Optical sensor and method for producing the same

Abstract: An optical sensor including a plurality of optical elements such as lenses (23,27), a polarizer (24), an analyzer (26), optical fibres (21,29), and a Pockels element or Faraday element (25). Light beams from a light source are transmitted through the optical elements of the optical sensor to optically measure quantitative values acting upon the optical elements on the basis modulation of the light beams received in a light receiver. The optical sensor includes a first synthetic resin (30) interposed between the optical elements to be in close contact with the optical elements without any clearance, and a second synthetic resin (30) of the same material as the first synthetic resin filled around the optical elements. The optical elements may be bonded to a base plate for adjusting optical axes of the optical elements, and the second synthetic resin may be filled around the optical elements and the base plate.

Description: This invention relates to a optical sensor for detecting fault points and fault sections, for example, at electric power transmission lines, distribution lines and transformer substations and the like, and a method for producing the optical sensor. Optical sensors have been known, for example, as disclosed in Japanese Patent Application Laid-open No. 62-54,170. As shown in Fig. 1, the disclosed known optical voltage sensor includes an optical fiber core 1, a plug 2, a microlens 3, a polarizer 4, a Pockels element 5, a quarter-wave plate 6, an analyzer 7, a reflecting mirror 8, a microlens 9, a plug 10 and an optical fiber core 11. A light receiver (not shown) receives light beams from a light source (not shown) through these optical elements 1-11 of the sensor. The voltage applied to the Pockels element 5 is optically measured on the basis of the modulation of the light beams received in the light receiver. In the optical voltage sensor shown in Fig. 1, the respective optical elements 1-11 are accommodated in a package 12 having therein a holder 13. The holder 13 is provided therein with a pipe 14 for holding the plug 2 and the microlens 3 on the input side and with a pipe 15 for holding the microlens 9 and the plug 10 on the output side. In order to prevent the moisture from entering the optical passages and reinforce against vibrations due to drop shock, the microlens 3, the polarizer 4, the Pockels element 5, the quarter-wave plate 6, the analyzer 7, the reflecting mirror 8, and the microlens 9 are joined with one another by means of a flexible adhesive 16a at boundaries on both sides of the Pockels element 5 and by means of a rigid adhesive 16b at remaining boundaries as shown in Fig. 2. Moreover, in order to unite these elements and the package 12, and more improve the resistance to the moisture and the vibrations due to drop shock, the respective optical elements are coated therearound with a flexible resin 17 and embedded in a rigid resin 18 by potting. Moreover, the package 12 is filled with Kevlar (Trade Mark) fibers 19 on the side of the optical cores 1 and 11 with respect to the holder 13. In the conventional optical voltage sensor described above, however, since the respective optical elements are bonded with each other by means of the adhesives 16a and 16b, residual stresses occur in the boundaries between them due to shrinkage of the adhesives when solidifying. Therefore, the optical elements may often be shifted from each other owing to change in external temperature to increase losses of light quantity and cause change in modulation. As a result, temperature characteristics of the instrument are detrimentally affected. Moreover, since the respective optical elements are coated with the flexible resin 17 and further embedded in the rigid resin 18 by potting, cracks may occur in the boundaries between the optical elements owing to thermal stresses caused by temperature changes due to difference between coefficients of thermal expansion of the flexible and rigid resins 17 and 18. Further, cracks may occur in the flexible and rigid resins 17 and 18. As a result, the optical elements may become susceptible to moisture, vibration due to drop shock. With the optical voltage sensor described above, moreover, all the optical elements are accommodated in the package 12 having the holder 13 which holds the plug 2 and the microlens 3 by the pipe 14 on the input side and the microlens 9 and the plug 10 by the pipe 15 on the output side. Therefore, the number of parts unavoidably increases, and the holder 13 and the package 12 fitted with each other are required to be produced with high accuracy. Accordingly, the instrument itself becomes expensive and the process for producing the instrument becomes complicated to lower the mass-productivity. US-A-4962990 shows an optical device in which optical elements, are mounted on an optical bench made of ceramics by means of optical adhesive. There are air gaps between the elements. Drawings referenced to as "prior art" in