JPS5934507A - Optical fiber terminal which prevents interference of returned light - Google Patents

Abstract

PURPOSE:To prevent the interference of the returned reflected light from a lens face, by inclining the end face of the lens to be connected to an optical fiber and the end face on the opposite side with respect to an optical axis, joining a transparent body having no refractive index distribution on the end face on the side opposite from the end face of the lens to be connected to the optical fiber in one body thereto, and inclining the surface of the transparent body with respect to the optical axis of the lens. CONSTITUTION:The end face 11A of a distributed index lens 11 on the side to be connected to an optical fiber 10 is the plane perpendicular to the optical axis of a lens, while the end face 11B on the opposite side is the plane inclined by a specified angle theta with respect to the face orthogonal with the optical axis of the lens. The connection is preferably accomplished by deviating the axial line of the fiber by the specified distance W1 from the optical axis of the lens toward the side face where the lens length is longest according to the angle theta of inclination of the lens end face in order to parallel the exit rays. The relation between the deviation W1 of the fiber and the angle theta of inclination of the lens face is expressed by W1=(No-1).theta/Nosq. rt. A. In the equation, No is the refractive index of the lens of the central axis thereof and A is the distribution constant in the above-described equation 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for connecting a gradient index lens to one end of an optical fiber to convert the light emitted from the fiber into parallel light, or to focus the parallel light and make it enter the fiber. The present invention relates to an optical fiber terminal which prevents interference of return reflected light.

When relaying the light beam transmitted through the optical fiber to another optical fiber or various optical signal processing devices, or when making the light beam from a light source enter the optical fiber, it is generally necessary to An optical fiber terminal structure is adopted.

/ In the figure, the optical fiber 9.2 is a gradient index lens, and the gradient index lens 2 has a refractive index of No on the central axis and a refractive index of N at a distance r in the radial direction from the central axis. J), but N (r) = NO(/-//
, zAr2) ・−=−=(1) However, A is made of a transparent cylindrical body such as glass or brass tinta, which has a distribution in which the refractive index decreases parabolically toward the periphery as expressed by a positive constant; Both end faces are parallel planes perpendicular to the central axis.

The length Z of the lens is an odd number multiple of the meandering period of the light ray that meanders through the lens, that is, A is the constant 2m in equation (1) above, which is a positive integer. As, Z= (2711+/)π/haryoshi.

At one end of the optical fiber as described above, the light ray 3 diffused and emitted from the optical fiber travels inside the gradient index lens 2 while drawing a sine curve, and then (3) becomes a parallel light ray and exits from the lens end surface 2A. .

Terminal lens like this! The parallel light rays emitted from the optical fiber are incident on other optical transmission means or optical signal processing means. For example, in an optical fiber connector, the light enters another gradient index lens placed opposite the lens 2, and then is focused while traveling through the lens and enters the other optical fiber S.

An optical fiber terminal configured by connecting a gradient index lens to the tip of the optical fiber can convert the diffused light rays emitted from the optical fiber into parallel rays, or converge the light incident in parallel rays to form the optical fiber. Although it has the advantage of being able to efficiently transmit data within the network, it also has the following problems.

In other words, when a light ray that has exited the optical fiber/glass and traveled through the lens exits from the lens end face 2A, a portion of the light ray is reflected by the lens end face 2A, and this reflected light 6 is the same as the light ray 3 that exits from the optical fiber. Since both light beams return by following the meridians, they interfere with each other, causing signal noise and the like.

Such return reflected light rays are not only caused by the end face of the lens on the exit side (ge), but also if there is another opposing lens l like the aforementioned optical fiber connector, the return reflected light ray 7 at the tip face 9A of this lens is also a problem. becomes.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a novel optical fiber terminal that eliminates the adverse effects of return reflected light at the end face of a lens.

The above purpose is to place the tip of an optical fiber closely or close to one end surface of a gradient index lens made of a transparent material with a distribution in which the refractive index is maximum on the central axis and decreases parabolically toward the periphery. This is achieved by tilting the end surface of the lens opposite to the optical fiber connection end surface with respect to the optical axis at one end of the optical fiber.

In addition, in the second invention of the present application, the tip of the optical fiber is closely or closely connected to one end surface of a gradient index lens made of a transparent material with a distribution in which the refractive index is maximum on the central axis and decreases parabolically toward the periphery. At one terminal of the optical fibers arranged in close proximity, a transparent body having no refractive index distribution is integrally bonded to the end surface of the lens opposite to the optical fiber connection end surface, and the surface of the transparent body is connected to the optical axis of the lens. tilt it against the

According to the above configuration, when the light rays emitted from the optical fiber exit from the inclined end face of the lens or the inclined surface of the transparent body bonded to the vertical end face of the lens, the return light rays reflected are the "outgoing" light rays inside the lens. Since the beam returns along a different route, there is no mutual interference with the outbound beam.

Embodiments of the present invention shown in the drawings will be described below.

