JP7544382B2 - Static Electricity Sensor - Google Patents

Description

The present invention relates to an electrostatic sensor that utilizes the phenomenon in which the light emission state changes depending on the electric charge.

Static electricity is generated everywhere due to various factors. Electronic devices are particularly susceptible to the effects of static electricity, which can cause malfunctions or breakdowns. Furthermore, in environments where dust and powder are flying around, such as factories, or in atmospheres where volatile substances are floating around, there is a risk of static electricity inducing explosions. To avoid such problems, it is necessary to detect the static electricity on charged objects and remove the electricity.

Traditionally, handheld detectors have been used to detect static electricity, but even smaller detectors are now being used so that they can be placed on production lines. However, to detect static electricity generated in narrow spaces such as inside semiconductor devices, detectors need to be made even smaller.

As a technology that meets such demands, for example, Patent Document 1 discloses a semiconductor electrostatic sensor that includes a silicon substrate and an insulating film formed on the silicon substrate. In this semiconductor electrostatic sensor, when a charge is injected into the electrode of the insulating film, and the potential of the electrode exceeds the electrostatic withstand voltage of the insulating film, the insulating film breaks down, and the amount of charge can be determined from the potential of the electrode at the time of the breakdown. Such a semiconductor electrostatic sensor can be formed on a silicon chip, making it possible to sufficiently miniaturize it.

Japanese Patent Application Laid-open No. 4-15566 (published on January 20, 1992)

The semiconductor electrostatic sensor described above uses sensor destruction as the principle for detecting static electricity, and therefore cannot measure static electricity repeatedly. In addition, the semiconductor electrostatic sensor described above constitutes a measuring instrument by being formed on a silicon substrate together with other circuits for outputting the amount of charge detected by the semiconductor electrostatic sensor. For this reason, there is a problem in that the elements that constitute the above circuit in measuring instruments that operate by electricity are easily destroyed by static electricity.

One aspect of the present invention aims to realize a small electrostatic sensor that operates stably against static electricity and can be used repeatedly.

In order to solve the above problems, an electrostatic sensor according to one aspect of the present invention includes an excitation light source that emits excitation light, a light-emitting element having a nonlinear optical medium formed on a semiconductor substrate, the nonlinear optical medium being excited by the excitation light and having a resonator that resonates at the excitation wavelength to generate light having the excitation wavelength or light having a wavelength different from the excitation wavelength, and a photodetector that detects the light emitted from the light-emitting element.

According to the above configuration, when light having a strong electric field such as a laser is incident on the nonlinear optical medium, the resonator generates light having the wavelength of the incident excitation light or light having a wavelength different from the excitation wavelength. When an electric charge is applied to the light-emitting element, the nonlinear optical effect exhibited by the nonlinear optical medium is reduced. This causes the light-emitting element to stop emitting light (no light emission) or to emit weak light. In this way, the light-emitting element's light-emitting state differs between normal light emission without charge and when a charge is applied, making it possible to detect static electricity. Furthermore, the light-emitting element is a device that operates when excitation light is incident on it, and is not an electrically driven device. Therefore, it is not destroyed by the influence of static electricity. Moreover, when the electric charge is removed from the nonlinear optical medium, the normal nonlinear optical effect is exhibited, making it possible to repeatedly detect static electricity.

In the electrostatic sensor, a photonic crystal structure having a large number of voids is formed on the semiconductor substrate, and the resonator is provided in the photonic crystal structure and may have a Raman resonance mode for Raman scattered light generated by the excitation light.

According to the above configuration, stimulated Raman scattering, which is a third-order nonlinear optical effect, occurs in the resonator. The resonator can generate Raman scattered light by utilizing the Raman gain obtained by this stimulated Raman scattering. The Raman gain changes linearly with respect to the optical density of the light incident on the resonator. The loss of the resonator is constant and does not depend on the optical density. Furthermore, the generated light is absorbed by free carrier absorption. The free carrier loss that occurs at this time changes nonlinearly with respect to the optical density. The resonator oscillates when the gain exceeds the sum of the resonator loss and the free carrier loss (loss sum).

When an electric charge is applied to the light-emitting element, the loss in the resonator increases. As a result, when the gain falls below the sum of the losses, the oscillation of the resonator stops or the resonance of the resonator becomes weak. This causes the light-emitting element to stop emitting light or the light it emits becomes weak. In this way, static electricity can be detected by causing the light-emitting element to stop emitting light or to weaken its emission.

In the electrostatic sensor, the resonator may confine the excitation light in an excitation light resonance mode, confine the Raman scattering light in a Raman scattering light resonance mode, and have a first Q value of 10,000 or more as the Q value of the excitation light resonance mode, and a second Q value of 100,000 or more as the Q value of the Raman scattering light resonance mode.

With the above configuration, the Q value of the resonator is high, so the loss of the resonator is significantly reduced. This allows the light emission range of the oscillator to be widened. Therefore, the difference between the loss of the resonator during light emission and the loss of the resonator that increases when an electric charge is applied becomes large. Therefore, the range of static electricity detection of the light-emitting element can be widened.

