JPS63179304A - Optical connector for reflection type light applied sensor system - Google Patents

Abstract

PURPOSE:To minimize Fresnel reflection on a connected end surface and to reduce the connection loss of an optical connector for optical fiber connection which is used for a reflection type light applied sensor system by charging matching oil which is nearly equal in refractive index to a core in the connec tion gap between plugs. CONSTITUTION:A three-terminal bidirectional optical branching and coupling device and an optical fiber connecting with a probe are connected by the connec tor by forming an oblique polished surface 15 having a tilt angle phi on the plug 10 on the side of the optical branching and coupling device. The matching oil 18 which in nearly equal to refractive index to the core of an optical fiber 9 and has high transparency is stuck on the gap part formed with an opposite- side plug 11 and they are connected while the oil is charging through an adapter 12. Further, the oblique polished surface phi and the normal NA value of the optical fiber satisfy phi<sin<-1> NA, and the core center distance does not increase. Thus, even when the optical fiber is extremely short, the Fresnel reflection on the connected surface end is minimized and the connection loss is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical connector for connecting optical fibers used in an optical signal transmission path of a reflective optical sensor system.

[Conventional technology]

First, an outline of a reflective optical sensor system configured as a distance measuring device will be explained with reference to FIG.

In the figure, 1 is a light emitting element such as a light emitting diode or a semiconductor laser, 2 is a three-terminal bidirectional optical branch/coupler, 3 is an optical connector, 4 is an optical fiber serving as a signal transmission path, and 5 is an optical fiber 4. A probe is attached to the tip, 6 is a mirror facing the probe 5, 7 is a light receiving element, and 8 is a signal processor for distance calculation consisting of a microcomputer and the like.

With this configuration, the output light beam RAYI of the light emitting element 1 is divided into optical branches and
Engagement device 2. Optical connector 3. The light is irradiated from the probe 5 to the mirror 6 via the optical fiber 4.

On the other hand, the return light beam RAY2 reflected by the mirror 6 enters the probe 5, and the optical fiber 4. Optical connector 3° optical branch/
The signal passes through the coupler 2 and is photoelectrically converted by the light receiving element 7. Further, the signal processor 8 calculates the distance 11j between the probe 5 and the mirror 6 and outputs it as a digital signal. In this case, the relationship between the light-receiving energy of the light-receiving element 7 and the measurement path @2 is attenuated in a quadratic curve as the distance Htt becomes longer, as shown in FIG. On the other hand, the light receiving energy received by the light receiving element 7 is the energy reflected by the mirror 6 and the output light RAYI at the optical fiber connection end face of the optical connector 3.
Therefore, the reflected energy due to Fresnel reflection inside the optical connector is unstable, and this Fresnel loss is the sum of the reflected energy due to Fresnel reflection.
This was a major cause of measurement error when measuring 7.

As a countermeasure for this, in the past, as shown in FIGS. 4 and 5, the optical branch/coupler 2 and the optical fiber 4 in FIG.
As an optical connector 3 that connects optical fibers between
In particular, a plug on the optical branch/coupler side is known in which the end face of the plug including the optical fiber is obliquely polished. Furthermore, the fourth
The figure is a partial sectional view of an optical connector, and FIG. 5 is an enlarged sectional view of an optical fiber connection part in the optical connector. In the figure, 9 is the core wire of the optical fiber, and 10 and 11 are plugs that connect to each other. 3 is the plug on the optical branching/coupling device 2 side in FIG. As shown by the polished surface 15, the end faces of the plug including the end face of the optical fiber 9 are obliquely polished to an angle of inclination Φ as shown in the figure, and the connection end face between the plugs 10 and 11 is indicated by the reference numeral 16. Air gaps are present.

By employing the above-mentioned obliquely polished optical connector, the propagation characteristics of the light ray 17 that has propagated from the light emitting element side through the optical splitter/coupler and inside the core 14 of the optical fiber 9 can be expressed by the following formula, as shown in FIG. The relationship is as follows. That is, in the figure, arwa〃π−θa −(%yr−Φ) −・・−−−
−−−−−−−(1) However, θa is θa = 5in
The critical angle of incidence or exit of a ray of light that can propagate in an optical fiber is expressed by -'NA (NA is the neutral aperture of the optical fiber), and Φ is the oblique polishing angle.

Here, if the oblique polishing angle Φ is selected so that Φ〉θa,
Above (in equation 11, θr > O, therefore core 13
The light reflection angle Φr with respect to the core central axis at the obliquely polished end face is Φ
r>θa, and the reflected return light from the end face of the optical connector becomes a radiation mode into the cladding 14 and does not propagate within the optical fiber (this makes it possible to reduce Fresnel reflections).

[Problem that the invention seeks to solve]

By the way, when the above-described obliquely polished optical connector is adopted for optical fiber connection between the optical branch/coupler 2 and the optical fiber 4 of the optical signal transmission line in the reflective optical sensor system shown in FIG. The following problems remain. That is, in general, the nominal NA of an optical fiber is a value when the optical fiber is sufficiently long, for example, IKm, and the NA
When the oblique polishing angle is Φ-15 degrees with an optical fiber of -0.21 degrees, the connection loss of the optical connector increases by about 0.5 dB at most compared to the case where the angle is Φ-0 degrees. Therefore, for long-distance optical fibers, the NA-0
Even an optical connector with an oblique polishing angle of Φ-15 degrees for an optical fiber with an angle of 21 degrees can be practically used to prevent Fresnel reflection.

