermoelectric transducer, it generates heat. When the thermoelectric transducer generates heat, thermal energy causes insulator layer110to heat and thereby the temperature of the electrode forming region rises. Another type of thermoelectric transducer is provided with a heat absorption function that absorbs thermal energy from its contacting member. For example, when a DC current is caused to flow in the foregoing Peltier device, its one plane generates heat and the other plane absorbs it. In addition, when the direction of a current that flows in the Peltier device is inverted, the heat generation plane and the heat absorption plane are inverted to each other. Thus, when the thermoelectric transducer is a Peltier device, the electrode forming region can be heated and cooled.

The temperature sensor is attached to a portion at which the thermal relationship with the electrode forming region is known (for example, a portion where the heat resistance is known). Thus, the temperature of the electrode forming region can be estimated based on the value detected by the temperature sensor.

When the temperature of the electrode forming region is controlled, a predetermined threshold is designated for the detected value of the temperature sensor based on the thermal relationship between the portion at which the temperature sensor is attached and the electrode forming region: if the detected value of the temperature sensor is lower than the threshold, the electrode forming region is heated by the thermoelectric transducer through insulator layer110; if the detected value of the temperature sensor is equal to or greater than the threshold, the electrode forming region is cooled by the thermoelectric transducer through insulator layer110. Such a process can maintain the temperature of the electrode forming region within a predetermined temperature range.

If the temperature of the electrode forming region does not need to be controlled with high accuracy, a heat dissipating device such as a heat sink may be used for temperature control device111so as to effectively dissipate heat generated in electrode section106that has been irradiated with high intensity light.

When the temperature of the electrode forming region is controlled, it is preferred that temperature control device111be formed as close to electrode section106as possible. Thus, it can be contemplated that temperature control device111is directly formed on a plane of electro-optical crystal104, the plane being in parallel with electrode section106.

However, since such a structure causes electro-optical crystal104having a high dielectric constant to be sandwiched by electrode section106and by temperature control device111composed of a heat sink or Peltier device that is a conductor, electrode section106and temperature control device111form a capacitor. Thus, the capacitance component of the capacitor restricts the operation speed (bandwidth) of the optical switch.

Thus, this embodiment has a structure in which insulator layer110made of an insulator having a lower dielectric constant than electro-optical crystal104is formed on a lower plane of electro-optical crystal104, the lower plane being parallel with electrode section106, and temperature control device111is formed in contact with insulator layer110. Thus, the temperature of electrode section106can be controlled to be as close as possible to the temperature of electrode sections106without it being necessary to increase the capacitance component, or the temperature can be controlled so that heat generated in electrode sections106can be dissipated.

Insulator layer110may be made of SiO2, SiN, a graphite sheet, a silicone, a low-k (low dielectric constant) material for semiconductor devices (organic polymer, SiOC, etc), or the like. When insulator layer110is made of SiO2, SiN, or the like, insulator layer110can be formed using an existing production facility for semiconductor devices.

On the other hand, when insulator layer110is made of a graphite sheet, a silicone, a low-k (low dielectric constant) material for semiconductor devices (organic polymer, SiOC, etc), or the like, since insulator layer110functions as a light absorption layer that absorbs light, insulator layer110absorbs light emitted from the relevant plane of electro-optical crystal104. Thus, effects in which stray light that occurs in electro-optical crystal104decreases and in which the extinction ratio of the optical switch improves can be obtained.

Since the optical switch according to this embodiment has a structure in which temperature control device111is formed on a plane of the electro-optical crystal, the plane being in parallel with electrode section106and being closest to electrode section106whose characteristics fluctuate the most as the temperature changes, the temperature in the proximity of electrode section106can be evenly and effectively controlled or heat in the proximity of electrode section106can be evenly and effectively dissipated. Thus, the direction of reflected light becomes stable as the temperature of refractive index change section108fluctuates and thereby the operation of the optical switch becomes stable.

In addition, since the direction of reflected light becomes stable, stray light that occurs in electro-optical crystal104decreases and also the extinction ratio of the optical switch improves. Moreover, since the temperature of electrode section106does not excessively rise, damage to electrode section106is prevented and thereby the reliability of the optical switch improves.

Moreover, since temperature control device111is formed through insulator layer110having a lower dielectric constant than electro-optical crystal104, the capacitance component increase slightly and thereby the restriction of the operation speed (bandwidth) of the optical switch is alleviated.

Furthermore, since the relevant plane of electro-optical crystal104is covered with temperature control device111that is a heat sink, a Peltier device, or the like, the durability of the optical switch against shock improves.

SECOND EMBODIMENT

FIG. 5shows a structure of an optical switch according to a second embodiment: (a) is a perspective view of the drawing; (b) is a sectional view of the drawing taken along line A-A of the optical switch shown inFIG. 5(a); (c) is a sectional view of the drawing taken along line B-B of the optical switch shown inFIG. 5(a).FIG. 6shows a structure of an exemplified modification of the optical switch according to the second embodiment: (a) is a perspective view of the drawing; (b) is a sectional view of the drawing taken along line A-A of the optical switch shown inFIG. 6(a); (c) is a sectional view of the drawing taken along line B-B of the optical switch shown inFIG. 6(a).

As shown inFIGS. 5(a) to5(c), the optical switch according to the second embodiment has the same structure as the optical switch shown inFIG. 2except that temperature control devices111are formed respectively through insulation layers110on a lower plane and an upper plane of electro-optical crystal104, the lower and upper planes being in parallel with electrode section106. Insulation layers110and temperature control devices111can be made of the same material as those in the first embodiment.

When temperature control devices111are formed respectively on the lower plane and upper plane of electro-optical crystal104through insulation layers110, the lower and upper planes being in parallel with electrode section106, the temperature in the proximity of electrode section106can become more stable than that of the optical switch according to the first embodiment.

