JPH03156406A - Multifiber optical rotary joint - Google Patents

Abstract

PURPOSE:To make it possible to process various application wavelength components only by one optical system and to reduce the production cost of a multifiber optical rotary joint by using two triangular prisms and changing the interval between the two triangular prisms. CONSTITUTION:A pair of triangular prisms 5, 6 are arranged oppositely to respective convergent lens groups so that one sides 5a, 6a of faces intersecting at right angles are vertically opposed to the optical path direction of the convergent lenses. A reflector 7 for reflecting the refracted optical path of one prism and making the reflected light incident or projecting the light upon/from the inclined faces 5b, 6b of the other triangular prism is arranged between the prisms 5, 6. Thereby, optical paths connecting plural corresponding lenses out of plural convergent lenses arranged on the rotor side and the fixed body side can be formed by the prisms 5, 6. Thereby, it is unnecessary to previously prepare many trapezoidal prisms having respectively different lengths considering a change in the wavelength to be used, so that the production cost can be remarkably reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for appropriately coupling optical signal transmission lines between a plurality of optical fibers installed on a rotating body and a fixed body with minimum transmission loss. It concerns a multi-core optical joint that can be used.

[Prior Art] The development of information transmission systems using optical fibers has been remarkable, and it is now possible to transmit information not only between stationary objects, but also between devices that have a fixed object on one side and a rotating object on the other, such as stacker cranes and cable reels. Control using optical signals has come to be required, and it has become necessary to suitably connect optical fibers for transmitting optical signals disposed on the rotating body side and the fixed body side, respectively.

If the optical fiber used is a single core, such a connection can be made by simply butting them together with a small gap, but
Transmitting a large amount of information through a single optical fiber requires multiplexing of optical signals, which inevitably makes the equipment complex and expensive.

To solve this problem, an accumulator system in which the optical fiber is wound into a coil as it rotates has been put into practical use, but it has the disadvantage of requiring individual design for each piece of equipment and limiting the number of rotations and rotation speed.

Therefore, the applicant previously proposed a multi-core optical rotary joint whose structure and principle are shown in FIGS. 6-8.

(Utility Model Application No. 6l-6818) In this method, a trapezoidal prism C as shown in FIG. 8 is arranged between the respective terminals of a plurality of rotating body side optical fibers and a plurality of corresponding fixed body side optical fibers, The trapezoidal prism C is moved at the angular velocity ωl of the rotating body
The optical fibers are rotated in the same direction with an angular velocity ω2 of 1/2 of A plurality of installed optical fibers are optically coupled to each other.

That is, between the angular velocity ωl of the rotating body in FIG. 8, the angular velocity ω2 of the trapezoidal prism, and the angular velocity ω3 of the output image reflected by the trapezoidal prism C, the output image is formed by (
1) The relationship of equation holds true.

ω3=-ω1+2ω2...(1) Now, if the angular velocity ω2 of the trapezoidal prism C is 1/2 of ωl, (1)
According to the formula, ω3=0, and the output image always remains stationary, so it is sufficient to place the end of the optical fiber on the fixed body side here.

FIG. 7 is an explanatory diagram illustrating how the rotating body maintains a static image as described above. This clearly shows how the emitted image does not rotate at all and remains stationary.

FIG. 6 shows how optical fibers a and b on the stationary side (in practice, up to eight optical fibers can be applied) and the optical fiber ab- on the rotating body are optically connected by applying the principle explained above. FIG. 2 is an explanatory diagram showing the basic configuration of the previously proposed multi-core optical rotary joint that can be combined.

The optical signals of the optical fibers a and b on the stationary body side are connected to the optical connector 1,
The light enters the trapezoidal prism C as parallel light through the converging lenses d and e held in the receptacles h and l through the light beam m,
In the figure, the optical signals that are refracted and reflected and emitted as shown by the dashed and dotted lines are incident on the focusing lenses f and g held in the receptacles j and k, and the respective optical signals are made to correspond to each other via the optical connectors o+p. This is to be coupled to the optical fiber row b- on the rotating body side.

In this case, the trapezoidal prism C has an angular velocity of 1 degree 1/2 of the rotating body in the same direction, which is shifted by arranging the gears A, B, C, and D with respect to the rotation of the rotating body shown by the arrow. Configured to be rotated.

