Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1995-03-07
1996-12-10
Turner, Samuel A.
Optics: measuring and testing
By particle light scattering
With photocell detection
385 12, G01B 902
Patent
active
055836372
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an optical electric field sensor for use in measurement of an electric field intensity within a spatial field, typically, in EMC measurement (noise measurement).
BACKGROUND ART
An optical waveguide Mach-Zehnder interferometer has a structure in which an optical waveguide is branched and one or both of branched optical waveguides are applied with an electric field parallel to a crystal axis thereof to phase-shift light beams propagating therein, which beams are thereafter combined again. Because a light intensity after combined is varied by the electric field applied thereto, the interferometer is used as an electric field sensor for detecting, by measurement of the light intensity, an electric field intensity applied to antennas connected to electrodes. The intensity of an outgoing light beam of the Mach-Zehnder interferometer exhibits a trigonometric function wave curve with respect to the electric field applied to the electrodes.
FIG. 1(a) shows one example of a conventional optical electric field sensor. As illustrated in the figure, the optical electric field sensor comprises an optical branched waveguide type interferometer formed on an LiNbO.sub.3 substrate by diffusion of Ti. One of two branched optical waveguides is provided with electrodes to form an optical modulator. The optical modulator is fixedly housed in a case 1 made of plastic. The electrodes of the optical modulator are connected to antennas 2, respectively. A polarization maintaining fiber 3 and a single mode fiber 4 are connected to a light incident side and a light outgoing side of the optical modulator, respectively. Connectors 6 are provided at the ends of fibers 3 and 4. An electric field spontaneously or forcedly generated is transmitted through the antennas to the electrodes to produce phase modulation in the optical waveguide. The light beam combined thereafter is modulated in intensity and, thus, has the light intensity corresponding to the electric field.
FIGS. 2(a)-2(d) show a conventional optical waveguide Mach-Zehnder interferometer used in the optical modulator illustrated in FIG. 1(a). As illustrated in FIG. 2(a), the optical waveguide Mach-Zehnder interferometer has a structure such that an optical waveguide is branched into branched optical waveguides 12 and 12 arranged on substrate 21, one or both of which are applied with an electric field 18 parallel to an optical axis through modulation electrodes 22 and 22 to provide phase-shift in the optical waveguides before being combined again. An input light beam is shown at 15 in FIG. 2(a), and an output light beam is shown at 16. Because a light intensity after combination is varied by the electric voltage applied thereto, the interferometer can be used as an electric field sensor for detecting, by measurement of the light intensity, an electric field intensity applied to antennas 2 as a low voltage applied across the modulation electrodes 22 and 22.
FIG. 3 shows an optical modulation characteristic of the Mach-Zehnder interferometer illustrated in FIG. 2(a). As illustrated in FIG. 3, an output intensity (relative intensity) of the light beam modulated in intensity by the Mach-Zehnder interferometer varies along a trigonometric function wave (sine wave) curve with respect to the applied voltage. In view of the above, adjustment (optical bias adjustment) is performed so that the light intensity is located at a linear variation point (a middle point between the maximum level and the minimum level) of the trigonometric function wave when the applied voltage is equal to 0 V. In this event, variation in light intensity and the applied electric field exhibit a proportional relationship. It is therefore possible, as an electric field sensor, to measure the applied electric field by the light intensity. In other words, such a characteristic is required for use as an electric field sensor.
The conventional optical electric field sensor, however, has a distance between the electrodes which is as small as several microns. If foreign substa
REFERENCES:
patent: 4528213 (1985-07-01), Nelson et al.
Tanabe Takanobu
Tokano Yuichi
Tokin Corporation
Turner Samuel A.
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