Optical Switching Device

1. Field of the Invention

The present invention relates to an improvement in an optical device which switches light transmission paths.

2. Prior Arts

One typical example of the conventional light path switching device is constructed as shown in FIG. 1, wherein a first optical fiber 1 is connected to a moving piece 2 of a magnetically responsive material such as iron and second and third optical fibers 5 and 5' are fixed on respective supporting members 4 and 4', which are secured on opposite inner walls of a box 41. A pair of coils 3 and 3' are provided so as to induce a magnetic force at excitation by currents therethrough to drive the moving piece 2 either to the side of the supporting member 4 or to that of the supporting member 4' responding to polarity of the currents. By driving the moving piece 2, the end face of the first optical fiber 1 is put in front of the end face of the second optical fiber 5 or that of the third optical fiber 5', so that light is transmitted from the optical fiber 1 to the optical fiber 5 or to the optical fiber 5'.

The abovementioned conventional light path switch has such shortcomings that the end part of the first optical fiber 1 is liable to damage in a relatively short time due to repeated shocks when driven between the supporting members 4 and 4', that a considerable gap is necessary between the end faces of the first and the second optical fibers 1 and 5 or between those of the first and the third optical fibers 1 and 5', and that it is difficult to construct a light path switch capable of selectively switching among three or more light paths.

Though there is known a light path switching device utilizing a lens system, it is too large and has an excessive loss of light for practical use.

The present invention provides a simple structured light path switching device with low loss and capable of switching among three or more light paths.

The present invention is an optical device comprising a focussing lens, at least two optical waveguides having their end faces on a focal plane of said focussing lens, a reflection means disposed in an opposite side to said focal plane with respect to said lens, and a means for controllably moving said reflection means such that rays issuing from one of said end faces of the optical waveguide and passing through said lens is reflected to pass through said lens in variable substantially inverse directions, including at least a direction for entering into another one of said end faces.

FIG. 1 is a perspective view showing an example of the conventional light path switch.

FIG. 2 is a schematic view showing principle of the device in accordance with the present invention.

FIG. 3(a) is a front view of an example of device embodying the present invention.

FIG. 3(b) is a sectional side view at the sectional plane I--I of FIG. 3(a).

FIG. 4 is a side view of another example in accordance with the present invention.

FIG. 5 is a perspective view of another example in accordance with the present invention.

FIG. 6 is a side view of another example in accordance with the present invention.

FIG. 7(a) is a front view of an example in accordance with the present invention.

FIG. 7(b) is a sectional side view at the sectional plane I--I of FIG. 7(a).

FIG. 8 is a sectional side view of another example in accordance with the present invention.

FIG. 9 is a block diagram of the electric circuit of the device of FIG. 7 or FIG. 8.

The present invention provides an optical device, wherein, as one example, switching of optical waveguide can be made without moving the optical fiber.

The principle of operation of the present invention is elucidated with reference to FIG. 2.

On a focal plane 9 of an optical convergence lens 6, a light source point 10 is provided. A reflection means 11 (a plane mirror) is disposed in an opposite side to said focal plane with respect to said lens 6. The normal line of the reflection plane of the reflection means 11 is selected to have a small angle .alpha..degree. to the axis 7 of the lens 6. If rays 12' are emanated from the focal point 8 on the focal plane 9, the rays 12' are converged by the lens 6 to form parallel rays 12. In such optical system, when the line connecting the point 10 and the optical center of lens 61 has an angle .theta. to the lens axis 7, rays emanated from the light source 10 and converged by the lens 6 becomes an inclined parallel rays 13 having the angle .theta. to the lens axis 7.

Provided that:

d . . . distance between the focal point 8 and the light source point 10.

f . . . focal length of the lens 6 (i.e., the distance between the points 61 and 8),

tan .theta.=(d/f) holds.

Then, when a relation 2.alpha.=.theta. holds, then rays, which are emanated from the light source 10 are converged into the parallel rays 13 by means of the lens 6, are reflected by the reflection means 11, thereby forming parallel rays 13' which are parallel to the lens axis 7, and which converge on the focal point 8. By means of known principle of geometric optics, when the light source is disposed at the focal point 8, then the reflected rays converges on the point 10. The distance between the focal point 8 and the point 10 responds to the angle .alpha.. As a conclusion, rays originated from the focal point 8 and reflected by the tilted reflection means 11 converges on a point on the focal plane 9. This law is utilized in the device of the present invention.

Hereinafter, the present invention is elucidated referring to FIGS. 3(a) to 9 showing several preferred exemplary embodiments.