With this configuration, based on the principle explained earlier,
In this optical rotary joint, when the rotating body rotates,
The trapezoidal prism C rotates in the same direction at half the angular velocity and acts to optically cancel the rotation of the rotating body. The connection relationship between the optical fiber and the output optical fiber is always guaranteed.

[Problem to be solved by the invention MMJ Now, in a trapezoidal prism C as shown in FIG. When the refractive index of is set to n, the relationship shown in equation (2) holds true.

L2 = H2(1+tan (θ2 43!n-'
Sin θz/n)) (2) BK-7 is used as the prism material, and the wavelength is 0.83μ.
When light of m passes through, the refractive index n = 1.5102, and if the prism deflection angle θ2 = 45°, then from the above equation (2), L2 = 4 between the prism length L2 and the prism diameter H2. , 25 XH2 arises.

Therefore, if the prism diameter H2 is increased to couple a large number of optical fibers, the prism length 2 will inevitably become longer.

Naturally, as the prism length becomes longer, the coupling loss between the optical fibers also increases.

FIG. 5 is a diagram showing the relationship between the length of the converging lens interval L (which is closely related to the prism length L2) shown in the figure and the coupling loss between optical fibers.

The standard outer diameter of the optical connector shown in FIG. 6 is 1011. For example, in a 4-core optical rotary joint, H2 = 2011111, and L2 = 8.
That means 5 cities.

As can be seen from Figure 5, the coupling loss between optical fibers tends to increase when the distance between the focusing lenses exceeds 50 cm, and at L = 85 m, it reaches 3.5 dB, which is not desirable. .

On the other hand, as can be seen from equation (2) above, the trapezoidal prism length L2 also depends on the prism deflection angle θ2 and the refractive index n of the prism material.

FIG. 4 shows the relationship between wavelength and refractive index when BK-7 is used as the prism material.

In optical communications, various wavelengths from 0.6 to 1.55 μm are used, and as shown in Figure 4, if there is a large difference in refractive index depending on the wavelength, the length will differ depending on the wavelength used. There is a problem in that it is necessary to prepare many types of trapezoidal prisms, which increases the cost accordingly.

An object of the present invention is to solve the problems of the prior art as described above, to make the distance between the focusing lenses much shorter than in the past, and thereby to significantly reduce the coupling loss of the optical fiber. By using a triangular prism instead of a trapezoidal prism, the spacing between the triangular prisms can be freely moved and changed, making it possible to respond to various applicable wavelengths with one type of optical system. The present invention aims to provide a novel multi-core optical rotary joint that enables significant cost reduction.

[Means for Solving the Problems] The present invention provides a multi-core optical rotary joint in which an optical system is provided between a rotary body and a fixed body so that the optical system itself can freely rotate coaxially with the rotary body. The optical system faces a plurality of converging lenses installed to input and output optical signals from the rotating body side and the fixed body side, respectively, and one side of the orthogonal surface thereof is aligned with respect to the optical path direction of the converging lenses. The composite includes a pair of triangular prisms arranged vertically opposite each other, and a reflector that reflects the optical path refracted by one triangular prism and makes it incident on the other triangular prism, and is installed on the rotating body side and the fixed body side, respectively. These optical systems are constructed so as to be able to combine the optical paths between the corresponding lenses of the focusing lenses, and these optical systems are constructed so that they can follow and rotate in the same direction as the rotating body at 1/2 the angular velocity of the rotating body by means of a variable speed gear i mechanism. The distance between the pair of triangular prisms can be changed according to the wavelength of the transmitted optical signal.

[Function] In the present invention, by using a pair of triangular prisms and a reflector, it is possible to exhibit the same effect as when using the previously proposed trapezoidal prism, thereby significantly shortening the distance between the focusing lenses. This not only makes it possible to significantly reduce coupling loss, but by configuring the distance between a pair of triangular prisms so that they can be moved and changed, it is no longer possible to prepare a variety of prisms with different lengths that suit the wavelength, unlike in the past. Instead, it makes it possible to deal with many wavelengths with one optical system, and can also derive a significant cost reduction effect.