However, the situation changes when the length of the optical fiber between the optical splitter/coupler 2 and the optical connector 3 is extremely short, as in the optical connector 3 in Fig. 2, and the situation changes as described in Fig. 5. θ8 becomes large.

That is, even if the nominal NA value is 0.21, if the optical fiber has extremely short dimensions, the NA value will actually be much larger, approaching 1. Therefore, in order to make θr>0 in the above equation (1), it is necessary to bring the oblique polishing angle Φ closer to Aπ.

Moreover, if the oblique polishing angle Φ is selected to be large, the center distance j of the core end surface of the optical fiber between the plugs is reduced as shown in FIG.
The void 16, represented by gap, increases.

As a result, a problem arises in which the connection loss of the optical connector increases significantly, making it impossible to put it into practical use.

An object of the present invention is to use an optical connector for connection between an optical branch/coupler on the transmitter/receiver side and an optical fiber of an optical signal transmission line in a reflective optical sensor system as shown in the second aspect. An object of the present invention is to provide an optical connector that can effectively prevent Fresnel reflection at the optical fiber connection end face while suppressing an increase in connection loss of the optical connector even when the length of the optical fiber is extremely short. be.

[Means for solving problems]

In order to solve the above problems, according to the present invention, the end faces of the plugs are obliquely polished, and the connecting gap between the plugs is filled with matching oil having approximately the same refractive index as the core of the optical fiber. shall be.

[Effect]

As mentioned above, when connecting optical connectors, by filling the connection gap between the obliquely polished plug and the mating plug with matching oil, the change in refractive index between the optical fiber connection end faces can be reduced. In addition to the effect of oblique polishing, the Fresnel reflection generated at the end face of the optical fiber can be significantly reduced even if the optical fiber is extremely short. Moreover, by filling the mating oil, there is no gap between the end faces of the plug, and the connection loss of the optical connector can be reduced accordingly.

〔Example〕

FIG. 1 shows a partial cross-sectional view of an optical connector according to an embodiment of the present invention corresponding to FIG. The gap portion is filled with matching oil indicated by reference numeral 18.

This matching oil 18 is a highly transparent oil that has a refractive index approximately equal to the refractive index of the core of the optical fiber 9, and when connecting the optical connector, the matching oil 18 is applied to the tip of the plug. Then, the plugs 10 and 11 are butt-connected via the adapter 12. As a result, the gap between the plugs 10 and 11 is filled with the matching oil 1B. Note that the bevel polishing angle Φ in the plug 10 is Φ<5 from the nominal NA value of the optical fiber.
The angle is selected such that the distance between the core centers of the optical fibers does not increase too much while satisfying the in-' NA. Specifically, for example, if the NA value of the optical fiber is 0.21, it is preferable to set the oblique polishing angle Φ to about 15 culm degrees.

According to the above configuration, the change in the refractive index of the optical fiber connection end between the plugs of the optical connector is caused by the matching oil 18.
In addition to the effect of oblique polishing, the Fresnel reflection generated at the connecting end face of the optical fiber can be significantly reduced compared to the conventional structure. Since no trace remains, connection loss can also be significantly reduced.

Note that if the optical fiber is a step index type optical fiber, the refractive index of the core of the optical fiber and the refractive index of the matching oil can be set to the same value in principle. In addition, in the case of graded-index optical fibers, although there is a distribution in the refractive index of the core, the change is very small.
This is a change of less than two digits after the decimal point. Therefore, it is possible to match the refractive index of the matching oil and the refractive index of the core within the range of at least one decimal place over the entire core region.

〔Effect of the invention〕

As described above, according to the present invention, the connecting gap between the plugs is filled with matching oil having approximately the same refractive index as the core of the optical fiber in a plug whose end face is obliquely polished. Even if is extremely short,
It is possible to provide an optical connector with high practical effects for optical fiber connection in a reflective optical sensor system, such as minimizing Fresnel reflection and connection loss at the connection end surface of the optical connector.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of an optical connector according to an embodiment of the present invention;
Fig. 2 is a schematic diagram of a reflective optical sensor system for distance measurement, which is a subject of the present invention, Fig. 3 is a characteristic diagram of distance measurement in Fig. 2, and Fig. 4 is a conventional obliquely polished optical connector. 5 is a partially enlarged sectional view of the optical fiber in FIG. 4, and FIG. 6 is a partially enlarged sectional view of the optical connector corresponding to FIG. 5 when the oblique polishing angle is increased. In each figure, 1: light emitting element, 2: optical branch/coupler, 3: optical connector,
4: optical fiber, 5 nib lobe, 6: mirror, 7: light receiving element, 8: signal processor, 9: optical fiber core wire, to,
tt nib lug, 12: adapter, 13: core of optical fiber, 14: cladding, 15: obliquely polished surface, 16: gap between connecting surfaces, 17: propagation in core Fig. 2 Fig. 4 Fig. 5

Claims (1)

[Claims] This is an optical connector for connecting optical fibers used in the optical signal transmission path of reflective optical sensor systems.The end face of the plug is obliquely polished, and the connection gap between the plugs has a refractive index that is approximately the same as the core of the optical fiber. An optical connector for a reflective optical sensor system characterized by being filled with matching oil.