Alternatively, as shown inFIGS. 6(a) to (c), the optical switch according to the second embodiment may have a structure in which temperature control devices111are formed respectively through insulation layers110on all planes of electro-optical crystal104other than a light incident plane and a light exit plane.

As shown inFIGS. 6(a) to6(c), when temperature control devices111are formed respectively through insulation layers110on all the planes of electro-optical crystal104other than the light incident plane and the light exit plane, the temperature in the proximity of electrode section106can become more stable than that of the optical switch shown inFIGS. 5(a) to5(c).

In addition, when all the planes of electro-optical crystal104other than the light incident plane and the light exit plane through which light is transmitted are covered respectively with insulation layers110, stray light that occurs in electro-optical crystal104decreases and the extinction ratio of the optical switch improves more significantly than that of the first embodiment. Moreover, since the temperature of electrode section106does not excessively rise, damage to electrode section106is prevented and thereby the reliability of the optical switch improves.

In particular, when insulator layers110are made of a graphite sheet, silicone, a low-k (low dielectric constant) material for semiconductor devices (organic polymer type, SiO, etc.), or the like and insulation layer110is also formed, for example, on the light exit plane from which reflected light exits, since insulation layer110also functions as a light absorption layer, reflection of unnecessary light on the light exit plane decreases. Thus, if transmitted light is used as output light of the optical switch, when insulator layer110is also formed on the exit plane of reflected light, since insulator layer110absorbs the exited light, stray light that occurs in the electro-optical crystal decreases and thereby the extinction ratio of the optical switch improves. This effect can improve further when insulator layer110is formed after a known anti reflection coat is formed on the light exit plane.

When all planes of electro-optical crystal104other than the light incident plane and the light exit plane from which light that has passed through the electrode section exits are covered respectively with temperature control devices111made of a temperature controlling heat sink or Peltier device, the durability of the optical switch against shock improves more significantly than that of the first embodiment.

Alternatively, when most of the planes of electro-optical crystal104are covered respectively with temperature control devices111, they can have an electromagnetic shielding effect. Thus, malfunction of the optical switch due to radio frequency noise and so forth decreases.

THIRD EMBODIMENT

FIG. 7shows a structure of an optical switch according to a third embodiment: (a) is a perspective view of the drawing; (b) is a sectional view of the drawing taken along line B-B of the optical switch shown inFIG. 7(a).

As shown inFIGS. 7(a) and (b), the optical switch according to the third embodiment has a structure in which a plurality of stages of electrode sections106(inFIGS. 7(a), (b), two stages are exemplified) are arranged on an optical path of incident light. Electrode planes composed of electrodes105of electrode sections106are arranged in parallel with each other.

When the optical switch as shown inFIGS. 7(a), (b) has a structure in which electrode section106that incident light reaches first reflects the incident light and the later stage of electrode section106reflects light that passes through the preceding stage of electrode section106, the intensity of light that is not reflected by each of electrode sections106, but that passes through each of electrode sections106, and that exits from the light exit plane can be decreased. Thus, the optical switch that is provided with a plurality of stages of electrode sections106as shown inFIGS. 7(a), (b) can improve the extinction ratio more significantly than the optical switch according to the first embodiment.

The third embodiment has a structure in which temperature control devices111are formed respectively through insulation layers110on the lower plane and the upper plane of electro-optical crystal104, the lower and upper planes being parallel with electrode sections106. Insulation layers110and temperature control devices111can be made of the same materials as those of the first embodiment.

Such a structure, like the first embodiment, allows the temperatures in the proximity of electrode sections106to become stable, the operation of the optical switch becomes stable and reliability thereof improves.

In addition, since the direction of the reflected light becomes stable, stray light that occurs in electro-optical crystal104decreases and thereby the extinction ratio of the optical switch improves.

Moreover, since temperature control devices111are formed respectively through insulator layers110having a lower dielectric constant than electro-optical crystal104, the capacitance component increase slightly and thereby the restriction of the operation speed (bandwidth) of the optical switch is alleviated.

Furthermore, since the relevant planes of electro-optical crystal104are covered respectively with temperature control devices111each of which is a heat sink, a Peltier device, or the like, durability of the optical switch against shock improves.

AlthoughFIGS. 7(a), (b) show an exemplified structure in which temperature control devices111are formed respectively through insulation layers110on the lower plane or upper plane of electro-optical crystal104, the lower plane or upper plane corresponding to electrode sections106, as shown inFIGS. 8(a), (b), temperature control devices111may be formed respectively through insulation layers110on the lower plane and upper plane of electro-optical crystal104, the lower and upper planes being parallel with electrode sections106.

Alternatively, in the structure where electrode sections106are arranged on the optical path of the incident light shown inFIGS. 7(a), (b), like the optical switch (second embodiment) shown inFIGS. 6(a), (b), temperature control devices111may be formed respectively through insulation layers110on all the planes of electro-optical crystal104other than the light incident plane and the light exit plane.

When the planes of electro-optical crystal104other than the light incident plane and the light exit plane are covered respectively with temperature control devices111through insulation layers110, the durability of the optical switch against shock or the like improves and malfunction of the optical switch due to radio frequency noise or the like decreases.

In particular, when insulator layers110are made of a graphite sheet, silicone, a low-k (low dielectric constant) material for semiconductor devices (organic polymer type, SiO, etc.), or the like and when insulation layer110is also formed, for example, on the light exit plane from which reflected light exits, since insulation layer110also functions as a light absorption layer, reflection of unnecessary light on the light exit plane decreases. Thus, if transmitted light is used as output light of the optical switch, when insulator layer110is also formed on the exit plane of reflected light, since insulator layer110absorbs the exited light, stray light that occurs in the electro-optical crystal decreases and thereby the extinction ratio of the optical switch improves. This effect can further improve when insulator layer110is formed after a known anti reflection coat is formed on the light exit plane.

