JP2774590B2 - Optical fiber spatial filter and manufacturing method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber type spatial filter used for speed measurement and the like, and a method for manufacturing the same.

[Related Art] A spatial filtering method using a spatial filter uses a specific spatial pattern mainly based on a distribution of light transmittance from an object having a certain spatial pattern.
This is a method for obtaining information such as the speed of an object and a defect in a pattern.

FIG. 5 shows an example of a velocity measurement system using a spatial filter. In FIG. 5, reference numeral 1 denotes a spatial filter, and reference numeral T denotes an object to be measured. This measurement target T is a spatial pattern f (x, y) in a two-dimensional orthogonal coordinate system (x, y).
And is moving at the speed V. Further, the spatial filter 1 has a spatial pattern h (x, y) designed as a specific spatial weighting function for the spatial pattern f (x, y).
y). The spatial filter 1 converts the spatial pattern f (x, y) of the measurement target T into h (x, y). This spatial pattern converted from f (x, y) to h (x, y) is condensed by an optical system 2 such as a lens provided at a position separated from the spatial filter 1 by a focal length, and the light is detected. The detection is performed by the detector 3. The photodetector 3 is located at a focal point on the opposite side of the spatial filter 1 across the optical system 2 and is connected to a frequency measuring device 4 such as a spectrum analyzer. The frequency measuring device 4 can measure the center frequency of the spatial pattern h (x, y) detected by the photodetector 3 and can measure the speed V of the measuring object T from this value. .

Such a spatial filter 1 has a spatial pattern h (x,
y), the spatial pattern f (x,
6), and has a spatial pattern k (x, y) of a row structure of N slits S having a width W and a length L as shown in FIG. 6, for example. The spatial load function of such a spatial filter 1 is also shown in FIG. Then, the width W of each slit S is 1 / the pitch P.
3, and as shown in FIG. 7, two series of the slit row A and the slit row B are prepared, and their outputs are differentially connected. The spatial filter 1 of the narrow band transmission type having the spatial frequency characteristics as shown in FIG. The dashed line in FIG. 8 indicates the slit width W and the low-frequency transmission characteristics of the differential configuration.

At this time, the differential output of FIG.
Has an average frequency ν proportional to, a substantially sinusoidal narrow-band irregular signal whose amplitude and phase fluctuate slowly,
The velocity V of the measuring object T can be measured by measuring the frequency ν, and the relationship between the frequency ν and the velocity V is given by the equation (I).

ν = m / P · V · cos θ (I) Here, m indicates the magnification of the optical system 2 used when projecting the spatial pattern f (x, y) of the measurement target T onto the spatial filter 1. And θ represents the deviation from the x-axis in the moving direction of the image of the spatial pattern f (x, y) projected on the spatial filter 1, as shown in FIG. The effects of m and cosθ are called a magnification effect and a cosine effect, respectively. The cosine effect indicates that a velocity component v _{1 in} a direction orthogonal to the slit width W of the velocity vector v of the measurement target T can be measured. It is shown.

Assuming now that the measurement target T having a pattern of f (x, y) is moving in one direction at a speed of v _{1 in} the x-axis direction and v _{2 in the} y-axis direction, at a certain point in time. The spatial pattern of this measurement target T at t is f (x−v ₁ t, y−v
₂ t). The space pattern f (x−v ₁ t, y−v ₂ t) of the measurement target T is referred to as the space pattern 1
Then, when the measuring light is condensed by the optical system 2, the intensity of the measuring light changes with time. If this is g (t), the intensity of the measuring light can be obtained by the formula (II). it can.

g (t) = ∬ _R f (x−v ₁ t, y−v ₂ t) h (x, y) dxdy
(II) In the formula (II), R represents a region of the spatial filter.

Since the spatial load function h (x, y) of the spatial filter is designed to select a specific spatial frequency component of the pattern f (x, y) of the measurement target, g in the above equation (II) Calculate v ₁ and v ₂ from the spatial frequency spectrum of (t),
The speed V of the measurement target T can be obtained.