To solve the above problems, an electrostatic sensor according to another aspect of the present invention includes an excitation light source that emits excitation light, a light-emitting element having a nonlinear optical medium formed on a semiconductor substrate, the nonlinear optical medium being provided with a waveguide that passes the excitation light or converts the excitation light into light having a wavelength different from the excitation wavelength, and a photodetector that detects the light emitted from the light-emitting element.

According to the above configuration, when an electric charge is applied to the light-emitting element, the nonlinear optical effect exhibited by the nonlinear optical medium is reduced. This causes the light-emitting element to stop emitting light (no light emission) or the light emitted by the light-emitting element to become weak. In this way, the light-emitting element's light-emitting state differs between normal light emission without electric charge and when electric charge is applied, making it possible to detect static electricity. Furthermore, the light-emitting element is a device that operates when excitation light is incident on it, and is not an electrically driven device. Therefore, it will not be destroyed by the effects of static electricity. Moreover, when the electric charge is removed, the nonlinear optical medium returns to exhibiting the normal nonlinear optical effect, making it possible to repeatedly detect static electricity.

The electrostatic sensor may further include a first optical fiber that guides the excitation light from the excitation light source to the light-emitting element, and a second optical fiber that guides the light from the light-emitting element to the photodetector.

According to the above configuration, the light-emitting element is connected to the excitation light source by the first optical fiber and to the photodetector by the second optical fiber. This allows the light-emitting element to be placed at a position away from the excitation light source and the photodetector. This makes it possible to detect static electricity in narrow spaces and small spaces where people cannot enter.

The electrostatic sensor may further include an optical branching device that branches the single first optical fiber connected to the excitation light source into a plurality of the first optical fibers, and the light-emitting element, the second optical fiber, and the photodetector may each be provided in a plurality of the light-emitting elements, and the plurality of branched first optical fibers may be individually connected to the plurality of the light-emitting elements, and the plurality of the second optical fibers may individually connect the plurality of the light-emitting elements and the plurality of the photodetectors.

According to the above configuration, the excitation light from the excitation light source is transmitted to each light-emitting element via multiple first optical fibers branched from a single first optical fiber by an optical brancher. This makes it possible to detect static electricity at multiple locations using a single excitation light source.

According to one aspect of the present invention, it is possible to realize a small electrostatic sensor that operates stably against static electricity and can be used repeatedly.

1 is a block diagram showing a configuration of an electrostatic sensor according to first and second embodiments of the present invention; 3 is a plan view showing a configuration of a light-emitting element in the electrostatic sensor. FIG. 1A is a plan view showing an enlarged view of the photonic crystal structure constituting the light-emitting device, with a microresonator at the center, and a diagram showing energy levels corresponding to regions of the photonic crystal with different hole spacings. FIG. FIG. 2 is a diagram showing the relationship between the pump light density in the microresonator and the Raman gain and the sum of losses, illustrating the mechanism of Raman laser oscillation and shutdown in the light-emitting device. FIG. 13 is a diagram showing the configuration of an experimental apparatus for carrying out an experiment to verify that the light-emitting element sample stops oscillating due to static electricity. FIG. 2 is a diagram for explaining the mechanism by which a sample is charged in the above experimental apparatus. FIG. 11 is a plan view showing a configuration of a light-emitting element in an electrostatic sensor according to a second embodiment of the present invention. FIG. 11 is a block diagram showing a configuration of an electrostatic sensor according to a third embodiment of the present invention.

[Embodiment 1]
The following will describe a first embodiment of the present invention with reference to FIGS. 1 to 6. FIG.

Figure 1 is a block diagram showing the configuration of an electrostatic sensor 101 according to embodiment 1.

As shown in FIG. 1, the electrostatic sensor 101 includes an excitation light source 1, an input optical fiber 2 (first optical fiber), a light-emitting element 3, an output optical fiber 4 (second optical fiber), and a light-receiving element 5 (photodetector).

The excitation light source 1 is a light source that emits excitation light that excites the microresonator 31 (resonator) included in the light-emitting element 3. As the excitation light source 1, a light source element such as a semiconductor laser or a super luminescent diode is used. A super luminescent diode (hereinafter referred to as an "SLD") is a light source element that has a broad spectrum like an LED and emits high-brightness light like a semiconductor laser.

The input optical fiber 2 is a light guide path that guides the excitation light emitted from the excitation light source 1 to the light-emitting element 3.

The light-emitting element 3 operates as a wavelength converter that converts the excitation light incident from the incident optical fiber 2 into light having a wavelength different from the wavelength of the excitation light (excitation wavelength) and outputs the light. The light-emitting element 3 will be described in detail later. Note that the light-emitting element 3 may directly emit the excitation light incident from the incident optical fiber 2 without changing its wavelength.

The output optical fiber 4 is a light guide path that guides the light output from the light-emitting element 3 to the light-receiving element 5.

