JPS6111711A - Optical fiber coupler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an improved apparatus for coupling a light source, such as a helium neon laser, to an optical fiber.

Such coupling causes laser light to be transmitted along the optical fiber.

Prior art helium neon lasers produce laser light that is visible, red, and has low beam divergence, with a typical beam diameter of 0.8M. It is often desirable to couple the laser light with a fiber optic device to transmit the laser light to a remote location from the laser. This may occur when there is insufficient space to mount the laser and associated power and control equipment.

Optical fibers consist of a glass core concentric to the axis of the fiber surrounded by glass cruts. The glass core has a slightly higher refractive index than the surrounding glass crud. Light incident on one end of an optical fiber is guided to the other end with little loss of intensity due to total internal reflection at the boundary between the high refractive index of the core and the lower refractive index of the cladding. A typical optical fiber has a diameter of approximately 0.125 m5. The core is typically 0.
It is in the key of 05. The fiber is housed within a flexible jacket for ease of handling and protection of the fiber. Such fiber optic cables have a diameter of approximately 3#III.

To facilitate installation and maintenance of the cable, both ends are provided with connectors that are inserted into mating receptacles of cooperating equipment. Connectors and receptacles allow the ends of optical fibers to cooperate with portions of optical systems that provide or receive light transmitted by the optical fibers at each end of the cable. the axial position of the optical fiber relative to the central part of the optical system;
Or the interval is also determined.

To achieve efficient coupling of a laser or other light beam into an optical fiber, the light must enter a narrow acceptance cone concentric with the axis of the fiber in the fiber core. The angle of this cone is specified by the numerical aperture of the fiber. Since the core of an optical fiber is much smaller than the diameter of the incident laser beam,
The beam diameter must be reduced by passing through a positive focal length lens before being added to the optical fiber. After passing through the lens, the beam reduces in diameter and forms an optical organ with its apex at the focal point of the lens. The beam then expands into a cone beyond the focal length. The result is a stiffened hourglass-shaped beam with a small diameter beam waist near the focal point.

By appropriately selecting the lens focal length, the beam waist can be made smaller than the diameter of the optical fiber, allowing almost all of the light to enter the optical fiber core. To do this, the rays exiting the lens enter the acceptance cone of the fiber, and the waist of the beam
The lens focus must be at the end of the fiber core.

Problems that the invention seeks to solve Considering the small dimensions, these criteria pose difficult problems in mechanical alignment. It will be understood that Problems are particularly present when fiber optic cables have plug-in connectors at the ends that allow the fiber optic cable to be removed and reinserted into receptacles in other parts of the optical system, or when connecting one cable to another. This becomes especially difficult when replacing. Plug-in connectors do not insert into the receptacle exactly the same way each time, and the connector and receptacle wear out with repeated insertions. Replacing one cable with another will change the positioning provided by the connector due to manufacturing tolerances.

For these reasons, alignment systems are often provided in conjunction with cable end connectors and receptacles to obtain the desired relative positional relationship between the light beam and the optical fiber. Existing alignment systems generally use a lens that has a fixed position relative to the path of the light beam. One end of the optical fiber is moved perpendicular to the optical transmission line by a complex sliding means to obtain the desired alignment. In other methods, the optical fiber is moved in an arc by a ball and socket joint to bring the end of the optical fiber into alignment with the light beam.

However, both methods are mechanically complex. Moreover, they lack durability, stability, and high adjustment resolution. For these and other reasons, they do not completely solve the problem of optimally coupling a light beam, such as a laser beam, into an optical fiber.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide improved means for aligning optical fibers with light in order to enhance the coupling between the fiber and the light beam.

Means for Solving the Problems In summary, the present invention uses a transparent plate that can refract laser light. A transparent plate is disposed in the optical beam path in front of the exposed end of the fiber optic cable. The plate may be made of glass. Means are provided for tilting the plate. As a result of this tilting, the light beam is displaced from its original path due to refraction that occurs within the plate. This displacement is used to center the laser beam on the exposed end of the cable. The ramp plate may be disposed between the optical fiber end and a lens having a fixed focal length that focuses the laser beam into the acceptance cone of the fiber. The lens may be adjusted so that the focal point of the lens is on the end of the optical fiber.

Example The present invention will be described in detail below with reference to the drawings.

