Optical magnetic-field sensor

Abstract: An optical magnetic-field sensor having a magnetooptical element (6), a polarizer (5), an analyzer (7) and a substrate (8) is provided seeking to decrease loss of the optical amount as well as temperature dependency of the modulation rate and prevent displacement and fall-away of the magnetooptical element from the polarizer and the analyzer. A synthetic resin adhesive agent is filled in a space (9) between the magnetooptical element and the polarizer and in a space (10) between the magnetooptical element and the analyzer, and the magnetooptical element, the polarizer and the analyzer are respectively adhered or bonded to the substrate.

Description: The present invention relates to optical magnetic-field sensors, such as are usable in a fault point-detecting system in electric power supply line networks, electric power distribution line networks, and transformer stations. Recently, in order to automatically detect fault points in electric power supply systems, optical magnetic-field sensors using optical single crystals, for example, BSO, etc., have been used practically. In these, a light beam emitted from a transmitter is transmitted through a magnetooptical element and detected by a receiver. If a system electric current is rapidly changed by short-circuiting or grounding, a magnitude of the electric field generated around the power supply line is changed to further change a polarized plane of the light beam transmitted through the magnetooptical element, so that the change is detected to judge an occurrence of a fault in the power supply line. In the optical magnetic-field sensors, a polarizer, a magnetooptical element and an analyzer are accommodated in a housing case with their optical axes aligned to each other. However, they have spaces between the magnetooptical element and polarizer or the analyzer, so that a great amount of the light beam is lost when transmitting through the optical magnetic-field sensor. Thus, heretofore, the distance between the transmitter and a detected fault point and the distance between the receiver and the detected fault point could not be increased to more than certain extents. The applicants disclosed in their Japanese Patent Application Laid-open No. 63-047,723 a technique of inserting an intermediate body, such as glass, etc. in the space between the magnetooptical element and the optical parts and adhering them to each other to release thermal expansion thereof. In this case also, losses of the amount of the light beam or optical amount at the interfaces between the intermediate body and the magnetooptical element or the optical parts were one of major problems. Large influence of temperature change over modulation rate was also a major problem. Meanwhile, Japanese Patent Application Laid-open No. 63-210,911 disclosed a technique of fixing the magnetooptical element and the optical parts respectively individually to the substrate via an intermediate body. However, in this case there arise problems in that a large amount of the light beam is lost, and the surface of the magnetooptical element adhered to the intermediate body tends to peel off owing to thermal stress generated by temperature change at e.g. transformer stations, so that the magnetooptical element is displaced and fallen away. Therefore, the technique has still problems as regards to durability for a long period of use. JP-A-1-244376 describes fixing of a magnetooptical element, a polarizer and an analyzer to a substrate having a positioning pattern effecting positioning of these elements, with gaps between these elements, and discurves disadvantages of being adhesive layers in the spaces between the elements. It would be desirable to be able to provide an optical magnetic-field sensor which could minimize the loss of the optical amount as well as the change of the modulation rate caused by thermal expansion and shrinkage of the magnetooptical element, and which could reduce or prevent displacement and fall-away of the magnetooptical element. The present invention is an optical magnetic-field sensor as set out in claim 1. The magnetooptical element, polarizer and analyzer are fixed to the substrate preferably by a resin adhesive agent which may be continuous with that filled into the spaces between these elements. The adhesive bond can provide the sole support for the elements against the substrate. For better understanding of the present invention, reference is made to the accompanying drawings, in which: Fig. 1 is a schematic view of an embodiment of the present optical magnetic-field sensor for automatically detecting a fault point; and Fig. 2 is a schematic cross-sectional view along the line II - II thereof. Hereinafter, the present invention will be explained in more detail with reference to examples. Example 1 Referring to Figs. 1 and 2 showing an embodiment of the present optical magnetic-field sensor, the input portion, the device portion and the output portion are positioned in a layout of substantially U-shaped arrangement; they may alternatively be positioned in a linear