this document show adjacent optical elements, which are not suggested on a bench, joined together by adhesive layers. The general problem addressed herein is to provide a novel construction of optical sensor and methods of making it. A preferred aim is to produce a sensor constructed to obtain good temperature characteristics and superior in the resistance to moisture, vibration and shock due to drop. It is also possible to provide a method which is able to produce such an optical sensor effectively in mass-production with low cost. In a first aspect of the invention, there is provided an optical sensor as set out in claim 1. In a further aspect of the invention, there is provided a method for producing an optical sensor as set out in claim 7 and a method as set out in claim 9. Thus, in the invention the optical elements are in close contact with a synthetic resin interposed between them, effectively without any clearance and embedded in a synthetic resin of the same material as the first synthetic resin. Therefore, it is possible to reduce thermal stresses in the sensor due to difference in thermal expansion coefficients so that temperature characteristics of the optical sensor can be effectively improved. Moreover, by the amelioration of the thermal stresses, the synthetic resins in the sensor may be free from cracks, crevices and damage. Accordingly, the optical sensor tends to have better resistances to moisture, vibration and shock due to fall so that the reliability of the optical sensor can be more improved. Using the method of the invention, moreover, an optical sensor may be produced by the repeatedly usable first and second base plates without requiring any package integral with a holder. Therefore, a method embodying the invention may produce the optical sensor with less number of parts used in producing the optical sensor. This is consistent with inexpensive production and good mass-productivity. By the method of the invention, furthermore, the optical sensor may be produced by using the first base plate made integral with the optical elements and the repeatedly usable second base plate. Therefore, a method embodying the invention may produce the optical sensor by the use of the number of parts in producing the optical sensor less than that in the prior art. This is consistent with inexpensive production and good mass-productivity. The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings. Fig. 1 is a sectional view illustrating an optical sensor of the prior art; Fig. 2 is a partial view illustrating in detail the principal optical elements of the optical sensor shown in Fig. 1; Fig. 3 is a front view illustrating one embodiment of the optical sensor according to the invention; Fig. 4 is a plan view of the optical sensor shown in Fig. 3; Fig. 5 is a side view of the optical sensor shown in Fig. 4; Fig. 6 is a cross-sectional front view illustrating one example of the base plate for adjusting optical axes of the optical elements to be used for producing the optical sensor shown in Figs. 3 to 5 according to the invention; Fig. 7 is a plan view of the base plate shown in Fig. 6; Fig. 8 is a longitudinal-sectional side view of the base plate shown in Fig. 7; Fig. 9 is a cross-sectional front view for explaining the method for producing the optical sensor shown in Figs. 3 to 5 according to the invention; Fig. 10 is a plan view for the same purpose as Fig. 9; Fig. 11 is a longitudinal-sectional side view for the same purpose as Fig. 9; Fig. 12 is a cross-sectional front view for the same purpose as Fig. 9; Fig. 13 is a plan view for the same purpose as Fig. 9; Fig. 14 is a longitudinal-sectional side view for the same purpose as Fig. 9; Fig. 15 is a front view illustrating another embodiment of the optical sensor according to the invention; Fig. 16 is a plan view of the optical sensor shown in Fig. 15; and Fig. 17 is a side view of the optical sensor shown in Fig. 16. Figs. 3, 4 and 5 illustrate an optical magnetic sensor as one embodiment of the optical sensor according to the invention in a front, a plan and a side view. The optical magnetic sensor comprises an optical fiber 21, a ferrule 22, a lens 23, a polarizer 24, a Faraday element 25, an analyzer 26, a lens 27, a ferrule 28 and an optical fiber 29. Light beams from a light source (not shown) are caused to pass through these optical elements 21 to 29. A light receiver (not shown) receives the light beams emitted from the optical fiber 29 after passed through these optical elements. Magnetic fields acted upon the Faraday element 25 are optically measured on the basis of the modulation of the light beams received in the light receiver. In this embodiment, the lens 23, the polarizer 24, the Faraday element 25, the analyzer 26 and the lens 27 are in intimate contact with a first synthetic resin (not shown) of epoxy or urethane type interposed between these optical elements without any clearances therebetween. Moreover, second and third synthetic resins 30, 30a of the same material as