The light receiving element 5 is an element that receives and detects the light from the light emitting element 3 guided by the output optical fiber 4. The light receiving element 5 is composed of, for example, a photodiode.

Next, the light-emitting element 3 will be described in detail. Figure 2 is a plan view showing the configuration of the light-emitting element 3 in the electrostatic sensor 101. Figure 3 is a plan view showing an enlarged view of the photonic crystal structure that constitutes the light-emitting element 3, with the microresonator 31 at the center, and a diagram showing the energy levels corresponding to regions with different spacing between the holes 3b in the photonic crystal.

As shown in FIG. 2, the light-emitting element 3 is a photonic crystal optical circuit equipped with a two-dimensional photonic crystal structure (photonic crystal structure). The two-dimensional photonic crystal structure is a structure in which a two-dimensional photonic crystal is formed by periodically arranging a large number of holes 3b in a silicon substrate 3a (semiconductor substrate) having a thickness of, for example, about 200 nm. The two-dimensional photonic crystal is a nonlinear optical medium. Note that, in addition to the silicon substrate 3a, a glass substrate, a sapphire substrate, etc. can also be used as the semiconductor substrate.

The two-dimensional photonic crystal structure has an input section 3c and an output section 3d. The input section 3c is a section where excitation light from the input optical fiber 2 is input, and the output section 3d is a section where light generated in the micro-waveguide 33 is output to the output optical fiber 4.

The two-dimensional photonic crystal structure has a portion (hereafter referred to as a line defect) in which the air holes 3b are blocked and continue to extend from the input portion 3c in the x direction. This portion functions as a micro-waveguide 32. The two-dimensional photonic crystal structure has a line defect that continues to extend from the output portion 3d in the reverse x direction. This portion functions as a micro-waveguide 33.

The photonic band structure of the two-dimensional photonic crystal structure is controlled by the diameter, spacing (lattice constant of the photonic crystal), shape, etc. of the holes 3b. In this embodiment, the spacing of the holes 3b is made different in two stages to obtain two different photonic band structures.

Specifically, the spacing between the air holes 3b in the y direction is uniformly 710 nm, and the spacing between the air holes 3b in the x direction is different, 410 nm and 420 nm, respectively. The diameter of the air holes 3b is 260 nm. The micro-waveguide 32 has a width of 781 nm between the air holes 3b in the y direction, and is formed as a waveguide that transmits incident light of wavelength λ (E). The micro-waveguide 33 has a width of 625 nm between the air holes 3b in the y direction, and is formed as a waveguide that transmits output light of wavelength λ (R).

In the plane of the silicon substrate 3a, a point defect region is provided in which several adjacent vacancies 3b in the x direction are filled, at positions separated by several vacancies 3b in the y direction (width direction of the light-emitting element 3) from each of the micro-waveguides 32 and 33. The point defect region functions as a micro-resonator 31. The micro-resonator 31 resonates at a specific wavelength λ(R) (excitation wavelength).

The microresonator 31 has a resonance mode (excitation resonance mode) for the wavelength λ (E) of the excitation light, and a resonance mode (Raman resonance mode) for the Raman scattered light emitted by the microresonator 31. As a result, the microresonator 31 is excited by the wavelength λ (E) and emits Raman scattered light of wavelength λ (R).

The microresonator 31 is formed in a short line shape by a series of point defects. Here again, to clearly distinguish it from the above-mentioned "line defects" that form the microwaveguides 32 and 33, the short line defect portion formed by a series of point defects that constitute the microresonator 31 is deliberately referred to as a "point defect."

Here, we will explain the effect of partially varying the spacing of the voids 3b in the light-emitting element 3. Figure 3 includes a plan view showing the structure of the photonic crystal constituting the light-emitting element 3, with the microresonator 31 (point defect region) enlarged and centered, and a diagram showing the energy levels corresponding to regions in the photonic crystal where the spacing of the voids 3b is different.

As shown in the upper part of FIG. 3, in the photonic crystal, the area in which the microresonator 31 due to the above-mentioned point defect is formed is divided into a central area A0 in the center, a first area A1 on the left side of the central area A0 in the figure, and a second area A2 on the right side of the central area A0 in the figure.

In the central range A0 of the point defect region, light confinement is achieved by utilizing the mode gap difference. This is achieved by forming a pair of light reflecting surfaces in the central range A0 of the point defect region using a photonic band gap that is generated by changing the surrounding structure to shift the band of the propagation wavelength. Specifically, the structure of the surrounding photonic crystal can be changed by changing the size of the holes 3b in the photonic crystal in the light reflecting surface region, or by slightly changing the position or spacing of the holes 3b (for example, by moving them closer to or further away from the waveguide).

As shown in the upper part of FIG. 3, two adjacent vacancies 3b in the first region A1 and the second region A2 are separated by a distance d. In contrast, two adjacent vacancies 3b in the central region A0 are separated by a distance d+Δd, which is Δd wider than the distance d. Thus, in the point defect region, the distance (lattice distance) between the vacancies 3b is different between the central region A0 and the first region A1 and second region A2. A heterostructure is formed because only the distance between the vacancies 3b in the central region A0 is wider by Δd.

