JPH04230712A - Optical fiber coupler - Google Patents

Abstract

PURPOSE: To couple two mutually separated fiber into a union fiber. CONSTITUTION: A main body 110 formed of a material which transmits light has a 1st hollow part 22 and a 2nd hollow part 24 formed on opposite flanks of the main body opposite to each other, the 1st and 2nd hollow parts have mutually parallel planes, and the 1st hollow part is essentially circular and has a diameter essentially equal to the diameter of the union fiber 16; and the 2nd hollow part has 2nd size nearly equal to the sum of the diameters of a 1st fiber 12 and a 2nd fiber 14, the union fiber is adhered to the 1st hollow part, and the 1st and 2nd fibers are both adhered to the 2nd hollow part.

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the optical construction of a bar code reading system.

Optical bar codes are widely used for manual control or automatic digital reading and are a very convenient way to encode information at moderate spatial densities. What all optical configurations of bar code systems have in common is that they detect the reflection of the coding material at a particular spot size, and that the change in the detected reflection corresponds to each white or black area in the bar code. It is used as an indicator of width. The detection spot size, determined by the particular optical configuration used, essentially determines the minimum bar width that can be used in the bar code itself, and thus has a significant impact on the information density that can be encoded.

Thus, it is generally desirable to construct an optical bar code reader with a small detection spot size. However, achieving very small spot sizes using optical images requires inherently more expensive components than the inexpensive components that would otherwise be desirable for bar code reading systems that have very large demands. you will need it. Additionally, if a very small spot size is used, the bar symbol, or at least the portion of it that is within the detection spot area, must be brightly illuminated. Thereby, a reasonable optical signal level needs to be coupled through the optical path to the detection element.

It is therefore an object of the invention to obtain an optical system for a bar code reader that has a very small detection spot size, has high optical efficiency and is inexpensive.

Another object of the invention is to provide an optical bar code reader arrangement that provides very bright illumination of a small detection spot area. Yet another object of the present invention is to
The object of the present invention is to provide an optical bar code reader configuration that has a detection spot width of 54 mm (0.010 inch) or less, provides very bright illumination of the detection spot, and is inexpensive to construct.

A further desirable aspect of optical bar code configurations is that the total power required for illumination is low. That is, if the paper on which the bar code is printed is simply flood-illuminated to obtain the high incident light intensity necessary to obtain the required optical signal-to-noise ratio, the illumination power required is: It would be oversized for use in many suitable applications.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical bar code reader configuration that does not require excessive illumination power to brightly illuminate a very small detection spot.

Yet another object of the present invention is to provide a bar code reader optical configuration with a fiber optic sensor that is capable of illuminating the detection spot with high intensity with low total illumination power.

The present invention provides a bar code reader that uses a Y-coupler to multiplex the illumination from the LED and the reflected signal from the optical bar code onto a single optical fiber. This Y-coupler separates the sensing element (eg phototransistor) from the illumination element and allows it to receive the detection signal from the bar code.

According to the present invention, a light source for illumination, a first optical fiber connected to the illumination light source, a photodetector, a second optical fiber connected to the photodetector, and the first and second fibers are provided. and a union fiber coupled in a Y-shape such that the first and second fibers are optically isolated from each other, whereby a bar symbol is also illuminated at the free end of the union fiber. A bar code reader optical system is obtained which can also read bar codes.

The present invention will be explained below with reference to the drawings. The present invention solves the problems associated with optical configurations for bar code readers, allows high brightness partial illumination of the detection spot without the need for significant illumination power, and uses a single fiber to illuminate the detection spot. Both illumination and transmission of reflected light from the detection spot to an active sensing element can be provided. Additionally, several inventive methods have been used to economically form Y-shaped couplers using resin fibers. The basic principle for performing a Y-coupler configuration is the first
The coupling from the union fiber to the union fiber and the coupling from the second fiber to the union fiber are considered good coupling, and the coupling from the union fiber to the first fiber and the second fiber is also good coupling, but the coupled light from the union fiber is is sent to the first and second fibers and is therefore attenuated by 3 dB. In contrast, the coupling from the first fiber to the second fiber is very weak.