FOURTH EMBODIMENT

FIG. 9shows a structure of an optical switch according to a fourth embodiment: (a) is a perspective view of the drawing; (b) is a sectional view of the drawing taken along line B-B of the optical switch shown inFIG. 9(a).

The optical switch according to the fourth embodiment has the same structure as the optical switch shown inFIG. 2except that anti reflection coats210are formed respectively on light incident plane204to which light enters and light exit plane205from which transmitted light exits.

Anti reflection coats210may be of any material, any film thickness, any film composition (regardless of single layer film or multi layer film), and so forth and may be formed using a known technique as long as they have an anti reflection effect against light having a predetermined wavelength.

When the optical switch has the structure in which anti reflection coats210are formed respectively on light incident plane204and light exit plane205from which transmitted light exits, unnecessary reflected light on light incident plane204and light exit plane205decreases. Thus, when transmitted light is used, for example, as a light output of the optical switch, since the use efficiency of the transmitted light increases, the extinction ratio of the optical switch improves.

Alternatively, the optical switch according to the fourth embodiment may have a structure in which anti reflection coat210is also formed on light exit plane206from which reflected light exits.FIGS. 9(a), (b) show an exemplified structure in which anti reflection coats210are formed respectively on light exit planes205,206.

When anti reflection coat210is also formed on light exit plane206from which reflected light exits, unnecessary reflected light on light exit plane206decreases. Thus, when transmitted light is used, for example, as light output of the optical switch, since light can easily exit from light exit plane206to the outside, stray light that occurs in electro-optical crystal104decreases and the extinction ratio of the optical switch improves.

Although the above description exemplifies that transmitted light is used as a light output of the optical switch, reflected light can be used as light output of the optical switch.

When the optical switch operates, since light reflects mostly on light incident plane204through which light passes and on light exit planes205,206, if anti reflection coats210are formed respectively on light incident plane204and light exit planes205,206, stray light can be decreased most effectively with the least amount of material.

Alternatively, anti reflection coats210may be formed respectively on other planes of electro-optical crystal104as well as light incident plane204and light exit planes205,206. In this case, since reflections of light on planes other than light incident plane204and light exit planes205,206decrease, stray light in electro-optical crystal104decreases more significantly and thereby the extinction ratio of the optical switch further improves.

Since the optical switches shown inFIG. 2andFIGS. 9(a), (b) have the structures in which light exit planes are switched depending on whether a voltage is applied to electrode section106, when exit light is to be turned on/off, any one of two exit lights needs to be extinguished by a light absorber or the like that is formed for example outside.

As shown inFIGS. 10(a), (b), the optical switch according to this embodiment may have a structure in which light absorption layer300is formed on a plane from which unused light exits, for example, light exit plane206that light reflected by electrode section106(reflected light) reaches. Light absorption layer300can be made of a material that easily absorbs light, for example, a graphite sheet or the like.

When the optical switch has a structure in which light absorption layer300is formed on the light exit plane, since the optical switch does not need to be provided with an external light absorber, it can be easily built in an optical module or the like. In addition, since an optical module or the like does not need to be provided with a light absorber, the entire device including the optical switch according to this embodiment can be miniaturized.

Alternatively, light absorption layers300may be formed respectively on other planes of electro-optical crystal104as well as any one of light exit planes205and206other than light incident plane204. In this case, since light scattered by electrode section106reaches planes other than light incident plane204and light exit planes205,206, light that exits to the outside of the crystal is absorbed by the light absorption layer and thereby stray light that occurs in electro-optical crystal104decreases more significantly. Thus, the extinction ratio of the optical switch can be further improved. In addition, since the optical switch does not need to be provided with a light absorber outside the crystal, the optical switch device can be easily miniaturized and can be easily built in equipment.

When light absorption layer300is made of a material having a high thermal conductivity such as a graphite sheet or a silicone and a temperature control device such as a Peltier device or the like is formed on light absorption layer300, the temperature of electro-optical crystal104can be effectively controlled.

Next, the degree of effect that can be obtained with the optical switch according to this embodiment will be described.

In the following, the case in which the transmitted light shown inFIG. 2is light output of the optical switch will be considered.

When the optical switch has a structure in which anti reflection coats210are not formed respectively on light incident plane204and light exit plane205from which transmitted light exits, light of around 5% reflects on these planes. Thus, when electrode section106that transmits 70% of the intensity of incident light is formed, the use efficiency of light of the optical switch amounts to around 63%.

In contrast, when the optical switch according to this embodiment has a structure in which anti reflection coats210are formed respectively on light incident plane204and light exit plane205from which transmitted light exits, light that reflects on these planes can be suppressed to around 1%. Thus, the use efficiency of light of the optical switch according to this embodiment amounts to 68% or greater.

FIFTH EMBODIMENT

FIG. 11shows a structure of an optical switch according to a fifth embodiment: (a) is a perspective view of the drawing; (b) is a sectional view of the drawing taken along line B-B of the optical switch shown inFIG. 11(a).

As shown inFIGS. 11(a), (b), the optical switch according to the fifth embodiment has a structure in which a plurality of stages of electrode sections106(inFIGS. 11(a), (b), two stages are exemplified) are arranged on an optical path of incident light.

When the optical switch as shown inFIGS. 11(a), (b) has a structure in which electrode section106that incident light reaches first reflects the incident light and the later stage of electrode section106reflects light that passes through the preceding stage of electrode section106, the intensity of light that is not reflected by each of electrode sections106, but that passes through each of electrode sections106, and that exits from the light exit plane can be decreased. Thus, the optical switch that is provided with a plurality of stages of electrode sections106as shown inFIGS. 11(a), (b) can improve the extinction ratio more significantly than the optical switch shown inFIG. 1.

In addition to the plurality of stages of electrode sections106, the optical switch according to the fifth embodiment has a structure in which anti reflection coats210are formed on light incident plane204and light exit planes205,206,207.