The photonic bands are designed as shown in the lower part of Figure 3. Specifically, within the region in which the heterostructure is formed, a first nanoresonant mode (first resonant mode) and a second nanoresonant mode (second resonant mode) exist. The second nanoresonant mode exists at a higher energy level, and the first nanoresonant mode exists at an energy level that is 15.6 THz (the Raman shift frequency of silicon) lower than the energy level in which the second nanoresonant mode exists. A well-shaped potential is formed at each energy level.

This well-shaped potential causes light to be trapped. The point defect region in the central range A0, where the lattice spacing is expanded by Δd, acts as a resonator that traps light using the two above-mentioned resonance modes. When excitation light corresponding to the second nanoresonance mode (excitation light resonance mode) is incident on the point defect region, the Raman scattered light corresponding to the excitation light is trapped in the first nanoresonance mode (Raman scattered light resonance mode), and the Raman scattered light leads to laser oscillation.

In this configuration, the spatial overlap between the excitation light and the Raman scattered light is large. This makes it possible to set the Q value (first Q value) of the nanoresonant mode that confines the excitation light (pump light) and the Q value (second Q value) of the nanoresonant mode that confines the Raman scattered light (Stokes light) to extremely high values of over 100,000 and over 1,000,000, respectively. Furthermore, this structure has the advantage that a frequency difference of 15.6 THz can be easily achieved across the entire optical communication wavelength band (1.3 to 1.6 μm) without compromising the above-mentioned advantages, i.e., it has a high degree of freedom in wavelength design.

The microresonator 31 thus formed emits non-laser light when an SLD is used as the excitation light source 1. When a semiconductor laser is used as the excitation light source 1, the microresonator 31 functions as a Raman scattering light enhancer or a Raman laser light source.

Next, we will explain how light is extracted by the light-emitting element 3.

As shown in FIG. 1, in the light-emitting element 3, light emitted from the excitation light source 1 is incident on the microwaveguide 32 from the incident part 3c via the incident optical fiber 2. When this excitation light reaches the microresonator 31 from the microwaveguide 32, as shown in FIG. 2, the second nanoresonant mode (corresponding to wavelength λ(E)) is excited in the microresonator 31 by evanescent optical coupling. As a result, the light of wavelength λ(E) is confined in the microresonator 31.

Then, in the microresonator 31, Raman scattered light (wavelength λ(R)) having energy lower than the Raman shift frequency is generated and trapped. When the intensity of the excitation light exceeds a certain level, the Raman scattered light leads to laser oscillation, and laser oscillation at wavelength λ(R) occurs in the microresonator 31. Here, for example, when the spacing d is 410 nm and Δd is 10 nm, laser oscillation occurs at a wavelength λ(R) of 1500 nm to 1600 nm.

Even if the intensity of the excitation light does not reach a certain level and does not result in laser oscillation, the light-emitting element 3 can function as a Raman scattering light enhancer to obtain strong wavelength-converted Raman scattering light.

The light generated by the microresonator 31 in the above manner is emitted from the emission section 3d of the light-emitting element 3. This light is guided to the light-receiving element 5 via the emission optical fiber 4. The light-receiving element 5 converts the incident light into an electrical signal and detects the light.

Next, the operation of detecting static electricity by the static electricity sensor 101 will be described. Figure 4 shows the relationship between the pump light density in the microresonator 31 and the Raman gain and sum of losses, which represents the mechanism of Raman laser oscillation and stoppage in the light-emitting element 3.

The microresonator 31 functions as a Raman amplifier. A Raman amplifier is an optical amplifier based on the Raman gain generated by the effect of stimulated Raman scattering. As shown in FIG. 4, the gain of the microresonator 31 (Raman gain) changes linearly with the optical density (pump photon density) of the excitation light incident on the microresonator 31.

On the other hand, the loss occurring in the microresonator 31 is constant and does not depend on the pump photon density. Also, the generated light is absorbed by free carrier absorption. At this time, the free carrier loss occurring in the microresonator 31 changes nonlinearly with respect to the pump photon density.

The microresonator 31 oscillates in the range indicated by the solid line in FIG. 4 where the Raman gain exceeds the sum of the loss of the microresonator 31 and the free carrier loss (the "loss sum" indicated by the dashed line). On the other hand, the microresonator 31 stops oscillating in the range indicated by the dashed line in FIG. 4 where the Raman gain is equal to or less than the loss sum.

Furthermore, when a charge is applied to the light-emitting element 3, the loss in the microresonator 31 increases, and the loss sum increases. As a result, when the Raman gain falls below the loss sum, the oscillation of the microresonator 31 stops, and the light-emitting element 3 stops emitting light, or the light emitted by the light-emitting element 3 becomes weak. Therefore, the light-receiving element 5 stops detecting light, or detects weak light, and the presence of static electricity is detected. In other words, static electricity can be detected because the light-emitting state of the light-emitting element 3 differs between normal light emission when no charge is present and when a charge is present.