Since the measurement using the spatial filter 1 is a measurement system using the optical principle, it is characterized in that accurate measurement without malfunction can be performed even in a special environment such as a strong electromagnetic field or a high temperature atmosphere. is there.

[Problems to be Solved by the Invention] However, in the measurement system shown in FIG. 5, since a large number of electrical devices are required for the configuration of the photodetector 3 and the frequency measurement device 4, these components are used for measurement. It is necessary to keep electrical equipment away from strong electromagnetic fields and high-temperature atmospheres.

However, the distance between the spatial filter 1 and the photodetector 3 is limited by the focal length of the optical system 2, and the conventional spatial filter 1 is obtained by transferring a certain spatial pattern on a flat glass plate by printing or the like. Therefore, since the spatial pattern subjected to the spatial filtering cannot be transmitted, when the measurement target T is in a strong electromagnetic field or under a high-temperature environment, the spatial pattern is used even if the spatial filtering can be performed. There was a disadvantage that measurement could not be performed.

Further, in the measurement system as shown in FIG. 5, a plurality of optical systems and electric elements are connected, and the configuration of the spatial filter 1 and its miniaturization are limited. Adjustment and use conditions were limited, and there was an inconvenience that handling was poor.

The present invention has been made in order to solve the above-mentioned problem. By using an optical fiber type waveguide as a spatial filter, it is possible to transmit a spatially filtered spatial pattern, and to measure a target T and a detector. Optical fiber spatial filters and their manufacture that enable measurement in special environments such as in strong electromagnetic fields or high-temperature environments while miniaturizing the tip of the measurement system and improving handling. The method is intended to provide.

[Means for Solving the Problems] An optical fiber spatial filter according to claim 1 of the present invention is characterized in that a layered core and a layered cladding are alternately laminated in the diameter direction of an optical fiber. ,
In such an optical fiber spatial filter, as described in claim 2, after arranging a plurality of waveguide glass plates, a sol-like glass member having a different refractive index from these glass plates is placed between the upper glass plates. It can be manufactured by filling a preform, spinning the preform in a direction perpendicular to the arrangement direction of the glass plates, and laminating a layered core and a layered clad.

[Operation] The optical fiber spatial filter according to claim 1 of the present invention is an optical fiber type waveguide having an operation of spatial filtering. Therefore, when this is used in a measurement system, a portion for performing spatial filtering and filtering are used. The space between the detector and the detector that detects the spatial pattern is detected by an optical fiber spatial filter, and the distance between them can be increased. An object can be easily measured.

In the method for manufacturing a spatial filter according to the second aspect, since the glass member of the core or the clad is manufactured using the sol-gel method, the arrangement of the core and the clad can be changed by using the fluidity of the sol. Therefore, a spatial filter having a desired spatial weighting function can be easily obtained.

EXAMPLES Hereinafter, the present invention will be described in detail.

FIG. 1 shows an embodiment of an optical fiber spatial filter 1 according to claim 1 of the present invention.

The optical fiber spatial filter 1 is an optical fiber including a plurality of layered cores 5 and a plurality of layered claddings 6, in which the cores 5 and the claddings 6 have a fixed spatial pattern, that is, a fixed spatial pattern. This is an optical fiber designed and arranged so as to show a load function h (x, y). In this example shown in FIG. 1, (N-1) clads 6 composed of a low-refractive-index member are interposed between N cores 5 composed of a high-refractive-index member and a long optical fiber. The cores 5 are formed as slits S by laminating each other along the direction. The spatial load function h (x, y) of the optical fiber spatial filter 1 is designed as a spatial pattern having a row structure of N slits S. When light having a spatial pattern f (x, y) from the measurement / measurement object T enters the optical fiber spatial filter 1 of the present invention, the light is transmitted through the cores 5... And the spatial pattern h (x , y), the spatial pattern f (x, y) becomes h
It is converted to (x, y) and spatial filtering is performed.