the first synthetic resin are filled around these optical elements and the ferrules 22 and 28 including the optical fibers 21 and 29 without any clearances. One embodiment of the method for producing the optical magnetic sensor shown in Figs. 3 to 5 will be explained hereinafter. Fig. 6 illustrates in a cross-sectional front view one example of a first base plate 31 for adjusting optical axes to be used in carrying out the method according to the invention. Figs. 7 and 8 are a plan view and a longitudinal sectional side view of the base plate shown in Fig. 6. The base plate 31 is integrally provided with a portion 32 for supporting the ferrule 22 and the lens 23, a portion 33 for supporting the lens 27 and ferrule 28, and a portion 34 for supporting the polarizer 24, the Faraday element 25 and the analyzer 26 so that the optical axes of these optical elements are properly aligned with each other when they are arranged on these portions 32, 33 and 34, respectively. In the embodiment shown, the portions 32 and 33 are formed by V-shaped grooves. The base plate 31 is preferably made of a material, for example, PTFE (Teflon R ) which is able to be easily removed from the optical elements after the synthetic resin 30 has solidified. As shown in Fig. 9 to 11, the respective optical elements are arranged on the base plate 31 at their predetermined positions, respectively, so that they are in close contact with the first synthetic resin interposed therebetween without any clearances. Thereafter, the second synthetic resin 30 of the same material as the first synthetic resin is filled around the optical elements in the base plate 31 and solidified (Figs. 9 and 11). The optical elements and the second synthetic resin 30 as a unitary body are then removed from the base plate 31 and are turned upside down so that the filled second synthetic resin 30 becomes on the lower side of the unitary body. As shown in Figs. 12, 13 and 14, the unitary body is then arranged in a second base plate 35 which is made of a material similar to that of the first base plate 31 but has a flat bottom. A third synthetic resin 30a of the same material as the first and second synthetic resins is then filled around the optical elements and the second synthetic resin 30 in the second base plate 35 and solidified. Thereafter, the optical elements and the second and third synthetic resins 30, 30a are removed from the second base plate 35 to obtain the optical magnetic sensor shown in Figs. 3 to 5. Figs. 15, 16 and 17 illustrate in a front, a plan and a side view another embodiment of the optical sensor according to the invention. The optical sensor is similar to the optical sensor shown in Figs. 3 to 5 with exception that a first base plate 31 is embedded together with optical elements in the second synthetic resin 30a. In this embodiment, a base plate 31 is made of a material, for example, alumina, zirconia or the like which is easily bonded to the synthetic resin used. The respective optical elements are bonded onto the base plate 31 so that the optical elements are in close contact with a first synthetic resin (not shown) interposed between the optical elements without any clearances, and then a second synthetic resin 30 of the same material as the first synthetic resin is filled in the base plate 31 and solidified. Thereafter, the optical elements together with the base plate 31 are turned upside down and arranged on a second base plate (not shown) having a flat bottom plate. A third synthetic resin 30a of the same material as the first and second synthetic resins is filled around the optical elements and the first base plate 31 in the second base plate and solidified in the same manner as in the first embodiment. The optical elements and the base plate 31 are then removed from the second base plate to obtain the optical sensor. The invention is not limited to the optical magnetic sensors described above. For example, a Pockels element may be used instead of the Faraday element 25, and a quarter-wave plate may be interposed between the polarizer 24 and the Pockels element or between the Pockels element and the analyzer 26 to obtain an optical voltage sensor. Moreover, the invention is effectively applicable to other optical sensors with analogous construction. As can be seen from the above description, with the sensor described it is possible to prevent thermal stresses in the sensor due to difference in thermal expansion coefficients so that temperature characteristics of the optical sensor can be effectively improved. Moreover, by the prevention of the thermal stresses, the resins in the sensor are free from cracks, crevices and damage. Accordingly, the optical sensor as described above can be superior in resistance to moisture, vibration and shock due to fall so that the reliability of the optical sensor can be more improved. Moreover, the method as described can produce the optical sensor from few parts and is inexpensive to carry out the method and superior in mass-productivity.

