JPH0140313B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a broadband optical voltage sensor using a bismuth silicon oxide BSO (hereinafter referred to as BSO) or bismuth germanium oxide BGO (hereinafter referred to as BGO) element. FIG. 1 is a diagram showing the configuration of a basic optical voltage sensor. 1 is an optical fiber, 2 is a rod lens, 3 is a polarizer, 4 is a quarter-wave plate, 5 is a BSO element or BGO element, 6 is an analyzer, and 7 is an input voltage source. Since the same explanation can be applied to both the BSO element and the BGO element, the following explanation will be made using the BSO element. The light that enters the optical fiber 1, passes through the rod lens 2, the polarizer 3, and the 1/4 wavelength plate 4, and enters the BSO element 5 depends on the magnitude of the voltage applied from the input voltage source 7 to the BSO element 5 via the electrodes. The state of polarization changes depending on the The optical voltage sensor detects the magnitude of the input voltage to be detected by knowing the state of this polarization. FIG. 2 is a diagram showing the conventional frequency characteristics of modulation sensitivity of the optical voltage sensor shown in FIG. Traditional
In optical voltage sensors using BSO elements,
As the frequency of the input voltage is changed, a mechanical resonance phenomenon occurs in the BSO element due to the piezoelectric phenomenon at a certain frequency. The mechanical stress caused by this resonance is further
Affects the refractive index of the BSO element. For this reason,
As shown in FIG. 2, the frequency characteristics of the modulation sensitivity of a conventional optical voltage sensor using a BSO element has the drawback of generating very large peaks a, b, c, etc. at specific frequencies. Therefore, conventional optical voltage sensors cannot be used for analysis that requires constant modulation sensitivity up to high frequency components such as high voltage surge phenomena. An object of the present invention is to provide an optical voltage sensor using a BSO element that can eliminate the influence of resonance phenomena and achieve a wide band. The present invention will be described in detail below with reference to the drawings. Figure 3 A shows the shape of the BSO element (length l x width w x
It is a figure showing the relationship between thickness b) and orientation. l×w
Assume that the x-axis and y-axis are taken in the plane as shown in the figure, and the z-axis is taken perpendicular to the l×w plane, that is, parallel to the thickness b. First, an analysis conducted by the inventor regarding the reason why the resonance phenomenon occurs in the BSO element due to the piezoelectric phenomenon will be explained. BSO is a single crystal belonging to point group 23, and its electrical, optical, and mechanical properties are detailed in, for example, "Crystal Physics Engineering" (written by Tomoya Ogawa, published by Shokabo). Generally, the piezoelectric effect of BSO is described by the piezoelectric basic equation (tensor equation) below. T _n = C _on S _o −e _jn E _j D _i = e _io S _o +ε _ij E _j …(1) Here, T _n : Stress, C _on : Elastic state funes, S _o : Strain, e _jn , e _io : piezoelectric e constant, E _j : applied voltage, D _i : electric flux density, ε _ij : permittivity. When BSO is used in the system shown in Figure 3A, the basic piezoelectric formula is as follows. T ₁ = C ₁₁ S ₁ + C ₁₂ S ₂ + C ₁₂ S ₃ T ₂ = C ₁₂ S ₁ + C ₁₁ S ₂ + C ₁₂ S ₃ T ₃ = C ₁₂ S ₁ + C ₁₂ S ₂ + C ₁₁ S ₃ T ₄ = C ₄₄ S ₄ T ₅ = C ₄₄ S ₅ T ₆ = C ₄₄ S ₆ −e ₁₄ E ₃ D ₁ = e ₁₄ S ₄ D ₂ = e ₁₄ S ₅ D ₃ = e ₁₄ S ₆ +ε ₁₁ E ₃ …(2) In equation (2), T 6 including E ₃ and T ₆ are directly affected by applying voltage to BSO.
_D3 . Here, T ₆ = T ₁₂ + T ₂₁ = (stress in the first direction acting on the second surface) + (stress in the second direction acting on the first surface), so in the end, when a voltage is applied, shear is applied to the BSO. Stress (shear stress) will act. Letting ξ _i be the displacement of the particles constituting the crystal in the x _i direction, the equation of motion is as follows. ρδ ² ξ _i / δt ² = δT _ij / δx _j ρ: Specific gravity, that is, According to equation (2), T ₁₂ = C ₄₄ S ₁₂ −e ₁₄ E ₃ T ₂₁ = C ₄₄ S ₂₁ −e ₁₄ E ₃ Furthermore, S ₁₂ = S ₂₁ 1/2 (δξ ₁ / δx ₂ + δξ ₂ / δx ₁ ), so in the end, equation (3) becomes becomes. The solution to equation (4) is ξ ₁ = ξ ₀₁ e ^jwt sin (γx ₂ + θ ₂ ) ξ ₂ = ξ ₀₂ e ^jwt sin (γx ₁ + θ ₁ ) …(5) However,