In FIG. 1, reference numeral 10 indicates a light beam generated by a helium neon laser or the like (not shown). code 1
2 shows a fiber optic cable containing an optical fiber 13 within an envelope 15. To couple the laser beam 10 into an optical fiber 13, the beam passes through a lens 14 with a positive focal length, a convergence angle smaller than the receiving forceps of the optical fiber, and a constriction of small diameter at the lens focal point. Becomes hourglass shaped. The lens 14 or the optical fiber 13 connects the laser beam 10
is located on the axis of the optical fiber 1, so that the focus of the lens is on the axis of the optical fiber 1
It is on the edge of 3. The optical fiber 12 is arranged in a holder 16 that can be moved perpendicular to the axis of the laser beam 10, thereby centering the beam waist on the axis of the optical fiber 13. Retainer 16 is mounted within frame 18 and spring 2
It is biased by 1 at 0 and is moved by the screw 22. It is convenient to provide similar moving means to move the optical fiber 12 above and below the plane of the paper. In this way the laser beam is coupled to the fiber optic cable.

FIG. 2 shows another device for obtaining such a bond. In the present device, frame 18 has a receptacle 24 for receiving a plug-in connector 26 on the end of fiber optic cable 12. A threaded collar 28 connects the connector 26 to the receptacle 24.
hold within. The lens 14A is attached to a plate 30 that can be rotated in the direction of the arrow, and positions the center of the laser beam 10 on the axis of the optical fiber 13. Screws 32 and 34, one of which may be spring loaded, provide the desired rotational movement and position the optical fiber 13 at the focal point of the lens 14.

As mentioned above, these techniques are mechanically complex and lack durability, stability, and high adjustment resolution.

FIG. 3 shows an improved device according to the invention.

The device is housed within body 35. A plate 36 made of a transparent material is disposed in the path of the laser beam 10 between the lens 14B and the end of the optical fiber 13.

For convenience of explanation, the plate 36 will be described here as being made of transparent glass. The plate 36 may have a disc-like shape and will be referred to as a disc hereinafter. The glass disk 36 has parallel surfaces through which laser light enters and exits. The frame 18B is provided with means by which the glass disk 36 can be tilted and shifted from a position perpendicular to the axis of the beam 10, as shown in FIG. 3, to some other angle other than 90° to the axis of the beam. ing.

For this purpose, the disk 36 is attached to the plate 38 by means of glue or the like. Plate 38 has an aperture 40 along the axis of laser beam 10. It is generally hemispherical and has a bulge 42 that abuts the end of receptacle 24 and allows plate 38 and glass disk 36 to tilt. Plate 38 is gimbaled in any suitable manner within body 18B for this purpose. Plate 38 is biased by spring 44 and tilted in the plane of the paper of FIG. 3 by screw 46. Advantageously, the second screw 46 is provided, as shown in FIG. 6, so that the plate 38 can be tilted in a plane perpendicular to the plane of the paper of FIG.

In operation, the converging sawtooth laser beam 10 exiting the lens 14B passes through a glass disk 36 disposed between the lens 14B and the optical fiber end 13. When the laser beam returns from the air through the glass disk 36 and back to the air, the portion of the conical beam that is incident on the disk 36 at an angle other than 90° undergoes refraction.

Refraction is the angular displacement caused by the different laser beam velocities in the glass and in the air on either side.

Assume that disk 36 is oriented perpendicular to the axis of laser beam 10, as shown in FIG. Under this condition the laser beam is not displaced off-axis.

However, the focal point of lens 14B and the beam waist of the focused laser beam 10 are moved farther than lens 14B as a result of refraction that occurs within glass disk 36. By positioning lens 14B with a threaded lens holder 48 within body 18B, the focus of lens 14B and the beam waist of laser beam 10 are returned to the end of optical fiber 13.

By tilting the glass disk 36 from the vertical position shown in FIG. 3, the laser beam exiting the disk can be displaced with respect to the laser beam incident on the disk due to refraction occurring within the glass disk 36. It is possible. Using this displacement, the beam waist of the focused laser beam 10 can be centered on the axis of the optical fiber 13.

FIG. 4 schematically shows the displacement of the incident and emitted laser beams caused by the inclination of the glass disk 36.

The amount of displacement obtained is quantitatively shown in FIG. For simplicity, only the axis of the laser beam 10 is shown in FIG.

The amount of displacement is expressed by the following equation.

where d - the output laser beam 10 for the incident laser beam;
The displacement of the axis of ?

■ - Thickness of the glass disk 36.

φ - the angle between the axis of the incident laser beam 10 in air and the normal to the plane of the glass disk 36, commonly referred to as the angle of incidence.

φ' - the angle between the axis of the laser beam 10 in the glass disk 36 and the normal to the plane of the glass disk 36, commonly referred to as the angle of refraction.

N - refractive index of air.