In such a structure, since unnecessary reflections on light incident plane204and light exit planes205,206,207decrease, the use efficiency of transmitted light increases, and reflected light on these planes tends to exit to the outside, then stray light that occurs in the electro-optical crystal decreases and thereby the extinction ratio of the optical switch further improves.

Like the fourth embodiment, the optical switch according to the fifth embodiment may have a structure in which anti reflection coats210are formed respectively on other planes of electro-optical crystal104as well as light incident plane204and light exit planes205,206,207. In this case, since reflections of light on planes other than light incident plane204and light exit planes205,206,207decrease, stray light in electro-optical crystal104decreases more significantly and thereby the extinction ratio of the optical switch further improves.

Like the fourth embodiment, the optical switch according to the fifth embodiment may have a structure in which light absorption layers300are formed respectively on planes from which unused light exits, for example, light exit planes206,207that light reflected on electrode sections106reaches (reflected light).FIGS. 11(a), (b) show an exemplified structure in which light absorption layers300are formed respectively on light exit planes206,207. Such a structure does not need to be provided with an external light absorber, it can be easily built in an optical module or the like. In addition, since an optical module or the like does not need to be provided with a light absorber, the entire device including the optical switch according to this embodiment can be miniaturized.

Like the fourth embodiment, when the optical switch according to the fifth embodiment has a structure in which light absorption layers300each are made of a material having a high thermal conductivity such as a graphite sheet or a silicone and temperature control devices such as Peltier devices or the like are formed respectively on light absorption layers300, the temperature of electro-optical crystal104can be effectively controlled.

SIXTH EMBODIMENT

FIG. 12shows a structure of an optical switch according to a sixth embodiment: (a) is a perspective view of the drawing; (b) is a sectional view of the drawing taken along line B-B of the optical switch shown inFIG. 12(a).

Like the optical switch according to the fifth embodiment, as shown inFIGS. 12(a), (b), the optical switch according to the sixth embodiment has a structure in which a plurality of stages of electrode sections106(in FIGS.12[a], [b], two stages are exemplified) are formed on an optical path of incident light.

In addition to the plurality of stages of electrode sections106, the optical switch according to the sixth embodiment has a structure in which anti reflection coats210are formed respectively on light incident plane204and light exit planes205,206,207and anti reflection coats and light absorption layers300are formed respectively on planes of electro-optical crystal104other than light incident plane204and light exit planes205,206,207.

Like the fourth and fifth embodiments, the optical switch according to the sixth embodiment may have a structure in which light absorption layers300are formed respectively on planes from which unused light exits, for example, light exit planes206,207that light reflected on electrode sections106(reflected light) reaches.FIGS. 12(a), (b) show an exemplified structure in which light absorption layers300are formed respectively on light exit planes206,207.

Like the optical switch according to the fifth embodiment,FIGS. 12(a), (b) show an exemplified optical switch having a structure in which a plurality of stages of electrode sections106are formed on an optical path of incident light; like the optical switch according to the fourth embodiment, when the optical switch according to the sixth embodiment has a structure in which one electrode section106is formed on an optical path of incident light, light absorption layers300may be formed respectively on planes of electro-optical crystal104other than light incident plane204and light exit plane205.

When anti reflection coats210and light absorption layers300are formed respectively on planes of electro-optical crystal104other than light incident plane204and light exit planes205,206,207, light that reaches electro-optical crystal104due to scattering or the like tends to exit to the outside of the crystal and the exited light is absorbed by light absorption layers300and thereby stray light that occurs in electro-optical crystal104further decreases. Thus, the optical switch according to the sixth embodiment can improve the extinction ratio more significantly than the optical switches according to the fourth embodiment and fifth embodiment.

When either anti reflection coats210or light absorption layers300are formed respectively on planes of electro-optical crystal104other than light incident plane204and light exit planes205,206,207, the effect in which stray light decreases can be obtained; however, when both anti reflection coats210and light absorption layers300are formed, the highest effect can be obtained and the extinction ratio of the optical switch improves most significantly.

Like the fourth and fifth embodiments, when the optical switch according to the sixth embodiment has a structure in which light absorption layers300each are made of a material having a high thermal conductivity such as a graphite sheet or a silicone and temperature control devices such as Peltier devices or the like are formed respectively on light absorption layers300, the temperature of electro-optical crystal104can be effectively controlled.

SEVENTH EMBODIMENT

FIG. 13shows a structure of an optical switch according to a seventh embodiment: (a) is a perspective view of the drawing; (b) is a sectional view of the drawing taken along line B-B of the optical switch shown inFIG. 13(a).

Like the optical switches according to the fifth and sixth embodiments, as shown inFIGS. 13(a), (b), the optical switch according to the seventh embodiment has a structure in which a plurality of states of electrode sections106(inFIGS. 13(a), (b), two stages are exemplified) are formed on an optical path of incident light.

Like the optical switch according to the sixth embodiment, in addition to the plurality of stages of electrode sections106, the optical switch according to the seventh embodiment has a structure in which anti reflection coats210are formed respectively on light incident plane204and light exit planes205,206,207and anti reflection coats210and light absorption layers300are formed respectively, in particular, on planes of electro-optical crystal104other than light incident plane204and light exit planes205,206,207, the planes being parallel with electrode sections106.

Light absorption layers300each are made of an insulator having a lower dielectric constant than the electro-optical crystal and temperature control devices111are formed in contact with light absorption layers300so as to control the temperature of electrode sections105or dissipate heat generated in electrode sections105.

Like the fourth embodiment and fifth embodiment, the optical switch according to this embodiment may have a structure in which light absorption layers300are formed on planes from which unused light exits, for example, light exit planes206,207that light reflected by electrode section106(reflected light) reaches.FIGS. 13(a), (b) show an exemplified structure in which light absorption layers300are also formed respectively on light exit planes206,207.