Figure 2 is a sectional view showing an example of an optical fiber terminal according to the present invention, where 10 is an optical fiber and // is a gradient index lens.

The optical fiber 10 connection side end surface of the gradient index lens //A is a plane perpendicular to the lens optical axis //2, but the opposite end surface //B is constant with respect to the plane perpendicular to the lens optical axis. Let us assume that the plane is tilted by an angle θ.

In a gradient index lens with one end surface being inclined, the lens length is different on both edge sides of the inclined end surface, so the lens length Z at the optical axis is the pitch length of the part. However, if the fiber axis is aligned with the optical axis of the lens and connected as in the conventional method, the emitted light beam will not be perfectly parallel light. □For this reason, an optical fiber -10
When connecting the fibers, it is desirable to deviate the fiber axis by a certain distance Wl from the lens optical axis toward the side surface where the lens length is the longest, depending on the lens end face inclination angle θ.

The relationship between the fiber polarization position W1 and the lens surface inclination angle θ in order to treat the diffused emitted light from the optical fiber as a point light source and make the emitted light from the lens completely parallel light is as follows: Wl = (No-/)・θ/ NOv'I...
...It can be expressed as (2).

In equation (2), No is the refractive index on the central axis of the lens.

A is a distribution constant in the above equation (1).

Regarding the lens surface inclination angle θ, its minimum limit is the third
As shown in the figure, it is necessary to choose a position so that the return reflected light beam /3 from the inclined end surface //B of the lens reaches at least a position away from the cladding portion 10B of the optical fiber 10 within the plane that includes the tip surface of the optical fiber 10. .

− If the conditions described in
The sum of the diameter of the core IOA and the thickness of the cladding layer 10B is R
As, λθ/NO1/i≧R (3).

To give a concrete numerical example, the core diameter of the optical fiber 10!
;Ottmz outer diameter is 72jμm, refractive index No-/, A, distribution constant Vl on the central axis of the gradient index lens //
The relationship between the lens surface inclination angle θ and the optical fiber deviation NW] and the deviation amount W2 of the return reflected light spot from the optical axis when r −0, 3, and 2 mm −2 is shown in the Oda diagram graph.

In Fig. 1, the horizontal axis shows the lens surface inclination angle θ, the vertical axis shows the deviation i W l l W2 in μm, and the straight line A shows the fiber deviation to make the emitted ray from the lens a perfectly parallel ray. The relationship between the amount Wl and θ is shown, and the straight line B shows the spot eccentricity W2 of the return reflected light with respect to each fiber deviation amount Wl described above.

In the graph of FIG. 1, the region ( By selecting the surface inclination angle θ corresponding to the shaded area), it is possible to avoid the return reflected light /3 from entering the optical fiber again.

In the case of the above numerical example, R = 75 μm, and from the same graph, the lowest limit of θ is approximately 22 milliradians (approximately 7.3 μm).
°).

FIG. 3 shows an optical fiber connector constructed using a pair of optical fiber terminals according to the present invention.

In this example, a pair of gradient index lens axes 20.2/ whose tip surfaces are inclined surfaces are arranged facing each other with their 4# lines aligned. ．． 2/ respectively at the rear ends of the optical fibers 2.2. ．． 23 are connected with their axes deviated from the lens optical axis toward the side where the lens length is the longest.

As a result, one optical fiber, 22 (
9) Of the light rays transmitted and emitted from the fiber 2.2, the return light reflected by the exit end face of the lens 20 returns to the position away from the fiber 2.2 as described above, and returns to the position away from the fiber 2.
Of the rays that come out from 0 and enter the opposing lens 2/, the ray 2j that is reflected at the tip surface also follows the same path as in the conventional case, and instead of being incident on the original fiber 2.2, it returns to the lens 2/. The light deviates from the inclined surface 2/B and is emitted in another direction.

Even if the reflected light were to enter the original lens 2θ again, it would be focused at a position away from the optical fiber 2.2 as described above, so it would not adversely affect the light emitted from the optical fiber.

In the above embodiments, the end faces of the gradient index lens were oblique sections, but as shown in Figure 6, both ends were made into parallel planes perpendicular to the optical axis.The gradient index lens 30 with a pitch length of 1 minute By bonding a non-parallel transparent plate 3/ having a wedge-shaped cross section and having a uniform refractive index throughout and similar to that of the lens 30 to one end surface 30A of the lens 30, the end surface J/A is aligned with the optical axis of the lens. A similar effect (10) can be obtained by configuring the surface to be inclined relative to 3.2.

In the case of the structure of this example, there is no need to deviate the axis of the connecting optical fiber 33 with respect to the lens optical axis, and it is sufficient to align both axes.

In the example of the off-line diagram, various methods can be used to connect the optical fiber 10 to the lens by shifting it by a predetermined amount Wl from the optical axis of the lens, but the following method is very easy and can be done with high precision. positioning can be performed.

