JP3502705B2 - Optical electric field sensor head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical electric field sensor for receiving an external electric field composed of an optical waveguide type modulator for performing intensity and phase modulation on incident light and an antenna connected to this modulator. Regarding

[0002]

2. Description of the Related Art An optical crystal substrate having an electro-optical effect,
An optical waveguide is formed by thermal diffusion of Ti or the like, and an electrode film is formed in the vicinity of this optical waveguide by sputtering, vapor deposition, or the like to form an optical modulator. An application using such an optical modulator is one that measures electromagnetic noise in space propagation.
Generally, in a field called EMC, a flat frequency characteristic in a wide band is desirable.

The structure of the optical electric field sensor is shown in FIG. Light output from the light source 1 such as an LD is input to the optical electric field sensor head 3. A voltage is generated between the antennas 31 attached to the optical electric field sensor head due to electromagnetic noise, and the voltage is applied to the electrode portion of the optical modulator to modulate the input light. The modulated light is output from the sensor head and E
It is converted back to an electric signal by the / O converter 5. After that, the returned electric signal is measured by the measuring device 6 such as an oscilloscope or a spectrum analyzer.

[0004]

FIG. 4 shows an optical electric field sensor used in conventional EMC noise measurement. The electrode film 9 is C
Since the optical modulator and the antenna were made of a metal having a low resistance value such as r-Au, in the frequency characteristic of sensitivity,
The resonance point appeared in a frequency band of about several hundred MHz to 1 GHz (when a half-wavelength dipole antenna having an antenna length of several tens to 300 mm was used). However, in the EMC noise measurement, since the flat sensitivity characteristic is required in the frequency band around DC to several GHz, the above resonance point becomes a problem.

Accordingly, an object of the present invention is to obtain an electric field sensor using a waveguide type optical modulator having a flat sensitivity characteristic in a wide frequency band.

[0006]

The present invention provides an optical modulator comprising an optical waveguide formed on an optical crystal substrate having an electro-optical effect, and an electrode provided near the optical waveguide, and the optical modulator. In an optical electric field sensor head composed of an antenna connected to an electrode of a container,
It is characterized in that it is made of a high resistance material having 0Ω.

Here, in the conventional electrode, a low resistance film of Cr, Au, or the like was formed by vapor deposition or the like, but this causes the resonance frequency to appear in the EMC measurement range. Therefore, the sensitivity improvement at the resonance point is suppressed by increasing the electrode resistance, and the frequency characteristic is flattened as a whole. Examples of the method for increasing the resistance include reducing the film thickness of conventional Cr, Au, etc., and mixing a low resistance material and a high resistance material.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to Examples.

FIG. 1 shows an embodiment of the present invention. Z-cut
Using a LiNbO ₃ substrate 7, a Y-axis-propagating Ti thermal diffusion optical waveguide 8 is patterned and manufactured to be a Mach-Zehnder interferometer. Next, ITO (In ₂ O ₃ +5 wt% S
nO ₂ ) and quartz glass were simultaneously sputtered, and this mixed film was formed to a film thickness of about 1 μm to form an electrode film 12. The film resistance at this time was about 230Ω. Here, since the electrode cannot be drawn out to the outside as it is (the ITO film cannot be soldered because it is an oxide glass), the Cr—Au electrode film 9 is formed on a part of the transparent electrode by vapor deposition and can be soldered. In this way, the lead wire was pulled out and connected to a brass rod to form a half-wavelength dipole antenna with a total length of about 300 mm, thereby forming an optical electric field sensor.

In the optical electric field sensor of the present invention, the antenna length used is actually 30 to 1000 mm. Therefore, since it is a half-wave dipole, the antenna length is 30 to 1
The frequency f corresponding to 000 mm is 5 GHz to 150 M
Hz. When Q = 1, C = 2PF (2 picofarads) from the equation of Q = 1 / 2πfCR. f is 5G
When the resistance R is calculated from Hz to 150 MHz, R is 16
Ω to 500Ω. That is, the resistance of the high resistance material is 16
It may be Ω to 500 Ω.

Further, this optical electric field sensor has a DC value of about 1 GHz.
When an electric field up to z is applied, the antenna factor is 80
It became almost flat at dB, and the influence of resonance around 400 MHz, which was observed in the optical electric field sensor made of the conventional low resistance electrode film, did not appear particularly. FIG. 2 shows frequency characteristics of sensitivity, where the horizontal axis represents frequency (MHz) and the vertical axis represents relative output intensity (dB). In the figure, the dotted line 13 indicates the resonance point of the conventional electrode.

[0012]

EFFECTS OF THE INVENTION By making the electrodes of the optical electric field sensor have high resistance, it is possible to suppress the protrusion of the sensitivity at the resonance point in the measurement frequency range,
The frequency characteristic can be flattened. As a result, there is no need to add a resistor to the optical modulator afterwards, and there are effects such as downsizing of the sensor head and the need for resistance. By controlling the electrode resistance in this way, the frequency sensitivity correction in the electric field measurement becomes unnecessary, and the measurement can be performed easily.

[Brief description of drawings]

FIG. 1 shows an ITO (In ₂ O ₃ +5 wt% Sn) of the present invention.
O ₂₎ and an enlarged perspective view of a portion of the light modulator with mixed electrode film of quartz.

FIG. 2 is a diagram showing frequency characteristics of an optical electric field sensor.

FIG. 3 is a diagram showing an example of an optical electric field sensor system.

FIG. 4 is an enlarged perspective view of a portion of an optical modulator having a conventional metal electrode.

[Explanation of symbols]

1 light source (LD etc.) 2 input polarization maintaining fiber 3 optical electric field sensor head 4 output single mode fiber 5 E / O converter 6 measuring instrument (oscilloscope, spectrum analyzer etc.) 7 LiNbO ₃ substrate 8 Ti diffusion optical waveguide 9 (Cr- Au) Electrode film 10 Lead wire 11 Solder 12 (ITO-quartz mixed) Electrode film 13 Resonance point of conventional electrode 14 Frequency characteristic (of high resistance electrode) 31 Antenna

Claims (2)

(57) [Claims] 1. An optical modulator comprising an optical waveguide formed on an optical crystal substrate having an electro-optical effect, an electrode provided in the vicinity of the optical waveguide, and an antenna connected to the electrode of the optical modulator. In the constructed optical electric field sensor head, the electrode is made of a high resistance material having 16Ω to 500Ω. 2. An optical electric field sensor head, wherein the high-resistance substance according to claim 1 is a material containing silicon dioxide and a conductive oxide as main components.