[Example] The present invention will be described below with reference to Examples.

FIG. 1 is a sectional view showing a specific configuration of a multi-core optical rotary joint according to the present invention.

In the figure, the top is a stationary fixed body, λ is a rotating body, and the bottom is an optical system holder.

The rotating body λ is configured to be able to rotate independently on a stationary body and by bearings 18 and 18, and furthermore, the optical system holding weight is arranged coaxially with the rotating body l and is supported by bearings 18 and 19.
It is configured to be freely rotatable separately from the rotating body.

4 is an optical fiber on the stationary body side shown as a representative example,
4- is an optical fiber on the side of the rotating body shown as a typical example.In addition to the single optical fiber shown in the figure, by adopting a pigtail method (description is omitted), eight optical fibers can be combined into one multi-purpose fiber. They can be connected to each other by a central optical rotary joint.

In the figure, 8a, 8b, 9a, and 9b are converging lenses for inputting and outputting light as parallel light in the optical path, and receptacles 16a on the upper side of the stationary body and on the side of the rotating body λ, respectively.
, 16b and 17a.

It is held and fixed to 17b as shown in the figure.

Further, 12a and 14a are optical fibers 4 and 4, respectively.
This is a ferrule for aligning the receptacles 16a and 17a with the plugs 13a and 15a to form an optical connector.

In the case of the previously proposed example described above, the converging lens 8 on the stationary body side
A trapezoidal prism C is arranged between a and 8b and the rotating body side converging lens 9a9b to perform refraction and reflection for input/output, but in the present invention, as shown in the figure, a trapezoidal prism A pair of triangular prisms 5 and 6 facing each other and disposed so that one side 5a and 6a of the orthogonal surfaces thereof are perpendicularly opposed to each other with respect to the optical path direction of the focusing lens.
are arranged, and these pair of triangular prisms 5 and 6
In between is an inclined surface 5b of the other triangular prism that reflects the optical path refracted by one prism.

It has a reflector 7 that causes the light to enter and exit the light beam 6b, and is configured to couple optical paths between corresponding lenses of the plurality of converging lenses installed on the rotating body side and the fixed body side, respectively.

20, 21, 22, and 23 are speed change gears for respectively changing the speed of the rotation of the rotating body 1 and giving the optical system holder 3 172 rotations of the rotating body λ in the same direction. The variable speed gear mechanism includes a gear 20 attached to the outer periphery of a rotating body λ, a gear 21 attached to a shaft 24 rotatably supported on a fixed body and meshing with the gear 20, and a gear 21 provided on the shaft 24. It mainly consists of a gear 22 that meshes with a gear 23 on the outer periphery of the optical system holder. The intermediate gears 21 and 22 are divided into two parts 21a, 21b and 22a, 22b so that there is a relative rotational shift in the rotation direction, and between the two divided gears,
A resilient member such as a spring is provided that resiliently biases these components in a direction that causes rotational deviation. Incidentally, 25 is a rotary gear, that is, a rotor, which transmits the rotation of the rotary part to the rotary body 2.

FIG. 2 shows a portion of the optical system of the multi-core optical rotary joint according to the present invention constructed as described above.

Now, the aperture (height) of the triangular prism is Hj, the length between both end faces is LJ, and the prism declination angle is 01 (this is 45°).
If the refractive index of the prism is n, then the relationship of equation (3) holds true.

L 1 = H1[tanθ s +jan(1
25° −5in-t n5inθ s ))
(3) Therefore, the prism diameter H1 is set to <20n, which is the same as the conventional example.
vr, prism deflection angle θ1 = 35°, wavelength 0.83 μm
Under the same condition that the prism refractive index n=1.5102, L1=56.8 curves.

That is, compared to the case where the conventional trapezoidal prism shown in FIG. 3 is used, the coupling loss in the present invention is 1.5 as shown in FIG.
5 dB, making it possible to achieve a loss reduction of 2 dB compared to the conventional example.

Furthermore, since the optical system is shortened by 28.2 mm as described above, the overall dimensions of the optical rotary joint can be reduced accordingly, making it possible to achieve overall compactness and weight reduction.

Next, the relationship between the wavelength and the length of the optical system will be considered.