If the shape of the spatial filter for converting the spatial pattern f (x, y) into h (x, y) is an optical fiber shape as shown in FIG. Output end 1b from which the converted spatial pattern h (x, y) is output
Can be set longer, the measurement target T
In a special environment such as a strong electromagnetic field or a high-temperature atmosphere, the emission end 1b can be set away from the special environment. Even in the case of using the photodetector, both the photodetector 3 and the center frequency measuring device 4 can be installed outside the special environment, so that accurate measurement can be performed.

Further, when the spatial filter is formed in an optical fiber shape, the space filter can be reduced in size, the measurement system can be easily installed on the measurement target T, and the handling property can be improved.

In the example shown in FIG. 1, the optical fiber spatial filter 1 has a circular cross section and shows a spatial pattern of a plurality of slit layer structures. Is not limited to this example, the core 5 and the clad 6 may be designed and set so as to exhibit a constant spatial load function h (x, y). The number of copies is not limited, and the sectional shape thereof is not limited, and may be elliptical or rectangular.

Such an optical fiber spatial filter 1 can be easily obtained by the method as described in claim 2. That is, after arranging a plurality of glass plates, a sol-like glass member having a different refractive index from the glass plate is filled between the waveguides to form a preform, and the preform is spun to form a certain spatial pattern. It can be obtained by using an optical fiber having the same.

For example, the optical fiber spatial filter 1 shown in FIG.
Can be obtained as follows.

First, N glass plates 7 to be optical fiber cores 5 are prepared. Although the glass plates 7 are not particularly limited, for example, as shown in FIG.
When a material having a refractive index lower than the refractive index of the glass plate 7 is filled, a slab waveguide or the like that can transmit light only in the two-dimensional direction of the y and z planes is formed. Can be used. A sol-like glass member 8 having a refractive index different from that of the glass plates 7 is filled between the N glass plates 7 to form a preform 9 as shown in FIG.
To form The glass members 8 have a different refractive index from the glass plates 7. When the glass members 8 have a higher refractive index than the glass plates 7, the glass members 8 have the cores 5. On the contrary, when the glass members 8 have a lower refractive index than the glass plates 7, the glass members 8.
.. Become claddings 6.

A sol-gel method can be used to fill the sol-like glass members 8 between the glass plates 7. The sol-gel method referred to here means, for example, hydrolyzing a silicon alkoxide solution such as Si (OC ₂ H ₅ ) _{4 as a} glass raw material into a viscous sol of silicon oxide, and converting the viscous sol into a wet gel body. It is a method of manufacturing and manufacturing the glass members 8. By this sol-gel method, the glass member 8 ...
FIG. 4 shows an example of a process for forming the.

First, a silicon alkoxide such as Si (OC ₂ H ₅ ) _{4 as} a glass raw material is dissolved in an alcohol solution of water and hydrochloric acid, and the mixture is stirred while being heated at 25 to 80 ° C. to hydrolyze the silicon alkoxide. Decompose into SiO ₂ and polymerize into viscous sol. Next, this viscous sol is further stirred while being heated at 25 to 80 ° C. to form a wet gel in which SiO ₂ is aggregated. Since the wet gel has an appropriate fluidity, it is impregnated or filled between the glass plates 7 shown in FIG. 2 and then dried to integrate the glass plates 7. Then, the integrated glass plates 7 are heated at 400 to 800 ° C. to sinter the wet gel to form glass members 8.
As shown in the figure, a preform 9 consisting of glass plates 7 and glass members 8 is obtained. The difference between the refractive indices of the glass members 8 and the glass plates 7 can be determined by preliminarily impregnating the glass plates 7 with various dopants such as rare earth metal oxides for adjusting the refractive index, and by adding various dopants to the silicon alkoxide solution. By adding a dopant, the refractive index of the glass members 8 can be changed. And as this dopant, P ₂
O ₅ , GeO ₂ , B ₂ O _3, etc., which change the refractive index of an optical fiber can be used.

The ratio of the thickness of each glass plate 7 to the thickness of the filling portion of the wet gel body that becomes the glass members 8 indicates a desired space pattern h (x, y). When the preform 9 is formed by filling the glass members 8 by such a sol-gel method, the refractive index and the filling thickness of the glass members 8 can be freely changed. x, y) can be obtained.