When anti reflection coats210and light absorption layers300are formed respectively on planes of electro-optical crystal104other than light incident plane204and light exit planes205,206,207, light that reaches electro-optical crystal104due to scattering or the like tends to exit to the outside of the crystal and the exited light is absorbed by light absorption layers300and thereby stray light that occurs in electro-optical crystal104further decreases. Thus, the extinction ratio of the optical switch improves.

When either anti reflection coats210or light absorption layers300are formed respectively on planes of electro-optical crystal104other than light incident plane204and light exit planes205,206,207, the effect in which stray light decreases can be obtained; however, when both anti reflection coats210and light absorption layers300are formed, the highest effect can be obtained and the extinction ratio of the optical switch improves most significantly.

In addition to the structure according to the seventh embodiment, as presented in the first to third embodiments, temperature control devices111may be also formed respectively on planes of electro-optical crystal104, the planes being closest to electrode section106that is formed on the optical path of the incident light and whose characteristics fluctuate the most as the temperature changes, and each of temperature control devices111may be a thermoelectric transducer such as a Peltier device that serves to control the temperature of electrode section106or a heat dissipating device such as a heat sink that serves to dissipate heat generated in electrode section106. When such a structure is used, the temperatures of electrode sections106can be controlled to be as close as possible to the temperature of electrode sections106without it being necessary to increase the capacitance component, or the temperature can be controlled so that heat generated in electrode sections106can be dissipated.

When the refractive index of electro-optical crystal104is changed according to an electric field applied thereon, the refractive index generally changes depending on the temperature of the crystal. When the magnitude of change of the refractive index fluctuates as the temperature changes, the intensity of output light of the optical switch also changes. Thus, to stabilize the operation of the optical switch, the temperatures at which the refractive index changes in electro-optical crystal104need to be maintained in a proper range.

Since the optical switch according to the seventh embodiment has the structure in which temperature control devices111are formed on planes of the electro-optical crystal, the planes being parallel with electrode sections106and being closest to electrode sections106whose characteristics fluctuate the most as the temperature changes, the temperatures in the proximities of electrode sections106can be evenly and effectively controlled or heat in the proximities of electrode sections106can be evenly and effectively dissipated. Thus, the direction of reflected light becomes stable as the temperatures of refractive index change sections108fluctuate and thereby the operation of the optical switch becomes stable.

In addition, since the direction of reflected light becomes stable, stray light that occurs in electro-optical crystal104decreases and also the extinction ratio of the optical switch improves. Moreover, since the temperatures of electrode sections106do not excessively rise, they are prevented from being damaged and thereby the reliability of the optical switch improves.

Moreover, since temperature control devices111are formed respectively through insulator layers110having a lower dielectric constant than electro-optical crystal104, the capacitance component increases slightly and thereby the restriction of the operation speed (bandwidth) of the optical switch is alleviated.

Furthermore, since the relevant planes of electro-optical crystal104are covered with temperature control devices111each of which is made of a heat sink, a Peltier device, or the like, the durability of the optical switch against shock improves.

EIGHTH EMBODIMENT

FIG. 14shows a structure of an optical switch according to an eighth embodiment: (a) is a side section view of the drawing; (b) is a plain view of the drawing.

The optical switch according to the eighth embodiment has the same structure as the optical switch shown inFIG. 2except that insulation section110that has a lower dielectric constant and a higher thermal conductivity than electro-optical crystal104is formed in contact with electrode lead-out sections109that apply a voltage to each of electrodes105from external power supply107and temperature control device111that controls the temperature of electrode section106or dissipates heat generated in electrode section106is formed on a plane of insulation section110.

Temperature control device111is a thermoelectric transducer such as a Peltier device that serves to control the temperature of electrode section106or a heat dissipating device such as a heat sink that serves to dissipate heat generated in electrode section106.

When temperature control device111is a thermoelectric transducer, a temperature sensor is attached to the optical switch so as to detect the temperature in the electrode forming region including electrode section106and refractive index change section108.

When a current is supplied from a current source (not shown) to the thermoelectric transducer, it generates heat. When the thermoelectric transducer generates heat, the thermal energy causes insulation section110to heat, causes electrode section106to heat through electrode lead-out sections109, and thereby causes the temperature of the electrode forming region to rise. Another type of thermoelectric transducer is provided with a heat absorption function that absorbs thermal energy from its contacting member. For example, when a DC current is caused to flow in the foregoing Peltier device, its one plane generates heat and another plane absorbs it. In addition, when the direction of a current that flows in the Peltier device is inverted, the heat generation plane and the heat absorption plane are inverted to each other. Thus, when the thermoelectric transducer is a Peltier device, the electrode forming region can be heated and cooled.

The temperature sensor is attached to a portion at which the thermal relationship with the electrode forming region is known (for example, a portion where the heat resistance is known). Thus, the temperature of the electrode forming region can be estimated based on the value detected by the temperature sensor.

When the temperature of the electrode forming region is controlled, a predetermined threshold is designated for the detected value of the temperature sensor based on the thermal relationship between the portion at which the temperature sensor is attached and the electrode forming region: if the detected value of the temperature sensor is lower than the threshold, the electrode forming region is heated by thermoelectric transducer through insulator layer110; if the detected value of the temperature sensor is equal to or greater than the threshold, the electrode forming region is cooled by the thermoelectric transducer through insulator layer110. Such a process can maintain the temperature of the electrode forming region within a predetermined temperature range.

When the temperature of the electrode forming region is to be always maintained at about the room temperature, only heat generated in the electrode forming region can be dissipated; temperature control device111may be a heat dissipating device such as a heat sink so as to effectively dissipate heat generated in electrode section106that has been irradiated with high intensity light.