or stream line arrangement. Explaining concretely, in the case 1 a substrate 8 is fixed on which an inlet and outlet side ferrule 3 and a rod lens 4 are respectively arranged, and a device portion is fixed which is composed of a polarizer 5, a magnetooptical element 6 and a analyzer 7 sequentially arranged in this order. In this embodiment, an inlet side collimator and an outlet side collimator are respectively constituted by a rod lens 4, a ferrule 3 and an optical fiber 2. Positionings of the magnetooptical element 6 and the respective optical parts may be performed by preliminarily providing a desired pattern, e.g., of recess(es) or projection(s),on the substrate 8. A space between the magnetooptical element 6 and the polarizer 5 and a space between the magnetooptical element 6 and the analyzer 7 are filled respectively by an adhesive agent 9, 10 made of synthetic resin to adhere or bond them to each other. As the adhesive agent 9, 10, preferably a cold setting type, thermosetting type or ultraviolet ray setting type resin having substantially the same refraction index as those of the magnetooptical element 6, the polarizer 5 and the analyzer 7, is used. As examples of the preferable synthetic resin, epoxy series resin or acrylate series resin, etc., may be mentioned. The magnetooptical element 6, the polarizer 5 and the analyzer 7 are adhered to the substrate 8 by means of an adhesive agent. Preferably, the adhesive agent made of a synthetic resin is filled into the spaces 9, 10 to a thickness of 0.001-0.5 mm. In the optical magnetic-field sensor as shown in Fig. 1, an incident light beam emanating from the rod lens 4 is passed through the polarizer 5 to become a linear polarized light beam, and passed through the magnetooptical element 6 to receive Faraday's rotation. The rotated light beam is passed through the analyzer 7 wherein the optical amount of the light beam is changed according to the Faraday's rotation thereof. This intensity of the analyzed beam thus corresponds to the magnetic field 11 acting on the magnetooptical element 6. According to the optical megnetic-field sensor of this embodiment, the space between the magnetooptical element 6 and the polarizer 5 and the space between the magnetooptical element 6 and the analyzer 7 are respectively filled with an adhesive agent 9, 10 made of a synthetic resin, so that the loss of the light beam at the spaces can be decreased. In addition, the magnetooptical element 6 is adhered to the polarizer 5, the magnetooptical element 6 is adhered to the analyzer 7, and the magnetooptical element 6, the polarizer 5 and the analyzer 7 are respectively adhered to the substrate 8, and hence the magnetooptical element 6 is made integral with the adjoining optical parts, namely, the polarizer 5 and the analyzer 7, so that the optical magnetic-field sensor is highly resistant to temperature change and dislocation and fall-away of the magnetooptical element 6 therefrom can be prevented for a long use thereof. Example 2 and Comparative Examples 1-2 In this example, more concrete experimental embodiments will be explained. In the arrangement of Fig. 1, a polarizer beam splitter as the polarizer 5, and the analyzer 7, a ceramic substance such as alumina as the substrate 8, and a thermosetting type epoxy series adhesive agent as the adhesive agent 9, 10, are used. In order to adhere the magnetooptical element 6, the polarizer 5 and the analyzer 7 respectively to the substrate 8, a thermosetting type epoxy series adhesive agent is also used. The thermosetting type epoxy series adhesive agent is preliminarily defoamed by evacuating in vacuo, and applied on both the end surfaces of the magnetooptical element 6 to a desired amount of usually 0.005-2.5 mg/mm 2 , and in this embodiment 0.05 mg/mm 2 , by a dispenser. Next, the polarizer 5 and the detector 7 are adhered on the two end surfaces of the magnetooptical element 6, and simultaneously the polarizer 5, the analyzer 7 and the magnetooptical element 6 are adhered to the substrate 8 by a thermosetting type epoxy series adhesive agent. The magnetooptical element 6 having the adhered polarizer 5 and the analyzer 7 on the ends thereof is pressed by a pressure of 1.5 g/mm 2 on both sides by a pressing jig thereof to adjust the thickness of the thermosetting type epoxy resin series adhesive agent 9, 10 to a constant thickness of 10 µm. The pressed magnetooptical element 6, the polarizer 5 and the analyzer 7 adhered and pressed on the substrate 8 with the pressing jig are put in a dryer and thermoset or cured at a curing condition of 82°C for 90 min. The polarizer 5 and the analyzer 7 in Fig. 1 usually have a horizontal thickness respectively of 3-7mm and a lateral width of 3-7 mm, and the magnetooptical element 6 in Fig. 1 has usually a horizontal thickness of 3-4 mm. In this way, an optical magnetic-field sensor of this example is obtained. For preparing a comparative optical magnetic-field sensor, the space between the magnetooptical element 6 and the polarizer 5 and the space between the magnetooptical element 6 and the analyzer 7 were occupied