N' - refractive index of glass disk 36;

As shown in FIGS. 4 and 5, by tilting the glass disk 36, the beam waist of the laser beam 10 can be moved so that it is applied to the axis of the optical fiber 13. From the above equation, it can be seen that the displacement ff1rdJ is directly proportional to the thickness ITJ of the glass disk 36 (1-).

By reducing the thickness of the glass disk 36, the glass disk 3
6 can be made small, and as a result, according to the coupling device of the present invention, very fine displacement adjustment and high resolution can be obtained. That is, the screw 46 is provided with a large number of rifts in order to obtain minute displacement of the laser beam 10. In this way, the laser beam position can be adjusted very precisely.

After positioning the axis of the laser beam 10 on the axis of the optical fiber 13 by tilting the glass disk 36, the lens 14
The position of the focal point relative to the end of the optical fiber 13 along the axis of the laser beam 10 of B is adjusted by the threaded barrel 48, and the focal point and beam waist are placed at the exposed end of the optical fiber 13 in the cable 12. position. A highly efficient coupling of the laser beam 10 to the optical fiber 13 is thus obtained.

Although the coupling device of the present invention has been described with respect to applying a laser beam 10 to an optical fiber 13 in a cable 12,
The device can also be used when a laser beam emerges from an optical fiber 13 and is applied to a lens 14. Additionally, although the light source has been described as being a laser, other light sources such as arc lamps may also be used in the present invention.

Glass disk 36 may be used without lens 14B if laser beam 10 is suitably dimensioned to be applied to the exposed end of optical fiber 13 by other means.

The glass disk 36 is preferably made of optical glass and has a polished surface for transmitting and receiving light. Although disk 36 is described above as being made of glass, it may be made of other suitable materials, such as quartz or plastic such as acrylic.

[Brief explanation of drawings]

FIG. 1 shows an example of a device for coupling a light beam to an optical fiber, FIG. 2 shows another example of a device for coupling a light beam to an optical fiber, and FIG. 3 shows a light beam according to the present invention. FIG. 4 is a diagram illustrating the detailed operation of the inclined transparent plate portion of the improved coupling device according to the present invention, and FIG. 5 is a diagram showing the improved coupling device according to the present invention. 6 is a cross-sectional view taken along line 6--6 of FIG. 3 showing the means for tilting the transparent plate section. 10... Light beam, 12... Optical fiber cable,
13...Optical fiber, :14.14B...Lens,
15...Encapsulation, 16...Cage, 18.188...
・Frame, 20°44...Spring, 22.32.34.46
...screw, 24...receptacle, 26...connector, 28...tsuba, 30.38...plate, 35...
Main body, 36... Glass disc, 40... Opening, 42.
...Bulge, 48...Lens holder.

Claims (8)

[Claims] (1) A transparent means capable of refracting the light beam, which is provided outside the optical fiber along the path of the light beam through which the light beam passes and is separated from the end of the optical fiber; tilting means for tilting the light beam from a position perpendicular to the path of the optical fiber to change the position of the light beam with respect to the end of the optical fiber as a result of refraction that occurs when the light beam passes through the transparent means; A coupling device that couples the ends of optical fibers. (2) The device according to claim 1, wherein the transparent means is made of glass. (3) the transparent means has a thickness between parallel light entrance and exit surfaces that controls the amount of displacement of the light beam for a given amount of tilt, and the thickness of the transparent means is desired for the coupling device; The device according to claim 1, which is selected depending on the resolution. (4) A claim including a lens spaced apart from the transparent means opposite to facing the optical fiber, the lens being disposed along the path of the light beam and applying the light beam to the transparent means. The coupling device according to item 1. (5) The coupling device according to claim 4, wherein the lens further has a positive focal length. (6) The coupling device according to claim 4, further comprising means for adjusting the position of the lens along the path of the light beam. (7) A coupling device that couples a laser beam to an optical fiber having a fixed acceptance cone by centering the laser beam that converges at an angle smaller than the acceptance cone at the end of the fiber, the path of the laser beam a lens having a positive focal length disposed along the optical fiber and spaced from the end of the optical fiber to focus the laser beam at an angle less than the acceptance cone of the optical fiber and with a focal point at the end of the optical fiber; , a transparent means capable of refracting the laser beam disposed along the path of the laser beam intermediate the lens and the end of the optical fiber; and the transparent means is tilted from a position perpendicular to the path of the laser beam; A coupling device comprising tilting means for centering the laser beam on the end of the optical fiber by changing the position of the laser beam as a result of refraction occurring within the transparent means. (8) The coupling device according to claim 7, further comprising adjusting means for adjusting the position of the lens along the laser beam path and adjusting the position of the focal point of the lens.