When an electric charge is applied to the light-emitting element 3, the loss in all resonant modes of the microresonator 31 increases. Therefore, the intensity of the light having the same wavelength as the excitation light emitted through the second nanoresonant mode also changes between normal times when no electric charge is present and when electric charge is present. Therefore, by capturing this change, static electricity can be detected.

When the excitation light is a laser light with a fixed wavelength, even a slight shift in the resonant wavelength of the resonant mode used for excitation will prevent the excitation light from being introduced into the microresonator 31, causing the microresonator 31 to stop oscillating. When a charge is applied to the microresonator 31, the resonant wavelength moves slightly, causing the microresonator 31 to stop oscillating. Therefore, when a laser light with a fixed wavelength is used as the excitation light, static electricity can also be detected by the above principle. Of course, if the wavelength of the excitation light is moved in accordance with the shift, the oscillation of the microresonator 31 will be restored, and the static electricity sensor 101 can be used repeatedly.

When the Q value of the microresonator 31 is high, the loss of the microresonator 31 decreases. This makes it possible to widen the range in which the Raman gain exceeds the sum of the losses (the range shown by the solid line in Figure 4). This means that the higher the Q value, the wider the range of static electricity that can be detected. In addition, there is a difference of one to three orders of magnitude in the output of the microresonator 31 between when the microresonator 31 is oscillating and when it is stopped. This allows for highly reliable static electricity detection.

Next, we will verify the detection of static electricity by the electrostatic sensor 101. Figure 5 is a diagram showing the configuration of an experimental device for conducting an experiment to verify that a sample 18 of a light-emitting element 3 stops oscillating due to static electricity. Figure 6 is a diagram for explaining the mechanism by which the sample 18 in the experimental device becomes charged.

As shown in FIG. 5, the experimental apparatus includes a tunable laser 11, an input optical system 12, an output optical system 13, a lamp 14, a camera 15 (photodetector), a static electricity generator 16, and a metal tip 17.

Sample 18 is a silicon chip formed with a structure similar to that of the light-emitting element 3. It emits Raman scattered light in response to incident laser light. This sample 18 does not have the micro-waveguide 33 of the light-emitting element 3. Therefore, the micro-resonator emits Raman scattered light in the z direction shown in Figure 2. The excitation wavelength of the micro-resonator is 1429 mm, and the wavelength of the Raman scattered light emitted by the micro-resonator is 1544 mm. The oscillation threshold of the micro-resonator is 0.5 μW.

The incident optical system 12 has a collimating lens 121, a polarizer 122, and a condensing lens 123. The incident optical system 12 converts the laser light (excitation light) emitted from the tunable laser 11 into parallel light by the collimating lens 121, passes a specific polarized light by the polarizer 122, and then focuses the light by the condensing lens 123 and makes it incident on the entrance part of the sample 18.

The output optical system 13 has a collimating lens 131, a beam splitter 132, a mirror 133, a condensing lens 134, and a long-pass filter 135. The output optical system 13 converts the Raman scattered light from the sample 18 into parallel light by the collimating lens 131, passes the light through the beam splitter 132 together with the light from the lamp 14, changes the direction of the light by the mirror 133, and then focuses the light by the condensing lens 134. The output optical system 13 also passes only components of the Raman scattered light focused by the condensing lens 134 that have wavelengths longer than a predetermined wavelength by the long-pass filter 135.

The camera 15 is, for example, a near-infrared (NIR) camera, and can capture clear images even in low light conditions. This makes it possible to observe (detect) minute amounts of light that pass through the long-pass filter 135.

The metal tip 17 is a tiny metal structure in a cone shape, with a tip diameter of 1 mm. The tip of the metal tip 17 is positioned 1 cm away from the sample 18. The static electricity generator 16 outputs a voltage of several kV to the metal tip 17. This causes the metal tip 17 to irradiate the sample 18 with a negative or positive charge.

By irradiating sample 18 with static electricity, no light was observed in the image observed by camera 15, confirming that the microresonator in sample 18 had stopped oscillating.

The principle by which static electricity stops the oscillation of a microresonator is explained below. As shown in Figure 6, corona discharge occurs when an electric charge is released from the tip of the metal tip 17. The electric charge generated by the corona discharge ionizes molecules M of nitrogen gas, oxygen gas, etc. in the air. The silicon tip of the sample 18 receives an electric charge E from the ions I on its surface. The electric charge E penetrates into the silicon tip except for the voids 18b, stopping the laser oscillation of the microresonator.

As described above, the electrostatic sensor 101 according to this embodiment includes an excitation light source 1 that emits excitation light, a light-emitting element 3 that emits light of a different wavelength from the incident excitation light, and a light-receiving element 5 that detects the light emitted from the light-emitting element 3. The light-emitting element 3 has a nonlinear optical medium formed on a silicon substrate. The light-emitting element 3 also has a microresonator 31 in the nonlinear optical medium that is excited by the excitation light from the excitation light source 1 and resonates at the excitation wavelength, thereby generating light having the excitation wavelength.