respectively by an optical glass of a thickness of 0.1 mm, adhered and fixed by an adhesive, and the polarizer 5 and the analyzer 7 were respectively adhered to rod lenses 4 by means of an adhesive agent to obtain an optical magnetic-field sensor of Comparative Example 1. For preparing another comparative optical magnetic-field sensor, the magnetooptical element 6, the polarizer 5 and the analyzer 7 were respectively individually adhered to the substrate 8 by means of an adhesive agent, and the space between the magnetooptical element 6 and the polarizer 5 and the space between the magnetooptical element 6 and the analyzer 7 were not filled by the optical glass and the adhesive agent 9, 10 to obtain an optical magnetic-field sensor of Comparative Example 2. These three optical magnetic-field sensors were measured for loss of optical amount, temperature dependency of the modulation rate, and the state of the magnetooptical element used for a long period, by the following measuring methods. Loss of optical amount; A LED light beam is incidented from the incident side end of the optical fiber 2 and an amount of light beam exited from the exit side end of the optical fiber 2 is measured. Temperature dependency of modulation rate; Each optical magnetic-field sensor is applied with an alternating magnetic field of 50 Hz and 8 kA / m (100 Oe), put in an isotherm tank, and subjected to three-cycles of a heat-cooling cycle of heating to 80°C and cooling to -20°C for 8 hours to measure the temperature dependency of the modulation rate in a temperature range of -20°C - +80°C. The result is expressed as a change relative to the output at 25°C by the following formula. Output (at 80 O C) - Output (at 25 O C) Output (at 25 O C) × 100(%) (+) Output (at -20 O C) - Output (at 25 O C) Output (at 25 O C) × 100(%) (-) wherein the output is detected as a voltage by an optical amount/voltage converter. State of the magnetooptical element 6 used for a long period; A heat-cooling cycle of heating to 80°C and cooling to -20°C in 30 min. of each sensor is repeated for 1,700 cycles, then each sensor is applied with an alternating magnetic field of 50 Hz and 8 kA / m (100 Oe) at 25°C to measure a change of the modulation rate due to displacement of the magnetooptical element 6. In addition, the package of the sensor is disassembled to observe the displacement and fall-away of the magnetooptical element 6. Each experiment was conducted for 10 test samples and an average value thereof used. Change of modulation rate used for a long period (Deviation from initial value) is expressed by a formula: Output (at 1700 cycle, 25 O C) - Output (at initial state, 25 O C) Output (at initial state, 25 O C) × 100 wherein the initial state means non-heated and non-cooled state. The measured results are shown in the following Table 1. According to the optical magnetic-field sensor of the present invention, the spaces between the magnetooptical element and the polarizer and between the magnetooptical element and the analyzer are respectively filled by an adhesive synthetic resin agent, so that the loss of optical amount at the spaces can be decreased. Also, the magnetooptical element, the polarizer and the analyzer are respectively adhered to the substrate, and hence the magnetooptical element as well as the polarizer and the analyzer are integrally adhered to the substrate, so that temperature dependency of the modulation rate of the sensor can be mitigated, and displacement and fall-away of the magnetooptical element from the polarizer and the analyzer can be prevented. Although the present invention has been explained with reference to specific values and embodiments, it will of course be apparent to those skilled in the art that the present invention is not limited thereto.

Claims: An optical magnetic-field sensor comprising optical parts in the form of a magnetooptical element (6), a polarizer (5), an analyzer (7), rod lenses (3) and ferrules (4), all carried by a substrate (8), the magnetooptical element, the polarizer and the analyzer being respectively adhered or bonded to the substrate (8) and the substrate having a positioning pattern effecting positioning of the optical parts, characterised in that a synthetic resin adhesive agent (9, 10) is filled in the space between the magnetooptical element (6) and the polarizer (5) and in the space between the magnetooptical element (6) and the analyzer (7). An optical magnetic-field sensor according to claim 1 in which the refractive index of the synthetic resin adhesive agent (9, 10) is substantially the same as those of the magnetooptical element, polarizer and analyzer which it contacts. An optical magnetic-field sensor according to claim 1 or claim 2 in which the synthetic resin adhesive agent (9,10) forms a body which also provides said adhesion or bonding to the substrate (8).

Inventors: OKAJIMA HISAKAZU, SEIKE SHOJI, YAMAMOTO MASANOBU, OKAJIMA, HISAKAZU, SEIKE, SHOJI, YAMAMOTO, MASANOBU
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1991
Main classification: G01R33
IPC codes: G01R31, G01R15, G01R33, G02F1