[Formula] γ=w/v, ξ ₀₁ and ξ ₀₂ are constants. This is the so-called face shear mode shown by solid lines and dotted lines in FIG. To summarize the above, in the coordinate system of Figure 3 A, BSO
When using , the piezoelectric phenomenon that occurs in the crystal is a plane shear vibration that occurs in the x-axis-y-axis plane,
It was found that there is almost no dependence on the thickness b in the z-axis direction. It is known that the resonance frequency _R in plane slip vibration is approximately given by the following equation. In the fundamental mode (m=n=1), this resonant frequency is It is indicated by. Here, ρ: specific gravity, C ₄₄ : piezoelectric states funes, l and w: length and width of the BSO element.
For BSO, piezoelectric states funes C ₄₄ = 0.25×
10'' (N/m ² ), specific gravity ρ = about 9.2×10 ³ (Kg/m ³ ).The inventor's experimental results and calculation results regarding the resonant frequency with respect to the size of the BSO element are shown below. Shown in 1.

[Table] As can be seen from Table 1, the experimental values are lower than the calculated values.
It is about 0.85 times, which is a relatively good agreement. In addition, the 7×5×2 BSO element in (1) where l and w are the same and only b differs, and the 7×
It can be seen that the resonant frequency hardly changes in the 5×1 BSO element. FIG. 4A is a diagram illustrating the frequency characteristics of modulation sensitivity of an optical voltage sensor using the BSO element of the present invention. Through the inventor's analysis and experiments mentioned above,
It was found that by using a Z-cut BSO crystal and transmitting light in the Z direction, the effects of plane-slip vibration can be avoided to a large extent, and therefore, the peak of modulation sensitivity of optical voltage sensors can be eliminated up to considerably high frequency components. Ta. In the field of high voltage applications, a so-called standard impulse waveform with a rise time of 1 μsec and a fall time of 40 μsec is often used, but in order to measure the standard impulse waveform with this sensor, the resonant frequency must be at least 500 KHz or higher. In order to obtain an optical voltage sensor with a high resonant frequency of 500KHz or more, the inventor used a BSO crystal as a Z-cut to pass light in the Z direction, and changed the size of the crystal to l in a plane perpendicular to the direction in which the light passes. When ×w, in equation (7),

It is proposed that it should be set so that [Formula] is satisfied. Further, the resonance phenomenon at a high frequency of 500 KHz or higher, for example, shown in FIG. 4A can be removed by limiting the signal band of the optical receiver section using a filter having the characteristics shown in FIG. 4B. By using the BSO element thus obtained as the BSO element 5 of the optical voltage sensor shown in FIG. 1, the frequency characteristics of the sensor can be improved and the frequency band can be increased.

[Brief explanation of drawings]

Figure 1 shows the configuration of a basic optical voltage sensor, Figure 2 shows the conventional frequency characteristics of the modulation sensitivity of the sensor in Figure 1, and Figure 3A shows the shape and orientation of the BSO element. Figure 4A is a diagram illustrating the frequency characteristics of the modulation sensitivity of an optical voltage sensor using the BSO element of the present invention, Figure 4B is a diagram showing the characteristics of the filter. It is a diagram. 1: Optical fiber, 2: Rod lens, 3: Polarizer, 4: 1/4 wavelength plate, 5: BSO element or BGO
Element, 6: Analyzer, 7: Input voltage source, a, b,
c: peak value, l x w x b: length x width x thickness of element.

Claims (1)

[Claims] 1. In an optical voltage sensor that detects a voltage applied to a bismuth silicon oxide BSO or bismuth germanium oxide BGO single crystal, the BSO or BGO single crystal is Z-cut and its size is in a plane perpendicular to the Z direction. Length l x width w within
(mm) so that the light passes in the Z direction.
An optical voltage sensor characterized by comprising a BSO or BGO element.