That is, as shown in the off view, the predetermined lens holder 3I
A gradient index lens // having an inclined end surface is fixed in I, and a parallel light beam 3S is made incident from this inclined end surface side, and a monitoring fiber 31 having the same specifications as the mounted fiber and this A fiber sleeve 37 is placed through which the tip of the fiber is passed, and the light emitted from the other end of the monitoring fiber 3 is received by the photodetector 3g, and the amount of received light is measured by the measuring device 39. The fiber sleeve 37 is moved in a direction perpendicular to the axis, and the fiber sleeve 37 and the lens boulder 31I are adhesively fixed at a position where the amount of light received by the detector 3g is maximum.

This allows the hole 41 of the fiber sleeve 37 to be removed during actual use.
! By passing the fiber tip through O and adhesively fixing the fiber and the fiber sleeve, this fiber will be connected at a position a predetermined deviation W] away from the lens optical axis in the above-described predetermined direction.

FIGS. 1 and 9 show specific structural examples of an optical fiber terminal according to the present invention.

For those with tooth profile, the tip end is located inside the lens holder 3g//B
A gradient index lens // having a sloped surface is fixed, and a protrusion II/ with a small diameter that has a margin larger than the inner diameter of this lens holder 3'l, and a protrusion part II/ with a diameter larger than the inner diameter of the remaining part From main body part tI2 to null fiber sleeve 3
7 into the lens holder 311, and remove the sleeve 37.
Pass the bare optical fiber wire 10 through the pore lO provided in the protrusion Il/ of the main body part, insert the tip of the covering material IlI covering the bare wire 10 into the large diameter hole 13 provided in the main body part, and insert the adhesive IIS. Fix it with. Then, a resin adhesive llj is filled between the inner wall of the lens holder and the outer periphery of the fiber sleeve protrusion through an adhesive inlet Ilb provided on the side wall (/, 2) of the lens holder 31 to permanently fix the two.

Note that Il, 7 is an air vent hole during resin injection.

In the example shown in FIG. 9, a fiber sleeve 37 is formed of metal, resin, etc. on the outside of an inner tube 50 made of a glass tube or the like having a hole approximately equal to the diameter of the bare fiber wire 10. It is also constructed by joining together large auxiliary members S/.

On the side wall of the lens holder 3'l, in addition to the adhesive inlet 1B and the air vent hole 7, there is a matching liquid injector approximately at the position of the lens end surface in order to interpose the refractive index matching liquid between the lens end surface and one end surface of the fiber. There is a separate entrance.

[Brief explanation of drawings]

FIG. 7 is a vertical cross-sectional view showing a conventional connector using one end of an optical fiber, FIG. 2 is a vertical cross-sectional view showing an embodiment of the present invention, and FIG. Fig. 1 is a vertical cross-sectional view showing the behavior, and Fig. 1 is a graph showing the relationship between the inclination angle θ of the lens surface in the terminal of the present invention, the eccentricity of the connecting fiber, and the eccentricity of the return reflected light beam. A vertical cross-sectional view showing an example of a connector using the terminal of the present invention, a vertical cross-sectional view showing another embodiment of the present invention, and a figure 7 showing a fiber sleeve for supporting the tip of the connecting fiber. FIG. 3 is a vertical cross-sectional view showing an example of a method for aligning the gradient index lens according to the invention. FIG. 1 is a vertical sectional view showing a specific structural example of one optical fiber terminal of the present invention, and FIG. 9 is a vertical sectional view showing another specific structural example of one optical fiber terminal of the present invention.

Claims (1)

[Claims] 1) The tip of an optical fiber is closely or closely connected to one end surface of a gradient index lens made of a transparent material with a distribution in which the refractive index is maximum on the central axis and decreases parabolically toward the periphery. An optical fiber terminal that prevents return light interference, characterized in that, in the optical fiber terminals arranged close to each other, the end surface of the lens on the opposite side from the optical fiber connection end surface is inclined with respect to the optical axis. 2. An optical fiber terminal according to claim 1, characterized in that the axis of the optical fiber is deviated from the optical axis of the lens to a side band where the lens length is the longest. 3) In the O ring claimed in the patent, the refractive index N (r) at a distance r from the central axis of the gradient index lens is N (
r) -No (i-/, /, 2Ar2), the angle of inclination of the inclined end face from the plane perpendicular to the optical axis is θ, and the amount of deviation of the connecting optical fiber from the lens optical axis is (No -/)・θ/
An optical fiber terminal characterized by being Nov'l. 4) Light in which the tip of an optical fiber is placed closely or close to one end surface of a gradient index lens made of a transparent material with a distribution in which the refractive index is maximum on the central axis and decreases parabolically toward the periphery. At one end of the fiber, a transparent body having no refractive index distribution is integrally bonded to the end face of the lens opposite to the optical fiber connection end face, and the surface of the transparent body is tilted with respect to the optical axis of the lens. An optical fiber terminal that prevents return light interference.