According to the above configuration, when an electric charge is applied to the light-emitting element 3, and light having a strong electric field such as a laser is incident on the nonlinear optical medium, the microresonator 31 generates light having an excitation wavelength different from the wavelength of the incident excitation light. When an electric charge is applied to the light-emitting element 3, the nonlinear optical effect exhibited by the nonlinear optical medium is reduced. This causes the light-emitting element 3 to stop emitting light (no light emission) or the light emitted by the light-emitting element 3 to become weak. In this way, static electricity can be detected by the difference in the light-emitting state of the light-emitting element 3 between normal light emission without charge and when a charge is applied.

In addition, since the light-emitting element 3 is formed on the silicon substrate 3a as a semiconductor substrate, it can be incorporated inside a semiconductor device manufactured by semiconductor process technology such as silicon process technology. This makes it possible to detect static electricity generated inside the semiconductor device. Furthermore, when the charge is removed, the nonlinear optical medium exhibits the normal nonlinear optical effect. This allows the electrostatic sensor 101 to repeatedly detect static electricity. Therefore, it is possible to realize a small electrostatic sensor that operates stably against static electricity and can be used repeatedly.

The light-emitting element 3 is a device that operates when excitation light is incident on it, and is not an electrically driven device. Therefore, it will not be destroyed by static electricity. Also, since electricity is not used to drive the light-emitting element 3, it is possible to use the light-emitting element 3 in environments where fire is likely to occur, and there is little risk of it inducing an explosion. Furthermore, since the light-emitting element 3 does not have any moving parts, it operates normally even in a vibrating environment without being affected by vibrations.

When the purpose is to eliminate static electricity, it is sufficient to confirm the presence of static electricity. Therefore, the static electricity sensor 101 is designed to detect static electricity.

In addition, in the electrostatic sensor 101, a photonic crystal structure in which a large number of voids are formed is formed on the silicon substrate 3a. The microresonator 31 is provided in the photonic crystal structure and has a Raman resonance mode for the Raman scattered light generated by the excitation light.

According to the above configuration, stimulated Raman scattering, which is a third-order nonlinear optical effect, occurs in the microresonator 31. The microresonator 31 can generate Raman scattered light by utilizing the Raman gain obtained by this Raman scattering. Also, as described above, when the loss of the microresonator 31 increases and the Raman gain falls below the loss sum, the microresonator 31 stops oscillating or the resonance of the microresonator 31 becomes weak. As a result, when the light-emitting element 3 stops emitting light or the light emitted by the light-emitting element 3 becomes weak, the light-receiving element 5 no longer detects light or detects weak light, so that static electricity can be detected.

The microresonator 31 has a first Q value of 10,000 or more and 3,000,000 or less, and a second Q value of 100,000 or more and 10,000,000 or less. The microresonator 31 may preferably have a first Q value of about tens of thousands, and a second Q value of about hundreds of thousands.

According to the above configuration, since the first Q value and the second Q value of the microresonator 31 are high, the loss of the microresonator 31 is significantly reduced. This allows the light emission range of the microresonator 31 to be widened. Therefore, by adjusting the intensity of the excitation light, it is possible to detect static electricity with a wide range of strengths. In other words, the static electricity detection sensitivity can be adjusted.

The electrostatic sensor 101 also includes an input optical fiber 2 that guides the excitation light from the excitation light source 1 to the light-emitting element 3, and an output optical fiber 4 that guides the light from the light-emitting element 3 to the light-receiving element 5.

According to the above configuration, the light-emitting element 3 is connected to the excitation light source 1 by the input optical fiber 2, and is connected to the light-receiving element 5 by the output optical fiber 4. This allows the light-emitting element 3 to be placed at a location away from the excitation light source 1 and the light-receiving element 5. This makes it possible to detect static electricity in remote locations. For example, it will become possible to perform remote sensing of static electricity in rockets, undersea cables, etc., which was previously difficult.

In the field of semiconductor manufacturing, in order to neutralize a charged silicon substrate, a static eliminator (such as an ionizer) irradiates the charged area with ions that are charged with the opposite polarity to the polarity of the charge on the silicon substrate. This electrically neutralizes the charged area of the silicon substrate, thereby eliminating the charge. Conventionally, the charged state of the silicon substrate is detected before static elimination, but because the spatial resolution of this detection is low, it is difficult to identify the range of ion irradiation. This can result in the inconvenience of not being able to sufficiently eliminate static electricity. In response to this, the electrostatic sensor 101 can be used to measure the spatial charge. Therefore, the charged state of the surface of the silicon substrate can also be easily detected.

The experimental device configured as described above can be used as an electrostatic sensor of the present invention.

Here, we explain a variation of this embodiment.

In the electrostatic sensor 101 according to this embodiment, the light-emitting element 3 has a microresonator 31 that exhibits a third-order nonlinear optical effect as stimulated Raman scattering. The electrostatic sensor according to the present invention is not limited to such a microresonator 31, and may include a light-emitting element having a resonator that exhibits other nonlinear optical effects.