Claims: An optical sensor having an assembly of optical elements including at least one lens (23,27), a polarizer (24), an analyzer (26), at least one optical fiber (21,29) and a Pockels or Faraday element (25), through which light beams are transmissible to optically measure quantitative values acting upon the Pockels or Faraday element, a first synthetic resin region interposed between adjacent ones of said optical elements without clearance, and a further synthetic resin region (30,30a) made of the same material as said first synthetic resin region and formed separately from said first synthetic resin region, said further synthetic resin region (30,30a) comprising first and second synthetic resin bodies (30,30a) together enveloping said assembly of optical elements on all six sides thereof, wherein said first synthetic resin body (30) contacts faces of said optical elements on a first side of said assembly and said second synthetic resin body (30a) covers a second side of said assembly opposite said first side and covers also third and fourth sides of said assembly which are opposed to each other and are disposed laterally with respect to said first and second sides in the lateral direction which is parallel to the light path through the Pockels or Faraday element (25), said first and second synthetic resin bodies being separately formed in situ. An optical sensor according to claim 1 wherein said second synthetic body (30a) contacts faces of said optical elements on said three other sides of said assembly thereof. An optical sensor according to claim 1 wherein between said second synthetic resin body (30a) and said optical elements there is a base plate (31) locating said optical elements. An optical sensor according to claim 3 wherein said base plate (31) comprises a surface on which said optical elements are arranged, said surface being formed with V-shaped grooves for aligning the optical axes of the optical elements with one another by locating the optical elements on the surface. An optical sensor according to claim 3 or claim 4 wherein said base plate (31) is made of a material selected from alumina and zirconia. An optical sensor according to any one of claims 1 to 5 wherein said synthetic resin material is selected from epoxy type and urethane type resins. A method for producing an optical sensor including an assembly including at least one lens (23,27) a polarizer (24), an analyzer (26), at least one optical fiber (21,29) and a Pockels or Faraday element (25), through which assembly light beams are transmissible to optically measure quantitative values acting upon the Pockels or Faraday element, the method comprising the steps of arranging the optical elements on a first base plate (31) for adjusting optical axes of the optical elements so that the optical elements are in close contact with a first synthetic resin interposed between adjacent ones of the optical elements to form said assembly, filling a second synthetic resin of the same material as the first synthetic resin against the optical elements on one side of said assembly and solidifying the filled second synthetic resin, removing the assembly of optical elements together with the solidified second synthetic resin (30) from the first base plate (31), turning the removed optical elements and the second synthetic resin upside down and arranging them on a flat bottom surface of a second base plate (35), filling a third synthetic resin of the same material as the first synthetic resin around the optical elements on the other sides of said assembly and solidifying the filled third synthetic resin, and removing the optical elements together with the second and third synthetic resins (30,30a) from the second base plate (35). A method according to claim 7 wherein said first base plate (31) is made of a material which is easily removable from the optical elements after the second synthetic resin (30) has been solidified. A method for producing an optical sensor including an assembly of including at least one lens (23,27) a polarizer (24), an analyzer (26), at least one optical fiber (21,29) and a Pockels or Faraday element (25), through which assembly light beams are transmissible to optically measure quantitative values acting upon the Pockels or Faraday element, the method comprising the steps of bonding the optical elements onto a first base plate (31) for adjusting optical axes of the optical elements so that the optical elements are in close contact with a first synthetic resin interposed between adjacent ones of the optical elements, filling a second synthetic resin of the same material as the first synthetic resin against the optical elements on one side of said assembly and solidifying the filled second synthetic resin, turning the assembly of optical elements upside down together with the first base plate (31) bonded therewith and the solidified second synthetic resin (30) and arranging them in this turned state on a flat bottom surface of second base plate (35), filling a third synthetic resin of the same material as the first synthetic resin around the optical elements and the first base plate on the other sides of said assembly and solidifying the filled third synthetic resin, and removing the optical elements together with the first base plate (31) and the second and third synthetic resins (30,30a) from the second base plate (35). A method according to any one of claims 7 to 9, wherein said synthetic resin is selected from epoxy type and urethane type resins. A method according to any one of claims 7 to 10 wherein as said first base plate (31) there is used a base plate (31) which comprises a surface on which said optical elements are arranged, said surface being formed with V-shaped grooves (32,33) for aligning the optical axes of the optical elements with one another when locating the optical elements on the first base plate.

Inventors: ASAI YUJI, YAMAMOTO MASANOBU, ASAI, YUJI, YAMAMOTO, MASANOBU
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1992
Main classification: G01R33
IPC codes: G02B6, G01R19, G01R1, G02F1, G01J1, G01R15, G01R33