When θs = 35' and wavelength = 0.85 μm, the refractive index n = 1.5098 from FIG.
=56.9111. Assuming that the wavelength used is 1.55 μm, n-=1.5010 from Figure 4 (
From formula 3), the optical system length Lz = 58.0 cm.

The difference in the length of the optical system caused by this change in the wavelength used is 58.0-56.9=1.1.

If optical systems of the same length are used even though the wavelengths used are different as described above, the output side will shift with each rotation, resulting in a very large coupling loss.

In the present invention, the holding part 10 of one of the triangular prisms 6 of the optical system holding unit is configured to be able to slide and move in its axial direction. Therefore, once the length l of the optical system that is fifl for the wavelength used is determined from equation (3), loosen the set screw 11 and slide the holding part 10 so that the prism 6 is at the 1&appropriate position. By moving and tightening the set screw 11 again to fix the holding part 10, the optical system can be always maintained at the optimum length for the wavelength used.

Conventionally, in order to use a trapezoidal prism with an appropriate length for different wavelengths as described above, it was necessary to prepare prisms for each length, which was extremely wasteful. However, according to the present invention, by simply adjusting the prism slide holding fi structure, one optical system can be used for all wavelengths, and the resulting cost reduction effect is extremely large.

[Effects of the Invention] As detailed above, according to the present invention, the length of the optical system can be reduced to about 67% compared to the conventional example using a trapezoidal prism, and the length of the collimating prism can be reduced by about 67%. Because the distance between the converging lenses can be shortened, not only can the transmission loss of light be greatly reduced, but the overall length of the optical rotary joint can also be shortened, making it lighter and more compact. Since the triangular prisms that make up the system can be easily moved and adjusted in the axial direction and fixed, a large number of trapezoidal prisms of different lengths are prepared in advance in case the wavelength used changes as in the conventional example. This eliminates the need for this, making it possible to significantly reduce costs economically.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment according to the present invention, FIG. 2 is an explanatory diagram for calculating the optical system, FIG. 3 is an explanatory diagram for calculating the optical system in the conventional example, and FIG. is a diagram showing the relationship between wavelength and refractive index when BK-7 is used as the prism material, Figure 5 is a diagram showing the relationship between focusing lens spacing and coupling loss, and Figure 6 is a diagram showing the basics of the conventional example. An explanatory diagram showing the configuration, Fig. 7 is an explanatory diagram showing how a rotating incident image becomes a stationary body as an outgoing image in a conventional example, and Fig. 8 shows the respective rotational angular velocities of an object and an outgoing image in a trapezoidal prism. It is an explanatory diagram. Top: Stationary body, λ: Rotating body, D: Optical system holder, 4.4-: Optical fiber 5.6: Triangular prism, 5a, 6a: Opposing vertical surfaces, 5b, 6b: Inclined surface, 7: Reflector , 8a, 8b, 9a, 9b: Focusing lens, 10 Nibrism slide holding part, 11: Set screw, 12a 14a: 13a, 15a: 16a, 16b, 17a, 17b: 18 19: 20.21, 22.23 : 24 : 25 : Ferrule, plug, receptacle, bearing, gear, shaft, rotating ring.

Claims (1)

[Claims] (1) A joint mechanism that allows signals transmitted by optical fiber to be optically transmitted and received between a rotating body and a fixed body, the joint mechanism itself being coaxial with the rotating body between the rotating body and the fixed body. An optical system configured to be freely rotatable is arranged separately, and the optical system faces orthogonal surfaces to a plurality of converging lenses installed to input and output optical signals from the rotating body side and the fixed body side, respectively. A pair of triangular prisms each having one side facing each other perpendicularly to the optical path direction of the converging lens, and a reflector that reflects the optical path refracted by one triangular prism and makes it incident on the other triangular prism, The optical system is configured to combine the optical paths between corresponding lenses of the plurality of focusing lenses installed on the rotating body side and the fixed body side, respectively, and these optical systems are connected to the rotating body at 1/2 the angular velocity of the rotating body by a variable speed gear mechanism. A multi-core optical rotary joint configured to be rotatable in the same direction as the triangular prisms, and configured to move and change the distance between the pair of triangular prisms in accordance with the wavelength of a transmitted optical signal.