In FIG. 3(a) and FIG. 3(b) which show a first example, on one end face 201 of a known light focussing rod lens 20 of about 1/4 pitch length, are contactingly disposed end faces of seven optical waveguides 23, 24, 25, 26, 27, 28 and 29. The end face of the waveguide 23 in the center position is disposed on the axis of the lens, and the end faces of the other six waveguides are disposed on the equal distance from the lens axis 203. On the other side of the rod lens 20 are disposed a tilted reflection means 21. The normal line of the reflection plane 22 of the reflection means 21 has an angle .alpha..degree. to the lens axis 203. Accordingly, the reflection plane 22 is tilted by .alpha..degree. to the plane 202 which is normal to the lens axis 203. When the angle .alpha. is selected to be a specified value, rays coming from the central waveguide 23 into the rod lens 20, reflected by the tilted reflection plane 22 and traveling through the rod lens 20 focuses and enters into the waveguide 24. When the reflection means 21 is turned clockwise by 60.degree. around the lens axis 203, the reflected rays focusses on the end face of the waveguide 29. By further turning the tilted reflection means, the reflected rays can be led to either of six waveguides 24, 25, 26, 27, 28 and 29.

When optical waveguides with core-diameter, clad-diameter and numerical aperture of 100 .mu.m, 150 .mu.m and 0.28, respectively, are used for the seven waveguides, together with a focussing rod lens 20 having 2 mm diameter and 20.8 mm pitch length, the angle .alpha. becomes .alpha..apprxeq.2.1.degree.. This is empirically confirmed. Average insertion loss of this example was about 1.0 dB. When a stop motor was used to drive the reflection means, the switching time was about 15 m sec. FIG. 4 shows another example, wherein the tilted reflection means 21 can be quickly driven by means of a piezo-electric driving means 30, so that switching of the optical waveguide can be made very quickly. The piezo-electric driving means 30 has a sandwich type bimorph structure having two layers of piezo-electric substance and electrodes. For each of the piezo-electric substance, 20 mm long and 0.2 mm thick PZT (lead titanium ziroconium oxide ceramic) can be used. A small reflection mirror 21 is bonded on the sandwich structured driving means 30, and a pair of stoppers 30' and 30' are disposed so as to define the right angles of the reflection mirrors 21. Other parts are constructed similarly to those of preceding example. By employing optical waveguides of 120 .mu.m outer diameter and focussing rod lens of 2 mm diameter and 32 mm pitch length, the angle .alpha. between the plane normal to the lens axis and the reflection plane of the reflection means 21 is about 1.0.degree..

By switching the impressed voltage across the electrodes of the piezo-electric driving means from -134 V to +134 V, by applying a step voltage, the driving means is driven by known piezo-electric effect, and changes the angle of the reflection means 21 and switches the optical waveguide. The time period for the switching of the optical waveguide is as short as only 15 m sec.

As an alternative configuration, the driving means 30 can be constituted by utilizing an electromagnet.

By selecting the angle of the reflection means intentionally to be out of the abovementioned theoretical angle, the incident light to the optical waveguide does not fully enter into the waveguide 24, and is partly lost. Accordingly, the device of FIG. 4 works also as a variable attenuator, or an optical modulator.

FIG. 5 shows another example comprising a semitransparent reflection means, for example, a filter 31, which for example reflects light of a wavelength .lambda..sub.1 but passes light of another wavelength .lambda..sub.2. The filter 31 is disposed in front of the reflection means 21. The filter 31 and the reflection means 21 are tilted by the same angle .alpha. to a normal plane to the lens axis. And both the filter 31 and the reflection means 21 are supported so as to be separately rotatable around the lens axis by known means. Other parts are constituted in the same way as the preceding example of FIG. 3(a) and FIG. 3(b).

Provided that two light signals .lambda..sub.1, and .lambda..sub.2 enter from the central waveguide 23 into the rod lens 20, the incident rays become parallel rays when get out of the other end of the rod lens 20. Then the rays of the wavelength .lambda..sub.1 are reflected by the filter 31, while those of the wavelength .lambda..sub.2 are reflected by the reflection means 21. Therefore, when the faces of the filter 31 and the reflection means 21 are in the position as shown in FIG. 5, the rays of the wavelength .lambda..sub.1 are focussed on the end face of the waveguide 24 and those of .lambda..sub.2 on that of 25. Accordingly, by turning the filter 31 and the reflection means 21 separately to a desired position, the rays of .lambda..sub.1 and of .lambda..sub.2 can be separately led into desired one of the waveguides 24 to 29. As a modification, by using a neutral reflection mirror in place of the filter 31 and by forming the reflection means 21 by a dichroic mirror, dividing the light in formation is also possible.

FIG. 6 shows a further modified example comprising two set of optical switches and is capable of switching the waveguide connection of these switches in an interlocked relation to each other. In FIG. 6, a pair of rod lenses 20 and 20' are disposed with their lens axis in parallelism to each other. On the faces of one end of both of the rod lenses 20 and 20' are connected bunches 100 and 100' of seven optical waveguides. For both rod lenses, a common reflection means 21 (a tilted plane mirror) is disposed with a rotatable supporting means 32'. The axis of the rotation of the reflection means 21 is disposed in parallelism with the axes of the rod lenses 20 and 20'. Other details are constituted in the same manner as those of the example of FIG. 3(a) and FIG. 3(b).