For example, the electrostatic sensor may include a light-emitting element having a microresonator that exhibits a nonlinear optical effect called stimulated Brillouin scattering. The electrostatic sensor may also include a light-emitting element having a tapered fiber-coupled microsphere resonator. The tapered fiber-coupled microsphere resonator circulates light incident on a transparent microsphere made of glass or the like through a tapered fiber inside the microsphere by total reflection on the inner surface of the microsphere, and confines only light of a wavelength with a uniform phase with a high Q value. The electrostatic sensor may also include a light-emitting element having a laser resonator that generates a sideband wave by adding phase modulation when a single-frequency laser light is incident, and emits light with a comb-shaped frequency spectrum (optical frequency comb). In these electrostatic sensors, the nonlinear optical effect is also reduced by adding an electric charge.

[Embodiment 2]
The second embodiment of the present invention will be described below with reference to Figures 1 and 7. For ease of explanation, components having the same functions as those described in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

Figure 7 is a plan view showing the configuration of the light-emitting element 3A in the electrostatic sensor 102.

As shown in FIG. 1, the electrostatic sensor 102 according to this embodiment includes an excitation light source 1, an input optical fiber 2, an output optical fiber 4, and a light receiving element 5, similar to the electrostatic sensor 10 described above. In addition, the electrostatic sensor 102 includes a light emitting element 3A instead of the light emitting element 3 in the electrostatic sensor 101.

Although not shown in FIG. 1, unlike the light-emitting element 3, the light-emitting element 3A does not have a microresonator 31. As shown in FIG. 7, the light-emitting element 3A is a photonic crystal optical circuit that includes a two-dimensional photonic crystal structure (photonic crystal structure) like the light-emitting element 3.

The two-dimensional photonic crystal structure has an incident portion 3c and an exit portion 3d. A line defect is formed in the two-dimensional photonic crystal structure, extending in the x-direction from the incident portion 3c to the exit portion 3d. This portion functions as a microwaveguide 34 (waveguide).

In the electrostatic sensor 102 configured in this manner, the light emitted from the excitation light source 1 enters the light emitting element 3A from the input section 3c via the input optical fiber 2 into the micro-waveguide 34. This excitation light passes through the micro-waveguide 34 and is output from the output section 3d.

Furthermore, when an electric charge is applied to the light-emitting element 3A, the loss of light passing through the micro-waveguide 34 increases, or the nonlinear optical effect exhibited by the nonlinear optical medium decreases. This causes the light-emitting element 3A to stop emitting light (no light emission) or to emit weak light. In this way, the light-emitting element 3A's light-emitting state differs between when it emits light normally without an electric charge and when an electric charge is applied, making it possible to detect static electricity.

The light-emitting element 3 can increase its sensitivity by having a microresonator 31. In contrast, the light-emitting element 3A does not have a microresonator 31, so it cannot achieve a sensitivity as high as that of the light-emitting element 3. However, the sensitivity of the light-emitting element 3A can be increased to a certain extent by increasing the amount of excitation light or forming a long microwaveguide 34.

When excitation light enters the micro-waveguide 34, excitation light of the same wavelength is emitted as is. In contrast, wavelength conversion of light using an optical waveguide that uses a nonlinear optical effect has already been achieved. In particular, research has been conducted into generating Raman scattered light in an optical waveguide, and this is possible in principle. Therefore, the light-emitting element 3A may convert the incident excitation light into light having a wavelength different from the excitation wavelength and emit it.

[Embodiment 3]
The third embodiment of the present invention will be described below with reference to Fig. 8. For ease of explanation, components having the same functions as those described in the first and second embodiments are denoted by the same reference numerals, and the description thereof will be omitted.

Figure 8 is a block diagram showing the configuration of the electrostatic sensor 103 according to the second embodiment.

As shown in FIG. 8, the electrostatic sensor 103 includes an excitation light source 1, like the electrostatic sensor 101 of embodiment 1 and the electrostatic sensor 102 of embodiment 2. The electrostatic sensor 103 also includes multiple input optical fibers 2, light-emitting elements 3 (or light-emitting elements 3A), output optical fibers 4, and light-receiving elements 5. The electrostatic sensor 103 also includes an optical splitter 6. Note that in the following explanation, the description of the light-emitting element 3A will be omitted, but the electrostatic sensor 103 operates in the same way when it includes the light-emitting element 3A as when it includes the light-emitting element 3.

The excitation light source 1 and the optical splitter 6 are connected by a single incident optical fiber 2. The optical splitter 6 and the multiple light-emitting elements 3 are connected by the same number of incident optical fibers 2 as the number of light-emitting elements 3. The optical splitter 6 is an optical device that splits the single incident optical fiber 2 connected to the excitation light source 1 into multiple incident optical fibers 2.

The light-emitting elements 3 are arranged at various locations where static electricity is to be detected. The multiple light-emitting elements 3 and the multiple light-receiving elements 5 are individually connected by multiple light-emitting optical fibers 4. It is preferable that the multiple light-receiving elements 5 are arranged together so that the light-emitting state of the multiple light-emitting elements 3 can be confirmed at one location.