FIG. 1 shows the system configuration obtained by the present invention. An illumination light source 1, for example an LED, is coupled to a first fiber 12. The light from the illumination light source passes through the Y-shaped coupler region 9 to the union fiber 1
6 and from there to the detection chip of the union fiber 16. This light illuminates a bar code 26 placed near the sensing chip. A portion of the reflected light from the detection spot area 28 set on the bar code pattern 26 is collected by the detection chip portion of the union fiber 16. This reflected light is then sent through the union fiber 16 and the Y-shaped coupler 9 to the first fiber 12 and the second fiber 14. The second fiber 14 is coupled to a photodetector element 30, such as a phototransistor. With this optical configuration, the detection spot 28 is very efficiently illuminated with the illumination light source and the reflected light from the bar code 26 is also coupled to the photodetector element 30 with reasonable efficiency.

These three fiber elements 12, 14, 1
It is desirable that all 6 have approximately the same diameter, but this is not an absolute requirement. Furthermore, although it is desirable that the fiber be round, this is not necessarily the case. This is because other shapes of optical fibers can achieve optical propagation efficiency comparable to that of round fibers.

Several different inventive methods of making the Y-connection itself are also described herein. Alternative embodiments use coaxial assembly elements or alternatively resin molded coupler bodies.

The present invention is preferably applied to a union of three resin-clad optical fibers. Figure 1 shows the assembled fiber coupler. union fiber 16
are housed in the male element 11 and two mutually separated fibers 12 and 14 are housed in the female element 10. The inner diameter of element 11 is equal to the diameter of one fiber (including clearance), and the inner diameter of element 10 is equal to the sum of the diameter of two fibers and the clearance. The outer diameter of element 11 is approximately equal to the inner diameter of element 10;
A tight mechanical match is provided between 0 and 11. Thus, element 11 is connected to fiber 1
6, and element 10 orients fibers 12 and 14. Because the cavity within element 10 is filled with a nearly index-matched cement (i.e., index-matched to the fiber core), surface roughness and irregularities at the ends of fibers 12, 14, and 16 will not interfere with light transmission. Does not cause clutter. elements 10, 11
It is preferable to use stainless steel, as this material has several advantages. First, it is opaque, so there is no stray light entering the optical system at the junction. Secondly, it is mechanically strong and highly durable. Third, stainless steel pipes with precisely controlled inner and outer diameters are commercially available, such as syringe tubing. Fourth, stainless steel tubes are easily cold formed. Elements 10 and 11 can therefore be provided with a slight flare to aid assembly. Elements 10 and 11 need not be made as short compared to the fiber diameter as shown in FIGS. Note that by providing ground clearance, quick assembly and accurate orientation can be achieved. The axes of all three fibers should be approximately parallel. The axis of fiber 16 remains the same even if the axes of all three fibers are extended to infinity.
2 and the axis of the fiber 14. In the preferred embodiment shown here, 0
．． Fibers with a 127 mm (0.005 inch) diameter polymethyl methacrylate (DuPont Crofon™ type) cladding were used, and epoxy adhesive was used to connect fibers 12, 14, and 16. It is used. The adhesive itself is index-matched to the fiber and causes little unwanted attenuation through the coupler.

FIG. 2 shows a process for assembling a coupler according to the invention. Fiber 16 is first placed in element 11 and fibers 12 and 14 are placed in element 10. fiber 12
and 14 must be arranged so that they are almost adjacent to each other even outside the element 10. The cavity within element 10 is then filled with transparent cement or adhesive. The refractive index of this adhesive almost matches that of the cores of the fibers 12, 14, and 16. Elements 10 and 11 are then brought together and the associated extrusion of adhesive removes air bubbles (which cause unwanted light scattering) from fiber 1.
6 and the ends of the fibers 12, 14 are avoided. After the glue dries, all elements are fixed in place, resulting in a very durable optical coupling.

[0017] If 0.127 mm (0.005 inch)
If a fiber of
It is desirable that the thickness be 7 mils (mm) or less. If this spacing is made large, a large amount of energy will be absorbed by the walls of the coupler 10. In any configuration, 3 dB loss is unavoidable when coupling one fiber to two fibers. However, the critical factors in coupling design are the losses within the coupling and the energy that is radiated rather than coupled into the output fiber.