In the device, by turning the reflection means around the shaft of its supporting means 32', the light from the central waveguides of bunches 100 and 100' are reflected by the reflection means 22 and are input to the respective upper waveguides of the bunches 100 and 100'. Therefore, by turning the single reflection means 21, both switches for the bunch 100 and for the bunch 100' can be driven simultaneously in the interlocking relation.

FIG. 7 shows another example, wherein a means for transmitting a controlling signal is provided in the system. In the device of FIG. 7, the end faces of the central waveguide 23 and that of the lower waveguide 25 are disposed symmetrically with respect to the lens axis 33. The axis of rotation 32 of the supporting means of the reflection means is selected to be parallel to the direction of the output rays which are issued from the central waveguide 23 to the rod lens 20 and put out of the rear end face of the rod lens 20. The reflection plane of the reflection means 21 is tilted by the angle .alpha. to the plane normal to the axis of rotation 32. By so constructing, when the reflection means is in the position shown in FIG. 7, the rays issued from the central waveguide 23 are, after reflection by the reflection means 21, put into the upper waveguide 24, while the rays originated from the central waveguide 23 and reflected by the rear end face 34 of the rod lens are put into the lower waveguide 25. When the reflection means 21 is rotated around its axis of rotation 32, the waveguide to which rays originated from the central waveguide 23 are put shifts from 24 to 26, 27, 28 and 29. Of course, the rays from the waveguide 23 are put into the waveguide 25, but this connection is not utilized since the waveguide 25 is already used to transmit the abovementioned partially reflected rays of the central waveguide 23. Irrespective of the position in the rotation of the reflection means, the waveguide 25 receives the abovementioned partially reflected rays of the central waveguide 23. Therefore, by superposing a control light signal for rotating the reflection means 21 on the information light signal to be put in the central waveguide 23, and by picking up the control light signal from the output of the waveguide 25, it is possible to switch the optical device totally by means of the light signals.

FIG. 9 shows a switching system utilizing the optical switch 44 in accordance with the examples of FIG. 7. In FIG. 9, a central machine 40 puts information signals I and control signals C into the central waveguide 23 and a partial output divided by the partial reflection is given to a control circuit 49 through the waveguide 25. The control circuit controls the position of the reflection means responding to the control signal given from the central machine 40. By means of the electrical output of the control circuit and by the rotating motion of the known driving means, the reflection means is rotated and thereby switches the optical waveguide to connect the waveguide 23 to a selected one waveguide 24, 26 or 27. By such connection, the terminal machine 41, 42 or 43 and the central machine 40 are connected by the optical waveguides with each other. Accordingly, light signal can be transmitted in either of desired directions, from the central machine to one of the terminal machine or vice versa.

As a modified example, the control light signal can be picked up from a surface of semitransparent reflection means such as a filter which is disposed in a normal plane to the lens axis immediately behind the rod lens 20 and capable of transmitting a specified wavelength and reflecting another specified wavelength used for the controlling signal.

FIG. 8 shows another example of an optical switch provided with a means for transmitting a controlling signal. On the front end face of a main focussing rod lens 20 are connected end faces of a specified number of optical waveguides (omitted from the drawing) similarly to the examples of FIGS. 3(a) and 3(b) and FIG. 5. Behind the rear face 205 of the main rod lens 20 is provided a tilted half mirror 21, which is tilted to have a specified angle to a plane normal to the lens axis, which partly passes and partly reflects the rays incident thereon. Further behind the half mirror 21, follows an additional focussing rod lens 22 and a photoelectric transducer 35. The rays which passed the half mirror 21 are focussed on the photoelectric transducer 35 by the additional rod lens 20', thereby to produce the control signal for rotating the half mirror 21. The half mirror 21 can be a filter which selectively passes rays of wavelength used as the control signal.

In any of the preceding examples, it is possible to give the transmitted signal a desired degree of attenuation by finely and continuously changing the tilt angle of the reflection means (or mirror) to make the reflected rays focus only partly on the end face of the designated waveguide.

As described above, the optical device in accordance with the present invention has the following advantages: The optical waveguide is permanently connected to the end face of the lens in a satisfactory condition and is not moved for switching, and accordingly the delicate end part of the optical waveguide is free from damage by switching operation and moreover the system has good transmission characteristics. When piezo-electric driving means are used to drive the reflection means, a very high speed switching, and a high speed change of attenuation, can be achieved hence modulation can be made. By adjusting the tilt angle of the reflection means, desired degree of attenuation can be given to the transmission signal. By employing a filter as the reflection means, selective switching for different wavelength signals can be made. By selecting the arragement of the end faces of the optical waveguides on the end face of the rod lens, taking of the control signal out of the information signal in the live transmission waveguide can be made without inserting an undersirable dividing network in the optical waveguide circuit, and without degeneration of the transmission characteristics.