As described above, when the refractive index of electro-optical crystal104is changed according to an electric field applied thereto, the refractive index changes depending on the temperature of the crystal. When the magnitude for which the refractive index changes fluctuates according to the temperature, the intensity of output light of the optical switch also changes. Thus, to stably operate the optical switch, the temperature at which the refractive index changes in electro-optical crystal104needs to be maintained in an appropriate range.

Since the optical switch shown inFIG. 2has a structure in which electrode section106is formed on an optical path of incident light, when electrode section106is irradiated with light, the temperature of electrode section106tends to rise. When the temperature of electro-optical crystal104in the proximity of electrode section106changes, as the temperature rise of electrode section106rises, the refractive index corresponding to the applied voltage also changes and thereby it becomes difficult to maintain the flatness of the refractive index interface of refractive index change section108. Thus, for the optical switch shown inFIG. 2, it is preferred that the temperatures of electrode section106and electro-optical crystal104that are formed in the proximity thereof be maintained constant.

Thus, as shown inFIGS. 14(a), (b), the optical switch according to this embodiment has a structure in which insulation section110that has a lower dielectric constant and a higher thermal conductivity than electro-optical crystal104is formed in contact with electrode lead-out sections109that apply a voltage to each of electrodes105from external power supply107and temperature control device111that controls the temperature of electrode section106or dissipates heat generated in electrode section106is formed on a plane of insulation section110. Thus, the temperature of electrode section106can be effectively controlled or heat generated in electrode section106can be effectively dissipated.

Since the optical switch according to this embodiment has a structure in which insulation section110is in contact with part of electrode section106(electrode lead-out section109), insulation section110does not disturb refractive index change section108that transmits or totally reflects incident light, refractive index change section108being formed by applying voltage to electrodes105.

Insulation section110may be made of SiO2, SiN, a graphite sheet, silicone, a low-k (low dielectric constant) material for semiconductor devices (organic polymer, SiOC, etc), or the like. When insulation section110is attached to electrode lead-out sections109using a bonding agent, the effect of insulation section110can be expected. In addition, when insulation section110is made of SiO2, SiN, or the like, insulation section110can be formed using an existing production facility for semiconductor devices.

Since the optical switch according to this embodiment has a structure in which insulation section110is formed in contact with part of electrode section106whose characteristics fluctuate the most as the temperature changes and that is formed on an optical path of incident light and thereby thermal energy of temperature control device111is transferred to insulation section110and to each of electrodes105, the temperature of the electrode forming region can be effectively controlled or heat generated in electrode section106can be effectively dissipated through electrodes105and insulation section110. Thus, even if the temperature of the electrode forming region fluctuates, since the temperature can be controlled in the proximity of electrode section106and refractive index change section108is stably formed, the operation of the optical switch becomes stable.

In addition, since refractive index change section108is stably formed and thereby the direction of reflected light becomes stable, stray light that occurs in electro-optical crystal104decreases and also the extinction ratio of the optical switch improves. Moreover, since the temperature of electrode section106does not excessively rise, damage to electrode section106is prevented and thereby the reliability of the optical switch improves.

When the optical switch according to this embodiment has a structure in which electrodes105that compose electrode section106are made of a material having a high thermal conductivity (for example, gold, platinum, copper, or the like), the temperature can be more effectively controlled and thereby the optical switch can more stably operate as the temperature fluctuates.

NINTH EMBODIMENT

FIG. 15shows a structure of an optical switch according to a ninth embodiment: (a) is a side sectional view of the drawing; (b) is a plan view of the drawing.

The optical switch according to the ninth embodiment has the same structure as the optical switch shown inFIG. 2except that insulation section110that has a lower dielectric constant and a higher thermal conductivity than electro-optical crystal104is formed in contact with electrode section106and temperature control device111that controls the temperature of electrode section106or dissipates heat generated in electrode section106is formed on a plane of insulation section110. In addition, the optical switch according to the ninth embodiment has a structure in which insulation section110and electrode section106are formed in the same shape in electro-optical crystal104.

Like the eighth embodiment, temperature control device111is a thermoelectric transducer such as a Peltier device that serves to control the temperature of electrode section106or a heat dissipating device such as a heat sink that serves to dissipate heat generated in electrode section106.

When temperature control device111is a thermoelectric transducer, a temperature sensor is attached to the optical switch so as to detect the temperature in the electrode forming region including electrode section106and refractive index change section108. The temperature sensor is attached to a portion at which the thermal relationship with the electrode forming region is known (for example, a portion where the heat resistance is known). Thus, the temperature of the electrode forming region can be estimated based on the value detected by the temperature sensor.

Like the eighth embodiment, when the temperature of the electrode forming region is controlled, a predetermined threshold is designated for the detected value of the temperature sensor based on the thermal relationship between the portion at which the temperature sensor is attached and the electrode forming region: if the detected value of the temperature sensor is lower than the threshold, the electrode forming region is heated by thermoelectric transducer through insulator layer110; if the detected value of the temperature sensor is equal to or greater than the threshold, the electrode forming region is cooled by the thermoelectric transducer through insulator layer110. Such a process can maintain the temperature of the electrode forming region within a predetermined temperature range.

When the temperature of the electrode forming region is to be always maintained at about room temperature, only heat generated in the electrode forming region can be dissipated; temperature control device111may be a heat dissipating device such as a heat sink so as to effectively dissipate heat generated in electrode section106that has been irradiated with high intensity light.

As shown inFIGS. 15(a), (b), the optical switch according to the ninth embodiment has a structure in which insulation section110having a lower dielectric constant and a higher thermal conductivity than electro-optical crystal104is formed in contact with not only electrode lead-out sections109but also with one entire plane of electrode section106. Since the contact area of insulation section110and electrode section106is greater than that of the optical switch according to the eighth embodiment, heat generated in electrode section106can be more effectively disseminated or the temperature of electrode section106can be more effectively controlled than the optical switch according to the eighth embodiment.