In the preferred embodiment, the inner surfaces of elements 10 and 11 are rough and light absorbing, so that the light emitted from the fibers impinging on the inner surfaces of element 10 is lost, although it is not radiated into the air. The optimal maximum air gap for a given material and fiber size is determined as follows. M1 is the refractive index of each fiber core, M2 is the refractive index of the fiber cladding, M3 is the refractive index of the material within element 10, d is the fiber diameter, and Dmax is the maximum deviation of the light exiting the end of the fiber from the fiber axis. When using the measured value, the following formula holds true.

[0019]

[Math 1]

[0020] Therefore, the optimum maximum air gap Xopt is as follows.

[0021]

[Math 2]

If the gap is smaller than this, the loss increases slightly, but this is not a problem in practice. However, when the air gap becomes larger than Xopt, the increase in loss becomes significant.

It will be apparent to those skilled in the art that a wide variety of equivalents and modifications to the preferred embodiments described above are possible, and that the inventive concepts described with respect to representative preferred embodiments are not intended to be limiting. It doesn't mean anything. For example, it is not necessary that fiber 16 be arranged symmetrically with respect to fibers 12 and 14. If the fiber 16 is slightly closer to either of the two fibers 12, 14, the properties will be slightly degraded, but the invention is still applicable. Similarly, misalignment of the fiber axis by a few degrees is acceptable.

In another embodiment of the invention, FIG. 3 shows a coupler body 110 according to the invention. It includes indentations 22, 24 into which two mutually separated fibers 12, 14 and a third union fiber 16 are glued. The axes of these three fibers should all be approximately parallel, so that the axis of fiber 16 is the same as that of fiber 12 when all fibers are extended to infinity.
and the axis of the fiber 14. The coupler body 110 includes an optical resin, which ideally should have an index of refraction matched to the resin optical fiber. For example, 0.
127 mm (0.005 inch) diameter polymethyl methacrylate (Dupont "Crofon"(TM) type)
If a clad fiber is used, the body of coupler 110 is made of polystyrene or polymethyl methacrylate. Additionally, epoxy adhesive is used to connect fibers 12, 14, 16 to coupler 110. The adhesive itself is index matched to the fiber and coupler so that there is little unwanted attenuation through the coupler.

If a fiber diameter of 0.127 mm (5 mils) is used, the ends of fiber 16 and fiber 14,
The air gap between the ends of 12 is 0.1778 mm (7 mil)
Or preferably less. If the air gap is made large, a large amount of energy will be radiated through the walls of coupler 110. A loss of 3 dB is unavoidable in any configuration that couples one fiber to two fibers. However, the decisive factor in coupling design is the loss within the coupling and the energy that is radiated rather than being delivered to the output fiber. The mechanical design of the present invention is such that all losses during bonding are avoided, although insignificant. However, as mentioned above, external radiation loss remains regardless of the fiber gap. In the presently preferred embodiment, each fiber has a diameter of 130 microns (5 mils), and the desired overall size of coupler 110 is approximately 3.8 mm (150 mils) along its major axis and approximately 150 mils along its minor axis. It is 2.9 mm (115 mil).

The optimal maximum gap length between the fiber ends for a given material and fiber size is determined as follows. The refractive index of each fiber core is M1, the refractive index of the fiber cladding is M2, the refractive index of the material in the coupler body 110 is M3, the fiber diameter is d, and the maximum deviation of light emitted from the end of the fiber is the fiber axis. Dm is the value measured from
When ax is set, the following equation holds true.

[0027]

[Math 3]

Therefore, the maximum optimal void length Xopt is as follows:

[0029]

[Math 4]

[0030] As the air gap becomes smaller, the loss increases slightly, but this is not a problem in practice. However, as the gap length increases beyond Xopt, the increase in loss becomes significant. Background light increases the noise level and degrades the signal-to-noise ratio, so it is desirable to keep stray light out of the fiber coupler. The shape of coupler body 110 contributes to the exclusion of background light. Furthermore, stray light can be eliminated by painting the coupler with the fiber in a predetermined position black.

FIG. 4 shows a molding process for economically constructing a coupler for use in the present invention. In order to maintain the void relationship mentioned above, the two male mold parts 1
8 and 20 should be mechanically limited in their movement so that the air gap between the internal planar surfaces of the two cavities formed is precisely controlled. Furthermore,
Note that the mold portion tapers very slightly so that its tapered sidewalls are formed into the two cavities formed within optical coupler 110. This facilitates assembly during manufacture and does not significantly degrade the optical properties. Since misalignment of the fiber axis within a few degrees is acceptable, a taper of several degrees in the wall of optical coupler 110 is also acceptable.