And the preform 9 molded in this way is
Spinning is performed in a direction perpendicular to the arrangement direction of the glass plates 7 which is the light guiding direction of the glass plates 7, that is, in the example shown in FIG. 3, along the Y-axis direction or the Z-axis direction. An optical fiber spatial filter 1 according to claim 1 of the present invention can be provided. This spinning step is not particularly limited as long as it can spin an optical fiber-shaped one from the preform 9, and a usual optical fiber spinning apparatus and process can be used. It is necessary to change the spinning speed and spinning temperature so that the spatial pattern h (x, y) of the spatial filter 1 can be realized.

[Effects of the Invention] As described above, the optical fiber spatial filter according to the first aspect of the present invention is formed by alternately stacking layered cores and layered claddings in the diameter direction of the optical fiber. Therefore, the size can be easily reduced, and it can be installed in close proximity to an object to be measured existing in any place, so that the degree of freedom in measurement is increased.

Further, the optical fiber spatial filter of the present invention is of an optical fiber shape, and can transmit a spatial pattern of the spatially filtered object to be measured. Since the distance between them can be increased by connecting them with the optical fiber spatial filter of the present invention, even when the object to be measured exists in a special environment such as a strong electromagnetic field or a high-temperature atmosphere, detection can be performed. Since the electrical devices constituting the unit can be installed and measured outside the special environment, accurate measurement can be performed.

Further, in the method for manufacturing a spatial filter according to claim 2 of the present invention, after arranging a plurality of glass plates, a sol-like glass member having a refractive index different from those of the glass plates is filled between the glass plates. The preform is then spun in a direction perpendicular to the direction in which the glass plates are arranged, and a layered core and a layered clad are laminated. A spatial filter having the weight function h (x, y) can be easily obtained.

In addition, since an optical fiber spatial filter having a desired spatial pattern can be easily manufactured, it is possible to contribute to an improvement in productivity.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of an optical fiber spatial filter according to claim 1 of the present invention, and FIG. 2 is a diagram of a waveguide suitably used in manufacturing the optical fiber spatial filter of the present invention. FIG. 3 is a schematic configuration diagram showing one example, FIG. 3 is a schematic configuration diagram showing one example of a preform used in one step of the method for manufacturing an optical fiber spatial filter of the present invention, and FIG. 4 is an optical fiber spatial filter of the present invention. FIG. 5 is a schematic diagram showing an example of a velocity measurement system using a spatial filter, and FIG. 6 is an example of a conventional spatial filter. FIG. 7 is a schematic configuration diagram showing the spatial load function of the spatial filter, FIG. 7 is a schematic configuration diagram showing the differential configuration of the slit array of the spatial filter shown in FIG. 6, and FIG. 7
FIG. 9 is a graph showing the spatial frequency of the differential configuration of the spatial filter shown in FIG. 9, and FIG.
It is the schematic which showed the relationship with the deviation | shift angle from an axis | shaft. 1 ... spatial filter, 5 ... core, 6 ... clad, 7 ... glass plate, 8 ... glass member, 9 ... preform.

──────────────────────────────────────────────────の Continuing on the front page (51) Int.Cl. ⁶ Identification code FI G02B 27/46 G02B 6/00 B (72) Inventor Katsuyuki Seto 1440 Mutsuzaki, Sakura-shi, Chiba Pref. 72) Inventor Naoki Shamoto 1440 Mutsuzaki, Sakura City, Chiba Prefecture Inside the Sakura Plant of Fujikura Electric Wire & Cable Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6/00 G02B 6/10 G02B 6/22 G02B 27/46 G01P 3/36

Claims (2)

(57) [Claims] An optical fiber spatial filter in which layered cores and layered claddings are alternately laminated in the diameter direction of an optical fiber. 2. After arranging a plurality of glass plates, a sol-like glass member having a refractive index different from those of the glass plates is filled between the upper glass plates to form a preform. A layered core and a layered clad are spun in a direction perpendicular to the arrangement direction of the optical fiber.