According to the electrostatic sensor 103 configured as described above, the excitation light from the excitation light source 1 is transmitted to each light-emitting element 3 via multiple incident optical fibers 2 branched from a single incident optical fiber 2 by the optical brancher 6. This makes it possible to detect static electricity at multiple locations using a single excitation light source 1.

For example, by arranging the light-emitting elements 3 at multiple locations where static electricity is likely to occur, such as on a production line, the light-emitting status of each light-emitting element 3 can be confirmed by the light-receiving element 5. This makes it possible to check the static electricity generation status at multiple locations at once. Therefore, it is easy to remove and analyze static electricity that occurs at multiple locations.

In addition, in a rocket, electrostatic sensors 103, each of which has a matrix of light-emitting elements 3 connected by an input optical fiber 2 and an output optical fiber 4, are placed on the interior wall or other areas that may become charged. When the location where the electrostatic sensor 103 is placed becomes charged, the light emission state from the electrostatic sensor 103 changes, allowing the monitor (such as a control room) to identify the location where charging has occurred. This makes it possible to prevent rocket launch failures by de-electrifying any charged locations that have been identified before the rocket is launched.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

1 Excitation light source 2 Incident optical fiber (first optical fiber)
3 Light emitting element 3a Silicon substrate 3b Hole 4 Emission optical fiber (second optical fiber)
5. Light receiving element (photodetector)
6 Optical splitter 15 Camera (photodetector)
31 Microresonator (resonator)
34 Microwaveguide (waveguide)
101-103 Electrostatic sensor

Claims (7)

an excitation light source that emits excitation light;
a light-emitting device having a photonic crystal structure in which a photonic crystal having a large number of voids arranged in a semiconductor substrate is formed, the light-emitting device being provided with a resonator that is excited by the excitation light incident on an incident portion provided in the photonic crystal structure and resonates at an excitation wavelength to generate light having the excitation wavelength or a wavelength different from the excitation wavelength;
a photodetector for detecting light emitted from an emission portion provided in the photonic crystal structure ,
the resonator is formed as a linear defect region in which the voids are filled, and has a pair of light reflecting surfaces formed by a photonic band gap caused by a structure of the photonic crystal around the central portion being different from a structure of the photonic crystal around both sides, such that a band of propagation wavelengths at a central portion in a linear direction extending linearly in the defect region is shifted from a band of propagation wavelengths at both sides on both sides of the linear direction of the central portion; and when loss in the resonator increases due to free carrier absorption caused by the presence of space charge due to static electricity, oscillation of the resonator stops or resonance of the resonator becomes weak, thereby stopping generation of light or weakening the generated light;
The electrostatic sensor is characterized in that the photodetector detects static electricity based on the detected light . 2. The electrostatic sensor according to claim 1 , wherein the holes are formed so that the resonator has a photonic band gap of a Raman resonance mode for Raman scattered light generated by the excitation light. 3. The electrostatic sensor according to claim 2, wherein the holes are formed so that the resonator confines the excitation light in a photonic band gap of an excitation light resonance mode, the Raman scattered light in a photonic band gap of a Raman scattering light resonance mode, the Q value of the excitation light resonance mode being a first Q value of 10,000 or more, and the Q value of the Raman scattering light resonance mode being a second Q value of 100,000 or more. an excitation light source that emits excitation light;
a light-emitting device having a photonic crystal structure in which a photonic crystal having a large number of voids arranged in a semiconductor substrate is formed, the light-emitting device being provided with a waveguide that passes the excitation light incident on an incident portion provided in the photonic crystal structure or converts the excitation light into generated light having a wavelength different from the excitation wavelength;
a photodetector for detecting generated light emitted from an emission portion provided in the photonic crystal structure ,
The waveguide is formed as a linear defect region in which the voids are filled, and the loss of light passing through the waveguide increases due to free carrier absorption caused by the presence of electrostatic space charge, thereby stopping the generation of light or weakening the light that is generated;
The electrostatic sensor is characterized in that the photodetector detects static electricity based on the detected light . The electrostatic sensor according to claim 4, characterized in that the waveguide converts the excitation light into Raman scattered light having a wavelength different from the excitation wavelength. a first optical fiber that guides the pumping light from the pumping light source to the incident portion of the photonic crystal structure ;
6. The electrostatic sensor according to claim 1, further comprising: a second optical fiber that guides the light from the emission portion of the photonic crystal structure to the photodetector. an optical splitter that splits the single first optical fiber connected to the pumping light source into a plurality of the first optical fibers;
a plurality of the light emitting elements, a plurality of the second optical fibers, and a plurality of the photodetectors are provided,
the plurality of branched first optical fibers are individually connected to the incident portions of the photonic crystal structures in the plurality of light-emitting elements,
7. The electrostatic sensor according to claim 6 , wherein the second optical fibers connect the emission sections of the photonic crystal structures to the photodetectors, respectively.

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