The shape of the second recess 24 is preferably oval as shown in FIG. However, other forms are also possible. Preferably, the second indentation 24 holds the sides of the fibers 12 and 14 so that they are not misaligned. However, the second indentation 24 is 2
It may be formed in the shape of a circle with double the diameter, in which case to prevent parallel rotation of the fibers 12 and 14,
A great deal of control is required for the assembly operation, which is difficult to achieve efficiently in this case. Thus, one important advantage of the preferred embodiment of the present invention is obtained by the lateral retention of fibers 12 and 14 within second recess 24. To obtain such lateral retention, the recess 24
is formed with a second dimension (over at least a portion of the recess) equal to one fiber diameter. For example, this depression 24 may be formed as two adjacent connected circular depressions having the same diameter and depth.

Once the optical coupler 110 is formed, assembly is simply a matter of wetting the end of each fiber with epoxy and placing it into the coupler fixture. Since precise assembly precision is not required, assembly can be done by hand or using simple automated manufacturing equipment.

Those skilled in the art will appreciate that a wide range of equivalents or modifications to the preferred embodiments described above are possible. The concept of the invention, which has been described with respect to exemplary preferred embodiments, is not intended to be limiting. For example, it is not necessary that fiber 16 be placed symmetrically with respect to fibers 12 and 14. If the fiber 16 were to be moved slightly closer to one of the two fibers 12 and 14, the properties would be slightly degraded, but the invention would still be applicable.

[0035] It will be apparent to those skilled in the art that numerous changes and modifications may be made in practicing the invention, which are not intended to be limiting except as defined in the claims.

The present invention thus provides an optical system for a bar code reader that has a very small detection spot size, has high optical efficiency, and is inexpensive.

The present invention further provides an optical bar code reader configuration that provides very bright illumination of a small detection spot area.

[0038] The present invention further provides 0.254 mm (0.01
To provide an optical bar code reader configuration that has a detection spot less than 0 inches wide, has a detection spot that is very brightly illuminated, and is inexpensive to construct.

Yet another desirable aspect of the optical bar code configuration is that the total power required for illumination is low. That is, if the paper on which the bar code is printed is simply flood-lit to obtain the high incident light intensity required to achieve the required optical signal-to-noise ratio, the illumination power required will be It would be too large to be used for other applications.

The present invention further provides an optical bar code reader configuration that does not require large illumination power to provide bright illumination of very small detection spots.

The present invention further provides a bar code reader configuration that includes a fiber optic detector and is capable of providing bright illumination of the detection spot with low total illumination power.

[Brief explanation of the drawing]

FIG. 1: Optical fiber Y according to a first embodiment of the invention.
It shows a letter-shaped bond structure.

FIG. 2 shows a method of assembling the Y-shaped joint structure of FIG. 1;

FIG. 3 shows an optical fiber Y-coupling structure according to a second embodiment of the invention.

4 shows a method of manufacturing and assembling the embodiment of FIG. 3; FIG.

[Explanation of symbols]

9 Y-shaped connection 10 Female element 11 Male element 12 First optical fiber 14 Second optical fiber 16 Union fiber 18 Male mold part 20　　　〃 22 Illumination light source 22, 24 Dent part 26 Bar code pattern 28 Detection spot 30 Photodetector 110 Coupler body

Claims (1)

[Claims] 1. An optical fiber coupler for coupling two mutually separated fibers into a union fiber, comprising a body of light-transparent material having first and second recessed portions; The first recessed portion and the second recessed portion are formed oppositely on opposite side surfaces of the main body, and each of the first and second recessed portions has a plane parallel to each other. , wherein the first recessed portion is essentially circular and has a diameter essentially equal to the diameter of the union fibers, and the second recessed portion is substantially circular and has a diameter substantially equal to the diameter of the union fibers, and the second recessed portion is substantially circular and has a diameter substantially equal to the diameter of the union fibers. a second dimension approximately equal to the sum of the diameters, the union fiber being adhered to the first recessed portion, and the first and second fibers both being adhered to the second recessed portion; A fiber optic coupler.