The optical switch according to this embodiment has a structure in which insulation section110and electrode section106are formed in the same shape in electro-optical crystal104. Since insulation section110and electrode section106are formed in the same shape, insulation section110can dissipate heat generated in electrode section106or control the temperature of electrode section106without disturbing refractive index change section108that transmits or totally reflects incident light, refractive index change section108being formed by applying a voltage to electrodes105.

Insulation section110may be made of SiO2, SiN, a graphite sheet, silicone, a low-k (low dielectric constant) material for semiconductor devices (organic polymer, SiOC, etc), or the like. When insulation section110is made of SiO2, SiN, or the like, insulation section110can be formed using an existing production facility for semiconductor devices.

Since the optical switch according to this embodiment has a structure in which insulation section110is fully in contact with electrode section106including electrode lead-out sections109, the contact area of insulation section110and electrode section106becomes large and thereby insulation section110can dissipate heat generated in electrode section106or control the temperature of electrode section106more effectively than the optical switch according to the eighth embodiment. Thus, even if the temperature of the electrode forming region fluctuates, since the temperature can be controlled in the proximity of electrode section106and refractive index change section108is stably formed, the operation of the optical switch becomes stable.

In addition, since refractive index change section108is stably formed and thereby the direction of reflected light becomes stable, stray light that occurs in electro-optical crystal104decreases and also the extinction ratio of the optical switch improves. Moreover, since the temperature of electrode section106does not excessively rise, damage to electrode section106is prevented and thereby the reliability of the optical switch improves.

In addition, since the optical switch according to this embodiment has a structure in which part of planes of each of electrodes105is covered with insulation section110having a lower dielectric constant than electro-optical crystal104, the capacitance between electrodes105is lower than that of the structure in which all planes of each of electrodes105are covered with electro-optical crystal104having a higher dielectric constant than electrodes105. Thus, power consumption of the optical switch according to this embodiment is lower than that of the optical switch according to the eighth embodiment. In addition, since the capacitance of the optical switch according to this embodiment decreases, high speed operation of the optical switch can be accomplished.

Like the eighth embodiment, when the optical switch according to this embodiment has a structure in which electrodes105that compose electrode section106are made of a material having a high thermal conductivity (for example, gold, platinum, copper, or the like), the temperature can be more effectively controlled and the optical switch can more stably operate as the temperature fluctuates.

TENTH EMBODIMENT

FIG. 16shows a structure of an optical switch according to a tenth embodiment: (a) is a side sectional view of the drawing; (b) is a plan view of the drawing.FIG. 17shows a structure of an exemplified modification of the optical switch according to the tenth embodiment: (a) is a side sectional view of the drawing; (b) is a plan view of the drawing.

The optical switch shown inFIGS. 16(a), (b) is the same as the optical switch shown inFIGS. 17(a), (b) except for the positions of electrode lead-out sections109that connect external power supply107to each of electrodes105.

As shown inFIGS. 16(a) and (b) andFIGS. 17(a) and (b), the optical switch according to the tenth embodiment has a structure in which a plurality of stages of electrode sections106(in FIGS.16[a]and [b] and FIGS.17[a] and [b], two stages are exemplified) are arranged on an optical path of incident light.

When the optical switch shown inFIGS. 16(a) and (b) andFIGS. 17(a) and (b) has a structure in which electrode section106that incident light reaches first reflects the incident light and the later stage of electrode section106reflects light that passes through the preceding stage of electrode section106, the intensity of light that is not reflected by each of electrode sections106, but that passes through each of electrode sections106, and that exits from the light exit plane can be decreased. Thus, the optical switch that is provided with a plurality of stages of electrode sections106shown inFIGS. 16(a) and (b) andFIGS. 17(a) and (b) can improve the extinction ratio more than the optical switch shown inFIG. 1.

The optical switch according to the tenth embodiment has a structure in which insulation sections110having a lower dielectric constant and a higher thermal conductivity than electro-optical crystal104are in contact with at least part of each of electrode sections106and temperature control devices111are formed on one end of each of insulation sections110.

Alternatively, like the eighth embodiment, insulation sections110may be formed in contact with only electrode lead-out sections109; like the ninth embodiment, insulation sections110may be formed fully in contact with electrode sections106including electrode lead-out sections109.

Materials of electrodes105that composes electrode section106, insulation sections110, and temperature control devices111can be the same as those of the eighth and ninth embodiments.

Since this structure allows heat generated in each of electrode sections106to be effectively dissipated or the temperature of each of electrode sections106to be effectively controlled, even if the temperatures fluctuate, since refractive index change sections108are stably formed in the proximities of electrode sections106, the operation of the optical switch becomes stable.

In addition, since the optical switch according to the tenth embodiment has a structure in which light (incident light) passes through a plurality of stages of electrodes106, the extinction ratio of the optical switch improves more significantly than the optical switches according to the eighth and ninth embodiments.

In addition, since refractive index change section108is stably formed and thereby the direction of reflected light becomes stable, stray light that occurs in electro-optical crystal104decreases and also the extinction ratio of the optical switch improves. Moreover, since the temperatures of electrode sections106do not excessively rise, electrode sections106are prevented from being damaged and thereby the reliability of the optical switch improves.

In addition, like the ninth embodiment, since the optical switch according to the tenth embodiment has a structure in which insulation sections110are fully formed respectively on electrode sections106including electrode lead-out sections109and thereby part of the planes of each of electrodes105is covered with insulation section110having a lower dielectric constant than electro-optical crystal104, the capacitance between electrodes105is lower than that of the structure in which all planes of each of electrodes105are covered with electro-optical crystal104having a higher dielectric constant than electrodes105. Thus, the power consumption of the optical switch according to this embodiment is lower than that of the optical switch according to the eighth embodiment. In addition, since the capacitance of the optical switch according to this embodiment decreases, high speed operation of the optical switch can be accomplished.

ELEVENTH EMBODIMENT

An eleventh embodiment presents a specific example of a device that is provided with optical switches according to any one of the first to tenth embodiments.

First, an image display device that is provided with optical switches according to the present invention will be described.

FIG. 18is a schematic diagram showing an exemplary structure of an image display device that is provided with optical switches according to the present invention. Image display device1401has laser light sources1402to1404, collimator lenses1405to1407, reflection mirror1408, dichroic mirrors1409,1410, horizontal scanning mirror1411, vertical scanning mirror1412, and optical switches1414to1416. Optical switches1414to1416are optical switches according to any one of the first to tenth embodiments.

Collimator lens1407, optical switch1416, and reflection mirror1408are successively arranged in the traveling direction of laser light emitted from laser light source1402. A collimated light beam that passes through collimator lens1407enters optical switch1416. Optical switch1416operates according to a control signal supplied from a control section (not shown). During an ON period of the control signal (voltage supply period), since a refractive index change region is formed according to a voltage applied to an electrode section, the refractive index change section reflects incident light. The reflected light deflects from an optical path that extends to reflection mirror1408. During an OFF period of the control signal (voltage supply stop period), incident light passes through optical switch1416and reaches reflection mirror1408.

Collimator lens1406, optical switch1415, and dichroic mirror1410are successively arranged in the traveling direction of laser light emitted from laser light source1403. A collimated light beam that passes through collimator lens1406enters optical switch1415. Like optical switch1416, optical switch1415also operates according to a control signal supplied from the control section (not shown). During an ON period of the control signal (voltage supply period), since a refractive index change region is formed according to a voltage applied to an electrode section, the refractive index change section reflects incident light. The reflected light deflects from an optical path that extends to dichroic mirror1410. During an OFF period of the control signal (voltage supply stop period), incident light passes through optical switch1415and reaches dichroic mirror1410.

Collimator lens1405, optical switch1414, and dichroic mirror1419are successively arranged in the traveling direction of laser light emitted from laser light source1404. A collimated light beam that passes through collimator lens1405enters optical switch1414. Like optical switches1415,1416, optical switch1414operates according to a control signal supplied from the control section (not shown). During an ON period of the control signal (voltage supply period), since a refractive index change region is formed according to a voltage applied to an electrode section, the refractive index change section reflects incident light. The reflected light deflects from an optical path that extends to dichroic mirror1409. During an OFF period of the control signal (voltage supply stop period), incident light passes through optical switch1414and reaches dichroic mirror1409.

Dichroic mirror1410is located at a position where a light beam that passes through optical switch1415and a light beam reflected by reflection mirror1408intersect each other. Dichroic mirror1410has a wavelength selective characteristic that causes light that passes through optical switch1415to be reflected and light reflected by reflection mirror1408to pass.

Dichroic mirror1409is located at a position where a light beam that passes through optical switch1414and a light beam reflected by dichroic mirror1410intersect each other. Dichroic mirror1409has a wavelength selective characteristic that causes light that passes through optical switch1414to be reflected and light that passes through dichroic mirror1410to pass.

Horizontally scanning mirror1411is located in the travelling direction of a light beam that passes through or is reflected by dichroic mirror1409and its operation is controlled according to a horizontal scanning control signal that is outputted from the control section (not shown). Vertical scanning mirror1412is located in the travelling direction of a light beam reflected by horizontal scanning mirror1411and its operation is controlled according to a vertical scanning control signal that is outputted from the control section (not shown).

Laser light sources1402,1403,1404emit laser lights corresponding to three primary colors of R, G, B, respectively.

The image display device shown inFIG. 18turns on/off optical switches1414,1415,1416and controls horizontal scanning mirror1411and vertical scanning mirror1412so as to display a color image on screen1413.

Next, an image forming device that is provided with an optical switch according to the present invention will be described.

FIG. 19is a schematic diagram showing an exemplified structure of an image forming device that is provided with an optical switch according to the present invention. Image forming device1501has laser light source1502, collimator lens1503, reflection mirror1504, scanning mirror1505, optical switch1506, fθ lens1507, and photoreceptor1508. Optical switch1506is an optical switch according to any one of the first embodiment to tenth embodiments.

Collimator lens1503, optical switch1506, and reflection mirror1504are successively arranged in the traveling direction of laser light emitted from laser light source1502. A collimated light beam that passes through collimator lens1503enters optical switch1506. Optical switch1506operates according to a control signal supplied from a control section (not shown). During an ON period of the control signal (voltage supply period), since a refractive index change region is formed according to a voltage applied to an electrode section, it reflects incident light. The reflected light deflects from the optical path extending to reflection mirror1505. During an OFF period of the control signal (voltage supply stop period), the incident light passes through optical switch1506and reaches reflection mirror1505.

Scanning mirror1505is located in the travelling direction of a light beam reflected by reflection mirror1505and its operation is controlled according to a scanning control signal that is outputted from a control section (not shown). Photoreceptor1508is irradiated with light that is reflected by scanning mirror1505and then passes through fθ lens1507.

The image forming device shown inFIG. 19turns on/off optical switch1506and controls scanning mirror1505so as to form an image on photoreceptor1508.

Alternatively, the image forming device shown inFIG. 19may be used as a device that directly projects a scanned image on photoreceptor1508without causing it to pass through fθ lens1507located immediately before photoreceptor1508.

The optical switches presented in the foregoing first to tenth embodiments and systems using them are just examples of the present invention and their procedures and structures can be changed without departing from the spirit of the present invention.

Now, with reference to the embodiments, the present invention has been described. However, it should be understood by those skilled in the art that the structure and details of the present invention may be changed in various manners without departing from the scope of the present invention.

This application claims priority based on Japanese Patent Applications No. 2008-322727, No. 2008-322734 and No. 2008-322735 filed on Dec. 18, 2008, the disclosure of which is incorporated herein by reference in its entirety.